Hemodynamic and Cardiac Monitoring
Core concepts
Interpret monitoring data in context. Noninvasive blood pressure cuff size and placement matter; arterial lines provide beat-to-beat data and allow blood gas sampling. Central venous pressure is a trend and not a reliable sole measure of volume responsiveness; dynamic measures (pulse pressure variation, passive leg raise, stroke volume variation) are more informative in selected patients.
ECG interpretation: recognize ischemia (ST changes), arrhythmias, and artifacts. Understand pulse oximetry limitations (poor perfusion, methemoglobin, carboxyhemoglobin, nail polish, motion). Capnography reflects ventilation and cardiac output; a sudden drop can mean embolism, hypovolemia, or circuit disconnection.
Shock physiology: hypovolemic, cardiogenic, distributive (septic, anaphylactic, neurogenic), and obstructive (tamponade, tension pneumothorax, pulmonary embolism). Match findings (warm vs cold, JVD, lung sounds) to the cause.
Traps
- Treating a single CVP number as an absolute volume gauge.
- Trusting pulse oximetry when perfusion is poor or abnormal hemoglobins are present.
- Missing that a sudden end-tidal CO2 drop may be an embolic event, not a ventilator problem.
- Confusing artifact with true arrhythmia on ECG.
Rule of thumb
When hemodynamics deteriorate, ask: pump, tank, pipes, or leak? Assess rhythm, volume, vascular tone, and obstruction together. Use trends and response to therapy rather than isolated numbers.
Worked example
A patient becomes hypotensive with tachycardia, distended neck veins, and muffled heart sounds after central line placement. Think cardiac tamponade; obtain urgent echocardiography and prepare for drainage rather than giving more fluid alone.