3.4 Antihypertensives, Vasopressors, and Inotropes

Every neuro ICU blood-pressure order is a cerebral blood-volume and CPP order in disguise. Lowering MAP with a venodilator can raise ICP. Raising MAP with a pure vasoconstrictor can drop cardiac output in a stunned heart. This section covers nicardipine, clevidipine, labetalol, hydralazine, the vasopressors, and the inotropes, with the receptor table the exam expects you to carry.

Antihypertensives used when the brain is on the line

Nicardipine is a dihydropyridine calcium-channel blocker and arterial dilator. It is titratable (often 5–15 mg/h, sometimes higher per protocol), has a short enough half-life for ICU use, and does not require an arterial line to start, though invasive monitoring is still wise in labile patients. Reflex tachycardia can occur. It is a workhorse after ICH, after thrombolysis when blood pressure must stay below post-lytic limits, and in hypertensive encephalopathy. It does not provide negative inotropy of the degree seen with beta blockade.

Clevidipine is an ultra-short arterial dihydropyridine in a lipid emulsion. On and off over minutes, it is useful when you need tight minute-to-minute control. Count the lipid calories. It is contraindicated in soybean or egg allergy and in defective lipid metabolism. Like nicardipine, it is an afterload reducer, not a venodilator of nitroglycerin class.

Labetalol blocks alpha-1 and beta receptors (intravenous alpha:beta ratio about 1:7). It lowers MAP by dropping cardiac output and causing some vasodilation. It is attractive in hyperadrenergic states (some ICH, cocaine still on board only with extreme caution regarding unopposed alpha, postoperative hypertension). Avoid it in decompensated heart failure, severe bradycardia, heart block, and bronchospasm. Boluses of 5–20 mg or a drip are both used; the drip is less tidy than nicardipine for many nurses because of longer offset.

Hydralazine is a direct arterial dilator. Onset is delayed and duration is unpredictable, with reflex tachycardia. It still appears as intermittent 10–20 mg intravenous doses when a drip is not available. Chronic hydralazine can cause drug-induced lupus; that is not the acute ICP issue. Unpredictability is the exam knock against hydralazine as monotherapy for a hyperacute blood-pressure ceiling after thrombolysis.

Why nitroprusside and nitroglycerin are the wrong reflex in high ICP

Sodium nitroprusside is an arterial and venous dilator. Venodilation increases cerebral blood volume and can raise ICP. It also risks cyanide toxicity, especially with high dose, prolonged infusion, and renal failure, and it can cause coronary steal. Nitroglycerin is predominantly a venodilator and likewise can increase cerebral blood volume and ICP; it is a poor choice for blood-pressure control in intracranial hypertension. If the patient has high ICP or an unsecured aneurysm with a tight blood-pressure goal, pick an arterial dilator (nicardipine or clevidipine) or labetalol—not a nitric-oxide venodilator.

Vasopressors

Norepinephrine is alpha-1 greater than beta-1. It raises MAP by vasoconstriction with some inotropy. It is first-line for septic and most distributive shock in contemporary critical care practice. In the neuro ICU it is also the usual first pressor when you need a higher MAP for CPP after TBI or for induced hypertension in delayed cerebral ischemia, provided the heart can tolerate afterload. Start at low mcg/min or mcg/kg/min ranges and titrate to a defined MAP or CPP; there is no virtue in a mystery drip rate without a target.

Phenylephrine is a pure alpha-1 agonist. MAP rises; reflex bradycardia is common; cardiac output may fall if the left ventricle cannot empty against the new afterload. It is useful when tachycardia or tachyarrhythmia makes norepinephrine’s beta-1 activity unwelcome, and in some anesthesia-related vasodilatory states. It is a weaker choice as the sole agent in low-output cardiogenic shock.

Vasopressin acts on V1 receptors to vasoconstrict, independent of catecholamine receptors. It is often added at a fixed low dose (commonly 0.03 units/min in septic shock pathways) as a norepinephrine-sparing adjunct. It has no inotropy and can cause digital and splanchnic ischemia at high doses. Acidosis blunts catecholamines more than vasopressin, which is one reason it remains useful in vasodilatory shock.

