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Biomedical subjects

C Weissman

Publications and source records attributed to C Weissman.

At least 55 records · Page 3Linked to original sources
PubMed1994

An in vitro evaluation of an instrument designed to measure oxygen consumption and carbon dioxide production during mechanical ventilation.

OBJECTIVE: To determine the ability of the Puritan-Bennett 7250 metabolic monitor to measure CO2 production and oxygen consumption (VO2) under simulated clinical conditions. DESIGN: An in vitro validation study. SETTING: Laboratory of a large university medical center. METHODS: An in vitro evaluation was performed by adding precise amounts of CO2 and nitrogen to a lung model to simulate CO2 production and VO2. CO2 production and VO2 values measured by the metabolic monitor were compared with simulated values at various FIO2 values (0.21 to 0.80), levels of positive end-expiratory pressure (0 to 20 cm H2O), and flow-by mode flow rates (0 to 20 L/min). This comparison was also made at increased peak airway pressures (60 cm H2O). The effects of various concentrations of oxygen on the accuracy of the CO2 production measurements were also examined. RESULTS: The measurements made by the instrument were within 7% of values predicted from the CO2 and nitrogen infusions. There was no effect of various oxygen concentrations on the accuracy of CO2 production measurements. CONCLUSION: Under the in vitro conditions tested, the metabolic monitor provided accurate measurements of VO2 and CO2 production.

Calorimetry, Indirect↗
PubMed1993

Arterial pulse contour analysis trending of cardiac output: hemodynamic manipulations during cerebral arteriovenous malformation resection.

OBJECTIVE: Intravascular pressure and cardiac output monitoring are frequently performed in the operating room and intensive care unit. Currently, cardiac output is only measured intermittently, although continuous measurement would be preferable. One method proposed for measuring cardiac output continuously is arterial waveform pulse contour analysis. This study examines the utility of trending cardiac output using pulse contour analysis during manipulations of blood pressure. METHODS: Eleven patients were studied while undergoing resection of cerebral arteriovenous malformations. Cardiac output measured by pulse contour analysis was compared with thermodilution cardiac output measurements in patients subjected to induced hypotension with esmolol and restoration of blood pressure with phenylephrine. RESULTS: Esmolol infusion resulted in a decrease in mean arterial pressure from 81 +/- 13 to 62 +/- 7 mm Hg (p < 0.025), a decrease in thermodilution cardiac output from 6.4 +/- 0.9 to 4.4 +/- 1.1 L/min (p < 0.025), and a decrease in pulse contour cardiac output from 6.2 +/- 1.0 to 4.5 +/- 0.9 L/min. Phenylephrine increased mean arterial pressure from 68 +/- 6 to 95 +/- 9 mm Hg with no change in either thermodilution or pulse contour cardiac output. CONCLUSIONS: This study demonstrates that during surgery for arteriovenous malformations in the brain, the pulse contour method was able to reflect cardiac output accurately during induced hypotension with esmolol and during restoration of blood pressure with phenylephrine.

Adolescent↗
PubMed1993

Stressing the critically ill patient: the cardiopulmonary and metabolic responses to an acute increase in oxygen consumption.

Critically ill patients frequently have compromised respiratory and hemodynamic function. Chest physical therapy has been previously shown to increase oxygen demand and therefore was used to examine how postoperative mechanically ventilated patients responded to an increased oxygen demand. We found that during chest physical therapy, oxygen consumption increased 52% +/- 37% (SD) over baseline values. There was a 35% +/- 32% increase in oxygen extraction and a 17% +/- 33% increase in oxygen delivery. Arterial and pulmonary artery pressures also increased. The cardiac output increase was due to increased heart rate with no change in stroke volume. The increases in minute ventilation and alveolar ventilation were not sufficient to eliminate the greater quantity of carbon dioxide produced, resulting in a small increase in PaCO2. There was no significant change in systemic vascular resistance. The increase in oxygen demand caused by chest physical therapy triggered an integrated physiological response that resulted in increased respiratory and cardiac performance. This in some ways, such as the lack of increase in systemic vascular resistance, resembles the response to exercise.

Adult↗
PubMed1993

Physiologic variables and fluid resuscitation in the postoperative intensive care unit patient.

