Anesthesia and analgesia
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Anesthesia and analgesia · Apr 1999
Randomized Controlled Trial Clinical TrialEvaluating T-wave amplitude as a guide for detecting intravascular injection of a test dose in anesthetized children.
Previous reports have suggested that accidental intravascular injection of an epinephrine-containing test dose increases T-wave amplitude in anesthetized children. We designed this study to prospectively determine whether changes in T-wave amplitude could be a reliable indicator for detecting intravascular injection. We studied 32 ASA physical status I infants and children (3.4 +/- 1.7 yr) undergoing elective minor surgeries during 1.0 minimum alveolar anesthetic concentration of sevoflurane and 67% nitrous oxide in oxygen. After the i.v. administration of atropine 0.01 mg/kg, the patients were randomly assigned to receive either saline (n = 16) or a test dose consisting of 1% lidocaine (0.1 mL/kg) with 1:200,000 epinephrine (0.5 microg/kg, n = 16) via a peripheral vein to simulate the intravascular injection of the test dose. Heart rate (HR) and systolic blood pressure (SBP) were recorded every 20 and 30 s, respectively, and the T-wave amplitude of lead II was continuously recorded for subsequent analysis. Of the 16 children receiving the test dose, 16, 13, and 16 developed increases in HR, SBP, and T-wave amplitude > or = 10 bpm, > or = 15 mm Hg, and > or = 25%, occurring at 30 +/- 7, 70 +/- 31, and 20 +/- 5 s, respectively. Because no patient receiving saline met these criteria, sensitivity, specificity, and positive and negative predictive values were all 100% based on the criteria using the T-wave amplitude and the peak HR. Our results suggest that changes in T-wave amplitude are as effective as HR for detecting the intravascular injection of an epinephrine-containing test dose in sevoflurane-anesthetized children. ⋯ To determine whether an epidurally administered local anesthetic is unintentionally injected into a blood vessel, a small dose of epinephrine is often added to a local anesthetic. We found that increases in T-wave amplitude by > or = 25% in lead II monitor electrocardiography are as effective as a heart rate increase > or = 10 bpm for detecting intravascular injection in sevoflurane-anesthetized children.
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Anesthesia and analgesia · Apr 1999
Randomized Controlled Trial Clinical TrialDo laryngeal mask airway devices attenuate liquid flow between the esophagus and pharynx? A randomized, controlled cadaver study.
In this randomized, controlled cadaver study, we tested the hypothesis that the standard laryngeal mask airway (LMA) and flexible laryngeal mask airway (FLMA) attenuate liquid flow between the esophagus and pharynx. Fifty fresh cadavers were studied in four LMA groups. Ten female cadavers had a size 4 LMA and 10 had a size 4 FLMA; 10 male cadavers had a size 5 LMA and 10 had a size 5 FLMA; 5 male and 5 female cadavers functioned as controls. The chest was opened, and the infusion set of a pressure-controlled, continuous flow pump was inserted into the esophagus and ligated into place. Esophageal pressure was increased in 2-cm H2O increments. Regurgitation pressure was the esophageal pressure at which fluid was first seen with a fiberoptic scope in the hypopharynx (control group) and above the cuff or within the bowl (LMA groups). This was performed in the LMA groups at 0-40 mL cuff volume in 10-mL increments. Mean (95% confidence interval) regurgitation pressure for the control group was 7 (6-8) cm H2O and for the LMA groups combined was 19 (17-20) cm H2O at 0 mL cuff volume, 47 (41-52) cm H2O at 10 mL, 51 (44-55) cm H2O at 20 mL, 52 (45-56) cm H2O at 30 mL, and 52 (45-55) cm H2O at 40 mL. The increase in regurgitation pressure with increasing cuff volume from 0 to 10 mL was statistically significant (P < 0.0001). Regurgitation pressure was higher for the LMA groups at all cuff volumes compared with the control group (P < 0.0001). There were no differences in regurgitation pressure among the LMA groups. We conclude that the correctly placed LMA and FLMA attenuate liquid flow between the esophagus and pharynx. ⋯ We have shown, in cadavers, that the correctly placed standard and flexible laryngeal mask airways attenuate liquid flow between the pharynx and esophagus.
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Anesthesia and analgesia · Apr 1999
ReviewAlcohol withdrawal in the surgical patient: prevention and treatment.
In the literature on AWS, there is repeated emphasis on performing a thorough preanesthesia assessment in patients with suspected chronic alcohol use. Because these patients are difficult to diagnose and to treat in surgical settings if complications arise, a multimodal approach is highly recommended (86). Ideally, AWS should be prevented by adequate prophylaxis. ⋯ The drug regimens must be individualized and symptom-oriented to treat hallucinations and autonomic signs. Dosages are generally larger than those in detoxification units. Other approaches to modulate the neuroendocrine-immune axis in patients with an increased risk of postoperative infectious complications look promising but await controlled trials.
