Showing papers in "Anesthesiology in 1987"

Epidural Anesthesia and Analgesia in High-risk Surgical Patients

Abstract: The authors conducted a randomized controlled clinical trial to evaluate the effect of epidural anesthesia and postoperative analgesia (EAA) on postoperative morbidity in a group of high-risk surgical patients. A total of 53 patients were admitted to the study, 28 received EAA, and 25 received standard anesthetic and analgesic techniques without EAA. Surgical "risk" was evaluated preoperatively and found to be comparable in the two groups. When compared to control patients, patients who received EAA had a reduction in the overall postoperative complication rate (P = 0.002) and in the incidence of cardiovascular failure (P = 0.007) and major infectious complications (P = 0.007). Urinary cortisol excretion, a marker of the stress response, was significantly diminished during the first 24 postoperative hours in the group receiving EAA (P = 0.025). Finally, hospital costs were significantly reduced for patients who received EAA (P = 0.02). The authors conclude that EAA exerted a significant beneficial effect on operative outcome in a group of high risk surgical patients.

Reduced narcotic requirement by clonidine with improved hemodynamic and adrenergic stability in patients undergoing coronary bypass surgery.

Abstract: The authors examined the effect of clonidine, a preferential alpha 2-adrenergic agonist, upon narcotic requirements, hemodynamics, and adrenergic responses during the perioperative period in patients undergoing CABG surgery. Anesthesia was provided by sufentanil supplemented with isoflurane; sodium nitroprusside was given as needed for hemodynamic control. Ten patients received oral clonidine preoperatively at the time of premedication, and again intraoperatively by nasogastric tube. Another group of ten untreated patients were otherwise managed identically. Intergroup differences in required anesthetic and vasoactive drug doses and recovery times were measured and evaluated, as well as hemodynamics and plasma catecholamines prior to induction, after intubation, and at intervals intra- and postoperatively. Patients who received clonidine required less diazepam prior to induction, and received 40% less sufentanil during the anesthetic period, than did untreated controls. More control patients required the addition of isoflurane to prevent hypertension. Mean blood pressures and heart rates were elevated at many sampling points in patients not treated with clonidine. Four of the clonidine-treated group required atropine for treatment of bradycardia in the pre-incision period. Plasma catecholamines were significantly lower throughout most of the study period in patients treated with clonidine. After cardiopulmonary bypass and postoperatively, cardiac outputs were significantly higher in the treated group. Patients who had received clonidine were extubated significantly earlier, and fewer of them shivered postoperatively. We conclude that perioperative treatment with clonidine reduced narcotic and anesthetic requirements, improved hemodynamics, reduced plasma catecholamines, and shortened the period of postoperative ventilation in patients undergoing coronary artery surgery.

Systolic blood pressure variation is a sensitive indicator of hypovolemia in ventilated dogs subjected to graded hemorrhage

Abstract: Systolic pressure variation (SPV) is defined as the difference between the maximum and minimum values of systolic blood pressure following a single positive pressure breath. An increase in the SPV is known to occur clinically during hypovolemia. This study aims to quantify SPV during graded hemorrhage in ventilated dogs, and to compare its reliability relative to other hemodynamic indicators of hypovolemia. Ten anesthetized dogs were mechanically ventilated with a fixed tidal volume. A continuously inflated vest was applied around the chest to maintain the ratio of lung to chest wall compliance similar to that of humans (0.83 +/- 0.12). SPV was further divided into delta up and delta down components relative to apneic (5 s) systolic blood pressure. Dogs were bled 5, 10, 20, and 30% of their estimated blood volume. The measured parameters best correlated to the amount of bleeding were SPV (rs = 0.993), delta down (rs = 0.981), and cardiac output (rs = 0.976). The SPV and its delta down component correlated to the degree of hemorrhage as well as the CO and the pulmonary capillary wedge pressure, and significantly better than the central venous pressure and the mean systemic blood pressure. Thus, SPV and its delta down component are accurate indicators of hypovolemia in ventilated dogs subjected to hemorrhage.

