The field of pediatric anesthesia has evolved substantially over the past 20 years and will continue to be influenced by many factors. There is an increasing number of fellowship-trained pediatric anesthesiologists who are specifically board-certified in pediatric anesthesia; growth in the US pediatric population is slowing; concern related to the neurodevelopmental consequences of anesthetic medications in pediatric patients is mounting; and hospitals may seek to be specially recognized based on their ability to care for pediatric surgical patients.^{1–4} This complex confluence of factors will affect the anesthetic care of pediatric patients. In this manuscript, we project how the balance of supply and demand for pediatric anesthesiologists might be affected.

In 1997, the Accreditation Council for Graduate Medical Education recognized fellowship training in pediatric anesthesiology.^{5} Since then, the subspecialty of pediatric anesthesiology has grown markedly. By 2016, there were 56 pediatric anesthesiology fellowship programs offering 205 pediatric anesthesiology positions annually.^{6} After completion of pediatric anesthesia fellowships, advanced second year pediatric anesthesiology fellowships in cardiac, education, pain medicine, quality and safety, and research are increasingly prevalent.^{7} Some academic centers now require that applicants complete an advanced second year pediatric anesthesiology fellowship to be considered for pediatric anesthesiology faculty positions, which may signal a tightening of the academic pediatric anesthesiology job market in those areas. A survey of pediatric anesthesiology program directors found that pediatric anesthesiology fellowship graduates from 2008 to 2010 outnumbered retiring academic faculty by 12 to 1, prompting the authors to question whether the anesthesia workforce could sustainably absorb the number of fellows undergoing training.^{8}

Growth in the US pediatric population (0–17 years), on the other hand, slowed to 3% between 2000 and 2010 relative to 14% growth between 1990 and 2000.^{2} The overall percentage of the US pediatric population is projected to decrease from 23% to 20% between 2014 and 2060.^{9} Data from the Kids’ Inpatient Database (KID), the largest publicly available all-payer pediatric inpatient care database in the United States, indicate that the ratio of inpatient pediatric cases to the pediatric population remained stable between 1997 and 2012, suggesting that as pediatric population growth slows, the number of inpatient procedures may also decrease.^{10} Compounding this issue, the use of nonoperative interventions for some pediatric conditions, like necrotizing enterocolitis and appendicitis, and the recent Food and Drug Administration Drug Safety Communication on the potentially adverse effects of general anesthetics on the neurodevelopment of young children, may result in a reduction in the annual number of pediatric procedures associated with anesthetic care.^{3,} ^{11–13} There may also be a shift in how and where pediatric surgical care is administered. The mission of the American College of Surgeon’s (ACS) Children’s Surgery Verification (CSV) Quality Improvement Program is to “improve the quality of children’s surgical care by creating a system that allows for a prospective match of every child’s individual surgical needs with a care environment that has optimal pediatric resources.”^{14,} ^{15} As such, an increased proportion of pediatric patients may receive care at academic medical centers or dedicated pediatric hospitals. Alternatively, community hospitals may enhance pediatric resources, including pediatric anesthesiologists, to meet CSV Quality Improvement Program requirements.^{16}

Given the shifting landscape of pediatric anesthesia, we believe that conducting a workforce analysis to determine how well a projected future supply of pediatric anesthesiologists is likely to match the needs of the pediatric population is feasible and relevant for workforce planning and to ensure that pediatric anesthesiologists will have access to sufficient case volumes to enable continued proficiency.^{15,} ^{17–20} Herein, we project the supply of pediatric anesthesiologists using recent studies of the composition of the overall anesthesiologist workforce; trends in relevant factors such as current age, gender, and retirement age; and estimate the anticipated demand for services using data from the US Census Bureau and the KID. Using methodology similar to that described by Shipman et al,^{21} the baseline model projections are accompanied by age- and gender-adjusted anesthesiologist supply, and sensitivity analyses of potential variations in fellowship position growth, retirement, pediatric population, inpatient surgery, and market share. The sensitivity analyses permit the evaluation of the effect of each model variable on the baseline model.

