JAMA Surgery published the study Association of Anesthesiologist Staffing Ratio With Surgical Patient Morbidity and Mortality on July 22, 2022. This was a landmark paper on the topic of anesthesiologist:CRNA staffing ratios, which documented that having physician anesthesiologists direct three or four operating rooms simultaneously for major noncardiac inpatient surgical procedures increased the 30-day risks of patient morbidity and mortality. The senior author was Sachin Kheterpal, MD, MBA, of the Department of Anesthesiology at the University of Michigan Medical School. The data was from a retrospective matched cohort study of major noncardiac inpatient surgical procedures performed from January 1, 2010, to October 31, 2017, and was conducted in 23 academic and private hospitals in the United States. 

The University of Michigan paper stated, “this study primarily analyzed physician-CRNA teams, the dominant practice model in US anesthesiology.” The physician-CRNA team, otherwise known as an anesthesia care team, is a model strongly supported by the American Society of Anesthesiologists.  The anesthesia care team is a system in which one anesthesiologist covers one, two, three, or four separate operating rooms, each room staffed by a Certified Registered Nurse Anesthetist (CRNA) or an anesthesia assistant (AA). From a very large initial data set of 3,624,399 operations, the University of Michigan authors calculated the staffing ratio of physician anesthesiologist: CRNA for each operation. The following types of cases were excluded: anesthesia care personally performed by a physician anesthesiologist working alone; anesthesia care which involved an anesthesia assistant; anesthesia care involving an anesthesia resident; and anesthesia care that occurred overnight, during weekends, or on holidays. After these exclusions were applied, the data set consisted of 866,453 operations, in which 1960 anesthesiologists provided care in 23 different hospitals.

Data was divided into four groups:

  • Group 1: one anesthesiologist covering one operation (48,555 patients)
  • Group 1-2 (reference group): one anesthesiologist covering more than one to no more than two overlapping operations (247,057 patients)
  • Group 2-3: one anesthesiologist covering more than two to no more than three overlapping operations (216,193 patients)
  • Group 3-4: one anesthesiologist covering more than three to no more than four overlapping operations (67,010 patients)

The four groups were studied regarding 30-day morbidity and mortality outcome data. The morbidities included cardiac, respiratory, gastrointestinal, urinary, bleeding, and infectious complications. Overall, morbidity and mortality occurred after 30,026 operations (5.19%).

The results:

Compared with patients in group 1-2, those in group 2-3 had a 4% relative increase in mortality and morbidity (5.06% vs 5.25%; P = .02). 

Compared with patients in group 1-2, those in group in group 3-4 had a 14% increase in risk-adjusted mortality and morbidity (5.06% vs 5.75%; P < .001).

The paper stated, “When 100,000 operations, which is typical annually for a major medical center, are considered, the increase in risk from 5.06% to 5.75% that we observed would translate to an additional 690 operations with adverse outcomes,” and “increased overlapping anesthesiologist coverage beyond 1 to 2 operations was associated with an increased risk of surgical patient morbidity and 30-day mortality. Because 313 million surgical procedures are performed worldwide each year, any small individual improvements in outcome can have major repercussions for public health. These results complement previous studies that have shown improved 30-day mortality and morbidity rates after complications when anesthesiologists directed anesthesia care.”

The results of this study may be criticized because the data was retrospective, but it’s unlikely any prospective study will ever be done randomizing major noncardiac inpatient surgeries to anesthesiologist:CRNA ratios of 1:1, 1:2, 1:3, and 1:4. The adoption of Electronic Medical Records (EMRs) brought on the arrival of Big Data such as in this paper, in which a Herculean total of over 3.6 million charts were studied. An EMR enables physicians to study trends and outcome data in ways that were previously impossible. Does the data from the University of Michigan study support the fact that decreased staffing by physician anesthesiologists in major noncardiac inpatient surgical procedures is associated with increased 30-day morbidity and mortality? Yes, it does. Will this conclusion change the future practice of anesthesiology? Perhaps, but probably not. Why not? Let’s examine the most likely reasons behind the increased anesthesiologist:CRNA staffing ratios:

  1. There may be an inadequate supply of physician anesthesiologists to staff all major noncardiac inpatient surgical procedures at anesthesiologist:CRNA ratios of 1:1 or 1:2. There were 31,130 anesthesiologists in the United States in 2021, and more than 55,000 CRNAs in the United States. There were approximately 21 million surgeries per year in the United States in 2014.   The ratio of the number of surgeries compared to the number of anesthesiologists (21,000,000/31,130) equals 675 surgeries per anesthesiologist, a busy caseload. But the geographical distribution of where anesthesiologists live is not random, with populations of MD anesthesiologists concentrated in urban and suburban areas, and populations of MD anesthesiologists less concentrated in rural areas. Some locations have an inadequate census of physician anesthesiologists to staff every case as solo practitioners or at an anesthesiologist:CRNA ratio of 1:1 or 1:2. 
  2. A higher anesthesiologist:CRNA ratio may be a strategy to decrease the cost of anesthesia care. This issue was examined in detail in the American Society of Anesthesiologists Monitor.  In this study, the reported average yearly salary for a CRNA was $202,000, and they worked 40 hours per week. The reported average yearly salary for a private practice anesthesiologist was $440,000, and they worked 55 hours per week.  Cost-analysis showed that with adequate numbers of CRNAs to staff anesthesia care teams and to cover breaks for working CRNAs, the anesthesiologist:CRNA ratios of 1:2 and 1:3 were actually more expensive than running the rooms with a solo anesthesiologist in each room. An anesthesiologist:CRNA ratio of 1:4 was only marginally (< 10%) less costly than running the rooms with a solo anesthesiologist in each room. 
Figure 3: 7 a.m. to 5 p.m. with break staff included. Because one needs 1.25 CRNAs per site to cover the 10-hour shifts, the cost savings for anesthesia care team model is further reduced. Anesthesia care team costs are compared to physician-only (MD-only). Spikes in costs are when the number of sites cannot be divided by the staffing ratio. 

