By using a database of more than 100 000 patients, we identified 3 types of ICUs: ICUs in which all patients are required to receive management by critical care physicians, ICUs in which no patients are managed by critical care physicians, and ICUs in which patients may or may not be managed by critical care physicians. Despite adjustment for severity of illness, we cannot demonstrate any survival benefit with management by critical care physicians. In fact, patients managed by critical care physicians had higher odds of mortality than patients managed by physicians not trained in critical care medicine.
Our results are surprising and completely contrary to previously published findings (7
). Almost all published studies on the impact of critical care physicians have demonstrated decreased morbidity or mortality with management by critical care specialists (24
To control for potential confounders by severity of illness and the tendency for sicker patients to be transferred to physicians trained in critical care, we used an expanded SAPS II (23
) and developed a propensity score. The expanded SAPS II was designed to better estimate the probability of mortality of patients admitted to ICUs than was possible with the older SAPS II system. To explore the possibility that some subgroups of patients might benefit from CCM more than others, we conducted several subgroup analyses. For almost all of the subgroups analyzed, risk for mortality associated with management by critical care physicians statistically significant increased.
What could account for these unexpected results? Several possible explanations must be considered. First, there may be residual confounders of severity not covered by either the expanded SAPS II or the propensity score. Our data indicate that patients cared for by pulmonary or critical care physicians for their entire ICU stay were sicker, as evidenced by higher median SAPS II scores. Our results are based on the ability to adjust the increased severity in patients managed by pulmonary or critical care physicians. Despite our attempts to adjust for severity to match patients in both groups for the purposes of comparison, no severity adjustment is perfect, and thus, there may be substantial unrecognized markers of severity in patients cared for by critical care physicians that remain unaccounted for. Some examples of residual unrecognized confounding include comorbid conditions and additional diagnoses not reported in the Project IMPACT database; responses to therapy; presence of protocols in some ICUs; presence and responsibilities of nonintensivist physicians, nurses, and other clinicians; and the influence of where and how long the patient received treatment before ICU admission (lead-time bias).
Second, we must consider the possibility that, for the patients in the Project IMPACT database, management by critical care physicians was associated with worse outcomes. Despite compelling evidence in the literature that care provided by trained critical care physicians leads to better outcomes, our data raise an important point: Although we believe that critical care physicians are trained and expertly skilled in the management of critically ill patients, perhaps some routine critical care practices and procedures may not be beneficial or cumulative use of more interventions may take a negative toll. Although further analyses and studies are needed to understand the possibility that care from critical care physicians is associated with higher hospital mortality, we speculate that there may be several plausible explanations. First, critical care physicians may use their own judgment to manage patients instead of using standardized protocols that may be associated with better outcomes. Second, because of their familiarity and expertise with procedures, they may use more procedures that subsequently lead to more complications. Their use of more procedures, such as placement of catheters and other invasive devices, may make critically ill patients more susceptible to life-threatening infections. Third, patients who receive care from a critical care physician may be transferred to different, unfamiliar physicians, whereas patients who receive care from non–critical care physicians may be more likely to receive ongoing care from physicians already familiar with them. Transfers may, be associated with greater chances of disruption in management and medical orders and create a greater likelihood of miscommunication and errors, all of which can have adverse consequences. This last possible explanation would be more noticeable in patients whose illnesses require less critical care expertise.
We do not claim that this list is exhaustive, but each speculation could be explored by future studies that examine the rates of protocol use, procedures, drug-resistant infections, and care for large groups of patients among physicians who are trained in critical care and those who are not.
Our study has several limitations. First, hospital mortality, rather than 30-day mortality, is the end point. Project IMPACT measures only ICU and hospital mortality. No information on the patients was collected after they left the hospital. Thus, the database contains no information on 30-day mortality. This allows for the possibility that the outcome between the 2 groups may be different at 30 days compared with hospital discharge. If more patients managed by non–critical care physicians died between hospital discharge and 30 days, our results might be very different. For this to be the case, non–critical care physicians would have to routinely discharge patients when they are sicker and at higher risk for death. The fact that more patients were discharged home by non–critical care physicians, rather than to extended care facilities, would seem to argue against this possibility.
Second, the process for identifying the management of patients has limitations. Data collectors at each institution decided, on the basis of training and instructions from Project IMPACT staff, whether to classify patients as managed by critical care physicians. Ultimately, this is a subjective process and may have led to unrecognized bias in the classification of patients.
Third, data elements for analysis are limited to those available in the Project IMPACT database. Limited information is available about the internal structure of each ICU in the database. For example, the presence of protocols, order sets, the length of experience of the nursing staff, the nurse–patient ratio on any particular day, and how many different groups of critical care physicians function within each ICU remain unknown. These and other factors may have had a strong, unrecognized influence on the outcomes of patients in a given ICU. In addition, the Project IMPACT database was not established to address the impact of critical care physician management on patient outcome.
Finally, the percentage of patients managed by full-time intensivists cannot be identified in the Project IMPACT database, and we therefore cannot assess the benefit of full-time, on-site management by ICU physicians. Treatment designated as “management entire stay by critical care physicians” includes all models of management in the ICU by board-certified or board-eligible critical care physicians, including full-time intensivists, office-based pulmonary critical care physicians seeing patients on rounds in the ICU once or twice a day, and private consulting groups with responsibility for critical care patients. Therefore, our study does not identify 1 particular model of critical care practice but rather a broad array of practice management styles provided by trained, board-certified or board-eligible critical care physicians. In the Project IMPACT database, we know little about the non–critical care physicians who manage patients in the ICU or the ICUs in which no patients are managed by critical care.
Future prospective studies should be designed to better answer the questions raised by our study, including characteristics that identify high-performing critical care units.
In conclusion, our study, which to our knowledge is based on the largest cohort ever analyzed to examine the relationship of CCM to survival of critically ill patients, found some unexpected results. Patients managed by critical care physicians for the entire ICU stay had a higher risk for death than patients managed by non–critical care physicians. Although all of the possible explanatory mechanisms we have mentioned may seem to portend badly for the practice of critical care medicine, we suggest that, if true, they are amenable to correction or mitigation through such efforts as guideline development and adherence, quality improvement, and systematic efforts to reduce errors. Given the complexity of critical illness, the need for dedicated critical care physicians seems inevitable, and strategies to assure best practices will help them to guarantee the best outcomes possible. Further research is needed to explain these findings and determine whether these results may be explained by unrecognized residual confounders of illness severity.
Critical care physicians or physicians without specialized critical care training may manage patients in intensive care units.
This study described 101 832 patients in 123 intensive care units in the United States. Patients managed by critical care physicians were sicker, had more procedures, and had higher hospital mortality rates than those managed by other physicians. Analyses that adjusted for severity of illness and the tendency for sicker patients to be managed by critical care specialists still showed higher mortality among patients managed by the specialists.
Unrecognized confounders might diminish or invalidate the unexpected finding of higher mortality among patients managed by critical care specialists.