Avner Sidi

Experimental closed head injury in rats: mechanical, pathophysiologic, and neurologic properties.

A model of closed head injury in rats was developed using a calibrated weight-drop device. The development of edema was studied in various brain regions (cerebral hemispheres, brain stem, cerebellum) using a linear specific gravity gradient column. Regional brain tissue density was measured within 1 min, at 15 and 60 min, 18 h, 4 and 10 days after injury to the left cerebral hemisphere, and was compared with values in sham-operated and control rats. Significant edema (i.e., reduced specific gravity) occurred only in the traumatized hemisphere and was maximal at 18 h. A neurologic severity score (NSS) was developed to evaluate the status of the rat after injury. Specific gravity was significantly correlated with NSS at 18 h after injury. The affected hemisphere displayed hemorrhagic lesions as early as one hour post head trauma (HT), which evolved into hemorrhagic necrosis at 18 h. A pathologic score, evaluated 18 h post HT based on size and severity of the lesion, was correlated with the NSS and evaluated for each rat at one hour and 18 h postimpact. This correlation was found to be highly significant. This model of brain injury may be useful in future studies on the effects of therapeutic agents.

Incorporating simulation-based objective structured clinical examination into the Israeli National Board Examination in Anesthesiology.

We describe the unique process whereby simulation-based, objective structured clinical evaluation (OSCE) has been incorporated into the Israeli board examination in anesthesiology. Development of the examination included three steps: a) definition of clinical conditions that residents are required to handle competently, b) definition of tasks pertaining to each of the conditions, and c) incorporation of the tasks into hands-on simulation-based examination stations in the OSCE format, including 1) trauma management, 2) resuscitation, 3) crisis management in the operating room, 4) regional anesthesia, and 5) mechanical ventilation. Members of the Israeli Board of Anesthesiology Examination Committee assisted by experts from the Israel Center for Medical Simulation and from Israels National Institute for Testing and Evaluation were involved in this process and in the development of the assessment tools, orientation of examinees, and preparation of examiners. The examination has been administered 4 times in the past 2 yr to 104 examinees and has gradually progressed from being a minor part of the oral board examination to a prerequisite component of this test. The pass rate ranged from 70% in resuscitation to 91% in regional anesthesia. The mean inter-rater correlations for all the checklist items, for the score based on the critical checklist items only, and for the general rating were 0.89, 0.86, and 0.76, respectively. The overall Kappa coefficients (the inter-rater agreement coefficient) for the total score and the critical checklist items were 0.71 and 0.76, respectively. The correlation between the total score and the general score was 0.76. According to a subjective feedback questionnaire, most (70%–90%) participants found the difficulty level of the examination stations reasonable to very easy and prefer this method of examination to a conventional oral examination. The incorporation of OSCE-driven modalities in the certification of anesthesiologists in Israel is a continuing process of evaluation and assessment.

Supplemental Oxygen Compromises the Use of Pulse Oximetry for Detection of Apnea and Hypoventilation During Sedation in Simulated Pediatric Patients

OBJECTIVE. The goal was to assess the time to recognition of apnea in a simulated pediatric sedation scenario, with and without supplemental oxygen. METHODS. A pediatric human patient simulator mannequin was used to simulate apnea in a 6-year-old patient who received sedation for resetting of a fractured leg. Thirty pediatricians participating in a credentialing course for sedation were randomly assigned to 2 groups. Those in group 1 (N = 15) used supplemental oxygen, and those in group 2 (N = 15) did not use supplemental oxygen. A third group (N = 10), consisting of anesthesiology residents (postgraduate years 2 and 3 equivalent), performed the scenario with oxygen supplementation, to ensure validity and reliability of the simulation. The time interval from simulated apnea to bag-mask ventilation was recorded. Oxygen saturation and Paco2 values were recorded. All recorded variables and measurements were compared between the groups. RESULTS. The time interval for bag-mask ventilation to occur in group 1 (oxygen supplementation) was significantly longer than that in group 2 (without oxygen supplementation) (173 ± 130 and 83 ± 42 seconds, respectively). The time interval for bag-mask ventilation to occur was shorter in group 3 (anesthesiology residents) (24 ± 6 seconds). Paco2 reached a higher level in group 1 (75 ± 26 mmHg), compared with groups 2 and 3 (48 ± 10 and 42 ± 3 mmHg, respectively). There was no significant difference between the groups in oxygen saturation values at the time of clinical detection of apnea (93 ± 5%, 88 ± 5%, and 94 ± 7%, respectively). CONCLUSIONS. Hypoventilation and apnea are detected more quickly when patients undergoing sedation breathe only air. Supplemental oxygen not only does not prevent oxygen desaturation but also delays the recognition of apnea.

