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Biomedical subjects

W J Sibbald

Publications and source records attributed to W J Sibbald.

At least 91 records · Page 5Linked to original sources
PubMed1994

Evaluation of new diagnostic technologies: bronchoalveolar lavage and the diagnosis of ventilator-associated pneumonia.

OBJECTIVE: To present criteria to aid intensive care workers in the assessment of diagnostic technologies, using the example of bronchoalveolar lavage for the evaluation of ventilator-associated pneumonia. DATA SOURCES: MEDLINE was used to search for articles published from 1969 to the present that concerned diagnostic tests, diagnostic technology, pneumonia, and critically ill patients. STUDY SELECTION: Clinical investigations, case control studies, case series, and experimental data on the use of bronchoalveolar lavage. Studies of diagnostic technology were also included. DATA EXTRACTION: We extracted relevant data in duplicate, independently. DATA SYNTHESIS: Diagnostic technology assessment should begin by establishing the capability of the technology under ideal or laboratory conditions, followed by an exploration of the range of possible uses as well as the accuracy of the test. Bronchoalveolar lavage is a well-established technology for the diagnosis of pneumonia in immunocompromised patients. Studies of the accuracy of bronchoalveolar lavage in ventilator-dependent but nonimmunocompromised patients have shown promising diagnostic accuracy. Accuracy, however, is insufficient for dissemination of a test; an evaluation of the impact of a test on management decisions and, most importantly, on patient outcome, is required. Investigators have not addressed the full impact of bronchoalveolar lavage, and, even if the test is accurate, there are reasons to doubt whether patients will be better off if the test becomes part of routine clinical practice. CONCLUSIONS: We present guidelines for the assessment of diagnostic technology, and apply them to bronchoalveolar lavage for the evaluation of ventilator-associated pneumonia. Bronchoalveolar lavage has been studied in both the laboratory and clinical setting, and the diagnostic sensitivity and specificity of this technique are high. Further randomized trials evaluating management decisions and patient benefit would facilitate decisions regarding the appropriate dissemination of bronchoalveolar lavage.

Bronchoalveolar Lavage Fluid↗
PubMed1993

Effect of stored-blood transfusion on oxygen delivery in patients with sepsis.

BACKGROUND: Red blood cell transfusion is commonly used to augment systemic oxygen delivery to supranormal levels in patients with sepsis. However, clinical studies have not consistently demonstrated that this therapeutic maneuver is accompanied by an increase in oxygen utilization at either the whole-body level or within individual organs. STUDY OBJECTIVES: To determine the effect of red blood cell transfusion on gastrointestinal and whole-body oxygen uptake. DESIGN: Prospective, controlled, interventional study. SETTING: Multidisciplinary intensive care unit of a tertiary care teaching hospital. PATIENTS: Twenty-three critically ill patients with sepsis undergoing mechanical ventilation. MEASUREMENTS AND MAIN RESULTS: Systemic oxygen uptake was measured by indirect calorimetry and calculated by the Fick method. Gastric intramucosal pH as measured by tonometry was used to assess changes in splanchnic oxygen availability. Measurements were made prior to transfusion of 3 U of packed red blood cells. These were then repeated immediately following transfusion, as well as 3 and 6 hours later. There was no increase in systemic oxygen uptake measured by indirect calorimetry in any of the patients studied for up to 6 hours posttransfusion (including those patients with an elevated arterial lactate concentration). However, the calculated systemic oxygen uptake increased in parallel with the oxygen delivery in all the patients. More importantly, we found an inverse association between the change in gastric intramucosal pH and the age of the transfused blood (r = -.71; P < .001). In those patients receiving blood that had been stored for more than 15 days, the gastric intramucosal pH consistently decreased following the red blood cell transfusion. CONCLUSION: We failed to demonstrate a beneficial effect of red blood cell transfusion on measured systemic oxygen uptake in patients with sepsis. Patients receiving old transfused red blood cells developed evidence of splanchnic ischemia. We postulate that the poorly deformable transfused red blood cells cause micro-circulatory occlusion in some organs, which may lead to tissue ischemia in some organs.