OBJECTIVE: To examine how critical surgical illness and its management alter some of the biochemical, physiologic, and hematologic parameters commonly used to monitor postoperative, critically ill patients. DESIGN: Prospective survey of 150 patients over 3 months. SETTING: University hospital surgical intensive care unit. PATIENTS: A total of 150 consecutive adult patients admitted to the surgery-anesthesiology intensive care unit. MATERIALS AND METHODS: The effects of surgery on serum albumin and total protein concentrations, and lymphocyte counts were investigated. This investigation was done by comparing the values before surgery with those values after surgery and by also comparing what happened after different types of surgery. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: After surgery, decreases in serum albumin concentrations were significantly related to the estimated blood loss and acute gain in body weight from intravenous fluid resuscitation. The decreases in serum albumin and total protein concentrations were greater after elective abdominal surgery than after elective thoracic surgery. Total lymphocyte counts were significantly (< 1000 cells/mm3) reduced only in patients undergoing abdominal surgery. CONCLUSIONS: Serum albumin and total protein concentrations and total lymphocyte counts were significantly reduced by surgical injury, with significantly greater decreases seen after abdominal than thoracic surgery. These decreases were caused, in large part, by the volume of intravenous fluid used in resuscitation and blood loss. The changes in these variables are thus dependent on the type of surgical stress and the perioperative fluid therapy.

Abdomen↗
PubMed1993

Alfentanil attenuates the cardiopulmonary response of critically ill patients to an acute increase in oxygen demand induced by chest physiotherapy.

Critically ill patients often are subjected to interventions that acutely increase oxygen demand and require increased output of the cardiac and respiratory systems. This study explored whether alfentanil could attenuate the response to chest physical therapy, a procedure that increases oxygen consumption by 40%-50%. Patients were examined during two consecutive therapy sessions. In random order, they received either a placebo or alfentanil (30 or 60 micrograms/kg) 2 min before treatment. In Group 1 (n = 11, 30 micrograms/kg alfentanil) only the arterial blood pressure increases induced by chest physical therapy were attenuated. In Group 2 (n = 12, 60 micrograms/kg) alfentanil attenuated the increases in heart rate, central venous pressure, and pulmonary artery systolic pressures as well as systemic blood pressure. Neither dose of alfentanil altered the increases in oxygen consumption, carbon dioxide elimination, oxygen delivery, or extraction ratio. Thus alfentanil attenuated the hemodynamic responses to chest physiotherapy in a dose-dependent fashion. This was likely due to its vagotonic actions. In contrast, alfentanil had no effect on the balance between oxygen demand and delivery during chest physiotherapy. There was thus a dissociation between the hemodynamic and metabolic responses.

Adult↗
PubMed1993

Dynamic respiratory patterns after laparoscopic cholecystectomy.

Important alterations in respiratory function have been observed after open cholecystectomy. These include a decrease in the abdominal tidal volume, forced vital capacity, and forced expiratory volume at 1 s. Laparoscopic cholecystectomy is a new procedure allowing removal of the gallbladder without a subcostal or midline incision. The result is less postoperative pain and earlier ambulation. This study sought to determine whether changes in rib cage and abdominal wall motion are different after laparoscopic than open cholecystectomy. Twelve otherwise healthy patients underwent respiratory inductive plethysmography prior to and one day after laparoscopic cholecystectomy. Frequency of resting breathing increased 29 percent after laparoscopic cholecystectomy (p = 0.03), while abdominal motion decreased 32 percent (p = 0.03). During coached abdominal breathing, rib cage tidal volume increased 70 percent (p = 0.005) and abdominal tidal volume decreased 29 percent (p = 0.01). These alterations in respiratory pattern after laparoscopic cholecystectomy were smaller in magnitude than those reported following the open procedure.

Adult↗
PubMed1992

Caloric requirements and supply in critically ill surgical patients.

