Learn — Critical care & emergencies

17 notes · 127 questions on the topic

Nutrition — NG tube feeding and TPN, CVP care

Nutritional support in surgery is the planned delivery of energy, protein, fluid, electrolytes and micronutrients to a patient who cannot eat enough, either enterally through a nasogastric, nasojejunal, gastrostomy or jejunostomy tube, or parenterally into a central vein. The governing rule is that if the gut works it is used, because enteral feed keeps the mucosal barrier and gut-associated immune tissue intact and lowers septic complications, while parenteral nutrition carries the risks of the central line, of hyperglycaemia and of liver dysfunction.

The adult surgical patient needs roughly 25 to 30 kcal/kg/day, 1.2 to 1.5 g/kg/day of protein and 30 to 35 mL/kg/day of water; in the first days of critical illness, hypocaloric or trophic feeding is accepted and full targets are reached gradually.
Nasogastric tube: measure the NEX distance from the tip of the nose to the earlobe to the xiphisternum (usually 50 to 60 cm in an adult), and confirm the position by aspirating gastric content and testing it on pH indicator paper — a pH of 5.5 or below confirms gastric placement. Radiography is required when no aspirate can be obtained, when the pH is higher, or when the patient is on acid suppression; the auscultation or whoosh test is unreliable and must never be used.
Feeding care: keep the head of the bed elevated 30 to 45 degrees during the feed and for at least an hour afterwards, flush with 30 mL of water before and after every feed and between every drug, give drugs one at a time in liquid form and never crush a modified-release or enteric-coated tablet into a feeding tube, and change the giving set every 24 hours.
Gastric residual volume is no longer measured routinely; where it is, feeding is held only above about 500 mL in 6 hours, and the response is to check the tube position, give a prokinetic and consider post-pyloric feeding rather than to abandon nutrition. A percutaneous endoscopic gastrostomy is preferred once tube feeding is expected to last more than about 4 weeks, and feeding can usually begin about 4 hours after it is placed.
Total parenteral nutrition runs through a dedicated lumen of a central line whose tip sits at the cavoatrial junction, because the solution exceeds 900 mOsm/L and would sclerose a peripheral vein; no drug, blood product or CVP measurement is put through that lumen, the bag and set are changed every 24 hours, capillary glucose is checked 4 to 6 hourly, electrolytes daily until stable, and liver function and triglycerides weekly.
Never stop parenteral nutrition abruptly: taper it or hang 10% dextrose at the same rate, because the pancreas is still producing the insulin the feed was driving and the patient becomes hypoglycaemic within the hour.
Refeeding syndrome threatens anyone who has eaten little for more than 5 days, with a body mass index under 16, unintentional weight loss over 15%, or already low potassium, phosphate or magnesium. Reintroduced carbohydrate triggers an insulin surge that drives phosphate, potassium and magnesium into cells, causing arrhythmia, cardiac failure, rhabdomyolysis, seizures and Wernicke encephalopathy — so start at no more than 10 kcal/kg/day (5 kcal/kg in the highest risk), give thiamine 200 to 300 mg and a B-complex before feeding and for the first 10 days, and correct the electrolytes while feeding rather than delaying the feed.
Central venous pressure is normally 2 to 8 mmHg (about 5 to 12 cmH2O), measured at end-expiration with the patient supine and the transducer or manometer zeroed to the phlebostatic axis at the fourth intercostal space in the mid-axillary line; a high CVP with hypotension suggests tamponade, tension pneumothorax or right heart failure and a low CVP with hypotension suggests hypovolaemia, but a single CVP reading is a poor predictor of whether a patient will respond to fluid.
Central line care is the CLABSI bundle: maximal barrier precautions and chlorhexidine at insertion, subclavian preferred over femoral for infection risk, a transparent semipermeable dressing changed every 7 days or a gauze dressing every 2 days and immediately if soiled or loose, scrub the hub for 15 seconds before every access, and review daily whether the line can come out.

Shock — types and management

Shock is acute circulatory failure in which the delivery of oxygen to the tissues no longer meets their metabolic demand, so cells switch to anaerobic metabolism and lactate rises. It is defined by perfusion and not by blood pressure, which is why a fit young trauma patient can have lost 30% of the blood volume with a systolic pressure that still reads normal — the pressure is the last thing to fall and the first thing that misleads.

Four groups: hypovolaemic (haemorrhage, burns, vomiting, diarrhoea, third-space loss), cardiogenic (myocardial infarction, arrhythmia, valve or pump failure), obstructive (tension pneumothorax, cardiac tamponade, massive pulmonary embolism) and distributive (septic, anaphylactic and neurogenic).
Bedside discrimination: hypovolaemic, cardiogenic and obstructive shock all give a low cardiac output with cold clammy peripheries, a narrow pulse pressure, a thready tachycardia and a capillary refill over 2 seconds; distributive shock gives a high output with warm peripheries, a wide pulse pressure and a bounding pulse. The central venous pressure is low in hypovolaemia and high in cardiogenic and obstructive shock.
The ATLS classes of haemorrhage in a 70 kg adult: class I is up to 15% (about 750 mL) with normal vital signs; class II is 15 to 30% (750 to 1500 mL) with a pulse over 100, a respiratory rate of 20 to 30, a narrowed pulse pressure, urine 20 to 30 mL/h and anxiety; class III is 30 to 40% (1500 to 2000 mL) with a pulse over 120, a falling systolic pressure, a respiratory rate of 30 to 40, urine 5 to 15 mL/h and confusion; class IV is over 40% with a pulse over 140, an unrecordable pressure, negligible urine and lethargy.
Haemorrhagic shock is treated by stopping the bleeding first, then warmed balanced crystalloid limited to about 1 litre followed by blood products in a 1:1:1 ratio of red cells, plasma and platelets; permissive hypotension (a systolic around 90 mmHg or a palpable radial pulse) is accepted until surgical control except in traumatic brain injury, where the systolic must be kept at 110 mmHg or above. Tranexamic acid 1 g over 10 minutes then 1 g over 8 hours is given within 3 hours of injury and does harm after that.
Septic shock is sepsis with a lactate above 2 mmol/L and a need for vasopressor to hold a mean arterial pressure of at least 65 mmHg despite adequate fluid; the hour-one bundle is measure lactate, take blood cultures before antibiotics, give broad-spectrum antibiotics, give 30 mL/kg of crystalloid for hypotension or a lactate of 4 or more, and start noradrenaline if the pressure does not respond.
Anaphylaxis is treated with adrenaline 0.5 mg of the 1 in 1000 solution intramuscularly into the anterolateral thigh, repeated every 5 minutes as needed; lie the patient flat with the legs raised (sit up only if breathing is the problem), give high-flow oxygen and fluid, and remember that steroids and antihistamines are adjuncts that never come before adrenaline and never treat the airway.
Neurogenic shock follows a cervical or high thoracic cord injury: sympathetic outflow is lost, so there is hypotension with a paradoxical bradycardia and warm, dry, pink peripheries. Treat with fluid, then noradrenaline or phenylephrine, and atropine for the bradycardia — but never label a trauma patient neurogenic until haemorrhage has been excluded. Spinal shock is a different thing: the transient loss of all reflexes and tone below the level of the cord lesion.
End points of resuscitation are perfusion end points, not a number on a cuff: a mean arterial pressure of 65 mmHg or more, urine output of 0.5 mL/kg/h in an adult and 1 mL/kg/h in a child, capillary refill under 2 seconds, an improving conscious level and a falling lactate with a correcting base deficit.