The specific aims of our analysis are to (1) project the number of pediatric anesthesiologists in the future workforce; (2) project pediatric anesthesiologist-to-pediatric population ratios (0–17 years); (3) project the mean number of inpatient pediatric procedures per pediatric anesthesiologist; and (4) evaluate the effect of alternative projections of individual variables on the model projections through 2035.

METHODS
Physician Supply Model
The future number of pediatric anesthesiologists is determined by the current supply; additions to the workforce from graduating fellows; and departures from the workforce through death, retirement, or the pursuit of alternative professional activities.^{21,} ^{22} We compiled a database of US-based pediatric anesthesiologists in the base year of 2015 by searching for and merging pediatric anesthesiologist data from 4 sources as of November 5, 2015: the American Board of Anesthesiology (theaba.org) pediatric anesthesiology written board examination registrants, National Provider Identifier (https://nppes.cms.hhs.gov , pediatric anesthesiology taxonomy code: 207LP3000X), Healthgrades database (Healthgrades.com) and the Society for Pediatric Anesthesia physician membership list as previously described.^{1} Consistent with other physician workforce analyses, an upper age limit of 75 years for clinically active pediatric anesthesiologists was used.^{21,} ^{23} For nearly three fourths (2956 of 4048) of identified pediatric anesthesiologists, age and year of primary American Board of Anesthesiology certification in anesthesiology were available. We then used linear interpolation to estimate the ages of the 997 (25%) anesthesiologists for whom age was not available, based on each individual’s date of primary board certification in anesthesiology.^{24} This method helps account for the older age of pediatric anesthesiologists who may have completed other residency training or activities before board certification in anesthesiology. The ages of the remaining 95 (2.4%) pediatric anesthesiologists for whom no age or primary board certification data were available were allocated proportionally to the overall pediatric anesthesiologist population. The gender of all anesthesiologists was available.

Age- and Gender-Based Full-Time Equivalent-Adjusted Estimate of Pediatric Anesthesiologist Supply
Consistent with overall changes in physician demographics, the population of pediatric anesthesiologists is increasingly female.^{1,} ^{25,} ^{26} In a 2013 survey of all anesthesiologists, female and older anesthesiologists reported working less clinical hours than their male and younger counterparts, respectively.^{25} To account for age- and gender-based differences in pediatric anesthesiologist work hours, an age- and gender-adjusted full-time equivalent (FTE) pediatric anesthesiologist supply was determined using the methodology described by the US Department of Health and Human Services.^{22} Age- and gender-specific mean weekly clinical work hour estimates were obtained from the RAND 2013 survey data of all anesthesiologists (RAND Corp, Matthew Baird, unpublished data, August 2016) and multiplied by the number of anesthesiologists in the respective age and gender cohorts to determine the total number of clinical hours supplied by pediatric anesthesiologists in the base year. For this analysis, we assume that 1.0 FTE is equal to 47.5 clinical hours per week, the mean number of clinical work hours per anesthesiologist in 2015. As an example, if the demographic characteristics of the anesthesiologist workforce change over time, such that anesthesiologists in 2035 provide a mean of 43 hours of patient care per week, each anesthesiologist in 2035 would then be counted as 0.91 FTE (43 h/47.5 h = 0.91).^{22}

Additions to the Workforce
Modeling Changes in the Pediatric Anesthesiology Fellowship Growth Rate.
The historical growth rate for pediatric anesthesiology fellowship positions was charted using the Accreditation Council for Graduate Medical Education Data Resource Books and linear regression plotted for the years 2002–2011.^{27} The linear regression formula was then used to compare the projected versus actual number of fellows in the validation years 2012–2016. The absolute mean and maximum differences in the number of projected versus actual fellows in the validation years were determined. The projections of the annual number of pediatric anesthesiology fellowship graduates were based on the linear growth model formula with sensitivity analysis for the mean validation year difference, maximum validation year difference, and ±20%. Finally, the total number of pediatric anesthesiologists in the workforce if fellowship positions plateau at 2015 levels (191/year) is projected.

