Cardiopulmonary Critical Patterns

Critical cardiopulmonary illness becomes dangerous when oxygen delivery fails. Oxygen delivery depends on adequate arterial oxygen content and adequate cardiac output. A patient can therefore become critically ill from severe hypoxemia, poor ventilation with rising carbon dioxide, circulatory failure, or several of these processes at once. The bedside picture often looks similar: tachypnea, tachycardia, anxiety, altered mentation, cool extremities, hypotension, rising lactate, or falling urine output. The cause determines the treatment. Hypoxemic respiratory failure reflects inadequate oxygen transfer. ARDS, pneumonia, pulmonary edema, and pulmonary embolism can all produce low oxygen saturation, but for different reasons. ARDS fills or collapses alveoli and creates shunt physiology: blood passes through poorly ventilated lung regions and remains under-oxygenated even when supplemental oxygen is increased. Pulmonary embolism creates a different mismatch: ventilated alveoli receive too little blood flow, while the right ventricle faces an abrupt increase in afterload. Hypercapnic respiratory failure reflects inadequate alveolar ventilation. In COPD exacerbation, airflow obstruction and respiratory muscle fatigue prevent adequate carbon dioxide elimination. The patient may initially be agitated and tachypneic; worsening fatigue can produce a slower respiratory rate,...