Basics of trauma

Trauma care follows the ATLS discipline of a primary survey with simultaneous resuscitation, adjuncts, a secondary survey and then definitive care, so that the injury which will kill first is found and treated first. It matters because in the first hour after injury the order in which things are done, not the completeness of the diagnosis, decides survival — the airway is cleared before the fracture is splinted, and the patient is re-examined from the beginning every time he deteriorates.

The primary survey is ABCDE and each problem is treated as it is found before moving on: A airway with cervical spine protection, B breathing and ventilation, C circulation with haemorrhage control, D disability or neurological status, E exposure with prevention of hypothermia.
Catastrophic external haemorrhage is dealt with at the same moment as the airway, the sequence written as <C>ABC in civilian practice and MARCH in military practice: direct pressure, a haemostatic dressing, and an arterial tourniquet applied 5 to 7 cm proximal to the wound and tightened until the bleeding stops, with the time of application written on it and never loosened by the nurse.
Airway: speak to the patient, because a patient who answers in a normal voice has a patent airway, is ventilating and is perfusing the brain. Use suction, a chin lift or jaw thrust without head tilt, and an oropharyngeal airway only in the unresponsive; a definitive cuffed tracheal airway is needed for a GCS of 8 or less, an expanding neck haematoma, inhalation burns, or an airway that cannot be protected, all with manual in-line stabilisation of the cervical spine.
Breathing: expose the neck and chest and look for the life-threatening injuries found in the primary survey — tension pneumothorax, open pneumothorax, massive haemothorax, tracheobronchial injury and cardiac tamponade; give high-flow oxygen through a reservoir mask and monitor with pulse oximetry and capnography.
Circulation: insert two short wide-bore (14 or 16 gauge) peripheral cannulae, send blood for grouping, cross-match and coagulation, give warmed fluid and then blood, and look in the five places a patient bleeds enough to die — on the floor and four more: the chest, the abdomen, the pelvis and retroperitoneum, the long bones, and the scene itself.
Disability: record the GCS with pupil size and reaction and any lateralising weakness, and check the capillary blood glucose, because hypoglycaemia, hypoxia and alcohol all imitate a head injury.
Exposure: undress the patient completely, log-roll once with four people to inspect the back, then cover with warm blankets, use warmed fluids and a forced-air warmer — hypothermia is one third of the lethal triad with acidosis and coagulopathy, and the trauma patient cools fast because he is wet, exposed and vasodilated by drugs.
Adjuncts to the primary survey: pulse oximetry, ECG, capnography, arterial blood gas with lactate and base deficit, chest and pelvic radiographs, extended FAST, and urinary and gastric catheters — but no urethral catheter when there is blood at the meatus or a suspected urethral injury, and no nasogastric tube when a cribriform plate fracture is suspected, where the orogastric route is used instead.
The secondary survey starts only when the primary survey is complete and the patient is responding: the AMPLE history (Allergies, Medications, Past illnesses and Pregnancy, Last meal, Events and Environment) and a head-to-toe examination of every region, orifice and finger, with tetanus prophylaxis, analgesia, splinting and definitive imaging.

Abdominal trauma

Abdominal trauma is blunt or penetrating injury to the abdominal cavity and its contents — the solid organs, the hollow viscera, the mesentery and the retroperitoneum. It matters because the abdomen is the commonest site of an initially unrecognised fatal injury: physical examination is unreliable in the intoxicated, head-injured, spinal-injured or distracted patient, so the decision to operate rests on the haemodynamic response to resuscitation rather than on the abdominal signs.

In blunt trauma the spleen and liver are the organs most often injured, and a lower rib fracture on either side should make you look at the organ beneath it. In penetrating injury the pattern differs by weapon: stab wounds most often injure the liver, then the small bowel, diaphragm and colon, while gunshot wounds most often injure the small bowel, then the colon and liver.
Anatomy decides the assessment: the anterior abdomen lies between the costal margins and the groins, the thoraco-abdominal region between the nipple line in front and the tip of the scapula behind and the costal margin — a penetrating wound there can injure both chest and abdomen and always risks a diaphragmatic tear; and the retroperitoneum, holding the kidneys, ureters, pancreas, duodenum, aorta and vena cava, is examined by neither FAST nor peritoneal lavage and needs contrast CT.
Extended FAST uses four abdominal windows — subxiphoid pericardial, right upper quadrant at Morison's hepatorenal pouch (the most sensitive in the supine patient), left upper quadrant perisplenic, and the pelvis behind the bladder — plus the pleural windows for pneumothorax and haemothorax. It detects roughly 200 mL or more of free fluid, takes minutes and is repeatable, but it cannot exclude hollow viscus, diaphragmatic, pancreatic or retroperitoneal injury.
Diagnostic peritoneal lavage is positive on immediate aspiration of 10 mL or more of blood, or of gastrointestinal content, bile or faeces; after lavage with a litre of warmed crystalloid it is positive with more than 100,000 red cells per cubic millimetre after blunt trauma (a much lower threshold of about 10,000 is used for a penetrating thoraco-abdominal wound), more than 500 white cells per cubic millimetre, or the presence of bile or amylase. The stomach and bladder are decompressed first, and it is largely replaced by FAST and CT.
Contrast-enhanced CT is the standard investigation in the haemodynamically stable patient, and it is the only test that grades a solid organ injury, shows active contrast extravasation and images the retroperitoneum; it must never be used in an unstable patient, because the scanner is a place with no surgeon and no light.
Immediate laparotomy is indicated by haemodynamic instability with a positive FAST or lavage, by peritonitis, by evisceration, by free intraperitoneal air or a ruptured diaphragm on imaging, by blood on rectal or gastric aspiration after penetrating injury, and by any gunshot wound that has crossed the peritoneum. Most stab wounds and most blunt solid organ injuries in a stable patient are managed without operation, with serial examination, bed rest and repeat imaging.
Non-operative management of a splenic or hepatic injury requires a stable patient with no peritonitis and no other reason to operate, nursed in a monitored bed with serial haematocrit; angioembolisation is used for a contrast blush. After splenectomy the patient needs vaccination against Streptococcus pneumoniae, Haemophilus influenzae type b and Neisseria meningitidis — about 2 weeks before an elective splenectomy or about 2 weeks after an emergency one — annual influenza vaccine, prophylactic penicillin at least through childhood and a lifelong medical alert card, because of overwhelming post-splenectomy infection.
Signs worth knowing: the seat-belt sign, a transverse bruise across the abdomen, predicts mesenteric and hollow viscus injury and an associated Chance fracture of the lumbar spine; Kehr's sign, pain referred to the left shoulder tip, means blood irritating the diaphragm from a splenic injury; Grey Turner's and Cullen's signs are late signs of retroperitoneal bleeding; Balance's sign is fixed dullness in the left flank.
Damage control surgery is used for the cold, acidotic, coagulopathic patient: pack the bleeding, control contamination, close temporarily, correct the physiology in intensive care and return at 24 to 48 hours. Afterwards watch for abdominal compartment syndrome — a sustained intra-abdominal pressure above 20 mmHg measured through the bladder, with new organ dysfunction.

