Perioperative outcomes in patients with BMI ⩾35 kg/m 2 undergoing robot-assisted radical prostatectomy in a centre employing high-risk preoperative services

Abstract

Objective:

To evaluate outcomes in patients with body mass index (BMI) ⩾35 kg/m² undergoing robot-assisted radical prostatectomy (RARP), at a centre incorporating a dedicated High-Risk Preoperative Assessment Clinic (PAC) and surgical-anaesthetic multidisciplinary team (MDT) for complex patients.

Patients and Methods:

Patients with BMI ⩾35 kg/m² (n = 50) undergoing RARP from August 2021 to July 2023 were compared to a random sample of patients with BMI <35 kg/m² (n = 186). Patient and cancer characteristics, perioperative, oncological and continence outcomes were compared.

Results:

A higher proportion of patients with BMI ⩾35 kg/m² were seen in High-Risk PAC and discussed in High-Risk MDT. Patients with BMI ⩾35 kg/m² had higher operating time (206 minutes vs 190 minutes, p = 0.035), estimated blood loss (300 mL vs 200 mL, p = 0.004) and incidence of ventilatory difficulties (15% vs 2.7%, p = 0.004). Postoperatively, there was no difference in unplanned PACU (post-anaesthesia care unit) admissions, postoperative complications, length of stay, readmissions, functional or oncological outcomes.

Conclusion:

Our results support RARP as a safe and feasible option for treatment of prostate cancer in a well-selected cohort of patients with BMI ⩾35 kg/m², in a high-volume surgical centre employing robust pre-assessment by anaesthetists with experience in high-risk cases, and joint decision-making in a surgical-anaesthetic MDT.

Level of evidence:

Keywords

Prostate cancer robot-assisted radical prostatectomy obesity perioperative outcomes oncological outcomes functional outcomes

Introduction

Obesity poses significant anaesthetic and surgical challenges during robot-assisted radical prostatectomy (RARP) and is associated with higher perioperative complication rates,¹ and increased operating time, estimated blood loss (EBL) and length of stay (LOS).^2–6 Obesity is also linked with increased risk of urinary stress incontinence, erectile dysfunction and inferior oncological outcomes.^1,7 Consequently, many centres utilise body mass index (BMI) cut-offs when determining eligibility for RARP. However, emerging evidence suggests that patients with high BMI (⩾35–40 kg/m²) can achieve comparable outcomes when undergoing RARP,^6,8,9 suggesting RARP may be safe in these populations under specific circumstances.

University College London Hospitals NHS Trust (UCLH) is a high-volume tertiary referral centre, performing over 800 RARPs annually. The institution has developed a structured multidisciplinary pathway to support the safe delivery of RARP in patients with increased perioperative risk, including those with severe obesity. At UCLH, patients with a BMI ⩾35 kg/m² are considered for RARP on an individualised basis, guided by a standardised preoperative assessment and optimisation protocol designed to enhance patient safety and surgical outcomes.

Where clinically appropriate, definitive surgery may be deferred to allow time for optimisation. During this period, patients may undergo active surveillance or receive anti-androgen therapy, depending on prostate cancer risk stratification and disease characteristics. This approach enables physiological optimisation while minimising oncological risk, particularly in patients with low- or intermediate-risk disease.

Following optimisation, patients are re-discussed at the multidisciplinary team (MDT) meeting to support shared decision-making regarding surgical suitability and timing. Considerations include medical comorbidities, residual anaesthetic risk, tumour stage, risk of progression and alternative treatment options. Once approved, patients are listed alongside standard-risk cases within the routine operating programme.

We conducted a service evaluation to assess perioperative, functional and oncological outcomes in patients with a BMI ⩾35 kg/m² undergoing RARP at UCLH.

Patients and methods

Preoperative pathway

All patients who have surgery as treatment option for their prostate cancer are discussed at a pre-operative surgical planning MDT meeting. This identifies risk factors that may increase operative difficulty (such as narrow pelvis, presence of a median lobe, abdominal wall mesh or hernia), or increase risk of poor functional or oncological outcomes.

