Joseph M. Messick

Correlation of regional cerebral blood flow (rCBF) with EEG changes during isoflurane anesthesia for carotid endarterectomy: critical rCBF

A prospective evaluation of regional cerebral blood flow (rCBF) (ipsilateral middle cerebral artery distribution) was determined using a 133Xe clearance technique in 31 ASA P.S. II–III patients anesthetized with isoflurane-50% N2O in O2 for carotid endarterectomy. Each patient was monitored with 16-channel EEG throughout anesthesia and surgery. Critical rCBF was defined as that flow below which EEG signs of ischemia occurred. Critical rCBF (T1/2 method of analysis) was <10 ml.100 g-1.min−1 (mean ± SE 5.9 ± 1.2) in the six patients in whom transient EEG changes occurred at the time of temporary surgical carotid artery occlusion. No EEG changes occurred with occlusion in the other 25 patients; mean (±SE) occlusion rCBF in this group was 18.9 ± 1.3 ml.100 g−1.min−1 (P <0.001). Preocclusion flows were not significantly different in the two groups. Critical rCBF during isoflurane anesthesia was less than that previously determined during halothane anesthesia (18–20 ml.100 g−1.min−1), and is compatible with the effects of isoflurane on CMRo2 and CBF.

Isoflurane and Cerebrospinal Fluid Pressure in Neurosurgical Patients

The effect of isoflurane on cerebrospinal fluid pressure (CSFP) was determined in 20 patients undergoing craniotomy for intracranial supratentorial neoplasm or hematoma. In 15 of these patients, following endotracheal intubation, hyperventilation sufficient to result in Paco2 25–30 torr was begun simultaneously with the introduction of 1 per cent isoflurane. In the remaining five patients ventilation was equivalent, but normocapnia was maintained by adding CO2 to the inspired gases. In the hypocapnic patients CSFPs did not increase above awake values (range 5–45 torr) following isoflurane administration. In the normocapnic patients CSFPs consistently increased. In three of these five patients the increases were precipitous, but were corrected rapidly by establishment of hypocapnia. The authors conclude that the known cerebral vasodilator properties of isoflurance can be countered effectively by hypocapnia. Furthermore, unlike the situation with halothane, it is not necessary to establish hypocapnia prior to introducing isoflurane in order to avoid CSFP increases.

Small risk of serious neurologic complications related to lumbar epidural catheter placement in anesthetized patients

Previous studies have identified pain during needle/catheter placement or during the injection of local anesthetic as a risk factor for the development of persistent paresthesias after regional anesthetic techniques. The performance of regional blockade on anesthetized patients theoretically increases the risk of postoperative neurologic complications, because these patients are unable to respond to painful stimuli. In this study, we evaluated the frequency of neurologic complications in 4298 thoracic surgical patients undergoing lumbar epidural catheter placement while under general anesthesia. Catheters were placed immediately after the induction and tracheal intubation or on completion of the surgical procedure, before emergence. Most epidural catheters (4220, or 98.2%) were used solely for postoperative analgesia; only 78 (1.8%) epidural catheters were used for intraoperative anesthesia. In 4239 (98.6%) patients, an opioid alone was administered. The remaining 56 (1.3%) patients received a local anesthetic or local anesthetic/opioid mixture epidurally. Analgesia was graded as excellent or good in 92.2% of patients. Side effects included sedation in 455 (10.6%), nausea or emesis in 328 (7.6%), pruritus in 116 (2.7%), and respiratory depression (pH ⩽7.3 and PaCO2 ≥50 mm Hg) in 308 (7.2%) patients. The mean duration of epidural analgesia was 2.4 ± 0.8 days (range, 0–10.7 days). There were no neurologic complications, including spinal hematoma, epidural abscess or catheter site infections, radicular symptoms, or persistent paresthesias (95% confidence interval, 0%–0.08%). In one patient, the epidural catheter broke during removal, and a portion was retained. The patient was notified; no long-term sequelae were noted. Six patients developed new neurologic symptoms or postoperative worsening of a previous neurologic condition unrelated to epidural catheterization. We conclude that the risk of neurologic complications associated with lumbar epidural catheter placement in anesthetized patients is small. However, the relative risk of this practice, compared with epidural catheter placement in awake patients, is unknown. IMPLICATIONS: We report no neurologic complications in 4298 patients undergoing epidural catheter placement while under general anesthesia. Although the risk of neurologic complications associated with lumbar epidural catheter placement in anesthetized patients is small, the relative risk compared with epidural catheterization in awake patients is unknown.

The risk-benefit ratio of intraoperative shunting during carotid endarterectomy. Relevancy to operative and postoperative results and complications.

