Infectious Diseases and Sepsis
The bundle logic
Sepsis questions test the sequence and the exceptions. Measure lactate, obtain cultures before antibiotics when it does not delay therapy, give broad-spectrum antibiotics within one hour for septic shock, give 30 mL/kg crystalloid for sepsis-induced hypoperfusion or shock, then start norepinephrine to keep MAP ≥65 mmHg. Source control (drainage, debridement, line removal) is as important as the drug.
Pharmacokinetics that gets tested
- Beta-lactams: extended or continuous infusion improves time above MIC for resistant organisms.
- Vancomycin: target AUC/MIC 400–600 rather than a trough alone; monitor renal function; infusion reactions are histamine-mediated (slow the rate, add antihistamine).
- Aminoglycosides: extended-interval dosing, monitor levels and renal function.
- Critically ill patients often have augmented renal clearance and need higher, not lower, doses.
Traps
Giving 30 mL/kg to every septic patient rather than those with hypoperfusion or shock; choosing metronidazole over oral vancomycin or fidaxomicin for Clostridioides difficile colitis; adding antimotility agents in C. difficile; assuming a normal procalcitonin excludes infection; delaying antibiotics to obtain cultures in an unstable patient; failing to adjust renally cleared agents.
Worked example
A 70 kg patient in septic shock with lactate 4 mmol/L: initial fluid 30 × 70 = 2100 mL of balanced crystalloid, reassess after each bolus for congestion, start norepinephrine if MAP remains under 65, and give antibiotics within the hour. Fluid is not repeated indefinitely if the patient no longer responds.
Rule of thumb
Antibiotics within 1 hour of septic shock recognition; fluids by reassessment, not by formula alone.