Intensive Care and Critical Care Medicine
Critical care questions concentrate on the first 24 hours: recognising and classifying shock, applying lung-protective ventilation, delivering the sepsis bundle, and getting the patient off the ventilator safely. Definitions matter - markers are awarded for using the Berlin and Sepsis-3 criteria correctly.
ARDS and mechanical ventilation
- Berlin definition: onset within one week of a known insult; bilateral opacities not fully explained by effusion, collapse or nodules; respiratory failure not primarily cardiac; P/F ratio 300 or less with PEEP at least 5 cmH2O. Severity is mild 200–300, moderate 100–200, severe below 100.
- Lung-protective settings: tidal volume 6 mL/kg predicted body weight (never actual weight), plateau pressure 30 cmH2O or less, driving pressure 15 or less, permissive hypercapnia, and PEEP titrated to oxygenation.
- Prone positioning for 16 hours a day when P/F is below 150; neuromuscular blockade for severe asynchrony; conservative fluid balance once shock has resolved.
Sepsis
Sepsis-3 is suspected infection plus an acute SOFA rise of 2 or more. Septic shock is a vasopressor requirement to keep MAP at 65 mmHg or above together with lactate above 2 mmol/L despite adequate fluid resuscitation. Give 30 mL/kg crystalloid within 3 hours, take blood cultures before antibiotics, start broad-spectrum antibiotics within 1 hour, use noradrenaline first-line, and add vasopressin and hydrocortisone in refractory shock.
Sedation and weaning
Target RASS −2 to 0 with daily interruption and CAM-ICU delirium screening. Extubate after a spontaneous breathing trial when P/F exceeds 200, PEEP is 8 or less, and the rapid shallow breathing index is below 105.
Worked example
A 60-year-old with influenza pneumonia has P/F 120 on PEEP 10 and a plateau of 32 cmH2O. Predicted body weight is 60 kg, so set tidal volume 360 mL, raise PEEP to 14, accept a PaCO2 of 55 mmHg, and prone for 16 hours. Reassess at 12 hours; if P/F remains below 100, discuss ECMO referral.
Traps
Using actual rather than predicted body weight; labelling cardiogenic pulmonary oedema as ARDS; delaying antibiotics while awaiting cultures; tolerating a plateau above 30; and forgetting thromboprophylaxis, glycaemic control and early enteral nutrition.