Thoracic trauma — pneumothorax and haemothorax

A pneumothorax is air and a haemothorax is blood in the pleural space; either abolishes the negative intrapleural pressure and collapses the lung, while a tension pneumothorax adds a one-way valve that pushes the mediastinum across and kinks the great veins, so it kills by obstructing venous return as much as by hypoxia. It matters because about 85% of all chest trauma is treated with a chest drain, oxygen and analgesia rather than a thoracotomy — the skill is recognising the few injuries in the primary survey that must be treated in the next minute.

Tension pneumothorax is a clinical diagnosis treated before any radiograph: respiratory distress, unilateral absent breath sounds with a hyper-resonant percussion note, the trachea deviated away from the affected side, distended neck veins (which may be absent if the patient is also bleeding), hypotension, and in a ventilated patient a sudden rise in airway pressure with a fall in blood pressure.
Immediate treatment is needle decompression followed always by a chest drain. ATLS 10th edition moved the adult site to the fifth intercostal space just anterior to the mid-axillary line using a cannula of at least 5 cm, because the chest wall at the second space is often too thick for the needle to reach the pleura; the second intercostal space in the mid-clavicular line remains the site in children and thin adults, and many units prefer an open finger thoracostomy.
An open or sucking chest wound is covered with a sterile occlusive dressing taped on three sides only, or a commercial vented chest seal, so that air escapes on expiration but cannot be drawn in on inspiration; a dressing sealed on all four sides converts an open pneumothorax into a tension pneumothorax. A chest drain is then placed through a separate site, away from the wound, and the defect is closed surgically.
Massive haemothorax means an immediate drainage of 1500 mL or more of blood, a continuing loss of more than 200 mL per hour for 2 to 4 hours, or a persisting need for blood transfusion — any of these is an indication for thoracotomy. Restore volume as the chest is drained, because releasing the tamponading blood can drop the pressure further.
The chest drain goes into the safe triangle, bounded by the lateral border of pectoralis major, the anterior border of latissimus dorsi, a horizontal line at the level of the fifth intercostal space or nipple, and the apex below the axilla; the tube is passed just above the upper border of the rib to avoid the neurovascular bundle running under the rib above, and a large 28 to 32 French tube is used for blood.
Underwater seal care: the tip of the tube stays 2 to 3 cm under the water, the bottle stays below the level of the patient's chest at all times, swinging of the fluid column with respiration shows the tube is patent and in the pleural space, and bubbling means an air leak. Do not clamp a bubbling drain and do not lift the bottle above the chest; clamp only briefly to change a bottle or to look for the source of a leak, and keep an occlusive dressing and a spare clamp at the bedside for accidental disconnection.
The drain is removed when there is no air leak, the lung is expanded on the radiograph and the drainage is under about 200 mL in 24 hours; it comes out at the end of a full expiration or during a held breath, with the prepared suture tied or an occlusive dressing applied immediately, and a check film taken afterwards.
Cardiac tamponade after penetrating chest injury gives Beck's triad of hypotension, distended neck veins and muffled heart sounds, with pulsus paradoxus and a positive pericardial view on FAST; pericardiocentesis is a holding measure and thoracotomy with a pericardial window is definitive.
Flail chest is three or more consecutive ribs fractured in two or more places, producing a paradoxically moving segment; the killer is the underlying pulmonary contusion, so the treatment is oxygen, excellent analgesia (intercostal block or epidural), careful fluid balance and chest physiotherapy, with ventilation reserved for respiratory failure rather than used for the flail itself.

Burns — classification and management

A burn is coagulative destruction of tissue by heat, chemicals, electricity, friction or radiation, graded by the depth of skin destroyed and by the percentage of total body surface area involved. Above roughly 15 to 20% of the body surface in an adult it stops being a skin problem and becomes a whole-body one — massive capillary leak and hypovolaemic burn shock in the first 24 hours, then a hypermetabolic, immunosuppressed state in which infection, not the burn itself, is what kills.

