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Biomedical subjects

J H Philip

Publications and source records attributed to J H Philip.

At least 19 recordsLinked to original sources
PubMed1991

The effects of bronchodilator-inhaler aerosol propellants on respiratory gas monitors.

Spurious readings from a mass spectrometer have been reported following the administration of aerosol bronchodilators. We quantified the response of various respiratory gas analyzers to the aerosol propellant of albuterol inhalant (Proventil). The mass spectrometer systems tested, two Advantage systems, a SARA system, and a Model 6000 Ohmeda system, all displayed artifactual readings in response to the albuterol propellant. Each metered dose of the Proventil brand of albuterol contains 4 ml of Freon 11 (trichloromonofluoromethane) and 11 ml of Freon 12 (dichlorodifluoromethane). The concentration of propellant was expressed in doses/L, where each liter of gas contains 0.4 vol % of Freon 11 and 1.1 vol % of Freon 12 per dose. In proportion to the concentration of albuterol propellant, the two Advantage systems showed substantial readings of isoflurane (%) when no isoflurane was present (13% and 16% per dose/L) and reduced readings of enflurane (-8% and -10% per dose/L) and carbon dioxide (CO2) (-3 and +5 mm Hg per dose/L). The SARA system showed substantial CO2 readings when no CO2 was present (5 mm Hg per dose/L) and displayed small enflurane readings (0.1% per dose/L) when no enflurane was present. The Model 6000 unit showed CO2 readings when no CO2 was present (5 mm Hg per dose/L). Neither the Raman spectrometer, the infrared spectrometers, nor the piezoadsorptive analyzer we tested showed an artifactual effect of albuterol propellant on any of its readings. Simulation and clinical tests demonstrated that a single dose of albuterol propellant into a breathing circuit at the onset of inspiration resulted in concentrations of 0.8 and 0.3 dose/L, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerosol Propellants↗
PubMed1991

Linking mass spectrometers to provide continuing monitoring during system failure.

Although multipatient monitoring with a time-shared mass spectrometer provides considerable cost advantages, failure of one component in a shared system can disrupt gas monitoring at all sites. We describe a simple method for linking two central mass spectrometer systems to provide continual monitoring during failure of one unit, without the need for time-consuming reconfiguration of individual patient sample line and display connections.

Equipment Failure↗
PubMed1990

Prediction of flow capability in intravenous infusion systems: implications for fluid resuscitation.

The pressure-flow (P-F) relationship for intravenous infusion systems is nonlinear and may be expressed by the quadratic model P = RLF + RTF2. The flow parameters RL and RT may represent the resistance of laminar and turbulent flow, respectively. In this study pressure and flow were measured, and RL and RT were calculated for several infusion tubings, catheter, and system components. We then developed a technique to identify the relative effect of various devices on achieving the higher flows needed for fluid resuscitation. A typical infusion system was chosen, and the experimentally determined flow parameters RL and RT of its components were used in the quadratic P-F relationship at P = 300 mm Hg. Devices in the infusion system were ranked, using a subtractive algorithm, according to their relative impediment to flow as measured by contribution to the pressure drop. The order of devices removed or replaced, from largest to least pressure drop, was as follows: fluid warmer, 16-gauge catheter, check valve, 14-gauge catheter, standard-bore Y tubing, 12-gauge catheter, and standard-bore stopcock, leaving 10-gauge catheter + wide tubing. Devices with large RT, such as fluid warmers and check valves that produce large pressure drops, should generally be avoided during fluid resuscitation when high flows are needed. A similar ordering of device removal or substitution (largest to least pressure drop) was determined using the traditional but incorrect linear P-F model, P = RF, and the order of devices chosen for elimination was different.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluid Therapy↗
PubMed1989

Positive end-expiratory pressure: implications for tidal volume changes in anesthesia machine ventilation.

In clinical practice, the addition of positive end-expiratory pressure (PEEP) into a standard anesthesia circle circuit decreases the delivered tidal volume (DTV) to a patient. We studied the magnitude of the delta DTV/delta PEEP relationship in two commonly used anesthesia systems. In addition, the magnitude of the delta DTV/delta PEEP relationship varies with both pulmonary compliance and volume of gas contained in the patient's breathing system between the ventilator and PEEP valve site, and this was also evaluated. Routine monitoring of expired tidal volume should be used whenever PEEP is added to an anesthesia circuit.

Anesthesia, Closed-Circuit↗
PubMed1989

Model for the physics and physiology of fluid administration.

