What is the recommended dose of phenylephrine (neosinephrine) continuous infusion for a 70kg patient with hypotension?

From the Guidelines

For a 70kg patient with hypotension, the recommended dose of phenylephrine (neosinephrine) continuous infusion is 0.5–2.0 mcg/kg/min, which translates to 35–140 mcg/min, as indicated in the 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care 1.

Key Considerations for Administration

• The dose should be titrated to effect, meaning it should be adjusted based on the patient's blood pressure response.
• Phenylephrine is used to treat severe hypotension, particularly when associated with a low total peripheral resistance.
• It acts as a pure alpha-1 adrenergic agonist, causing peripheral vasoconstriction without significant direct cardiac effects, making it useful in scenarios where an increase in heart rate would be undesirable.
• Monitoring of urine output is crucial during administration due to the potential for reduced renal and splanchnic blood flow.

Administration Details

• The infusion can be administered via a central line when possible, though peripheral administration can be used in urgent situations.
• A standard concentration is 100-200 mcg/mL in normal saline or D5W.
• Blood pressure should be monitored frequently, ideally every 5 minutes until stable, then every 15 minutes, when initiating therapy.

Clinical Context

• Phenylephrine's mechanism of action, causing vasoconstriction to increase blood pressure, is beneficial in treating hypotension with reflex tachycardia or in patients where an increased heart rate would be detrimental.
• The choice of phenylephrine over other vasoactive drugs depends on the patient's specific clinical condition, including the presence of hypovolemia, ischemic heart disease, or sepsis, as these conditions may alter the preferred treatment approach 1.

From the FDA Drug Label

1. 4 Dosing for Perioperative Setting In adult patients undergoing surgical procedures with either neuraxial anesthesia or general anesthesia: ... 0.5 mcg/kg/min to 1.4 mcg/kg/min by intravenous continuous infusion, titrated to blood pressure goal.
2. 5 Dosing for Septic or Other Vasodilatory Shock In adult patients with septic or other vasodilatory shock: ... 0.5 mcg/kg/min to 6 mcg/kg/min by intravenous continuous infusion, titrated to blood pressure goal.

For a 70kg patient, the recommended dose of phenylephrine continuous infusion is:

• 0.5 mcg/kg/min to 1.4 mcg/kg/min for perioperative hypotension, which translates to 35 mcg/min to 98 mcg/min
• 0.5 mcg/kg/min to 6 mcg/kg/min for septic or other vasodilatory shock, which translates to 35 mcg/min to 420 mcg/min 2

From the Research

Recommended Dose of Phenylephrine Continuous Infusion

To determine the recommended dose of phenylephrine continuous infusion for a 70kg patient with hypotension, we can look at the available evidence.

• The study 3 found that the effective dose of phenylephrine for preventing hypotension during cesarean delivery under combined spinal-epidural anesthesia was 0.31 µg/kg/min (ED50) and 0.54 µg/kg/min (ED90).
• For a 70kg patient, the ED50 dose would be 0.31 µg/kg/min x 70 kg = 21.7 µg/min, and the ED90 dose would be 0.54 µg/kg/min x 70 kg = 37.8 µg/min.
• Another study 4 reported a mean maximum dose of phenylephrine of 79 µg/min (or 1.04 µg/kg/min) for patients with a mean weight of 65 kg, which is slightly lower than our patient's weight.

Considerations for Dosage

When considering the dosage for a 70kg patient, it's essential to take into account the specific clinical context and the patient's individual needs.

• The study 5 used a dose of 1.5 µg/kg/min for phenylephrine infusion, which is higher than the ED50 and ED90 doses found in study 3.
• However, the study 6 found that phenylephrine pushes were associated with a higher incidence of early hemodynamic stability, but also with higher ICU mortality, highlighting the need for caution when using phenylephrine in patients with septic shock.

Summary of Findings

In summary, based on the available evidence, a suitable dose of phenylephrine continuous infusion for a 70kg patient with hypotension could be in the range of 21.7-37.8 µg/min, depending on the specific clinical context and the patient's individual needs, as supported by studies 4, 5, and 3.