Spectral analysis of sudden bradycardia during intrathecal meperidine anesthesia.
OBJECTIVE
Severe bradycardia occurring suddenly during spinal anesthesia, although rare, is potentially fatal. Bradycardias are more common after intrathecal meperidine. We report two such episodes occurring in elderly male patients undergoing transurethral surgery.


METHODS
Subarachnoid block was provided using 50 mg meperidine. Autonomic function was assessed by measuring heart rate (HR) variability using R-R intervals from standard electrocardiographic recordings. Frequency-domain spectra were constructed from 512 heartbeats, and an autoregressive method was used to calculate spectral power.


RESULTS
In both patients, bradycardia (HR <50 beats/min) occurred after about 10 minutes and was associated with severe hypotension and a 10- to 100-fold increase in spectral density in both the low (0.04-0.15 Hz), mainly sympathetic, and the high (0.15-0.40 Hz), mainly parasympathetic, frequency bands. These spectral increases were subsequently attenuated by intravenous atropine. Heart rate slowing was noted to be periodic, or oscillatory, in one patient.


CONCLUSIONS
Sudden increases in vagal, or parasympathetic, activity probably accounted for bradycardia.
Department of Anaesthesia and Intensive Care, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin.
L A
LA
Critchley
S
S
Chan
Y H
YH
Tam
D000759:Adjuvants, Anesthesia / Q000008:administration & dosage / Q000009:adverse effects*; D000368:Aged; D000775:Anesthesia, Spinal / Q000009:adverse effects*; D001919:Bradycardia / Q000139:chemically induced*; D004562:Electrocardiography / Q000379:methods; D006801:Humans; D007278:Injections, Spinal; D008297:Male; D008614:Meperidine / Q000008:administration & dosage / Q000009:adverse effects*
D000759:Adjuvants, Anesthesia; D008614:Meperidine