In 2011, a survey of pediatric anesthesiology fellowship directors identified that over 75% of graduating pediatric anesthesiology fellows over the 3-year period from 2008 to 2010 took positions “involving greater than 90% pediatric care” (151 of 296) or “majority pediatric care” (81 of 296) in the pediatric anesthesiology workforce “with the remainder caring primarily for adults.”^{8} The baseline model used for this analysis therefore assumes that 75% of pediatric anesthesiology fellows remain in the pediatric anesthesiology workforce. We assumed that the gender distribution of pediatric anesthesiology fellows entering the workforce would remain unchanged from the mean distribution over the 3 years leading up to the base year, and the median age of 36 years for males and females entering the workforce would remain unchanged.^{28}

Modeling Changes in the Proportion of Graduating Pediatric Anesthesiology Fellows Who Remain in the Pediatric Anesthesia Workforce.
Factors like market conditions and geographic preferences of graduating pediatric anesthesiology fellows may influence the percentage of graduating fellows who remain in the pediatric anesthesiology workforce. As part of the sensitivity analysis modeling, we project the total number of pediatric anesthesiologists if 95% and 50% of graduating fellows remain in the pediatric anesthesiology workforce.

Departures From the Workforce
Modeling Changes in the Rates of Retirement.
The number of anticipated annual retiring anesthesiologists, given the mean and median retirement age of 64 for all anesthesiologists, was calculated (RAND Corp; Matthew Baird, personal communication). For the baseline model, we assumed that the mean and median age of retirement would remain unchanged over the 20-year projection. Anesthesiologists in the base year who were over the median retirement age, but under the maximum age of 75 years, were modeled to remain in the workforce until the age of 75 years.

The age at which anesthesiologists retire has increased over time, but may fluctuate based on a variety of factors. We modeled scenarios in which the annual number of projected retirees changed by ±25% and ±50%, from the baseline projections to evaluate the effect on the overall supply of pediatric anesthesiologists.

Demand
Modeling Alternative Pediatric Population Projections.
The projected ratio of pediatric anesthesiologists to the pediatric population in the baseline model is projected using the 2012 US Census Bureau Middle Series Population Projections.^{29} To model the impact of alternative pediatric population projections, we also report the ratio of pediatric anesthesiologists to the pediatric population using the 2012 US Census Bureau Low-Series and High-Series Population Projections.^{29}

Modeling Changes in the Number of Inpatient Pediatric Procedures.
The annual number of inpatient pediatric procedures requiring anesthesia was estimated using the KID. The KID is the largest publicly available all-payer pediatric inpatient care database in the United States developed for the Healthcare Cost and Utilization Project by the Agency for Health care Research and Quality.^{10} The KID reports the estimated number of inpatient procedures, based on the International Classification of Diseases, 9th Revision, Clinical Modification codes, for patients under 5 years, 5–13 years, and 14–17 years, every 3 years from 1997 to 2012. The database does not include ambulatory procedures or procedures for patients in observation status admitted for <24 hours.^{10} Pediatric ambulatory procedure data are much less complete.^{30–32} Data from the National Survey of Ambulatory Surgery on the number of ambulatory pediatric cases exist for the years 1996 and 2006 only. Given these limited historical data, we were unable to project the number of future pediatric ambulatory procedures.

The KID includes inpatient procedures that do not require anesthesia (eg, blood transfusion, peritoneal dialysis, bone marrow transplant) and those that are not typically thought of as in the purvue of pediatric anesthesiologists (eg, cesarean delivery, dilation, and curettage). Procedures that require anesthesia may also be age dependent (eg, magnetic resonance imaging). Because some of the 5- to 13-year-old patients will be able to undergo procedures requiring cooperation without anesthesia, only patients <5 years old were deemed to require anesthesia for procedures requiring a high-degree of cooperation (eg, radiology imaging procedures). Two authors (M.M., R.A.) selected the procedures thought to require anesthesia; the complete list is available in Supplemental Digital Content 1, Appendix A, http://links.lww.com/AA/C50 .

