Pema Dorje

Evaluation of a cerebral oximeter as a monitor of cerebral ischemia during carotid endarterectomy.

BackgroundStroke is an important contributor to perioperative morbidity and mortality associated with carotid endarterectomy (CEA). This investigation was designed to compare the performance of the INVOS-3100 cerebral oximeter to neurologic function, as a means of detecting cerebral ischemia induced by carotid cross-clamping, in patients undergoing carotid endarterectomy with cervical plexus block. MethodsNinety-nine patients undergoing 100 CEAs with regional anesthesia (deep or superficial cervical plexus block) were studied. Bilateral regional cerebrovascular oxygen saturation (rSO2) was monitored using the INVOS-3100 cerebral oximeter. Patients were retrospectively assigned to one of two groups: those in whom a change in mental status or contralateral motor deficit was noted after internal carotid clamping (neurologic symptoms; n = 10) and those who did not show any neurologic change (no neurologic symptoms; n = 90). Data from 94 operations (neurologic symptoms = 10 and no neurologic symptoms = 84) were adequate for statistical analyses for group comparisons. A relative decrease in ipsilateral rSO2 after carotid occlusion (calculated as a percentage of preocclusion value) during all operations (n = 100) was also calculated to determine the critical level of rSO2 decrease associated with a change in neurologic function. ResultsThe mean (± SD) decrease in rSO2 after carotid occlusion in the neurologic symptoms group (from 63.2 ± 8.4% to 51.0 ± 11.6%) was significantly greater (P = 0.0002) than in the no neurologic symptoms group (from 65.8 ± 8.5% to 61.0 ± 9.3%). Logistic regression analysis used to determine if a change in rSO2, calculated as a percentage of preclamp value, could be used to predict change in neurologic function was highly significant (likelihood ratio chi-square = 13.7;P = 0.0002). A 20% decrease in rSO2 reading from the preclamp baseline, as a predictor of neurologic compromise, resulted in a sensitivity of 80% and specificity of 82.2%. The false-positive rate using this cutoff point was 66.7%, and the false-negative rate was 2.6%, providing a positive predictive value of 33.3% and a negative predictive value of 97.4%. ConclusionMonitoring rSO2 with INVOS-3100 to detect cerebral ischemia during CEA has a high negative predictive value, but the positive predictive value is low.

Postoperative Complications in Obese and Nonobese Patients

BackgroundPostoperative complications are undesirable and potentially common in the increasing obese population of surgical patients. There is a scarcity of recent and reliable studies comparing postoperative morbidity and mortality in obese and nonobese patients. The aim of this study was to evaluate the prevalence, pattern, and severity of postoperative complications in obese and nonobese surgical patients.MethodsA retrospective review and analysis of adult postoperative complications recorded on an electronic database was conducted. The database covered a period of 4 years and consisted of 7,271 cases of postoperative complications that occurred within 30 days of noncardiac moderate or major surgery. Appropriate data and variables were compared between obese and nonobese patients using the SPSS program.ResultsThe rate of postoperative complications was 7.7%. Obese patients had a higher prevalence of myocardial infarction (P = 0.001), peripheral nerve injury (P = 0.039), wound infection (P = 0.001), and urinary tract infection (P = 0.004). ). Morbidly obese patients had a higher mortality rate of 2.2% compared with 1.2%; for all other patients (P = 0.034) and a higher prevalence of tracheal reintubation (P = 0.009) and cardiac arrest (P = 0.015). Obese patients had higher American Society of Anesthesiologists (ASA) physical status scores than other patients (P = 0.001).ConclusionsObese patients have a significantly higher risk of postoperative myocardial infarction, wound infection, nerve injury, and urinary infection. Obesity is an independent risk factor for perioperative morbidity, and morbid obesity is a risk factor for mortality.