Lung collapse and gas exchange during general anesthesia: effects of spontaneous breathing, muscle paralysis, and positive end-expiratory pressure

Abstract: Lung densities (atelectasis) and pulmonary gas exchange were studied in 13 supine patients with no apparent lung disease, the former by transverse computerized tomography (CT) and the latter by a multiple inert gas elimination technique for assessment of the distribution of ventilation/perfusion ratios. In the awake state no patient had clear signs of atelectasis on the CT scan. Lung ventilation and perfusion were well matched in most of the patients. Three patients had shunts corresponding to 2-5% of cardiac output, and in one patient there was low perfusion of poorly ventilated regions. CT scans after 15 min of halothane anesthesia and mechanical ventilation showed densities in dependent lung regions in 11 patients. A shunt was present in all patients, ranging from 1% in two patients (unchanged from the awake state) to 17%. Ventilation of poorly perfused regions was noted in nine patients, ranging from 1-19% of total ventilation. The magnitude of the shunt significantly correlated to the size of dependent densities (r = 0.84, P less than 0.001). Five patients studied during spontaneous breathing under anesthesia displayed both densities in dependent regions and a shunt, although of fairly small magnitude (1.8% and 3.7%, respectively). Both the density area and the shunt increased after muscle paralysis. PEEP reduced the density area in all patients but did not consistently alter the shunt. It is concluded that the development of atelectasis in dependent lung regions is a major cause of gas exchange impairment during halothane anesthesia, during both spontaneous breathing and mechanical ventilation, and that PEEP diminishes the atelectasis, but not necessarily the shunt.

Effects of methemoglobinemia on pulse oximetry and mixed venous oximetry

Abstract: The performance of three commercially available pulse oximeters was assessed in five anesthetized dogs in which increasing levels of methemoglobin were induced. Hemoglobin oxygen saturation in each dog was monitored with three pulse oximeters (Nellcor N-100, Ohmeda 3700, and Novametrix 500) and a mixed venous saturation pulmonary artery catheter (Oximetrix Opticath). Arterial and mixed venous blood specimens were analyzed for PaO2, PaCO2, and pHa using standard electrodes. An IL-282 Co-oximeter was used on the same specimens to determine oxyhemoglobin and methemoglobin as percentages of total hemoglobin. Methemoglobin levels of up to 60% were induced by intratracheal benzocaine. As MetHb gradually increased while the dogs were breathing 100% inspired oxygen, the pulse oximeter saturation (SpO2) overestimated the fractional oxygen saturation (SaO2) by an amount proportional to the concentration of methemoglobin until the latter reached approximately 35%. At this level the SpO2 values reached a plateau of 84-86% and did not decrease further. When, at fixed methemoglobin levels, additional hemoglobin desaturation was induced by reducing inspired oxygen fraction, SpO2 changed by much less than did SaO2 (regression slopes from 0.16 to 0.32). Thus, at high methemoglobin levels SpO2 tends to overestimate SaO2 by larger amounts at low hemoglobin saturations. Plots of SpO2 versus functional saturation (oxyhemoglobin/reduced hemoglobin plus oxyhemoglobin) show an improved but still poor relationship (regression slopes from 0.32 to 0.46). The Oximetrix Opticath pulmonary artery catheter behaves similarly but provides somewhat better agreement with functional saturation than do the pulse oximeters in the presence of methemoglobinemia. Pulse oximetry data (SpO2) should be used with caution in patients with methemoglobinemia.

