Correction of sampling bias in a cross-sectional study of post-surgical complications.

Cross-sectional designs are often used to monitor the proportion of infections and other post-surgical complications acquired in hospitals. However, conventional methods for estimating incidence proportions when applied to cross-sectional data may provide estimators that are highly biased, as cross-sectional designs tend to include a high proportion of patients with prolonged hospitalization. One common solution is to use sampling weights in the analysis, which adjust for the sampling bias inherent in a cross-sectional design. The current paper describes in detail a method to build weights for a national survey of post-surgical complications conducted in Israel. We use the weights to estimate the probability of surgical site infections following colon resection, and validate the results of the weighted analysis by comparing them with those obtained from a parallel study with a historically prospective design.

Effect of infections on 30-day mortality among critically ill patients hospitalized in and out of the intensive care unit.

BACKGROUND: This analysis is part of a multicenter study conducted in Israel to evaluate survival of critically ill patients treated in and out of intensive care units (ICUs). OBJECTIVE: To assess the role of infection on 30-day survival among critically ill patients hospitalized in ICUs and regular wards. DESIGN: All adult inpatients were screened on four rounds for patients meeting ICU admission criteria. Retrospective chart review was used to detect presence and type of infection. Mortality was ascertained from day of meeting study criteria to 30 days thereafter. ANALYSIS: The effect of infection on mortality among patients, treated in and out of the ICU, was compared using Kaplan Meier survival curves. Multivariate Cox models were constructed to adjust interdepartmental comparisons for case-mix differences. RESULTS: Of 641 critically ill patients identified, 36.8% already had an infection on day 0. An additional 40.2% subsequently developed a new infection during the follow-up period, ranging from 64.6% in the ICU to 31.5% in regular wards (p < .001). Resistant infections were more prevalent in ICUs. Infection was independently associated with an increase in mortality, regardless of whether the patient was admitted to the ICU. There was no difference in the adjusted risk of mortality associated with an infection diagnosed on day 0 vs. an infection diagnosed later. Risk of dying was similar in resistant and nonresistant infections. Adjusting for infections, survival of ICU patients was better relative to patients in regular wards (adjusted hazard ratio = 0.7). Among the different types of infection, risk of mortality from pneumonia was significantly lower in ICUs relative to regular wards. There was a protective effect in ICUs among noninfected patients. CONCLUSION: The risk of acquiring a new infection is greater in the ICU. However, risk of mortality among ICU patients was lower for the most serious infections and for those without any infection.

Survival of critically ill patients hospitalized in and out of intensive care.

OBJECTIVE: A lack of intensive care units beds in Israel results in critically ill patients being treated outside of the intensive care unit. The survival of such patients is largely unknown. The present study's objective was to screen entire hospitals for newly deteriorated patients and compare their survival in and out of the intensive care unit. DESIGN: A priori developed intensive care unit admission criteria were used to screen, during 2 wks, the patient population for eligible incident patients. A screening team visited every hospital ward of five acute care hospitals daily. Eligible patients were identified among new admissions in the emergency department and among hospitalized patients who acutely deteriorated. Patients were followed for 30 days for mortality regardless of discharge. SETTING: Five acute care hospitals. PATIENTS: A total of 749 newly deteriorated patients. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Crude survival of patients in and out of the intensive care unit was compared by Kaplan-Meier curves, and Cox models were constructed to adjust the survival comparisons for residual case-mix differences. A total of 749 newly deteriorated patients were identified among 44,000 patients screened (1.7%). Of these, 13% were admitted to intensive care unit, 32% to special care units, and 55% to regular departments. Intensive care unit patients had better early survival (0-3 days) relative to regular departments (p=.0001) in a Cox multivariate model. Early advantage of intensive care was most pronounced among patients who acutely deteriorated while on hospital wards rather than among newly admitted patients. CONCLUSIONS: Only a small proportion of eligible patients reach the intensive care unit, and early admission is imperative for their survival advantage. As intensive care unit benefit was most pronounced among those deteriorating on hospital wards, intensive care unit triage decisions should be targeted at maximizing intensive care unit benefit by early admitting patients deteriorating on hospital wards.

Graft survival and its determinants: a 3 year national experience with liver transplantation in Israel.

