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The Effect of Large Dose Oxytocin Infusion on Blood Pressure
Abstract Number: T-72
Abstract Type: Original Research
Introduction-Routinely used to minimize bleeding as an uterotonic, oxytocin has important adverse cardiovascular effects. Rosseland et al.1 reported a decrease of 28 mmHg after an IV bolus of 5 U oxytocin. However, when given as an infusion at 30 U/hr, Kim et al.2 noted no significant blood pressure (BP) changes. Because high dose oxytocin (80 U/hr) is the standard protocol at University of Alabama-Birmingham (UAB), we examined whether this infusion rate would affect maternal hemodynamics.
Methods-We conducted a retrospective review of patients scheduled for elective Cesarean sections with spinal anesthesia from November 2008 through June 2010 at UAB. Hypertensive disorders of pregnancy were excluded. To avoid confounding effects, we included patients who did not receive ephedrine or phenylephrine within 10 minutes prior and 10 minutes after the start of the oxytocin infusion (80U in 500 mL at 500 ml/hr). The following data: Systolic, mean, diastolic BP and body mass index (BMI) were extracted. Our sample size calculation indicated at least 119 patients were needed to detect a 5 mm Hg BP difference (SD 15 mmHg, alpha = 0.05, power = 0.95). A paired t-test determined whether observed changes in BP were significantly different from a hypothesized zero change.
Results-294 patients fit our inclusion criteria. We observed statistically (p > 0.001) and clinically meaningful reductions in mean and diastolic BP (mean BP:-3.2±10.1 mmHg, diastolic BP: - 6.5±14.3 mmHg). The effect of oxytocin is a significant increase in pulse pressure by 7.9 mmHg with 25% of women experiencing an 17 mmHg or greater decrease in diastolic BP (95% CI: -7.8 mmHg, -4.5 mmHg), and a 10 mmHg or greater reduction in mean arterial BP (95% CI: -4.0 mmHg, -1.6 mmHg), as illustrated in Table 1. We observed no significant correlation of BMI and the degree of BP decrease.
Conclusion-Oxytocin, when administered at 80 U/hr, reduces BP significantly. Certain populations may poorly tolerate these physiologic alterations; examples are patients who experienced significant blood loss or those with cardiovascular diseases. This subset may benefit from a lower oxytocin concentration.
1.) Rosseland LA, et al. Changes in BP and CO during cesarean delivery: the effects of oxytocin and carbetocin compared with placebo. Anes. 2013:119:541-51
2.) Kim TS, et al. Hemodynamic effects of cont. IV injection and bolus plus cont. IV injection of oxytocin in cesarean section. Kor J Anes. 2011;61:482-7