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Anesthesia and analgesia · Apr 1999
Comparative StudyExposure to sevoflurane and nitrous oxide during four different methods of anesthetic induction.
The National Institute for Occupational Safety and Health-recommended exposure levels for nitrous oxide exposure are 25 ppm as a time-weighted average over the time of exposure. The exposure limit for halogenated anesthetics (without concomitant nitrous oxide exposure) is 2 ppm. Inhaled sevoflurane provides an alternative to i.v. induction of anesthesia. However, the inadvertent release of anesthetic gases into the room is likely to be greater than that with induction involving i.v. anesthetics. We therefore evaluated anesthesiologist exposure during four different induction techniques. Eighty patients were assigned to one of the induction groups to receive: 1) sevoflurane and nitrous oxide from a rebreathing bag, 2) sevoflurane and nitrous oxide from a circle circuit, 3) propofol 3 mg/kg, and 4) thiopental sodium 5 mg/kg. Anesthesia was maintained with sevoflurane and nitrous oxide via a laryngeal mask. Trace concentrations were measured directly from the breathing zone of the anesthesiologist. During induction, peak concentrations of sevoflurane and nitrous oxide with the two i.v. methods rarely exceeded 2 ppm sevoflurane and 50 ppm nitrous oxide. Concentrations during the two inhalation methods were generally <20 ppm sevoflurane and 100 ppm nitrous oxide. During maintenance, median values were near 2 ppm sevoflurane and 50 ppm nitrous oxide in all groups. Sevoflurane concentrations during inhaled induction frequently exceeded the National Institute for Occupational Safety and Health-recommended exposure ceiling of 2 ppm but mostly remained <20 ppm. Exposure during the maintenance phase of anesthesia also frequently exceeded the 2-ppm ceiling. We conclude that operating room anesthetic vapor concentrations are increased during inhaled inductions and remain increased with laryngeal mask ventilation. ⋯ We compared waste gas concentrations to sevoflurane and nitrous oxide during four different induction methods. During inhaled induction with a rebreathing bag or a circle circuit system, waste gas concentrations frequently exceed National Institute for Occupational Safety and Health limits of 2 ppm sevoflurane and 50 ppm nitrous oxide. Therefore, we recommend that people at risk (e.g., women of child-bearing age) should pay great attention when using this technique.
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Anesthesia and analgesia · Apr 1999
Comparative StudyEffects of isoflurane, ketamine, and fentanyl/N2O on concentrations of brain and plasma catecholamines during near-complete cerebral ischemia in the rat.
We postulated that adrenergic responses to global cerebral ischemia are anesthetic-dependent and similar in both brain and arterial blood. Rats were anesthetized with isoflurane (1.4%), ketamine (1 mg x kg(-1) x min(-1)), or fentanyl (25 microg x kg(-1) x h(-1))/70% N2O. The carotid arteries were occluded for either 20 min with mean arterial pressure (MAP) 50 mm Hg (incomplete ischemia) or 10 min with MAP 30 mm Hg (near-complete ischemia). Norepinephrine was measured in hippocampal microdialysate. Norepinephrine and epinephrine were measured in arterial plasma. In both hippocampus and plasma, basal norepinephrine was similar among anesthetics. During incomplete ischemia, hippocampal norepinephrine was twofold greater with fentanyl/N2O than with isoflurane (P = 0.037), but plasma norepinephrine and epinephrine were similar and unchanged among all three anesthetics. During near-complete ischemia, hippocampal norepinephrine was threefold greater with ketamine than fentanyl/N2O (P = 0.005), whereas plasma norepinephrine and epinephrine were markedly greater with fentanyl/N2O than with ketamine (P < 0.0005) or isoflurane (P = 0.05). There was no correlation between norepinephrine concentrations in hippocampus and plasma for either incomplete or near-complete ischemia. This study demonstrates that adrenergic responses to global ischemia are anesthetic-dependent, particularly during more severe insults. The absence of a correlation between plasma and brain catecholamine concentrations indicates that adrenergic responses to ischemia are independent in brain and blood. ⋯ It has been proposed that anesthetics modulate cerebral ischemic outcome by influencing peripheral adrenergic responses to ischemia. This experiment demonstrates that anesthetics differentially modulate adrenergic responses to ischemia but that effects in plasma and brain are independent. This suggests that events detected in the peripheral circulation do not implicate direct mechanisms of action of catecholamines at the neuronal/glial level.