When and how to initiate norepinephrine, dopamine, dobutamine, and vasopressin in critically ill patients?

Initiation of Vasopressors and Inotropes in Critically Ill Patients

Norepinephrine should be used as the first-choice vasopressor for fluid-refractory shock, starting at 0.05-0.1 μg/kg/min and titrating by 0.05-0.1 μg/kg/min every 5-15 minutes to achieve a target mean arterial pressure (MAP) ≥65 mmHg. 1, 2

Initial Assessment and Monitoring

• Establish arterial line monitoring when using vasopressors 2
• Monitor key parameters:
  • Blood pressure (target MAP ≥65 mmHg)
  • Heart rate
  • Urine output (target ≥0.5 ml/kg/h)
  • Skin perfusion
  • Mental status
  • Lactate clearance
  • Renal and liver function tests 2

Vasopressor Therapy Algorithm

First-Line Therapy:

1. Norepinephrine:
   • Initial dose: 0.05-0.1 μg/kg/min
   • Titration: 0.05-0.1 μg/kg/min every 5-15 minutes
   • Target: MAP ≥65 mmHg 1, 2
   • Administration: Infuse into a large vein (preferably antecubital fossa) using an infusion pump 2

Second-Line Therapy (if target MAP not achieved):

1. Add Vasopressin:

   • Dose: Up to 0.03 U/min (fixed dose)
   • Purpose: To raise MAP or decrease norepinephrine requirements
   • Note: Not recommended as single initial vasopressor 1, 2

2. Add Epinephrine:

   • Consider when additional agent is needed to maintain adequate blood pressure
   • Particularly useful if there's evidence of myocardial depression 1, 2

Alternative Vasopressor:

1. Dopamine:
   • Use only in highly selected patients with:
     • Low risk of tachyarrhythmias
     • Absolute or relative bradycardia
   • Initial dose: 2-5 μg/kg/min for renal perfusion effects
   • Titration: Increase by 5-10 μg/kg/min increments up to 20-50 μg/kg/min as needed
   • Caution: Evidence suggests worse outcomes with dopamine compared to norepinephrine 1, 3
   • Not recommended for renal protection 1

Inotropic Therapy

When to Start Inotropes:

1. Dobutamine:

   • Indication: Evidence of persistent hypoperfusion despite adequate fluid loading and vasopressor use
   • Dosage: 2.5-20 μg/kg/min
   • Benefits: Potent inotrope with intrinsic vasodilating action that may counteract excessive vasoconstriction from norepinephrine 1, 2
   • Note: Improved capillary and gut blood flow observed with norepinephrine plus dobutamine compared to high-dose dopamine or epinephrine 1

2. Milrinone:

   • Consider in "cold" shock (low cardiac index) 2
   • Particularly useful when beta-blockade is contributing to hypotension 2

Special Considerations

• Fluid Status: Ensure adequate volume resuscitation before or concurrent with vasopressor initiation 2

  • Administer isotonic crystalloid boluses of 20 mL/kg to restore intravascular volume
  • Continue fluid boluses (up to 60 mL/kg in first hour) while monitoring for signs of fluid overload

• Vasopressor Weaning: Gradually decrease the dose while expanding blood volume with IV fluids to prevent marked hypotension 3

• Monitoring for Adverse Effects:

  • Excessive vasoconstriction
  • Organ ischemia
  • Hyperglycemia
  • Tachycardia and tachyarrhythmias 4, 5
  • Decreased urine output (may indicate need to reduce dosage) 3

• Cardiogenic Shock:

  • Vasopressin is not recommended for cardiogenic shock without ScvO2/CO monitoring 1
  • Consider dobutamine for myocardial dysfunction 2

Practical Dosing Tips

• Use infusion pumps, preferably volumetric pumps, for administration 3
• If disproportionate rise in diastolic pressure (marked decrease in pulse pressure) is observed, decrease infusion rate 3
• If unnecessary fluid expansion is a concern, adjust drug concentration rather than increasing flow rate 3
• More than 50% of adult patients are maintained on doses less than 20 μg/kg/min of dopamine 3

Pitfalls to Avoid

• Do not administer dopamine solution if darker than slightly yellow or discolored 3
• Avoid adding sodium bicarbonate or other alkalinizing substances to dopamine as it is inactivated in alkaline solution 3
• Avoid routine administration of fluid boluses in patients with severe febrile illness who do not present with shock 2
• Do not use hydroxyethyl starches for fluid resuscitation in septic shock 2
• Avoid using inotropic agents unless the patient is symptomatically hypotensive or hypoperfused 2

By following this algorithm for initiating vasopressors and inotropes, clinicians can provide appropriate hemodynamic support for critically ill patients while minimizing adverse effects.