Robert W. Vaughan

Volume and pH of Gastric Juice in Obese Patients

Volume and pH of Gastric Juice in Obese Patients ROBERT VAUGHAN;SPOMENKO BAUER;LESLIE WISE; Anesthesiology

Precision and Accuracy of Intraoperative Temperature Monitoring

Using tympanic membrane (TM) temperature as a standard for core temperature, we quantitated the accuracy and precision of seven other temperature monitoring sites during anesthesia, namely, the nasopharynx, esophagus, rectum, bladder, axilla, forehead, and great toe. Accuracy was quantitated as the difference between TM temperature and the temperature at each of the other sites; precision was quantitated as the correlation between TM temperature and the temperature at each of the other sites. Results indicate that the accuracy of measurements made using the great toe, forehead, and axilla is less than the accuracy of measurements made using the nasopharynx, esophagus, bladder, and rectum. Precision of measurements made using the nasopharynx, esophagus, and bladder is greater than the precision at the axilla, forehead, and rectum, and much higher than the precision at the great toe. Measurements of body temperature using the nasopharynx, esophagus, and bladder are recommended for intraoperative use as providing the best combination of accuracy and precision.

Halothane Biotransformation in Obese and Nonobese Patients

Serum levels of inorganic fluoride, trifluoracetic acid, and bromide ion were measured at various time intervals following two hours of halothane anesthesia in 17 morbidly obese and eight nonobese patients. Ionic fluoride, a marker of reductive halothane metabolism, increased in the obese but not the nonobese patients. This is of concern since reductive halothane metabolism is associated with hepatoxicity in animals. In addition, serum bromide levels were higher after 48 h in the obese patients compared to the nonobese patients (mean ± SE, 1,311 ± 114 vs. 787 ± 115 μM, P < 0.01). Sedative levels of bromide were not attained in any patient. Peak trifluoracetic acid levels were similar in the two patient groups. Sex, age, medication intake, and smoking history had no influence on the halothane metabolite levels found in this study.

Intraoperative arterial oxygenation in obese patients.

Although obese patients have been shown to represent a particularly high risk group with respect to hypoxemia both pre and postoperatively, no data exist to delineate the intraoperative arterial oxygenation pattern of these patients. Furthermore, no one has studied the effects of a change in operative position or a subdiaphragmatic laparotomy pack on arterial oxygenation (PaO2). Sixty-four adults undergoing jejunoileal bypass for morbid exogenous obesity, with a mean weight of 142.0 ± 31.4 kg and a mean age of 33.3 ± 10.4 years, were studied. Twenty-five patients (Group I) were maintained in the supine position throughout the operative procedure, while the remaining 39 patients (Group II) were changed to a 15° head down position 15 minutes after a control blood sample was taken. Four additional markedly obese patients were studied to determine the effect of an abdominal pack of PaO2 values.The following findings were demonstrated: 1) 40% oxygen did not uniformly produce adequate arterial oxygenation for intra-abdominal surgery in otherwise healthy obese patients; 2) placement of a subdiaphragmatic abdominal laparotomy pack without a change in operative position resulted in a consistent fall in PaO2 in each patient to less than 65 mm Hg even though 40% oxygen was being administered; and 3) a change from supine to a 15° head down operative position resulted in a significant (P < 0.001) reduction in mean PaO2 (73.0 ± 26.3 mm Hg). Seventy-seven per cent of these patients demonstrated PaO2 values of less than 80 mm Hg on 40% oxygen.Because of these findings, serious consideration should be given to the routine use of the Trendelenberg position intraoperatively in obese patients. However, if one elects this posture, prudence would dictate careful monitoring and maintenance of arterial oxygenation. Certainly, in obese patients, the intraoperative combination of the head down position and a subdiaphragmatic laparotomy pack should be avoided. In addition, since our data were collected in obese but otherwise healthy, young patients free of cardiorespiratory disease, special attention should be directed at the continuous measurement of arterial oxygenation in the older obese patient with either intrinsic dysfunction of vital organs (heart, lung, liver, kidney) or surgical disorders (peritonitis, sepsis).

The Effect of Massive Weight Loss on Arterial Oxygenation and Pulmonary Function Tests

Pulmonary function tests (PFTs) and arterial oxygenation were studied 24 hours preoperatively and again at varying times (5 to 20 months) during the postoperative weight loss of 37 morbidly obese patients. Among PFTs, expiratory reserve volume (ERV) demonstrated the most significant (P < 0.001) improvement with weight loss. No clinically relevant differences were found after weight loss in FEV1, FVC, or MMEF. In 11 patients whose arterial blood gases were sampled before and after weight loss, a significant correlation was demonstrated between change in ERV and change in Pao2 (r = 0.59, P < 0.05) and P(A-a)o2 (r = 0.76, P < 0.01). When weight loss is expressed as either change in body mass index (δBMI) or as a change in percent of ideal weight (δwt), there existed a weight loss threshold for improvement in arterial oxygenation. A δBMI of greater than 20 or a δ wt more than 100 per cent resulted in a significant improvement in Pa02 (P < 0.01) or P(A-a)01 (P < 0.05). These data suggest that morbidly obese patients do not meaningfully improve FEV1, FVC, or MMEF with massive weight loss. However, there is a significant improvement in ERV that directly correlates with improvement in both Pa02 and P(A-a)02.

