Pulmonary Medicine and Respiratory Failure
Differentiate hypoxemic (type 1) from hypercapnic (type 2) respiratory failure and the mechanisms behind each: V/Q mismatch, shunt, diffusion impairment, hypoventilation. Know the management of COPD exacerbation (bronchodilators, systemic steroids, antibiotics when indicated, controlled oxygen targeting SpO2 88-92%, and noninvasive ventilation for hypercapnic acidosis) and asthma (early steroids, inhaled bronchodilators, magnesium for severe cases, avoid routine antibiotics). Understand the approach to pleural effusion (Light's criteria) and the recognition of tension pneumothorax as a clinical diagnosis requiring immediate decompression.
Traps
Questions love oxygen targets: too much oxygen in COPD can worsen hypercapnia, and a normal SpO2 does not exclude a large shunt. Recognize that a patient with a rising respiratory rate and normal oxygen saturation may still be tiring. Do not delay intubation for a patient with exhaustion, silent chest, or worsening acidosis. Know that noninvasive ventilation is contraindicated in altered mental status, hemodynamic instability, and unprotected airway.
Worked example
A COPD patient with pH 7.25, PaCO2 70, and SpO2 90% on 2 L nasal cannula is a candidate for bilevel noninvasive ventilation. If mental status deteriorates or pH worsens, escalate to intubation.