Cerebral Oximetry in Patients Undergoing Carotid Endarterectomy Under Regional Anesthesia

BACKGROUND AND PURPOSE Near-infrared spectroscopy is a technique that can potentially monitor changes in cerebral oxygenation. There are at present limited clinical data regarding the value of this technology in relating neurological outcome to cerebrovascular hemoglobin oxygen saturation (ScO2). This investigation reports changes in ScO2 due to carotid cross-clamping during carotid endarterectomy in awake patients. METHODS ScO2 was monitored in 38 adult patients undergoing 41 carotid endarterectomies under regional anesthesia. Ipsilateral and contralateral hemispheres were monitored simultaneously during 36 operations, with ipsilateral monitoring alone in the remaining 5 operations. RESULTS No significant difference was detected between ipsilateral and contralateral ScO2 during preclamp or postclamp periods. Carotid cross-clamping caused a statistically significant (P < .01) decrease in the ipsilateral ScO2, which decreased from 71.8 +/- 6.91% to 65.8 +/- 8.2%, while the contralateral ScO2 remained stable at 70.5 +/- 7.5% and 70.3 +/- 7.9%. The change in ipsilateral ScO2 ranged from +2.6% to -28.6% of the preclamp value. The difference between ipsilateral and contralateral ScO2 during cross-clamping was statistically significant (P < .001). The duration of cross-clamping was 39 +/- 11 minutes (range, 18 to 89 minutes). The decrease in ipsilateral ScO2 was highly variable from patient to patient and did not correlate with the duration of cross-clamping. CONCLUSIONS These results suggest that carotid artery occlusion causes a statistically significant but variable decrease in ScO2 in the majority of patients. Data in this investigation provide a range of ScO2 values that was not associated with a clinically detectable neurological dysfunction.

An assessment of contributions made by extracranial tissues during cerebral oximetry.

This study was designed to determine the extent of contribution made by extracranial tissues to estimation of regional cerebrovascular saturation (ScO2) during cerebral oximetry. Thirty four patients undergoing carotid endarterectomy under regional anesthesia were studied. Bilateral ScO2 monitoring with two INVOS 3100 A cerebral oximeters was used. Effect of occlusion of external carotid artery (ECA) for five minutes on ScO2 readings followed by occlusion of internal and common carotid arteries was studied. ScO2 readings at 1 minute intervals were stored on computer disks for off-line analysis. Numerical data were subjected to a two way repeated measures analysis of variance to study the effect of side (ipsilateral or contralateral) and phase (pre clamp, ECA clamp, ICA clamp and post clamp) of operation. A value of p<0.05 was considered significant. There was no significant change in ScO2 on the contralateral side. On the ipsilateral hemisphere ScO2 decreased from 67.4+/-8.5 to 65.6+/-8.3 with ECA occlusion and to 61.4+/-9.6 after ICA occlusion returning to 64.8+/-9.8 after all clamps were released. Decrease after ECA occlusion was not significant (p = 0.12) while that after ICA occlusion was significant when compared to pre clamp value (p<0.001). After release of all clamps ipsilateral ScO2 returned toward baseline but remained significantly lower (p<0.05) than pre clamp values. When readings from two hemispheres were compared, a significant difference (p<0.001) was noted during ICA occlusion only. We conclude that the mathematical algorithm used for calculation of ScO2 by INVOS 3100 A cerebral oximeter measures predominantly the intracranial cerebrovascular saturation.

Akathisia and anesthesia : Refusal of surgery after the administration of metoclopramide

kathisia (from the Greek for “not to sit”) is a distressing side effect of some medications often #prescribed to patients (1,2). Akathisia usually presents with objective motor restlessness and subjec- tive mental changes. Perioperative medications known to produce akathisia include droperidol, met- oclopramide, perphenazine, prochlorperazine, nalox- one, and flumazenil. Patient refusal to have surgery after the administration of droperidol has been repeat- edly reported (3,4), but our literature search revealed only one case report of the cancellation of surgery after the administration of metoclopramide (5). We believe that central nervous system side effects of this severity may be rare, but less severe effects of meto- clopramide and other medications may be more com- mon than appreciated. It is possible that there is sub- stantial underdiagnosis and misinterpretation of acute akathisia because of unfamiliarity with the condition (6). We report two cases of the cancellation of surgery by patients in our institution who displayed akathisia- like symptoms after they received an IV bolus of met- oclopramide. After these episodes, we changed the way metoclopramide is given preoperatively.

