Anesthesia and analgesia
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Anesthesia and analgesia · Jun 1999
ReviewHypothesis: volatile anesthetics produce immobility by acting on two sites approximately five carbon atoms apart.
All series of volatile and gaseous compounds contain members that can produce anesthesia, as defined by the minimum alveolar anesthetic concentration (MAC) required to produce immobility in response to a noxious stimulus. For unhalogenated n-alkanes, cycloalkanes, aromatic compounds, and n-alkanols, potency (1 MAC) increases by two-to threefold with each carbon addition in the series (e.g., ethanol is twice as potent as methanol). Total fluorination (perfluorination) of n-alkanes essentially eliminates anesthetic potency: only CF4 is anesthetic (MAC = 66.5 atm), which indicates that fluorine atoms do not directly influence sites of anesthetic action. Fluorine may enhance the anesthetic action of other moieties, such as the hydrogen atom in CHF3 (MAC = 1.60 atm), but, consistent with the notion that the fluorine atoms do not directly influence sites of anesthetic action, adding -(CF2)n moieties does not further increase potency (e.g., CHF2-CF3 MAC = 1.51 atm). Similarly, adding -(CF2)n moieties to perfluorinated alkanols (CH2OH-[CF2]nF) does not increase potency. However, adding a second terminal hydrogen atom (e.g., CHF2-CHF2 or CH2OH-CHF2) produces series in which the addition of each -CF2- "spacer" in the middle of the molecule increases potency two- to threefold, as in each unhalogenated series. This parallel stops at four or five carbon atom chain lengths. Further increases in chain length (i.e., to CHF2[CF2]4CHF2 or CHF2[CF2]5CH2OH) decrease or abolish potency (i.e., a discontinuity arises). This leads to our hypothesis that the anesthetic moieties (-CHF2 and -CH2OH) interact with two distinct, spatially separate, sites. Both sites must be influenced concurrently to produce a maximal anesthetic (immobility) effect. We propose that the maximal potency (i.e., for CHF2[CF2]2CHF2 and CHF2[CF2]3CH2OH) results when the spacing between the anesthetic moieties most closely matches the distance between the two sites of action. This reasoning suggests that a distance equivalent to a four or five carbon atom chain, approximately 5 A, separates the two sites. ⋯ Volatile anesthetics may produce immobility by a concurrent action on two sites five carbon atom lengths apart.
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Anesthesia and analgesia · Jun 1999
Multicenter Study Clinical TrialMiddle latency auditory evoked responses and electroencephalographic derived variables do not predict movement to noxious stimulation during 1 minimum alveolar anesthetic concentration isoflurane/nitrous oxide anesthesia.
The electroencephalogram (EEG) and middle latency auditory evoked responses (MLAER) have been proposed for assessment of the depth of anesthesia. However, a reliable monitor of the adequacy of anesthesia has not yet been defined. In a multicenter study, we tested whether changes in the EEG and MLAER after a tetanic stimulus applied to the wrist could be used to predict subsequent movement in response to skin incision in patients anesthetized with 1 minimum alveolar anesthetic concentration (MAC) isoflurane in N2O. We also investigated whether the absolute values of any of these variables before skin incision was able to predict subsequent movement. After the induction of anesthesia with propofol and facilitation of tracheal intubation with succinylcholine, 82 patients received 1 MAC isoflurane (0.6%) in N2O 50% without an opioid or muscle relaxant. Spontaneous EEG and MLAER to auditory click-stimulation were recorded from a single frontoparietal electrode pair. MLAER were severely depressed at 1 MAC isoflurane. At least 20 min before skin incision, a 5-s tetanic stimulus was applied at the wrist, and the changes in EEG and MLAER were recorded. EEG and MLAER values were evaluated before and after skin incision for patients who did not move in response to tetanic stimulation. Twenty patients (24%) moved after tetanic stimulation. The changes in the EEG or MLAER variables were unable to predict which patients would move in response to skin incision. Preincision values were not different between patients who did and did not move in response to skin incision for any of the variables. MLAER amplitude increased after skin incision. We conclude that it is unlikely that linear EEG measures or MLAER variables can be of practical use in titrating isoflurane anesthesia to prevent movement in response to noxious stimulation. ⋯ Reliable estimation of anesthetic adequacy remains a challenge. Changes in spontaneous or auditory evoked brain activity after a brief electrical stimulus at the wrist could not be used to predict whether anesthetized patients would subsequently move at the time of surgical incision.