OBJECTIVE: To compare the caloric intake with the caloric requirements in postoperative patients being fed enterally via nasoenteric tubes, parenterally, or by both enteral and parenteral methods. DESIGN: Descriptive study. SETTING: Surgical ICU in a university teaching hospital. PATIENTS: Sample of 22 mechanically ventilated postoperative patients, mean age 62 +/- 17 yrs, selected from among those patients routinely scheduled to receive enteral or parenteral nutrition or both, for greater than or equal to 4 days. The patients were studied for a total of 144 study days. INTERVENTION: Eight patients received total parenteral nutrition, eight patients received enteral nutrition, and six patients received both parenteral and enteral nutrition. MEASUREMENTS: Resting energy expenditure was measured by using indirect calorimetry, and daily nutritional intake was quantitated. RESULTS: The patients who received parenteral, or enteral plus parenteral nutrition received an average of 80% of their caloric requirements, while those patients who received only enteral nutrition received only 68% of their caloric requirements. There was more day-to-day variation in nutrient intake in the enteral group (40% +/- 56%) than in the parenteral group (12.2% +/- 24%, p less than .001). CONCLUSIONS: Enteral nutrition delivered via nasoenteric tubes as the sole delivery method in postoperative critically ill patients resulted in an inadequate and inconsistent nutrient supply. The use of parenteral or parenteral plus enteral nutrition resulted in more stable and adequate feeding than feeding by enteral nutrition alone.

Adult↗
PubMed1992

Flow-volume relationships during spontaneous breathing through endotracheal tubes.

OBJECTIVE: Breathing spontaneously through an endotracheal tube is often equated with "breathing through a straw." The objective of this study was to examine whether endotracheal tubes functionally act as tubular resistors in patients during tidal breathing, machine-initiated breaths, and vital capacity maneuvers. DESIGN: Descriptive study. SETTING: University hospital surgical ICU. PATIENTS: Eighteen mechanically ventilated, critically ill, postoperative patients (34 to 87 yrs). MEASUREMENTS: Flow-volume loops were recorded during tidal and machine breaths, as well as during vital capacity maneuvers. The loops were inspected visually for evidence of air flow limitation. Expiratory characteristics were examined using the ratio of expiratory volume in 1 sec to the expiratory volume in 0.5 sec and the ratio of expiratory volume in 1 sec to peak expiratory flow rate. The ratio of expiratory volume in 1 sec to that in 0.5 sec (greater than 1.5) and the ratio of expiratory volume in 1 sec to peak expiratory flow rate (greater than 10 mL/L/min) are seen with upper airway obstruction. MAIN RESULTS: Mean spontaneous tidal volume was 361 +/- 92 (SD) mL and vital capacity was 1104 +/- 16 mL, while the ratio of expiratory volume in 1 sec to that in 0.5 sec was 1.57 +/- 0.17 and 1.7 +/- 0.1 (p less than .05), respectively. The ratio of expiratory volume in 1 sec to peak expiratory flow rate was 9.9 +/- 1.7 during tidal breathing and 12.9 +/- 1.2 (p less than .05) during vital capacity maneuvers. CONCLUSIONS: Endotracheal tubes of the diameters used in these adult postoperative patients (7 and 8 mm) cause only minimal limitation to air flow during the small volumes and low-flow rates observed during tidal breathing. Evidence of greater air flow limitation was seen during vital capacity maneuvers.

Adult↗
PubMed1992

Postthoracotomy respiratory muscle mechanics during incentive spirometry using respiratory inductance plethysmography.

We undertook this study to characterize the postthoracotomy compartmental displacement and respiratory mechanical changes occurring during and after the performance of the incentive spirometry maneuver. We also evaluated the effect of recumbency angle on compartmental recruitment. Sixteen patients were randomized to perform incentive spirometry either at 30 degrees or 60 degrees recumbency angle. They were studied using respiratory inductance plethysmography to measure tidal volume, respiratory frequency, inspiratory time, rib cage motion/tidal volume ratio, inspiratory duty cycle, and inspiratory flow. Patients were studied before surgery and on postoperative days 1 and 3. Statistical analysis was accomplished using multiple measures ANOVA with post-hoc Student's t-tests when appropriate. Preoperative incentive spirometry augmented VT by increasing both VT/TI and TI. Postoperatively, the incentive recruitment of VT was reduced, a result of a decrease in TI and TI/TTOT; VT/TI was unchanged. There was postoperative decrease of AB and AB/VT during incentive spirometry, greatest in the 60 degrees group. Our results characterize the nature of the respiratory recruitment afforded by incentive spirometry, before and after thoracotomy. We also found evidence of postthoracotomy diaphragmatic derecruitment during incentive spirometry exacerbated by a high recumbency angle.

