Laurent Delaunay

Clonidine Comparably Decreases the Thermoregulatory Thresholds for Vasoconstriction and Shivering in Humans

Background:Clonidine stops postoperative shivering, but its underlying mechanism of action is unknown. Clonidine may impair central control of thermoregulation or act on peripheral receptors. Accordingly, the authors tested the hypothesis that clonidine reduces both the vasoconstriction and shivering thresholds, a pattern consistent with central thermoregulatory impairment. Methods:Seven healthy volunteers participated in the study. Thermoregulatory vasoconstriction was evaluated using forearm minus fingertip, skin-temperature gradients; values exceeding 4° C were considered to be significant vasoconstriction. Systemic oxygen consumption (&OV0312;O2) was measured with a canopy system. In addition, shivering was qualitatively evaluated using a simple scale, graduated from 0 (no shivering) to 2 (intense shivering). The tympanic membrane temperatures triggering significant vasoconstriction and grade 1 shivering were considered to be the thresholds for the two thermoregulatory responses. Measurements were performed after a 10-min steady state period and during cooling by central venous infusion of Ringers lactate solution at 4° C. Each subject was evaluated at two sessions, separated by at least 48 h. They were randomly and blindly assigned to received either an intravenous bolus of 75 µg clonidine or a placebo before cooling. When the shivering score equaled 2, 75 µg clonidine was injected intravenously, and repeated if necessary, to completely stop shivering. Results:Clonidine significantly decreased the thermoregulatory threshold for shivering by 0.6 ± 0.3° C (mean ± SD). Similarly, the threshold for cutaneous vasoconstriction was significantly reduced by 0.5 ± 0.2° C. Additional clonidine administration always stopped shivering, at whatever temperature it occurred. Conclusions:This study confirms that clonidine administration stops shivering, and suggests that it acts by impairing central thermoregulatory control. That an additional dose of clonidine stops shivering in subjects already given one dose, indicates that the effect of clonidine is dose dependent.

Effect of thoracic epidural anesthesia combined with general anesthesia on segmental wall motion assessed by transesophageal echocardiography

Patients scheduled for vascular surgery are considered at risk for perioperative cardiac complications. Choice of anesthetic in such patients is guided by a desire not to adversely affect myocardial function. On the basis of data from laboratory studies, thoracic epidural anesthesia (TEA) has been advocated to prevent myocardial ischemia. The aim of this study was to assess whether TEA combined with general anesthesia has any effect on segmental wall motion (SWM) monitored by transesophageal echocardiography in these patients. Patients received alfentanil, midazolam, vecuronium, and 50% N2O in oxygen, and ventilation was controlled after orotracheal intubation; 12.5 mL of 2% lidocaine HCl was injected through an epidural catheter placed at T6-7 or T7-8. Hemodynamic measurements and transesophageal echocardiographic recordings were obtained before and 10, 20, 30, 40, and 60 min after lidocaine injection. Segmental wall motion was graded a posteriori by two independent experts on a predetermined scale (from 1 = normal to 5 = dyskinesia). A decrease greater than or equal to 2 grades was considered an SWM abnormality indicative of ischemia. Thoracic epidural anesthesia induced a decrease in systemic arterial blood pressure, heart rate, and cardiac index. The SWM score decreased slightly from 1.34 +/- 0.68 to 1.27 +/- 0.64 (mean +/- SD) (at 10 and 20 min, respectively) (P less than 0.05). Patients were a posteriori analyzed according to whether they had documented coronary artery disease or not. The SWM score before TEA was significantly higher in patients with documented coronary artery disease (1.51 +/- 0.88 vs 1.17 +/- 0.51, respectively; P less than 0.05) and did not change significantly after TEA.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of preoperative normovolemic hemodilution on left ventricular segmental wall motion during abdominal aortic surgery.