Effect of isoflurane on the extent of myocardial necrosis and on systemic hemodynamics, regional myocardial blood flow, and regional myocardial metabolism in dogs after coronary artery occlusion.

Anesthetized dogs were studied in two protocols to determine the effect of isoflurane on the extent of myocardial injury resulting from left anterior descending coronary artery (LAD) occlusion. In 22 dogs (11 treated with isoflurane 1% inspired, beginning 1 hr after LAD occlusion and 11 control) myocardial infarct size measured postmortem after 6 hr of LAD occlusion was significantly less with isoflurane than without it, 23.4 ± 3.8% Us 36.2 ± 2.4% of left ventricle; regional myocardial blood flow (RMBF) did not differ between groups and hemodynamic differences were slight. Fifty-two other dogs underwent two 15-min periods of LAD occlusion separated by 2 hr of reperfusion. Without isoflurane (n = 12), hemodynamic, RMBF, and regional metabolic data did not differ between the two occlusion periods. When isoflurane 1.3% inspired was administered during one of the two occlusion periods by random assignment, coronary perfusion pressure, left ventricular stroke work index, and systolic left ventricular pressure decreased more than when isoflurane was not administered. Both oxygen (O2) consumption and supply in ischemic myocardium decreased proportionately during LAD occlusion, but more so with isoflurane. Neither lactate production, potassium release, glucose extraction, nor coronary venous carbon dioxide (CO2)or O2 content differed between LAD occlusion periods with and without isoflurane. Thus, isoflurane decreased the extent of myocardial necrosis produced by LAD occlusion but neither XMBF nor metabolic indications were improved during transitory ischemia.

Methylene Blue and Indocyanine Green Artfactually Lower Pulse Oximetry Readings of Oxygen Saturation. Studies in Dogs

The effects of fluorescein, methylene blue, and indocyanine green on hemodynamic variables and on pulse oximetry and co-oximetry measurements of arterial hemoglobin oxygen saturation (SaO2) and oxyhemoglobin percentage (% HbO2) were evaluated in 16 anesthetized dogs in vitro by cooximetry (% HbO2) and in vivo by pulse oximetry (SaO2). The light absorbance (optical density) in plasma (range 500 to 800 nm) was measured by a spectrophotometer. Fluorescein did not affect oximetry measurements, plasma light absorbance in the range measured, or hemodynamic variables. Methylene blue caused dose-dependent decreases in measurements made with both forms of oximetry for up to 30 minutes, the decrease being greater and longer lasting with pulse oximetry (P < 0.05). Hemodynamic measurements in 5 dogs showed that methylene blue (1 to 5 mg/kg) increased arterial pressure transiently, after which cardiac output, stroke index, and left ventricular stroke work index decreased and left ventricular end-diastolic pressure and systemic and pulmonary vascular resistances increased (P < 0.05 with 5 mg/kg). Methemoglobin concentration measured by co-oximetry increased significantly (to 19.9 ± 1.4%, P < 0.05) 1 minute after 5 mg/kg of methylene blue was injected. Methylene blue had a dose- and time-dependent effect on plasma light absorbance, and this effect peaked in the 660- to 670-nm range. The data do not distinguish the relative contributions of physiology (hemodynamic change), chemistry (methemoglobin production), and physics (optical properties) to the decrease in pulse oximetry and co-oximetry measurements that follows injection of methylene blue. Indocyanine green affected neither hemodynamic variables nor co-oximetry readings but decreased pulse oximetry readings for up to 10 minutes dose dependently. With doses of 0.1 to 3.0 mg/kg of indocyanine green plasma light absorbance peaked at 805 nm but increased dose dependently for up to 30 minutes at 660 nm. Methylene blue and indocyanine green (and, by implication, other dyes with plasma light absorbance peaks in the 600- to 1,000-nm range) artifactually alter oximetric detection of arterial hemoglobin oxygen saturation and oxyhemoglobin percentage.