BACKGROUND: There is a dearth of organs for liver transplantation in Israel. Enhancing our understanding of factors affecting graft survival in this country could help optimize the results of the transplant operation. OBJECTIVES: To report 3 years national experience with orthotopic liver transplantation, and to evaluate patient and perioperative risk factors that could affect 1 year graft survival. METHODS: The study related to all 124 isolated adult liver transplantations performed in Israel between October 1997 and October 2000. Data were abstracted from the medical records. One-year graft survival was described using the Kaplan-Meier survival curve and three multivariate logistic regression models were performed: one with preoperative case-mix factors alone, and the other two with the addition of donor and operative factors respectively. RESULTS: Of the 124 liver transplantations performed, 32 failed (25.8%). The 1 year survival was lower than rates reported from both the United States and Europe but the difference was not significant. Of the preoperative risk factors, recipient age > 60 years, critical condition prior to surgery, high serum bilirubin and serum hemoglobin < or = 10 g/dl were independently associated with graft failure, adjusting for all the other factors that entered the logistic regression equation. Extending the model to include donor and operative factors raised the C-statistic from 0.79 to 0.87. Donor age > or = 40, cold ischemic time > 10 hours and a prolonged operation (> 10 hours) were the additional predictors for graft survival. A MELD score of over 18 was associated with a sixfold increased risk for graft failure (odds ratio = 6.5, P = 0.001). CONCLUSIONS: Graft survival in Israel is slightly lower than that reported from the U.S. and Europe. Adding donor and operative factors to recipient characteristics significantly increased our understanding of 1 year survival of liver grafts.

Negative impact of 'old-to-old' donations on success of cadaveric renal transplants.

The effect of 'old-to-old' cadaveric renal transplants on operative complications and graft survival was assessed in all 325 patients undergoing solitary cadaveric renal transplantations in Israel during a 3-yr period. Preoperative information and hospital course data were abstracted from the charts. Results were analyzed using Kaplan-Meyer survival curves, univariate and multivariate Cox models. Overall, 62 (19.1%) grafts failed within a year. Failure rate was 46.2% for 'old-to-old' transplants compared with 15.5% for all other donor/recipient age combinations (p < 0.0001). 'Old-to-old' transplants remained independently associated with graft failure in a multivariate Cox model after controlling the effect of other risk factors. 'Old-to-old' transplants were also associated with increased operative complications relative to other age combinations. The decision to use 'old-to-old' transplants, even when donors are scarce, is problematic and should be reconsidered.

Factors associated with primary and secondary graft failure following cadaveric kidney transplant.

The risk profile for primary renal graft failure is largely unknown because of its inclusion with secondary failures or its exclusion from analysis. This study compares characteristics of the cadaveric transplant recipients who experienced primary failure, secondary failures or survived with a functioning graft for at least 6 months. Medical records of all cadaveric kidney-transplant patients performed in Israel over a 3-yr period 1997-2000 were reviewed. Fisher's exact test and multinomial regression models were used to assess the association of demographic, pre-operative and operative risk factors with the two types of failure outcomes. Of 325 grafts, 54 (16.6%) failed of which half were primary failures. Univariate analysis demonstrated a significant trend of increasing proportion of patients with specific risk factors from the functioning grafts group to the secondary and to the primary graft failure groups. Independent risk factors for primary graft failure included 'surgical complications', 'donor's age > or =60 yr', 'waiting for transplant > or =6 yr', and 'human leukocyte antigen-DR (HLA-DR) mismatch', based on the multivariate model. These factors may reflect the scarcity of organ donations in Israel, which leads to a prolonged waiting time, higher tolerance for HLA-DR mismatches, and utilization of kidneys from elderly donors.

Survival of critically ill patients hospitalized in and out of intensive care units under paucity of intensive care unit beds.

OBJECTIVE: The demand for intensive care beds far exceeds their availability in many European countries. Consequently, many critically ill patients occupy hospital beds outside intensive care units, throughout the hospital. The outcome of patients who fit intensive care unit admission criteria but are hospitalized in regular wards needs to be assessed for policy implications. The object was to screen entire hospital patient populations for critically ill patients and compare their 30-day survival in and out of the intensive care unit. DESIGN: Screening teams visited every hospital ward on four selected days in five acute care Israeli hospitals. The teams listed all patients fitting a priori developed study criteria. One-month data for each patient were abstracted from the medical records. SETTING: Five acute care Israeli hospitals. PATIENTS: All patients fitting a priori developed study criteria. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Survival in and out of the intensive care unit was compared for screened patients from the day a patient first met study criteria. Cox multivariate models were constructed to adjust survival comparisons for various confounding factors. The effect of intensive care unit vs. other departments was estimated separately for the first 3 days after deterioration and for the remaining follow-up time. Results showed that 5.5% of adult hospitalized patients were critically ill (736 of 13,415). Of these, 27% were admitted to intensive care units, 24% to specialized care units, and 49% to regular departments. Admission to an intensive care unit was associated with better survival during the first 3 days of deterioration, after we adjusted for age and severity of illness (p =.018). There was no additional survival advantage for intensive care unit patients (p =.9) during the remaining follow-up time. CONCLUSIONS: The early survival advantage in the intensive care unit suggests a window of critical opportunity for these patients. Under economic constraints and dearth of intensive care unit beds, increasing the turnover of patients in the intensive care unit, thus exposing more needy patients to the early benefit of treatment in the intensive care unit, may be advantageous.