Postoperative arterial blood gas measurement in obese patients: effect of position on gas exchange.

The effect of position change on blood gas exchange was studied in 22 markedly obese, otherwise healthy, women both preoperatively and postoperatively. There was a statistically significant decrease in arterial oxygen tension and a simultaneous reduction both in the arterial carbon dioxide tension and the base excess with the assumption of the supine versus the semirecumbent position on postoperative days one and two. However, no positional difference was demonstrable in any variable by the third postoperative day. This study indicates that in obese patients during the first 48 hours after abdominal surgery, assumption and maintenance of the semirecumbent posture is a valuable therapeutic adjunct to improve arterial oxygenation.

Effect of position (semirecumbent versus supine) on postoperative oxygenation in markedly obese subjects.

In 22 markedly obese, otherwise healthy, women studied postoperatively on each of days 1 through 3 after intra-abdominal operation, the effect of position change on arterial oxygenation was assessed. There was a statistically significant decrease in Pao2, an increase in A-aDo2 and a simultaneous modest reduction in Paco2 with the assumption of the supine position on postoperative days 1 and 2, but no positional difference demonstrable in any studied variable by day 3. This report suggests that during the first 48 hours after abdominal surgery in obese patients, assumption and maintenance of the semirecumbent posture is a valuable therapeutic modality to improve arterial oxygenation.

General Anesthesia for Morbidly Obese Patients — An Examination of Postoperative Outcomes

Specific postoperative outcomes were assessed in 67 morbidly obese subjects who received general anesthesia for gastric stapling. Each patient was randomly assigned to receive N2O;O2 combined with fentanyl (n = 20), enlurane (n = 24), or halothane (n = 23). Time from last skin stitch until the patient opened eyes on command was significantly less for the fentanyl group (3.0 ± 0.7 min) than for the enflurane group (13.2 ± 1.9 min) or the halothane group (17.4 ± 2.9 min) with P < 0.05. However, no significant differences in time from last skin stitch to extubation were noted among the fentanyl (16.2 ± 7.4 min), enflurane(15.2 ± 1.6 min),and halothane (21.6 ± 5.8 min) groups (P > 0.05). Recovery room (RR) admission temperatures were similar for the three groups: fentanyl, 36.1 ± 0.1° C; enflurane, 35.7 ± 0.2° C; and halothane, 36.0 ± 0.1° C (P > 0.05). Total RR time was not significantly different: fentanyl, 108 ± 6 min, enflurane, 118 ± 4 min; and halothane, 112 ± 10 min (P > 0.05). In addition, no difference in RR and 24-hour postoperative narcotic (meperidine) requirements was demonstrated among the anesthetic groups. These data suggest that increased lipid solubility of volatile anesthetics (halothane or enflurane) produces neither delayed awakening nor prolonged recovery time in morbidly obese subjects. Considering the early (24 hour) postoperative outcomes studied, there is little to commend one general anesthetic technique over another in the obese subset of the population.

Part I: Cardiopulmonary consequences of morbid obesity

Abstract Markedly obese patients represent a unique subset of the population. The condition of obesity is related to physiological derangements of the cardiovascular system, deleterious effects of the mechanical and gas exchange function of the lung, severe biochemical derangements in the liver, and changes in normal endocrine functions. Therapy for and research efforts in obesity require a thorough understanding of the definition, measurement, and classification of obesity. The ability to assess pertinent physiological and biochemical alternations is a prerequisite for studying and caring for these patients. A subsequent review will address the biochemical derangements of morbid obesity. The present communication will focus on the physiologic derangements of the cardiopulmonary system unique to marked obesity.

Serum Inorganic Fluoride Levels in Obese Patients during and after Enflurane Anesthesia

Serum ionic fluoride levels in 24 markedly obese patients (127.6 ± 6.0 kg) and seven nonobese control subjects (67.3 ± 1.2 kg) were compared during and following enflurane anesthesia (<2.0 MAC hr). Peak serum fluoride levels were higher (28.0 ± 1.9 vs 17.3 ± 1.3 μM/L, p < 0.01) and the rate at which fluoride levels increased was more rapid (slope 5.6 VS 2.5 μM/L/hr) in obese patients than in control patients. No clinical evidence of nephrotoxicity was found in either group. Vasopressin resistance tests were not performed, and thus it is unknown whether subclinical nephrotoxicity occurred in either study group. Possible reasons for increased enflurane metabolism in obesity are discussed. These possibilities include differences in fluoride ion kinetics, hepatic delivery and penetration of volatile anesthetics, and altered hepatic microsomal enzyme activity. Obesity rather than weight is an important determinant of anesthetic biotransformation.