Showing papers in "Anesthesiology in 1989"

Prevention of Intraoperative Anesthesia Accidents and Related Severe Injury through Safety Monitoring

Abstract: Among 1,001,000 ASA Physical Status I and II patients (a subset of the 1,329,000 anesthetics administered from 1976 through mid-1988 in the nine component hospitals of the Harvard Department of Anaesthesia), there were 11 major intraoperative accidents solely attributable to anesthesia (five deaths, four cases of permanent CNS damage, and two cardiac arrests with eventual recovery) among the 70 cases reported to the insurance carrier. Review of these accidents revealed that unrecognized hypoventilation was the most common cause (seven cases). These seven accidents and one other due to discontinuation of inspired oxygen in all likelihood would have been prevented by appropriate response to earlier warnings generated by the "safety monitoring" principles mandated by the Harvard minimal monitoring standards. Analysis suggests capnography (although not mandated) would be the best monitor of ventilation. An important associated issue was the apparent inadequacy of supervision of residents and C.R.N.A.s. The eight preventable accidents represent 88% of the projected insurance payout. Only one accident occurred after the 1985 adoption of the standards (in the month following their implementation). From that time through mid-1988, there have been 319,000 anesthetics without a major preventable intraoperative injury. Although not statistically significant, the accident rate in the target population of healthy people is reduced more than threefold. This and the case analyses support the contention that nearly all the inevitable mishaps (technical or from errors in judgement) that occur during anesthesia can be identified through safety monitoring early enough to prevent most major patient injuries. This improved clinical outcome should lessen the medical-legal and malpractice insurance burdens of anesthesiologists.

Absorption characteristics of transdermally administered fentanyl.

Abstract: Fentanyl was administered intravenously and transdermally to eight surgical patients to determine the systemic bioavailability and rate of absorption of the transdermally administered drug. Serum fentanyl concentrations reached a plateau approximately 14 h after placement of the transdermal fentanyl

Randomized Trial of Primary Anesthetic Agents on Outcome of Coronary Artery Bypass Operations

Abstract: To examine the role of primary anesthetic agent on outcome of coronary artery bypass grafting operations, 1,012 patients were prospectively randomized to receive enflurane (257), halothane (253), isoflurane (248), or sufentanil (254). Except for administration of the primary anesthetic, anesthesia management was standardized for all patients. The randomized groups did not differ in demographic characteristics, extent of coronary artery disease, chronic antianginal therapy, hemodynamic characteristics including new myocardial ischemia at arrival to the operating room, and surgical characteristics that might influence the rate of postoperative myocardial infarction or death. From anesthetic induction to start of cardiopulmonary bypass, new ST segment depression appeared in 310 (30.4%) patients and was not different among primary anesthetic groups (28.0-33.5%). Similarly, the incidence of postoperative myocardial infarction (3.6-4.7%) and death (1.2-2.4%) was not different. Although intraoperative hypotension was twice as common in patients receiving any volatile anesthetic and hypertension twice as common with sufentanil, tachycardia (greater than or equal to 110 bpm) was not related to any primary anesthetic (4.3-9.1%) and was the only hemodynamic abnormality significantly related to intraoperative ischemia. The strongest predictor of intraoperative ischemia was ischemia on arrival to the operating room. The authors postulate that approximately 90% of new myocardial ischemia observed during anesthesia is the manifestation of silent ischemia observed in patients before operation and only 10% is related to anesthetic management. They conclude that, despite differences in the hemodynamic consequences of the primary anesthetics studied, none of the primary anesthetics influenced outcome and the primary role of the anesthesiologist in management of these patients is control of heart rate.

The importance of transtracheal jet ventilation in the management of the difficult airway.

Abstract: The Importance of Transtracheal Jet Ventilation in the Management of the Difficult Airway Jonathan Benumof;Mark Scheller; Anesthesiology

Postoperative apnea in former preterm infants: prospective comparison of spinal and general anesthesia.