Adenine↗
PubMed1993

Pulmonary artery catheterization. Can there be an integrated strategy for guideline development and research promotion?

OBJECTIVES: To review the evidence regarding indications for pulmonary artery catheterization (PAC) in critically ill patients, and to propose a guideline-generating process that would encourage randomized controlled trials of PAC. DATA SOURCES: Computerized and manual search for randomized trials involving PAC as an integral part of the protocol, published as of October 1992. Manual search for guidelines endorsed by specialty societies and/or proposed by expert panels following an explicit group process. DATA SYNTHESIS: Four trials suggest benefit from PAC for pre- or perioperative management of high-risk surgical patients. Two others indicate that PAC for low-risk aortic aneurysm surgery confers no advantages. Use of PAC to guide therapy aimed at improved mixed venous oxygen saturation was beneficial compared with usual care with PAC in two small trials among patients with septic shock and severe trauma. Other PAC indications are either untested or inadequately tested by small trials. Large trials are needed, but trials to date have been impeded by clinicians' uncertainty about PAC and unwillingness to randomize critically ill patients. No published guidelines for PAC have used a formal group process and/or a hierarchical review of evidence to demarcate proven from unproven indications. CONCLUSIONS: We propose a research-promoting expert panel on indications for PAC. Aided by a critical literature review, experts would rate case scenarios on the need for routine PAC with or without a specified intervention strategy. Future trials should test indications where there is either consensus about the uncertainty of need for PAC, or interpanelist disagreement owing to inconclusive evidence. This process could facilitate practice guideline development, utilization management, and large trials of PAC and related interventions.

Cardiac Catheterization↗
PubMed1993

Clinical utility and cost-effectiveness of an air suspension bed in the prevention of pressure ulcers.

OBJECTIVE: To determine, in critically ill patients at risk, both the clinical utility and cost-effectiveness of using an air suspension bed in the prevention of pressure ulcers. DESIGN: Randomized, parallel group, controlled clinical trial with accompanying cost-effectiveness analysis. SETTING: 30-bed multidisciplinary intensive care unit. PATIENTS: 100 consecutive patients at risk for the development of pressure ulcers randomly assigned to receive treatment on either an air suspension bed or a standard intensive care unit bed. Patients considered at risk were those at least 17 years of age with an Acute Physiology and Chronic Health Evaluation II (APACHE II) score greater than 15 who had an expected intensive care unit stay of at least 3 days. MAIN OUTCOME MEASURES: The development of pressure ulcers by site and severity and the costs associated with each of the two programs. RESULTS: The air suspension bed was associated with fewer patients developing single, multiple, or severe pressure ulcers. In patients at risk, the use of an air suspension bed in the prevention of pressure ulcers was a cost-effective therapy. CONCLUSIONS: Despite intense nursing care, pressure ulcers are more prevalent in the critically ill patient population than in the general hospital population. Air suspension therapy provides a clinically effective means of preventing pressure ulcers in these patients. In patients at risk, air suspension therapy was a cost-effective means of managing pressure ulcers compared with the standard hospital bed.

Adolescent↗
PubMed1993

A survey of charting in critical care units.

OBJECTIVES: To determine what data are currently being collected at the critical care bedside, the role of flow sheets in storing these data, and what other forms and locations are used to store critical care data. DESIGN: We undertook a descriptive survey in a nonrandom sample of acute care hospitals with designated critical care units. Flow sheets were reviewed, and interviews with critical care nurses and physicians were conducted according to a predefined questionnaire. Finally, compliance in the surveyed hospitals with previous recommendations and existing guidelines on data collection and storage was then determined. SETTING: Fifteen "teaching" and 19 "nonteaching" acute care hospitals in the Province of Ontario. RESULTS: A lack of standardization of flow-sheet design and of the specific data included on these flow sheets was identified. Abbreviations were inconsistent. Little collaboration between physician and nonphysician members of the critical care team was identified in flow-sheet design. Variance between units in their collection of physiologic data was remarkable. Finally, few units surveyed used quantifiable illness severity scoring to describe their unit population. CONCLUSIONS: The lack of standardization regarding key information that should be collected and archived in critical care units identifies important risk management and quality assurance issues. There is a need for agreement on what information should be collected and maintained at the bedside in order to provide quality patient care.