Estimating anesthetic depth by electroencephalography during anesthetic induction and intubation in patients undergoing cardiac surgery

Intravenous (IV) anesthesia titrated to continuous computer-processed electroencephalograms (EEGs) was studied in 32 consecutive patients undergoing cardiac surgery. Anesthesia was induced with fentanyl 50 micrograms/kg with no EEG monitoring (n = 16) or 25 to 50 micrograms depending on changes in EEG (n = 16). EEG, oxygen saturation by pulse oximeter, intra-arterial blood pressure (BP), central venous pressure (CVP), and pulmonary artery pressure (PAP) (n = 18) were monitored continuously. Cardiac output (CO), CVP, PAP, spectral-edge frequency for each hemisphere, and BP were recorded before induction, immediately before intubation, and 1 and 5 minutes after intubation. With EEG monitoring, intubation was performed when spectral-edge frequency decreased to 10 Hz or less. Recall and pain were investigated 2 to 12 weeks postoperatively. With EEG, the amount of fentanyl used before intubation was significantly lower (39.7 +/- 2 micrograms/kg; p less than 0.005) than without EEG (50 micrograms/kg). The decrease in BP (% change) was less with than without EEG; mean changes in BP between preinduction and preintubation were -7.4% +/- 3.8% and -16.5% +/- 3.1% and between preinduction and 1 minute after intubation 0.3% +/- 3.4% and -12.5% +/- 3.5%, respectively. Percent changes in mean BP between intubation and 1 minute after were 9.6% +/- 4.0% with EEG and 5.2% +/- 3.0% without EEG. No patient in either group had recall. The authors conclude that using EEG monitoring to estimate depth of anesthesia during induction and laryngoscopy may increase safety in high-risk patients undergoing cardiac surgery.

Prolonged neuromuscular blockade and ventilatory failure after renal transplantation and cyclosporine

In a retrospective one-year study, we documented respiratory failure or prolonged neuromuscular blockade in eight of 65 patients with chronic renal failure who had received either vecuronium (four of 29 patients) or atracurium (four of 36 patients) during anaesthesia for kidney transplantation. We reviewed the charts of the patients and recorded all aspects of medication and anaesthesia to try to determine whether there might be a single factor associated with this high incidence (12 per cent) of respiratory failure. Anaesthesia for all patients was induced with thiopentone, isoflurane, and N2O/O2. Tracheal intubation was facilitated with muscle relaxants in a single bolus of vecuronium, 0.07 to O.1 mg · kg−1, or atracurium, 0.3 to 0.5 mg · kg−1. Additional doses were given according to neuromuscular activity, which was monitored visually by response to train-of-four and tetanic stimulation. Anaesthesia was maintained with fentanyllisoflurane and N2O/O2. After induction of anaesthesia, each patient received methylprednisolone, cefazolin, mannitol infusion for 24 hr beginning at the start of renal artery anastomosis, and either azathioprine (n = 57) or cyclosporine (n = 8). Relaxation was evaluated toward the end of the operation by train-of-four stimulation. Neuromuscular blockade was reversed with edrophonium (0.75-1 mg · kg−1) or neostigmine (0.06–0.08 mg · kg−1). The eight patients with prolonged neuromuscular blockade received ventilatory support for one to three hours after operation. Respiratory failure was significantly more frequent inpatients who received cyclosporine (P < 0.05).RésuméEn un an, quatre des 36 patients qui avaient reçu de l’atracurium et quatre des 29 autres qui avaient eu du vécuronium lors de leur transplantation rénale ont été affligés d’un bloc neuromusculaire prolongé ou d’un épisode de défaillance respiratoire. L’induction de l’anesthésie avec du thiopental, de isoflurane et du protoxyde d’azote précédait l’injection d’un bolus de 0,07 à 0,1 mg · kg−1 de vécuronium ou de 0,3 à 0,5 mg · kg−1 d’atracurium avant l’intubation de la trachee. L’évaluation visuelle de la réponse neuromusculaire au train-de-quatre ondes ou la stimulation tétanique guidait l’énjection de doses additionnelles alors quon ajoutait du fentanyl au régime d’isoflurane et de protoxyde d’azote. Après l’induction, on injectait en plus de la méthylprednisolone, de la céfazoline et du mannitol (perfusé pendant 24 h suite à l’anastomose de l’artére rénale) soit de l’azathioprine (n = 57) soit de la cyclosporine (n = 8). A la fin de l’intervention, on contrail le bloc neuromusculaire résiduel (évalué avec le train-de-quatre ondes) avec 0,75 à 1 mg · kg−1 avec 0,06 à 0,08 mg · kg−1 de néostigmine. On dut supporter mécaniquement la ventilation des huit patients au bloc neuromusculaire persistant pour une période d’une à trois heures. En retrospective, ces épisodes de défaillance respiratoire survenaient de préférence chez ceux qui avaient reçu de la cyclosporine (P < 0,05).

