British journal of anaesthesia
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Comment Letter Case Reports
Severe vasovagal attack during regional anaesthesia for caesarean section.
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We measured breath interval to characterize the time course of opioid effect in anaesthetized patients breathing spontaneously during knee replacement surgery with concurrent regional nerve blockade. Breath interval was recorded before and after a single dose of fentanyl 0.75 microgram kg-1 i.v. Breath interval was measured between the start of successive inspirations, identified by a decrease in carbon dioxide concentration, sampled at the laryngeal mask connection. ⋯ End-tidal carbon dioxide concentrations increased from a baseline of 6.6 (0.9)% to a peak of 8.2 (0.8)%. Breath interval was a useful and reproducible method of monitoring the duration of opioid effect in anaesthetized patients breathing spontaneously when surgical stimulation was not affecting the CNS. The data provide information on the duration of action of fentanyl and could guide dosage.