Preoperative normovolemic hemodilution (PNH) has been proposed for patients scheduled to undergo aortic surgery. Coronary artery disease is frequent in these patients. The aim of the study was to assess the effect of PNH on hemodynamics and segmental wall motion (SWM) evaluated by transesophageal echocardiography in such patients. Twenty patients with coronary artery disease were allocated randomly to either PNH or no PNH; PNH was performed after anesthetic induction using dextran 60,000. Patients were operated on under general anesthesia and monitored intraoperatively with electrocardiographic lead CM5, radial and pulmonary artery catheters, and transesophageal echocardiography positioned to obtain a short-axis view. Hemodynamic and transesophageal echocardiographic data were collected after anesthetic induction and after PNH, before and 5 min after aortic clamping, after unclamping, and at the end of surgery. Aortic clamping induced a significant increase in systemic vascular resistance and arteriovenous difference in oxygen and a decrease in cardiac index (P < 0.05), but the effect of aortic clamping was inversely related to hemodilution. The SWM score (graded from 1 = normal to 5 = dyskinesia) was significantly increased after aortic clamping, mainly in the anterior segment (P < 0.05). Four patients in the control (no PNH) group and one in the PNH group developed new SWM abnormalities indicative of myocardial ischemia during surgery (P = NS). This study suggests that PNH may improve hemodynamic tolerance to aortic clamping in patients with coronary artery disease. The observed changes in SWM indicate that PNH may not worsen myocardial ischemia in patients scheduled to undergo aortic surgery.

Clonidine Does Not Impair Redistribution Hypothermia After the Induction of Anesthesia

Clonidine is commonly given for premedication, and it impairs normal thermoregulatory responses to warm and cold stimuli while depressing sympathetic tone.We studied the effect of premedication by clonidine on redistribution hypothermia induced by the induction of anesthesia. Sixteen ASA physical status I or II patients were randomly assigned to receive either clonidine 150 [micro sign]g or a placebo. Anesthesia was induced 45 min later by thiopental, fentanyl, and vecuronium IV and was maintained by the administration of 0.6% isoflurane. We monitored central core (tympanic) temperature and skin surface temperatures at the forearm and the fingertip during the 2 h after the induction of anesthesia before surgery. We estimated skin blood flow at the level of the forearm by using laser Doppler during the same period. The core temperature decreased comparably in the two groups of patients, from 37.1 +/- 0.2[degree sign]C to 35.3 +/- 0.4[degree sign]C and from 37.1 +/- 0.2[degree sign]C to 35.5 +/- 0.3[degree sign]C in the clonidine and placebo groups, respectively. The forearm-fingertip surface temperature gradient decreased similarly in the two groups. There was no evidence of cutaneous vasoconstriction. The laser Doppler index at the fingertip increased similarly in the two groups, as did the forearm-fingertip temperature gradient. We conclude that premedication with clonidine does not significantly impair the profile of central hypothermia induced by heat redistribution after the induction of anesthesia. Implications: The induction of general anesthesia is associated with redistribution hypothermia. This study shows that premedication with oral clonidine does not worsen the decrease in core temperature resulting from general anesthesia. (Anesth Analg 1998;87:168-72)

Use of ultrasound for lower extremity.

Purpose of review To explore the recent advances in the use of ultrasound for lower extremity blocks, including approaches to the lumbar and sacral plexus blocks. Recent findings Procedures of the lower extremity often require blocks of the lumbar and sacral plexuses. The use of ultrasound offers some advantages, including the possibility to directly visualize the distribution of local anesthetics. Summary Lower extremity blocks under ultrasound guidance often require advanced skills because of the depth of target nerves. This review summarizes the recent advances in the use of ultrasound guidance over traditional techniques.

Thermoregulation and shivering during epidural anaesthesia

Hypothermia occurs during epidural anaesthesia. It is initially related to a shift of body heat from the central core to the periphery. It may produce shivering which appears as a normal response to a decrease in central core temperature.

Lumbar and sciatic nerve blocks for postoperative analgesia

Different approaches for performing lumbar or sacral plexus nerve blocks are reviewed. Lumbar nerve blocks may be achieved either by anterior or posterior approaches, while local anaesthetic solutions may be injected either in the psoas or the fascia iliaca compartment.