Correlates of self-rated health in people with diabetic peripheral neuropathy: a longitudinal study.

AIM: Self-rated health, a measure of self-reported general health, is a robust predictor of morbidity and mortality in various populations, including persons with diabetes. This study examines correlates of self-rated health in adults with diabetic peripheral neuropathy (DPN). METHODS: Participants recruited from the UK and USA (n = 295; mean (± sd) age: 61.5 ± 10.7 years; 69% male; 71% type 2 diabetes) rated their health at baseline and 18 months. DPN severity was assessed using the neuropathy disability score and the vibration perception threshold. Validated self-report measures assessed neuroticism, DPN-symptoms of pain, unsteadiness and reduced sensation in feet, DPN-related limitations in daily activities, DPN-specific emotional distress and symptoms of depression. RESULTS: In the fully adjusted baseline model, younger age, presence of cardiovascular disease and higher depression symptom scores showed likely clinically meaningful independent associations with worse health ratings. Being at the UK study site and presence of nephropathy indicated potentially meaningful independent associations with lower baseline health ratings. These predictors were largely consistent in their association with health ratings at 18 months. CONCLUSION: Results identify independent correlates of health ratings among adults with DPN. Future research should investigate the clinical implications of associations and examine changes in these variables over time and potential effects on changes in health perceptions. If these associations reflect causal pathways, our results may guide interventions to target issues that are likely to have an impact on subjectively experienced health as an important patient-reported outcome in DPN care.

Trajectories of PTSD risk and resilience in World Trade Center responders: an 8-year prospective cohort study.

BACKGROUND: Longitudinal symptoms of post-traumatic stress disorder (PTSD) are often characterized by heterogeneous trajectories, which may have unique pre-, peri- and post-trauma risk and protective factors. To date, however, no study has evaluated the nature and determinants of predominant trajectories of PTSD symptoms in World Trade Center (WTC) responders. METHOD: A total of 10835 WTC responders, including 4035 professional police responders and 6800 non-traditional responders (e.g. construction workers) who participated in the WTC Health Program (WTC-HP), were evaluated an average of 3, 6 and 8 years after the WTC attacks. RESULTS: Among police responders, longitudinal PTSD symptoms were best characterized by four classes, with the majority (77.8%) in a resistant/resilient trajectory and the remainder exhibiting chronic (5.3%), recovering (8.4%) or delayed-onset (8.5%) symptom trajectories. Among non-traditional responders, a six-class solution was optimal, with fewer responders in a resistant/resilient trajectory (58.0%) and the remainder exhibiting recovering (12.3%), severe chronic (9.5%), subsyndromal increasing (7.3%), delayed-onset (6.7%) and moderate chronic (6.2%) trajectories. Prior psychiatric history, Hispanic ethnicity, severity of WTC exposure and WTC-related medical conditions were most strongly associated with symptomatic trajectories of PTSD symptoms in both groups of responders, whereas greater education and family and work support while working at the WTC site were protective against several of these trajectories. CONCLUSIONS: Trajectories of PTSD symptoms in WTC responders are heterogeneous and associated uniquely with pre-, peri- and post-trauma risk and protective factors. Police responders were more likely than non-traditional responders to exhibit a resistant/resilient trajectory. These results underscore the importance of prevention, screening and treatment efforts that target high-risk disaster responders, particularly those with prior psychiatric history, high levels of trauma exposure and work-related medical morbidities.

Dimensional structure and course of post-traumatic stress symptomatology in World Trade Center responders.