Abstract: Thirty-six former preterm infants undergoing inguinal hernia repair were studied. All were less than or equal to 51 weeks postconceptual age at the time of operation. Patients were randomly assigned to receive general or spinal anesthesia. Group 1 patients received general inhalational anesthesia with neuromuscular blockade. Group 2 patients received spinal anesthesia using 1% tetracaine 0.4-0.6 mg/kg in conjunction with an equal volume of 10% dextrose and 0.02 ml epinephrine 1:1000. In the first part of the study, infants randomized to receive spinal anesthesia also received sedation with im ketamine 1-2 mg/kg prior to placement of the spinal anesthetic (group 2 A). The remainder of group 2 patients did not receive sedation (group 2 B). Respiratory pattern and heart rate were monitored using an impedance pneumograph for at least 12 h postoperatively. Tracings were analyzed for evidence of apnea, periodic breathing and/or bradycardia by a pulmonologist unaware of the anesthetic technique utilized. None of the patients who received spinal anesthesia without ketamine sedation developed postoperative bradycardia, prolonged apnea, or periodic breathing. Eight of nine infants (89%) who received spinal anesthesia and adjunct intraoperative sedation with ketamine developed prolonged apnea with bradycardia. Two of the eight infants had no prior history of apnea. Five of the 16 patients (31%) who received general anesthesia developed prolonged apnea with bradycardia. Two of these five infants had no prior history of apnea. When infants with no prior history of apnea were analyzed separately, there was no statistically significant increased incidence of apnea in children receiving general versus spinal anesthesia with or without ketamine sedation. Because of the small numbers of patients studied, and the multiple factors that may influence the incidence of postoperative apnea (e.g., prior history of neonatal apnea), standard postoperative respiratory monitoring of these high-risk infants is still recommended following all anesthetic techniques.

Role of monitoring devices in prevention of anesthetic mishaps: a closed claims analysis.

Abstract: Anesthesiologist-reviewers examined 1,175 anesthetic-related closed malpractice claims from 17 professional liability insurance companies. The claims were filed between 1974 and 1988. The reviewers were asked to determine if the negative outcome was preventable by proper use of additional monitoring devices available at the time of the review even if not available at the time the incident occurred, and if so, which devices could have been preventative. In 1,097 cases sufficient information was available to make a judgment regarding preventability of the morbidity or mortality by application of additional monitoring devices. It was determined that 31.5% of the negative outcomes could have been prevented by application of additional monitors. Using the insurance industry's scale of 0 (no injury) to 9 (death), the median severity of injury for incidents deemed preventable was 9 compared with 5 for those deemed not preventable (P less than 0.01, scale detailed in text). The severity of injury scores were the same for preventable mishaps occurring during regional or general anesthesia, suggesting that additional monitoring devices may be equally efficacious in preventing serious negative outcomes during either regional or general anesthesia. The judgements or settlements of the incidents judged preventable by additional monitoring were 11 times more costly (P less than 0.01) than those mishaps not judged preventable. The monitors determined by the reviewers to be most useful in mishap prevention were pulse oximetry plus capnometry. Applied together, these two technologies were considered potentially preventative in 93% of the preventable mishaps.(ABSTRACT TRUNCATED AT 250 WORDS)

Perioperative analgesia with subarachnoid fentanyl-bupivacaine for cesarean delivery.

Abstract: Addition of fentanyl to bupivacaine administered for spinal anesthesia for cesarean delivery was evaluated in 56 ASA physical status 1 term parturients. Preservative-free saline was added to 0, 2.5, 5, 6.25, 12.5, 25, 37.5, or 50 μg featanyl to make a 1 ml total volume, which was injected intratheca

Prognostic Importance of Postbypass Regional Wall-Motion Abnormalities in Patients Undergoing Coronary Artery Bypass Graft Surgery

