James H. Philip

A randomized, double-blind comparison of the NK1 antagonist, aprepitant, versus ondansetron for the prevention of postoperative nausea and vomiting

BACKGROUND: Antiemetics currently in use are not totally effective. Neurokinin-1 receptor antagonists are a new class of antiemetic that have shown promise for chemotherapy-induced nausea and vomiting. This is the first study evaluating the efficacy and tolerability of the neurokinin-1 receptor antagonist, aprepitant, for the prevention of postoperative nausea and vomiting. METHODS: In this multicenter, double-blind trial, we randomly assigned 805 patients receiving general anesthesia for open abdominal surgery to a preoperative dose of aprepitant 40 mg orally, aprepitant 125 mg orally, or ondansetron 4 mg IV. Vomiting, nausea, and use of rescue therapy were assessed over 48 h after surgery. Treatments were compared using logistic regression. RESULTS: Incidence rates for the primary end point (complete response [no vomiting and no use of rescue] over 0–24 h after surgery, tested for superiority of aprepitant) were not different across groups (45% with aprepitant 40 mg, 43% with aprepitant 125 mg, and 42% with ondansetron). The incidence of no vomiting (0–24 h) was higher with aprepitant 40 mg (90%) and aprepitant 125 mg (95%) versus ondansetron (74%) (P < 0.001 for both comparisons), although between-treatment use of rescue and nausea control was not different. Both aprepitant doses also had higher incidences of no vomiting over 0–48 h (P < 0.001). No statistically significant differences were seen among the side effect profiles of the treatments. CONCLUSIONS: Aprepitant was superior to ondansetron for prevention of vomiting in the first 24 and 48 h, but no significant differences were observed between aprepitant and ondansetron for nausea control, use of rescue, or complete response.

Variation in PCO2 between Arterial Blood and Peak Expired Gas during Anesthesia

Arterial PCO2 (PaCO2) can be continuously and noninvasively estimated by monitoring peak expired CO2 tension (PpeCO2). The practice of calibrating the estimate by an initial measurement of PaCO2 assumes that the difference in PCO2 tension between arterial blood and expired gas P(a-pe)co2 remains constant. We examined the stability of P(a-pe)CO2 during anesthesia in 15 patients undergoing major surgery. Mean P(a-pe)CO2 values ranged from 0.8–7.9 torr with maximum P(a-pe)CO2 values ranging from 4.5–13.0 ton. Calibration of P(a-pe)CO2 based on a single initial measurement of PaCO2 often over- or underestimated PaCO2. Mean estimated PaCO2 from calibrated P(a-pe)CO2 varied from - 7.9–6.4 torr with extreme estimates of — 12.8–12.3 torr. No consistent correlation was shown between P(a-pe)CO2 and duration of anesthesia, variations in ventilation, blood pressure, blood-gas tensions, PpeCO2 or temperature. We conclude that estimation of PaCO2 by monitoring PpeCO2 is not invariably reliable.

Critical incidents associated with intraoperative exchanges of anesthesia personnel.

It is a common practice for anesthetists to substitute for one another, especially for short breaks during long surgical procedures. The assets and liabilities of this practice of relief have not been examined previously. In the course of gathering 1,089 reports of preventable errors and failures associated with anesthesia management, we identified 96 which involved a relief anesthetist. This subset was examined in search of common characteristics and patterns of cause and discovery of errors.In 28 incidents, the relief anesthetist discovered an error or the cause of an error. In 10 incidents, the process of relief was identified as having contributed to the commission of an error. Although 70 of the 1,089 incidents were associated with substantive negative outcomes, e.g., death, cardiac arrest, or extended ICU stay, none of those incidents was caused by a relieving anesthetist. There is a strong implication that relief is beneficial more often than not even aside from the presumed beneficial effect on the vigilance of the primary anesthetist (the latter effect was outside the scope of this study). From the descriptions of the causes and discoveries of errors in these relief-related incidents, guidance can be drawn for the safe and effective conduct of the intraoperative exchange of anesthesia personnel.