BACKGROUND: Post-traumatic stress disorder (PTSD) in response to the World Trade Center (WTC) disaster of 11 September 2001 (9/11) is one of the most prevalent and persistent health conditions among both professional (e.g. police) and non-traditional (e.g. construction worker) WTC responders, even several years after 9/11. However, little is known about the dimensionality and natural course of WTC-related PTSD symptomatology in these populations. METHOD: Data were analysed from 10 835 WTC responders, including 4035 police and 6800 non-traditional responders who were evaluated as part of the WTC Health Program, a clinic network in the New York area established by the National Institute for Occupational Safety and Health. Confirmatory factor analyses (CFAs) were used to evaluate structural models of PTSD symptom dimensionality; and autoregressive cross-lagged (ARCL) panel regressions were used to examine the prospective interrelationships among PTSD symptom clusters at 3, 6 and 8 years after 9/11. RESULTS: CFAs suggested that five stable symptom clusters best represent PTSD symptom dimensionality in both police and non-traditional WTC responders. This five-factor model was also invariant over time with respect to factor loadings and structural parameters, thereby demonstrating its longitudinal stability. ARCL panel regression analyses revealed that hyperarousal symptoms had a prominent role in predicting other symptom clusters of PTSD, with anxious arousal symptoms primarily driving re-experiencing symptoms, and dysphoric arousal symptoms primarily driving emotional numbing symptoms over time. CONCLUSIONS: Results of this study suggest that disaster-related PTSD symptomatology in WTC responders is best represented by five symptom dimensions. Anxious arousal symptoms, which are characterized by hypervigilance and exaggerated startle, may primarily drive re-experiencing symptoms, while dysphoric arousal symptoms, which are characterized by sleep disturbance, irritability/anger and concentration difficulties, may primarily drive emotional numbing symptoms over time. These results underscore the importance of assessment, monitoring and early intervention of hyperarousal symptoms in WTC and other disaster responders.

Abdominal diameter index: a more powerful anthropometric measure for prevalent coronary heart disease risk in adult males.

AIM: The authors wished to compare the strength of association of several anthropometric measures of body size and fat distribution among themselves and in comparison with other known risk factors for prevalent coronary heart disease (CHD). METHODS: Prevalent CHD was assessed in 466 middle-aged, male, multiracial Triborough Bridge and Tunnel Authority officers in New York City by verified history, electrocardiogram or exercise stress test. Anthropometric measures included body mass index, waist, hip and thigh circumferences, waist-hip ratio, waist-thigh ratio, sagittal abdominal diameter and abdominal diameter index (sagittal abdominal diameter/thigh circumference). Results were compared with other CHD risk factors measured simultaneously (history of diabetes, smoking, blood pressure, lipid profile, apolipoproteins A and B, lipoprotein (a), homocysteine, fibrinogen, urinary microalbumin, serum vitamin E and ferritin) and a calculated 10-year CHD risk using a Framingham algorithm (10-year Framingham CHD risk). RESULTS: CHD was found in 29 individuals. Of the six anthropometric measures, abdominal diameter index gave the largest and most significant standardized odds ratio (OR) for CHD [1.80, 95% confidence interval (CI) 1.20, 2.71], equivalent to 10-year Framingham CHD risk. Men in the highest compared with the lowest tertile of abdominal diameter index had a univariate OR of 5.47 (95% CI 1.55, 19.28) which was the only anthropometric measure that remained significant after adjusting for 10-year Framingham CHD risk. CONCLUSIONS: For middle-aged American men, abdominal diameter index may be the most powerful anthropometric measure of risk for prevalent CHD.

Outcome prediction model for very elderly critically ill patients.

CONTEXT: Very elderly critically ill patients have three possible hospital outcomes: discharge to home, discharge to a skilled nursing or rehabilitation facility, or death. The factors associated with these outcomes are unknown. OBJECTIVE: To develop a three-outcome prediction model for very elderly critically ill patients. DESIGN: Retrospective chart abstraction with ordered logistic regression analysis. SETTING: Academic medical center. PATIENTS: Four hundred and fifty-five patients 85 yrs or older admitted to intensive care units (ICU) during 1996 and 1997. MEASUREMENTS AND MAIN RESULTS: A fitted ordinal logistic regression predictive model was developed using data from 243 patients hospitalized in 1996, and validated on data from 212 patients hospitalized in 1997. Model variables include age, gender, baseline support level, type of ICU, heart rate at ICU admission, use of mechanical ventilation, vasopressors or a pulmonary artery catheter during the ICU stay, and the development of respiratory, neurologic or hematologic failure or sepsis while in the ICU. When tested on the 1997 data, the model was well calibrated and had a high discriminant index. CONCLUSIONS: This mathematical model can be used to predict the risks of these three hospital outcomes for this population of patients. These predictions can provide a context when discussing goals and expectations with patients, families, and other healthcare providers and to aid in hospital discharge planning.

