“…As such, we included receipt of blood products as a potential surrogate for hypotension. We created control indicator variables as follows: patient transferred in from another hospital (coded 1 if transferred in, 0 if not transferred in), receipt of blood products (ICD-9-CM procedure codes 99.00Y99.09), presence of massive spleen disruption (ICD-9-CM 865.04, 865.14), and presence of other abdominal injuries (ICD-9-CM 86 (3,4,6,8). Hospital characteristics such as teaching status, hospital location (rural vs. urban), and hospital bed size (small, medium, and large) were also included as control variables.…”