Guidelines for sedation by nonanesthesiologists during diagnostic and therapeutic procedures

Abstract The increasing use of sedation to enhance patient comfort during diagnostic and therapeutic procedures has been noted by the joint Commission of Accredited Healthcare Organizations, specialty societies, and the public. Although anesthesiologists, by virtue of training and experience, possess unique qualifications to provide such sedation services, their availability remains somewhat limited by primary commitments to the operating room, intensive care unit, or pain service. The Risk Management Committee of the Department of Anaesthesia of Harvard Medical School has made specific recommendations to the Harvard-affiliated hospitals for anesthesiologists who participate in institutional-level committees in setting guidelines for such services when they are provided by nonanesthesiologists. Specific consideration is given to facilities, backup emergency services, equipment, education and training, issues of informed consent, documentation, and release of patients from medical care. These recommendations emphasize the collaboration of the department of anesthesia and other departments that provide sedation services in formulating policies and procedures that reflect values intrinsic to the practice of anesthesiology.

Continuous Thermal Measurement of Cardiac Output

A thermal-dilution technique for the continuous measurement of cardiac output has been developed. It employs pulmonary-artery sensing of low-level periodic thermal signals generated in the right ventricle of the heart. A resistive element in a modified Swan Ganz®catheter is energized with a periodic electrical waveform. The resulting thermal signal is diluted by blood flow and attenuated by mixing within the heart. Sensed by a thermistor in the pulmonary artery, the thermal signal is processed by a microprocessor-based instrument using a suitable mathematical model. With multiple signal frequencies, separate estimates of the flow-dependent and mixing-dependent attenuation components become possible, allowing continuous monitoring of cardiac output. This technique works well in anesthetized, mechanically ventilated animals, even with average power levels as low as 4 W and corresponding temperature increases of a few hundredths of a degree centigrade. Based on measurements of pulmonary artery thermal noise spectra in humans, we infer that similar performance levels should be attainable with mechanically ventilated human subjects. However, noise spectra from spontaneously breathing critically ill patients suggest that signal-to-noise ratios would be less than satisfactory in that group unless increased signal power is allowed or improved algorithms are developed.

Gas Man® — An example of goal oriented computer-assisted teaching which results in learning

SummaryGas Man® is an educational computer simulation program (8). The goal of the program is for the user to learn the theory and application of inhalation anesthesia uptake and distribution. The program and accompanying text are designed to be used by medical students, pharmacy students, anesthesia residents, nurses, practicing anesthesiologists, and medical equipment technicians and engineers. After using the program, the learner should understand the time course of patient response to inhalation anesthesia. He should know the factors which influence patient response and be able to predict their impact in specific situations.The key to Gas Mans success are:1.A well-defined and valid educational goal, teaching anesthesia uptake and distribution.2.An identifiable and testable set of educational objectives.3.A specific set of learner tasks to achieve those objectives, the acutal simulation exercises.4.The appropriate educational medium, computer simulation and graphics.5.Effective software implementation, the Gas Man Program.

Defining Segments and Phases of a Time Capnogram

The division of a time capnogram into inspiratory and expiratory segments is arbitrary and results in the inability of a time capnogram to detect rebreathing instantaneously. Demarcation of a time capnogram into inspiratory and expiratory components using gas flow signals will not only facilitate prompt detection of rebreathing, but will also allow application of standardized and physiologically appropriate nomenclature for better understanding and interpretation of time capnograms. A Novametrix® CO2-SMO plus respiratory profile monitor (Novametrix Medical Systems, Wallingford, CT) was used to obtain a simultaneous display of CO2 and respiratory flow waveforms on a computer screen during spontaneous and controlled ventilation using a circle system with the inspiratory valve competent (no rebreathing) and with the valve displaced (rebreathing). Because the response time of the CO2 analyzer was similar to the response time of the flow sensor, a comparison was made between the two waveforms to determine the inspiratory segment (Phase 0) and the expiratory segment of the time capnogram and its subdivisions (Phases I, II, and III). The end of expiration almost coincides with the downslope of the CO2 waveform in the capnograms when there is no rebreathing. However, in the presence of rebreathing, the alveolar plateau is prolonged and includes a part of inspiration (Phase 0), in addition to the expiratory alveolar plateau (Phase III). Implications Presently, the division of a time capnogram into inspiratory and expiratory segments is arbitrary. Demarcation of a time capnogram into various components using the gas flow signals facilitates prompt detection of the cause of abnormal capnograms that can widen the scope of future clinical applications of time capnography.