Epinephrine is a potent alpha and beta agonist. It raises MAP, inotropy, and chronotropy, and it is first-line in anaphylaxis and in many cardiac-arrest algorithms. It increases lactate (beta-2 driven aerobic glycolysis), which confuses sepsis lactate trends. It is appropriate in low-output shock with vasodilation, or when norepinephrine plus vasopressin is not enough, accepting more arrhythmias and more myocardial oxygen demand.

Dopamine is dose-labeled as dopaminergic, then beta, then alpha, but that bedside folklore is unreliable. The SOAP II trial and subsequent practice moved dopamine out of first-line septic shock because of arrhythmias. It is rarely the right default in a modern neuro ICU.

Inotropes and CPP-targeted use

Dobutamine is a beta-1 (and some beta-2) agonist. It increases inotropy and can vasodilate. MAP may rise if output rises more than resistance falls, or MAP may fall. Use it when echocardiography or mixed-venous data show a low-output, high-filling-pressure heart (stress cardiomyopathy after SAH, TBI-associated cardiac injury) and you still need CPP.

Milrinone is a phosphodiesterase-3 inhibitor: inotrope plus vasodilator. It is renally cleared. Hypotension is the neuro-ICU tax. Some teams use milrinone in SAH for delayed cerebral ischemia with a stunned ventricle or for angiographic vasospasm adjuncts, but you must be ready to add norepinephrine so CPP does not collapse. A milrinone-only strategy in a hypotensive, high-ICP patient is self-defeating.

CPP-targeted therapy after TBI follows the relationship CPP = MAP − ICP (or MAP − CVP if that is higher and there is no ICP monitor, which is a cruder surrogate). BTF 4th Edition discussion commonly targets CPP 60–70 mmHg. Pushing CPP much above 70 mmHg with volume and pressors increases acute respiratory distress syndrome risk without clear neurologic gain. After aneurysmal SAH, once the aneurysm is secured, delayed cerebral ischemia is treated with euvolemia and induced hypertension, not the old hypervolemia-hemodilution-hypertension triple-H bundle. Unsecured aneurysms still need blood-pressure ceilings to limit rebleeding; induced hypertension waits until the aneurysm is treated.

Receptor map and neuro-ICU cautions

Worked scenarios

A 62-year-old with ICH has SBP 230 mmHg and a stiff, high ICP. Start nicardipine or clevidipine toward the guideline blood-pressure range for ICH without overshooting into hypotension. Do not start nitroprusside because venodilation can raise cerebral blood volume.

A 45-year-old with SAH day 7, secured coil, new hemiparesis, and MAP 75 mmHg gets induced hypertension with norepinephrine toward a MAP that improves the deficit, with euvolemia—not a 3-liter albumin hypervolemia protocol.

A 70-year-old with pneumonia, lactate 5 mmol/L, and MAP 55 mmHg after fluids gets norepinephrine first. Add vasopressin if high-dose norepinephrine is needed. Dopamine is not the opener.

A 50-year-old with aneurysmal SAH, apical ballooning, cardiac index 1.6 L/min/m2, and ICP 18 mmHg may need dobutamine or milrinone plus a vasopressor so CPP stays in the 60s. Milrinone alone that drops MAP to 60 mmHg with ICP 18 mmHg yields CPP 42 mmHg—below a TBI-style CPP floor and a poor DCI plan.

Exam traps

Treating high ICP with nitroprusside because it is the fastest arterial-line drug in the cardiac ICU. Using dopamine as default septic shock therapy. Induced hypertension before aneurysm securing. Targeting CPP 90 mmHg with gallons of fluid after TBI. Choosing phenylephrine as the only drug for cardiogenic shock. Starting milrinone for DCI and ignoring the new hypotension. Forgetting that labetalol is the wrong antihypertensive in decompensated systolic failure with pulmonary edema.