To estimate the number of inpatient pediatric procedures requiring anesthesia from 2015 to 2035, we first determined the historical number of inpatient pediatric procedures per 1000 pediatric population for every 3 years between 1997 and 2012 using KID and US Census data (Supplemental Digital Content 1 and 2, Appendix A, http://links.lww.com/AA/C50 , Appendix B, http://links.lww.com/AA/C51 ). The mean and standard deviation (SD) of the historical rates were calculated. We then projected the future number of inpatient procedures by multiplying the historical mean (±SD) procedures per 1000 pediatric population by the 2012 US Census Bureau Middle Series Population Projections.

The rate of inpatient cases per 1000 pediatric population may change if pediatric anesthesiologists become involved in the sedation/anesthesia of children currently not under their routine care, or if changes in market conditions limit anesthesiologist involvement in the care of children for certain procedures. If the number of inpatient procedures per 1000 pediatric population changes over time, the number of procedures per pediatric anesthesiologist will change. To model this, we project the number of procedures per pediatric anesthesiologist if the rate of procedures per 1000 pediatric population in the KID varies from the 1997 to 2012 mean and SD rate by ±25% (eg, [mean + mean × 0.25] ± [SD + SD ± 0.25]). To create what we consider the upper and lower bounds of the inpatient population projections, we multiplied the high estimate of procedures per 1000 pediatric population by the 2012 US Census High-Series Population Projections, and the low estimate of procedures per 1000 pediatric population by the Low-Series Population Projections.

Modeling the Market Share of Inpatient Pediatric Anesthesia Cases.
The effect of the ACS CSV Quality Improvement Program guidelines may result in a shift of pediatric cases performed in adult general hospitals to pediatric centers.^{16} Using the 2009 KID, Somme et al reported that “as many as 40% of all pediatric inpatient surgical procedures are being performed in adult general hospitals.”^{33} If there is a reduction in the proportion of pediatric patients cared for in adult general hospitals, pediatric anesthesiologists may assume care for more patients than the baseline model suggests. We model the effect of 3 scenarios on the projected number of inpatient procedures per pediatric anesthesiologist in which

60% of inpatients age 0–17 years are cared for by pediatric anesthesiologists;
Inpatients age 0–4 years gradually transition care to pediatric anesthesiologists (from 60% to 100% over 20 years), but 60% of inpatients 5–17 years still receive care by pediatric anesthesiologists; and
Inpatients age 0–17 years gradually transition care to pediatric anesthesiologists (from 60% to 100% over 20 years).
Key model variables and assumptions are summarized in Supplemental Digital Content 3, Table 1, http://links.lww.com/AA/C52 . The Stanford Hospital institutional review board designated this analysis as exempt from review (Protocol #33830).

RESULTS Table.: Pediatric Anesthesiologist Workforce Model Projections

There were 4048 US pediatric anesthesiologists identified in 2015, of whom, 4020 (99.3%) were under the age of 75 years at that time.^{1} Over the 13-year period from 2002 to 2015, pediatric anesthesiology fellowship positions increased by 162%, from 73 to 191 positions per year (Table ).

Baseline Model
If pediatric anesthesiology fellowship positions continue to grow at the historical linear growth rate, 75% of graduating fellows remain in the pediatric anesthesiology workforce, and the mean retirement age remains 64 years, the projected number of pediatric anesthesiologists in the workforce in 2035 will be 6022, an increase of 50% over 2015 levels (Figure 1 ).

Figure 1.: Projected number of pediatric anesthesiologists in the workforce if pediatric anesthesiology fellowship positions continue to grow at the historical linear growth rate, 75% of graduating fellows remain in the pediatric anesthesiology workforce, and the mean retirement age remains 64 y old.

Over the 20-year period from 2015 to 2035, the pediatric population is projected to grow from 74.5 to 81.5 million, an increase of 9.4%.^{29} Given the projected growth of the pediatric anesthesiology workforce relative to the pediatric population, the number of pediatric anesthesiologists per 100,000 pediatric population is projected to increase from 5.4 in 2015 to 7.4 in 2035, an increase of 37%.