Depth: superficial epidermal (first degree) burns are red, dry, painful, blanch on pressure, do not blister and heal in about 7 days without scarring; superficial partial-thickness burns blister, are moist, pink, blanch briskly and are very painful, healing in 2 to 3 weeks; deep partial-thickness burns are blotchy red and white with sluggish or absent capillary refill and reduced pinprick sensation, take more than 3 weeks and scar, so they are usually grafted; full-thickness (third degree) burns are dry, leathery, white, brown or charred, do not blanch and are insensate because the nerve endings are destroyed, and always need excision and grafting.
Wallace rule of nines in the adult: head and neck 9%, each upper limb 9%, each lower limb 18%, front of trunk 18%, back of trunk 18% and the perineum 1%. The patient's own palm with the fingers held together is about 1% of that patient's body surface and is used for scattered burns.
The child is different because the head is proportionately larger: in an infant the head is 18% and each lower limb 13.5%, and from the age of one year you subtract 1% from the head and add 0.5% to each lower limb for every year of age until adult proportions are reached at about 10 years. The Lund and Browder chart is the accurate method at any age and is the one used in burns units.
Only partial-thickness and full-thickness burns are counted in the total body surface area — simple erythema is never included, and including it is the commonest reason for a grossly over-calculated fluid prescription.
Parkland (Baxter) formula: 4 mL of Ringer's lactate multiplied by body weight in kilograms multiplied by the percentage total body surface area burned, given over the first 24 hours, with HALF in the first 8 hours counted from the TIME OF THE BURN and not from the time of admission, and the remaining half over the following 16 hours. ATLS 10th edition starts adults with thermal burns at 2 mL/kg per percent and children at 3 mL/kg per percent and titrates upward; either way the formula is only a starting rate.
Fluid is titrated to urine output, not to the formula: 0.5 mL/kg/h (about 30 to 50 mL/h) in an adult, 1 mL/kg/h in a child under 30 kg, and 1 to 2 mL/kg/h with high-voltage electrical injury or visible myoglobinuria. Children also need maintenance fluid containing dextrose because their glycogen stores are small.
Airway and inhalation injury: burns sustained in an enclosed space, facial burns, singed nasal hairs, soot in the mouth or in the sputum, hoarseness, stridor or a brassy cough mean the airway will swell — intubate early, before oedema makes it impossible. A normal pulse oximeter reading does not exclude carbon monoxide poisoning because the machine reads carboxyhaemoglobin as oxyhaemoglobin, so give 100% oxygen (which shortens the carboxyhaemoglobin half-life from about 4 hours to about 1 hour) and measure the level.
A full-thickness circumferential burn of a limb acts as a tourniquet and of the chest as a corset: check distal pulses, capillary refill and sensation hourly, elevate the limb, and prepare for escharotomy — an incision through the eschar along the mid-axial lines, which is not the same as a fasciotomy and which in true full-thickness skin needs little anaesthesia but always needs a surgeon.
First aid and early care: stop the burning, remove clothing and all jewellery, cool with running water at about 15 degrees Celsius for 20 minutes within the first 3 hours and never with ice, then keep the patient warm; cover with cling film laid in strips rather than wrapped, or a clean sheet, and apply nothing else — no toothpaste, ghee, ink or oil. Irrigate chemical burns copiously for at least 20 minutes and do not attempt to neutralise them. Give tetanus prophylaxis, adequate opioid analgesia and early enteral feeding, and do not give prophylactic systemic antibiotics.
Refer to a burns unit for partial-thickness burns over 10% of the body surface, any full-thickness burn, burns of the face, hands, feet, genitalia, perineum or over a major joint, electrical and chemical burns, inhalation injury, burns in the very young or very old or with significant comorbidity, and burns with associated trauma. Silver sulfadiazine 1% is the classic dressing but is avoided on the face, in sulfonamide allergy, at term in pregnancy and in the young infant.

Urethral trauma

Urethral trauma is a partial or complete tear of the urethra, divided at the urogenital diaphragm into posterior injuries of the prostatomembranous urethra, which accompany pelvic fractures, and anterior injuries of the bulbar and penile urethra, which follow a straddle blow or instrumentation. It matters because the reflex to relieve a full bladder with a catheter is exactly the wrong move: a blind catheter converts a partial tear into a complete one and adds stricture, incontinence and impotence to the original injury.

Posterior urethral injury is almost always associated with a pelvic fracture, especially the straddle and Malgaigne patterns, in which the membranous urethra shears at the prostatic apex. The signs are blood at the external urinary meatus — the cardinal sign — inability to pass urine with a palpably full bladder, perineal or scrotal bruising, and a high-riding or impalpable prostate on rectal examination.
Anterior urethral injury follows a fall astride a bar, a bicycle crossbar or a manhole edge, crushing the bulbar urethra against the inferior surface of the pubic symphysis; it is also caused by instrumentation and by penile fracture. If Buck's fascia remains intact the haematoma is confined to the penile shaft as a sleeve; if it ruptures, extravasation is limited by Colles' and Scarpa's fascia into the classic butterfly-shaped perineal bruise that spreads into the scrotum and up the abdominal wall but never down into the thighs.
The rule that answers most exam questions: with any suspicion of urethral injury, DO NOT pass a urethral catheter. The investigation is a retrograde urethrogram — contrast extravasating with none reaching the bladder means a complete rupture, while extravasation with contrast also filling the bladder means a partial tear.
Immediate management is to divert the urine with a suprapubic catheter placed under ultrasound guidance, followed by delayed urethroplasty at about 3 months for a complete posterior rupture once the haematoma has resolved; a partial anterior tear may be managed with a suprapubic catheter alone or a single gentle attempt at a small catheter by a urologist, and heals with fewer strictures.
Complications are the reason for the caution: urethral stricture is close to universal after a complete rupture and needs long-term follow-up with uroflowmetry, while erectile dysfunction from injury to the cavernous nerves and urinary incontinence follow posterior injuries in a substantial minority.
Look for the injuries that travel with it. A pelvic fracture bleeds heavily from the presacral venous plexus, so apply a pelvic binder at the level of the greater trochanters rather than the iliac crests, do not repeatedly spring the pelvis, and treat the haemorrhage before the urethra. Bladder injury may coexist: an intraperitoneal rupture, typically a dome tear from a blow to a full bladder, needs laparotomy and repair, while an extraperitoneal rupture with a pelvic fracture is usually managed with catheter drainage alone.
Female urethral injury is rare and is associated with pelvic fracture and vaginal laceration, so the vagina must always be examined — a missed tear becomes a urethrovaginal fistula.
Nursing responsibility: record blood at the meatus explicitly, write NO URETHRAL CATHETER on the notes and at the head of every handover, stop anyone who reaches for the catheter trolley, monitor for bladder distension and pain, keep the patient nil by mouth pending theatre, and after suprapubic catheterisation secure the tube, record hourly output and observe the site for leakage.

Basics of ventilator

Mechanical ventilation is the delivery of gas to the lungs under positive pressure through an endotracheal or tracheostomy tube, or through a tight-fitting mask in non-invasive ventilation, taking over the work of breathing when the patient cannot oxygenate, cannot ventilate or cannot protect the airway. It matters postoperatively because settings are prescribed against predicted body weight rather than the scale weight, and because the ventilated patient's commonest preventable harms — barotrauma, ventilator-associated pneumonia and unplanned extubation — are all nursing-sensitive.

