Vasopressin 

Vasopressin (AVP) = endogenous non-catecholamine vasopressor

  • Synthesized in: hypothalamus
  • Released from: posterior pituitary
  • Also called: Antidiuretic Hormone (ADH)

Receptor Physiology 

Receptor

Location

Action

Clinical Effect

V1a

Vascular smooth muscle

↑ IP3 → ↑ Ca²⁺

Vasoconstriction (main ICU use)

V2

Renal collecting duct

↑ cAMP → aquaporin insertion

Water reabsorption (antidiuresis)

V1b (V3)

Pituitary

↑ ACTH release

Minor ICU relevance
  • Vasopressin acts via non-adrenergic pathway → effective in catecholamine-resistant shock

Important CCM Concept:
In septic shock → relative vasopressin deficiency


Hemodynamic Effects

Parameter

Effect

SVR

↑↑ (strong vasoconstriction)

MAP

↑

HR

Neutral / ↓ (no β stimulation)

CO

May ↓ (due to ↑ afterload)

Pulmonary vascular resistance

Slight ↑

Renal blood flow

Preserved or improved (low dose)

Indications in ICU 

1. Septic Shock 

  • Add to Norepinephrine
  • Indication:
    • NE requirement ≥ 0.25–0.5 µg/kg/min
  • Dose:
    • 0.03 units/min fixed dose (NOT titrated)

 According to Surviving Sepsis Campaign:

  • Recommended as second-line vasopressor

2. Catecholamine-Resistant Shock

  • Septic / vasoplegic / post-cardiac surgery shock

3. Vasoplegic Shock (Post-Cardiopulmonary Bypass)

4. Variceal Bleeding

  • Splanchnic vasoconstriction → ↓ portal pressure

5. Diabetes Insipidus (Central)

  • Use analog: Desmopressin

Vasopressin vs Norepinephrine 

Feature

Vasopressin

Norepinephrine

Receptor

V1

α1, β1

Mechanism

Non-adrenergic

Adrenergic

Tachycardia

No

Yes

Use

Add-on

First-line

Shock refractory cases

Excellent

Less effective

Vasopressin Deficiency in Septic Shock

Phases:

  1. Early → high AVP
  2. Late → relative deficiency

Mechanisms:

  • Pituitary depletion
  • Impaired baroreceptor response

 Clinical implication:
→ Rationale for vasopressin supplementation

 Adverse Effects 

System

Effect

Skin

Ischemia, necrosis (digits)

GI

Mesenteric ischemia

Cardiac

↓ CO, arrhythmias

Renal

Oliguria (high dose)

Electrolytes

Hyponatremia

Others

Reduced splanchnic perfusion

 Contraindications / Caution

  • Severe ischemic heart disease
  • Peripheral vascular disease
  • Mesenteric ischemia
  • Hypovolemia (must correct first)

 Key Trials

VASST Trial

  • Compared NE vs NE + vasopressin
  • Result:
    • No mortality benefit overall
    • Benefit in less severe shock subgroup