This article describes a model designed to provide an understanding of fluid flow in intravenous systems and human subjects. Experiments were developed which demonstrate that the model can represent common clinical situations. The model depicts physical devices as ideal resistors, pressure sources, and flow sources. The patient's venous system is depicted as a combination of ordinary and Starling resistors. For flows between 0 and 300 ml/hr, both physical devices and patients are adequately represented by a straight line representing the pressure-flow relationship (PFR): pressure = opening pressure + flow X resistance, where the slope is the resistance to fluid flow and the intercept is the opening pressure. The PFR for a normal vein is characterized by a flat slope (vein resistance = 22 +/- 20 mm Hg/L/hr, mean +/- SD) and a low intercept (opening pressure = 15 +/- 8 mm Hg). The PFR for a partially obstructed vein has a resistance equal to that of an unobstructed vein and an opening pressure elevated approximately equal to the pressure obstructing the vein. For perivascular tissue, the PFR has a steep slope (tissue resistance = 1,125 +/- 1,376 mm Hg/L/hr), while tissue opening pressure depends on the amount of fluid infused. At the onset of fluid extravasation (infiltration), tissue pressure usually is lower than venous pressure (8 +/- 8 versus 15 +/- 8 mm Hg), until fluid fills the distensible tissue compartment. In clinical practice, when infiltration or obstruction occurs, flow decreases and the clinician adjusts the roller clamp until correct flow resumes; no problem is obvious. The combined model for the intravenous tubing and venous systems explains the behavior of current clinical infusion devices.

Biophysical Phenomena↗
PubMed1989

The theoretical effect of carboxyhemoglobin on the pulse oximeter.

The relationship between arterial oxygen saturation as measured by the pulse oximeter (SpO2) and the fractional arterial oxygen saturation (SaO2) in the presence and absence of carboxyhemoglobin (COHb) has been derived according to the theory of absorption spectroscopy. We find that our theoretically derived correction equation is similar to that found in the technical literature of Nellcor. However, the correction equations presented by Barker and Tremper and the technical literature of Ohmeda differ substantially from our equation when sufficient quantities of reduced hemoglobin are present and the fractional COHb saturation (SaCO) is high. Our approximated equation, derived from the Lambert-Beer law, is SaO2 = SpO2 (1 - 0.932 SaCO) + 0.032 SaCO. The equation of Barker and Tremper is SaO2 = SpO2 - 0.9 SaCO. The Nellcor equation is SaO2 = SpO2 (1 - SaCO).

Carboxyhemoglobin↗
PubMed1989

An evaluation of the effectiveness of a computer simulation of anaesthetic uptake and distribution as a teaching tool.

Gas Man is an interactive, microcomputer-based simulation and tutorial designed to teach the principles of anaesthetic uptake and distribution. Using two resident groups, one at a primary university-teaching hospital and the other at a medical school affiliated community hospital, the authors compared residents' knowledge of the subject prior to exposure to the tutorial and the average time spent using the program during a self-paced instruction period. Both groups not only significantly improved their knowledge of uptake and distribution 8 weeks after using this program, but wished to spend additional time with it, implying that it was a pleasant and satisfying way to learn. Computer simulation has the potential to be an important teaching tool in an anaesthesia residency training programme.

Anesthesiology↗
PubMed1989

Postanesthesia care unit standards for anesthesiologists. Board of Directors of the American Society of Post Anesthesia Nurses.

The following article describes postanesthesia care unit standards for anesthesiologists as developed by the Harvard Anesthesia Department's Risk Management Committee, Harvard Medical School. The standards were endorsed by the ASPAN Board of Directors, April 10, 1988. It is hoped that publication of these standards will assist PACU nurses in evaluating the anesthesia support they receive in their respective settings.

Anesthesiology↗
PubMed1989

Spinal needles.

Explore the source record for details and available documents.

Anesthesia, Spinal↗
PubMed1988

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.

Adult↗
PubMed1987

Hypoxemia during ambulatory gynecologic surgery as evaluated by the pulse oximeter.

Pulse oximetry was used to determine the incidence of intraoperative hypoxemia in 108 patients undergoing ambulatory gynecologic operation. Eleven (10%) experienced moderate desaturation (arterial oxygen saturation less than 90%), and 5 (5%) suffered severe hypoxemic episodes (arterial oxygen saturation less than 85%). Among patient risk factors--including operation, body habitus, smoking habits, history of asthma, age, and airway characteristics--an association with moderate hypoxemia was found only with nonlaparoscopic gynecologic operation, obesity, and age over 35 years, and an association with severe hypoxemia was found only with obesity and age over 35. Among operative events--including inspired oxygen concentration, position, mode of ventilation, and anesthesia phase--an association with moderate hypoxemia was found only with the lithotomy position, manual ventilation, and arousal. The cost per patient of monitoring with a pulse oximeter is about +1.35. A cost-benefit analysis reveals that a mortality rate of 1 in 40,000 among patients who actually become moderately hypoxemic would justify the cost of monitoring arterial oxygen saturation. We conclude that pulse oximetry should be part of routine anesthetic monitoring.

Adult↗
PubMed1987

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.

Adult↗