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Biomedical subjects

C Weissman

Publications and source records attributed to C Weissman.

At least 37 records · Page 2Linked to original sources
PubMed1997

Urinary pyridinium cross-link excretion is increased in critically ill surgical patients.

OBJECTIVES: To determine: a) the rate of pyridinium cross-links of collagen excretion, breakdown products of bone, in critically ill surgical patients in the intensive care unit (ICU); and b) the relationship between cross-link excretion and nitrogen excretion and balance to ascertain whether collagen breakdown products contribute to protein losses during a hypercatabolic state. DESIGN: Observational study starting on the first postoperative day to 20 days or until discharge. SETTING: A surgical ICU in a University hospital. PATIENTS: Nine mechanically ventilated, postoperative surgical patients (73 +/- 3 [SD] yrs), receiving routine parenteral nutrition (18% protein) and 17 age-matched healthy subjects. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Resting energy expenditure was determined daily for < or = 5 days after admission, and energy intake was set at 1.04 times the initial energy expenditure; thereafter, values of intake were reset weekly. Daily 24-hr urine samples were analyzed for cross-links, total and urea nitrogen, calcium, and creatinine for 20 days or until discharge. Two urine samples were also analyzed for cross-links in the healthy subjects. The excretion of cross-links from the surgical patients was markedly higher (p < .001) than in the healthy subjects, and calcium balance was significantly negative (p < .05). Patients who were discharged from the ICU within 5 days showed a lower rate of cross-link excretion (p < .02) and less day-to-day variability, compared with those patients who stayed longer, whether calculated over the course of the study or over the first 2 days in the ICU. There was no correlation between cross-links and energy expenditure, nitrogen excretion, or balance. CONCLUSIONS: The rate of cross-link excretion in critically ill patients: a) is markedly increased; b) is greater within the first two postoperative days in those patients who have an extended stay (> 5 days) in the ICU; and c) is independent of the rate of nitrogen excretion. These findings suggest that critically ill postoperative patients experience an acute breakdown of collagen, which is likely due to resorption of bone or possibly comes from other collagen sources.

Aged↗
PubMed1997

Can hospital discharge diagnoses be used for intensive care unit administrative and quality management functions?

OBJECTIVE: To determine whether hospital discharge diagnoses can be used for intensive care unit (ICU)-related activities. DESIGN: Comparison between the diagnoses coded by physicians at the time of ICU admission and those diagnoses coded by medical records personnel. SETTING: University hospital adult surgical ICU. PATIENTS: Consecutive ICU admissions (n = 622). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The ICU admission and hospital discharge codes were compared in two ways. Initially, each discharge code was subtracted from the corresponding ICU admission code. There was no difference in 150 (24%) cases. In 216 (35%) patients, the codes differed by +/-10. In 221 (36%) instances, the codes differed by >200. The secondary discharge diagnoses were also compared with the ICU admission diagnoses. In 56 patients, the ICU admission diagnosis was one of the secondary diagnoses. The second comparison involved having two physicians not associated with the study examine each pair of codes to determine if the two diagnoses were medically different. Review of the codes by physicians not involved in the study found that in 318 (48%) patients, the two diagnoses were not different, i.e., the codes were either the same or the codes were so similar as not to functionally change the actual diagnosis. CONCLUSIONS: The primary discharge diagnosis often failed to reflect the reason for ICU admission, making it impossible to consistently establish the reason for ICU admission from the discharge data. The reason for ICU admission was also frequently not included among the secondary discharge diagnoses. Administrative data are therefore not useful for ICU quality management and other functions. Intensivists need to establish their own databases.

Abstracting and Indexing↗
PubMed1997

Insights into the increased oxygen demand during chest physiotherapy.

