Cardiovascular System: Hemodynamic Monitoring and Instability
This domain tests hemodynamic interpretation, adherence to monitoring standards, and recognition and management of instability during sedation and anesthesia. Questions often present a blood pressure and heart rate trend and ask what to do next.
Monitoring standards
- Basic standards include continuous pulse oximetry, continuous capnography when an advanced airway is placed, electrocardiography, noninvasive blood pressure at least every 5 minutes, temperature, and a qualified provider present throughout.
- Mean arterial pressure equals systolic plus twice diastolic, divided by three. Organ perfusion generally requires a MAP of at least 65 mmHg.
- Shorten cycling intervals for unstable patients; a reassuring reading from ten minutes ago is not a current vital sign.
Determinants and drug effects
- Blood pressure equals cardiac output times systemic vascular resistance; cardiac output equals heart rate times stroke volume, and stroke volume depends on preload, afterload and contractility.
- Propofol causes vasodilation and myocardial depression. Dexmedetomidine causes initial hypertension followed by bradycardia and hypotension. Etomidate is hemodynamically neutral. Ketamine is sympathomimetic and may raise heart rate and pressure.
Worked example
During colonoscopy under propofol and fentanyl, a 74-year-old falls from 148/82 to 78/44 with a heart rate of 46. Reasoning: propofol vasodilation, opioid-mediated bradycardia, and hypovolemia from bowel preparation are acting together. Stop the drug, recheck the reading and confirm a pulse, give oxygen, start fluids, give atropine for symptomatic bradycardia, and add a vasopressor per protocol while reassessing. Look for bleeding, sepsis, anaphylaxis and pneumothorax rather than assuming the cause is sedation.
Arrhythmias and emergencies
- In unstable bradycardia, atropine may be considered when vagal tone is suspected; if it fails, move to pacing or a catecholamine infusion without delay.
- Local anesthetic systemic toxicity: stop injection, secure the airway with 100 percent oxygen, control seizures with a benzodiazepine, and give 20 percent lipid emulsion at 1.5 mL/kg bolus followed by infusion; avoid vasopressin and calcium channel blockers.
Traps that cost marks
- Treating a possibly artifactual or kinked-cuff reading with drugs instead of repeating the measurement.
- Attributing hypotension only to sedation when the differential is far wider.
- Waiting too long before escalating from atropine to pacing in high-grade block.