Robert J. Byrick

Cardiopulmonary function and pulmonary microemboli during arthroplasty using cemented or non-cemented components. The role of intramedullary pressure.

An experimental model was designed to investigate the role of intramedullary pressure on cardiopulmonary function and pulmonary pathology during arthroplasty using cemented and non-cemented components. Twenty-four dogs were divided randomly into three groups: a group that received a non-cemented implant in which low intramedullary pressure was generated, a group that received a cemented implant, and one that received bone wax and an implant; high intramedullary pressures were generated in the latter two groups. Bone wax was used to generate high intramedullary pressures without the use of bone cement. In the group with the non-cemented implant, few pulmonary microemboli and no significant cardiorespiratory changes were found. In the groups that received bone wax and an implant or the cemented implant, there were many pulmonary microemboli and significant cardiorespiratory changes, including decreased arterial oxygen tension, increased pulmonary arterial pressure, and increased intrapulmonary shunt fraction. There was no evidence that methylmethacrylate monomer was responsible for the cardiorespiratory changes in the group with the cemented implant.

Evaluation of predictive ability of APACHE II system and hospital outcome in Canadian intensive care unit patients.

OBJECTIVES To evaluate the ability of the acute Physiology and Chronic Health Evaluation II (APACHE II) scoring system to predict patient outcome in two Canadian intensive care units (ICUs). To compare the severity of illness and outcome of Canadian ICU patients with existing United States data. DESIGN Prospective data collection on 1,724 Canadian ICU patients for validation of the APACHE II system. Comparison of the outcome of Canadian ICU patients to retrospective United States data on 4,087 patients from the 1985 APACHE II multicenter study. SETTING Canadian data from two university teaching hospital ICUs. United States data from 13 ICUs, ten of which were in university teaching hospitals. PATIENTS Consecutive patients admitted to adult medical/surgical ICUs. Coronary care unit, neurosurgical and cardiac surgery patients were excluded. INTERVENTIONS None. MEASUREMENTS AND MAIN RESULTS For each patient, demographic data, diagnosis, APACHE II score and hospital survival data were collected. The predicted risk of death was calculated for each patient using the APACHE II risk of death equation. The accuracy in outcome prediction of the APACHE II system was assessed by means of the receiver operating characteristic curve, 2 x 2 decision matrices and linear regression analysis. The severity of illness and hospital mortality for the Canadian patients was compared with that of United States patients from the 1985 APACHE II multicenter study. In 1,724 Canadian ICU patients, the mean +/- SEM APACHE II score was 16.5 +/- 0.2. The predicted death rate was 24.7% and the observed death rate was 24.8%. Using receiver operating curve analysis, good correlation was found between predicted outcome and observed outcome. The area under the curve was 0.86. From the 2 x 2 decision matrix constructed for a predicted risk of death of 0.5, 83% of patients were correctly classified. The sensitivity was 50.9% and the specificity was 93.6%. When observed death rate was plotted against predicted death rate, linear regression analysis gave an r2 of .99. Canadian patients had a higher death rate and APACHE II score than the United States patients. After controlling for severity of illness using the APACHE II score, the Canadian and United States death rates were similar. CONCLUSIONS The ability of the APACHE II system in predicting group outcome is validated in this Canadian ICU population by receiver operating characteristic curve, 2 x 2 decision matrices and linear regression analysis. The Canadian patients had a higher overall hospital death rate than the United States patients. After controlling for severity of illness using APACHE II scores, the hospital death rate was comparable between the Canadian and United States patients.

High-volume, high-pressure pulsatile lavage during cemented arthroplasty.

To determine the efficacy of high-volume, high-pressure pulsatile lavage in the prevention of cardiopulmonary dysfunction and fat embolism during cemented arthroplasty, we studied twenty-eight mongrel dogs that had had a bilateral cemented arthroplasty. Significant increases in pulmonary-artery pressure and pulmonary vascular resistance, accompanied by decreases in arterial oxygen tension and increases in intrapulmonary shunt fraction (Qs/Qt), characterized cardiopulmonary dysfunction after bilateral cemented arthroplasty when no lavage was used. Low-volume, low-pressure manual lavage did not significantly alter these physiological changes, but there was a significant reduction in the number of fat emboli that were demonstrated in the lungs as compared with the no-lavage group. High-volume, high-pressure pulsatile lavage of the intramedullary cavity after reaming significantly reduced the changes in pulmonary-artery pressure, pulmonary vascular resistance, arterial oxygen tension, and intrapulmonary shunt fraction (Qs/Qt). In the pulsatile-lavage group, the number of fat microemboli that were found in the lungs was reduced to 25.7 per cent of those found in the no-lavage group. We concluded that meticulous high-volume, high-pressure pulsatile lavage reduces both pulmonary physiological derangements and fat emboli during bilateral cemented arthroplasty in dogs.

