01Determinants of Blood Pressure
BP = the force exerted by circulating blood on the vessel walls. (MAP − CVP) = CO × SVR
Cardiac Output (CO) = HR × SV - Cardiac Index (CO/BSA) normal range 2.6–4.2 L/min/m² - Infants: SV relatively fixed → CO depends mainly on HR - Adults: SV plays a major role, especially when tachycardia is undesirable (CAD, HOCM, AS)
Stroke Volume (SV) depends on: 1. Preload — LVEDV 2. Afterload — SVR accounts for 95% of impedance to ejection 3. Contractility — EF is the most clinically useful index (normal LV EF ~60%)
02Components & Pulse Pressure
SBP, DBP, MAP Pulse Pressure (PP) = SBP − DBP - Normal ~40 mmHg at rest, up to ~100 with exertion - Narrow PP (< 25 mmHg): aortic stenosis, coarctation, tension pneumothorax, myocardial failure, shock, damping - Wide PP (> 40 mmHg): aortic regurgitation, PDA, atherosclerotic vessels, thyrotoxicosis, AVM, pregnancy, anxiety
03Intraoperative Hypertension — DDx
Always start with: "Is this measurement real?" (check cuff size, position, transducer level)
- Light anesthesia — most common
- Pain (sympathetic activation from surgical stimulation)
- Chronic hypertension (uncontrolled or under-medicated)
- Illicit drug use (cocaine, amphetamines)
- Hypermetabolic state (MH, thyrotoxicosis, NMS, serotonin syndrome)
- Elevated ICP — Cushing's triad: HTN + bradycardia + irregular respirations
- Autonomic hyperreflexia (spinal cord lesion > T5)
- Endocrine (pheochromocytoma, hyperaldosteronism)
- Hypervolemia
- Drug contamination (intentional — local with epi — or unintentional)
- Hypercarbia
04Treatment of Hypertension
Temporize with fast-onset, short-acting drugs, then diagnose and treat the cause.
- Deepen anesthesia: propofol bolus, ↑ volatile
- Add analgesia: opioid (fentanyl 25–100 mcg)
- Short-acting vasodilators:
- Clevidipine — CCB in lipid emulsion (looks like propofol); 0.5–32 mg/h
- Nitroglycerin — venous > arterial dilation
- Nitroprusside — arterial > venous; cyanide toxicity risk; very expensive
- Avoid NTG/NTP in intracerebral hemorrhage (cerebral vasodilator → ↑ ICP)
- β-blockers:
- Esmolol — affects HR >> BP
- Labetalol — combined α + β, longer acting
- Hydralazine — less predictable kinetics; longer acting
05Antihypertensive Comparison
| Drug | Bolus | Onset | Peak | Duration | Infusion |
|---|---|---|---|---|---|
| Clevidipine | 50–100 mcg | 1 min | 2–4 min | 5–15 min | 0.5–32 mg/h |
| Nitroglycerin | 10–50 mcg | 1 min | 1–3 min | 3–5 min | 0.1–1 mcg/kg/min |
| Nitroprusside | 10–50 mcg | < 1 min | 1 min | 1–10 min | 0.1–1 mcg/kg/min |
| Labetalol | 5–10 mg | 2–5 min | 10–15 min | 45 min – 6 h | — |
| Esmolol | 10–20 mg | 1 min | 2 min | 10 min | 50–300 mcg/kg/min |
| Hydralazine | 5 mg | 5–20 min | 15–30 min | 2–6 h | — |
06Intraoperative Hypotension — DDx
Start with measurement error: cuff size/position, transducer level, damping.
Then by mechanism: - Preload (hypovolemia): hemorrhage, evaporative loss, diuretics, prolonged NPO, vasodilation from anesthetics, positioning, PEEP, pneumoperitoneum, vena cava compression - Afterload (vasodilation): induction agents, volatiles, sepsis, anaphylaxis, sympathectomy from neuraxial block - Contractility: MI, cardiomyopathy, severe acidosis, hypocalcemia, β-blocker overdose - Obstruction: tension PTX, cardiac tamponade, PE, dynamic LVOT obstruction (HOCM), auto-PEEP - Rhythm: bradycardia, tachyarrhythmia, heart block
07Pressor Comparison
| Drug | Receptors | Bolus | Infusion | Notes |
|---|---|---|---|---|
| Phenylephrine | α1 | 50–200 mcg | 20–200 mcg/min | Reflex bradycardia; avoid in low-CO |
| Ephedrine | Mixed α/β indirect | 5–10 mg | — | Tachyphylaxis; ↑ HR |
| Norepinephrine | α1 + β1 | — | 0.02–1 mcg/kg/min | First-line for vasodilatory shock |
| Epinephrine | α + β (dose-dep) | 10–100 mcg | 0.02–0.2 mcg/kg/min | Arrest 1 mg; anaphylaxis 0.3 mg IM |
| Vasopressin | V1 | 1–2 U | 0.01–0.04 U/min | Catecholamine-sparing |
| Dopamine | DA, β, α (dose) | — | 1–10 mcg/kg/min | Arrhythmogenic; falling out of favor |
| Dobutamine | β1 >> β2 | — | 2–20 mcg/kg/min | Inotrope; ↓ SVR; for low CO |
| Milrinone | PDE-3 | 50 mcg/kg load | 0.125–0.5 mcg/kg/min | Inodilator; pulmonary vasodilator |