Abstract: Regional wall motion abnormalities (RWMA) detected by intraoperative transesophageal echocardiography (TEE) are thought to be sensitive markers of myocardial ischemia. To assess the prognostic significance of RWMA as compared with other less costly technologies such as electrocardiography (ECG) and hemodynamic measurements [blood pressure (BP) and pulmonary artery (PA) pressure], 50 patients were prospectively studied who were undergoing elective coronary artery bypass graft (CABG) surgery using continuous TEE, ECG (Holter), and hemodynamic measurements during the prebypass, postbypass, and early postoperative intensive care unit (ICU) periods (first 4 h). Echocardiographic and ECG evidence of ischemia was characterized during each of these three periods and related to adverse clinical outcomes (postoperative myocardial infarction, ventricular failure, and cardiac death). Clinicians were blinded to the TEE and ECG information. The prevalence of myocardial ischemia during the perioperative periods was as follows: prebypass, 20% (TEE) versus 7% (ECG); postbypass, 36% (TEE) versus 25% (ECG); ICU 25% (TEE) versus 16% (ECG). Neither prebypass TEE ischemia nor ECG ischemia occurring in any of the three periods predicted adverse outcome. In contrast, postbypass TEE ischemia was predictive of outcome: six of 18 patients with postbypass TEE ischemia had adverse outcomes versus 0 of 32 without TEE ischemia (P = 0.001). Seventy-three percent of the echocardiographic ischemic episodes occurred without acute change (+/- 20% of control) in heart rate, BP, or PA pressure. The authors conclude that: 1) prebypass myocardial ischemia was relatively uncommon, 2) the incidence of ECG and TEE ischemia was highest in the postbypass period, and 3) postbypass RWMA were related to adverse clinical outcome.

Determination of intra-abdominal pressure using a transurethral bladder catheter: clinical validation of the technique.

Abstract: The determination of intra-abdominal pressures (IAP) may be useful in many clinical situations. The authors recently demonstrated in the canine model a close correlation between actual IAP and the bladder pressure measurements obtained from a transurethral catheter. The purpose of this study was to clinically validate this technique. The authors studied 16 patients, and compared IAP in three positions (supine, with compressions, and semi-erect) utilizing both direct intraperitoneal pressure monitoring and the pressure obtained with a transurethral bladder catheter. Their results demonstrated a linear relationship between the two methods described, with a mean r value of 0.95 in the supine and semi-erect positions, and 0.99 with abdominal compressions (P less than 0.0001). The authors conclude that transurethral monitoring of bladder pressure offers a safe, simple, and highly accurate method for evaluating IAP at the bedside. Studies evaluating the indication for its use in the operating room and intensive care settings appear warranted.

Epidural Clonidine Analgesia following Surgery: Phase I

Abstract: Epidurally administered clonidine has been reported to produce postoperative analgesia. To assess the efficacy, safety, and appropriate dose of epidural clonidine for postoperative analgesia, clonidine (range, 100–900 μg in 100 μg increments) was injected in 22 patients following abdominal surgery o

Effect of pulmonary artery catheterization on outcome in patients undergoing coronary artery surgery.

Abstract: Previous studies have suggested that low-risk cardiac surgical patients may be safely managed without pulmonary artery catheterization (PAC). However, no prospective studies have determined whether PAC improves outcome in higher risk patients compared with that following central venous pressure (CVP) monitoring alone. The authors prospectively examined the incidence of and factors related to perioperative morbidity and mortality in 1094 consecutive patients undergoing coronary artery surgery managed with elective PAC (n = 537) or with CVP (n = 557). Perioperative risk factors and demographics that predict morbidity and mortality after cardiac surgery were used to quantify risk classification. Outcome was judged by length of ICU stay, occurrence of postoperative myocardial infarction, in-hospital death, major hemodynamic aberrations, and significant noncardiac systemic complications. No significant differences in any outcome variables were noted in any group of patients with similar quantitative risk classification managed with or without PAC, including those in the highest risk class. In addition, there were no significant differences in outcome among the 39 patients who would have been managed with CVP monitoring only, but who subsequently developed a clinical need for PAC based on the occurrence of serious hemodynamic events compared to patients who had PAC performed electively. This study suggests that PAC does not play a major role in influencing outcome after cardiac surgery, that even high-risk cardiac surgical patients may be safely managed without routine PAC, and that delaying PAC until a clinical need develops does not significantly alter outcome, but may have an important impact on cost savings.