Critical Care↗
PubMed1993

Postoperative utilization of critical care services by cardiac surgery: a multicenter study in the Canadian healthcare system.

OBJECTIVES: To describe patterns of critical care services used after cardiac surgery and to evaluate whether variations in the process of care influence outcome. DESIGN: Multicenter, prospective study. SETTING: A convenience sample of four cardiac surgical units: three in university-affiliated (teaching) hospitals and one in a nonteaching regional referral center. PATIENTS: A "consecutive sample" of 335 patients after cardiac surgery in four hospitals. INTERVENTIONS: Data were collected regarding all cardiac surgery patients admitted to the critical care units in the four test hospitals. MEASUREMENTS AND MAIN RESULTS: The critical care unit and hospital lengths of stay and survival were followed. The Therapeutic Intervention Scoring System (TISS) was used to assess the intensive care unit (ICU) interventions used during the first 24 hrs in the ICU and for the final 24 hrs before discharge from the ICU. The severity of illness on admission was assessed using the Acute Physiology and Chronic Health Evaluation (APACHE) scoring system. For patients having similar procedures (e.g., aortocoronary bypass and nonaortocoronary bypass procedures) and with similar outcome (mortality/total hospital length of stay), we found significant differences in the pattern of ICU resource utilization among hospitals. Significant (p < .05) differences in unit length of stay were related to varying factors in different hospitals. In hospital unit A, the type of procedure and preoperative chronic health status influenced unit length of stay (aortocoronary bypass 2.8 +/- 1.7 days; nonaortocoronary bypass 8.7 +/- 8.9 days) because length of stay was different for differing procedure groups. In hospital unit B, the critical care management system and lack of step-down (intermediate care) unit availability resulted in an increased unit length of stay for aortocoronary bypass patients (5.1 +/- 4.5 days) as compared with the other units (mean ICU lengths of stay of 2.8, 2.3, and 3.0 days, respectively). Unit B kept patients for monitoring purposes and had a reduced need for critical care nursing on the day of discharge (TISS = 7.5 +/- 5.5) as compared with the other units (mean TISS scores of 27.4, 23.2, and 21.5). CONCLUSIONS: Significant differences exist among hospitals in the same healthcare system in the utilization of critical care services for cardiac surgery. In spite of these differences, for similar patient "input," the outcome (mortality and hospital lengths of stay) appeared similar. Assessments of utilization of critical care must focus on more detailed specific issues than unit length of stay, and must include factors such as availability of intermediate care areas, the unit management system, chronic health status, and the operative procedures performed, if a utilization management process is to effect improved resource use in critical care.

Canada↗
PubMed1993

Changes in myocardial blood flow rates during hyperdynamic sepsis with induced changes in arterial perfusing pressures and metabolic need.

OBJECTIVE: To determine whether hyperdynamic sepsis is associated with dysregulation in the control of myocardial blood flow rates unrelated to hypotension or the use of anesthetic agents. DESIGN: Prospective, nonrandomized, controlled trial. SETTING: Experimental laboratory. SUBJECTS: Fifteen mature male sheep (34 to 61 kg). INTERVENTIONS: Data were recorded in study subjects before and after the induction of sepsis following cecal ligation and perforation. Data were then recorded during: a) an infusion of prostaglandin E1 (PGE1), which decreased mean arterial perfusing pressure; and b) an infusion of zymosan-activated plasma, which increased mean pulmonary arterial pressures. MEASUREMENTS AND MAIN RESULTS: Myocardial blood flow rates were measured by the radiolabeled microsphere technique and cardiac index was measured by the thermodilution technique. Cardiac index (change delta) postcecal ligation and perforation minus baseline (+2.3 +/- 1.0 L/min/m2; p < .01) was increased in the septic study. Blood flow rate to the left ventricle was simultaneously increased, and was not further affected when the PGE1 infusion decreased the mean arterial perfusing pressures (-19 +/- 4%). During the infusion of zymosan-activated plasma, mean pulmonary arterial pressures increased (50 +/- 30%) and right ventricular blood flow was increased (zymosan minus postcecal ligation and perforation study: delta 17.8 +/- 50 mL/100 g/min; p < .01). CONCLUSIONS: In this model of hyperdynamic sepsis, increases in blood flow to both the left and right ventricles were positively coupled to changes in respective ventricular work. From the interventional PGE1 and zymosan-activated plasma infusion studies, we found no evidence to support previous suggestions that the regulation of myocardial blood flow rates according to changes in perfusing pressure and/or metabolic oxygen need is significantly altered during hyperdynamic sepsis.

