Safety of Intrahospital Transport Among Ventilated Critically Ill Patients
Abstract & Commentary
By Eric C. Walter, MD, MSc, Pulmonary and Critical Care Medicine, Northwest Permanente and Kaiser Sunnyside Medical Center, Portland. Dr. Walter reports no financial relationships relevant to this field of study.
SYNOPSIS: In this prospective, multicenter cohort study, intrahospital transport of ventilated patients was common and associated with complications. Whether these complications are directly attributable to the transport is questionable.
SOURCE: Schwebel C, et al. Safety of intrahospital transport in ventilated critically ill patients: A multicenter cohort study. Crit Care Med 2013; 41:1919-1928.
The transport of any patient within a hospital involves removing them from their care setting. When patients are critically ill and ventilated, the challenges and potential risks of transport are magnified. This paper used a very large, multicenter, prospective cohort of more than 6000 ventilated critically ill patients in France to better understand the risks associated with intrahospital transport (excluding transport to the operating room).
Intrahospital transport was common; 28.6% of patients experienced one or more transports. The vast majority of transports were to the CT scanner (93.6%). Patients who were transported were sicker than patients who never required transports. They were more likely to be sedated (79% vs 43%), to be on vasopressor support (53% vs 47%), and had a higher Simplified Acute Physiology Score II (50 vs 45). They were also more likely to be on parenteral support (53% vs 47%) and have arterial (54% vs 41%) or central catheters (64% vs 51%).
Because of the differences in severity of illness, the authors developed a propensity score for transport in order to try to identify complications of transport. A propensity score was calculated by identifying factors associated with transport. These factors were then used to generate a score that estimated the propensity of transport. This score was then applied to both patients who were and were never transported in an effort to match patients and control for both measured and unmeasured confounders. After controlling for the propensity for transport, the ICU length of stay was longer among transported patients than never transported patients (7 vs 3 days). A long list of complications occurred more often in transported patients, including severe bleeding, deep vein thrombosis, pneumothorax, ventilator-associated pneumonia, atelectasis, hypoglycemia, and hyperglycemia. Interestingly, despite the increased complications, there was a trend toward decreased mortality among patients who were transported (28% vs 35%).
Schwebel and colleagues should be commended for their attempt to understand such a common but difficult topic to study. Intuitively, it makes sense that intrahospital transfers of ventilated patients might place patients at risk for complications. The authors conclude that their data prove this. I think this conclusion is overstated. It is hard to understand how a trip to the CT scanner could cause deep venous thrombosis or hypernatremia. The data strongly suggest that patients who were transported were sicker than those who were not transported. It is more likely that the sickest patients required more transports out of the ICU for procedures or imaging and that the severity of illness in this population accounted for many of the observed complications. The authors appropriately attempted to control for this bias by calculating a propensity score. However, I am not convinced that the propensity score was enough to account for all unmeasured confounders in this study.
It would be unwise to fully dismiss this study. Transports are risky times for ventilated ICU patients but are often not given much thought. While this study does not prove that intrahospital transports of ventilated patients lead to more complications, it also does not prove a lack of complications.