engleski

Remifentanil attenuates the phrenic long term facilitation in rats subjected to acute intermittent hypoxia

Long term facilitation (LTF) is sustained augmentation of respiratory motor output elicited by acute intermittent hypoxia (AIH), and is considered as a form of the central nervous system plasticity. It has been demonstrated in urethane‐ anaesthetized rats. Different anesthetics might alter the expression of LTF. Recent studies point to central inhibitory effect of opioids on the hypoxic ventilatory response in humans. It remains unknown whether opioids modify expression of phrenic LTF. The goal of this study was to investigate whether intravenous infusion of remifentanil would depress phrenic LTF in the model of AIH in urethane- anaesthetized rats. The phrenic nerve activity was recorded in 16 adult, male, Sprague‐Dawley rats, bilaterally vagotomised, paralysed and mechanically ventilated. The phrenic nerve recordings monitored central respiratory activity. The animals were divided in 2 groups ; urethane-anaesthetized (1.2 g/kg i.p., n=6) and urethane‐anaesthetized + remifentanil infusion (0.5 μg/kg/min i.v., n=10). Rats were exposed to five, 3‐min hypoxic episodes (FiO2=0.09), separated by 3 minutes of hyperoxia (FiO2=0.5). Phrenic nerve amplitude (PNA), burst frequency (f), inspiratory time (Ti), expiratory time (Te) and total respiratory cycle duration (Ttot) were analyzed during 5 hypoxias and 15, 30, and 60 minutes after the final hypoxic episode, and compared to the baseline values prior to the first hypoxic episode. At the end of experiment, infusion of remifentanil was stopped and phrenic nerve activity was compared to baseline values prior to remifentanil infusion. Isocapnia was successfully maintained throughout the protocol. There was a significant increase of PNA (138.8  28.3 %, P<0.001) in urethane‐anaesthetized group 60 minutes after the last hypoxic episode compared to the baseline values, i.e. the LTF was induced. In the remifentanil group no significant changes of PNA were recorded at any time point after the last hypoxic episode, i.e. no LTF was observed. Remifentanil infusion prolonged Ti (0.84 s vs. 0.51 s, P<0.001), whereas Te and Ttot were not significantly changed. After remifentanil infusion was stopped, PNA was not significantly different compared to baseline values prior to infusion. Intravenous infusion of remifentanil attenuated phrenic LTF in urethane-anaesthetized rats following AIH protocol.

opioids; anaesthesia; long-term facilitation

nije evidentirano