Innovation in surgical oncology Vrielink, Otis
DOI:
10.33612/diss.173351128
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Vrielink, O. (2021). Innovation in surgical oncology. University of Groningen.
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Chapter 4
Multicentre study evaluating the surgical learning curve for posterior
retroperitoneoscopic adrenalectomy
O.M. Vrielink, A.F. Engelsman, P.H.J. Hemmer, J. de Vries, W.M.C.M. Vorselaars, M.R. Vriens, A. Karakatsanis, P. Hellman,
M.S. Sywak, B.L. van Leeuwen, M. el Moumni, S. Kruijff
Background: Posterior retroperitoneoscopic adrenalectomy has gained international popularity in the past decade. Despite major advantages, including shorter duration of operation, minimal blood loss and decreased post-operative pain, many surgeons still prefer laparoscopic transperitoneal adrenalectomy. It is likely that the unfamiliar anatomic environment, smaller working space and long learning curve impede implementation.
The present study assessed the number of procedures required to fulfil the surgical learning curve for posterior retroperitoneoscopic adrenalectomy.
Methods: The first consecutive posterior retroperitoneoscopic adrenalectomies performed by four surgical teams from university centres in three different countries were analysed. The primary outcome measure was duration of operation. Secondary outcomes were conversion to an open or laparoscopic transperitoneal approach, complications and recovery time. The learning curve cumulative sum (LC-CUSUM) was used to assess the learning curves for each surgical team.
Results: A total of 181 surgical procedures performed by four surgical teams were analysed. The median age of the patients was 57 years (range 15-84) and 61.3 per cent were female. Median tumour size was 25 (range 0.4-8.5) mm. There were no significant differences in patient characteristics and tumour size between the teams. The median duration of operation was 89 (range 29-265) min. There were 35 perioperative and postoperative complications among the 181 patients (18.8 per cent); 17 of 27 postoperative complications were grade I. A total of nine conversions to open procedures (5.0 per cent) were observed. The LC-CUSUM analysis showed that competency was achieved after a range of 24-42 procedures.
Conclusion: In specialized endocrine surgical centres between 24 and 42 procedures are required to fulfil the entire surgical learning curve for the posterior retroperitoneoscopic adrenalectomy.
4 INTRODUCTION
Laparoscopic adrenalectomy has been performed since the early 1990s, and has shown favourable results over open surgery, including decreased blood loss, postoperative pain and complications, and shorter hospital stay.1-3 It rapidly replaced the traditional open technique and became the standard approach, especially for benign small- to medium- sized adrenal tumours. With improvements in technique and instruments it is also feasible for large benign tumours.4,5 In the setting of adrenocortical carcinoma, careful and complete surgical resection is of utmost importance so laparoscopic resection should not be attempted.6
Different minimally invasive approaches exist for adrenalectomy, including the laparoscopic transperitoneal, lateral retroperitoneal and posterior retroperitoneal approach.7 Both transperitoneal and retroperitoneal approaches have proven to be safe and effective.
Currently, the laparoscopic transperitoneal approach is most frequently performed and is considered to be the standard procedure.4 Since its introduction and standardization by Walz and colleagues8, the posterior retroperitoneal approach has gained popularity.
This offers a more direct route to the adrenal glands, without the need to mobilize and dissect adjacent fragile intra-abdominal organs, such as the liver, pancreas and spleen.
Other advantages are its feasibility in obese patients and in those with a medical history of abdominal surgery, with the avoidance of peritoneal adhesions. Furthermore, there is no need to reposition patients with an indication for bilateral adrenalectomy. Despite several published reportsshowing shorter duration of surgery, less blood loss, decreased postoperative pain, faster recovery and improved cost-effectiveness, many surgeons still perform lateral transperitoneal adrenalectomy (LTA).9-12
In clinical practice, several barriers to adopting posterior retroperitoneoscopic adrenalectomy (PRA) exist, including the unfamiliar anatomic environment and smaller working space, with a potential long learning curve. For an experienced endoscopic surgeon, the learning curve will mostly depend on reorientation in the insufflated retroperitoneal space. For LTA, approximately 20-40 cases are required to overcome the learning curve.13-15 The length of the learning curve for PRA, a potential barrier to adoptation of the procedure, has not been fully assessed. The aim of this study was to analyse the number of procedures needed to safely fulfil the learning curve for PRA.