OBJECTIVES: To determine the mechanism responsible for the increase in oxygen consumption (VO2) during chest physical therapy. Specifically, to examine the hypothesis that muscular activity is the major contributor to the increase in oxygen demand. DESIGN: Prospective, observational study. SETTING: University hospital surgical intensive care unit. PATIENTS: Phase one included 13 patients who were mechanically ventilated after coronary artery bypass surgery. Phase two involved seven mechanically ventilated patients who had undergone major vascular or abdominal surgery. INTERVENTIONS: Phase one involved turning patients to the lateral decubitus position. During the second phase, patients were given midazolam (0.15 microg/kg) 2 mins before an initial chest physiotherapy session and midazolam plus vecuronium (0.7 mg/kg) before a subsequent session. Physiologic measurements were made during the resting periods before and following each session, as well as at the completion of the intervention. MEASUREMENTS AND MAIN RESULTS: Turning patients to the lateral position resulted in significant increases in oxygen uptake and CO2 elimination (VCO2). VO2 increased from 219 +/- 21 (SD) mL/min at rest to 324 +/- 58 mL/min (p <.05) with turning. These increases in oxygen demand were met by increases in both oxygen delivery (852 +/- 238 mL/min at rest to 1116 +/- 430 mL/min, p < .05) and extraction (0.27 +/- 0.7 at rest to 0.32 +/- 0.09, p < .05). There were associated increases in hemodynamic and respiratory variables including heart rate and systolic blood pressure. The administration of vecuronium completely suppressed the 50% increases in VO2 and VCO2 seen without the use of a muscle relaxant. The increases in systolic blood pressure were unaffected by vecuronium. The magnitude of the increase in PaCO2 (32 +/- 5 torr [4.3 +/- 0.7 kPa] at rest to 36 +/- 5 torr [4.8 +/- 0.7 kPa] during therapy, p < .05), was not accentuated by vecuronium (30 +/- 4 torr [4.0 +/- 0.5 kPa] to 35 +/- 6 torr [4.7 +/- 0.8 kPa], p < .05) despite a lack of any increase in minute ventilation or respiratory rate. This change was due to the parallel suppression of VCO2. CONCLUSIONS: The increase in metabolic demand during chest physiotherapy is the result of increased muscular activity as evidenced by the suppression of VO2 following the administration of the muscle relaxant and the observation that turning a patient into the lateral decubitus position produces similar increases in VO2. The increases in blood pressure and cardiac output are due to another mechanism, most likely enhanced sympathetic output. The increase in physiologic activity produced by chest physiotherapy is thus secondary to both exercise-like and stress-like responses.

Aged↗
PubMed1997

Analyzing intensive care unit length of stay data: problems and possible solutions.

OBJECTIVES: To explore methods of evaluating the length of stay patterns of intensive care unit (ICU) patients. It was hypothesized that the mean does not adequately describe the typical length of stay (central tendency) because distribution patterns are often markedly skewed by patients with extended stays. Therefore, other descriptors are needed. In addition, ways are needed to identify outliers-patients with stays longer or shorter than the bulk of the data. DESIGN: Review of retrospective data. SETTING: University hospital surgical ICU. PATIENTS: Representative data included all (4,499) patients admitted over a 6-yr period. Each was assigned to a diagnostic group that represented either a frequently performed surgical procedure (e.g., thymectomy) or in cases where there was no predominant procedure, a surgical discipline (e.g., otolaryngology). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The frequency distributions were usually skewed to the right and included two populations of interest: The portion with the majority of observations ("body"), which described "typical" behavior, and the "tail", which provided information on outliers. The average of the mean lengths of stay of all diagnostic groups was higher than the average of the medians (3.9 +/- 1.8 [SD] vs. 2.7 +/- 1.1 days, p < .001) and modes (2.1 +/- 1.2 days, p < .001), reflecting the rightward skewness of the length of stay frequency distributions. The median +/- 1 day included 75 +/- 13% of the patients, thus confirming that the median was the most useful descriptor of central tendency. Various methods were used to identify outliers. Histograms of the frequency distributions were examined and outliers visually identified. Conventional outlier analysis labeled as outliers patients staying greater than two standard deviations from the mean stay. This method underestimated the number of outliers when the distributions were skewed to the right. Another method involved designating a specific length of stay (e.g., 7 or 10 days) or percentage of patients as the outlier threshold. Each method designated different numbers of patients as outliers. CONCLUSIONS: When analyzing length of stay data it is important to visually examine the frequency distribution because it is often skewed to the right. This skewness renders traditional parameters such as the mean and standard deviation less useful for describing the typical length of stay. Instead, the median, mode, and harmonic mean should be used. When reporting length of stay, some indication of the characteristics of the data should be presented. A graph of the frequency distribution rapidly allows the reader to determine its shape. A simple method is to report the mean, median, and range.

