The effect of low‐dose ketamine on fentanyl‐induced respiratory depression

This study evaluated if adding low-dose ketamine to fentanyl could offer a haemodynamically stable drug combination with little respiratory side-effects. Eight healthy, consenting male volunteers received in a random, cross-over and double-blind fashion both fentanyl 2 micrograms.kg-1 + ketamine 0.25 mg.kg-1 and fentanyl 2 micrograms.kg-1 + placebo. The fentanyl and placebo reduced minute ventilation, alveolar ventilation and oxygen consumption (p < 0.05), with little effect on haemodynamics. After fentanyl and ketamine, the decrease in minute ventilation and alveolar ventilation was attenuated compared to the placebo-containing combination (p < 0.05), but with a simultaneous increase in oxygen consumption (p < 0.05) and stimulation of haemodynamics (p < 0.05). Both treatments decreased oxygen saturation and arterial oxygen pressure similarly. Ketamine thus attenuated the fentanyl-induced reduction in ventilation without preventing the decrease in blood oxygenation. In conclusion, combining low-dose ketamine to fentanyl offers no benefits in terms of preventing respiratory depression.