Thomas E. Macnamara

Surgical stress in humans is acompanied by an increase in plasma beta-endorphin immunoreactivity

Abstract Surgical stress, but not anesthesia induction, produced a significant increase in plasma beta-endorphin immunoreactivity in eight patients undergoing abdominal surgery. This increase was closely correlated with a parallel increase in plasma cortisol. Post-operative morphine administered for pain relief was associated with a significant reduction in plasma levels of both beta-endorphin and cortisol. These results demonstrate the responsiveness of the endorphin system to acute stress in humans and provide additional evidence linking plasma beta-endorphin to the hypothalamic-pituitary-adrenal axis.

Electroencephalographic changes during whole body hyperthermia in humans

Abstract As part of a protocol of the National Cancer Institute, 21 selected patients were submitted to total body hyperthermia for treatment of metastatic carcinoma. Elevation body temperature up to 41.8°C for 2 h was achieved using a computer driven external heating system. Patients were sedated during treatment. To ensure the safety of the procedure, a battery of physiological parameters was monitored. Continuous EEG recordings were carried out in all patients. Analysis of the EEG included visual assessment, compressed spectral array and power spectrum. EEG data were compared mainly to body temperature, state of consciousness and drug administration. Consciousness during the treatment varied from very light sedation to light anesthesia, with some rare delirious episodes. No motor seizures were observed. All EEG recordings demonstrated major changes in both rhythmicity and amplitude (slower and lower) indicating a diffuse decrease of cortical activity during the hyperthermia period. All changes reversed themselves during the cooling period. Spectral power showed a statistically significant inverse relationship with temperature. At temperatures above 41°C, decrease in total EEG spectrum was not related to decrease in clinical reactivity. The degree of EEG slowing varied with the extent and duration of the hyperthermia, and was totally reversible within a few hours of cooling, without evidence of any EEG or neurological sequelae. However, at temperatures above 41.5°C, EEG changes compatible with metabolic or toxic encephalopathy were observed. Possible mechanisms are discussed.

Effects of Enflurane on Brainstem Auditory Evoked Responses in Humans

The effects of enflurane anesthesia on brainstem auditory evoked responses (BAERs) was determined in 10 patients with normal hearing undergoing various surgical procedures. Arterial blood pressure, body temperature, and arterial PCO2 were controlled during the 2− to 5-hour recording sessions. End-tidal enflurane concentrations were continuously recorded on a Chemetron Medspect II mass spectrometer in three subjects. BAERs were obtained by, and recorded on, a Nicolet CA 1000, from C2 with reference to A1 or A2, with a 2000 click-averaging for each measurement. Enflurane administered at clinical concentrations (0.5% to 3%) produced consistent changes in BAER latencies. The waves significantly affected (p < 0.01) were waves III, IV, and V and interpeak latency I-V. The magnitude of these changes was related to the concentration of enflurane and was magnified by temporarily decreasing the PaCO2. These findings confirm similar data obtained in animals which have shown the same effects at doses that can produce generalized seizure activity. BAER analysis shows that changes predominate at the pons and midbrain levels and affect the brainstem conduction time, which likely reflects the action of enflurane on the activity of the reticular activating system.

Age and the Spread of Local Anesthetic Solutions in the Epidural Space

Sensory level of anesthesia following the epidural injection of 20 ml of 1.5% lidocaine with epinephrine (1:200,000) in 238 adult males averaged T7.7, T5.6, and T5.1 at 10, 20, and 30 minutes, respectively. Patient age had no significant effect on local anesthetic requirements per spinal segment per unit height until age 40 years, above which age the calculated amount of local anesthetic decreased significantly to 0.62 ml from 0.69 ml/segment/meter of height. Above age 40 there was no further decrease in epidural anesthetic requirement with advancing age. Patient height was inversely related to sensory level (p < 0.001). Time required for anesthesia to recede to T,2 averaged 164 minutes and was slightly but significantly (p < 0.05) prolonged with advancing age.

An Evaluation of Liquid-crystal Thermometry as a Screening Device for Intraoperative Hyperthermia

Disposable liquid-crystal temperature-trend indicators were evaluated under clinical conditions that simulated the development of intraoperative hyperthermia during anesthesia. Comparison was made to forehead thermistors for rapidity, accuracy, and linearity of response as well as correlation with esophageal and rectal thermistor recordings. The liquid-crystal monitors were comparable to the forehead thermistors in both rapidity and linearity of response, but not in accuracy. A linear correlation existed with the esophageal thermistor temperatures. Carrelation with the rectal temperatures was not as exact. It is concluded that liquid-crystal thermometers may adequately serve as screening devices for intraoperative hyperthermia.