Bias↗
PubMed1996

Mice homozygous for a modified beta-amyloid precursor protein (beta APP) gene show impaired behavior and high incidence of agenesis of the corpus callosum.

The amyloid precursor protein (beta APP) gene of the mouse was disrupted by homologous recombination; however, contrary to expectation, brain and other tissues still contained beta APP-specific RNA, albeit at a level 5-10 fold lower than wild-type and lacking the disrupted exon, which had been spliced out. The brain contained shortened beta APP-specific protein at a low level. Mutant mice were severely impaired in spatial learning and exploratory behavior and showed increased incidence of agenesis of the corpus callosum.

Agenesis of Corpus Callosum↗
PubMed1996

Modulating effects of propofol on metabolic and cardiopulmonary responses to stressful intensive care unit procedures.

OBJECTIVE: Patients in the intensive care unit (ICU) undergo acute increases in metabolic and cardiopulmonary demands in response to routine care interventions, such as chest physical therapy. This study examined whether the short-acting drug, propofol, could blunt the responses to chest physical therapy. DESIGN: Prospective, randomized, crossover (placebo vs. drug) study. SETTING: University hospital surgical ICU. PATIENTS: Postoperative ICU patients being ventilated in the synchronized intermittent mandatory ventilation mode. INTERVENTIONS: Two groups of 16 patients were studied. Each patient received two successive sessions of chest physical therapy. In random fashion, one was preceded by the administration of placebo and the other by an intravenous bolus of propofol (0.75 mg/kg in one group and 0.35 mg/kg in the other group). Each session was preceded and followed by a period of rest. MEASUREMENTS AND MAIN RESULTS: The increases in oxygen uptake, CO2 elimination, oxygen delivery, heart rate, and systolic blood pressure associated with chest physical therapy were attenuated with the low dose and suppressed with the high dose of propofol. The Paco2 concentration was slightly increased during both placebo and drug administration. CONCLUSIONS: Propofol, in the doses administered in this study, significantly reduced the hemodynamic and metabolic stresses caused by chest physical therapy.

Adult↗
PubMed1995

Do synthetic adrenergic agents interfere with the measurement of endogenous plasma catecholamine concentrations?

PURPOSE: It is common to administer synthetic sympathomimetic and sympatholytic agents in the intensive care unit and operating room. The present study examines whether such agents, as well as the products of catecholamine metabolism, interfere with the quantitation of endogenous catecholamines by high-performance liquid chromatography. METHODS: Samples of drugs and metabolites were assayed before and after alumina extraction and their relative retention times were compared with dopamine, norepinephrine, and epinephrine relative retention times. Blood samples from patients receiving these drugs were also assayed for their interferences with catecholamine determination. RESULTS: Phenylephrine interfered with the quantitation of epinephrine. Isoproterenol's peak was so delayed it appeared in the following chromatogram. Dobutamine had two small peaks in vitro, whereas in the patient samples only one peak was identified; the other was probably masked by the dopamine peak. Labetalol had one peak when the pure drug was assayed but multiple peaks in patient samples, that were probably caused by metabolites of labetalol. CONCLUSION: Synthetic adrenergic agents and catecholamine metabolites can potentially interfere with the quantitation of the endogenous catecholamines. Thus, it is important to examine whether such interference occurs when conducting high-performance liquid chromatography assays.

Adrenergic Agents↗
PubMed1995

Pressure support ventilation attenuates the cardiopulmonary response to an acute increase in oxygen demand.

Critically ill patients undergo interventions, such as chest physical therapy, that acutely increase metabolic rate. Previous observations revealed that chest physical therapy is accompanied by increases of 40 to 50% in oxygen consumption (Vo2) and 40% in minute ventilation contributes to the rise in Vo2 and its associated hemodynamic responses. This was done by increasing mandatory ventilatory support during the chest physical therapy session: In phase 1 the mandatory ventilation rate was increased by 35% and in phase 2 pressure support ventilation 15 cm h2O was added. In phase 1 (n = 12), the increase in mandatory rate did not attenuate the chest physical therapy induced rises in heart rate, arterial blood pressure and Vo2. The increase in minute ventilation when the mandatory rate was increased prevented a rise in PaCO2. In phase 2 (n = 15), no change in the increase in Vo2 with chest physical therapy was observed with the addition of pressure support. Yet the rises in heart rate and systemic and pulmonary artery pressures were attenuated, as was the increase in PaCO2. Respiratory rate did not increase as much with pressure support. There appears to be a role for pressure support ventilation in attenuating the pulmonary and hemodynamic responses to interventions that increase oxygen demand.

