In: Anesthesia4 Mar 2010
The use of the conscious inhalation sedative nitrous oxide has a long history of success and safety in the dental office provided that supplemental oxygen is administered. Nitrous oxide-oxygen inhalation sedation has a rapid onset and recovery, provides varying degrees of analgesia, and has minimal respiratory, cardiovascular, and other adverse effects. This is likely the most common form of sedation performed by dentists today. Unfortunately, this technique does not always provide adequate sedation for all dental patients who need it. Alternative techniques, such as intravenous sedation, have therefore been developed.
Inhalation sedation with drugs other than nitrous oxide has not been popular for several reasons. Unlike nitrous oxide, most inhalation anesthetics have a pungent odor and therefore are not well accepted by the conscious patient. Additionally, most of these anesthetics produce a relatively slow onset and recovery. Potent inhaled volatile anesthetics are considered ”complete” anesthetics in that they produce hypnosis, amnesia, analgesia, and muscle relaxation in appropriate doses. Desflurane and sevoflurane are 2 relatively new inhaled anesthetics which have rapid onset and recovery. Desflurane is particularly pungent and unpleasant for the awake patient to inhale. Sevoflurane, on the other hand, is pleasant-smelling and well tolerated for mask induction of general anesthesia in both adults and children.
The potential for using sevoflurane as a sedative has recently been explored, but only on volunteers not undergoing a surgical procedure. If this drug as a single agent were to provide deep sedation with profound amnesia, analgesia, and hypnosis coupled with a rapid onset and recovery, another valuable technique for outpatient ambulatory sedation would become available.
Intravenous deep sedation is commonly used in dentistry and medicine for many surgical procedures. One of the most common forms of deep intravenous sedation used by dentist and physician anesthesiologists is a combined technique using midazolam, fentanyl, and propofol. These drugs all have a short alpha half-life and provide for relatively clear awakening following procedures in which adequate local anesthesia can be obtained.
The purpose of this study was to compare 2 deep sedative techniques: sevoflurane in oxygen inhaled via a nasal hood; and an intravenous combined drug technique using baseline sedation with fentanyl and midazolam followed by a propofol infusion.
Sevoflurane (CF2H-0-CH[CF3]2), like desflurane, is a highly fluorinated volatile ether anesthetic. The substitution of fluorine for other halogens is thought to produce a blood: gas solubility one-half to one-third that of isoflurane (Figure 1). This low blood: gas solubility provides for a rapid increase in alveolar concentrations during induction of anesthesia, a more rapid decrease in alveolar concentrations during elimination, and more precise control of alveolar concentration during maintenance of anesthesia. The vapor pressure of sevoflurane is 170 mm Hg and is similar to that of enflurane. Sevoflurane has a minimum alveolar concentration (MAC), the alveolar concentration required to prevent movement upon skin incision in 50% of patients, of approximately 2.0% for the 30- to 60-year-old patient, with significant variability based on age and physical status. The 4‘MAC awake,” the alveolar concentration abolishing appropriate response to command in 50% of patients, is 0.61%, approximately one-third MAC, for sevoflurane. The importance of MAC awake is that at this concentration, the capacity to learn new information is suppressed and amnesia is typically present. The fact that this low alveolar concentration produces amnesia makes this agent potentially useful as a deep sedative agent.
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Figure 1. The chemical structures of inhalation anesthetic agents.
The stability of sevoflurane has been extensively studied. Sevoflurane is resistant to degradation by acids, but there is significant temperature-dependent degradation by bases such as soda lime or Baralyme used for removing carbon dioxide in anesthetic circuits. The breakdown product is an olefin (CFH2-0-C[ = CF2][CF3]), termed compound A, which is of concern because it is lethal in rodents at a concentration of 400 ppm. The use of an open, scavenged system such as a nasal hood for administration of sevoflurane in dentistry would not be expected to produce this undesirable product since rebreathing is negligibl878e and carbon dioxide absorbers are not used. order levitra
Another concern with sevoflurane involves its vulnerability to biodegradation, producing organic and inorganic fluoride in both animals and humans. Approximately 3% of sevoflurane taken up is metabolized. Potential hepatic and renal toxicity, while possible, have not been realized as evidenced by only two cases of hepatic injury and none for renal injury reported from Japan, where more than 1 million patients have been anesthetized with this agent. Sevoflurane, like all of the other potent inhalation agents, can induce malignant hyperthermia in susceptible individuals.
The physiological effects of sevoflurane are similar to other agents such as isoflurane and desflurane. Sevoflurane causes apnea at 1.5 to 2.0 MAC. It decreases the ventilatory response to increased carbon dioxide levels and, like other inhalation anesthetics, may relax bronchial smooth muscle. The circulatory effects of sevoflurane have similarities to both isoflurane and halothane. Sevoflurane decreases blood pressure in a dose-dependent fashion, in part by decreasing peripheral vascular resistance. Although cardiac output tends to be preserved, depression of myocardial contractility can occur and excessive levels can produce cardiovascular collapse. Like most other ether anesthetics, sevoflurane should not sensitize the myocardium to arrhythmias caused by epinephrine nor predispose to ventricular dysrhythmias. There is a small but measurable decrease in coronary vascular resistance with sevoflurane. Splanchnic circulation, including renal blood flow, is preserved. The central nervous system effects of sevoflurane are similar to other inhaled anesthetics.
Blog invites submissions of review articles, reports on clinical techniques, case reports, conference summaries, and articles of opinion pertinent to the control of pain and anxiety in dentistry.