Indications: apnoea or respiratory arrest, a respiratory rate above about 35 a minute with exhaustion, hypoxaemia with a PaO2 below 60 mmHg despite high-flow oxygen (a PaO2/FiO2 ratio under 200), a rising PaCO2 with a pH below 7.25, a Glasgow Coma Scale of 8 or less with an unprotected airway, and shock with a high work of breathing.
Modes: controlled mandatory ventilation (the machine does everything, used when the patient is paralysed), assist-control (every breath, whether patient- or machine-triggered, is a full set breath), SIMV (mandatory breaths synchronised with the patient's own, with spontaneous breaths between), pressure support (every breath is patient-triggered and pressure-assisted — the weaning mode), and CPAP or BiPAP for non-invasive support.
Usual starting settings for an adult: tidal volume 6 to 8 mL/kg of predicted body weight, rate 12 to 16 a minute, FiO2 started at 1.0 and weaned to the lowest that keeps SpO2 at 92 to 96%, PEEP 5 cmH2O, and an inspiratory to expiratory ratio of 1:2.
Lung-protective ventilation in ARDS follows the ARDSNet protocol: tidal volume 6 mL/kg of predicted body weight (reduced to 4 mL/kg if needed), plateau pressure kept at or below 30 cmH2O, driving pressure below about 15 cmH2O, higher PEEP taken from the FiO2/PEEP table, permissive hypercapnia accepting a pH down to about 7.20, and prone positioning for 16 hours a day when the PaO2/FiO2 ratio is below 150.
Predicted body weight, calculated from height and sex, sets the tidal volume — a patient with a predicted weight of 70 kg gets about 420 mL at 6 mL/kg — because obesity enlarges the abdomen, not the lungs.
Alarms are information, not noise: a high-pressure alarm means secretions, a kinked or bitten tube, bronchospasm, coughing or pneumothorax, and a low-pressure or low-volume alarm means a disconnection, a circuit leak or a deflated cuff. Assess the patient before silencing the alarm, and if the cause is not obvious, disconnect and ventilate by bag with 100% oxygen while calling for help.
The ventilator care bundle: head of the bed elevated 30 to 45 degrees, daily sedation interruption paired with a spontaneous breathing trial, oral care with chlorhexidine and subglottic suction, cuff pressure kept at 20 to 30 cmH2O, suction only when indicated rather than by routine, plus thromboprophylaxis and stress-ulcer prophylaxis.
Weaning criteria: the underlying cause is improving, the patient is awake, cooperative and haemodynamically stable on FiO2 of 0.4 or less with PEEP of 5 or less, and the rapid shallow breathing index (respiratory rate divided by tidal volume in litres) is under 105 — then a 30- to 120-minute spontaneous breathing trial on pressure support or a T-piece, a cuff-leak check, and extubation with oxygen, suction and physiotherapy ready.
Complications: barotrauma and pneumothorax, ventilator-associated pneumonia developing after 48 hours, oxygen toxicity with a prolonged FiO2 above 0.6, reduced venous return and hypotension from high PEEP, diaphragm weakness from over-sedation, and delirium.

Triage — START and disaster

Triage is the sorting of casualties so that treatment order is set by clinical urgency and by the resources actually available, and it is the first clinical act performed at any incident. In the emergency department the sickest patient is treated first, but in a mass-casualty incident, where casualties outnumber staff and equipment, the rule changes to the greatest good for the greatest number: a casualty with unsurvivable injury is tagged expectant and the team's hands go to those who can be saved, which is why triage must be taught before it is needed and re-done at every stage.

START stands for Simple Triage And Rapid Treatment and assesses each adult casualty in under 60 seconds on three things — Respirations, Perfusion and Mental status; only two treatments are allowed during the sweep, opening the airway and controlling major external haemorrhage, and cardiopulmonary resuscitation is not performed because it consumes the rescuer.
The first move is to call out that everyone who can walk should move to a named area: all of them are tagged GREEN (minor, delayed for hours), and that single sentence often clears half the scene before any casualty is touched.
Respirations: if the casualty is not breathing, open the airway with a head tilt and chin lift or a jaw thrust — if breathing starts the tag is RED, and if there is still no breathing the tag is BLACK; a respiratory rate over 30 per minute is RED.
Perfusion: with a rate under 30, check the radial pulse or capillary refill — an absent radial pulse or a capillary refill longer than 2 seconds is RED, and any major external bleeding is controlled with direct pressure or a tourniquet at that moment.
Mental status: with breathing and perfusion adequate, ask the casualty to follow a simple command — failure to obey, or any altered level of consciousness, is RED; a casualty who breathes under 30, perfuses well and obeys commands but cannot walk is YELLOW.
The four tags are RED or Priority I, immediate — life-threatening but salvageable, such as airway obstruction, tension pneumothorax, major haemorrhage or shock; YELLOW or Priority II, delayed — can safely wait one to two hours, such as long-bone fractures and stable abdominal injuries; GREEN or Priority III, minor — the walking wounded; and BLACK or Priority 0, dead or expectant, who receive comfort care only.
JumpSTART is the paediatric version for children of roughly 1 to 8 years and exists because children arrest from respiratory causes: an apnoeic child with a palpable pulse is given five rescue breaths before any decision, and the respiratory limits are under 15 or over 45 breaths per minute rather than 30.
Triage is dynamic and repeated — at the scene, at the casualty collection point, on arrival in hospital and after every intervention — because a YELLOW who is bleeding internally becomes a RED, and a tag is a snapshot, not a diagnosis.
Inside the hospital the same logic is applied through the five-level Emergency Severity Index, where level 1 is resuscitation and level 5 is non-urgent, or the Manchester Triage System; under-triage, which sends a seriously injured casualty to a lower category, is the dangerous error and is kept to a few per cent, while a high rate of over-triage is accepted as the price of that safety.

Ventricular fibrillation — defibrillation

Ventricular fibrillation is chaotic, disorganised depolarisation of the ventricular myocardium in which no coordinated contraction occurs, so there is no cardiac output, no pulse and no consciousness. It is a shockable rhythm and the only treatment that restores an organised rhythm is electrical defibrillation, delivered as early as possible, because survival falls by roughly 7 to 10 percent for every minute that passes before the first shock and untreated fibrillation degenerates into asystole.

Ventricular fibrillation and pulseless ventricular tachycardia are managed identically: immediate high-quality chest compressions and defibrillation as soon as the device is attached and charged.
Energy: a biphasic defibrillator uses the manufacturer's recommended dose, usually 120 to 200 joules for the first shock and an equal or higher dose thereafter, and the maximum is used if the recommendation is unknown; a monophasic machine uses 360 joules for every shock; children receive 2 joules per kilogram for the first shock, 4 joules per kilogram for the second and 4 joules per kilogram or more subsequently.
Compressions resume immediately after the shock and continue for 2 minutes before the rhythm is rechecked, and neither a pulse check nor a rhythm check is done straight after the shock; the pre-shock and post-shock pauses are kept under 10 seconds.
High-quality CPR in an adult is a rate of 100 to 120 compressions per minute at a depth of 5 to 6 cm with complete chest recoil, a compression-to-ventilation ratio of 30:2 without an advanced airway, and continuous compressions with one breath every 6 seconds once an advanced airway is in place.
Adrenaline 1 mg intravenously or intraosseously is given every 3 to 5 minutes and, in a shockable rhythm, is given after the second shock rather than at the outset; amiodarone 300 mg is given after the third shock with a further 150 mg if needed, and lidocaine 1 to 1.5 mg per kilogram is the alternative.
The reversible causes are searched for in every arrest as the five Hs and five Ts: hypovolaemia, hypoxia, hydrogen ion excess, hypo- or hyperkalaemia and hypothermia; tension pneumothorax, tamponade, toxins, pulmonary thrombosis and coronary thrombosis.
Safety before every shock: announce and confirm that everyone is clear, remove flowing oxygen from the chest, dry a wet chest, remove any transdermal patch, and place the pad at least 8 cm away from an implanted pacemaker or defibrillator.
Waveform capnography guides the resuscitation: an end-tidal carbon dioxide persistently below 10 mmHg after 20 minutes suggests a poor outcome, while an abrupt rise towards 35 to 40 mmHg signals return of spontaneous circulation.
After return of circulation the priorities are targeted temperature management between 32 and 36 degrees Celsius for at least 24 hours, oxygen saturation kept at 92 to 98 percent, normocapnia, a mean arterial pressure of at least 65 mmHg and urgent coronary angiography when the ECG shows ST elevation.