METHODS
A multicentre study was undertaken at the Departments of Surgery of the University Medical Centre Groningen, University Medical Centre Utrecht, Uppsala University Hospital and Royal North Shore Hospital in Sydney. The study was conducted according to the declaration of Helsinki.16 The Medical Ethical Committee granted a waiver for the Medical Research Involving Human Subjects Act (METC registration no. 2016492).
Data collection by chart review was approved by the institutional review boards of the hospitals.
The first 50 consecutive PRAs performed by individual surgeons and their teams were included in the analysis. Both unilateral and bilateral procedures were included; bilateral procedures were considered as two separate procedures (left and right). All surgical procedures were carried out between December 2006 and October 2016. Patients underwent endoscopic adrenal surgery for various indications, including primary aldosteronism, pheochromocytoma, Cushing’s syndrome, non-functioning adenoma, adrenal metastases and adrenal cysts. Indications for PRA in patients with metastases were ectopic Cushing’s as a consequence of a paraneoplastic manifestation of lung cancer, a malignant peripheral nerve sheath tumour in a patient diagnosed with multiple endocrine neoplasia type 1 and solitary metastases of colorectal cancer or melanoma.
Baseline demographic information, including the patients’ age, sex, previous medical history, ASA fitness grade, BMI, tumour size and tumour histopathology, as well as clinical and operative outcomes, were obtained from prospectively maintained databases at the participating hospitals.
Primary and secondary endpoints
The primary outcome measure was duration of operation, defined as the time in minutes between initial incision and closure of the surgical wounds. Secondary outcomes were conversion to an open or laparoscopic transperitoneal approach, perioperative and/or postoperative complications and recovery time. The recovery time was defined as the time in days from surgery until discharge from hospital. Postoperative complications were graded using the Clavien-Dindo complication classification.17
Surgical technique
PRA was carried out with the patient under general anaesthesia. Endotracheal intubation was performed at the supine position, before placing the patient prone. The first incision was made just below the tip of the 12th rib and the retroperitoneal space dissected bluntly with a finger. The second and third ports were then placed lateral and medial
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to the initial incision site. After carbon dioxide insufflation at a pressure of 15-25 mmHg, Gerota’s fascia was dissected to expose the superior pole of the kidney. Adrenalectomy was performed by detaching the adrenal gland from adjacent structures and ligation of the adrenal vein. The resected adrenal gland was placed in a retrieval bag and removed through the first incision site. No repositioning of the patient was undertaken during bilateral procedures.
The procedures were performed by surgical teams consisting of one or two experienced endoscopic endocrine surgeons. If necessary, the patients were monitored before and after surgery by an endocrinologist (according to hospital protocols) to prevent hypocortisolism.
Implementation of PRA into clinical practice
The implementation of PRA varied among the surgical teams (teams A-D) (Table 1).
All teams reviewed videos of PRA before implementation. Teams B, C and D visited professor Walz in Essen to observe procedures at his clinic. Continued proctoring was performed in the clinic of teams B and C during the first couple of procedures. One dedicated endocrine surgeon implemented PRA independently (team D), whereas the others went through the learning curve in a team, consisting of two dedicated endocrine surgeons.
Table 1 Implementation method for each surgical team
Team A Team B Team C Team D
No. of procedures 50 31 50 50
Recruitment period December
2016 to May 2013
October 2015 to October
2016
December 2017 to May
2011
September 2012 to August 2015
Review of videos Yes Yes Yes Yes
Proctor visit
No. of procedures observed Interval between proctor visit and implementation (months)
No - -
Yes 14
5
Yes 7 3
Yes 8 1
Proctor at own clinic No Yes Yes No
Previous experience with PRA Yes (residency)
Yes (fellowship)
No No
Alone versus team Team Team Team Alone
PRA, posterior retroperitoneoscopic adrenalectomy.
Statistical analysis
Baseline characteristics are presented as median (range) for continuous variables, and count with percentage for categorical variables. Kruskal-Wallis test and χ2 test respectively were used to compare the four surgical teams. P <0.050 was considered statistically significant. The association between independent variables and duration of operation was assessed by univariable and multivariable linear regression. Departure from linearity was assessed by categorizing the continuous variables. Backward selection was used for developing a multivariate model, with step-by-step elimination of the least significant variables until the p-value was less than 0.20.
