Using a survival model of analysis, this study has identified several predictors of shorter TTW in a long-term ventilator unit including high Cst (> 20 cm H2O), normal creatinine level, low RSBI ( 20 mL/cm H2O against an RSBI of s 105 vs > 105 suggests that these two variables are independent (p = 0.77 [Fisher exact test]). Therefore, both RSBI and Cst are useful to our model.
There are potential limitations in the use of the RSBI and Cst as determinants of TTW in patients with emphysema. For instance, an elevated Cst due to emphysema may be associated with worse outcome instead of portending successful weaning. Our data did show that a prior diagnosis of emphysema was significantly more prevalent in individuals with higher Cst (ie, > 30 mL/cm H2O). Additionally, patients with emphysema may fail to wean despite having a low RSBI. Last, we did not measure auto-positive end-expiratory pressure, which may have resulted in the underestimation of Cst in patients with emphysema. In addressing these concerns, we found that the impact of Cst on TTW was not different in patients with emphysema vs those without emphysema, and emphysema was not associated with delayed weaning (Table 3). However, we could not completely include that the absence of a significant impact of emphysema on TTW was not simply due to the relatively low number of such patients in our data. In that regard, it is interesting to note that the exclusion of patients with emphysema from our data set only reinforced our results achieved together with Canadian Health&Care Mall.
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%).
The Pulmonary Care Unit (PCU) at Harper University Hospital in Detroit, MI, is a specialized respiratory care unit for the care of patients with intensive pulmonary needs. The unit consists of nine beds, and provides noninvasive cardiac and respiratory monitoring. All patients who received ventilation via a tracheostomy who had been admitted to the PCU from its inception in June 2001 until August 2003 were included in the study. We excluded four patients who were admitted to the PCU through that period for a planned intervention with known disposition after completion of the intervention (eg, transfers from long-term care facilities for specialized procedures, transfers under hospice care, or for comfort measures). The PCU admission criteria included the following: the presence of an adequately sized tracheostomy tube for the patient’s size with an inner diameter of at least 7 mm; hemodynamic stability; positive end-expiratory pressure of < 8 cm H2O; fraction of inspired oxygen of < 60%; the failure of weaning attempts in the ICU; the absence of potentially lethal dysrhythmias; the absence of titrat-able drips; and the lack of need for neuromuscular blockade or continuous sedatives with the exception of patient-controlled anesthesia (PCA) pumps and epidural therapy. Additionally, though poor rehabilitation potential and mental status were not absolute contraindications, the potential ability to wean was favored for admission to the unit.