Inhaled Anesthetics

Cardiovascular function is frequently preserved during N₂ O administration. Some reports showed deterioration of cardiac function with N₂ O-opioid combinations.^[351] Segmental wall motion abnormalities in areas of marginal myocardial perfusion was demonstrated in dogs when N₂ O and opioids are combined.^[538] However, in clinical studies of patients with ischemic cardiac disease, the addition of N₂ O to fentanyl or sufentanil was not to associated with any new ST-segment changes or segmental wall motion abnormalities.^[539] It was reported that N₂ O produced analgesia that was partially mediated by the release of a proenkephalin-derived family of endogenous opioid peptides.^[540] This suggests that interaction between opioids and N₂ O is neither synergistic nor additive. Combining N₂ O with an opioid in a balanced technique may not best employ drug interaction synergism. Although amnesia and intraoperative conditions may be somewhat improved, N₂ O does not produce any effects that are not already produced by either an opioid or a sedative-hypnotic.

Volatile anesthetics are frequently combined in low doses (one third to one half the MAC) with opioids in order to ensure amnesia and to promote immobility and hemodynamic stability.^[541] Low concentrations of volatile anesthetics in combination with opioids are usually well tolerated in patients with normal, as well as compromised, ventricular function. ^[541] Low concentrations of isoflurane have been effectively and safely used to treat intraoperative hypertension during high-dose sufentanil anesthesia for coronary artery surgery.^{[542] [543]}

Clinical trials of opioids supplemented with newer volatile anesthetics for cardiac surgery demonstrate well-preserved cardiac output and minimal decreases in mean arterial blood pressure.^{[544] [545]} Myocardial ischemia may not, however, always be ameliorated by approaches that combine opioids with potent inhaled agents in spite of apparent "good" hemodynamic control.

Some of the potent inhaled anesthetics can increase sympathetic nervous system activity and may increase the risk of myocardial ischemia in the cardiac patient.^{[546] [547]} Prior administration of fentanyl, in doses as low as 1.5 µg/kg, can markedly attenuate such responses.^[546] Alfentanil (10 µg/kg) is also effective in attenuating these effects.