Double-blind, placebo-controlled trial of famotidine in children with abdominal pain and dyspepsia: global and quantitative assessment.

To determine the benefit of using an H2-receptor antagonist in children with abdominal pain and dyspepsia, 25 such children were enrolled in a double-blind, placebo-controlled trial of famotidine. Global and quantitative pain assessments were done before and after each treatment period. The quantitative assessment was calculated based on the abdominal pain score that was the sum of three components. Based on the global evaluation, there was a clear benefit of famotidine over placebo (68% vs 12%). Using the quantitative assessment, however, the mean improvement of the score using famotidine versus placebo was not statistically significant (3.37+/-3.53 vs 1.66+/-2.7). There was a significant improvement in this score during the first treatment period regardless of medication used (period effect: P = 0.05). A subset of patients with peptic symptoms demonstrated a significant drug effect that outweighed the period effect (drug effect: P = 0.01; period effect: P = 0.02). We conclude that famotidine subjectively improves the symptoms of children with recurrent abdominal pain but not objectively using the derived score. However, famotidine is significantly more effective than placebo among children with peptic symptoms. The use of this simple scoring scale may facilitate selecting those children who will benefit from H2-receptor antagonist therapy.

The utility of an in-hospital observation period after discontinuing intravenous antibiotics.

PURPOSE: To determine whether observing patients overnight in the hospital after intravenous antibiotics have been discontinued is a useful way to identify important clinical events. SUBJECTS AND METHODS: We performed a retrospective chart review of patients admitted during a 6-month period to a tertiary care teaching hospital with a primary diagnosis of either pneumonia, urinary tract infection, or cellulitis who were treated with intravenous antibiotics. Charts were abstracted for patient characteristics, including comorbid illnesses and laboratory values, as well as for evidence of recurrent infection or other adverse events. RESULTS: Of the 374 patients in the study, 63 (17%) were discharged on the day intravenous antibiotics were discontinued. These patients were 10 years younger (P = 0.0009) and had fewer comorbid illnesses (P = 0.02) than those who were observed in the hospital. Recurrent infection was noted in 3 (1%; 95% confidence interval 0.2% to 3%) of the 308 patients who were observed. A mild adverse antibiotic reaction was also noted in three observed patients. The readmission rate to the same institution for recurrent infection was 3% for patients with an observation period and 2% for patients without an observation period (P = 0.70). CONCLUSIONS: Observing patients overnight in the hospital after discontinuing intravenous antibiotics is a common clinical practice. There was an extremely low incidence of adverse events during the observation period, and the events that did occur would have been discovered in an outpatient setting. In-hospital observation after discontinuing intravenous antibiotics is unnecessary for most patients with pneumonia, urinary tract infection, or cellulitis and greatly increases health-care costs.

Study of a needleless intermittent intravenous-access system for peripheral infusions: analysis of staff, patient, and institutional outcomes.

