Opioid analgesic drugs anesthesia

Opioid analgesic drugs (OADs), particularly fentanyl and its analogs alfentanil, remifentanil, and sufentanil, are extensively used for anesthesia and analgesia. Administration of intravenous hypnotics and OADs as a high dose opioid, low dose hypnotic (usually a benzodiazepine such as midazolam) has found wide application in cardiac anesthesia and to produce procedural sedation for endoscopy, catheterizations, and a variety of other surgical procedures where sedation and... 

Etomidate is a carboxylated imidazole that can be used for induction of anesthesia in patients with limited cardiovascular reserve. Its major advantage over other intravenous anesthetics is that it causes minimal cardiovascular and respiratory depression. Etomidate produces a rapid loss of consciousness, with minimal hypotension even in elderly patients with poor cardiovascular reserve. The heart rate is usually unchanged, and the incidence of apnea is low. The drug has no analgesic effects, and coadministration of opioid analgesics is required to decrease cardiac responses during tracheal intubation and to lessen spontaneous muscle movements. Following an induction dose, initial recovery from etomidate is less rapid (< 10 minutes) compared with recovery from propofol. 

Several drugs are used intravenously, alone or in combination with other drugs, to achieve an anesthetic state (as components of balanced anesthesia) or to sedate patients in intensive care units who must be mechanically ventilated. These drugs include the following (1) barbiturates (thiopental, methohexital) (2) benzodiazepines (midazolam, diazepam) (3) opioid analgesics (morphine, fentanyl, sufentanil, alfentanil, remifentanil) (4) propofol (5) ketamine and (6) miscellaneous drugs (droperidol, etomidate, dexmedetomidine). Figure 25-2 shows the structures of... 

Recovery is sufficiently rapid with most intravenous drugs to permit their use for short ambulatory (outpatient) surgical procedures. In the case of propofol, recovery times are similar to those seen with sevoflurane and desflurane. Although most intravenous anesthetics lack antinociceptive (analgesic) properties, their potency is adequate for short superficial surgical procedures when combined with nitrous oxide or local anesthetics, or both. Adjunctive use of potent opioids (eg, fentanyl, sufentanil or remifentanil see Chapter 31) contributes to improved cardiovascular stability, enhanced sedation, and perioperative analgesia. However, opioid compounds also enhance the ventilatory depressant effects of the intravenous agents and increase postoperative emesis. Benzodiazepines (eg, midazolam, diazepam) have a slower onset and slower recovery than the barbiturates or propofol and are rarely used for induction of anesthesia. However, preanesthetic administration of benzodiazepines (eg, midazolam) can be used to provide anxiolysis, sedation, and amnesia when used as part of an inhalational, intravenous, or balanced anesthetic technique. 

Opioids interact specifically with opioid receptors that are present throughout the body but are of primary importance within the CNS. Opioid drugs are used widely in both human and veterinary medicine as adjuncts to anesthesia and post-operatively because of their efficacy as analgesics and their relative safety even in critically ill or compromised patients. However, there are significant species differences in the pharmacological response to opioid administration and their use in the horse has been limited by undesirable physiological and behavioral side-effects and equivocal or short duration of analgesic efficacy (Bennett Steffey 2002). 

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