Hidehiro Suzuki

Nitrous oxide decreases the threshold for vasoconstriction less than sevoflurane or isoflurane

The core temperature triggering thermoregulatory arteriovenous shunt constriction is designated the threshold for vasoconstriction.High thresholds are generally desirable because vasoconstriction helps prevent further core hypothermia by decreasing cutaneous heat loss and constraining metabolic heat to the core thermal compartment. Previous studies suggest that nitrous oxide (N2 O) may inhibit thermoregulatory vasoconstriction less than comparable doses of volatile anesthetics. To confirm this impression, we tested the hypothesis that 0.5 minimum alveolar anesthetic concentration (MAC) N (2) O combined with 0.5 MAC sevoflurane or isoflurane would reduce the vasoconstriction threshold less than 1.0 MAC sevoflurane or isoflurane. With institutional review board approval, we studied 40 patients, aged 20-60 yr, undergoing open abdominal surgery. No premedication was given. Ten patients each were anesthetized with: 1) N2 O (50%) and 0.5 MAC sevoflurane (1%); 2) sevoflurane alone (2%); 3) N2 O (60%) and 0.5 MAC isoflurane (0.6%); and, 4) isoflurane alone (1.2%). A forearm minus fingertip, skin temperature gradient >or=to0 degrees C was considered significant vasoconstriction; the esophageal temperature triggering vasoconstriction identified the threshold. Morphometric characteristics were comparable in each group. The threshold for vasoconstriction was 35.8 +/- 0.3 degrees C in the patients given 50% N2 O combined with 0.5 MAC sevoflurane, which was significantly greater than that in those given 1.0 MAC sevoflurane: 35.1 +/- 0.4 degrees C. Similarly, the threshold for vasoconstriction was 35.9 +/- 0.3 degrees C in the patients given 60% N2 O combined with 0.5 MAC isoflurane, which was significantly greater than that in those given 1.0 MAC isoflurane: 35.0 +/- 0.5 degrees C. We thus conclude that N2 O impairs thermoregulation less than sevoflurane or isoflurane. (Anesth Analg 1995;80:1212-6)

The threshold for thermoregulatory vasoconstriction during nitrous oxide/sevoflurane anesthesia is reduced in the elderly

Elderly patients become more hypothermic during surgery, shiver less postoperatively, and take longer to rewarm than younger patients.Similarly, the vasoconstriction threshold (triggering core temperature) is reduced approximately 1 degrees C in elderly patients during nitrous oxide/isoflurane anesthesia. Accordingly, we tested the hypothesis that the vasoconstriction threshold in the elderly is also reduced approximately 1 degrees C during nitrous oxide and sevoflurane anesthesia. Eleven young patients aged 30-50 yr and 14 elderly patients aged 60-80 yr were anesthetized with nitrous oxide (50%) and sevoflurane (1%). Mean skin temperature was calculated from four sites. Fingertip blood flow was estimated using forearm minus fingertip skin-temperature gradients, with a gradient of 0 degrees C identifying onset of vasoconstriction. The distal esophageal temperature triggering onset of vasoconstriction identified the threshold for this thermoregulatory defense. The data from five patients who did not vasoconstrict at minimum core temperatures of 33-34 degrees C were eliminated, leaving 10 patients in each group. The vasoconstriction threshold was significantly less in the elderly (35.0 +/- 0.8 degrees C) than in younger patients (35.8 +/- 0.3 degrees C), despite similar mean skin temperatures (mean +/- SD, P < 0.01, Students t-test). Age dependence of thermoregulatory vasoconstriction during nitrous oxide/sevoflurane anesthesia is similar to that previously observed during nitrous oxide/isoflurane anesthesia. (Anesth Analg 1997;84:1029-33)

Electroanesthesia studies: a new current pattern and control of fading.