OBJECTIVE: To assess the effect on staff- and patient-related complications of a needleless intermittent intravenous access system with a reflux valve for peripheral infusions. DESIGN: A 6-month cross-over clinical trial (phase I, 13 weeks; phase II, 12 weeks) of a needleless intermittent intravenous access system (NL; study device) compared to a conventional heparin-lock system (CHL, control device) was performed during 1991 on 16 medical and surgical units. A random selection of patients was assessed for local intravenous-site complications; all patients were assessed for the development of nosocomial bacteremia and device-related complications. Staff were assessed for percutaneous injuries and participated in completion of product evaluations. A cost analysis of the study compared to the control device was performed. SETTING: A 1,100-bed, teaching, referral medical center. PATIENTS AND STAFF PARTICIPANTS: 594 patients during 602 patient admissions, comprising a random sample of all patients with a study or control device inserted within a previous 24-hour period on study and control units, were assessed for local complications. The 16 units included adult inpatient general medicine, surgical, and subspecialty units. Pediatrics, obstetrics-gynecology, and intensive-care units were excluded. All patients on study and control units were assessed for development of nosocomial bacteremia and device-related complications. All staff who utilized, manipulated, or may have been exposed to sharps on study and control units were assessed for percutaneous injuries. Nursing staff completed product evaluations. INTERVENTION: The study device, a needleless intermittent intravenous access system with a reflux valve, was compared to the control device, a conventional heparin lock, for peripheral infusions. RESULTS: During the study, 35 percutaneous injuries were reported. Eight injuries were CHL-related; no NL-related injuries were reported (P=.007). An evaluation of 602 patient admissions, 1,134 intermittent access devices, and 2,268 observed indwelling device days demonstrated more pain at the insertion site for CHL than NL; however, no differences in objective signs of phlebitis were noted. Of 773 episodes of positive blood cultures on study and control units, 6 (0.8%) were device-related (assessed by blinded investigator), with no difference between NL and CHL. Complications, including difficulty with infusion (P<.001) and disconnection of intravenous tubing from device (P<.001), were reported more frequently with CHL than with NL. Of nursing staff responding to a product evaluation survey, 95.2% preferred the study over control device. The projected annual incremental cost to our institution for hospitalwide implementation of NL for intermittent access for peripheral infusions was estimated at $82,845, or $230 per 1,000 patient days. CONCLUSIONS: A needleless intermittent intravenous access system with a reflux valve for peripheral infusions is effective in reducing percutaneous injuries to staff and is not associated with an increase in either insertion-site complications or nosocomial bacteremia. Institutions should consider these data, available institutional resources, and institution-specific data regarding the frequency and risk of intermittent access-device-related injuries and other types of sharps injuries in their staff when selecting the above or other safety devices.

Effects of practice setting on quality of lipid-lowering management in patients with coronary artery disease.

We undertook a study to determine whether there were differences in the quality of lipid management in patients with coronary artery disease (CAD) in 2 different practice settings (which represent different socioeconomic classes), and to determine the level of compliance with the National Cholesterol Education Program guidelines by academic physicians in managing patients with CAD. A retrospective cross-sectional study was performed using a systematic chart review of 270 medical records (131 from the cardiology clinic, 139 from the cardiology private practice) of patients with known CAD at an academic tertiary care center in New York City. The total proportion of patients with CAD having a lipid profile ordered in the clinic and private suite was 43%. Of these people, 22% had a low-density lipoprotein cholesterol (LDL) < or = 100 mg/dl and 54% had an LDL < or = 130 mg/dl (10% and 23% of the total population, respectively). The total proportion of patients taking lipid-lowering medications was 29%. When comparing the quality of treatment between the 2 settings, there were no statistically significant differences in the percentages of patients who had lipid profiles measured (40% clinic vs 47% private suite, p >0.10), in the percentage of patients with LDL < or = 130 mg/dl (50% clinic vs 57% private suite, p >0.10) or in the weighted percentage of patients taking lipid-lowering medications (29% clinic vs 48% private suite, p = 0.099). The performances of individual physicians, however, varied widely. The percentages of patients with lipid profiles measured by individual physicians ranged from 0% to 83%, while the percentages of patients on drug treatment by a physician ranged between 10% and 88%. These findings indicate that socioeconomic differences, represented by different practice settings, do not account for differences in the screening for, control of, or use of medications in managing hyperlipidemia. Rather, individual physicians are accountable for differences in lipid management.

Evaluation of costs and benefits of advances in cytologic technology. International Academy of Cytology Task Force summary. Diagnostic Cytology Towards the 21st Century: An International Expert Conference and Tutorial.