3. A high anesthesiologist:CRNA ratio may increase the income per anesthesiologist. When one anesthesiologist directs multiple CRNAs in multiple operating rooms, that solitary physician anesthesiologist can increase his billing for the day. Medical direction of 2-4 concurrent anesthesia procedures: When two to four concurrent anesthesia procedures are medically directed, report with modifier QK. Services submitted with modifier QK will be reimbursed at 50% of the applicable fee.” 

Medical direction of four CRNAs –> the anesthesiologist can bill 50% of Physician Allowed Amount and 50% of CRNA Allowed Amount.

With four operating rooms directed by one anesthesiologist, the 1st, 2nd, 3rd, and 4th operating rooms can each be billed at 50% of the anesthesia fee. Billing for four rooms simultaneously can increase the income for that solitary anesthesiologist over that time period. An anesthesiologist working alone, without CRNAs, can only attend to one patient, and can only bill services for a single patient. An analogy is a taxicab or Uber driver who can only bill for one ride at a time. The only way for a solo taxi driver or Uber driver to earn more money is to give more rides, and the only way for a solo anesthesiologist to earn more money is to do more cases for more hours of time.

The senior author of the University of Michigan study was Sachin Kheterpal, MD, MBA from the Department of Anesthesiology, yet the study was published in a surgical journal, JAMA Surgery, rather than an anesthesiology journal.Did anesthesiology journals reject the opportunity to publish the study? I don’t know. It’s pertinent that surgeons care greatly about the outcomes of surgeries they perform, and surgeons are less concerned with the economics of anesthesia staffing. Surgeons reading this study will no doubt conclude that an anesthesia group covering major noncardiac inpatient surgical cases with 1:3 or 1:4 anesthesiologist:CRNA staffing ratios are exposing their patients to an increased risk of morbidity and mortality.

Will this study change the anesthesiologist:CRNA staffing ratios in the future? My gut impression is that it will not. Anesthesiologists do not routinely read JAMA Surgery and may be quick to dismiss the findings. Surgeons may complain to their anesthesia colleagues that they do not want 1:3 or 1:4 anesthesiologist:CRNA staffing ratios for their major noncardiac inpatient surgical patients, but it’s unlikely they will have any power to enact change if the anesthesiologists don’t want to change. Why would anesthesiologists not move away from 1:3 or 1:4 anesthesiologist:CRNA staffing ratios? See the three reasons above: an inadequate supply of physician anesthesiologists; the quest to decrease anesthesia costs; and the goal of maximizing anesthesiologist income by directing 3 or 4 operating rooms at the same time.

I asked the anesthesia chairman of a large health-maintenance organization (HMO) how his group assigned anesthesia staffing, and his reply was that they used tiered staffing. A demanding case such as an open-heart surgery or a craniotomy was staffed by a solo physician anesthesiologist. In contrast, simple low-risk cases such as bunion repairs or carpal tunnel repairs on healthy patients were staffed by the maximal anesthesiologist:CRNA ratio of 1:4. The spectrum of remaining cases fell between these two extremes, and the anesthesiologist:CRNA ratio was assigned according to the difficulty and the risk of the anesthetic.

As a patient, how do you feel about all this? Would you be concerned if you were to be anesthetized by an anesthesia care team utilizing a 1:3 or 1:4 anesthesiologist:CRNA staffing ratio? In the University of Michigan study, if your surgery was a major noncardiac inpatient surgery during daytime hours, the data showed that your anesthesia team is putting you at increased risk for 30-day morbidity and mortality. The University of Michigan study only examined inpatient surgeries, so if you’re having outpatient ambulatory surgery, this study does not apply to your surgery. In 2014, outpatient surgery outnumbered inpatient surgery by 11,474,800 to 10,303,000. But if you or your family member are scheduled for major noncardiac inpatient surgery, it’s important to ask the question of what the anesthesiologist:CRNA staffing ratio will be while you or your family member are asleep, and how much of the time will your anesthesiologist be in the operating room.

If I was to be cared for by an anesthesiologist:CRNA ratio of 1:3 or 1:4 for a major noncardiac inpatient surgery during daytime hours, I would raise an objection before the anesthetic started, and I would direct my objection at both the attending anesthesiologist and the attending surgeon. Based on the data from the University of Michigan study, I would request an anesthesiologist:CRNA ratio of no higher than 1:2, or I would request a solo anesthesiologist to attend to me.

I’d suggest you do the same.




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