Effects of Fentanyl on the Response of Plasma Beta-Endorphin Immunoreactivity to Surgery

Beta-endorphin appears to play a definite role in the biologic response to stress and in the endogenous mechanism of pain perception. Opiates exogenously administered during surgery decrease or even suppress the activation of “stress hormones” such as ACTH and cortisol. In the present study, the authors tried to assess the effects of fentanyl administration on plasma beta-endorphin immunoreactivity PBE(ir) during surgical stress. In one group of nine patients, a standard enflurane-based general anesthetic technique without opiates was used for a staging laparotomy. A second group of ten patients undergoing the same type of surgery received fentanyl (10–20 μg/kg) as the primary anesthetic drug. In both groups, multiple blood samples were collected prior to, during, and after surgery, following the same time protocol. PBE(ir), plasma cortisol and, in five patients, plasma ACTH were determined by radioimmunoassay. There was no significant change in PBE(ir) in either group after anesthetic induction. Unlike the enflurane group, the fentanyl group did not demonstrate any significant increase from baseline in PBE(ir) during surgery. There was a significant group difference between enflurane and fentanyl in PBE(ir) levels for both “early” and “late” surgery values, but not for the “awake” values (recovery period) where both groups had elevated PBE(ir) levels. Plasma cortisol and plasma ACTH changes followed a trend similar to those of PBE(ir). The suppression of both cortisol and PBE(ir) responses during surgery after administration of fentanyl provides further evidence for the involvement of the endorphin system in the stress response and for its physiologic association with the hypothalamo pituitary axis.

Morphine-induced respiratory depression following bilateral carotid endarterectomy.

Severe respiratory depression was observed after preanesthetic medication with morphine and scopolamine in an adult patient with chronic obstructive pulmonary disease who 1 month earlier had been premedicated with the same combination without incident. In the intervening period, however, the patient had undergone a bilateral carotid endarterectomy. W e postulate that loss of carotid body chemoreceptor function after the bilateral carotid endarterectomy (1) produced the respiratory depression associated with administration of morphine.

The sitting position and anesthetic spread in the epidural space.

It is well known that anesthetic spread during spinal anesthesia is greatly affected by the position of the patient during and after injection of the anesthetic. However, the effect of the patient’s position on the spread of epidural anesthetics has not been clearly established. Bromage reported less cephalad spread of local anesthetics when injected into the epidural space with the patient in the sitting position than when injected with the patient in the horizontal-latera1 position (1). Nishimura et al., on the other hand, reported an insignificant effect of the sitting position on the epidural anesthetic spread (2). Because of these conflicting reports, this study was designed to further evaluate the effect that having the patient in the sitting position has on spread of local anesthetics injected into the lumbar epidural space.

Prolonged induction with exaggerated chamber enlargement in Ebstein's anomaly.

Ebstein’s anomaly occurs in less than 1% of congenital heart disease (1). The major anatomic deviation involves downward displacement of the tricuspid valve. This is frequently associated with enlargement of the right atrium and with a sizeable atrialized ventricular chamber (2). Thus, the potential exists for varying degrees of blood pooling in the large, hypocontractile portion of the heart. We report a case in which anesthesia for surgical correction of Ebstein’s anomaly was complicated by an extremely prolonged intravenous induction time, with subsequent hypotension. This was thought to be the result of pooling of blood volume in the large right atrium.

Effects of patient age, pH of cerebrospinal fluid, and vasopressors on onset and duration of spinal anesthesia.

&NA; Two hundred twenty‐two spinal anesthesias were administered with 10 mg. of tetracaine and 1 ml. of 10 percent dextrose to investigate the effects of vasopressors, patient age, and pH of cerebrospinal fluid on the onset and duration of spinal anesthesia. Neither the differences in overall age, cerebrospinal fluid pH, nor the addition of vasopressors had any significant effect on onset. Duration, however, was significantly prolonged by the addition of vasopressors, 53 percent prolongation by 0.2 mg. of epinephrine and 72 percent prolongation by 2 mg. of phenylephrine.