ISSUES: Uterine cervical cytology smears are among the most cost-effective cancer prevention interventions available, but they are not infallible, and new or modified technologies have been and will be proposed to improve diagnostic accuracy. Before these new technologies are accepted, their performance attributes will be carefully studied and defined. Equally important in this era of fiscal constraints are cost/benefit analyses, for which we review certain guidelines. CONSENSUS POSITION: In an effort to control rising costs in the health care sector, there has been a strong incentive to move toward a market system, and a variety of forces are acting to drive down expenditures. These same pressures will continue to be brought to bear on the providers of cervical cytology services. It must be emphasized that the technical knowledge required to define cost-effective medical practice lies within the medical profession itself, which must recognize the following: (a) Resources are finite; (b) Elimination of fraud, abuse and waste is not enough to bring health care expenditures down to levels considered acceptable to government and business; (c) The medical profession must take the responsibility to identify the health and economic consequences of the services it provides and make wise recommendations for allocation of resources to optimize health consequences. The analysis of costs and benefits must be viewed from a societal perspective and presented in terms of the marginal impact on current practice. This does not mean that new technologies must reduce cost; on the contrary, improvements in health can be expected to come at a price, but at a price commensurate with value gained in lives saved or in added quality adjusted life years. To be of value, a new technology for cervical cytology must be more effective in preventing cervical carcinoma. Dysplasia is considered a precursor of carcinoma, and detection of dysplasia has been a surrogate for prevention of cervical carcinoma, but dysplasia does not always lead to carcinoma, least of all mild dysplasia, and policy makers ultimately will insist that a favorable change in health outcome be effected by new technology before it is allocated resources. Alternatively, new technologies may lower cost, perhaps by modifying screening or rescreening procedures according to known risk; by improved cytopreparatory techniques that simplify, improve or speed screening; or by monitoring devices that minimize screening error. In each case the performance attributes of the instrument or human instrument process should be evaluated in the intended use environment. ONGOING ISSUES: While current cervical cytology methodology is one of the most effective means of cancer prevention, there continues to be development of new techniques to increase the sensitivity and specificity of this test. With present fiscal constraints, these will be subject to stringent cost/benefit analyses in which the medical profession must play a key role. Such analyses can be quite complicated, considering the additional costs or cost savings of clinical follow-up procedures and the reliability of dysplasias detected by cytology as a surrogate for cervical carcinoma in calculating quality of life years saved.

Effect of a bicultural community health worker on completion of diabetes education in a Hispanic population.

OBJECTIVE: To determine the effect of a bicultural community health worker (CHW) on completion of diabetes education in an inner-city Hispanic patient population and to evaluate the impact of completion of the education program on patient knowledge, self-care behaviors, and glycemic control. RESEARCH DESIGN AND METHODS: Patients were randomized into CHW intervention and non-CHW intervention groups. All patients received individualized, comprehensive diabetes education from a certified diabetes nurse educator after baseline demographic information, diabetes knowledge, diabetes self-care practices, and glycohemoglobin levels were assessed. Rates of education program completion were determined. Diabetes knowledge, self-care practices, and glycohemoglobin levels were reassessed at program completion and at a later postprogram follow-up medical appointment and compared to baseline. Logistic regression analysis and the Mantel-Haenszel chi 2 statistic were used to determine the effect of the CHW assignment on program completion. Analyses of covariance were performed with end-of-treatment behavior scores, knowledge scores, and glycohemoglobin levels as outcome variables, controlling for baseline values and testing for the effect of CHW assignment. RESULTS: Of 64 patients enrolled in the study, 40 (63%) completed and 24 (37%) dropped out before completing the diabetes education program. Of the patients having CHW intervention, 80% completed the education program, compared with 47% of patients without CHW intervention (P = 0.01). "Dropouts" were younger (age 47.5 +/- 12.5 years [mean +/- SD]) compared with patients who completed the program (55.9 +/- 9.9 years) (P = 0.004). Dropout status showed no significant relationship to educational level achieved or literacy level. For the program "completers," knowledge levels and selected self-care practices significantly improved, and glycohemoglobin levels improved from a baseline level of 11.7% to 9.9% at program completion (P = 0.004) and 9.5% at the postprogram follow-up (P < 0.001). The effect of the CHW assignment on program completion, controlling for financial status and language spoken, was extremely robust (P = 0.007). The effect of the CHW on knowledge, self-care behavior, or glycohemoglobin outcome variables was not statistically significant. CONCLUSIONS: These findings suggest that intervention with a bicultural CHW improved rates of completion of a diabetes education program in an inner-city Hispanic patient population irrespective of literacy or educational levels attained. Our data further suggests that completion of individualized diabetes educational strategies leads to improved patient knowledge, self-care behaviors, and glycemic control.