The relative risk of shunting versus not shunting during carotid endarterectomy was analyzed retrospectively in 1935 cases undergoing carotid endarterectomy for carotid ulcerative stenosis. The need for shunting was based on a correlation between electroencephalographic changes and a fall in cerebral blood flow below the critical level required for adequate perfusion during the period of carotid occlusion. Patients were divided into four risk categories for surgery, based on medical and neurological risks and angiographic findings. Shunts were required in 30% of the low risk group and 56% of the high risk group. Based on the severity of reductions of cerebral blood flow during the period of carotid occlusion it is concluded that 12% of all patients would have sustained a major deficit, 15% a minor or transient deficit, and 20% a transient deficit without shunting. The risk of shunting 792 cases in this series was 0.5%. Overall minor morbidity, major morbidity, and mortality each approximated 1% in this series.

Simultaneous cerebral blood flow measured by direct and indirect methods

Abstract By diversion of the sagittal sinus blood flow of the dog, obliteration of the extracerebral veins communicating with the sinus, and determination of the amount of brain drained by the sagittal sinus, direct cerebral flow was measured and compared to indirect measurements determined by the modified Kety-Schmidt method using krypton-85 (85Kr) as the tracer gas. Twenty-two comparisons were made in 7 dogs at flows ranging from 25 to 98 ml. per 100 gm. per minute. In individual dogs small systematic differences in the values for cerebral blood flow generally were observed; the discrepancies could not be accounted for entirely by the method of converting direct flow (milliliters per minute) to flow per unit weight (ml./100 gm./min.). For the group no systematic difference was apparent and the results are considered confirmative evidence of the validity of the modified Kety-Schmidt method. When the calculations of indirect flows were made from a 10-minute saturation period with 85Kr and without extrapolation of the arteriovenous difference of 85Kr to infinity, a systematic error was introduced, resulting in a 5 to 10% overestimation at normal and low flow levels. The method for direct measurement of sagittal sinus flow offers promise for further laboratory studies of cerebral blood flow and metabolism.

Internal carotid artery stump pressure and cerebral blood flow during carotid endarterectomy: modification by halothane, enflurane, and innovar.

Carotid endarterectomy requires temporary surgical occlusion of the involved carotid artery. During occlusion, the minimally acceptable (critical) internal carotid artery stump pressure is reported to be 50 torr, whereas for regional cerebral blood flow (rCBF), a critical range is reported to be 18–24 ml/100 g/min. During 90 carotid endarterectomies. rCBF and stump pressure were measured and the EEG continuously monitored. A positive correlation between rCBF and stump pressure (i.e., when both were either above or below their respective critical values) was observed in only 58 percent of the cases. In 28 per cent stump pressures of less than 50 torr were observed despite rCBFs above 24 ml/100 g/min and normal EEGs. In 8 per cent stump pressures were more than 50 torr but rCBFs were less than 18 ml/100 g/min and EEG changes of ischemia were commonly observed. In the remaining 6 per cent rCBFs were marginal (18–24 ml/100 g/min) while stump pressures were more than 50 torr and EEG changes were not observed. The relationship between stump pressure and rCBF was influenced by the anesthetic. In the absence of transient ischemia during occlusion (that is, rCBF > 18 ml/100 g/min), halothane and enflurane anesthesia were associated with significantly higher rCBFs and lower stump pressures than was neuroleptanesthesia. Pre-occlusion and post-occlusion rCBF measurements also demonstrated cerebral vasodilation by halothane and enflurane (halothane > enflurane) and vasoconstriction by neuroleptanesthesia. It is concluded that stump pressure is an unreliable index of CBF during carotid occlusion and that its relationship to CBF is considerably influenced by the anesthetic.

Epidural analgesia shortens postoperative ileus after heal pouch-anal canal anastomosis

PURPOSE A retrospective study was conducted to determine whether epidural analgesia would speed recovery from postoperative ileus in patients undergoing ileal pouch-anal canal anastomosis. METHODS Among 85 patients who underwent proctocolectomy with ileal pouch-anal canal anastomosis at the Mayo Medical Center between January 1, 1991 and October 31, 1992, 44 were treated for postoperative pain with continuous infusion of epidural fentanyl citrate supplemented by intravenous morphine on request, while 41 controls were given only systemic morphine sulfate as needed. RESULTS The patients in the two groups were matched and similar with regard to preoperative and operative risk factors and postoperative morbidity. No operative mortality occurred. Epidural fentanyl analgesia resulted in less need for nasogastric suction and intravenous fluids, more rapid discharge of fecal content, more rapid return to oral intake, and shorter hospitalization. CONCLUSION Epidural analgesia with fentanyl citrate shortened postoperative ileus after proctocolectomy and ileal pouch-anal canal anastomosis.