Learning curve cumulative sum (LC-CUSUM) analysis was used to assess the learning curve for each surgical team. LC-CUSUM analysis was designed to determine when a surgeon reaches a predefined level of performance while learning a new procedure.18 The LC-CUSUM analysis tests the null hypothesis that the performance of a surgeon is unacceptable. A score is computed after each procedure, with success and failure yielding an increase of decrease respectively in the total score. Once the predefined level of performance (decision limit h) is reached, the null hypothesis is rejected, and the performance of surgeon considered acceptable. Graphically, the LC-CUSUM score is mapped to the y axis and the number of procedures to the x axis. The performance of a surgeon or surgical team is considered unacceptable as long as the score remains below the predefined threshold (decision limit h). Once the score increases with successes and limit h is reached, the performance is considered acceptable and the surgical team competent. Duration of operation with conversion rate was used for the LC-CUSUM analysis. In a recent systematic review11, PRA was compared with LTA in terms of duration of operation, blood loss, length of hospital stay, conversion and mortality. In the largest case series19, mean operating time was 138 minutes after a 14-year experience with LTA and PRA, confirming that the learning curve had been fulfilled. Based on this study and the other studies included in the systematic review11,18, an operating time of 130 minutes or more was defined as an incompetent performance. Conversion was also considered to represent an incompetent performance.
Acceptable and unacceptable failure rates are ideally set according to empirical data. In the absence of empirical training data concerning PRA or LTA, adequate performance was defined as a 20 per cent failure rate with an acceptable deviation of 10 per cent.
Inadequate performance was defined as a 35 per cent failure rate. The performance of LC-CUSUM tests is expressed in terms of average run length, defined as the mean number of procedures before an alarm occurs under the null and alternative hypotheses respectively.18 Based on simulations with 10.000 samples of 50 procedures under the adequate and inadequate performance levels, the probability of an alarm was calculated
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for various limits of h. A limit for h at 1.5 was chosen, giving a true-discovery rate of 81%
(the risk of declaring a trainee not proficient when their performance was acceptable was limited to 19 per cent (100-81)) and a false-discovery rate of 15 per cent (the risk of declaring a trainee proficient when their performance was unacceptable was limited to 15 per cent) over 50 procedures.
SPSS version 22.0 (IBM, Armonk, New York, USA) and R (R Foundation for Statistical Computing, Vienna Austria) software was used for statistical analysis.
RESULTS
In total, 181 procedures were undertaken by four surgical teams (Table S1, supporting information). Three of the four teams performed more than 50 adrenalectomies, and one team carried out 31 adrenalectomies. Baseline patient and tumour characteristics are summarized in Table 2. The median age of all patients was 57 (range 15–84) years, and the cohort comprised 111 females (61.3 per cent) and 70 males (38.7 per cent). Median BMI was 27 (range 15–55) kg/m2. In terms of location, 89 tumours (49.2 per cent) were located on the left side, 70 (38.7 per cent) on the right side, and 22 (12.2 per cent) were bilateral.
The median overall tumour size was 25 (range 4–85) mm. Histology of the removed lesions showed that there were 79 adenomas (43.6 per cent), 51 pheochromocytoma (28.2 per cent), 20 instances of hyperplasia (11.0 per cent), 11 adrenal metastases (6.1 per cent) and 20 other lesions (11.0 per cent) (including adrenal cysts and myelolipomas). Baseline patient characteristics and tumour size were similar (Table 2), but there was a significant difference in tumour histopathology (p = 0.006) between the four surgical teams.
Learning curve
The median overall duration of operation was 89 (range 29-265) minutes. Figure 1 shows the number of procedures performed by each surgical team in relation to the LC-CUSUM score. The surgical teams reached competency after 24, 29, 40 and 42 procedures, demonstrated by crossing the threshold (limit h).
