Effect of Flumazenil on Ventilatory Drive during Sedation with Midazolam and Alfentanil

Background: Patients who receive a combination of a benzodiazepine and an opioid for conscious sedation are at risk for developing respiratory depression. While flumazenil effectively antagonizes the respiratory depression associated with a benzodiazepine alone, its efficacy in the presence of both a benzodiazepine and an opioid has not been established. This study was designed to determine whether flumazenil can reverse benzodiazepine-induced depression of ventilatory drive in the presence of an opioid.

Methods: Twelve healthy volunteers completed this randomized, double-blind, crossover study. Ventilatory responses to carbon dioxide and to isocapnic hypoxia were determined during four treatment phases: (1) baseline, (2) alfentanil infusion; (3) combined midazolam and alfentanil infusions, and (4) combined alfentanil, midazolam, and "study drug" (consisting of either flumazenil or flumazenil vehicle) infusions. Subjects returned 2-6 weeks later to receive the alternate study drug.

Results: Alfentanil decreased the slope of the carbon dioxide response curve from 2.14 +/- 0.40 to 1.43 +/- 0.19 l [dot] min sup -1 [dot] mmHg sup -1 (x +/- SE, P < 0.05), and decreased the minute ventilation at PET CO2 = 50 mmHg (V with dotE 50) from 19.7 +/- 1.2 to 14.8 +/- 0.9 l [dot] min sup -1 (P < 0.05). Midazolam further reduced these variables to 0.87 +/- 0.17 l [dot] min sup -1 [dot] mmHg sup -1 (P < 0.05) and 11.7 +/- 0.8 l [dot] min sup -1 (P <0.05), respectively. With addition of flumazenil, slope and V with dot sub E 50 increased to 1.47 +/- 0.37 l [dot] min sup -1 [dot] mmHg sup -1 (P < 0.05) and 16.4 +/- 2.0 l [dot] min sup -1 (P < 0.05); after placebo, the respective values of 1.02 +/- 0.19 l [dot] min sup -1 [dot] mmHg sup -1 and 12.5 +/- 1.2 l [dot] min sup -1 did not differ significantly from their values during combined alfentanil and midazolam administration. The effect of flumazenil differed significantly from that of placebo (P < 0.05). Both the slope and the displacement of the hypoxic ventilatory response, measured at PET CO2 = 46 +/- 1 mmHg, were affected similarly, with flumazenil showing a significant improvement compared to placebo.     

Geriatric anesthesia implications

The geriatric patient will continue to pose challenges during the perianesthesia period. By age 80, the older adult has experienced many physiological and anatomical changes, many starting during the 4th decade of life. Changes in tissue mass and function in major organ systems demand special perianesthetic care planning to optimize patient outcomes. Understanding the physiology of aging will assist the perianesthesia nurse in planning perianesthesia care for their patients. Consequently, emphasis should be placed on cautious preanesthesia screening and evaluation, so that astute diagnosis and treatment of comorbid diseases are thoughtfully considered in relationship to the type of anesthesia when caring for the postanesthesia patient. For this article the term geriatric refers to those persons 65 years of age or older.     

Electromyographic monitoring of profound surgical muscle relaxation during cardiac anesthesia

Quantitative assessment of neuromuscular block produced by large doses of nondepolarizing neuromuscular blocking agents during cardiac surgery is not possible with conventional methods of monitoring. Various posttetanic responses can, however, be elicited, even when no twitch response is present. Posttetanic responses measured by electromyography were used in this study. Twenty-four male patients undergoing coronary bypass surgery were anesthetized with sufentanil plus diazepam. Neuromuscular block was provided either with pancuronium 0.1 mg/kg or with vecuronium 0.07 mg/kg initially and supplemented with small increments when indicated. Neuromuscular block was monitored from the hypothenar muscle. The ulnar nerve was stimulated by train-of-four, with supermposed periodic tetanic stimuli to evoke posttetanic responses, once every 7 to 15 minutes. The tetanically potentiated responses were detectable during 96% ± 3.6 (vecuronium) and during 97% ± 3.7 (pancuronium) of the entire intraoperative period, while the nonpotentiated electromyographic responses were present for less than 50% of the time. The sum (of the amplitudes) of 6 posttetanic responses is significantly (p<0.05) greater than the sum of 6 nonpotentiated responses and than the size of a single-peak posttetanic response when compared with the normal, nonpotentiated responses. Higher-frequency tetanic stimuli (100 or 200 Hz) produced greater posttetanic responses (p<0.05) than did the 50-Hz tetanic stimulus. There were only slight or no significant differences in the degree of posttetanic potentiation between pancuronium and vecuronium either before, during, or after cardiopulmonary bypass. With posttetanic responses, we could detect changes in the level of neuromuscular block that occur during cardiac surgery and that are related to cardiopulmonary bypass, cooling, rewarming, and large doses of corticosteroids and antibiotics. Furthermore, it was not necessary to extend the arm or to use an arm board (on which the hand is immobilized when using mechanical monitoring methods) during cardiac surgery.     