Figure 2.: Mean projected number of inpatient procedures per pediatric anesthesiologist.

The mean (±SD) number of inpatient pediatric procedures per 1000 pediatric population in the KID from 1997 to 2012 was 14.14 ± 0.42 (Supplemental Digital Content 2, Appendix B, http://links.lww.com/AA/C51 ). Based on this rate and the future projected pediatric population, the mean number (±SD) of annual inpatient procedures per anesthesiologist is projected to decrease by 27% (from 262 ± 8 to 191 ± 6 cases) between 2015 and 2035 (Figure 2 ).

Age- and Gender-Adjusted Model
In 2015, the pediatric anesthesiology workforce was 56.4% male; however, the majority of pediatric anesthesiologists under 40 years were female.^{1} As the older, predominantly male, pediatric anesthesiologists leave the workforce, the proportion of female pediatric anesthesiologists will increase to approximately 54% by 2035. Due to differences in estimated mean weekly work hours based on age and gender (Supplemental Digital Content 4, Appendix C, http://links.lww.com/AA/C53 ), changes in the age- and gender-adjusted pediatric anesthesiologist supply will result in a 0.7% reduction in the supply of FTE anesthesiologists in the workforce in 2035 relative to the baseline model (Table ). The projected age- and gender-adjusted number of pediatric anesthesiologists per 100,000 pediatric population is also shown in the Table .

Modeling Changes in Pediatric Anesthesiology Fellowship Growth Rate
The number of annual pediatric anesthesiology fellowship positions has consistently grown over time, following a linear growth pattern from 2002 to 2016 (R ^{2} = 0.96).^{27} If the number of positions continue to increase at the historical linear growth rate, the number of annual pediatric anesthesiology fellows will reach 367 by the year 2035, a 92% increase over the 2015 base year level (Figure 3 ). The following alternative future fellowship position growth rates were also modeled based on the difference in the projected versus historical number of fellowship positions in the validation years: ±6.2% (mean), ±11.5% (maximum), and ±20% (>3 SDs above/below the mean). Finally, the total number of pediatric anesthesiologists in the workforce is projected if the number of pediatric anesthesiology fellows plateau at 2015 levels (191/y).

Figure 3.: Projection model of pediatric anesthesia fellowship growth rate (mean, maximum, and ±20% error margins), and projected retirement rates.

Figure 4.: Effect of changes in the following parameters on the number of projected pediatric anesthesiologists in the workforce: (A) pediatric anesthesiology fellowship growth rate; (B) proportion of graduating pediatric anesthesiology fellows who remain in the pediatric anesthesia workforce; and (C) retirement rates.

The projected number of pediatric anesthesiologists in the workforce given these alternative fellowship growth rates is shown in Figure 4 . If the baseline model is adjusted such that pediatric anesthesiology fellow positions plateau at 2015 levels (191/y), there will be a projected 4644 pediatric anesthesiologists in the workforce in 2035, a 15% increase over 2015 levels.

Modeling Changes in the Proportion of Graduating Pediatric Anesthesiology Fellows Who Remain in the Pediatric Anesthesia Workforce
If fellowship positions continue to grow at the historical rate and 95% of graduating pediatric anesthesiology fellows remain active in the pediatric anesthesia workforce, there will be 7153 pediatric anesthesiologists in 2035, a 78% increase from 2015 base year levels. If fellowship positions continue to grow at the historical rate but 50% of pediatric anesthesiologists remain active in the pediatric anesthesia workforce, there will be 4608 pediatric anesthesiologists in 2035, a 15% increase from the 2015 base year levels (Figure 4B ).

Changes in Retirement Rates
The projected number of pediatric anesthesiologists retiring per year is shown in Figure 3 , and reflects a retirement age of 64 years. The annual number of retiring pediatric anesthesiologists is projected to peak in the year 2026 at 154. Given the possibility that the annual number of retirees may increase or decrease based on various factors, we modeled the effect of an alternative number of retirees per year on the pediatric anesthesiology workforce. If the annual number of pediatric anesthesiologists who retire decreases by 25% or 50%, there will be a 9% (6582) or 19% (7142) increase in the total pediatric anesthesiology workforce from the baseline projection by 2035, respectively. Alternatively, if the annual number of pediatric anesthesiologists who retire increases by 25% or 50%, there will be a 9% (5462) or 19% (4898) decrease in the total pediatric anesthesiology workforce from the baseline projection in 2035, respectively (Figure 4C ).