Transjugular intrahepatic portosystemic shunt related paradoxical air embolism during orthotopic liver transplantation

To the Editor, During the dissection phase of an orthotopic liver transplant, a 63 yr old man developed widespread ST depression and cardiovascular collapse. Transesophageal echocardiography (TEE) revealed air in both ventricles associated with new onset biventricular dilation and dysfunction. The surgeons found a failed staple line placed inadvertently across a transjugular intrahepatic portosystemic shunt (TIPS), which was now splinting the right hepatic vein open. Control of air entrainment was achieved with caval clamping. Trendelenberg positioning was employed to prevent air entering the right ventricular outflow tract. Following resuscitation, a full echocardiographic examination was undertaken. Air was seen extending into the aortic root but was not demonstrated in the coronary circulation. Patent foramen ovale (PFO) was not demonstrated on colour Doppler. A plausible explanation for this paradoxical air embolism is intrapulmonary shunting. Intrapulmonary shunt recruitment is thought to occur by a pressure dependent baffle mechanism exacerbated in this case by increased pulmonary artery pressures from air embolus. Potentially catastrophic hemodynamic changes occur frequently during orthotopic liver transplantation (OLT) and require rapid and accurate diagnosis. During the dissection phase, hepatic manipulation causes intermittent obstruction to venous return. The anhepatic phase involves clamping the portal vein and inferior vena cava, both of which cause a significant reduction in venous return. Reperfusion syndrome ([30% decrease in mean arterial pressure for at least 1 min) is seen in 42% of patients. Associated physiologic changes include increased pulmonary pressures, right ventricular dysfunction, bradycardia, acidosis, and hypothermia. Given the multiple causes of hypotension and hemodynamic instability during OLT, the assessment of cardiac preload and function is easily justified. In comparison with a pulmonary artery catheter, TEE has the distinct advantage of being a relatively non-invasive procedure. TEE allows direct visualization of the heart, permitting monitoring of volume status, contractility, and overall function. In addition, TEE provides valuable information when less common complications occur, such as large pleural effusions, tension pneumothorax, or pulmonary embolism. TEE is especially helpful in the management of disorders such as acute pulmonary hypertensive crisis, intracardiac clot formation, and hypertrophic cardiomyopathy. The initial fear of rupturing esophageal varices is an exceedingly uncommon complication and has not yet been reported despite widespread intra-operative use. We would like to raise four points: (1) baseline TEE for OLT should seek to specifically identify trans-pulmonary shunts; (2) liver transplant candidates may be at increased risk of paradoxical embolism even if they do not have a PFO or severe hepatopulmonary syndrome; (3) one should note the presence of a TIPS that may contribute to life threatening air emboli during liver dissection; and (4) TEE is increasingly used in liver transplantation and can aid in the rapid diagnosis of a potentially underestimated issue of OLT air embolism.

Management of emergence agitation.

petencies give an indication of the ability of an SHO to perform basic anaesthetic skills, these skills are not adequate by themselves to allow safe independent practice. A course covering the management of critical incidents should form part of the basic curriculum for novice anaesthetists prior to being placed on the on-call rota. Having the opportunity to manage these types of cases in a controlled simulator environment adds to both the enjoyment and the efficacy of the learning process.

Tense diaphragm in tension pneumothorax.

To the Editor:—In the case report by Ibrahim et al., in which a 64-kg man developed tension pneumothorax and systemic air embolism during positive pressure ventilation with a rather large tidal volume of 1,000 ml, there seems to have been unnecessary delay before a chest tube relieved the left-sided pneumothorax with immediate improvements in hemodynamic parameters. The exact time between the circulatory collapse and the chest tube placement that relived the tension pneumothorax is not clear. But there seems to have been enough time to perform, along with routine resuscitation, a transesophageal echocardiographic study of the cardiac chambers and a fiberoptic study and manipulation of the airway before the pneumothorax was relieved by chest tubes. The patients abdomen was open for pancreatic debridement at the time of circulatory collapse. Under these circumstances, the tension pneumothorax can be diagnosed/ruled out by examination of the diaphragm by the operating surgeons. If the diaphragm is tense and bulging down into the abdomen, the tension pneumothorax can initially be relieved via an opening through the diaphragm followed by a formal chest tube placement on the same side. This approach not only avoids unnecessary delay in the definite therapy for pneumothorax, but also eliminates the need for bilateral chest tubes in unilateral pneumothorax. We have personal experience in managing intraoperative spontaneous tension pneumothorax using the diaphragm sign during laparotomy on a patient with cystic fibrosis (unpublished data, September 1995). When pneumothorax occurs during laparoscopic procedures, the status of the diaphragm may be visualized using the laparoscope.