Female↗
PubMed1992

Patterns of sedation and analgesia in the postoperative ICU patient.

Control of pain, discomfort, and agitation is an integral part of the postoperative management of critically ill patients. We examined the sedative and analgesic practices in a surgical ICU during two six-month periods, one in 1986-1987 and the other in 1989-1990. Narcotics, especially morphine and Fentanyl, were the most commonly used drugs. The amount of Fentanyl received by the endotracheal patients in the 1986-1987 group was quite large, 5.5 +/- 4.3 (SD) mg/day. The use of midazolam during the second survey period was associated with a reduced dose of narcotics in artificially ventilated patients receiving continuous intravenous Fentanyl and morphine. The use of epidural Fentanyl, especially following thoracic surgery, was greatly increased during the second study period. More work is needed to assess the effects and effectiveness of ICU sedative and analgesic regimens.

Adult↗
PubMed1992

Evaluation of respiratory inductive plethysmography in the measurement of breathing pattern and PEEP-induced changes in lung volume.

STUDY OBJECTIVE: To assess the accuracy of the respiratory inductive plethysmography in the measurement of PEEP-induced changes in end-expiratory lung volume during mechanical ventilation and its accuracy and stability in the measurement of ventilation during controlled mechanical ventilation and spontaneous breathing. DESIGN: An open comparison between two methods using a criterion standard. Either a pneumotachometer (mechanically ventilated patients) or a spirometer (spontaneously breathing subjects) was used as the reference method. SETTING: Tertiary care center; a multidisciplinary intensive care unit and a metabolic research unit. PATIENTS: Six mechanically ventilated, paralyzed postoperative open heart surgery patients, six spontaneously breathing COPD patients, and eight healthy volunteers. INTERVENTIONS: Stepwise increases and reductions of PEEP from zero to 12 cm H2O during controlled mechanical ventilation; repeated validation of the calibration of the respiratory inductive plethysmography (RIP) in both mechanically ventilated and spontaneously breathing subjects. MEASUREMENTS AND RESULTS: The baseline drift of the RIP in vitro was 10 ml/150 min and in a ventilated model it was 20 ml/150 min. In mechanically ventilated patients, the mean error of the calibration after 150 min was within +/- 5 percent. Change in end-expiratory lung volume (EELV) during the stepwise increase of PEEP up to 12 cm H2O was 849 +/- 136 ml with the RIP and 809 +/- 125 ml with the pneumotachometer (PT), and during the stepwise reduction of PEEP it was 845 +/- 124 ml and 922 +/- 122, respectively (not significant [NS]. The mean difference between methods in the measurement of change in EELV was -6.6 +/- 3.5 percent during increasing and 6.6 +/- 6.7 percent during decreasing PEEP (NS). Both in mechanically ventilated and spontaneously breathing subjects, the difference between methods was significant for VT and VT/TI. The difference in VT was -2.2 +/- 0.2 percent during mechanical ventilation, -1.1 +/- 0.5 percent in spontaneously breathing COPD patients, and 2.9 +/- 0.4 percent in healthy volunteers (NS between groups). CONCLUSIONS: The RIP is sufficiently accurate for the measurement of PEEP-induced changes in EELV during controlled mechanical ventilation. The accuracy of tidal volume measurement is similar during mechanical ventilation and spontaneous breathing. The calibration of the RIP is stable enough for bedside monitoring of changes in lung volumes.

Adult↗
PubMed1992

Assessing hypermetabolism and hypometabolism in the postoperative critically ill patient.