Modeling Alternative Pediatric Population Projections
Based on the 2012 US Census Middle Series Population Projections, there will be 7.4 pediatric anesthesiologists per 100,000 pediatric population by 2035 in the baseline model. If the low-series population projections are used, there will be 7.6 pediatric anesthesiologists per 100,000 pediatric population. If the high-series population projections are used, there will be 7.2 pediatric anesthesiologists per 100,000 pediatric population (Table ).

Modeling Changes in the Projected Number of Inpatient Procedures Per Pediatric Population Figure 5.: Effect of changes in the following parameters on the projected number of inpatient procedures per pediatric anesthesiologist: (A) projected number of inpatient procedures per pediatric population; (B) market share of inpatient pediatric anesthesia cases; and (C) concurrent changes in fellowship growth rate, number of pediatric anesthesiologists who remain in workforce, and market share.

If the mean number of inpatient procedures per 1000 pediatric population in the KID differs by ±25% from the baseline mean (±SD) projection rate (14.14 ± 0.42), the number of projected inpatient procedures per pediatric anesthesiologist in 2015 will correspondingly increase/decrease as shown in Figure 5 .

Modeling the Market Share of Inpatient Pediatric Anesthesia Cases
The number of inpatient cases per anesthesiologist was modeled for a scenario in which some or all of the 40% of pediatric patients who receive care in adult general hospitals shift to pediatric centers. If pediatric anesthesiologists cared for 60% of pediatric inpatients, the mean number (±SD) of inpatient procedures per pediatric anesthesiologist is 157 ± 5 in 2015. If that trend continues to 2035, the projected mean number (±SD) of inpatient procedures per pediatric anesthesiologist will be 115 ± 3, a 27% reduction from the 2015 level. If, over the course of 20 years, there is a shift such that 100% of 0- to 4-year olds are cared for exclusively by pediatric anesthesiologists and 60% of 5- to 17-year olds are cared for by pediatric anesthesiologists, the projected mean number (±SD) of inpatient procedures per pediatric anesthesiologist will be 153 ± 4, essentially the same as in the base year. If 100% of all inpatients 0–17 years old transition care over that 20-year period to pediatric anesthesiologists, the projected mean number (±SD) of inpatient procedures per pediatric anesthesiologist is 191 ± 6 in 2035, a 22% increase from the 2015 level (Figure 5B ).

Modeling Concurrent Changes in Fellowship Growth Rate, Number of Pediatric Anesthesiologists Who Remain in Workforce, and Market Share
Several concurrent changes were modeled to test the effect on the mean projected number of inpatient procedures per pediatric anesthesiologist. If fellowship positions do not increase from 2015 levels (191/y), 75% of graduating fellows stay in the pediatric anesthesiology workforce, and pediatric anesthesiologists care for 60% of 0- to 17-year olds, the mean number of inpatient cases per pediatric anesthesiologist will only slightly decrease from 2015 levels. Given the same set of circumstances but pediatric anesthesiologists care for 100% of 0- to 4-year olds (and 60% of 5- to 17-year olds), the mean number of inpatient cases per pediatric anesthesiologist will increase by 27% from 2015 levels (Figure 5C ).

