Response to the Valsalva manoeuvre after spinal anaesthesia

The waveform from a Criticare 504 pulse oximeter was recorded during the performance of a standard Valsalva manoeuvre in 20 patients before and after spinal anaesthesia. The pulse oximeter waveform showed changes typical of the expected heart rate and pulse volume changes seen in each phase of the Valsalva manoeuvre. There were no significant changes in the typical pulse volume changes of the Valsalva manoeuvre after spinal anaesthesia, which achieved a sensory block ranging in upper extent from T3-T12. There was, however, a significant delay in recovery of the pulse volume in phase 4 of the Valsalva manoeuvre after spinal anaesthesia from a mean (SD) of 3.1 (0.9) s to 6.2 (3.1) s (p less than 0.05). There was also a significant reduction in reflex bradycardia seen in phase 4. However, this was found only at 5, 10 and 15 min after spinal anaesthesia and was not associated with a significant change in Valsalva ratio or maximum-to-minimum rate ratio. The study confirms that the normal response to a standard Valsalva manoeuvre is suppressed only mildly during spinal anaesthesia in normovolaemic fit patients.