Cardiovascular stimulation induced by rapid increases in desflurane concentration in humans results from activation of tracheopulmonary and systemic receptors.

BACKGROUND

It was hypothesized that stimulation of rapidly adapting airway receptors produces the transient (2-4 min) circulatory responses to rapid increases in desflurane concentrations greater than 6%. Accordingly, it was reasoned that increasing the concentration of desflurane in one lung, without altering the concentration of desflurane in systemic blood, should cause cardiovascular stimulation, whereas once the airway receptors had adapted to the stimulation, an initial increase in the systemic concentration of desflurane should have little effect.

METHODS

After placement of a double-lumen endotracheal tube in four volunteers and establishment of a steady-state level of 4% desflurane in both lungs, the desflurane concentration was rapidly increased from 4% to 8% in one lung while decreasing it in the other, thereby obviating any increase in the systemic desflurane blood concentration (confirmed by analysis). After returning the desflurane end-tidal concentration to 4% in both lungs, this process was repeated for the contralateral lung thereby having exposed both lungs to 8% desflurane without increasing the systemic desflurane concentration. After returning desflurane concentration to 4%, it was increased in both lungs simultaneously to 8% and consequently in blood to 8% of an atm.

RESULTS

Rapid increases in desflurane concentrations in either lung, but not blood, significantly increased heart rate (17 +/- 5 beats/min, mean +/- SE, P < 0.05) and mean arterial blood pressure (15 +/- 5 mmHg, P < 0.05), but a greater increase in heart rate (43 +/- 5 beats/min, P < 0.05) and mean arterial blood pressure (46 +/- 11 mmHg, P < 0.05) occurred when both lungs were exposed simultaneously to rapidly increased desflurane concentration for the second time within 90 min. This result did not differ from the increase occurring on another day when both lungs and blood were exposed for the first time that day to 8% desflurane (heart rate 40 +/- 7 beats/min, P = 0.8; mean arterial blood pressure 40 +/- 3 mmHg, P = 0.5).

CONCLUSIONS

It was concluded that at least two sites respond to a rapid increase in desflurane concentrations greater than 6%: one site in the airways and/or lungs, and at least one other in a highly perfused tissue(s). The systemic site contributes more importantly.