DISCUSSION
If the current trajectory of increases in the number of subspecialty-certified pediatric anesthesiologists continues, coupled with projected patterns of inpatient pediatric procedural care, the growth in the overall supply of pediatric anesthesiologists will likely exceed the growth in inpatient demand through 2035. This implies that to achieve equilibrium of supply and demand there would likely need to be a combined decrease in the pediatric anesthesiologist growth rate and an increase in demand for their services. The decrease in pediatric anesthesiologist growth rate could take the form of a reduction in the growth of fellowship positions, fewer graduating fellows who remain in the pediatric anesthesiology workforce, and/or increase in retirements. An increase in demand for pediatric anesthesiologist services would likely require the redistribution of pediatric procedures from general anesthesiologists to pediatric anesthesiologists and/or an increase in the number of pediatric procedures requiring anesthesia. We believe that changes of a large magnitude are unlikely to occur in the near term given the recent history of fellowship growth, general trend to increasing retirement ages, and the geographic distribution of pediatric patients relative to pediatric anesthesiologists, which would make a complete shift of care of any age cohort to pediatric anesthesiologists unlikely.

As with other physician specialties, there are large differences in geographic access of the pediatric population to pediatric anesthesia care in the United States.^{34–36} The majority (90%) of pediatric anesthesiologists practice in urban settings and substantial geographic heterogeneity in pediatric anesthesiologist geographic distribution exists. As a result, 2.7 million (13.8%) US children ages 0–4 years live >50 miles from the nearest identified pediatric anesthesiologist practice location.^{35} Anesthesiologists with pediatric expertise are needed in rural settings; however, it is well known that physicians do not preferentially practice where the need is greatest.^{37} Simply adding pediatric anesthesiologists to the workforce is not likely to significantly reduce geographic disparities in access to care. Further, the addition of pediatric anesthesiologists to areas where geographic disparities exist is not likely to benefit the pediatric population if underlying systems of pediatric care are underdeveloped or do not exist. To improve geographic access to care, pediatric systems of care must be developed and incentives for pediatric anesthesiologists to practice in these underserved areas should be considered.

The addition of pediatric anesthesiologists to areas where sufficient numbers already practice is not likely to benefit patients. Maintaining competence in pediatric anesthesia requires that pediatric anesthesiologists continue to care for an adequate number of pediatric patients.^{19} If less common pediatric procedures are distributed among a greater number of pediatric anesthesiologists, individual anesthesiologist experience with these less common procedures will also decrease and potentially erode the skills needed to care for patients with complicated illnesses. The ACS Children Surgery Verification Quality Improvement Program requires that anesthesiologists with pediatric expertise perform 25 anesthetics per year for patients under age 24 months.^{4} Achieving even this arbitrary minimum threshold for competency may not be possible in some hospitals or practice settings if procedure ratios for pediatric anesthesiologists decrease in the future. We believe that competency with more complicated pediatric patients almost certainly requires that the pediatric anesthesiologist care for more than 25 pediatric patients per year.

An increase in the number of pediatric anesthesiologists relative to demand also has the potential to adversely affect graduating fellow career decisions. The baseline model projects that 75% of pediatric anesthesia fellowship graduates remain in the pediatric anesthesiology workforce. The potential exists that in the future, more pediatric anesthesiologists will care for pediatric patients on an occasional basis only. The concentration of pediatric anesthesiologists in areas where an adequate number already exist and the increases in the number of pediatric anesthesiologists relative to available positions may partially explain the willingness of some pediatric anesthesiology fellowship graduates to complete advanced second year pediatric fellowships increasingly required for employment in academic institutions or exclusively pediatric facilities.

The findings of this workforce analysis are consistent with other pediatric physician workforce analyses that note rapid growth in training programs relative to growth in the pediatric population. In the early 2000s, general pediatricians faced an oversupply relative to demand leading to calls for the reduction in the number of trainees.^{21} Similarly, neonatologists entering the workforce far outpaced the rise in birth rates and the regional supply varied widely.^{35} More recently, some leaders in the field of pediatric cardiology have called to curtail the increase in pediatric cardiology fellowships in North American training positions due to increased difficulty encountered by graduating trainees in finding positions.^{38}