Is discharge policy a balanced decision between clinical considerations and hospital ownership policy? The CABG example.

OBJECTIVES: To explore to what extent patient discharge from the hospital is a balanced decision between clinical considerations and management policy; specifically: (1) to assess the role of patient risk as a determinant of discharge in comparison with administrative factors such as hospital ownership; (2) to evaluate whether variations in discharge policy were translated into differences in clinical outcomes. METHODS: A national study of coronary artery bypass surgery was used as an example. The population included 4778 patients undergoing coronary artery bypass surgery in 14 institutions. The mode of discharge day, rather than the mean, was used as the best indicator of discharge policy. Parametric survival model was used to assess factors associated with the day of discharge. RESULTS: The mode of discharge day varied widely among institutions. This variation between 4 and 7 days after surgery corresponded to hospital ownership. The mode of discharge day was almost invariant to the patients' risk, but serious postoperative complications resulted in prolonged stay for a minority of the patients. The influence of hospital ownership prevailed over patient insurance carriers. Differences in discharge policies were not associated with increased risk of late mortality or rehospitalization. CONCLUSIONS: Discharge policy beyond the rare occurrence of dramatic patient postoperative complications was mainly dependent on hospital owner's cost-effectiveness considerations. However, despite the weight given to administrative factors in the decision-making process, it did not affect the outcome of care.

Effect of perioperative complications on excess mortality among women after coronary artery bypass: the Israeli Coronary Artery Bypass Graft Study (ISCAB).

BACKGROUND: Widely observed excess mortality among women after coronary artery bypass grafting is still largely unexplained, although case-mix factors have been identified. We evaluated the contribution of perioperative complications to the risk of 180-day mortality among women while adjusting for case-mix factors. METHODS: This is part of a prospective, 1-year nationwide Israeli coronary artery bypass graft study of 1029 female and 3806 male patients. Deaths within 180 days were independently ascertained. Case-mix risk strata were obtained from a pooled Cox survival model (including all subjects and study variables) by using the adjusted coefficients corresponding to the case-mix factors within the model. Sex-specific mortality associated with perioperative complications was evaluated within the strata. In addition, sex-specific Cox models were constructed. RESULTS: Higher mortality among women compared with that among men was significant within the pooled model (hazard ratio, 1.4; P =.038) and was evident early in the postoperative period. Women tended to cluster in the highest risk quartile compared with men (39.8% vs 20.9%, P <.001). However, although the incidence of perioperative complications was similar for the 2 sexes, the associated mortality for a given perioperative complication was higher among women. Sex-specific Cox models confirmed the above findings. For example, the hazard ratio for women with low postoperative hemoglobin was 6.9, whereas for men, the hazard ratio was 3.9. CONCLUSIONS: The role of perioperative factors in the excess mortality among women after coronary artery bypass grafting shifts the focus of attention from the selection of women for the operation to the in-hospital experience. Improving the outcome for women will entail efforts to prevent complications in the perioperative period.

Evaluating inter-hospital variability in mortality rates over time, allowing for time-varying effects.

In outcome studies, quality of care in various institutions is typically assessed by comparing observed to expected outcome rates, after adjusting for patients' case-mix factors in logistic regression models. However, differences in patterns of outcome rates over time, especially when there is a distinction between the determinants affecting early and later events, are rarely studied. We use six-month mortality after coronary artery bypass graft operation (CABG) as an example. We present a statistically valid approach to estimate expected survival curves for different subgroups, based on a Cox survival model with time-varying effects. Bootstrap confidence intervals around the expected survival curves are constructed. This approach is applied for examining the pattern of deviation of high-mortality hospitals after CABG. Implications for quality assessment in comparative outcome studies are discussed.