Alprostadil↗
PubMed1993

Differential impairment of vascular reactivity of small pulmonary and systemic arteries in hyperdynamic sepsis.

We postulated that the redistribution of organ blood flow that occurs in hyperdynamic sepsis is secondary to organ-specific alterations in vascular reactivity. Chronically instrumented rats were randomized to cecal ligation and perforation (CLP) (n = 12) or to a control procedure (n = 11). Cardiac output increased from 107 +/- 23 ml/min at baseline to 152 +/- 32 ml/min at 24 h after CLP (p = 0.037 versus control values). Mean blood pressure did not change in either group. Small arterial ring segment (100- to 200-microns effective lumen radius) from the pulmonary, renal, celiac, and femora arteries were obtained for determination of in vitro responsiveness. Maximal contractile responses to three receptor-operated contractile agonists were significantly depressed in the pulmonary (p = 0.001) and the celiac (p = 0.001) arteries from CLP versus control rats. The renal artery showed a trend toward decreased responsiveness (p = 0.049), but not difference was seen in the femoral artery (p = 0.172). EC50 values were unchanged. A similar, but less marked, pattern was observed for KCI-induced contractions in that depressed responses were noted in the pulmonary (p = 0.045) and celiac (p = 0.064) arteries. Vasodilator responses to acetylcholine were normal in all vessels. Nitroprusside relaxant responses were enhanced in the pulmonary artery (p = 0.022), but they were normal in the other vessels. We conclude that hyperdynamic, normotensive sepsis is associated with an organ-specific alteration of vascular smooth muscle function that particularly affects receptor-operated contractile responses. The differential expression of this altered vascular responsiveness between organs may contribute to the observed variance in regional blood flows in sepsis.

Animals↗
PubMed1993

Does implementing pulse oximetry in a critical care unit result in substantial arterial blood gas savings?

OBJECTIVES: To examine the impact of pulse oximetry on the use of arterial blood gas and other laboratory determinations and to examine predictors of the use of arterial blood gas measurements. DESIGN: Before (preoximetry)/after (postoximetry) study. SETTING: Thirty-bed multidisciplinary critical care unit. PATIENTS: Consecutive admissions of 300 patients (150 before and 150 after oximetry). MEASUREMENTS: For each patient examined, the number of arterial blood gas determinations, serum electrolyte levels, complete blood chemistries, arterial lactate levels, and creatinine samples were recorded for the initial 9 days of the stay in the critical care unit. These data were stratified by nursing shift (day vs night) and by the source of the admission (medical vs surgical). Other information collected included demographic variables, the severity of illness, the length of stay in the critical care unit, and various ventilatory parameters. RESULTS: Introducing pulse oximetry was associated with a marginal (10.3 percent; p < 0.025) reduction in the use of arterial blood gas determinations. This decrease was accounted for by changes occurring on the night shift and in the surgical patient. These findings were also observed for serum electrolyte determinations. No significant differences in the use of arterial blood gas measurements were found for medical patients. No significant differences were found in the use of arterial lactate levels, complete blood chemistries, or creatinine determinations. Significant predictors of arterial blood gas determinations included the number of days intubated, the number of ventilator orders, the number of days on an inspired oxygen content (FIO2) greater than 50 percent, and the acute physiology and chronic health evaluation II (APACHE II) score. CONCLUSIONS: The implementation of pulse oximetry in this manner gives an idea how effective the technology will be in reducing the use of arterial blood gas determinations without guidelines for the use of pulse oximetry. As only a marginal decrease was observed in the total population of medical and surgical patients, and only on the night shift, formal and standardized guidelines for the most efficient use of pulse oximetry should be considered. If these were considered, pulse oximetry may indeed make a significant contribution to improving the efficiency of care services.

