What is the recommended algorithm for initiating, dosing, monitoring, and weaning vasopressors in adult patients with shock after adequate fluid resuscitation (≈30 mL/kg crystalloid) when MAP remains <65 mm Hg?

Vasopressor Management in Adult Shock After Adequate Fluid Resuscitation

Initiation Criteria

Start norepinephrine immediately when MAP remains <65 mmHg after administering at least 30 mL/kg crystalloid within the first 3 hours, or emergently in severe shock even before fluids are complete if diastolic pressure is critically low. 1

• Establish central venous access for safe administration (peripheral line acceptable initially to avoid delays) 1, 2
• Place an arterial catheter for continuous blood pressure monitoring as soon as practical 1, 2
• Never delay vasopressor initiation while pursuing aggressive fluid resuscitation in severe hypotension 2

Dosing Algorithm

First-Line: Norepinephrine

Begin norepinephrine at 0.05–0.1 µg/kg/min (approximately 5–10 µg/min for a 70 kg adult) and titrate every 10–15 minutes to achieve MAP ≥65 mmHg. 1, 2

• Standard MAP target: ≥65 mmHg for most patients 1, 3
• Chronic hypertension: Target 70–85 mmHg because their autoregulatory curve is shifted rightward 1, 3
• Elderly patients (>75 years): Consider lower target of 60–65 mmHg, which may reduce mortality compared to higher targets 3, 4
• Elevated intra-abdominal pressure (>12 mmHg): Increase MAP target by roughly the measured compartment pressure (e.g., aim for MAP >80 mmHg if IAP is 15 mmHg) 3

Second-Line: Vasopressin

Add vasopressin at a fixed dose of 0.03 units/min when norepinephrine reaches 0.1–0.25 µg/kg/min and MAP remains <65 mmHg. 2, 5

• Vasopressin must always be added to norepinephrine, never used as monotherapy 1, 2
• Do not exceed 0.03–0.04 units/min except as salvage therapy; higher doses cause cardiac, digital, and splanchnic ischemia without additional benefit 1, 2, 5
• For septic shock specifically: Start at 0.01 units/min and titrate by 0.005 units/min every 10–15 minutes to maximum 0.03 units/min 2
• Vasopressin preferentially constricts efferent arterioles, producing better urine output and creatinine clearance than norepinephrine at the same MAP 2

Third-Line: Epinephrine

Add epinephrine starting at 0.05 µg/kg/min (approximately 3.5 µg/min for 70 kg) when MAP cannot be achieved with norepinephrine plus vasopressin, titrating in increments of 0.03 µg/kg/min up to maximum 0.3 µg/kg/min. 2, 6

• Epinephrine causes transient lactic acidosis through β2-adrenergic stimulation of skeletal muscle, interfering with lactate clearance as a resuscitation endpoint 7
• Higher risk of cardiac arrhythmias compared to norepinephrine (ventricular arrhythmias RR 0.35; 95% CI 0.19–0.66) 7
• FDA-approved dosing for septic shock: 0.05–2 mcg/kg/min IV infusion, titrated to MAP goal 6

Inotropic Support: Dobutamine

Add dobutamine 2.5–20 µg/kg/min when MAP is adequate (≥65 mmHg) but signs of tissue hypoperfusion persist—particularly with myocardial dysfunction (elevated filling pressures, low cardiac output, cold extremities, confusion). 1, 2, 7

• Dobutamine addresses cardiac output rather than vascular tone 2
• Do not use dobutamine to raise MAP; it can worsen hypotension through vasodilation at low doses 2
• Frequently precipitates atrial and ventricular arrhythmias at higher doses 2

Monitoring Beyond MAP

MAP alone is insufficient—you must concurrently assess tissue perfusion markers every 2–4 hours: 1, 3

• Lactate clearance: Obtain baseline and repeat within 6 hours if elevated; aim for normalization 1, 3
• Urine output: Target ≥0.5 mL/kg/h as indicator of renal perfusion 1, 3
• Mental status: Regular neurologic checks to assess cerebral perfusion 1, 3
• Skin perfusion: Capillary refill ≤2 seconds, warm extremities, palpable peripheral pulses 1, 3
• Central venous oxygen saturation (ScvO₂): Target ≥70% (or mixed venous ≥65%) 1

Weaning Protocol

Begin down-titration gradually once hemodynamic stability is achieved and maintained—defined as sustained MAP ≥65 mmHg with adequate tissue perfusion markers for at least 2 consecutive hours. 2

• Wean incrementally over time, such as decreasing doses every 30 minutes over a 12–24 hour period 6
• Maintain continuous surveillance of arterial pressure, urine output hourly, lactate every 2–4 hours, mental status, and peripheral perfusion 2
• Do not delay weaning once stability criteria are met; prolonged high-dose norepinephrine increases mortality risk 2

Agents to Avoid

Dopamine

Dopamine is strongly contraindicated as first-line therapy—it increases absolute mortality by 11% and produces significantly more arrhythmias compared to norepinephrine. 2, 7

• Only acceptable indication: highly selected patients with bradycardia and low risk of tachyarrhythmias 1, 2
• Low-dose dopamine for renal protection is strongly contraindicated (Grade 1A recommendation) 1, 2

Phenylephrine

Phenylephrine is not recommended except in three specific circumstances: (1) norepinephrine-induced serious arrhythmias, (2) documented high cardiac output with persistent hypotension, or (3) salvage therapy when all other agents have failed. 2, 8

• Pure α-agonist can lower cardiac output through reflex bradycardia and increased afterload 2
• May raise blood pressure on the monitor while actually worsening tissue perfusion 2
• FDA dosing for septic shock: 0.5–6 mcg/kg/min continuous infusion (no bolus); doses above 6 mcg/kg/min show no incremental benefit 8

Refractory Shock Management

For shock refractory to catecholamines and vasopressin after ≥4 hours of high-dose therapy, add hydrocortisone 200 mg/day IV (e.g., 50 mg every 6 hours or continuous infusion). 1, 2

• Do not use routine hydrocortisone in patients who achieve hemodynamic stability with fluids and vasopressors 1
• Consider angiotensin II for rapid rescue in profound hypotension unresponsive to standard catecholamine vasopressors, especially in vasoplegic shock 2, 9

Critical Pitfalls to Avoid

• Do not assume MAP of 65 mmHg is adequate for all patients—chronic hypertension, elevated compartment pressures, and other scenarios require higher targets 3
• Do not rely solely on MAP—normal MAP can coexist with severe tissue hypoperfusion ("cold shock") 1, 3, 10
• Do not combine dopamine with epinephrine due to additive adverse effects 2
• Do not escalate vasopressin beyond 0.03–0.04 units/min—this causes end-organ ischemia without additional hemodynamic benefit 2
• Do not use phenylephrine as first-line therapy—it may raise blood pressure while worsening tissue perfusion 2
• Do not continue dobutamine when cardiac output is adequate or elevated—it may exacerbate hypotension and increase arrhythmia risk 2