Dexmedetomidine produces a hypnotic-anesthetic action in rats via activation of central alpha-2 adrenoceptors.

Abstract: Dexmedetomidine, a highly selective and potent alpha-2 adrenoceptor agonist, reduces halothane anesthetic requirements by over 90% in rats. The present study examined whether dexmedetomidine produces a hypnotic-anesthetic action in rats. Dexmedetomidine induced a hypnotic-anesthetic state in rats characterized by loss of righting reflex at doses greater than or equal to 0.1 mg/kg. This response was dose-dependent between 0.1 and 3 mg/kg. Alpha-2 adrenoceptor antagonists that cross the blood-brain barrier (antipamezole and idazoxan) decreased the hypnotic-anesthetic action of dexmedetomidine in a dose-dependent fashion. In contrast, the alpha-2 antagonist, L-659,066, which does not penetrate into the CNS did not affect dexmedetomidine-induced hypnosis. Antagonists for the other adrenoceptors not only failed to reduce the hypnotic-anesthetic action of dexmedetomidine but in some cases even potentiated this effect. Thus, prazosin, an alpha-1 adrenoceptor antagonist, significantly enhanced the hypnotic-anesthetic property of dexmedetomidine. Antagonists with beta-2 receptor blocking properties also enhanced dexmedetomidine-induced hypnosis. Selective beta-1 receptor antagonists did not affect the hypnotic action of dexmedetomidine. These results suggest that dexmedetomidine produces a hypnotic-anesthetic action in rats via activation of central alpha-2 adrenoceptors.

Epidural Clonidine Analgesia for Intractable Cancer Pain: Phase I

Abstract: Intrathecally administered clonidine has been reported to produce analgesia in cancer patients tolerant to intrathecal opiates. To assess the efficacy, safety, and appropriate dose of epidurally administered clonidine for the treatment of cancer pain, clonidine (range, 100-900 micrograms in 100-micrograms increments) was injected in nine patients with severe, intractable cancer pain. Clonidine produced analgesia, as measured by change in verbal pain scores, lasting more than 6 h. Clonidine also decreased blood pressure, although this effect was well tolerated and no patient met criteria for receiving iv ephedrine (greater than 30% decrease in mean arterial pressure not responsive to 500 ml iv crystalloid infusion). Clonidine decreased heart rate 10-30% and produced transient sedation. Serum glucose and cortisol and oxyhemoglobin saturation were not altered by clonidine. Clonidine was absorbed in a dose-dependent manner into the systemic circulation, although absorption and elimination kinetics were highly variable. Following study seven patients received epidural clonidine/morphine infusions at home for periods of up to 5 months with sustained analgesia. These results suggest that epidurally administered clonidine may offer effective analgesia in patients with severe, intractable cancer pain.

A Prospective Study of Protected Bronchoalveolar Lavage in the Diagnosis of Nosocomial Pneumonia

Abstract: The value of a new technique of protected bronchoalveolar lavage not requiring bronchoscopy was prospectively evaluated for the diagnosis of nosocomial pneumonia in two groups of critically ill patients. The control group was comprised of 29 patients free of any pulmonary disease whose lungs were ventilated for a mean time of 14 +/- 9 days (mean +/- SD). The pneumonia group was comprised of 30 patients with histologically proven nosocomial pneumonia whose lungs were ventilated for a mean time of 11 +/- 8 days. All patients of the pneumonia group died, and postmortem lung biopsies were taken for bacteriologic and pathologic examination. Twice a week in the control group or within the day preceding death in the pneumonia group, distal bronchial samples were obtained by a technique of protected bronchoalveolar lavage performed at the bedside. Fifty-one distal bronchial samples were bacteriologically analyzed in the control group and 30 in the pneumonia group. The sensitivity of a positive protected bronchoalveolar lavage for diagnosing nosocomial pneumonia was 80%, whereas the specificity was 66%. In 73% of the patients of the pneumonia group, the microorganisms isolated in the protected bronchoalveolar lavage and in the lung culture were partially (16%) or completely in agreement (57%). Among the 43 microorganisms isolated in the lung cultures, 74% were recovered by the protected bronchoalveolar lavage technique. This study shows that the protected bronchoalveolar lavage is an accurate technique for the diagnosis of nosocomial pneumonia. Because the technique is simple, noninvasive, easily repeatable at the bedside, and enables gram staining, it represents an attractive alternative to the fiberoptic bronchoscopy technique using a plugged double-sheathed brush.

