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Shorter, Obese Patients Receive Less Bupivacaine and Phenylephrine When a Spinal Dosing Chart Based on Height and Weight is Used: A Retrospective Review
Abstract Number: T2A-4
Abstract Type: Original Research
Objective: Determine the effects of a spinal dosing regimen based on height and weight1,2.
Methods: Subjects aged 18 years and older undergoing Cesarean sections under spinal anesthesia at our hospital from February 1, 2014 to April 30, 2017 who received 12 mg, 10.5 mg, 9 mg, and 7.5 mg doses bupivacaine 0.75% with dextrose as a spinal anesthetic were included in the study. Demographic and obstetric information, including height and weight, along with dose of phenylephrine used, documentation of high spinal, and whether the patient required general anesthesia were retrieved from the medical record.
Results: 900 subjects met inclusion criteria; 245, 404, 199, and 52 subjects received 12 mg, 10.5 mg bupivacaine 0.75% with dextrose Subjects who received 7.5 mg, 9 mg, and 10.5 mg of bupivacaine 0.75% with dextrose as a spinal anesthetic for Cesarean section required a median of 40 mcg, 80 mcg, and 80 mcg of phenylephrine within 20 minutes of spinal placement, respectively. This phenylephrine requirement was significantly different from subjects who received 12 mg bupivacaine 0.75% with dextrose (median 160 mcg phenylephrine, p < 0.0001). The subjects in each dosing group differed significantly in height (p < 0.0001) and weight (p = 0.0051). 21 (8.6%), 130 (32.2%), 64 (32.2%), and 30 (57.7%) of subjects in the 12 mg, 10.5 mg, 9 mg, and 7.5 mg groups, respectively, had heights and weights that matched the dose prescribed by the dosing chart. When considering only subjects who had the corresponding spinal anesthetic dose matched for height and weight, subjects in the 7.5 mg, 9 mg, and 10.5 mg groups had a higher use of phenylephrine (160 mcg, 160 mcg, and 120 mcg, respectively) compared to all subjects in the respective dosing groups.
Conclusions: Subjects who were obese and shorter received lower doses of local anesthetic for spinal anesthesia and needed less phenylephrine within 20 minutes of spinal placement. Interestingly, many of these subjects were not exactly matched for spinal dose based on height and weight yet an overall benefit of lower spinal dose and phenylephrine use without a difference in conversion to general anesthesia persisted.
1. Spinal dosing chart original creation by Michael Hofkamp, M.D.
2. Harten JM, Boyne I, Hannah P et al. Effects of a height and weight adjusted dose of local anaesthetic for spinal anaesthesia for elective Caesarean section. Anaesthesia. 2005;60(4):348-53