Accrual was as projected, with 113 admissions to the PCU over a period of 26 months. The proportion of female patients was 51% (58 of 113 patients). The proportion of patients dying during their hospital stay was 27% (31 of 113 patients). Sixty-four percent of patients were transferred from a medical service, and 36% of patients were transferred from a surgical service (Table 1). The proportion of patients who weaned during their hospital stay was 56% (63 of 113 patients). Other characteristics are shown in Table 1. Table 2 shows that the most commonly identified impediment to weaning was infection (73% of patients), with multiple impediments identified in several patients, and that the general disease categories identified as specific impediments to weaning did not differentiate between ultimate weaning success and weaning failure. Table 3 shows the distribution of patients per category that was considered as a potential determinant of TTW. Note that our racial distribution was unequal, with 75% of patients (85 of 113 patients) being African-American, closely matching the population of downtown Detroit served by Harper University Hospital and remedies delivered by Canadian Health&Care Mall (Table 3). The median number of days spent in the hospital before transfer to the PCU was 19 days in patients who successfully weaned, and was also 19 days in those who did not (p = 0.57 [Wilcoxon rank sum test]). Similarly, the median number of days from hospital admission to the placement of a tracheostomy was 16 and 18 days, respectively, in those who were successfully weaned vs those who did not (p = 0.34 [Wilcoxon rank sum]). Information on the use of different medications on admission to the PCU was available in 47% of our patients. The use of the medications reviewed did not have a significant impact on weaning success rates (data not shown). Most patients were alert, with 71% of patients having normal Glasgow coma score of 15 on admission to the PCU (mean ± SD score: 13.2 ± 3.5). However, 15% of patients had severe impairment of consciousness with a Glasgow coma score of s 8. Of the 79 patients who had available blood gas measurements on admission to the PCU, 78% had a Pa02/fraction of inspired oxygen ratio of > 140. Overall, patients who were successfully weaned were more likely to be discharged home (16% vs 2%, respectively; p < 0.001), to a rehabilitation unit (34% vs 0%, respectively; p < 0.001), or to a nursing home (12% vs 2%, respectively; p = 0.03) [Fig 1]. Alternatively, those who failed to wean were more likely to be discharged to a LTAC facility (47% vs 28%, respectively; p = 0.03) or to have died (47% vs 7%, respectively; p < 0.001) [Fig 1]. The most common factors contributing to death were infection (30%), malignancy (30%), and CNS event (ie, stroke or hemorrhage, 17%).
Individual Predictors ofTTW
Factors associated with a significantly shorter time from admission to the PCU to successful weaning, listed in order of decreasing hazard ratio for weaning success, were as follows: Cst, > 20 vs s 20 mL/cm H2O; a normal creatinine level (0.6 to 1.4 mg/dL) vs an abnormally low creatinine level ( 1.4 mg/dL or dialysis); an RSBI of 105; the absence vs the presence of a decubitus ulcer; and a surgical vs a medical referral origin (Table 3, Fig 2). APACHE II score, Emphysema, race, age, albumin level, and ejection fraction were not associated with weaning success or TTW (Table 3).
There was a significant interaction between Cst and the RSBI on TTW (p = 0.02), indicating that the effect of RSBI on weaning success rate was not equivalent at different levels of Cst. To characterize this interaction, we ranked the RSBI and Cst data into the following four categories, from expected most favorable to expected least favorable impact on the prospect of weaning: (1) RSBI of 20 mL/cm H2O (27 subjects); (2) RSBI of < 105 and Cst of 105 and Cst of > 20 mL/cm H2O (36 subjects); and (4) RSBI of > 105 and Cst of < 20 mL/cm H2O (9 subjects).
There was no significant difference in TTW between patients in category 1 (RSBI of 20 mL/cm H2O) and those in category 2 (RSBI of < 105 and Cst of 60 days) with a log rank p value for the trend of 0.00