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Sevoflurane and isoflurane abolished the phrenic long term facilitation in rats

Phrenic long-term facilitation (pLTF) is manifested by prolonged increase in phrenic nerve activity after episodes of acute intermittent hypoxia (AIH). The goal of the study was to explore the effects of sevoflurane and isoflurane monoanaesthesia at equal MAC values on induction of pLTF in rats, compared to urethane anaesthesia. After Biomedical Ethics Committee approval, Sprague-Dawley adult, male rats, BM of 300-350 g were used. Two experimental groups of nine animals each (sevoflurane and isoflurane) and one control group of seven animals (urethane) were formed. After achieving adequate depth of anaesthesia animals were tracheotomysed, mechanically ventilated and bilaterally vagotomised. Femoral veins and arteries were cannulated for saline infusion, blood pressure monitoring and arterial blood sampling. Phrenic nerve was dissected and recorded. After obtaining the planned level of anaesthesia (1.4 MAC for sevoflurane and isoflurane and 1.2 mg/kg for urethane intraperitoneally), animals were exposed to AIH protocol (5x3 min hypoxic episodes with FiO₂=0.09, separated by 3 min pause with FiO₂=0.5). The same level of anaesthesia was maintained to the end of the experiment. Peak phrenic nerve amplitude (PNA), respiratory frequency (f), and breathing rhythm parameters were analyzed during hypoxic episodes and at 15, 30, and 60 min after the last hypoxic episode and compared to baseline values (immediately before the first hypoxic episode). Data are presented as mean±SEM. A repeated measure ANOVA was used for analysis. Statistical significance was set at P<0.05. In both experimental groups average PNA decreased at 60 min after the last hypoxic episode compared to baseline values, i.e. pLTF was abolished. In sevoflurane group PNA decreased by 31.0±11.0% (P<0.01) and in isoflurane group decreased by 44.6±12.7% (P<0.01). In control (urethane) group average PNA increased by 108.7±25.3% (P<0.01) 60 min after the last hypoxic episode compared to baseline values, i.e. pLTF was induced. During all five hypoxic episodes average PNA increased in both experimental groups and in control group compared to baseline values, i.e. hypoxic ventilatory response (HVR) was preserved. Sevoflurane and isoflurane monoanaesthesia at 1.4 MAC abolished the pLTF compared to urethane anaesthesia.

anaesthetic volatile; hypoxia; research animal

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