Diagnosis of diaphragmatic trauma with helical CT in a swine model.

OBJECTIVE: The purpose of this study was to determine whether diaphragmatic injury can be accurately diagnosed with helical CT in a swine model. The hypothesis of our study was that thin-section helical CT with sagittal and coronal reformations can reliably detect injury of the diaphragm. MATERIALS AND METHODS: The study was performed in a swine model because of the similarity of the swine thorax to the human thorax. Ten swine had a limited abdominal helical CT (enteral contrast; 3-mm collimation; pitch, 1) before and after surgical creation of a 6-cm posterolateral laceration in the left hemidiaphragm. A repeat scan was obtained after 5 cm of gastric fundus was sutured through the laceration. The gastric fundus was used because it is the most commonly herniated viscus in human diaphragmatic injury. No IV contrast was used. Control, laceration, and herniation scans were reconstructed with 1.0-mm overlap and reformated in axial, sagittal, and coronal planes. Three observers scored each reformation as control or injury (defined as laceration or herniation) in a blinded and randomized fashion. RESULTS: Using helical CT, the observers were able to distinguish diaphragmatic injury from controls (p < .0001). The sensitivity and specificity were 92% and 87%, respectively, for sagittal reformations; 85% and 87%, respectively, for coronal reformations; and 73% and 80%, respectively, for axial reformations. Sagittal reformations proved superior to coronal or axial reformations (p = .01). The results were independent of individual observers: We found no significant difference in accuracy among the three observers. CONCLUSION: Helical CT can accurately detect diaphragmatic injury in a swine model.

"Race" specificity and the femur/stature ratio.

This inquiry explores a series of problems related to the femur/stature ratio first raised by Feldesman et al. (1990). In particular, we used a revised data set and a more elaborate research protocol to address questions pertaining to: (1) whether the femur/stature ratios of three quasigeographic "races" ("Blacks," "Whites," "Asians") are statistically significantly different; (2) whether these are statistically (as opposed to biologically) coherent groups; and (3) whether the "race"-specific ratios are more accurate than the simple generic femur/stature ratio. We used ANOVA, ANOCOVA, post hoc analysis, k-means cluster analysis, linear discriminant functions, and approximate randomization to determine whether the group differences in the ratio were significant, and to assess the coherence of the "racial" groups themselves. We used validation procedures including mean absolute deviation, mean squared error, and Pitman's measure of closeness of a known sample of 798 femur/stature pairs to compare the accuracy of the generic ratio and the group-specific ratios. The results confirmed that the "Black" femur/stature ratio is significantly different from those of "Whites" and "Asians"; however, group coherence was poor, with results barely better than chance. We found that "race"-specific ratios slightly outperform the generic ratio when "race" is certain, but the gains are small for the assumptions required. More significantly, however, we found that when "race" attribution is uncertain or unknown, as in paleoanthropology, the wrong ratio (or the wrong regression equation) performs poorer than the generic femur/stature ratio. As a result, we recommend that researchers continue using the generic femur/ stature ratio to estimate stature in pre- and protohistoric populations. An alternative equation, a generic regression, yields even better stature estimates; however, we urge further study before recommending that researchers use this instead of the more thoroughly tested generic femur/stature ratio.

Fluctuation in mixed venous oxygen saturation in critically ill medical patients: a pilot study.