Noninvasive Monitoring of Cerebral Perfusion by Transcranial Doppler During Fulminant Hepatic Failure and Liver Transplantation

Survival in patients with fulminant hepatic failure (FHF) treated medically, rather than surgically, ranges from 12%-67% (mean 39%), depending on the cause of the disease (1). The major cause of mortality is increased intracranial pressure (ICI’) from brain edema (2). For patients with a poor prognosis (3), orthotopic liver transplantation may be the definitive treatment (41, even though, only a few years ago, some considered this treatment ineffective by the time patients reached Grade 4 encephalopathy (5). ICI’ monitoring allows physicians to use specific therapy to control intracranial hypertension. Continuous measurement of ICI’ perioperatively in the management of FHF has been associated with a survival rate of 54%74% in a series of six to 23 patients (6-9), which is generally higher than with medical means (l), and was as high as 92% for the selected group who had undergone liver transplantation (6). Such invasive monitoring, however, is especially risky in FHF patients with coagulopathy, in whom the incidence of bleeding from ICI’ monitoring ranges from 5%-22% (6,8) with a mortality rate of 60% (6). Although the use of ICI’ monitoring for FHF has become more routine (8), not all centers support the use of this invasive monitoring. We describe a patient with FHF and brain edema who underwent liver transplantation and whose cerebral perfusion was monitored noninvasively by transcranial Doppler (TCD) imaging, as well as invasively by ICI’. The noninvasive technique provided adequate information when cerebral perfusion was low, comparable with the invasive technique, and allowed intracranial hypertension to be diagnosed and treated effectively.

Pulse oximetry fails to accurately detect low levels of arterial hemoglobin oxygen saturation in dogs.

The accuracy of two commercially available pulse oximeters (the Ohmeda Biox 3700, software version “J,” and the Nellcor N-100) in detecting low levels of arterial hemoglobin oxygen saturation (SaO2) was evaluated in 10 dogs in which hypoxia was induced by stopping the fresh gas flow into the anesthesia machine circle system. Measurements made in vivo with the pulse oximeters, with detectors placed on the tongue, were compared with measurements made in vitro using an IL 282 CO-Oximeter as SaO2 decreased toward zero. Measurements from the two oximeters correlated poorly over the range from 0 to 100% SaO2 (r = 0.69). In this range, the correlation between Nellcor N-100 measurements and those of the CO-Oximeter had an r of 0.82, a regression line slope of 0.82, and a y intercept of 14.8; the correlation between the Ohmeda Biox 3700 and the CO-Oximeter had an r of 0.83, a regression line slope of 0.66, and a y intercept of 32.7. The correlation with the CO-Oximeter was similar for both the Ohmeda and the Nellcor pulse oximeters at an SaO2 of 80% or more. However, when SaO2 was less than 80%, measurements by pulse oximetry correlated less well with CO-Oximeter measurements (r = 0.62, slope = 0.64, and y intercept = 21.0 for Nellcor; r = 0.71, slope = 0.67, and y intercept = 32.4 for Ohmeda). When SaO2 was less than 60%, both oximeters inaccurately indicated the co-oximetry values (r = 0.36 and y intercept = 26.1 for the Nellcor; r = 0.48 and y intercept = 33.2 for the Ohmeda). In this animal model, with pulse oximeter measurements obtained from the tongue and with rapidly decreasing SaO2, measurements of SaO2 by pulse oximetry become inaccurate in comparison with co-oximetry measurements at low levels of SaO2.

Objective Structured Clinical Examination-based assessment of regional anesthesia skills: the Israeli National Board Examination in Anesthesiology experience.

Simulation techniques are increasingly being used in anesthesia training programs and to a lesser extent in evaluation of residents. We describe 7 years of experience with Objective Structured Clinical Examination–based regional anesthesia assessment in the Israeli National Board Examinations in Anesthesiology. We believe this is the first use of such mock scenarios for the assessment of regional anesthesia for the important purpose of national accreditation. During the study period, 308 candidates were examined in 1 of 8 different blocks. The total pass rate was 83%(257 of 308), ranging from 73% to 91%. The interrater correlation for total, critical, and global scores were 0.84, 0.88, and 0.75, respectively. Technological and cost constraints preclude actual assessment of regional anesthesia. However, testing formats that more closely reflect clinical practice are potentially valuable adjuncts to traditional examinations.