Adult↗
PubMed1995

Metabolic measurements in the critically ill.

Measurements of VO2 and VCO2 can be used to calculate REE, which can be used to determine the caloric requirements and metabolic state of critically ill patients. These measurements are made using the gas exchange method--measuring the minute ventilation and the differences between the inspired and expired concentrations of oxygen and carbon dioxide. Mechanical ventilation provides a challenging environment in which to make these measurements because of elevated oxygen concentrations, fluctuating airway pressures, and humidity. Careful attention must be paid to details to ensure accurate measurements under these conditions.

Calorimetry, Indirect↗
PubMed1994

Replication step.

Explore the source record for details and available documents.

Biological Evolution↗
PubMed1994

Encoding a post-operative coronary artery bypass surgery care plan in the Arden Syntax.

The Arden Syntax for medical logic modules (Arden) was used to test the feasibility of encoding large, complex care plans. The critical portions of an existing paper-based care plan for the management of patients following coronary artery bypass graft (CABG) surgery were encoded in Arden and an X-windows user-interface was developed. The Arden Syntax proved adequate for encoding all of the necessary functions of the care plan. The limitations of the current Arden Syntax and possible additions to Arden are discussed.

Artificial Intelligence↗
PubMed1994

Midazolam attenuates the metabolic and cardiopulmonary responses to an acute increase in oxygen demand.

Critically ill patients are subjected to routine clinical activities that increase oxygen demand. This results in increased heart rate, blood pressure, minute ventilation, and oxygen delivery in patients with often already compromised cardiopulmonary systems. This study examines whether the benzodiazepine, midazolam, could attenuate the increase in metabolism, respiration, and circulation seen during chest physical therapy. Two groups of mechanically ventilated postoperative patients were studied. One group (n = 15) received, in random order, 0.015 mg/kg of midazolam and placebo prior to two consecutive chest physical therapy sessions, while the other (n = 13) received 0.030 mg/kg and placebo. Both doses of midazolam significantly attenuated the increases in oxygen consumption, heart rate, and systemic blood pressure observed during placebo administration. The cardiac output increase was also attenuated. Although midazolam reduced minute ventilation and respiratory rate, no excess CO2 retention occurred when the drug was administered likely as the result of reduced CO2 production. The administration of midazolam (0.015 mg/kg and 0.030 mg/kg) prior to chest physical therapy reduces metabolic, hemodynamic, and ventilatory responses to chest physical therapy.

Adult↗
PubMed1994

Response of critically ill patients to increased oxygen demand: hemodynamic subsets.

OBJECTIVE: To ascertain how patients with different abnormalities of oxygen transport at rest respond to an acute increase in oxygen demand. DESIGN: Observational study with retrospective assignment to subgroups, based on resting oxygen extraction ratio or increased cardiac output. SETTING: University hospital surgical intensive care unit (n = 96). PATIENTS: Postoperative, mechanically ventilated, critically ill patients (n = 96). INTERVENTION: Chest physical therapy. MEASUREMENTS AND MAIN RESULTS: Metabolic, hemodynamic, and respiratory measurements were made during an initial rest period and then during chest physical therapy. During chest physical therapy, patients (n = 10) having low resting oxygen extraction ratios (< or = 0.20) increased oxygen extraction, without changing oxygen delivery (DO2); while those patients (n = 19) with high resting oxygen extraction ratios (> or = 0.30) increased DO2, but not oxygen extraction. Patients (n = 46) with oxygen extraction ratios between 0.2 and 0.3 had an intermediate response; both DO2 and oxygen extraction increased. The group (n = 19) with increased resting cardiac output (> 9 L/min) and associated low resting oxygen extraction ratios and high DO2 values, increased their extraction of oxygen during chest physical therapy. CONCLUSIONS: The response to an acute increase in oxygen demand was influenced by resting conditions and was characterized by the use of "reserve" capacity. Patients with a resting hyperdynamic state (high DO2 and low oxygen extraction) were able to further increase oxygen extraction during the increase in oxygen demand.

Adolescent↗
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↗