Anesthesia and hypertension: the effect of clonidine on perioperative hemodynamics and isoflurane requirements

Abstract: Thirty patients (ASA physical status II-III) with a history of arterial hypertension, whose blood pressure (BP) control varied from normotension to moderate hypertension (diastolic BP less than 110 mmHg), scheduled for elective surgery under general anesthesia, were randomly assigned to two groups. Group 1 was premedicated 90-120 min prior to induction with diazepam 0.15 mg X kg-1 po; group 2, in addition, received clonidine 5 micrograms X kg-1 po. Anesthetic depth was assessed by on-line aperiodic analysis of the electroencephalogram. Following lidocaine 1 mg X kg-1 and fentanyl 2 micrograms X kg-1 (group 1 only), anesthesia was induced with thiopental 3-4 mg X kg-1 and vecuronium 0.1 mg X kg-1 was used to facilitate endotracheal intubation. Anesthesia was maintained with isoflurane in N2O/O2 and supplemented by fentanyl. In group 2, clonidine produced a rapid preoperative control of systolic and diastolic BP from 166 +/- 32/95 +/- 14 to 136 +/- 80 +/- 11 (P less than 0.01), was more effective in blunting the reflex tachycardia associated with laryngoscopy and endotracheal intubation than lidocaine-fentanyl pretreatment. It significantly reduced the intraoperative lability (coefficient of variation) of systolic (P less than 0.01) and diastolic BP and heart rate (HR) (P less than 0.05), and resulted in significantly slower HR during recovery (P less than 0.01). Anesthetic requirements for isoflurane were reduced 40% (P less than 0.01) in group 2; narcotic supplementation was also significantly reduced (P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Accuracy of Response of Six Pulse Oximeters to Profound Hypoxia

Abstract: Oxygen saturation, SpO2%, was recorded during rapidly induced 42.5 +/- 7.2-s plateaus of profound hypoxia at 40-70% saturation by 1 or 2 pulse oximeters from each of six manufacturers (NE = Nellcor N100, OH = Ohmeda 3700, NO = Novametrix 500 versions 2.2 and 3.3 (revised instrumentation), CR = Criticare CSI 501 + version .27 and version .28 in 501 & 502 (revised instrumentation), PC = PhysioControl Lifestat 1600, and MQ = Marquest/Minolta PulseOx 7). Usually, one probe of each pair was mounted on the ear, the other on a finger. Semi-recumbent, healthy, normotensive, non-smoking caucasian or asian volunteers (age range 18-64 yr) performed the test six to seven times each. After insertion of a radial artery catheter, subjects hyperventilated 3% CO2, 0-5% O2, balance N2. Saturation ScO2, computed on-line from mass spectrometer end-tidal PO2 and PCO2, was used to manually adjust FIO2 breath by breath to obtain a rapid fall to a hypoxic plateau lasting 30-45s, followed by rapid resaturation. Arterial HbO2% (Radiometer OSM-3) sampled near the end of the plateau averaged 55.5 +/- 7.5%. ScO2% (from the mass spectrometer) and SaO2% (from pH and PO2, by Corning 178) differed from HbO2% by + 0.2 +/- 3.6% and 0.4 +/- 2.8%, respectively. The mean and SD errors of pulse oximeters (vs. HbO2%) were: (table; see text) The plateaus were always long enough to permit instruments to demonstrate a plateau with ear probes, but finger probes sometimes failed to provide plateaus in subjects with peripheral vasoconstriction. Nonetheless, SpO2 read significantly too low with finger probes at 55% mean SaO2.(ABSTRACT TRUNCATED AT 250 WORDS)

The Minimum Alveolar Concentration (MAC) of Sevoflurane in Humans

Abstract: Forty surgical patients were divided into two groups and anesthetized with either sevoflurane and oxygen or sevoflurane, oxygen, and nitrous oxide. The minimum alveolar concentration (MAC) for sevoflurane required to prevent movement in response to surgical incision in healthy patients was 1.71 +/- 0.07% (SE). The AD95 (anesthetic ED95) that prevented 95% of patients from moving was 2.07%. The addition of 63.5% end-tidal nitrous oxide allowed a reduction in the alveolar sevoflurane concentration to 0.66 +/- 0.06% (SE). The reduction in sevoflurane MAC was 61.4%. The AD95 for sevoflurane with 63.5% end-tidal nitrous oxide was 0.94%.

