Investigation of systemic bupivacaine toxicity using the in situ perfused working heart-brainstem preparation of the rat.

BACKGROUND

The inadvertent systemic administration of bupivacaine has been associated with fatal cardiovascular collapse. Systemic bupivacaine may affect neural control of the cardiovascular system in addition to having toxic actions on the heart. The study tested the hypothesis that systemic bupivacaine has toxic effects on brainstem cardiorespiratory control.

METHODS

The working heart-brainstem preparation (WHBP) of rat was used to examine the actions of bupivacaine administered either by arterial injection or brainstem microinjection. The WHBP is a decerebrate rostral-half of a bisected rat, which is artificially perfused with a carbogenated Ringer solution via the aorta. Phrenic nerve activity, perfusion pressure, and electrocardiographic results were recorded.

RESULTS

Systemic bupivacaine (3 microg/ml) evoked a prolonged pressor response (10.5 +/- 5 mmHg) associated with marked bradycardia (-45 +/- 22 beats/min) and prolonged the PR and QRS intervals of the electrocardiogram. The amplitude of respiratory sinus arrhythmia was attenuated (64 +/- 15%) by bupivacaine without affecting activity recorded from the phrenic nerve. Bupivacaine selectively attenuated the baroreflex gain (55 +/- 19%) but had no effect on the peripheral chemoreflex-evoked bradycardia. The bradycardia elicited by stimulation of the aortic depressor nerve was inhibited by bupivacaine, indicating baroreflex inhibition within the brainstem. Furthermore, bilateral microinjections of bupivacaine in the nucleus of the solitary tract reversibly inhibited the baroreflex.

CONCLUSIONS

These results demonstrate that arterial concentrations of bupivacaine that previously were shown to be cardiotoxic can selectively affect key cardiovascular control processes within the brainstem. Such impairment of neural cardiovascular control may contribute to the cardiovascular collapse associated with systemic bupivacaine.