Cardioversion vs defibrillation

Both cardioversion and defibrillation depolarise the whole myocardium at once so that the sinus node can resume control, but cardioversion is synchronised to the R wave while defibrillation is not. Synchronisation exists to keep the shock out of the vulnerable period on the T wave, because a shock landing there provokes ventricular fibrillation, so the rule is simple: a rhythm with a pulse is cardioverted in sync, and a pulseless or disorganised rhythm is defibrillated out of sync.

Synchronised cardioversion is used for an unstable tachyarrhythmia that still has a pulse and an identifiable R wave, and electively for atrial fibrillation, atrial flutter and supraventricular tachycardia that have not responded to drugs.
Typical initial biphasic energies are 50 to 100 joules for a regular narrow-complex tachycardia such as supraventricular tachycardia or atrial flutter, 120 to 200 joules for atrial fibrillation, and 100 joules for monomorphic ventricular tachycardia with a pulse, escalating stepwise if the first shock fails.
Defibrillation is unsynchronised and is used for ventricular fibrillation, pulseless ventricular tachycardia and polymorphic ventricular tachycardia, at 120 to 200 joules biphasic or 360 joules monophasic.
Polymorphic ventricular tachycardia is irregular and has no reliable R wave for the machine to track, so the defibrillator will not discharge in synchronised mode; it is treated as ventricular fibrillation with an unsynchronised shock.
The synchronise button must be pressed and the sync markers seen sitting on the R waves before the shock, and on most machines synchronisation must be reselected before every further shock; if the patient deteriorates into ventricular fibrillation during the procedure, synchronisation is turned off and the shock is delivered immediately.
Elective cardioversion of atrial fibrillation lasting 48 hours or longer, or of unknown duration, requires at least 3 weeks of therapeutic anticoagulation beforehand and 4 weeks afterwards, or a transoesophageal echocardiogram excluding left atrial thrombus first; a haemodynamically unstable patient is cardioverted immediately with anticoagulation started as soon as possible.
A conscious patient is sedated and given analgesia with consent taken, kept nil by mouth for an elective procedure, and monitored with oxygen, suction, airway equipment and resuscitation drugs immediately available.
Instability that mandates immediate synchronised cardioversion means hypotension, acutely altered mental status, signs of shock, ischaemic chest discomfort or acute heart failure occurring because of the tachyarrhythmia.
Safety is identical for both: conductive gel or self-adhesive pads correctly placed, no one touching the patient or the trolley, oxygen moved away from the chest, and a clear verbal all-clear before the discharge.

Defibrillator — AED

An automated external defibrillator is a portable device that analyses the cardiac rhythm through adhesive pads and advises or delivers a shock only when it detects ventricular fibrillation or pulseless ventricular tachycardia. It is designed for use by anyone, trained or untrained, because early defibrillation is the single intervention that most improves survival from out-of-hospital cardiac arrest, where every minute of delay reduces survival by roughly 7 to 10 percent.

The adult chain of survival is recognition of arrest and activation of emergency response, immediate high-quality CPR, rapid defibrillation, advanced resuscitation, post-cardiac-arrest care and recovery, and the automated defibrillator occupies the third link.
CPR is started at once and never delayed to fetch or set up the device; as soon as the defibrillator arrives, one rescuer attaches the pads while another continues compressions, and compressions stop only for the analysis and the shock.
Standard pad placement is anterolateral: one pad below the right clavicle at the right upper sternal border and the other over the left mid-axillary line at about the fifth to sixth intercostal space, clear of breast tissue; anteroposterior placement is an accepted alternative.
Infants and children under 8 years or under about 25 kg need paediatric attenuated pads or a dose attenuator; if only adult pads are available they are used rather than withholding defibrillation, placed front and back so that they do not touch each other.
No one touches the patient during analysis or shock delivery, the chest is dried and the patient moved off a wet or metal surface, dense chest hair is shaved if the pads will not adhere, transdermal patches are removed and the skin wiped, and pads are placed at least 8 cm from an implanted pacemaker or defibrillator.
After a shock, chest compressions resume immediately for 2 minutes without a pulse check, and the device re-analyses at the end of that cycle; pads stay attached for handover and transport.
If the machine advises no shock, compressions resume immediately, because a non-shockable rhythm still needs CPR and adrenaline rather than a shock.
The device is safe in pregnancy, with manual left uterine displacement continued during compressions, and safe on a patient rescued from water once they are moved to a dry surface and the chest is dried.
The pre-shock and post-shock pauses are kept under 10 seconds, and pad electrodes and battery expiry dates are checked as part of the routine equipment check on every shift.

Cardiac monitor

A cardiac monitor is continuous bedside or telemetric display of the electrocardiogram, usually from three or five electrodes, so that rate and rhythm are watched beat by beat rather than sampled by a twelve-lead recording. It shows electrical activity only and never proves that blood is moving, which is why pulseless electrical activity exists and why every alarming trace is answered by looking at the patient before looking at the screen.

Three-electrode placement under the AHA colour code is white to the right shoulder or right infraclavicular area, black to the left shoulder, and red to the left lower chest at the costal margin, remembered as white on the right and smoke over fire; a five-lead set adds green to the right lower chest and brown as the chest lead.
Many machines in India carry the IEC colour code instead: red to the right arm, yellow to the left arm, green to the left leg and black to the right leg, so the colours are confirmed against the machine before the electrodes go on.
Lead II is the best single monitoring lead because it lies along the axis of atrial depolarisation and gives the largest, most upright P wave; lead V1 or MCL1 is the best lead for deciding whether a wide beat is ventricular in origin or a bundle branch block.
Electrodes are placed on flat skin over bone or muscle-free areas, away from the sites where defibrillator pads will go, and the skin is clipped of hair, cleaned, dried and lightly abraded first, with electrodes changed every 24 to 48 hours or whenever the gel dries.
Alarms are set to the individual patient and never switched off: heart rate upper and lower limits, asystole, ventricular fibrillation and ventricular tachycardia; alarm fatigue from unadjusted default limits is a recognised cause of patient death, so the limits are customised rather than the alarms silenced.
Artefact recognition saves unnecessary emergencies: a wandering baseline is movement or a loose electrode, a fine tremor mimics atrial fibrillation, a 50 Hz interference pattern is electrical, and a flat line in a patient who is talking is a disconnected lead.
The monitor measures amplitude and rate but not blood pressure or perfusion, so a normal-looking complex with no palpable pulse is pulseless electrical activity and needs cardiopulmonary resuscitation, not a lead check.
A rhythm strip is printed and mounted at the start of each shift, with every rhythm change, before and after any antiarrhythmic drug or shock, and each strip is labelled with the date, time, lead and the patient's identification.