Blood Chemical Analysis↗
PubMed1993

Modeling mortality in the intensive care unit: comparing the performance of a back-propagation, associative-learning neural network with multivariate logistic regression.

The objective of this study was to compare and contrast two techniques of modeling mortality in a 30 bed multi-disciplinary ICU; neural networks and logistic regression. Fifteen physiological variables were recorded on day 3 for 422 consecutive patients whose duration of stay was over 72 hours. Two separate models were built using each technique. First, logistic and neural network models were constructed on the complete 422 patient dataset and discrimination was compared. Second, the database was randomly divided into a 284 patient developmental dataset and a 138 patient validation dataset. The developmental dataset was used to construct logistic and neural net models and the predictive power of these models was verified on the validation dataset. On the complete dataset, the neural network clearly outperformed the logistic model (sensitivity and specificity of 1 and .997 vs. .525 and .966, area under ROC curve .9993 vs. .9259), while both performed equally well on the validation dataset (area under ROC of .82). The excellent performance of the neural net on the complete dataset reveals that the problem is classifiable. Since our dataset only contained 40 mortality events, it is highly likely that the validation dataset was not representative of the developmental dataset, which led to a decreased predictive performance by both the neural net and the logistic regression models. Theoretically, given an extensive dataset, the neural network should be able to perform mortality prediction with a sensitivity and a specificity approaching 95%. Clinically, this would be an extremely important achievement.(ABSTRACT TRUNCATED AT 250 WORDS)

Hospital Mortality↗
PubMed1992

Problems in assessing the technology of critical care medicine.

Technology assessment is becoming increasingly important in the area of critical care due both to the explosion of technology associated with this discipline and to the realization that future demand for these health care resources will undoubtedly exceed the ability to pay. Technology assessment remains both confusing and controversial to many physicians. This review tries to address some of the confusion by reviewing the basic strategies involved in this process. From there, problems and prospects for the evaluation of critical care as a program are presented, followed by the assessment of components within the area of critical care. Finally, recommendations are made on how technology assessment could proceed in the future to best achieve the efficient provision of this service.

Critical Care↗
PubMed1992

Interaction of sepsis and sepsis plus sympathomimetics on myocardial oxygen availability.

The ability to regulate myocardial blood flows (Q) in accord with changing myocardial O2 needs may be depressed in sepsis. This could be an important concern when sympathomimetics are used to augment systemic oxygen delivery (QO2) in this syndrome as increased myocardial O2 needs may accompany an infusion of this class of drugs. Therefore after measuring the effect of sepsis on myocardial O2 metabolism, we then infused various sympathomimetics to evaluate the sepsis+sympathomimetic interaction on myocardial QO2. We measured Q to the left (LV) and right (RV) ventricles by the radioactive microsphere technique in 36 unanesthetized mature sheep, before and during the infusion of dopamine, dobutamine, dopexamine, norepinephrine, salbutamol, or placebo. Randomly selected for infusion, these drugs were titrated to augment the thermodilution-derived cardiac index (CI) by greater than 20%. This study was repeated 24-48 h after cecal ligation and perforation had resulted in a hyperdynamic septic state [change (delta) in CI = sepsis - baseline = +54%; P less than 0.01]. During the septic study, both Q-LV (delta = +80%; P less than 0.01) and Q-RV (delta = +84%; P less than 0.01) were increased above baseline values; the augmented Q to both LV and RV was directly correlated with the arterial perfusion pressure (PA) x CI product and the mean pulmonary artery pressure (PPA) x CI product, respectively. Only 23% of study animals demonstrated net transmyocardial lactate production during the septic study. When the infusion of sympathomimetics was accompanied by an increase in the PPA x CI and PA x CI products, a further increase in both Q-RV and Q-LV, respectively, occurred. Also, neither the ventricular endocardial-to-epicardial flow ratios nor transmyocardial lactate extraction were modified by the sympathomimetics infusion. We conclude that the septic response to infection in this animal model was not accompanied by significant abnormalities in the metabolic regulation of myocardial QO2 (R. E. Cunnion, G. L. Scher, and M. M. Parker, Circulation 73: 637-644, 1986).

