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Rising age, rates of obesity and comorbidity in surgical patients requiring anaesthesia

Updated: Mar 6, 2023

A snapshot survey data from the 7th National Audit Project of the Royal College of Anesthetists (NAP7) in the UK reveals an extremely worrying picture of increasing age, rates of obesity, and complexity of surgical patients requiring anaesthesia in the UK.

Figure 1: Trends in age and BMI over time in the NAP5–7 activity survey populations. Trends in age and BMI between NAP cycles. Data show (a) proportion of the activity survey population by age in non-obstetric patients and the BMI distribution in the (b) non-obstetric and (c) obstetric populations. NAP5 (white bars); NAP6 (red bars); NAP7 (black bars). Proportions show the relative change in the population proportion within the group between NAP5 and NAP7. ↑, increase; ↓, decrease; ↔, no change. Percentages may not total 100 due to rounding. Credit: Anaesthesia (2023). DOI: 10.1111/anae.15989

The snapshot activity survey collected patient-level data from all cases under the care of an anaesthetist in UK hospitals delivering anaesthesia in November 2021. Anaesthetists recorded details of all cases undertaken over four days at their institution through an online survey capturing anonymous patient characteristics and aesthetic details. Of 416 hospital sites invited to participate, 352 (85%) completed the activity survey. A total of 24,172 reports were included in the final dataset. This research is the first set of results available from NAP7, with the full report due to be published in November 2023.


While the authors found that working patterns in terms of day of the week, time of day and surgical specialties were similar to previous NAP reports, some worrying trends were evident. Between the NAP5 (2013) and NAP7 (2021) surveys and excluding those patients who were pregnant, the estimated median age of patients increased by 2.3 years (50.5 to 52.8 years).

"The fact that the population requiring surgery with anaesthesia is 2.3 years older than nine years ago has important implications. Although this may seem a modest increase in age, the all-cause mortality in the general population increases approximately 10% for each year of advancing age and doubles as age increases 6–7 years; and thus a 2.3-year increase in age equates to an approximately 27% increase in all-cause mortality” explained Dr Andrew Kane, Fellow, Health Services Research Center, Royal College of Anesthetists, London, UK, and lead author of the study.

“This increase in age is likely to interact with peri-operative risk, most notably for those patients who are elderly, meaning that morbidity, mortality and health care costs might all be expected to have risen.”


The report also found that the median BMI of patients increased from 24.9 kg/m2 (the borderline of what is classified as normal weight and overweight) to 26.7 (overweight).

"We are seeing an increase in both the proportion of patients who are living with obesity presenting for anaesthesia and surgery and in the extent of the obesity. Just 10 years ago, the median BMI of the surgical population was at the top of the 'normal' BMI category, and now in NAP7 it is 'overweight' - such that it is hard to argue that normal weight is indeed still normal,” the authors write. “While the proportion of overweight patients in this survey is consistent with the population as a whole, the proportion of patients living with obesity is higher: patients with a BMI over 30 kg/m2 now represent one in three patients presenting to anaesthetists. This increase is most marked in obstetric patients who require aesthetic care to assist childbirth."

Complex surgical cases

Anaesthetists and surgeons use the ASA (American Society of Anesthesiology physical status) scale to provide a measure of the complexity/comorbidity of surgical patients where 1 is the least complex and 5 the most complex. The proportion of patients scored as ASA 1 (least complex) decreased from 37% in NAP5 (2013) to 24% in NAP7 (2021). The proportion of patients with an ASA score of 2 (with controlled long term health issues such as high blood pressure or diabetes) increased from 39% in NAP5 to 45% in NAP7. The proportion of patients who scored ASA 3 (such as those who have had a previous heart attack or stroke) increased from 18% in NAP5 to 25% in NAP7, while the proportion of very high risk (ASA 4) patients was similar (3% in NAP 5 / 4% in NAP7). The authors believe these numbers represent actual changes in the patient mix presenting to NHS hospitals for surgery.

"These data show increasing age, obesity and comorbidity trends leading to an increasingly complex peri-operative workload. The extent to which these trends would have occurred without the COVID-19 pandemic is unclear, but they must be addressed in this new post-pandemic era,” added study co-author, Dr Jasmeet Soar, Consultant in Anesthesia and Intensive Care Medicine, Southmead Hospital, North Bristol NHS Trust, Bristol, UK.

The survey was taken as a snapshot of activity during a year in which surgical activity was still affected by COVID-19. The authors comment that this might alter extrapolations in terms of absolute case activity but does not alter the findings reported here.

"This study shows important patient changes that all increase the workload of anaesthetic, surgical and perioperative teams. Patients undergoing anaesthesia and surgery in the UK have, over the last decade, become older, more likely to be living with obesity and more medically unwell” explained study co-author, Professor Tim Cook, Consultant in Anesthesia and Intensive Care Medicine, Royal United Hospitals Bath NHS Foundation Trust, Bath, UK, and Honorary Professor, School of Medicine, University of Bristol. “All these factors interact to make anesthetic and surgical care more complicated and higher risk. Safely managing patients with these characteristics requires more time in the operating theater and can lead to slower recovery and more complications after surgery, both of which can require a longer time spent in hospital. These trends are a threat to current efforts to reduce the huge surgical waiting list. Any increases in the trends we have seen in this report will add to pressures on hospital services and we need to make national efforts to get patients fitter for surgery."

"These results confirm that what we have observed in our day-to-day work caring for patients is a nationwide trend. It is a worrying picture, but there are things that we can do to better prepare many patients for their operation through greater emphasis on perioperative carem” said Dr Fiona Donald, president of the Royal College of Anesthetists. “We can help patients by supporting them to improve their health while they are waiting, for example through access to smoking cessation services and providing practical advice on changes to diet and exercise that can make a big difference."

The findings were reported in the paper, 'Patient characteristics, anaesthetic workload and techniques in the UK : an analysis from the 7th National Audit Project ( NAP7 ) activity survey', published in Anaesthesia. To access this paper, please click here


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