Position and motion of the human diaphragm during anesthesia-paralysis.

Abstract: Regional motion of the human diaphragm was determined by high-speed, three-dimensional x-ray computed tomography. Six healthy volunteers were studied first while awake and breathing spontaneously and again while anesthetized-paralyzed and their lungs ventilated mechanically. Tidal volume (VT) and respiratory frequency were similar during both conditions. Three subjects were studied while they were supine and three while they were prone. During spontaneous breathing, movement of dependent diaphragm regions was greater than that of nondependent regions in four of six subjects. In five of the six subjects, dorsal diaphragm movement exceeded ventral movement regardless of body position. The volume displaced by the diaphragm (delta Vdi) was similar to VT in supine subjects but tended to be less than VT in prone subjects. After induction of anesthesia-paralysis, the end-expiratory position of the diaphragm did not change consistently in supine subjects, whereas a consistent cephalad volume shift occurred in prone subjects. During anesthesia-paralysis and mechanical ventilation, delta Vdi was reduced to approximately 50% of VT in both body positions. In the supine position, the pattern of diaphragm motion during mechanical inflation was nearly uniform. By contrast, in the prone position, the motion was nonuniform, with most motion occurring in the dorsal (nondependent) regions. It is concluded that the dominant influence on diaphragm motion may be some anatomical difference between the crural and costal diaphragm regions rather than the abdominal hydrostatic pressure gradient.

Does choice of anesthetic agent significantly affect outcome after coronary artery surgery

Abstract: A prospective study of 1094 consecutive adult patients undergoing coronary revascularization was undertaken to determine the effect of anesthetic technique on outcome. Patients received one of five primary techniques: high-dose fentanyl (greater than 50 micrograms/kg), moderate-dose fentanyl (less than 50 micrograms/kg), sufentanil (3-8 micrograms/kg), diazepam (0.4-1 mg/kg) with ketamine (3-6 mg/kg) or halothane (0.5-2.5% inspired concentration after thiopental induction). Supplemental inhalation anesthesia (enflurane, halothane, or isoflurane) was used in 60% of cases where the primary technique was intravenous based. Patients in the above anesthetic groupings had similar perioperative demographic and risk classifications. The overall incidence of postoperative myocardial infarction, postoperative low cardiac output state, and in-hospital death were 4.1, 5.6, and 3.1%, respectively. There were no significant differences in the incidence of these occurrences or in the incidence of serious pulmonary, renal, or neurologic morbidity or length of ICU stay among primary anesthetic techniques nor among supplemental inhalation agent groups. Multivariate discriminant analysis of this data suggests that a multitude of factors are significantly more important than anesthetic technique as determinants of outcome after coronary artery surgery.

Prostaglandin E1 and Nitroglycerin Reduce Pulmonary Capillary Pressure but Worsen Ventilation—Perfusion Distributions in Patients with Adult Respiratory Distress Syndrome

Abstract: Pulmonary artery hypertension associated with adult respiratory distress syndrome (ARDS) may increase microvascular filtration pressure by increasing pulmonary capillary pressure (PCP). To evaluate the potential to reverse this consequence of pulmonary artery hypertension, the effects of short-term