Margin of safety in positioning modern double-lumen endotracheal tubes

Abstract: The authors have defined the margin of safety in positioning a double-lumen tube as the length of tracheobronchial tree over which it may be moved or positioned without obstructing a conducting airway. The purpose of this study was to measure the margin of safety in positioning three modern double-lumen tubes (Mallinkrodt [Broncho-Cath], Rusch [Endobronchial tubes], and Sheridan [Broncho-Trach]). The margin of safety in positioning a: 1) left-sided double-lumen tube (all manufacturers) is the length of the left mainstem bronchus minus the length from the proximal margin of the left cuff to left lumen tip; 2) Mallinkrodt right-sided double-lumen tube is the length of the right mainstem bronchus minus the length of the right cuff; and 3) Rusch right-sided double-lumen tube is the length of the right upper lobe ventilation slot minus the diameter of the right upper lobe. The length of the right and left mainstem bronchi were measured by in vivo fiberoptic bronchoscopy (n = 69), in fresh cadavers (n = 42), and in lung casts (n = 55), and the diameter of the right upper lobe bronchus was measured in lung casts (n = 55). The average +/- SD male left and right mainstem bronchial lengths were 49 +/- 8 and 19 +/- 6 mm, respectively, the average +/- SD female left and right mainstem bronchial lengths were 44 +/- 7 and 15 +/- 5 mm, respectively, the average right upper lobe bronchial diameter was 11 mm, the proximal left cuff to left lumen tip distance was 30 mm, the length of the Mallinkrodt right cuff was 10 mm, and the length of the Rusch right upper lobe ventilation slot was 15 mm. The average margin of safety in positioning left-sided double-lumen tubes ranged 16-19 mm for the different manufacturers. The average margin of safety in positioning Mallinkrodt right-sided double-lumen tubes was 8 mm, and the margin of safety in positioning Rusch right-sided double-lumen tubes ranged 1-4 mm, depending on French size. The authors concluded that left-sided double-lumen tubes are much preferable to right-sided double-lumen tubes because they have a much greater positioning margin of safety, and that proper confirmation of proper position of either a left- or right-sided double-lumen tube should be aided by fiberoptic bronchoscopy, because the absolute distances that constitute the margin of safety are extremely small.

Population pharmacokinetics of alfentanil: the average dose-plasma concentration relationship and interindividual variability in patients.

Abstract: The population pharmacokinetic parameters describing the plasma concentration versus time profile of alfentanil in patients undergoing general anesthesia were determined from 614 plasma concentration measurements collected in four previously reported studies with a total of 45 patients. A nonlinear regression analysis evaluating the effect of six concomitant variables revealed a significant influence of body weight on the volume of the central compartment (Vc), and a decrease with age of total body clearance (CL) and of redistribution rate from the deep compartment (k31). A small but significant effect of sex on the Vc was also observed. The duration of anesthesia and the concomitant administration of inhalational anesthetics had no effect on alfentanil pharmacokinetic parameters. The mean CL and Vc for alfentanil in a 70-kg male, aged less than 40 yr, were estimated as 0.356 1/min and 7.77 1, respectively. After correction for age, body weight, and sex, the remaining interindividual variability of alfentanil kinetics (expressed as coefficient of variation) was 48% for CL and 33% for Vc. These population pharmacokinetic parameter estimates should increase the accuracy of predicting concentration-time profiles for intravenous alfentanil infusions. A computer program is presented that allows prediction of the alfentanil plasma concentration and the 68% interval limits of the prediction from the study data analysis.

Correlation of endotracheal tube size with sore throat and hoarseness following general anesthesia

Abstract: Correlation of Endotracheal Tube Size with Sore Throat and Hoarseness Following General Anesthesia DAVID STOUT;MICHAEL BISHOP;JOCHEN DWERSTEC;BRUCE CULLEN; Anesthesiology

The effect of carbon monoxide inhalation on pulse oximetry and transcutaneous PO2.

