Intravenous anesthesia


Anesthesia and Pain Medicine. 2005 Sept. 9(3): 115-121
ⓒ Korean Society for Intravenous Anesthesia
What is an Optimal Intramuscular Dose of Phenylephrine for the Prevention of Spinal Anesthesia-Induced Hypotension?
Il Sang Jung, M.D.1, and Sang Kyi Lee, M.D.1,2
1Department of Anesthesiology and Pain Medicine and 2Research Institute of Clinical Medicine, Chonbuk National University Medical School, Jeonju, Korea

Background: Hypotension is the most common complication of spinal anesthesia. Phenylephrine is an alpha-agonist and raises blood pressure by increasing systemic vascular resistance. Thus, phenylephrine may be effectively used for the prevention of spinal anesthesia-induced hypotension. We tried to investigate the optimal intramuscualr (IM) dose of phenylephrine for the prevention of spinal anesthesia-induced hypotension.
Methods: Sixty-two patients, aged from 16 to 65 years, ASA physical status 1 2 undergoing spinal anesthesia for elective surgery were randomly enrolled. Normal saline 1 ml (Group 1), phenylephrine 1.5 mg (Group 2), and phenylephrine 3.0 mg (Group 3) was injected into the deltoid muscle respectively. Blood pressure and heart rate were measured every 1 3 minutes until 30 minutes after spinal anesthesia. The sensory block height was targeted for T4. The incidence of hypotension (> 20% decrease), hypertension (> 20% increase), and bradycardia (> 20% decrease) was compared among three groups. Also, percent changes of mean arterial pressure (MAP) and heart rate during time course were compared in each group and among three groups.
Results: The incidence of hypotension and percentage reductions of MAP in Group 2 and 3 had significant differences compared with Group 1 (P < 0.05). Group 3 had a significantly higher incidence of hypertension compared with Group 1 (P < 0.05). The incidence of bradycardia was not significantly different among three groups.
Conclusions: The prophylactic IM injection of 1.5 mg of phenylephrine is a safe and effective dose of reducing the incidence of hypotension associated with spinal anesthesia in normal adult patients.
Key words : hypotension, phenylephrine, spinal anesthesia
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