Effects of Pain and Audiovisual Stimulation on the Opioid-induced Depression of the Hypoxic Ventilatory Response

Background: Normoxic and hypoxic ventilation are influenced by chemoreceptor and nonchemoreceptor drives. Although inhalational anesthetics blunt hypoxic ventilation, this effect is reversed by audiovisual stimulation but not by pain. Opioids reduce both normoxic and hypoxic ventilation, but their interaction with pain and audiovisual stimulation has not been fully reported.

Methods: Isocapnic, acute hypoxic ventilatory responses (AHRs) were measured in 11 volunteers. AHR and normoxic ventilation were measured under the following conditions: (1) eyes closed, no audio stimulation (low wakefulness); (2) low wakefulness conditions plus painful thermal stimulation; and (3) playing a computer game (high wakefulness), each with and without remifentanil infusion.

Results: The average (+/- sd) remifentanil dose was 0.035 +/- 0.012 [mu]g [middle dot] kg-1 [middle dot] min-1. Both normoxic and hypoxic ventilation were significantly reduced by the remifentanil infusion under all three conditions. The AHR values under low wakefulness conditions were 0.33 +/- 0.19 and 0.89 +/- 0.49 l [middle dot] min-1 [middle dot] sat-1 with and without remifentanil, respectively (P < 0.05). High wakefulness significantly increased AHR with and without remifentanil, whereas low wakefulness with pain did not. However, high wakefulness with remifentanil did not increase the AHR back to what was observed during low wakefulness without remifentanil.