Abstract: Five dogs were anesthetized, intubated, and ventilated with various mixtures of oxygen, nitrogen, and carbon monoxide. Each dog was monitored with arterial and pulmonary artery catheters, a transcutaneous PO2 analyzer, and two pulse oximeters. An IL-282 Co-oximeter was used to periodically measure arterial oxyhemoglobin (O2Hb) and carboxyhemoglobin (COHb) as percentages of the total hemoglobin. The PaO2, PaCO2, and pHa were measured in the same blood specimens using standard electrodes. When the inspired oxygen concentration was reduced in the absence of COHb, the pulse oximeter saturation (SpO2) estimated O2Hb with reasonable accuracy. COHb levels were then varied slowly from 0-75% in each dog. As the COHb level increased and oxyhemoglobin decreased, both pulse oximeters continued to read an oxygen saturation of greater than 90%, while the actual O2Hb fell below 30%. In the presence of COHb, the SpO2 is approximately the sum of COHb and O2Hb, and, thus, may seriously overestimate O2Hb. The pulse oximeter, as the sole indicator of blood oxygenation, should, therefore, be used with caution in patients with recent carbon monoxide exposure. On the other hand, transcutaneous PO2 falls linearly as COHb increases, and reaches about one-fifth of its initial value at the highest COHb levels despite the maintenance of constant arterial PO2.

The effects of dextrose infusion and head position on neurologic outcome after complete cerebral ischemia in primates: examination of a model.

Abstract: The hypothesis that iv dextrose infusion prior to--and head position during--cerebral ischemia would influence the severity and pattern of neurologic injury was tested in primates. Fifteen pigtail monkeys weighing 3.3 +/- 0.2 kg (mean +/- SE) were subjected to 17 min complete cerebral ischemia followed by 24 h intensive care treatment and neurologic assessment for an additional 72 h. Monkeys were given 50 ml iv infusions of either dextrose 5% in 0.45% saline solution (n = 8) or lactated Ringer's solution (n = 7) during the preparatory period. This volume corresponds to approximately 1 1/70 kg individual. These same monkeys were placed in either the lateral (n = 3), prone (n = 5), or supine (n = 7) position during the ischemic period. Two monkeys failed to meet preestablished protocol criteria and were excluded from data analysis. Blood glucose immediately preischemia in the dextrose-treated group (181 +/- 19 mg X dl-1) was not significantly greater than in the group given lactated Ringer's solution (140 +/- 6 mg X dl-1; P = 0.07). Dextrose infusion resulted in significantly greater cerebral injury at 96 h postischemia when comparing both neurologic (P less than 0.05) and histopathology (P less than 0.05) scores. Specifically, dextrose administration resulted in the greatest injury to the insular cortex, thalamus, Purkinje cells, and substantia nigra. Although blood glucose was less than 250 mg X dl-1 in all monkeys at the time of complete cerebral ischemia, there was a high correlation between blood glucose rank and neurologic function rank (rs = 0.76; P less than 0.005). The authors were unable to note any effect of head position on the distribution of histopathologic lesions. Prior to removing the brain for histopathologic studies, four monkeys were given repeat infusions of 50 ml dextrose 5% in 0.45% saline solution over 11 +/- 1 min. These infusions produced increases in blood glucose from 56.7 +/- 7.6 to 244 +/- 24.9 mg X dl-1 (P less than 0.01) and increases in brain glucose from 1.64 +/- 0.22 to 5.11 +/- 0.48 mumol X g-1 (P less than 0.01).

Continuous Infusion Epidural Analgesia during Labor: A Randomized, Double-blind Comparison of 0.0625% Bupivacaine / 0.0002% Fentanyl Versus 0.125% Bupivacaine

Abstract: The analgesic efficacy of the continuous epidural infusion of 0.0625% bupivacaine/0.0002% fentanyl was compared with the infusion of 0.125% bupivacaine alone in a randomized, double-blind study of nulliparous women. Each patient received, in sequence: 1)3 ml of 0.5% bupivacaine with 1:200,000 epinep

Anesthetic mishaps: breaking the chain of accident evolution.