Influence of Mannitol and Dopamine on Renal Function during Elective Infrarenal Aortic Clamping in Man

The impact of elective infrarenal aortic clamping on parameters of renal function was evaluated in 27 extracellular fluid volume expanded patients. Significant transient decreases (p less than 0.05) in glomerular filtration rate were observed in all three groups either in the early or late post-clamp release period, despite maintenance of hemodynamic stability. This study documents transient decreases in glomerular filtration rate which occurred following release of the infrarenal aortic cross-clamp. No clinically important benefit from the use of mannitol and dopamine over extracellular fluid volume expansion with saline alone was demonstrated in the prevention of the changes in renal function associated with aortic cross-clamping.

Pulmonary effects of fixation of a fracture with a plate compared with intramedullary nailing - A canine model of fat embolism and fracture fixation

Fat-embolism syndrome and pulmonary dysfunction may develop in multiply injured patients who have a fracture of a long bone. Although early fixation of a fracture is beneficial, intramedullary nailing may exacerbate pulmonary dysfunction by causing additional embolization of marrow fat. We examined the pulmonary effects of the timing and method of fixation of a fracture in a canine fat-embolism model. Fat embolism was induced in forty-one adult dogs by reaming the ipsilateral femur and tibia followed by pressurization of the intramedullary canal. The animals were divided into a control group of eight dogs that had induction of fat embolism alone and an experimental group of thirty-three dogs that had induction of fat embolism and internal fixation of a transverse fracture of the middle of the contralateral femoral shaft. In the control group, four dogs each were killed four hours and twenty-four hours after induction of fat embolism. In the experimental group, a femoral fracture was created and fixation was performed four hours after embolic showering in fifteen animals and twenty-four hours after embolization in eighteen animals. The two experimental groups were subdivided according to the method of fixation of the fracture: eleven dogs each had application of a plate, nailing without reaming, and nailing with reaming. The pulmonary arterial pressure and the alveolar-arterial gradient were measured preoperatively, during induction of fat embolism, and as long as one hour after fixation of the fracture but before the animal was killed. The lungs, brain, and kidneys were examined for pathological and physiological evidence of intravascular fat. The intravascular fat persisted for twenty-four hours after induction of pulmonary fat embolism. Pulmonary arterial pressure remained elevated at four hours after the embolic showering, before creation and fixation of the fracture. By twenty-four hours after the induction of fat embolism, pulmonary arterial pressure had returned to the baseline level. Neither the creation nor the fixation of the fracture affected pulmonary arterial pressure. In the animals that had fixation of a fracture four hours after embolization, both nailing with reaming and nailing without reaming produced alveolar-arterial gradients that were higher than the baseline values, whereas fixation with a plate did not change the alveolar-arterial gradient significantly from the baseline value. In addition, the alveolar-arterial gradients in the animals that had nailing with reaming and nailing without reaming four hours after embolization were, respectively, four and 3.5 times higher than that in the animals that had fixation of the femur with a plate. In the animals that had fixation twenty-four hours after embolization, none of the methods for fixation affected the alveolar-arterial gradient. The amount of embolic fat in the lungs, brain, and kidneys was not affected by fixation of the fracture when it was performed at either the four-hour or the twenty-four-hour time-interval. Scores for pulmonary edema were increased by fixation of the fracture, but there was no difference among the scores associated with the three methods of fixation. CLINICAL RELEVANCE: The findings of the present study indicated that the amount of intravascular fat persisting in the lungs, kidneys, and brain twenty-four hours after pressurization of the intramedullary canal is not affected by the method of fixation of the fracture. Fixation of a fracture is associated with minimum evidence of acute inflammation and has no effect on pulmonary artery pressure. The development of pulmonary dysfunction from fat emboli depends on other factors, not just on the presence of fat in pulmonary vessels. It appears that the method of fracture fixation has little influence on the outcome of treatment.

Hypotension during cemented arthroplasty. Relationship to cardiac output and fat embolism

An episode of hypotension is common during cemented joint replacement, and has been associated with circulatory collapse and sudden death. We studied the mechanism of hypotension in two groups of six dogs after simulated bilateral cemented arthroplasty. In one group, with no lavage, the insertion of cement and prosthesis was followed by severe hypotension, elevated pulmonary artery pressure, decreased systemic vascular resistance and a 21% reduction in cardiac output. In the other group, pulsatile intramedullary lavage was performed before the simulated arthroplasties. Hypotension was less, and although systemic vascular resistance decreased, the cardiac output did not change. The severity of the hypotension, the decrease in cardiac output and an increase in prostaglandin metabolites were related to the magnitude of pulmonary fat embolism. Pulsatile lavage prevents much of this fat embolism, and hence the decrease in cardiac output. The relatively mild hypotension after lavage was secondary to transient vasodilation, which may accentuate the hypotension caused by the decreased cardiac output due to a large embolic fat load. We make recommendations for the prevention and management of hypotension during cemented arthroplasty.