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limit h
0.0 0.5 1.0 1.5
0 10 20 30 40 50
Observations
LC−CUSUM score
Surgical team A B CD
Figure 1 Learning curve for each surgical team. The consecutive number of procedures is shown in relation to the learning curve cumulative sum (LC-CUSUM) score. The performance of the surgical team is considered inadequate as long as the score remains below the predefined threshold (limit h). The learning phase is completed when limit h is crossed
Table 2 Baseline patient and tumour characteristics by surgical team
Team A (n = 50) Team B (n = 31) Team C (n = 50) Team D (n = 50) p†
Age (years)* 55.5 (25-76) 56 (32-78) 56.5 (19-84) 60(15-83) 0.547‡
Sex ratio (M:F) 25:25 12:19 12:38 21:29 0.058
ASA fitness grade 0.069
I 5 (10.2) 0 (0) 3 (6) 8 (16)
II 36 (73.5) 22 (71) 33 (66) 25 (50%)
III 8 (16.3) 9 (29) 14 (28) 17 (34)
IV 0 (0) 0 (0) 0 (0) 0 (0)
BMI, kg/m2* 27.1 (20.0-54.5) 27.3 (19.5-39.8) 26.9 (14.9-44.3) 27.5 (18.0-40.4) 0.689‡
Surgical approach 0.089
Left 23 (46) 16 (52) 22 (44) 28 (56)
Right 21 (42) 7 (23) 22 (44) 20 (40)
Bilateral 6 (12) 8 (26) 6 (12) 2 (4)
Tumour size (mm) * 34 (6-67) 25 (11-85) 22.5 (10-50) 28.5 (4-82) 0.720‡
Tumour histopathology 0.006
Adenoma 20 (40) 8 (26) 22 (44) 29 (58)
Hyperplasia 7 (14) 3 (10) 6 (12) 4 (8)
Pheochromocytoma 18 (36) 11 (35) 12 (24) 10 (20)
Adrenal metastases 1 (2) 7 (23) 2 (4) 1 (2)
Other 4 (8) 2 (6) 8 (16) 6 (12)
Values in parentheses are percentages unless indicated otherwise; * values are median (range).
†χ2 test, except ‡ Kruskal-Wallis test.
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Table 2 Baseline patient and tumour characteristics by surgical team
Team A (n = 50) Team B (n = 31) Team C (n = 50) Team D (n = 50) p†
Age (years)* 55.5 (25-76) 56 (32-78) 56.5 (19-84) 60(15-83) 0.547‡
Sex ratio (M:F) 25:25 12:19 12:38 21:29 0.058
ASA fitness grade 0.069
I 5 (10.2) 0 (0) 3 (6) 8 (16)
II 36 (73.5) 22 (71) 33 (66) 25 (50%)
III 8 (16.3) 9 (29) 14 (28) 17 (34)
IV 0 (0) 0 (0) 0 (0) 0 (0)
BMI, kg/m2* 27.1 (20.0-54.5) 27.3 (19.5-39.8) 26.9 (14.9-44.3) 27.5 (18.0-40.4) 0.689‡
Surgical approach 0.089
Left 23 (46) 16 (52) 22 (44) 28 (56)
Right 21 (42) 7 (23) 22 (44) 20 (40)
Bilateral 6 (12) 8 (26) 6 (12) 2 (4)
Tumour size (mm) * 34 (6-67) 25 (11-85) 22.5 (10-50) 28.5 (4-82) 0.720‡
Tumour histopathology 0.006
Adenoma 20 (40) 8 (26) 22 (44) 29 (58)
Hyperplasia 7 (14) 3 (10) 6 (12) 4 (8)
Pheochromocytoma 18 (36) 11 (35) 12 (24) 10 (20)
Adrenal metastases 1 (2) 7 (23) 2 (4) 1 (2)
Other 4 (8) 2 (6) 8 (16) 6 (12)
Values in parentheses are percentages unless indicated otherwise; * values are median (range).
†χ2 test, except ‡ Kruskal-Wallis test.
Factors associated with duration of operation
The following variables were included in univariate analyses: age, sex, BMI, ASA grade, side of procedure, tumour size and tumour histopathology. Sex correlated significantly with duration of operation in univariate analysis, and operating time was longer in males (β = 23.46, 95 per cent c.i. 11.92 to 35.01) (Table 3).
A multivariate analysis was subsequently performed, with all variables included in the univariable analyses entered in the model. After adjusting the analyses by using backward selection, BMI and sex remained in the model (Table 4). Important confounders with a p
<0.20 were BMI over 30 kg/m2 (β = 10.96, -1.66 to 23.59, p = 0.088) and male sex (β = 21.93, 10.20 to 33.66, p <0.001).
Recovery time and complications
The median recovery time until discharge from hospital was 2 (range 1-19) days. A total of 35 perioperative and postoperative complications occurred in 34 patients (18.8 per cent).
There were four major perioperative complications including bleeding of the superior polar artery with posthaemorrhagic shock, bleeding of the 12th intercostal artery due to damage from port insertion treated by embolization, spleen laceration treated with splenectomy and prolonged intubation for hypercapnia. There were also four grade 1 perioperative complications. Postoperative complications were minor in most patient, and 17 of 27 were grade 1. No significant difference was seen in the number of perioperative and postoperative complications between the surgical teams (p = 0.275).
