Propofol inhalational

Hypnotics. Common hypnotics are thiopental, propofol, midazolam, etomidate, ketamine and inhaled anesthetics. The incidence of hypersensitivity reactions with thiopental is rare. Recently, thiopental was involved in less than 1% of allergic reactions in France [9]. Ever since Cremophor EL, used as a solvent for some non-barbiturate hypnotics, has been avoided, many previously reported hypersensitivity reactions have disappeared. In the last French surveys, reactions to propofol accounted for less than 2.5% of allergic reactions, and reactions to midazolam, etomidate or ketamine appear to be really rare [9]. Finally, no immune-mediated immediate hypersensitivity reaction involving isoflurane, desflurane or sevoflurane has been reported despite their wide use. 

Opioids play an important role in anesthetic practice. Opioid analgesics potentiate the efficacy of anesthetics. They can be given as part of the premedication as well as during the operation. Examples of short acting agents with high potency are fentanyl, sufentanyl, alfentanil and remifentanil. Because of their hemodynamic stability these agents can be used for patients with compromised myocardial function. Respiration must be maintained artificially and may be depressed into the postoperative period. They are usually supplemented with inhalation anesthetic, benzodiazepines or propofol. 

Propofol can be used for induction as well as maintenance of anesthesia. It is very lipophilic and induction of anesthesia takes place within 30 seconds. After a single dose the patient awakes in approximately 5 minutes and after anesthesia by continuous intravenous administration of longer duration recovery may take 10-15 minutes. It can be used in combination with the usual range of premedications, analgesics, muscle relaxants and inhalation anesthetic agents. 

Rapid recovery and its antiemetic properties make propofol anesthesia very popular as an induction agent for outpatient anesthesia. Propofol can also be used to supplement inhalational anesthesia in longer procedures. Both continuous infusion of propofol for conscious sedation and with opioids for the maintenance of anesthesia for cardiac surgery are acceptable techniques. 

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. 

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. 

Many diagnostic, therapeutic, and minor surgical procedures require neither general anesthesia nor the availability of specialized equipment and facilities necessary for inhaled anesthesia. In this setting, regional or local anesthesia supplemented with midazolam or propofol and opioid analgesics may be a more appropriate and safer approach than general anesthesia. 

A continuous intravenous infusion of propofol can be used to maintain anaesthesia. This technique of total intravenous anaesthesia is becoming more popular because the quality of recovery may be better than after inhalational anaesthesia. 

A 35-year-old man developed recurrent respiratory depression after being given alfentanil 0.0125 mg/kg for vitreoretinal surgery (5). General anesthesia was induced with a combination of propofol, rocuronium, and alfentanil, subsequent inhalation of isoflurane, and three additional doses of alfentanil (total 0.04 mg/kg over 2 hours). The pulse oxygen saturation fluctuated and was as low as 89% 180 minutes after extubation. 

The risk of postoperative nausea and vomiting has been studied in a randomized, controlled trial of total intravenous anesthesia with propofol versus inhalational... 

Susceptibility factors and prophylaxis Although malignant hyperthermia is usually associated with the muscle relaxant suxamethonium, all inhalational anesthetics have been implicated and will be unsafe if risk factors for this condition are present, for example a family history or one of the congenital muscle disorders (76). This must be considered in patients at risk, as there are readily acceptable alternatives, such as propofol (77) and midazolam (78). 

Sneyd JR, Carr A, Byrom WD, Bilski AJ. A meta-analysis of nausea and vomiting following maintenance of anaesthesia with propofol or inhalational agents. Eur J Anaesthesiol 1998 15(4) 433-45. 

Propofol is being examined for its potential as a routine i.v. induction agent in the horse, as well as a component of TIVA, as an alternative to maintenance of anesthesia with inhalant agents. Propofol has not been adopted for widespread use in equine anesthesia yet and cost plays a role currently. 

Figure 2 Chemical structures for (a) inhalational anesthetics and (b) the intravenous anesthetic propofol.

Prototypical Compounds Inhalational agents Halothane Isoflurane Enflurane, Sevoflurane. Intravenous agents Propofol... 

Chemical Formula Inhalational - Halothane C2HBrClF3 Isoflurane C3H2CIF5O Enflurane C3H2OCIF5 Sevoflurane C4H3F7O. Intravenous -Propofol C12 HjgO... 

Volatile anesthetics are administered exclusively via inhalation. Propofol is administered only intravenously. Exposure by other routes would not be anticipated. 

Operationally, anaesthetics can be classified as inhalational or intravenous. The most used compounds of this last group are thiopental, propofol and ketamine recently, new synthetic opioids related to phenylpiperidines (phentanyl and its congeners, sufentanil, alfentanil, remifentanil) are also used. 

Antimuscarinic drugs are used as premedication to prevent salivation and bronchial secretions during an operation and to protect the heart from arrhythmias caused by inhalation anaesthetics such as halothane and propofol. They are less commonly used nowadays because modern anaesthetics are less irritant. 

Intravenous anaesthetics are used to induce general anaesthesia, followed by an inhalation anaesthetic for maintenance, and for short surgical procedures. Propofol is commonly used for both induction and maintenance anaesthesia. 

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. 

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