Abstract: Anesthesia and surgery are a risk for all, the healthy as well as the sick. While the prevention of adverse outcomes in healthy patients is paramount, enhancement of safety for critically ill patients is also essential, since they are more likely to suffer a SNO after a critical incident. Dangers originate from a variety of sources, not solely from errors by the anesthesiologist. Simple incidents of all description are inevitable, and we should focus on promoting recovery as well as avoiding error. Processes that lead to negative outcomes after critical incidents should be investigated to reduce the uncertainty complexity associated with managing the human body during anesthesia, and to establish the most effective detection and recovery techniques. Outcome studies are lacking, and clinical and animal research is highly dependent on the chosen model or population, making the results hard to apply to variable clinical conditions. Wherever possible, a consensus should be sought on therapeutic and adverse effects of drugs and techniques in common, specific patient populations. These can serve as a basis for developing therapeutic plans, recognizing that customizing to individuals is always necessary. A mainstay of anesthetic practice already involves attempts to loosen couplings, by keeping homeostatic mechanisms intact when possible (awake intubation, regional anesthesia); providing temporal buffers (titration of drugs, and use of drugs with short onset times and rapid termination of effect); and providing safety margins using appropriate pre-treatments (pre-oxygenation, atropine in children, etc.). Further means of loosening coupling should be identified and promoted. Specific attention to recovery from simple incidents should attack several facets of the problem.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional anatomy of the brachial plexus sheath: implications for anesthesia.

Abstract: Anatomical study of the brachial plexus of 18 cadavers was undertaken to confirm the presence and significance of "septa" dividing the brachial plexus or axillary sheath. Dissection demonstrated that the sheath consists of multiple layers of thin connective tissue surrounding the various elements of the neurovascular bundle. These septa are incomplete, however, forming small bubble-like pockets when solution is injected. Single injections of methylene blue and Latex solutions into the axillary sheath resulted in immediate dye staining of median, radial, and ulnar nerves, despite the presence of septa. These data demonstrate that there are connections between compartments within the sheath and, therefore, do not support the need for multiple injections when performing an axillary block.

Morphine pharmacokinetics in early infancy

Abstract: The pharmacokinetics of morphine in ten infants less than or equal to 10 weeks of age who were receiving morphine infusions were determined. Infants 1-4 days of age (newborns) showed longer elimination half-lives than the older infants (6.8 vs. 3.9 h). Clearance in the newborns is less than one-half that found in older infants (6.3 vs. 23.8 ml X min-1 X kg-1). The combination of lower clearance and longer elimination half-life in newborns (0-7 days) may well explain a prolonged duration of action for morphine in very young infants, but other etiologies are needed to explain the respiratory sensitivity believed to persist in older infants.

Epsilon-aminocaproic Acid for Treatment of Fibrinolysis during Liver Transplantation

Abstract: Orthotopic liver transplantation is frequently associated with surgical bleeding that requires massive blood transfusion. 1 The surgical bleeding is compounded by preexisting coagulopathy, dilutional coagulopathy, fibrinolysis, and, possibly, disseminated intravascular coagulation.2 In a recent series of patients undergoing liver transplantation, the degree of coagulopathy and volume of transfusion decreased with the introduction of replacement therapy guided by the frequent thrombelastographic monitoring of the coagulation system and the use of heparin-coated veno-venous bypass.3,4 However, active fibrinolysis, manifest as generalized oozing from a previously dry surgical field and unresponsive to replacement therapy, has been a major difficulty in the intraoperative management of liver transplantation. Since the early experience in hepatic transplantation, activation of the fibrinolytic system has been recognized,5,6 and, although antifibrinolytic treatment appears beneficial, it has been used only sporadically. Von Kaulla et al., on the basis of postoperative thrombotic complications in patients with hepatic neoplasms, suggested that administration of e-aminocaproic acid (EACA) might be harmful in transient fibrinolysis,6 whereas Flute et al. suggested a possible beneficial role of EACA in patients receiving liver transplants.7 Thus far, antifibrinolytic therapy has been empirical; its indications have been ill defined, monitoring of fibrinolysis has been inadequate, and, usually, a large dose of EACA has been used in cases of uncontrolled bleeding. We designed the present study to investigate the significance of fibrinolysis, to evaluate the clinical effectiveness of EACA, and to identify a clinically effective dose of EACA in patients receiving liver transplants.