Needle Bevel Direction and Headache after Inadvertent Dural Puncture

Abstract: To study the effect of needle bevel direction on the incidence and severity of headache following inadvertent dural puncture occurring during the identification of the epidural space, the authors randomly assigned obstetric anesthesia residents to identify epidural space with the bevel of the epidural needle oriented either parallel or perpendicular to the longitudinal dural fibers. If dural puncture occurred, an observer unaware of the needle bevel direction, daily assessed the presence and severity of any subsequent headache. Of the 1,558 women who received epidural analgesia during this study, 41 women suffered dural puncture, 20 with the needle bevel oriented perpendicular to the longitudinal dural fibers and 21 with the needle bevel inserted parallel to the dural fibers (NS). Fourteen of 20 women in the group in which the needle bevel was perpendicular to dural fibers developed a moderate to severe headache, whereas only five of 21 in the group in which the needle bevel was parallel to dural fibers did so (P less than 0.005). Similarly, we administered a therapeutic blood patch to ten of 20 women in the perpendicular group but to only four of 21 in the parallel group (P less than 0.05). Thus, identifying the epidural space with the needle bevel oriented parallel to the longitudinal dural fibers limits the size of the subsequent dural tear and, therefore, lowers the incidence of headache should dural perforation occur.

The dose response of caudal morphine in children.

Abstract: The authors compared the duration of analgesia and the frequency of side effects of three doses of caudal epidural morphine in children aged 1.2–7.9 yr. Caudal catheters were inserted in 32 children, randomly assigned to receive 0.033 mg · kg−1, 0.067 mg · kg−1, or 0.10 mg · kg−1 of preservative-fre

Effects of local anesthesia on nerve blood flow: studies using lidocaine with and without epinephrine

Abstract: Peripheral nerves have a dual blood supply of intrinsic exchange vessels in the endoneurium and an extrinsic plexus of supply vessels in the epineurial space that cross the perineurium to anastomose with the intrinsic circulation. The extrinsic supply is responsive to adrenergic stimuli. In this study we measured nerve blood flow in rat sciatic nerves with a laser Doppler flow probe. Normal saline, solutions of 1% or 2% lidocaine HCl with and without 1:200,000 epinephrine, or 1:200,000 epinephrine in normal saline were topically applied to the nerves to determine their effect on nerve blood flow. At the end of the subsequent 10-min recording period, blood flow was significantly depressed for all of the solutions tested except saline. Reductions of blood flow ranged from 19.3% for 1% lidocaine HCl to 77.8% for 2% lidocaine HCl with epinephrine. Epinephrine by itself significantly reduced nerve blood flow; when added to local anesthetic solutions, it reduced nerve blood flow to a greater extent than the reduction caused by anesthetics alone. There was an additional significant reduction in nerve blood flow when the epinephrine groups were compared with the pure local anesthetic groups.

Effect of ropivacaine on cutaneous capillary blood flow in pigs.

Abstract: The effect of subcutaneous infiltration of ropivacaine and bupivacaine on local cutaneous blood flow was assessed by the laser Doppler method. One milliliter of each of ten test solutions (ropivacaine 0.25% and 0.75%, bupivacaine 0.25% and 0.75%, and saline, each with and without added epinephrine 5 micrograms/ml) was injected subcutaneously at separate sites on the side of each pig (n = 6). Skin blood flow was measured by laser Doppler at all sites before and 5, 10, 15, and 30 min after injection. Subcutaneous injection of ropivacaine 0.25% or 0.75% decreased cutaneous blood flow by a maximum of 52% +/- 11% and 54% +/- 14% (mean +/- SE), respectively. In contrast, bupivacaine 0.25% or 0.75% increased flow by 90% +/- 32% and 82% +/- 48%, and injection of saline increased blood flow by 32% +/- 17%. Cutaneous blood flow after the injection of ropivacaine was significantly lower than after injection of bupivacaine or saline, and was also lower than at the uninjected control site (P = 0.0009). All of the solutions with epinephrine decreased blood flow to a similar extent (48-73%, P = 0.3). The ability of ropivacaine to produce cutaneous vasoconstriction offers several advantages over the other local anesthetics presently available for infiltration anesthesia.

Manual evaluation of residual curarization using double burst stimulation: a comparison with train-of-four.