Conversion to open surgery was necessary in nine procedures (5.0 per cent). Reasons for these conversions were difficulty in localizing the adrenal gland, limited space, adhesions, morbid obesity and bleeding. The number of conversions differed significantly between the surgical teams (p = 0.007). There were seven conversions in team A, none in Team B and one each in teams C and D.
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Table 3 Univariable linear regression analyses of explanatory variables for duration of surgery
β P
Age, years
<40 Reference
40-65 7.83 (-7.57, 23.24) 0.317
>65 14.22 (-3.60, 32.03) 0.117
Sex
F Reference.
M 23.46 (11.92-35.01) <0.001
BMI (kg/m2)
<20 -12.09 (-42.10, 17.92) 0.428
20-30 Reference.
>30 10.95 (-2.12, 24.02) 0.100
ASA fitness grade
I Reference.
II 5.78 (-15.18, 26,74) 0.587
III 17.08 (-5.61, 39.77) 0.139
Side of procedure
Left Reference.
Right -0.71 (-12.51, 11.09) 0.906
Tumour size (mm)
<20 Reference.
20-40 -0.88 (-15.00, 13.24) 0.903
>40 1.95 (-16.07, 19.97) 0.831
Tumour histopathology
Adenoma Reference.
Hyperplasia 6.5 (-13.80, 26.81) 0.528
Pheochromocytoma 8.77 (-5.62, 23.17) 0.231
Metastases 5.11 (-17.25, 27.48) 0.652
Other -0.04 (-19.93, 19,86) 0.997
Values in parentheses are 95 per cent confidence intervals.
Table 4 Multivariate regression analysis of explanatory variables for duration of surgery
β P
Sex
F Reference.
M 21.93 (10.20, 33.66) <0.001
BMI (kg/m2)
<20 -3.57 (-32.91, 25.76) 0.810
20-30 Reference.
>30 10.96 (-1.66, 23.59) 0.088
Values in parentheses are 95 per cent confidence interval
4 DISCUSSION
In this multicentre study, the learning curve for PRA was assessed in four specialized endocrine surgical centres in three different countries. The learning curve for PRA ranged from 24 to 42 procedures. Complication and conversion rates were low, and there was no major morbidity, demonstrating the safety of introducing this procedure into clinical practice. The present findings confirm that PRA can be implemented safely in institutions still performing LTA.
PRA has low complication and conversion rates, making it hard to use these outcome parameters alone to analyse the learning curve. In most previous studies7,20,21, duration of operation was used to assess the learning curve. Therefore, operating time was chosen as the primary endpoint in analysis of PRA learning curve in the present analysis. In previous studies9,11,22, the median duration of operation varied. Walz and colleagues8 reported an operating time of 124 min in their initial series of 30 patients, which is longer than the median of 89 min for PRA reported here. This discrepancy may be explained by the initial development and standardization of the method per se; indeed, Walz and co-workers23 reported a decreasing operating time in following years. In several other studies7,9,11,23, including a recent systematic review11 comparing laparoscopic and retroperitoneoscopic adrenalectomy, the duration of operation varied widely for PRA from 50 to 221 min. The difference in experience with PRA could be one explanation for this variation, van Uitert et al.24 reported the operating time in the introduction phase: a median of 100 min for the first 20 procedures, declining to 83 min for procedures 21-40. Similar results were noted in an initial experience by Barczyński and colleagues. These findings are consistent with the median operating time of 89 min in the present study.
In this multicentre study, the number of procedures required to overcome the learning curve for PRA is comparable with that for LTA: 24-42 versus 20-40 procedures respectively.13-15,25,26 However, LTA is technically more challenging, whereas PRA is more difficult in terms of orientation in an unfamiliar anatomical environment. In literature, the number of procedures required to overcome the learning curve PRA ranges from 15-257,21 to 7024. In the present study, the number of procedures needed to master PRA in four specialized endocrine surgical centres also varied, from 24 to 42.
