Propofol Nitrous oxide

Many of the drugs used in modern anaesthetic practice have an effect on the CT7 and vomiting centre either directly or indirectly, e.g. stimulation of the vestibular apparatus, stimulation of the CTZ by opioid agonist drugs, and an anti-emetic effect of propofol or emetogenic effect of nitrous oxide. Propofol... 

There is good evidence that propofol exerts an anti-emetic effect. The mechanism of this is unclear, but animal studies have shown that it may involve depleting the area postrema of serotonin as well as direct GABA-mediated inhibition, or inhibition of dopamine release in the brain. This probably requires a plasma concentration of over 350 ng-mL-1, and therefore will be seen when propofol is used as an induction agent for very short cases, or when it is used as an infusion in longer cases. Nitrous oxide... 

An anxious 5-year-old child with chronic otitis media and a history of poorly controlled asthma presents for placement of ventilating ear tubes. General anesthesia is required for this short elective ambulatory surgery procedure. What preanesthetic medication should be administered Which of the three commonly used anesthetic techniques would you choose to use in this situation (1) inhalational anesthesia with sevoflurane for induction and maintenance in combination with nitrous oxide, (2) intravenous anesthesia with propofol for induction and maintenance of anesthesia in combination with remifentanil, or (3) balanced anesthesia using propofol for induction of anesthesia followed by a combination of sevoflurane and nitrous oxide for maintenance of anesthesia ... 

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. 

A 61-year-old woman undergoing mitral valve surgery received fentanyl, midazolam, nitrous oxide, and propofol infusion 3 mg/kg/hour during a 5-hour anesthetic. She developed lactic acidosis soon after the completion of surgery and required reintubation and ventilation. The peak lactate concentration, which occurred 1 day later, was 14.3 mmol/1. There was also mild disturbance of liver function. She eventually recovered. 

Recovery is sufficiently rapid with many intravenous drugs to permit their extensive use for short ambulatory (outpatient) surgical procedures. In the case of propofol, recovery times are similar to those seen with the shortest-acting inhaled anesthetics. The anesthetic potency of intravenous anesthetics, including thiopental, ketamine, and propofol, is adequate to permit their use as the sole anesthetic in short surgical procedures when combined with nitrous oxide and opioid analgesics. 

In 113 patients undergoing general anesthesia, intravenous midazolam 15 mg slowed recovery of the twitch height after vecuronium and atracurium compared with diazepam. The recovery index was not altered (162). However, in another study in 20 patients, midazolam 0.3 mg/kg did not affect the duration of blockade, recovery time, intensity of fasciculations, or adequacy of relaxation for tracheal intubation produced by suxamethonium 1 mg/kg, nor the duration of blockade and adequacy of relaxation for tracheal intubation produced by pancuronium 0.025 mg/kg in incremental doses until 99% depression of muscle-twitch tension was obtained (161). Furthermore, in 60 patients undergoing maintenance anesthesia randomly assigned to one of six regimens (etomidate, fentanyl, midazolam, propofol, thiopental plus nitrous oxide, or isoflurane plus nitrous oxide), midazolam did not alter rocuronium dosage requirements (165). 

Uses. Nitrous oxide is used to maintain surgical anaesthesia in combination with other anaesthetic agents, e.g., isoflurane or propofol, and, if required, muscle relaxants. Entonox provides analgesia for obstetric practice, for emergency management of injuries, and during postoperative physiotherapy. 

A randomized prospective trial in 60 children undergoing outpatient anesthesia showed a 30% shorter time from discontinuation of anesthesia to eye opening and return to full wakefulness in patients receiving propofol alone compared with halothane + nitrous oxide anesthesia (14). Propofol was associated with a 17% incidence of emesis compared with 58 and 53% for halothane + nitrous oxide and propofol + nitrous oxide anesthesia respectively. 

The characteristics of sevoflurane anesthesia have been compared with those of target-controlled infusion of propofol in 61 day-case adults undergoing surgery (25). All received nitrous oxide 50% and fentanyl 1 pg/kg. After insertion of a laryngeal mask airway the propofol target concentration was reduced from 8 to 4 pg/ml and the... 

Crawford MW, Lerman J, Sloan MH, Sikich N, Halpern L, Bissonnette B. Recovery characteristics of propofol anaesthesia, with and without nitrous oxide a comparison with halothane/nitrous oxide anaesthesia in children. Paediatr Anaesth 1998 8(l) 49-54. 

Visser K, Hassink EA, Bonsel GJ, Moen J, Kalkman CJ. Randomized controlled trial of total intravenous anesthesia with propofol versus inhalation anesthesia with iso-flurane-nitrous oxide postoperative nausea with vomiting and economic analysis. Anesthesiology 2001 95(3) 616-26. 

Nelskyla K, Korttila K, Yli-Hankala A. Comparison of sevoflurane-nitrous oxide and propofol-alfentanil-nitrous oxide anaesthesia for minor gynaecological surgery. Br J Anaesth 1999 83(4) 576-9. 

Convulsions have been reported in two patients with no history of epilepsy after induction of anesthesia with propofol (44). However, in a crossover comparison in 20 epileptic patients undergoing cortical resection, in which the effects on the electrocorticogram of either propofol or thiopental during isoflurane + nitrous oxide anesthesia were studied, propofol caused no greater proconvulsive effect than thiopental, which is used to treat status epilepticus (45). In spite of occasional reports, a true epileptogenic effect of propofol remains to be proven. 

Preliminary investigations of intramuscular droperidol, nitrous oxide, and intravenous propofol have yielded favorable results in the treatment of acute migraine headache. Future studies may establish a more defined role for these agents in migraine management. 

Fentanyl, ketamine, midazolam, propofol, thiopental Enflurane, desflurane, halothane, isoflurane, nitrous oxide, sevoflurane... 

When nitrous oxide, oxygen, and propofol are used for maintenance of general anesthesia, supplementation with analgesics and neuromuscular-blocking agents is usually required. Induction of anesthesia with propofol is frequently... 

FIGURE 82 Propofol, like thiopental, induces anesthesia rapidly, but the maintenance of anesthesia may require nitrous oxide, inhalational anesthetics, and opioids. Propofol does not impair hepatic or renal functions. 

CNS depressants (e.g., hypnotics/sedatives, inhalational anesthetics, narcotics) can increase the CNS depression induced by propofol. Morphine premedication with nitrous oxide decreases the necessary propofol maintenance infusion rate and therapeutic blood concentrations when compared to nonnarcotic (e.g., lorazepam) premedication. In addition, the induction dose requirements of propofol may be reduced in patients with IM or IV premedication, particularly with narcotics alone or in combination with sedatives. These agents may increase the anesthetic effects of propofol and may also result in more pronounced decreases in systolic, diastolic, and mean arterial pressures and cardiac output. 

In general, the effects of the combined use of general anaesthetics are at least additive. The required dose of propofol will be lower if it is given with nitrous oxide, halothane or isoflurane. The anaesthetic effects of propofol and sevoflurane appear to be additive in ECT, and synergy has been reported between propofol and eto-midate. 

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