Postoperative Apnea in Preterm Infants

Abstract: Preterm infants may become apneic during the immediate post-operative period. To define this risk, the authors studied prospectively the breathing patterns of 47 preterm infants less than 60 weeks postconception with pneumocardiograms before and after general inhalational anesthesia. Eighteen infants (37%) had prolonged apnea (greater than 15 s) postoperatively, and an additional seven infants (14%) had short apnea (6-15 s) postoperatively. An infant's risk of prolonged and short postoperative apnea was related to a young postconceptional age (P less than 0.05) and to a history of necrotizing enterocolitis (P less than 0.01). Furthermore, as the postconceptional age of the infant increased, the risk of postoperative apnea decreased proportionately (P less than 0.025). Among the 18 infants with prolonged apnea, 83% experienced multiple apneic episodes. Manual stimulation was required in order for breathing to return in 13 (72%) of the infants. Breathing resumed spontaneously in four (22%) of the infants, and one infant required mechanical ventilation due to repeated prolonged apnea. The first apneic event occurred within 2 h postoperatively in 13 of the infants (72%); the remaining five infants (28%) had their initial apneic episode as late as 12 h after operation. The postoperative time to the last prolonged apneic event was inversely related to the postconceptional age (P less than 0.01, r = -0.70) and extended up to 48 h postoperatively. The preoperative pneumocardiogram was not a reliable test for predicting postoperative apnea (sensitivity 56%, specificity 83%).(ABSTRACT TRUNCATED AT 250 WORDS)

Closed-loop feedback control of methohexital anesthesia by quantitative EEG analysis in humans.

Abstract: A combined pharmacokinetic and pharmacodynamic model of methohexital was used to establish and evaluate feedback control of methohexital anesthesia in 13 volunteers. The median frequency of the EEG power spectrum served as the pharmacodynamic variable constituting feedback. Median frequency values from 2-3 Hz were chosen as the desired EEG level (set-point). In 11 volunteers, the feedback system succeeded in maintaining a satisfactory depth of anesthesia (i.e., unresponsiveness to verbal commands and tactile stimuli). During feedback control, 75% of all measured median frequency values were in the preset range of 2-3 Hz. This distribution of median frequency was obtained by applying random stimulation (six different acoustic and tactile stimuli) to the volunteers approximately every 1.5 min. The decrease of median frequency from baseline to anesthetic values was primarily induced by increasing the fractional power in the frequency band of 0.5-2 Hz from 12.6 +/- 4.5% (mean +/- SD) to 46.0 +/- 2.5%. The median time to recovery (as defined by opening eyes on command) after cessation of the feedback control period was 20.6 min (10.7-44.5 min) when median EEG frequency was 5.2 Hz (4.7-8.4 Hz). The average requirement of methohexital (mean +/- SD) during the 2 h was 1.02 +/- 0.16 g. It is concluded that pharmacokinetic-pharmacodynamic models of intravenous anesthetics established previously may be used to form a suitable background for model-based feedback control of anesthesia by quantitative EEG analysis. This approach gives a possible solution to the problem of adapting pharmacokinetic and pharmacodynamic data to individuals when using population mean data as starting values for drug therapy.

Isoflurane when compared to enflurane and halothane decreases the frequency of cerebral ischemia during carotid endarterectomy.

Abstract: Data from the records of patients who underwent 2223 carotid endarterectomies at the Mayo Clinic between January 1, 1972, and December 31, 1985, were abstracted to compare the effects of isoflurane, enflurane, and halothane on the critical cerebral blood flow (CBF) (i.e., the CBF below which the maj

Mishaps with patient-controlled analgesia.

Abstract: 2 cas de depression respiratoire profonde par surdosage en analgesiques narcotiques meperidine et sufentamil suite a des erreurs d'administration

C5a and thromboxane generation associated with pulmonary vaso- and broncho-constriction during protamine reversal of heparin.

