To the Editor Dr Neuman and colleagues1 concluded that although regional anesthesia was associated with shorter hospital stays following hip fracture surgeries than with general anesthesia, there was no significant difference in 30-day mortality.
In their analysis, patients who lived closer to hospitals that specialized in regional anesthesia were matched to patients who lived closer to hospitals that specialized in general anesthesia under the assumptions that patients seek care for hip fractures at hospitals near their homes and that regional anesthesia use varies across hospitals. Although distance is a factor in a patient’s choice of hospital, it is just one of many.2 Without exact patient addresses, Neuman et al1 used the linear distance between the center of the patient’s zip code and the hospital. However, driving distance, hospital reputation, and insurance network participation seem more likely to be associated with a patient’s hospital choice. These assumptions and the inaccuracy of the distance calculations raise concerns about hospital proximity as a strong instrumental variable.3
Bulka CM, Wanderer JP, Ehrenfeld JM. Anesthesia Technique and Outcomes After Hip Fracture Surgery. JAMA. 2014;312(17):1801. doi:10.1001/jama.2014.11229