Patient Mortality Not Linked to Intensivist Caseloads

By Betty Tran, MD, MSc

Associate Professor of Medicine, Division of Pulmonary and Critical Care Medicine, Northwestern University Feinberg School of Medicine, Chicago

SYNOPSIS: In this retrospective cohort study in the United States from 2018-2020, there was no significant association between intensivist-to-patient ratio and patient mortality and no effect modification by having physicians-in-training, nurse practitioners, and physician assistants present.

SOURCE: Kahn JM, Yabes JG, Bukowski LA, Davis BS. Intensivist physician-to-patient ratios and mortality in the intensive care unit. Intensive Care Med 2023;49:545-553.

Prior studies examining the relationship between intensivist-to-patient ratios and intensive care unit (ICU) mortality have yielded mixed results. In addition, they have significant methodological limitations that fail to account for intensivists covering more than one ICU by using only ICU level census data and by using intensivist-to-patient ratios that are averaged over the entire ICU length of stay, which neglects the effect of day-to-day variation on outcomes.

To address this question more rigorously, Kahn et al made a number of methodologic changes in how the primary exposure was defined to directly measure intensivist-to-patient ratios and to account for the possibility for a non-linear relationship between that and mortality, how ICU caseloads are modeled to account for daily changes with time-varying covariates, and through a series of sensitivity analyses to test the robustness of the results.

Using the University of Pittsburgh Medical Center’s electronic health record-based registry of ICU patients admitted between 2018 and 2020, each ICU patient was linked to an attending for each day of their ICU stay to generate intensivist daily caseloads as counts. Alternatively, the primary exposure also was studied as a binary variable of whether the intensivist’s daily caseload was over the sample-wide average of 11.8 and a binary variable of whether the caseload was over the recommended threshold of 14. In addition, continuous variables equal to the rolling sum of days each caseload was over the average and over the recommended threshold also were studied. The primary outcome was 28-day ICU mortality.

A number of sensitivity analyses were performed. These included: whether the effect of high caseload on ICU mortality varied depending on the presence of physicians-in-training, nurse practitioners, or physician assistants; a model limited to only mechanically ventilated patients; a model assuming patients who died in the hospital after their ICU stay as having died at ICU discharge; and using a model categorizing caseload by quintile, to name a few.

In total, 51,656 patients admitted to 29 ICUs in 10 hospitals were analyzed. The mean age was 63.4 ± 17 years, most were admitted through the emergency department, 33% were mechanically ventilated, and mean Sequential Organ Failure Assessment (SOFA) score was 4.0 ± 2.8 on admit. Mean daily caseload across all intensivist days was 11.8 ± 5.7 (median 11), with a daily range of five to 24. Regarding the primary outcome, there was no association between intensivist daily caseload and ICU mortality, regardless of how the primary exposure was modeled. The presence of physicians-in-training, nurse practitioners, or physician assistants did not modify the effect of intensivist caseload on ICU mortality. Results were similar in nearly all the sensitivity analyses.

COMMENTARY

The COVID-19 pandemic tested the healthcare system in a multitude of ways, but arguably most profoundly in the ICU, where intensivists worked longer hours and more shifts to care for a surge of critically ill patients. Although this study purposefully excluded the COVID-19 pandemic surges, it underscores the resilience of intensivists in caring for the sickest, most complex patients in the hospital, their ability to flex their skills to see higher caseloads without a change in ICU patient mortality, and the ability of ICUs in general to function at a high level with consistent outcomes even during times of capacity strain. This might be accomplished at the ICU level with specific, up-to-date protocols for patient management (e.g., indication/contraindication/procedure to initiate extracorporeal membrane oxygenation), through teams of experienced and highly skilled support staff (i.e., nursing, respiratory therapy, pharmacy), and at the individual intensivist level where patients may be triaged with more time being spent on the more complex patients who are most likely to benefit from ICU-level care and responsibilities delegated to the correct parties (i.e., residents, fellows, nurse practitioners).

Although no association was found between higher intensivist caseloads and ICU mortality, the authors appropriately emphasized that this finding does not imply that high caseloads have no bearing on other important outcomes. It is feasible that higher daily caseloads for intensivists may be linked to near-miss events, patient/surrogate satisfaction due to less time to establish rapport and/or limited communication, quality of teaching for learners of varying levels on the care team, ICU burnout, and intensivist work-life balance. Multiple studies have explored the nurse-to-patient ratio and its effect on patient outcomes, such as mortality, readmissions, and length of stay, as well as nursing job satisfaction and burnout.^1,2 Similar studies with more advanced methodologic analyses as employed in this study are long overdue in terms of studying patient-to-physician ratios in an effort to optimize both patient outcomes and intensivists’ well-being.

REFERENCES

1. McHugh MD, Aiken LH, Sloane DM, et al. Effects of nurse-to-patient ratio legislation on nurse staffing and patient mortality, readmissions, and length of stay: A prospective study in a panel of hospitals.
   Lancet 2021;397:1905-1913.
2. Aiken LH, Clarke SP, Sloane DM, et al. Hospital nurse staffing and patient mortality, nurse burnout, and job dissatisfaction. JAMA 2002;288:1987-1993.