Critical Care Medicine
Shock and respiratory failure
Critical care questions hinge on definitions and first principles. Shock is inadequate tissue perfusion, not simply low blood pressure; classify by physiology (hypovolemic, cardiogenic, distributive, obstructive) and treat the cause. Sepsis is life-threatening organ dysfunction from infection, identified by a SOFA score rise; qSOFA is a bedside prompt, not a diagnostic test. Lactate and capillary refill help track resuscitation, but normal blood pressure does not exclude compensated shock.
ARDS is acute hypoxemia with bilateral opacities not explained by cardiac failure, PaO₂/FiO₂ ≤300 mmHg on PEEP ≥5 cmH₂O. Ventilate with 6 mL/kg predicted body weight, plateau pressure ≤30 cmH₂O, appropriate PEEP, and permissive hypercapnia. Prone positioning improves survival in moderate-to-severe ARDS. Fluids should be reassessed dynamically; vasopressors support pressure while the cause is treated.
Traps
Using SIRS criteria to diagnose sepsis; giving large crystalloid boluses without reassessment; forgetting that low tidal volume is based on predicted, not actual, body weight; targeting a normal PaCO₂ at the cost of barotrauma.
Worked example
Predicted body weight for a 170 cm man: 50 + 2.3 × (67 − 60) ≈ 66 kg; 6 mL/kg ≈ 400 mL tidal volume. Set initial rate 12–16/min and titrate to pH and plateau pressure.