BCG vaccination to prevent tuberculosis in health care workers: a decision analysis.

OBJECTIVE: To perform a decision analysis to determine the optimal strategy to prevent tuberculosis (TB) in health care workers with negative tuberculin skin tests. METHODS: We used a Markov model to study the occurrence of events each year and compared BCG vaccination to annual tuberculin testing plus isoniazid (INH) preventive therapy for those who become skin test positive. The outcome measures studied were the number of cases and deaths from TB and BCG and/or INH adverse reactions over 10 years. RESULTS: Annual tuberculin testing decreases the number of TB cases by 9% and BCG vaccination decreases the number by 49%, relative to no prevention intervention. BCG vaccination results in fewer deaths than annual tuberculin testing if the workplace incidence of Mycobacterium tuberculosis infection is greater than 0.06%, BCG vaccination effectiveness exceeds 3%, or the rate of fatal BCG adverse reactions is less than 15 times the rate reported in the literature. CONCLUSIONS: BCG vaccination results in less morbidity and mortality than annual tuberculin skin testing for health care workers in workplaces with documented TB transmission despite comprehensive infection control policies and procedures. Current policy on the prevention of TB among health care workers should be reconsidered.

Cost-effectiveness of rescreening conventionally prepared cervical smears by PAPNET testing.

OBJECTIVE: This study explored the cost-effectiveness of the use of PAPNET testing-supplemental, neural network-based testing used to increase the accuracy of cervical smear screening practice. STUDY DESIGN: Using a model adapted from one developed under contract from the United States Congress Office of Technology Assessment to evaluate cost-effectiveness of cervical cancer screening in elderly women, the study evaluated U.S. women aged 20-64. The study reviewed various screening intervals and examined the course of follow-up (i.e., repeat abnormal smear vs. immediate colposcopy) to offer a range into which most routine medical practice will fall. RESULTS: Assuming a false negative rate of 25% for low grade squamous intraepithelial lesion (SIL) and 15% for high grade SIL and applying increased sensitivity of 30% from PAPNET, we can expect a cost of $48,474 per life-year saved among biennially screened women. For women screened triennially, as recommended by most groups, the cost per life-year saved is $25,185. CONCLUSION: The PAPNET rescreening program is an economical approach to decreasing mortality and morbidity from cervical cancer and compares favorably to other commonly used interventions and diagnostic procedures.

Interpretation of the tuberculin skin test.

