Intraoperative Management and Hemodynamic/Respiratory Physiology
What you must understand
Manage the triad of anesthesia: hypnosis, analgesia, and muscle relaxation, while maintaining perfusion and oxygenation. Understand hemodynamic monitoring: arterial line waveform and pulse pressure variation, central venous pressure limitations, and goal-directed fluid therapy. Learn the physiology of mechanical ventilation (tidal volume, PEEP, plateau pressure, driving pressure) and lung-protective strategies. Understand oxygen delivery and consumption, mixed/central venous saturation, and lactate as perfusion markers. Know how to manage hypotension by mechanism (preload, contractility, afterload, rhythm) and how to recognize and treat intraoperative events such as anaphylaxis, malignant hyperthermia, and venous air embolism.
Traps in questions
Common traps: treating CVP as a reliable volume marker (it is not); assuming a normal blood pressure means adequate perfusion (lactate and urine output matter); and forgetting that high plateau pressure reflects compliance/airway issues, not just tidal volume. Watch for pulse pressure variation as a fluid-responsiveness indicator only in controlled ventilation with adequate tidal volume and no arrhythmia. Malignant hyperthermia traps: earliest sign is often unexplained rising EtCO2 and tachycardia, not hyperthermia; treat with dantrolene and stop triggering agents.
Rule of thumb
For hypotension, ask "is it preload, pump, pipes, or rhythm?" and treat the mechanism. For rising EtCO2 with tachycardia and rigidity, stop volatile agents and give dantrolene immediately.
Worked example: During laparoscopy, EtCO2 rises and peak airway pressure increases. Consider CO2 insufflation absorption and pneumoperitoneum; adjust ventilation and assess for subcutaneous emphysema.