Abstract: Double burst stimulation (DBS) is a new mode of stimulation developed to reveal residual neuromuscular blockade under clinical conditions. The stimulus consists of two short bursts of 50 Hz tetanic stimulation, separated by 750 ms, and the response to the stimulation is two short muscle contractions

Effects of clonidine on anesthetic drug requirements and hemodynamic response during aortic surgery.

Abstract: The authors studied in a double-blind placebo-controlled study the effects of oral preoperative administration of 5 μg/kg clonidine upon the alfentanil and droperidol requirements, hemodynamic lability, distribution of the values of heart rate and blood pressure, and plasma noradrenaline levels, in two groups of ten normotensive patients undergoing infrarenal aortic surgery. The amounts of alfentanil supplementing a standardized continuous infusion, injected to maintain hemodynamic stability, were statistically identical between the groups (P = 0.23). The amount of droperidol, however, was significantly less (P = 0.004) in the group of patients that received clonidine. The norepinephrine plasma concentrations, during the entire procedure, were lower (P = 0.001) in the clonidine group. The variability of the heart rate, systolic (SBP) and diastolic (DBP) blood pressure recorded every 5 s, and assessed by the calculation of the coefficients of variation for each patient, showed no difference between the clonidine and the placebo group. However, when the values recorded were compared to the preoperative baseline values, and divided into three categories (baseline ± 20% - greater than 20% decrease vs. baseline - greater than 20% increase vs. baseline), the clonidine group showed a higher frequency of low heart rate and fewer episodes of tachycardia. The frequency of SBP hypertension was lower and of SBP hypotension higher in the clonidine group. After induction of anesthesia, but before surgery, there were more episodes of DBP hypotension in the clonidine group, but during dissection and vascular sutures the placebo group experienced more episodes of DBP hypotension, owing probably to the greater amount of droperidol injected. The authors conclude that the preoperative administration of clonidine decreased the need to supplement anesthetic, and modifies the profile of distribution of heart rate and blood pressure.

Changes in Ventilation, Oxygen Uptake, and Carbon Dioxide Output during Recovery from Isoflurane Anesthesia

Abstract: Recovery from inhalation anesthesia is often marked by the occurrence of postoperative tremor that resembles shivering, which is known to be associated with an increase in oxygen uptake (VO2), CO2 output (VCO2), and minute ventilation (VE). This study determined the time course of the ventilatory changes observed during the first hour of recovery from isoflurane anesthesia. Ten patients (ASA PS 1) scheduled for minor orthopedic surgery (knee arthroscopy) were included in this study. Anesthesia was induced with thiopental (5 mg/kg) and maintained with 70% N2O and isoflurane (1-2%) in oxygen, allowing spontaneous ventilation. In the recovery room, after N2O had been discontinued, patients were connected to a Beckman Metabolic measurement cart, which allowed a continuous monitoring of VE, VO2, VCO2, and PETCO2. Postoperative tremor was observed in all patients within 7.1 +/- 1.2 min (mean +/- SEM) after isoflurane discontinuation and was associated with a marked increase in the following: VO2, from 173 +/- 26 ml/min at the end of anesthesia to 457 +/- 88 ml/min; VCO2, from 149 +/- 18 ml/min at the end of anesthesia to 573 +/- 98 ml/min; and VE, from 6.8 +/- 0.7 l/min at the end of anesthesia to 16.6 +/- 2.8 l/min (values obtained 20 min after isoflurane discontinuation). In three patients during intense shivering, VO2, VCO2, and VE reached peak values higher than 800 ml/min, 1,300 ml/min and 30 l/min, respectively. This study shows that postoperative tremor following isoflurane anesthesia may be associated with prolonged and large increases in oxygen uptake, CO2 output, and minute ventilation.

Isoflurane for refractory status epilepticus: a clinical series.