The steepness of a learning curve is related to several factors, including proper theoretical knowledge followed by practical training, the complexity of a procedure, previous experience with other procedures, proctorship and mentoring.13,25 The ability to visit an institution with expertise in the technique is crucial to successful adaptation
placement of incisions and careful positioning of the patient, to create a good exposure to the intended surgical area. Incorrect placement of skin incisions leads to frustration and clashing of instruments in this small operative field. These factors are best learned by observing an experienced team before first attempting the procedure. After this, continued mentorship during the introductory phase is preferable, making the technique easier to master during the learning curve period. This is, however, difficult in practice owing to a paucity of adequate local mentors around the world. With rapid advances in technology, another option would be telementoring. Telementoring involves an experienced physician remotely observing and guiding a less experienced caregiver in a particular procedure.28 It could be a safe and feasible way of assisting surgeons in learning a new technique.29 Another aspect related to the learning curve is the volume of procedures performed in a surgical unit, which should be substantial. If the annual caseload is too low, it will be hard to overcome the learning curve at all.
In the present study, the various factors that potentially influencing the learning curve differed in the four participating centres. During the learning curve, three of four centres worked together in surgical teams, consisting of two dedicated endocrine surgeons.
However, team D fulfilled the learning curve alone and took the longest to master the procedure. Potentially, operating together accelerates fulfilment of the learning curve as the assistant surgeon learns important orientation skills even when only holding the camera, and is able to coach the operating surgeon at the same time. All but one surgical team (team A) visited professor Walz in Essen to learn from his expertise. Two centres (teams B and C) invited a proctor into their own institution for their first procedures. Team B, the first to fulfil the learning curve, combined a visiting proctor, continued proctoring at their own clinic and working in a surgical team. Although team A did not visit a proctor or invite a proctor into their own institution, they reached their learning curve after 29 procedures. However, team A had a higher conversion rate than the other surgical teams.
The combination of a visiting proctor, continued proctoring at a surgeon’s own clinic and working in a team consisting of two dedicated surgeons has a beneficial impact on fulfilling the learning curve of PRA.
This study has several limitations. First, the learning curve might be influenced by method of implementation, which differed between the four specialized endocrine centres. On the other hand, the variation in implementation method could also be seen as one of the strengths of this study. It provides insight into the effect of different ways of implementing PRA on the learning curve. Second, it must be underlined that duration of operation is not the sole endpoint for assessing competency. However, the complication rate for this procedure is too low for a LC-CUSUM analysis to be carried out with this parameter alone. Third, as not all patients were eligible for PRA and patients were probably carefully
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selected for the first few procedures, there is a potential selection bias. Even so, the cohort comprised a homogeneous group, with no significant differences in patient characteristics and tumour size. Finally, owing to the retrospective nature of this study, there are missing data and data may be biased by variations in recoding methods used in the electronic databases.
Apart from the surgical learning curve, the implementation of PRA involves more aspects of learning. The anaesthetist, theatre personnel and surgical team are often unfamiliar with the correct prone position. During the introductory phase, positioning of the patient will take substantially more time and attention. Furthermore, the prone position combined with the high retroperitoneal carbon dioxide pressures used during the procedure create a higher serum partial pressure of carbon dioxide (pCO2). During the learning curve, the first PRA procedures often take longer, causing the serum pCO2 to rise. Therefore, an anaesthetist with experience in prone procedures, such as spinal procedures, is preferably required. Excellent collaboration and communication are necessary between the surgical team and anaesthetist, especially during the initial procedures.
PRA demands reorientation in a new surgical retroperitoneal environment. The procedure can be implemented safely in specialized endocrine surgical centres; between 24 and 42 procedures are required to fulfil the entire surgical learning curve. The present result can encourage institutions to implement PRA in patients with adrenal tumours.
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SUPPLEMENTARY INFORMATION
Table S1 Baseline patient and tumour characteristics
Total (n = 181) Gender, n (%)
Male 70 (38.7)
Female 111 (61.3)
Age, median (range), yr. 57.0 (15.0 – 84.0)
ASA score, n (%)
ASA I 16 (8.9)
ASA II 116 (64.4)
ASA III 48 (26.7)
ASA IV 0 (0.0)
BMI, median (range), kg/m2 27.1 (14.9 – 54.5)
Surgical approach, n (%)
Left 89 (49.2)
Right 70 (38.7)
Bilateral 22 (12.2)
Tumour size, median (range), mm. 25.0 (4.0 – 85.0)
Tumour histopathology, n (%)
Adenoma 79 (43.6)
Hyperplasia 20 (11.0)
Pheochromocytoma 51 (28.2)
Adrenal metastases 11 (6.1)
Other 20 (11.0)
ASA, American Society of Anaesthesiologists. BMI, Body Mass Index.