To determine whether a patient is hypermetabolic or hypometabolic, measured resting energy expenditure is compared with estimated (or predicted) energy expenditure. The latter is calculated using equations derived from measurements made in groups of healthy individuals. Body weight or body surface area are among the variables used in these equations. Yet, in critically ill patients, body weight often rises because of fluid resuscitation. This study examined the differences between using preoperative, postoperative, and ideal body weights on the determination of hypermetabolism and hypometabolism in mechanically ventilated, critically ill patients. When the elevated postoperative weights were used instead of the preoperative ones to predict energy expenditure, the degree of hypermetabolism was underestimated. Subtracting the weight of the cumulative net fluid balance from the postoperative weight was found to accurately reflect preoperative weight. The influence of various predictive equations on the magnitude of hypermetabolism was also explored. In conclusion, it is important, when determining hypermetabolism or hypometabolism, to consider the influence of the specific predictive equation used and the effect of resuscitation fluid.

Aged↗
PubMed1991

Subthreshold argon-laser irradiation elicits a pronounced vitreal prostaglandin E2 response.

Chorioretinal production of prostaglandin type E2 (PGE2) as well as changes in vitreal protein and PGE2 concentrations were studied following retinal irradiation with low-power laser energy that caused ophthalmoscopically invisible ("subthreshold") laser burns. This was compared with changes following ophthalmoscopically visible ("suprathreshold") laser burns. Our results demonstrate that with in eyes exposed to the lower-power levels, the enhancement in vitreal PGE2 concentration persisted for a longer period and was more pronounced than in eyes exposed to the suprathreshold levels (a 3-fold and a 2-fold increase above baseline values, respectively). Protein leakage into the vitreous was noted only in the suprathreshold group, indicating a blood-retinal barrier (BRB) disruption. The findings of persistent, excessive PGE2 vitreal levels with no protein leakage in the subthreshold group suggest a possible anti-inflammatory role for PGE2 following low-power laser exposure.

Animals↗
PubMed1991

Argon laser irradiation of rabbits' eyes-changes in prostaglandin E2 levels.

Laser irradiation of the eye is a widely used therapeutic measure in various ocular disorders. We investigated in laser-treated rabbits' eyes the changes in prostaglandin E2 (PGE2) levels of the tissue affected by the laser (the retina/choroid) and of its adjacent vitreous over a two-week period. The parameters studied were; PGE2 in vitro production by the retina/choroid, as well as PGE2 and protein levels in the vitreous, the latter indicative of a break in the blood retinal barrier (BRB). The effect of noncoherent light exposure used for illumination, and that of the mechanical manipulation involved (sham exposure) were also studied. Following laser exposure vitreal PGE2 levels were increased two-fold above baseline (days three and 14), whereas light exposure resulted in a single peak. PGE2 in vitro production by the retina/choroid in the laser-exposed group was elevated throughout the observation period, peaking twice (days 3 and 14), in the light-exposed group the enhanced production was evident during a shorter period, whereas in the sham group it remained unchanged from baseline. An elevation in vitreal protein levels to above baseline levels occurred in both the laser- and, to a lesser degree, in the noncoherent light-exposed groups, but not in the sham group. Our study demonstrated an enhanced PGE2 in vitro production by retina/choroid of laser-exposed eyes, which might be attributable to the additive effect of the laser induced trauma, and the noncoherent light photochemical changes; the clinical significance of the recurrent increase in vitreal PGE2 levels in laser-treated eyes might be related to its anti-inflammatory properties.

Animals↗
PubMed1991

Prostaglandin E2 changes in the retina and optic nerve of an eye with injured optic nerve.

Changes in arachidonic acid metabolism were studied in the optic nerve, the chorioretina, and in the vitreous following crush injury to the optic nerve of rats. Crush injury led to: (i) a 3.9-fold increase in optic nerve prostaglandin type E2 in vitro production which peaked on day 5 and was followed by a gradual decline, but was still significantly higher than baseline levels by day 12; (ii) a two-fold increase in the chorioretina prostaglandin type E2 in vitro production which peaked on day 1, and resumed baseline levels by day 3; (iii) a 3.5-fold increase in vitreous prostaglandin type E2 levels on day 1 which remained at 1.5-2 times higher than baseline levels for the rest of the study period (12 days). The findings indicate that the pattern of changes in prostaglandin type E2 production by the optic nerve (consisting mostly of white matter) is different from that described for injured brain tissues. The prolonged accumulation of vitreal prostaglandin type E2 in eyes with damaged optic nerve may lead to undesirable effects on the retina beyond those directly manifested in the retina by altered axonal flow in the injured optic nerve.

Animals↗