Abstract: General anesthesia has been recommended to control convulsive status epilepticus that is refractory to conventional anticonvulsant therapy. Halothane has been the recommended agent, but without experimental justification. Isoflurane, which has no reported organ toxicity and produces electrographic suppression at clinically useful concentrations in normal humans, should be a better volatile anesthetic for this purpose. The efficacy and safety of isoflurane administered to control convulsive status epilepticus were assessed on 11 occasions in nine patients in seven North American hospitals. Isoflurane, administered for 1-55 h, stopped seizures in all patients and was able to be titrated to produce burst-suppression patterns on electroencephalograms. Blood pressure support with iv fluids and/or pressor infusions was required in all of the patients. Seizures resumed upon discontinuation of isoflurane on eight of 11 occasions. Six of the nine patients died. The three survivors sustained cognitive deficits. In one patient urine fluoride concentrations were elevated, although not to nephrotoxic levels. These cases suggest that isoflurane 1) is an effective, rapidly titratable anticonvulsant; 2) does not reverse underlying causes of the refractory seizures; and 3) usually necessitates hemodynamic support with fluids and/or pressors. Isoflurane may be administered for seizures, but only when iv agents in anesthetic doses are ineffective or produce unacceptable side effects.

Intravenous propofol during cesarean section: placental transfer, concentrations in breast milk, and neonatal effects. A preliminary study.

Abstract: Placental transfer and neonatal effects of propofol were investigated in 21 women undergoing elective cesarean section under general anesthesia This study was conducted in two separate phases according to the use of propofol In both phases, anesthesia was induced with an iv bolus of 25 mg/kg of propofol In phase 1 (n = 10), anesthesia was maintained with 50% nitrous oxide in oxygen and halothane In phase 2 (n = 11), a continuous infusion of propofol at a rate of 5 mgkg-1h-1 was started after the induction dose Maternal venous and umbilical cord arterial and venous samples were obtained at delivery The propofol concentration in whole blood was measured with a high performance liquid chromatography method Where possible, breast milk/colostrum was expressed for both phases postoperatively and a sample of blood was collected during phase 2 from neonates via a heel prick 2 h after birth Propofol crossed the placenta, as demonstrated by concentrations found in umbilical venous blood in phase 1 (013-075 micrograms/ml) and in phase 2 (078-137 micrograms/ml) At delivery, the ratio of the drug concentration in umbilical venous blood to that in maternal blood was 070 +/- 006 for phase 1 and 076 +/- 010 for phase 2 The ratio of propofol concentration in the umbilical artery to that in the umbilical vein was 109 +/- 004 for phase 1 and 070 +/- 005 for phase 2(ABSTRACT TRUNCATED AT 250 WORDS)

Recovery of airway protection compared with ventilation in humans after paralysis with curare.

Abstract: d-Tubocurarine (dTc) was administered intravenously to six healthy unanesthetizted volunteers to assess the sensitivity to neuromuscular blockade of those muscles involved in protecting the airway against obstruction and/or aspiration relative to the muscles of inspiration. Each subject was given an intravenous bolus of dTc followed by an infusion to allow three different levels of inspiratory muscle weakness as measured by maximum inspiratory pressure (MIP). Levels of MIP were control (–90 cm H2O), –60, –40, and –20 cm H2O. Vital capacity (VC), hand grip strength (HGS), and end-tidal CO2 (PETco2) were obtained at each level. At each level of weakness and at intermediate values during recovery, muscles of airway protection were functionally assessed by noting the MIP at which the maneuver could be accomplished and the MIP at which they could not. The mean of these two values was calculated for each subject. The tests were: 1) ability to swallow, 2) ability to perform a valsalva maneuver, 3) prevent obstruction of the airway, and 4) ability to approximate teeth. These were compared with head lift and straight leg raising. At maximum neuromuscular blockade (MIP of –20 cm H2O), VC was 2.0 liters, HGs was 0, and PETco2 was normal. Muscles of airway protection were still incapacitated. Swallowing returned above MIP of –49 cm H2O, approximation of teeth above –42 cm H2O, airway obstruction above –39 cm H2O, and valsalva above –33 cm H2O. Thus, although ventilation may be adequate at MIP = –25 mmHg, the muscles of airway protection are still nonfunctional. Further reversal of neuromuscular blockade must be accomplished before a patient whose trachea is extubated can protect the airway. All subjects who could accomplish a head lift could perform the airway protective maneuvers.