As with any workforce analysis that attempts to project future conditions, we acknowledge that there are limitations to this approach and the study’s assumptions should be considered when interpreting these results. Due to a lack of sufficient historical data on ambulatory surgical care, from which to model future case projections, this workforce analysis does not account for ambulatory procedures. Ambulatory pediatric procedures, commonly requiring sedation or anesthesia, may represent an increasingly important setting for pediatric anesthesiologists. According to the American Hospital Association, between 1993 and 2013, there was an approximately 10% increase in outpatient versus inpatient surgeries in community hospitals.^{39} If there is growth in the number of ambulatory pediatric cases performed per year, with a sustained number of inpatient procedures, the supply of pediatric anesthesiologists may more closely align with the projected demand. Conversely, if any increase in cases in the ambulatory setting were attributable to a redistribution of inpatient cases, the trends described will not be affected. The projected number of inpatient procedures does not account for geographic or demographic variables. We attempted to create a more sophisticated statistical model to project the future number of inpatient procedures by training and testing a multivariate regression and random forest prediction model using patient region, age, sex, and procedure type as features. Due to the random missing elements across years in the KID demographic data, these analyses produced results less accurate than those of the simple linear model. More consistent data capture in the KID (ie, less random missing demographic elements) would allow for a more detailed projection of inpatient pediatric procedure volumes. This analysis also does not account for additions to the pediatric anesthesiology workforce due to non-US–trained pediatric anesthesiologists, as these data are not readily available; however, this addition would only exacerbate any workforce imbalance. Reduction in the pediatric anesthesiologist workforce due to mortality was not modeled, but is not likely to significantly impact these findings given that the modeled age of retirement is 64 years, the life-expectancy and retirement ages of physicians are increasing, and the future supply of pediatric anesthesiologists far exceeds demand in the baseline projections. Additionally, projections concerning the future number of pediatric anesthesiologists are predicated on the idea that anesthesiology residents will continue to pursue pediatric anesthesiology fellowship. If anesthesiology residents perceive that fewer opportunities exist in the workforce for pediatric anesthesiologists, or if significant changes occur in the structure of pediatric anesthesiology fellowship (eg, mandatory extension of fellowship duration), it is conceivable that fewer anesthesiology residents may be willing to undergo subspecialty training in pediatric anesthesiology. We projected a wide range of future number of pediatric anesthesiology fellows; however, if the annual number of pediatric anesthesiology fellows declines substantially from the 2015 baseline, these projections will not be valid. We relied on the KID inpatient data sample to project the future number of inpatient pediatric procedures, and used the projected pediatric population as a surrogate estimate of demand; however, we acknowledge that these data may not fully characterize the future needs of the pediatric population. Finally, the important work of pediatric anesthesiologists outside of the operating room in pediatric pain, intensive care, quality improvement, patient safety, hospital leadership, or other endeavors are not quantified. We took the utmost care to project the future supply and demand based on what we believe are reasonable assumptions and included sensitivity analyses of individual variables to evaluate the effect of these variables on the overall model.

Moving forward, future research should evaluate if and how pediatric anesthesia care patterns shift with the implementation of the ACS CSV Quality Improvement Program. It is interesting and potentially important to know what proportion of pediatric patients, stratified by age, geographic location, and practice setting, is cared for by pediatric anesthesiologists versus general anesthesiologists or midlevel providers. Other questions ultimately need to be answered to reach the goal of optimal alignment of skilled care providers and the specific patient populations they serve. What is the experience of recent pediatric anesthesiology fellowship graduates with regard to the care they provide for infants and children? How can we better align the supply of pediatric anesthesiologists with the geographic demand for services? How do changes in these practice patterns relate to pediatric patient outcomes?

The field of pediatric anesthesiology continues to grow and evolve. We should make an effort to understand how our decisions today will affect the care of children and the workforce in the future.

DISCLOSURES
Name: Matthew K. Muffly, MD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Name: Mark Singleton, MD.

Contribution: This author helped write the manuscript.

Name: Rita Agarwal, MD, FAAP.

Contribution: This author helped analyze the data and write the manuscript.

Name: David Scheinker, PhD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Name: Daniel Miller, BS.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Name: Tyler M. Muffly, MD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Name: Anita Honkanen, MD, MS, FAAP.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

This manuscript was handled by: James A. DiNardo, MD, FAAP.

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