Animals↗
PubMed1992

Increased right ventricular compliance in response to continuous positive airway pressure.

The right ventricular hemodynamic effects of incremental continuous positive airway pressure (CPAP) were assessed in 16 studies in nine unanesthetized, spontaneously breathing sheep. In seven sheep, studies were performed before and after the induction of sepsis. CPAP was applied in four increments of 4 mm Hg via a cuffed tracheostomy tube. Cardiac output, right ventricular ejection fraction (RVEF) and right ventricular end-diastolic volume (RVEDV) were assessed by thermodilution. In this model, incremental CPAP produced similar effects in septic and nonseptic studies. Cardiac output was preserved by a progressive increase in heart rate (106 +/- 25 to 126 +/- 29, p less than 0.05) in spite of a significant decline in stroke volume index (49 +/- 7 to 43 +/- 7, p less than 0.05). Transmural pulmonary artery pressure and pulmonary vascular resistance index increased with incremental CPAP whereas RVEF declined (0.38 +/- 0.05 to 0.31 +/- 0.05, p less than 0.05). Transmural right atrial pressure declined significantly (7.7 +/- 1.7 to 4.8 +/- 2.9, p less than 0.05) whereas RVEDV was unchanged. In this study incremental CPAP was associated with an enhancement of right ventricular compliance. Further, right ventricular preload was preserved in spite of the measured increase in intrathoracic pressure and cardiac output was maintained in the face of a CPAP-related increase in right ventricular afterload by compensatory increases in heart rate and right ventricular work.

Animals↗
PubMed1992

Definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis. The ACCP/SCCM Consensus Conference Committee. American College of Chest Physicians/Society of Critical Care Medicine.

An American College of Chest Physicians/Society of Critical Care Medicine Consensus Conference was held in Northbrook in August 1991 with the goal of agreeing on a set of definitions that could be applied to patients with sepsis and its sequelae. New definitions were offered for some terms, while others were discarded. Broad definitions of sepsis and the systemic inflammatory response syndrome were proposed, along with detailed physiologic parameters by which a patient may be categorized. Definitions for severe sepsis, septic shock, hypotension, and multiple organ dysfunction syndrome were also offered. The use of severity scoring methods when dealing with septic patients was recommended as an adjunctive tool to assess mortality. Appropriate methods and applications for the use and testing of new therapies were recommended. The use of these terms and techniques should assist clinicians and researchers who deal with sepsis and its sequelae.

Critical Care↗
PubMed1992

The effect of various sympathomimetics on the regional circulations in hyperdynamic sepsis.

Because sepsis is characterized by a depression in vascular reactivity, we hypothesized that changes in organ blood flows (Q) would differ between the nonseptic and septic state during the infusion of sympathomimetics. Therefore we examined the (sepsis x organ Q) interaction during the infusion of five sympathomimetics in 36 mature, awake sheep before and after cecal ligation and perforation produced hyperdynamic sepsis. A 3-hour infusion of dobutamine, norepinephrine, dopamine, dopexamine, or salbutamol was compared with that of placebo during both nonseptic and septic studies; drug infusion was titrated to an increase in cardiac index of greater than 20%. Increased plateau infusion doses of norepinephrine (+305%), salbutamol (+275%), dopamine (+70%), and dobutamine (+49%) were required to achieve predefined treatment guidelines during the septic versus nonseptic study. Few differences in the regional effects of individual sympathomimetics were found in the nonseptic study, although infusion of sympathomimetics was accompanied by a redistribution of systemic Q toward the heart and away from the brain, kidney, small intestine, liver, and pancreas. In the septic study, however, the sympathomimetic infusions were not accompanied by the redistribution of Q away from small intestine and liver that was demonstrated in the nonseptic study. Therefore (1) the depressed vascular reactivity in hyperdynamic sepsis altered the dose profile of exogenous sympathomimetics required to augment systemic Q, and (2) the (sepsis x sympathomimetic) interaction was characterized by a depression in the anticipated redistribution of organ Q from "nonvital" to "vital" circulations.

Animals↗