Severe Bradycardia during Spinal and Epidural Anesthesia Recorded by an Anesthesia Information Management System

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Abstract
Background: Bradycardia and asystole can occur unexpectedly during neuraxial anesthesia. Risk factors may include low baseline heart rate, first-degree heart block, American Society of Anesthesiologists physical status 1, beta-blockers, male gender, and high sensory level. Anesthesia information management systems automatically record large numbers of physiologic variables that are combined with data input from the anesthesiologist to form the anesthesia record. Such large databases can be scanned for episodes of bradycardia. Methods: To select spinal and epidural anesthetics that did not also involve general anesthesia, 57,240 automated anesthesia records were scanned. Obstetrical patients and patients younger than age 12 yr were excluded. The electronic records selected were then scanned for episodes of moderate (heart rate < 50 and >/= 40 beats/min) or severe (heart rate < 40 beats/min) bradycardia. Results: A total of 6,663 cases (11.6%) met the inclusion criteria. Among the 677 cases of bradycardia (10.2%) were 46 cases of severe bradycardia (0.7%). In the final multivariate logistic regression analysis, baseline heart rate less than 60 beats/min (P </= 0.0001) and male gender (P </= 0.05) contributed significantly to risk for a severe bradycardia episode (odds ratio [OR]), 14.1 and 95% confidence interval [CI], 6.9-28.0, and OR, 2.1 and 95% CI, 1-4.3, respectively). For the 631 episodes of moderate bradycardia (9.5%), the final multivariate model included baseline heart rate less than 60 beats/min (OR, 16.2; 95% CI, 12.4-22.0), age younger than 37 yr (OR, 1.4; 95% CI, 1.1-1.7), male gender (OR, 1.4; 95% CI, 1.2-1.8), nonemergency status (OR, 1.7; 95% CI, 1.2-2.4), beta-blockers (OR, 1.6; 95% CI, 1.1-2.3), and case duration (OR, 2.0; 95% CI, 1.6-2.4) as significant risk factors. Time of occurrence of a bradycardia event was distributed widely across the entire duration of a case. Conclusions: Moderate or severe bradycardia may occur at any time during neuraxial anesthesia, regardless of the duration of anesthesia. Low baseline heart rate increases the risk for bradycardia.