Anesthesia/anesthetics fentanyl

Concomitant anesthesia - Certain forms of conduction anesthesia, such as spinal anesthesia and some peridural anesthetics, can alter respiration by blocking intercostal nerves. Fentanyl can also alter respiration through other mechanisms. 

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. 

Analgesic efficacy and clinical use Alfentanil is a shortacting potent opioid with analgesic and anesthetic properties (Larijani and Goldberg, 1987). It is less potent than fentanyl but administration can be better controlled. It is mostly used as a supplement to general anesthesia or as a primary anesthetic e.g. in cardiac surgery. Intra-... 

Analgesic efficacy and clinical use Fentanyl (Clotz and Nahata, 1991) is a potent analgesic and anesthetic compound. It is used for the treatment of severe acute and chronic pain, as a pre-medication or adjunct to anesthesia and as a primary anesthetic for the induction or maintenance of anesthesia. In combinations with neuroleptics e.g. droperidole, it induces a pain free and calm state known as neuroleptanalgesia (Foldes, 1973). In this condition, surgery can be performed in an awake patient, who is able to cooperate with the surgeon. 

Analgesic efficacy and clinical use Sufentanil (Rosow, 1984 Monk et al., 1988) is a very potent fentanyl analog with analgesic and anesthetic properties and a more rapid onset and a shorter duration of action. It is used for perioperative analgesia, short duration anesthesia and as an adjunct to various anesthetic procedures including neuroleptanalgesia (Isaacson, 1992). 

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... 

Adjunctive use of potent opioids (eg, fentanyl and related compounds) contributes cardiovascular stability, enhanced sedation, and profound analgesia. Other intravenous agents such as the benzodiazepines (eg, midazolam, diazepam) have slower onset and recovery features and are rarely used for induction of anesthesia. However, preanesthetic administration of benzodiazepines can be used to provide a basal level of sedation and amnesia when used in conjunction with other anesthetic agents. 

The combination of droperidol and fentanyl is a fixed ratio preparation called innovar. Since droperidol is a neuroleptic substance, innovar is said to produce neurolept analgesia if combined with a more potent anesthetic, innovar produces neuroleptic anesthesia. A neuroleptic has adrenergic blocking as well as sedative, antiemetic, and anticonvulsant properties. Since innovar can cause extrapyramidal muscle movements, it is contraindicated in Parkinson s patients. 

The addition of fentanyl 1 pg/ml to ropivacaine 7.5 mg/ml did not improve nerve blockade by axillary brachial plexus anesthesia in a double-blind, randomized study in 30 patients undergoing orthopedic procedures (31). In another double-blind, randomized study, 60 patients receiving axillary brachial plexus blockade were given 0.25% bupivacaine 40 mg, 0.25% bupivacaine 40 mg plus fentanyl 2.5 pg/ml, or 0.125% bnpivacaine 40 mg plus fentanyl 2.5 pg/ml (32). The addition of fentanyl 2.5 pg/ml prolonged sensory and motor blockade without any improvement in the onset of anesthesia and no significant increase in adverse effects. These two studies have reaffirmed the current position of conflicting results in studies of the benefits of adding fentanyl to local anesthetics for peripheral nerve blockade. 

Fentanyl (0.001 mg/kg i.v.) can be used with xylazine (0.44 mg/kg i.v.) for anesthetic premedication. Fentanyl is sometimes used as an anesthetic adjunct during inhalation anesthesia to improve analgesia. The pharmacokinetics of fentanyl make it ideal for administration by constant rate infusion and it can be administered intra-operatively at a rate of 0.001-0.004 mg/kg/h after a 0.001 mg/kg loading dose. To prevent excitement or locomotory stimulation in recovery, the infusion should be discontinued 30 min prior to recovery or the horse should be sedated with xylazine (0.1 mg/kg i.v.) prior to recovery. 

Another nonbarbiturate anesthetic is the imidazole carboxylate etomidate. Even though it produces no analgesia, it is used with fentanyl (see later) to produce very rapid anesthesia induction. The drug s appeal is its minimal effect on respiration and the cardiovascular system. Unlike many of the volatile compounds, it produces no annoying histamine release. It does cause intermittent muscle twitching. 

The structure of fentanyl and related compounds are given in Table 24.4. Fentanyl is a p agonist with approximately 80 times greater potency than morphine. Fentanyl has been used in combination with nitrous oxide for balanced anesthesia and in combination with droperidol for neurolepalgesia. The advantages of fentanyl over morphine for anesthetic procedures are its shorter duration of action (1-2 hours) and the fact that it does not cause histamine release on intravenous injection. 

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