Transient Neurologic Symptoms after Spinal Anesthesia: An Epidemiologic Study of 1,863 Patients

Background: Recent evidence suggests that transient neurologic symptoms commonly follow lidocaine spinal anesthesia. However, information concerning factors that affect their occurrence is limited. Accordingly, to evaluate many potential risk factors, the authors undertook a prospective, multicenter, epidemiologic study.

Methods: On a voluntary basis, anesthetists at 15 participating centers forwarded a data sheet on patients who had spinal anesthesia to a research nurse blinded to the details of anesthesia and surgery. A subset was randomly selected for follow-up. The pressure of transient neurologic symptoms, defined as leg or buttock pain, was the principal outcome variable. Logistic regression was used to control for potential confounders, and adjusted odds ratios and confidence intervals were used to estimate relative risk.

Results: During a 14-month period, 1,863 patients were studied, of whom 47% received lidocaine, 40% bupivacaine, and 13% tetracaine. Patients given lidocaine were at higher risk for symptoms compared with those receiving bupivacaine (relative risk, 5.1; 95% CI, 2.5 to 10.2) or tetracaine (relative risk, 3.2; 95% CI, 1.04 to 9.84). For patients who received lidocaine, the relative risk of transient neurologic symptoms was 2.6 (95% CI, 1.5 to 4.5) with the lithotomy position compared with other positions, 3.6 (95% CI, 1.9 to 6.8), for outpatients compared with inpatients, and 1.6 (95% CI, 1 to 2.5) for obese (body mass index >30) compared with nonobese patients.     

Cerebral Emboli and Serum S100β During Cardiac Operations

Background. The glial protein S100β has been used to estimate cerebral damage in a number of clinical settings. The purpose of this investigation was to determine the correlation between cerebral microemboli and S100β levels during cardiac operations.

Methods. Transcranial Doppler ultrasonography was used to measure emboli in the right middle cerebral artery. Emboli counts (n = 111) were divided into five time periods: (1) incision to aortic cannulation; (2) aortic cannulation to cross-clamp onset; (3) cross-clamp onset to cross-clamp release; (4) cross-clamp release to decannulation; and (5) decannulation to chest closure. The level of S100β (n = 156) was measured at baseline, at the end of cardiopulmonary bypass, then 150 and 270 minutes after cross-clamp release.

Results. The level of S100β correlated with age, cardiopulmonary bypass time, cross-clamp time, and number of emboli at time period 2. Although cardiopulmonary bypass time was univariately associated with S100β level, it became nonsignificant in a multivariable model that included age and cross-clamp time.

Conclusions. The correlation of S100β level with emboli measured during cannulation (time period 2) supports the hypothesis that cannulation is a high-risk time period for cerebral injury.     

A Comparison of the Intubation Conditions between Mivacurium and Rocuronium during Balanced Anesthesia

Background: Comparisons of the intubation conditions with mivacurium and rocuronium from previous reports are confounded by the use of varied induction regimens. The authors compared intubation conditions of mivacurium, rocuronium, and a placebo at 90 s and their recovery profiles during anesthesia with nitrous oxide, oxygen, and propofol.

Methods: After induction with midazolam, fentanyl, and propofol in a randomized blinded study, 100 patients received one of the following treatments: 0.25 mg/kg mivacurium in divided doses (0.15 mg/kg followed by 0.1 mg/kg 30 s later); 0.45, 0.6, 0.9, or 1.2 mg/kg rocuronium; or placebo. Evoked thumb adduction was measured throughout. Intubation was attempted 90 s after the initial dose of mivacurium and other treatment doses by a "blinded" physician. Intubating conditions were graded as excellent, good, poor, or not possible. Spontaneous recovery was studied until a 25% initial twitch height was reached. Mean arterial blood pressure and heart rate changes between groups were determined before induction through 6 min after administration of the study drugs.

Results: There were no important changes or intergroup differences in mean arterial blood pressure and heart rate. Intubation conditions were good or excellent for both mivacurium and rocuronium at the 0.9 mg/kg dose (93%) and at the 1.2 mg/kg dose (100%). Rocuronium at the 0.6 mg/kg dose was excellent in 27% of patients, whereas rocuronium at the 0.45 mg/kg dose had the least number of excellent conditions and the most poor or not possible assessments. Patients given placebo could not be intubated. Times to maximum blockade for 0.9 and 1.2 mg/kg rocuronium were the shortest. The times to 25% recovery for 0.6 mg/kg rocuronium (mean +/- SD = 27 +/- 8.6 min), 0.9 mg/kg (43.1 +/- 10.8), and 1.2 mg/kg (62.3 +/- 17.4 min) were significantly longer than were those for mivacurium (17.4 +/- 6.2 min).     

The Use of Conscious Sedation for Outpatient Dermatologic Surgical Procedures

BACKGROUND: Dermatologic surgery has undergone increasing levels of sophistication over the past few decades. Commensurate with this demand, an established anesthesia technique called conscious sedation has been employed. OBJECTIVES: Methods for performing office-based conscious sedation are described. Recommendations are made regarding prerequisites for conscious sedation in an office setting, patient selection, complications management, and postoperative discharge requirements. CONCLUSION: The goals of anesthesia are to provide for patient safety and comfort, to increase patient acceptance of the procedure, and to enhance the surgeon's efficiency and satisfaction.