The prevalence of hypoxemia detected by pulse oximetry during recovery from anesthesia

Pulse oximetry was used to assess the prevalence of hypoxemia (arterial oxygen saturation of 90% or less) at various times in the immediate postoperative period: five minutes after arrival, 30 minutes later, and just before discharge. Among 149 inpatients studied, one or more hypoxemic measurements were made in 21 (14%) during their postoperative course. Of 92 outpatients, 1 (1%) was found to be hypoxemic. For inpatients, the prevalence of hypoxemia preoperatively, 5 minutes after arrival in recovery, 30 minutes later, and at discharge was 2%, 4%, 6%, and 9%, respectively. Patient factors associated with a significantly higher prevalence of hypoxemia were obesity (22%), body cavity surgical procedures (24%), age over 40 years (18%), American Society of Anesthesiologists physical status (I, 7%; II, 17%; III, 18%; IV, 100%), duration of anesthesia longer than 90 minutes (18%), and intraoperative administration of greater than 1,500 ml of fluid (20%). Unrecognized hypoxemia in postsurgical inpatients with or without these risk factors is common. Therefore routine monitoring of these patients with a pulse oximeter is suggested.

Studies of nontraumatic osteonecrosis. The role of core decompression in the treatment of nontraumatic osteonecrosis of the femoral head.

This study reports a five-year experience with core decompression for treatment of nontraumatic osteonecrosis of the femoral head. There were 25 patients (39 hips) with predominantly steroid-associated osteonecrosis followed postoperatively for a minimum of two years. All patients were evaluated functionally, roentgenographically, histologically, and hemodynamically. At latest follow-up examination, two of 12 hips (17%) with Stage I disease, seven of 12 hips (58%) with Stage IIA disease, four of four hips with Stage IIB disease, and nine of 11 hips (82%) with Stage III disease have progressed roentgenographically and/or clinically. A lack of correlation between pressure manometrics, venography, and clinical outcome in this study suggests that mechanisms other than progressive ischemia may be involved. Current indications for core decompression are Ficat Stage 0, I, and IIA (sclerotic predominant) disease.

Epidural space as a Starling resistor and elevation of inflow resistance in a diseased epidural space.

Background and Objectives. The origin and the presence of negative pressure in the epidural space as well as the relationship of the extent of epidural anesthesia to epidural pressure has long been a subject of controversy. To further elucidate epidural pressure and its time course, the pressure at the needle tip was continuously measured as it traversed the interspinous ligament and the ligamentum flavum. Methods. In a group of 22 patients, fluid was infused under gravity, and in a second group of 25 patients, boluses of fluid were administered at controlled infusion rates and under gravity. The volume‐pressure‐flow relationship was thus measured in one of two ways, either with a manual syringe and pressure transducer or with a pressure‐monitoring‐computer‐controlled volumetric infusion pump. Results. Natural pressure, (i.e., pressure in the epidural space before instrumentation is applied) could be approached when the space was first entered before fluid was infused (initial pressure); or after fluid had been infused (residual pressure). Epidural pressure could be extrapolated from the upsweep of the volume‐pressure‐flow relationship by projecting it back to just before the first injection. The extrapolated pressure lay between the initial and residual pressures. Medicinal solution placed in the barrel of the syringe did not infuse under gravity until the syringe barrel was lifted to a certain height, at which flow began and continued at a perceptible rate, with very little or no further increase in height required to maintain flow. The pressure at which flow began was the critical opening pressure, a characteristic of a Starling resistor. Furthermore, resistance to inflow of fluid was related to the presence or absence of natural or surgical disease in the epidural space. Resistance was significantly higher in the diseased than in the surgical group, at 114 (range, 22‐226) mm Hg/L/h versus 46 (range, 8‐86) mm Hg/L/h. Three phases were seen in the pressure‐time recordings. Conclusions. Volume‐pressure‐flow relationships in the epidural space can be explained by a model in which epidural and subarachnoid pressures are inextricably related with the Starling pressure, dependent on the subarachnoid pressure. This model suggests reasons why spread of anesthetics might be difficult to predict.