ASA Monitoring Standards and Magnetic Resonance Imaging

Some patients, often because of age or altered mental state, require general anesthesia or monitored anesthesia care and sedation if adequate magnetic resonance imaging (MRI) is to be accomplished. This study evaluated whether patients can be monitored during MRI with 1.5-tesla scanners in a manner which complies with ASA monitoring standards without causing degradation of image quality. Ten volunteers were scanned in the MRI without sedation. Monitors meeting ASA standards were placed and electronic artifact produced by the magnetic resonance (MR) scanner was evaluated, after which two scans of the head and two of the chest were performed. One of each pair of scans was obtained with the monitors functioning and one with them turned off. Four radiologists, blinded as to whether the monitors were turned on or off, independently evaluated the 20 pairs of scans. Differences in diagnostic quality and image degradation between the scans were evaluated and scores assigned. All monitors functioned appropriately during the scans, with the exception of the electrocardiogram (ECG) which was grossly distorted to the extent that only ventricular rate could be evaluated. None of the head or body scans was nondiagnostic; however, images with the monitors off were of better quality overall than with them on. Two types of noise were generated and are described. During the head scans, three of seven monitoring combinations caused degradation of the images, while four were judged clinically adequate. During the body scans, two of six monitoring combinations created noticeable noise, while four introduced no significant noise. Ungated cardiac scans were nondiagnostic. With the exception of the described limits of ECG interpretation, monitoring configurations can be designed to meet the ASA standards during MRI with 1.5-tesla scanners. To minimize electronic noise generated by monitors, monitoring equipment should be tested in the MR setting where it is to be used. (Anesth Analg 1994;79:1141–7)

Anesthesia for transsphenoidal surgery of the hypophyseal region.

For pituitary surgery—by either the transcranial or the transsphenoidal approach—anesthetic management conforms to the general principles of neuroanesthesia as discussed in texts and review articles. In addition, the endocrine functions and the anatomic situation of the pituitary gland must be considered. Preoperative and perioperative evaluation of the patients endocrine status and appropriate therapeutic measures are important. Preservation of neurohypophyseal function and, frequently, of adequate adenohypophyseal function is an advantage of the transsphenoidal approach to the sella. Potential problems with the transsphenoidal technic include damage to suprasellar and parasellar structures and hazards associated with intraoperative or postoperative bleeding. Anesthetic aspects peculiar to the transsphenoidal approach include positioning of the patient, surgical use of solutions containing epinephrine and topical cocaine, intraoperative air studies, and management of emergence. Anesthesia for the transsphenoidal approach to the sella is discussed on the basis of our experience with 148 surgical procedures in 142 patients.

Analgesia After Thoracotomy: Effects of Epidural Fentanyl Concentration/Infusion Rate

After thoracotomy some patients have discomfort, primarily in the rostral portion of their incisions.In this prospective, randomized study in 66 patients after lateral thoracotomy we evaluated whether, for equal fentanyl dosage in micrograms per kilogram, epidural infusion (lumbar catheter) of fentanyl 5 micro gram/mL provided better segmental analgesia (including the rostral portion of the incision) than a 10-micro gram/mL concentration infused at a rate half that used in the 5-micro gram/mL group. Ketorolac was used as an analgesic adjunct for nonincisional pain. Postoperative epidural fentanyl infusion included a 1-micro gram/kg initial dose and an initial infusion rate of 1 micro gram centered dot kg-1 centered dot h-1 in both the 5-micro gram/mL and 10-micro gram/mL groups. Patients were evaluated for comfort level and pain relief while resting, taking a deep breath, coughing, and ambulating at eight times over 3 days using two visual analog scales for overall comfort and a verbal rating score (VRS) for segmental analgesia. There were no significant differences in demographics, surgical procedure, intraoperative fentanyl dose, side effects, rates of epidural fentanyl infusion, or total epidural fentanyl doses at 12, 24, 36, 48, and 60 h postbolus. Analgesia was effective in both groups. Although overall comfort levels were lower (i.e., indicated greater comfort) in the 5-micro gram/mL group in 6 of 8 visual analog scores (VASs) for comfort level and 20 of 24 VRSs for comfort level scores, and mean VRSs for the rostral portion of the incision were lower (i.e., indicated greater comfort) in the 5-micro gram/mL group at 21 of 24 evaluation subsets (one statistically significant), statistical significance was achieved in only six evaluation subsets. There were no significant differences between the two groups in averages of comfort level scores for the upper, middle, and lower portions of the incisions. Ketorolac was not a confounding variable. Lumbar epidural infusions of fentanyl can provide effective analgesia after thoracotomy; using lower concentrations at higher infusion rates is beneficial for some patients. (Anesth Analg 1995;81:973-81)