Abstract: The authors conducted a study in humans to determine the mediators associated with acute pulmonary vaso- and broncho-constriction occurring episodically with protamine reversal of heparin anticoagulation. Of 48 adult patients investigated prospectively after termination of cardiopulmonary bypass, two presented a sudden increase of airway pressure, acute pulmonary hypertension, and systemic hypotension 1-3 min after right atrial protamine injection. In these two subjects, plasma levels of C5a increased from 0.7 and 2.2 to 9.8 and 9.9 ng/ml, respectively, and thromboxane B2 increased from 0.26 and 0.34 to 7.5 and 16.2 ng/ml 1 minute after drug injection. A third subject not identified prospectively had an identical reaction and mediator profile (C5a, 10.2 ng/ml; TxB2, 18.6 ng/ml at 1 min). The plasma levels of these mediators were unchanged in the remaining patients (C5a, 0.7 +/- 1.1 [x +/- S.D.] to 0.6 +/- 0.9 ng/ml; TxB2, 0.16 +/- 0.12 to 0.15 +/- 0.07 ng/ml). Plasma histamine was not involved in this type of reaction, but increased from 0.7-10.4 ng/ml in a fourth patient who became hypotensive without acute pulmonary hypertension, bronchoconstriction, or elevation of C5a or TxB2. The authors' data indicate that the generation of high plasma levels of C5a anaphylatoxins and thromboxane is associated with pulmonary vaso- and broncho-constriction induced by protamine reversal of heparin in humans.

Anesthetic depression of myocardial contractility: a review of possible mechanisms.

Abstract: The bulk of experimental evidence indicates that anesthetics do not produce their negative inotropic effect via an inhibitory action on mitochondrial electron transport. Anesthetics decrease energy need, rather than energy production. Anesthetics also decrease the rate of sequestration of Ca2+ by mitochondria, but, again, this appears not to be an important cause of reduced myocardial contractility. The role played by direct anesthetic depression of the myofibrils in reducing contractility is uncertain. Most experimental evidence now available suggests that significant myofibrillar depression, measured in terms of inhibition of actomyosin ATPase activity or inhibition of force production, occurs only at anesthetic concentrations which are high compared to concentrations employed clinically. This would seem to indicate that the myofibrils are not an important target for anesthetics in regard to the production of depressed myocardial contractility. However, the experimental act of removing myofibrils from their intracellular environment, or of removing the sarcolemma or making it hyperpermeable, appears to prevent some regulatory myofibrillar phosphorylation reactions from taking place. As stated by Winegrad, "certain forms of regulation of the cardiac myofibril are fragile and can be seen only when cellular constituents and structure are maintained." It is possible that this type of regulation is susceptible to inhibition by anesthetics. Methods for preserving this regulation are available, and will need to be employed before a depressant action of anesthetics on the myofibril can be definitely dismissed as a significant cause of the inhibition of cardiac contractility. A single study, of intracellular Ca2+ levels in the intact cell (where myofibrillar regulation was presumably preserved), has indicated that halothane may decrease myofilament Ca2+ sensitivity. However, for reasons stated above, this study cannot be taken as unequivocal proof of such an action. Despite the fact that the normal action potential is little affected by anesthetics, the sarcolemma appears to play a pivotal role in the production of anesthetic-induced contractile depression. Significant depression of the rate of upstroke of the slow (Ca2+-mediated) action potential by clinical concentrations of both inhalation and intravenous anesthetics has been demonstrated by several workers. This has been interpreted to mean that anesthetics inhibit the influx of Ca2+ through the slow channel, and such has been confirmed (to date, for halothane and thiamylal) by direct measurement of the slow inward Ca2+ current using a voltage clamp technique.(ABSTRACT TRUNCATED AT 400 WORDS)

A comparison of the cerebral protective effects of isoflurane and barbiturates during temporary focal ischemia in primates.

Abstract: Isoflurane has protective properties during experimental global brain ischemia or hypoxia. However, this has not been evaluated in the more common case of focal ischemia, e.g., as caused by middle cerebral artery occlusion (MCAO). The authors therefore compared the effects of isoflurane, thiopental,