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Anesthesia and analgesia · Jun 1999
Patients with malignant osteopetrosis are at high risk of anesthetic morbidity and mortality.
The anesthetic literature contains no focused discussion of the perioperative management and risks of children with malignant autosomal recessive osteopetrosis (osteopetrosis). We retrospectively analyzed the perioperative morbidity and mortality rates encountered in the anesthetic management of children with osteopetrosis. We compared the perioperative mortality rate for this patient population with that for other pediatric patients in our institution and that reported in the literature for children and other high-risk patients. We also investigated the inability to intubate the tracheas of children with osteopetrosis compared with other pediatric patients in our institution. Using Fisher's exact test, patients with osteopetrosis were found to have a higher likelihood of perioperative mortality compared with other children or all ASA physical status III, but not ASA physical status IV, patients (P < 0.05). Finally, we discovered that children with osteopetrosis were more likely to have tracheas that could not be intubated than other pediatric patients in our institution. We conclude that children with osteopetrosis are at risk of adverse respiratory events and mortality associated with these adverse events. ⋯ Osteopetrosis is a rare disease that increases perioperative morbidity and mortality. By performing a retrospective chart review, we found that this increased perioperative morbidity and mortality is primarily related to airway and respiratory factors. Anesthetic management strategies should consider the factors that cause the high frequency of adverse airway events in this patient population.
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Anesthesia and analgesia · Jun 1999
Randomized Controlled Trial Comparative Study Clinical TrialPreoperative oral antiemetics for reducing postoperative vomiting after tonsillectomy in children: granisetron versus perphenazine.
In a prospective, randomized, double-blinded trial, we evaluated the efficacy of two antiemetics given orally, granisetron and perphenazine, for preventing postoperative vomiting after tonsillectomy with or without adenoidectomy in children. One hundred pediatric patients, ASA physical status I, aged 4-10 yr, received either granisetron 40 microg/kg or perphenazine 70 microg/kg (n = 50 each) orally 1 h before surgery. We used a standard general anesthetic technique. The rate of complete response, defined as no emesis and no need for rescue antiemetic medication, during 0-3 h after anesthesia was 86% with granisetron and 60% with perphenazine; the corresponding rate 3-24 h after anesthesia was 86% and 62%, respectively (P < 0.05). No serious adverse events were observed in any of the groups. In conclusion, preoperative oral granisetron is more effective than perphenazine for preventing postoperative vomiting in children undergoing tonsillectomy with or without adenoidectomy. ⋯ We compared the efficacy of granisetron and perphenazine given orally for preventing postoperative vomiting after tonsillectomy with or without adenoidectomy in children. Preoperative oral granisetron was more effective than perphenazine.
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Anesthesia and analgesia · Jun 1999
Randomized Controlled Trial Comparative Study Clinical TrialGranisetron/dexamethasone combination for reducing nausea and vomiting during and after spinal anesthesia for cesarean section.
We compared the efficacy of granisetron plus dexamethasone with that of granisetron alone for preventing nausea and vomiting in parturients undergoing cesarean section under spinal anesthesia. In a randomized, double-blinded manner, 120 patients received either granisetron 3 mg (Group I, n = 60) or granisetron 3 mg plus dexamethasone 8 mg (Group II, n = 60) IV immediately after clamping of the fetal umbilical cord. A complete response, defined as no emetic symptoms and no need for another rescue antiemetic medication in the intraoperative, postdelivery period was 83% in Group I and 98% in Group II (P = 0.008); the corresponding rates during the first 24 h after surgery was 85% and 98% (P = 0.016). No clinically serious adverse events were observed in any of the groups. In conclusion, the prophylactic use of a granisetron/dexamethasone combination is more effective than granisetron alone for reducing nausea and vomiting in patients during and after spinal anesthesia for cesarean section. ⋯ Intraoperative, postdelivery, and postoperative nausea and vomiting are distressing to patients undergoing cesarean section under spinal anesthesia. The combination of granisetron plus dexamethasone was evaluated and found to be effective for preventing these emetic symptoms.