Arterial blood gas (ABG) interpretation

An arterial blood gas measures the pH, the partial pressures of carbon dioxide and oxygen and the bicarbonate in arterial blood, and from those values it tells you whether the patient's acid-base state and oxygenation are safe. Interpreting it is a fixed five-step drill, and because every emergency, intensive care and dialysis question in the recruitment papers eventually comes back to an arterial blood gas, that drill is worth more marks than almost any other single skill in medicine.

Normal values are pH 7.35 to 7.45, PaCO2 35 to 45 mmHg, HCO3 22 to 26 mEq/L, PaO2 80 to 100 mmHg breathing room air, SaO2 95 to 100% and base excess between minus 2 and plus 2 mEq/L.
Step 1 is the pH: below 7.35 is acidaemia and above 7.45 is alkalaemia. Step 2 is the PaCO2: if it moves in the OPPOSITE direction to the pH the problem is respiratory. Step 3 is the HCO3: if it moves in the SAME direction as the pH the problem is metabolic. Step 4 is to decide whether the other system has compensated. Step 5 is to read the PaO2 and saturation separately, because oxygenation is a different question from acid-base.
The mnemonic is ROME, respiratory opposite and metabolic equal, and compensation never overshoots — a compensating system brings the pH back towards 7.40 but never past it, so the side of 7.40 on which the pH sits identifies the primary disorder even in a fully compensated gas.
Respiratory acidosis is hypoventilation from COPD, opioid overdose, neuromuscular weakness or airway obstruction. Respiratory alkalosis is hyperventilation from pain, anxiety, fever, sepsis, pulmonary embolism, high altitude or early salicylate poisoning.
Metabolic acidosis comes from diabetic ketoacidosis, lactic acidosis, renal failure, severe diarrhoea with bicarbonate loss and poisons. Metabolic alkalosis comes from prolonged vomiting or nasogastric suction, diuretics, hypokalaemia and excess alkali.
The anion gap is sodium minus the sum of chloride and bicarbonate, normally 8 to 12 mEq/L, and it splits metabolic acidosis in two: a HIGH gap means acid has been added (MUDPILES — methanol, uraemia, diabetic ketoacidosis, propylene glycol, isoniazid or iron, lactic acidosis, ethylene glycol and salicylates), while a NORMAL gap means bicarbonate has been lost, as in diarrhoea or renal tubular acidosis.
The anion gap must be corrected for albumin — add about 2.5 mEq/L to the measured gap for every 1 g/dL that serum albumin falls below 4 g/dL — or a high-gap acidosis will be missed in a malnourished or nephrotic patient.
Winter formula checks whether respiratory compensation for a metabolic acidosis is adequate: the expected PaCO2 equals 1.5 times the bicarbonate plus 8, give or take 2. A PaCO2 higher than predicted means an added respiratory acidosis and a lower one means an added respiratory alkalosis.
Sampling technique is examinable and it matters: perform a modified Allen test before radial puncture, use a pre-heparinised syringe, expel any air bubble at once, cap and mix the sample, send it within about 15 minutes or transport it on ice, and press the puncture site for at least 5 minutes, or 10 minutes if the patient is anticoagulated.
Know the confounders: an air bubble raises the PaO2 and lowers the PaCO2, a delayed sample lets the cells consume oxygen and generate acid, a venous sample gives a falsely low PaO2, and pulse oximetry reads falsely high in carbon monoxide poisoning.

PEEP — indications and contraindications

Positive end-expiratory pressure is the pressure deliberately held in the airway at the end of expiration so that alveoli do not collapse between breaths; it raises the functional residual capacity, recruits flooded and collapsed alveoli, reduces intrapulmonary shunt and so improves oxygenation at a lower and safer inspired oxygen fraction. It is also the setting that most directly trades oxygenation against circulation, because every centimetre of water raises intrathoracic pressure, reduces venous return and can overdistend healthy lung.

Indications are hypoxaemic respiratory failure with diffuse alveolar collapse or flooding — ARDS above all, plus cardiogenic pulmonary oedema, atelectasis, post-operative lung collapse, and any patient needing a high inspired oxygen fraction to hold saturation.
Physiological PEEP is 3 to 5 cm H2O, which replaces the pressure normally held by a closed glottis; usual therapeutic settings are 5 to 15 cm H2O, and ARDS is titrated on the ARDSNet PEEP/FiO2 table so that PEEP rises as FiO2 rises.
Lung-protective ventilation goes with PEEP: tidal volume 6 mL/kg of predicted (not actual) body weight, plateau pressure kept at or below 30 cm H2O, driving pressure (plateau minus PEEP) at or below 15 cm H2O, and permissive hypercapnia accepted as long as the pH stays around 7.30 or above.
The Berlin definition grades ARDS by the PaO2/FiO2 ratio measured on a PEEP of at least 5 cm H2O: mild 200 to 300, moderate 100 to 200, severe below 100; prone positioning for 16 hours or more a day is indicated when the ratio is below 150.
Complications: barotrauma and pneumothorax, reduced venous return with hypotension and falling cardiac output, reduced renal and hepatic perfusion with falling urine output, raised intracranial pressure through impaired cerebral venous drainage, overdistension of normal alveoli with increased dead space, and fluid retention.
Cautions and relative contraindications: untreated tension pneumothorax and an undrained pneumothorax, hypovolaemia and shock until volume is restored, unilateral lung disease (PEEP overdistends the good lung and diverts blood to the bad one), bronchopleural fistula, raised intracranial pressure, and obstructive disease with air trapping where extrinsic PEEP is set below the measured intrinsic PEEP.
Auto-PEEP (intrinsic PEEP) is trapped gas from incomplete exhalation in asthma and COPD; it is found by an expiratory hold manoeuvre and it is treated by lengthening expiratory time, reducing respiratory rate and treating bronchospasm, not by adding more PEEP blindly.
Nursing care protects the pressure: use inline closed suction so the circuit is never opened, avoid unnecessary disconnection and bagging, keep the head of the bed at 30 to 45 degrees, and remember that a patient on high PEEP can desaturate profoundly within seconds of a disconnection.
Assessment after every PEEP change is paired: saturation, blood gas and compliance on the one hand, and blood pressure, heart rate and urine output on the other, because the setting that fixes the lung can empty the circulation.

