American Society of Anesthesiologists (ASA) Classification of
Surgical Patients
The ASA classification of the patients was assigned at the time of
surgery by the attending anesthesiologist, through the respective
billing codes. Analysis of these codes revealed that over 37% of
patients were classified as either ASA I or ASA II (Figure 3). However,
the percentage of patients receiving preoperative anesthesiology
consults who were ASA I or ASA II declined over the study period (Figure
4). ASA class I or II consults were slightly more likely to be ordered
by surgeons under age 36 and over age 60 (Figure 5). Patients undergoing
cataract surgery had a higher likelihood of receiving an anesthesia
consultation if they had an ASA I or II, whereas knee implant,
chest/abdominal muscle repair, bladder excision, and coronary artery
bypass were more likely to have a consult if they were ASA III-V (Table
3). Furthermore, there was notable variability in consults by
geographical region. In Ontario, healthcare geographical regions have
traditionally been divided into fourteen Local Health Integration
Networks (LHIN). In 2003, the proportion of consultations that were ASA
I/II ranged by LHIN from 38.6% to 68.8% of all preoperative anesthesia
consults. In 2017, this proportion ranged by LHIN from 20.2% to 33.2%
of all preoperative anesthesia consults.