Critical Care Basics

Critical care does not begin only after admission to an intensive care unit. It begins when a patient can no longer maintain oxygenation, ventilation, circulation, or neurologic function without urgent support. The immediate threat is failed oxygen delivery to tissues. Oxygen delivery depends on adequate arterial oxygen content and cardiac output. A patient with severe anemia, poor cardiac output, or shock may have an acceptable oxygen saturation yet still have inadequate tissue oxygen delivery. Conversely, a patient with a falling saturation may deteriorate rapidly even before blood pressure changes. The body compensates before it fails. Increased respiratory rate, tachycardia, cool skin, anxiety, and reduced urine output may appear while blood pressure remains normal. Hypotension is often a later sign of circulatory failure, particularly in a previously healthy adult. A “normal” blood pressure must therefore be interpreted alongside mental status, skin perfusion, respiratory effort, urine output, and the patient’s baseline. An experienced nurse notices trajectory. A patient who is newly drowsy, needs more oxygen than an hour ago, or has become too breathless to finish a sentence is deteriorating even if...