Effects of surgical skin incision on respiration in patients anaesthetized with enflurane.

We measured ventilation in 12 subjects anaesthetized with enflurane (end-tidal concentration 1.25-1.45%) and nitrous oxide to assess the effect of surgical stimulation on ventilation in humans. Tidal volume and respiratory timing were measured by pneumotachograph before and just after a standardized surgical skin incision. Surgical stimulation increased ventilation by increasing tidal volume, which increased progressively over the first five breaths after incision. The first breath after the stimulus was prolonged, but the timing of the subsequent breaths returned rapidly to the duration observed before incision. Ventilation increased from median 3.6 (quartiles 2.9, 4.3) to 5.4 (3.8, 7.0) litre min-1 (P < 0.01). The increased tidal volume was not associated consistently with shortening of inspiratory duration.