OBJECTIVE: To reinterpret epidemiologic information about the tuberculin test (purified protein derivative) in terms of modern approaches to test characteristics; to clarify why different cutpoints of induration should be used to define a positive test in different populations; and to calculate test characteristics of the intermediate-strength tuberculin skin test, the probability of Mycobacterium tuberculosis infection at various induration sizes, the area under the receiver operating characteristic (ROC) curve, and optimal cutpoints for positivity. METHODS: Standard epidemiologic assumptions were used to distinguish M. tuberculosis-infected from -uninfected persons; also used were data from the U.S. Navy recruit and World Health Organization tuberculosis surveys; and Bayesian analysis. RESULTS: In the general U.S. population, the test's sensitivity is 0.59 to 1.0, the specificity is 0.95 to 1.0, and the positive predictive value is 0.44 to 1.0, depending on the cutpoint. Among tuberculosis patients, the sensitivity is nearly the same as in the general population; the positive predictive value is 1.0. The area under the ROC curve is 0.997. The probability of M. tuberculosis infection at each induration size varies widely, depending on the prevalence. The optimal cutpoint varies from 2 mm to 16 mm and is dependent on prevalence and the purpose for testing. CONCLUSIONS: The operating characteristics of the tuberculin test are superior to those of nearly all commonly used screening and diagnostic tests. The tuberculin test has an excellent ability to distinguish M. tuberculosis-infected from -uninfected persons. Interpretation requires consideration of prevalence and the purpose for testing. These findings support the recommendation to use different cutpoints for various populations. Even more accurate information can be gotten by interpreting induration size as indicating a probability of M. tuberculosis infection.

In vitro glycolysis of whole blood can detect primed neutrophils in septic ICU patients.

The purpose of this study was to develop a bedside assay based on the in vitro glycolysis of a whole blood sample that could detect primed neutrophils (PMNs). A mathematical index of the PMN response to exogenous stimulation with phorbol myristate 13-acetate (PMA), called the Delta value, was derived by comparing the increase in glycolysis for paired blood samples with and without PMA to that expected from normal subjects. Delta values for systemic inflammatory response syndrome/sepsis patients (9.09 +/- 7.61) (N = 36) were significantly higher than normal controls (2.02 +/- 1.76) (N = 51), nonsepsis ICU patients (3.81 +/- 2.80) (N = 14) and patients in septic shock (2.33 +/- 3.04) (N = 10) (p < .05). Delta values were consistently reflected in parallel measurements of increased reactive oxygen species production by neutrophils detected cytofluorometrically. PMN priming can be simply and rapidly detected by an assay based on the numbers of PMNs and erythrocytes and the measured rates of in vitro glycolysis of paired whole blood samples with and without PMA.

Mixed venous O2 saturation: measured by co-oximetry versus calculated from PVO2.

OBJECTIVE: The objectives of our study were (1) to compare mixed venous saturations calculated by a blood gas machine with those measured directly by a co-oximeter; and (2) to compare the sensitivities and specificities of VO2s derived from these values. METHODS: Charts were retrospectively reviewed of all MICU patients [n = 16] between December 1, 1991 and January 31, 1992, who required pulmonary artery catheters for their usual care and who had hemoglobin saturations of mixed venous blood concurrently measured by both a co-oximeter (Co-Ox Model 482, Instrumentation Lab, Lexington, MA) and a blood gas analyzer (Nova Biomedical StatLab5, Waltham, MA) which uses a variant of the Severinghaus equation to calculate SVO2 from PVO2). Data used at the time of each SVO2 measurement to calculate oxygen consumption (VO2) further was collected. RESULTS: Available for analysis were 118 mixed venous blood samples. Although the SVO2 values had a correlation coefficient of 0.807 (95% confidence interval [CI] 0.736 to 0.861, Fisher's z-transform), when VO2s were calculated, the blood gas analyzer calculated saturations had a sensitivity of only 58.3% and a specificity of 89%, when compared with those calculated using the saturations measured by the co-oximeter. Attempts to mathematically improve upon the Severinghaus equation and upon an additional four regression equations used by other blood gas analyzers resulted in universally worse sensitivity. CONCLUSION: If SVO2s calculated by a blood gas machine--rather than those co-oximetrically measured--are used to calculate VO2s, 42% of patients with low O2s will be misclassified as normal and 11% of normals will be misclassified as low. This total error appears to be the result of measurement error by the PO2 electrode of the blood gas analyzer and shifts of the oxyhemoglobin dissociation curve, which are not accounted for in the equation that is used to calculate saturation from measured PO2. We were not able to improve mathematically the sensitivity of any of the available regression equations used by blood gas analyzers to calculate SVO2 from PVO2. Therefore, it remains necessary to use co-oximetrically measured saturations when calculating VO2.