HIS STUDY is part of a continuing inquiry T into the possibility of producing clinical anesthesia solely by the application of electrical current or currents. Every form of current we have used to date has presented some disadvantage in terms of its effects on test subjects. Unidirectional current-direct current and unidirectional square pulses causes iontophoresis and tissue injury. Bidirectional current in reasonable intensities does not injure tissue. Sine wave current, a bidirectional form, does not injure tissue but is severely limited by its constant ratio of average-to-peak current. This relationship is serious in electroanesthesia (EA ) studies; the peak current is critical, and with sine wave, high average current must be applied to achieve the required peak current.

Anesthetic management for cesarean section in a mother after the Fontan procedure.

At the age of 14, she experienced recurrent episodes of symptomatic supraventricular tachycardia. At 17 years of age, a Fontan procedure was carried out, in which the right atrium was connected to the main pulmonary artery with closures of the VSD and the Blalock-Hanlon shunt. She recovered uneventfully from the operation. Since the Fontan repair, and throughout her pregnancy, she has had a normal activity level (New York Heart Association Class I) and has taken no medication. At 37 weeks of gestation she was admitted to our hospital for delivery. Cesarean delivery was planned at 38 weeks of gestation. On preoperative maternal physical examination, no cyanosis, clubbing, or edema was noted. Her hematocrit was 36%, hemoglobin oxygen saturation was 93% while breathing room air, and an electrocardiogram revealed sinus rhythm with a rate of 80bpm, occasional supraventricular premature beats, right axis deviation, and first-degree atrioventricular block. Maternal echocardiography showed that the atrioventricular relationship was complex, with concordant crisscross heart, and the left ventricular size was relatively small. Therefore, echocardiographic measurements of left and right ventricular dimensions, left ventricular wall thickness, and left atrial size were not possible. However, twodimensional echocardiographic estimation of her ventricular function suggested that, throughout her pregnancy, her ventricular contraction was reasonably good for a post-Fontan patient. Mild regurgitation of the mitral valve was noted, but the degree did not change during pregnancy. The pattern of blood flow in the pulmonary artery also did not change significantly during pregnancy, and the peak velocity in the pulmonary artery, which was observed during ventricular diastole, was 0.6–0.8m·s21 throughout her pregnancy. On the patient’s arrival in the operating room, monitoring by electrocardiogram, as well as automated arterial blood pressure and pulse oximetry monitoring, was begun. The arterial blood pressure was 120/ Address correspondence to: M. Komori Received for publication on August 28, 1998; accepted on March 10, 1999 Anesthetic management for cesarean section in a mother after the Fontan procedure

A decrease in seizure susceptibility to lidocaine in kindled epileptic rats

Lidocaine induces electroencephalographic seizures and generalized convulsions at large doses. It is possible that epileptic patients are more susceptible to the proconvulsant effect of lidocaine. Using a kindling model of epilepsy, we examined whether the seizure susceptibility to lidocaine increases in epileptic rats. Kindled epileptic rats were prepared by repeated, initially subconvulsive, electrical stimulations applied to the amygdala for 9–14 days through a chronically implanted electrode, resulting in the establishment of a long-lasting epileptic focus. Unexpectedly, kindled rats had significantly less susceptibility to the proconvulsant action of IV lidocaine. Lidocaine-induced convulsions were observed in 11%, 75%, and 77% of control rats at 7.5, 10.0, and 12.5 mg/kg, respectively, compared with 0%, 25%, and 37% of amygdala-kindled rats, respectively. We also demonstrated that small doses of lidocaine suppressed kindled seizures in a dose-dependent manner. We conclude that the critical mechanisms underlying lidocaine-induced seizures differ from the mechanisms underlying kindled epileptogenesis. Furthermore, the establishment of a kindled epileptic focus decreases susceptibility to the proconvulsant action of lidocaine. Implications Susceptibility to the proconvulsant action of lidocaine is significantly lower in kindled epileptic rats compared with nonepileptic rats.