OBJECTIVE: To determine fluctuation in mixed venous oxygen saturation in critically ill medical patients during a period of rest. DESIGN: Nonexperimental, descriptive. SETTING: The medical and coronary intensive care units in a large county hospital in south-central Texas. PATIENTS: Twenty critically ill patients, aged 19 to 85, who had placement of a pulmonary artery catheter capable of continuous monitoring of mixed venous oxygen saturation. The majority had a diagnosis of respiratory failure and required mechanical ventilation. METHODS: Mixed venous oxygen saturation was recorded each minute for a 2-hour period in either early morning or late afternoon hours. Minute-by-minute values obtained during a 30-minute period of rest were used to determine fluctuation. The lowest and highest mixed venous oxygen saturation values during the period were used to calculate percent changes from average values (fluctuation). RESULTS: The range of fluctuation was +/- 6% of the average mixed venous oxygen saturation value for 80% of the sample. Four patients had a greater range of fluctuation: however, their actual mixed venous oxygen saturation values were within a clinically acceptable range. No significant differences in percentage of low or high fluctuation were noted for the following variables: time of day, medication administration, oxygen delivery, oxygen consumption and average mixed venous oxygen saturation. The percentage of low fluctuation was significantly lower for four patients who were not mechanically ventilated. CONCLUSIONS: Knowledge of normal fluctuation enables the care giver to evaluate changes in mixed venous oxygen saturation in response to activities and/or treatments. Additional study of fluctuation in homogenous groups of critically ill patients is warranted.

Risk of major elective operation after myocardial revascularization.

Although an increased surgical risk of ischemic myocardial disease is widely accepted, amelioration of this risk after coronary artery bypass is poorly defined. We compared the outcomes of major elective general and peripheral vascular operations in 181 patients with prior coronary artery bypass grafting (CABG) with outcomes in an age-, gender-, and procedure-matched group without prior CABG (NOCABG). Despite the perception of a greater operative risk in the CABG patients (more CABG patients in American Society of Anesthesiologists [ASA] class III and fewer in ASA class I, p < 0.001), mortality (1.1% CABG versus 2.8% NOCABG) and morbidity (18.8% CABG versus 18.5% NOCABG) rates in the two groups were not significantly different. For patients who have undergone successful CABG, it appears that: (1) the risk of subsequent elective major general and vascular surgical operations is similar to that of an age-, gender-, and procedure-matched cohort, and (2) the mortality rate after elective operations is low.

Effect of backrest position on mixed venous oxygen saturation in patients with mechanical ventilation after coronary artery bypass surgery.

A quasi-experimental study was conducted to examine the effect of backrest position on mixed venous oxygen saturation (SvO2) in patients with mechanical ventilation after coronary artery bypass graft surgery. A convenience sample of 30 subjects was randomly assigned to one of three positions: 20 degrees, 40 degrees, or flat (control). Baseline data were collected with patients in the flat position. The backrest was elevated according to the position designated for each group, and data were collected at 0, 5, 15, and 30 minutes. Subjects in the experimental groups were then returned to the flat position, and measurements were repeated. By use of two-way analysis of variance statistics, no significant differences from baseline were found in SvO2 among the three groups, among the measurement times, or among the positions and times. Findings support elevating the backrest up to 40 degrees according to patient comfort, for patients 6.0 to 9.5 hours after coronary artery bypass graft surgery if they are up to 70 years of age, have no lung disease, are receiving optimal ventilation with up to 5 cm H2O of positive end-expiratory pressure, have normal temperature, and are hemodynamically stable.

The relationship between mixed venous oxygen saturation and cardiac output in mechanically ventilated coronary artery bypass graft patients.

This study examined the relationship between mixed venous oxygen saturation (SvO2) and cardiac output (CO) in coronary artery bypass graft (CABG) surgery patients, age 35 to 70 years, who were 6.0 to 9.5 hours postoperative, hemodynamically stable, and receiving mechanical ventilation. A total of five paired measurements of SvO2 and thermodilution CO's were recorded on 30 subjects during a 45 minute time period. Correlations between SvO2 and CO for the entire sample ranged from 0.27 (NS*) to 0.45 (p less than or equal to 0.01). Additional analysis was done to determine if continuous infusions of vasoactive drugs influenced the relationship between the variables. Correlations for those on continuous vasoactive medications ranged from 0.21 to 0.31 (NS). Correlations for subjects who did not require vasoactive infusions were higher, ranging from 0.53 (NS) to 0.81 (p less than or equal to .01). Although many results were statistically significant, correlations less than 0.7 should not be used for clinical decision making. SvO2 reflects the overall tissue oxygenation and should not be used as a substitute for CO measurements in the CABG patient in the early hours after cardiac surgery.