Hypertensive emergency vs urgency

A hypertensive emergency is a severe rise in blood pressure, usually above 180/120 mmHg, accompanied by acute damage to a target organ — brain, eye, heart, aorta, kidney or placenta — and it needs an intravenous drug titrated in a monitored bed within the hour. A hypertensive urgency is the same pressure with no acute organ damage, and it is managed with oral drugs and review over days, because dropping that patient's pressure quickly causes harm and buys nothing. The two are separated by examination and investigation, never by the number on the monitor.

The reading alone never decides: the same 200/130 mmHg is an emergency when there is papilloedema, chest pain, focal weakness or a rising creatinine, and an urgency when there is none of that.
Target-organ damage to search for: hypertensive encephalopathy, intracerebral haemorrhage or ischaemic stroke, acute left ventricular failure with pulmonary oedema, acute coronary syndrome, aortic dissection, acute kidney injury, grade III to IV retinopathy with haemorrhages, exudates or papilloedema, microangiopathic haemolysis, and eclampsia or pre-eclampsia with severe features.
The general target is a fall in mean arterial pressure of no more than 25% in the first hour, then to about 160/100 mmHg over the next 2 to 6 hours, and to normal over 24 to 48 hours; a faster fall outruns the rightward-shifted cerebral and coronary autoregulation curve and causes stroke, blindness and infarction.
Aortic dissection is the exception that demands speed: a systolic pressure below 120 mmHg and a heart rate below 60/min within about 20 minutes, with an intravenous beta-blocker such as esmolol or labetalol given before any vasodilator so that reflex tachycardia does not increase the shearing force on the tear.
In acute ischaemic stroke the pressure is left alone unless it exceeds 220/120 mmHg; if thrombolysis is planned it must be brought below 185/110 mmHg before the drug and held below 180/105 mmHg for the next 24 hours.
In pregnancy, treatment of severe hypertension starts at 160/110 mmHg with intravenous labetalol, intravenous hydralazine or oral nifedipine and aims for a systolic of 140 to 150 mmHg and a diastolic of 90 to 100 mmHg rather than normal, because placental perfusion depends on it; magnesium sulfate is given alongside for seizure prophylaxis and is not an antihypertensive, and ACE inhibitors and angiotensin receptor blockers are contraindicated.
Drug choice follows the damaged organ: nitroglycerin for pulmonary oedema and acute coronary syndrome, esmolol or labetalol for dissection, labetalol or nicardipine for encephalopathy and stroke, phentolamine for phaeochromocytoma or stimulant toxicity, and a loop diuretic only when the patient is genuinely fluid-overloaded.
Sodium nitroprusside acts within seconds but the bottle and line must be shielded from light, and it is avoided in renal failure and pregnancy because thiocyanate and cyanide accumulate.
A beta-blocker given alone in phaeochromocytoma or cocaine toxicity leaves alpha stimulation unopposed and drives the pressure higher — alpha blockade with phentolamine comes first.
Sublingual short-acting nifedipine has no place in a hypertensive crisis: the fall is uncontrolled and unpredictable and has caused stroke and myocardial infarction.
Nursing observation is what makes titration safe — a high-dependency or intensive care bed, continuous ECG, an arterial line or an automated cuff every 5 minutes while the infusion runs, hourly urine output, hourly neurological observations, and a documented fundus examination, which is the cheapest evidence of target-organ damage in the building.

Cardiogenic shock

Cardiogenic shock is end-organ hypoperfusion caused by the heart's own failure to pump, with a systolic blood pressure below 90 mmHg for at least 30 minutes, or the need for vasopressors to hold it there, despite adequate or raised filling pressures. The classic haemodynamics are a cardiac index below 2.2 L/min/m2 with a pulmonary capillary wedge pressure above 15 mmHg, and the bedside translation is a cold, clammy, confused, oliguric patient with a rising lactate. It complicates roughly 5 to 10% of ST-elevation infarcts and is the commonest cause of death among patients who reach hospital alive after a myocardial infarction.

Extensive left ventricular infarction is the commonest cause, but the mechanical complications — papillary muscle rupture with acute mitral regurgitation, ventricular septal rupture and free-wall rupture with tamponade — appear 2 to 7 days after the infarct and are surgically correctable, so an urgent echocardiogram is part of the diagnosis and not an afterthought.
Hypoperfusion is defined at the bedside and not by the blood pressure alone: cold mottled peripheries, capillary refill over 3 seconds, altered mentation, urine output below 0.5 mL/kg/h and a serum lactate above 2 mmol/L.
The shock differential turns on the neck veins and the periphery — cardiogenic shock has a raised jugular venous pressure with cold peripheries and a narrow pulse pressure, hypovolaemic shock has flat neck veins, septic shock is warm with a wide pulse pressure, and obstructive shock from tamponade, tension pneumothorax or massive pulmonary embolism also raises the neck veins but has its own chest signs.
Right ventricular infarction is the one cardiogenic shock that responds to fluid: hypotension with a raised jugular venous pressure and clear lung fields after an inferior infarct is treated with a careful fluid bolus while nitrates, morphine and diuretics are withheld.
SCAI stages the severity from A (at risk) and B (beginning shock, with hypotension or tachycardia but no hypoperfusion) through C (classic shock needing support) to D (deteriorating despite support) and E (extremis with refractory arrest), and the value of the ladder is that stage B is where escalation still changes the outcome.
Norepinephrine is the first-choice vasopressor because dopamine causes more arrhythmia and worse survival in cardiogenic shock; dobutamine is the inotrope added for low cardiac output, and milrinone is an alternative that also vasodilates and accumulates in renal impairment.
The treatment that changes survival is early revascularisation of the culprit lesion by primary PCI or surgery, not the drugs that hold the pressure up while it is being arranged.
The intra-aortic balloon pump is no longer routine in infarct-related cardiogenic shock because it did not reduce mortality in trials, while percutaneous microaxial pumps and veno-arterial ECMO are used in selected patients at centres equipped to support them.
Resuscitation targets are a mean arterial pressure of at least 65 mmHg, urine output of at least 0.5 mL/kg/h, warming peripheries and a falling lactate, and the lactate trend is a better guide to progress than the blood pressure reading.
Hypoxia, acidosis, arrhythmia and electrolyte disturbance are corrected in parallel, because acidosis blunts the response to every inotrope, and potassium and magnesium are kept in the normal range to prevent ventricular arrhythmia.
Nursing monitoring is continuous: ECG, an arterial line or 5-minutely non-invasive pressure, hourly urine output through an indwelling catheter, hourly fluid balance, peripheral temperature and capillary refill, and every vasoactive drug on a dedicated line through a syringe pump that is never flushed or bolused.

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