Structural models for intermediate care areas.

OBJECTIVE To describe structural models of intermediate care units used for critically ill patients. DATA SOURCES Three multidisciplinary units with varying structures and functions of intermediate care areas (ICAs) are described. DATA SYNTHESIS Advantages and limitations for each of the three models are outlined. The structural models described are the conventional isolated ICA model, the parallel model, and the integrated model of ICA. CONCLUSION Each structural model has advantages and limitations. Selection of the appropriate ICA model for an institution depends on the specific circumstances and needs of the institution. Each of the three models can facilitate improved utilization of critical care resources.

Pulmonary and systemic fat embolization after medullary canal pressurization: A hemodynamic and histologic investigation in the dog

BACKGROUND The potential to produce fat embolism may be important in determining the ideal method and timing of fracture treatment in patients with preexisting lung injury. METHODS Four dogs underwent femoral and tibial canal reaming and pressurization. Blood gas samples were analyzed, and pulmonary arterial pressure was monitored at 1 and 72 hours. Animals were killed 72 hours postoperatively, and the lungs, kidneys, and brain were examined histologically and compared with equivalent specimens from four control dogs that had not undergone femoral and tibial canal reaming and pressurization. RESULTS Postmortem, intravascular fat persisted for 72 hours after induction of pulmonary fat embolism. Mean PaO2 was unchanged from baseline at 72 hours after canal pressurization. Canal pressurization caused a sustained increase in pulmonary arterial pressure (p=0.02) for 1 hour after canal pressurization. The mean pulmonary edema score at 72 hours was 29+/-3. Only a scant polymorph infiltrate (zero to two polymorphs per high-power field) was present at any time. No hyaline membranes were seen at any time. The percentage area occupied by intravascular fat in the lungs was 0.0214+/-0.0058 at 72 hours. No signs of ischemia or inflammation were seen in either the cerebral or the renal specimens. CONCLUSION This study is the first to show that intravascular fat persists in the lungs, kidneys, and brain for 72 hours after canal pressurization and, by itself, does not cause pathologic evidence of acute inflammation.

Impact of an intermediate care area on ICU utilization after cardiac surgery.

We compared utilization of a 14-bed respiratory ICU before and after establishing an intermediate care area (ICA) for patients recovering from cardiac surgery. Availability of the four-bed ICA significantly reduced the duration of ICU stay in patients who had undergone aortocoronary bypass or valvular cardiac surgery, and no potentially preventable deaths resulted from early ICU discharge. Use of an ICA should also decrease ICU utilization for other low-risk monitored patients.

Pulmonary artery occlusion pressure estimation: How confident are anesthesiologists?*

ObjectiveThe pulmonary artery catheter is a controversial device, and randomized evaluation of its effectiveness has been demanded. Accurate estimation of pulmonary artery occlusion pressure is important for optimal use of the pulmonary artery catheter. Anesthesiologists use the pulmonary artery catheter frequently but have not been surveyed about confidence in pulmonary artery occlusion pressure estimation. Our objective was to determine the ability of practicing cardiovascular anesthesiologists to estimate pulmonary artery occlusion pressure accurately and measure their confidence in this estimate. DesignCross-sectional survey. SettingAll academic and community hospitals in English-speaking Eastern Canada and selected centers in Western Canada and the United States. PatientsCardiovascular anesthesiologists. InterventionsNone. Measurements and Main ResultsWe measured agreement with expert-defined timing of pulmonary artery occlusion pressure estimation, estimation of a sample pulmonary artery occlusion pressure trace, and management of a hypothetical clinical complication (air embolism). Seventy-seven percent of 345 anesthesiologists responded. Agreement about the optimal timing of pulmonary artery occlusion pressure estimation (89%) and the management of air embolism (85%) was near expectations (expected 90%). However, the pulmonary artery occlusion pressure waveform was interpreted accurately by only 61%, whereas 28% disagreed and 11% were uncertain. Significant positive associations (p = .016) between continuing medical education items and accurate interpretation were observed. ConclusionsEstimation of a sample pulmonary artery occlusion pressure trace by practicing anesthesiologists was in only modest agreement with expert assessment and published standards. Anesthesiologists demonstrated substantially less confidence in pulmonary artery occlusion pressure estimation than in the optimal timing of pulmonary artery occlusion pressure estimation. Before the effectiveness of the pulmonary artery catheter in clinical care can be systematically assessed, efforts are needed to enhance accuracy and consistency of pulmonary artery occlusion pressure estimation.