Patients considered for RARP then undergo a uniform triage process to assess surgical suitability and perioperative risk. This incorporates functional assessment, medical comorbidity evaluation and anthropometric measures. Functional capacity is assessed using the Duke Activity Status Index (DASI),¹⁰ a validated estimate of cardiorespiratory reserve. Medical history is reviewed in detail, with particular emphasis on cardiovascular, respiratory and neurological comorbidities that may increase perioperative risk during prolonged robotic surgery in a steep Trendelenburg position. Additional consideration is given to uncontrolled chronic conditions, including diabetes mellitus, hypertension (HTN) and obstructive sleep apnoea (OSA). Patients with a BMI ⩾35 kg/m² undergo further assessment focusing on fat distribution, as central obesity is associated with increased technical complexity and physiological stress during pneumoperitoneum. These triage criteria were developed collaboratively through a joint anaesthetic–surgical high-risk clinic, and informed by institutional experience, and evidence from the published literature on perioperative risk stratification in high BMI and medically complex patients undergoing robotic pelvic surgery.

Patients identified as potentially high-risk based on initial screening are reviewed in a High-Risk MDT comprising two consultant urological surgeons and a consultant anaesthetist. The MDT facilitates comprehensive evaluation of surgical feasibility, anaesthetic risk and oncological appropriateness. Patients deemed suitable for further assessment are referred to a dedicated High-Risk Preoperative Assessment Clinic (PAC). Patients can also be referred to High-Risk PAC by surgeons based on individual concerns without MDT.

The High-Risk PAC is led by the same consultant anaesthetist with specialist expertise in high-risk RARP. The clinic focuses on detailed risk assessment, patient counselling and targeted optimisation of comorbidities. Interventions may include cardiopulmonary investigations, optimisation of medical therapy, reinforcement of continuous positive airway pressure (CPAP) therapy where indicated, and referral to relevant specialist services.

Study design and participants

Patients undergoing RARP between August 2021 and July 2023 were retrospectively identified using a data search on our electronic patient record system. All 53 patients with BMI ⩾35 kg/m² who underwent RARP during this period were included in the initial local service evaluation, and a random sample of 200 patients with BMI <35 kg/m² were selected for comparison, by assigning a random number to each patient using the Microsoft Excel RAND formula.

The study was registered and approved as a service evaluation with the local Audit and Quality Improvement Registry; therefore, formal ethical approval was not required. Approval was also obtained from the Trust Caldicott Guardian and Information Governance Department prior to publication.

Patients who had enrolled in the National Data Opt-Out were removed from the data prior to publication as per UCLH Trust policy; 17 patients included in the initial service evaluation were removed (n = 3 from the ⩾35 kg/m² group and n = 14 from the BMI <35 kg/m² group), to give a final cohort size of 50 patients with BMI ⩾35 kg/m² and 186 patients with BMI <35 kg/m². In addition, in line with Trust Information Governance regulations, frequencies of less than five patients are reported as ‘<5’ to avoid potentially identifiable data.

Data extraction

Patient and cancer characteristics, perioperative and surgical management and outcome data were collected from the electronic patient record and a prospectively maintained RARP database. Every attempt was made locate missing data but where data is missing, percentage data completeness is given in results tables. Where no completeness value is given, there was no missing data.

Baseline patient and cancer characteristics

Patient characteristics included age, BMI at time of surgery, American Association of Anaesthesiologists (ASA) grade, comorbidities and calculated Charlson Comorbidity Index.¹¹ Cancer characteristics included clinical and pathological staging, preoperative prostate-specific antigen (PSA) and Gleason score. In addition, prostate gland size and membranous urethral length (MUL) were collected as these are reported predictors of functional outcomes.¹²

Perioperative and surgical management

Preoperative management details included High-Risk PAC review and discussion in High-Risk MDT. Surgical management included grade of primary operating surgeon, nerve sparing, surgical approach (Retzius Sparing or standard) and lymph node dissection. Nerve sparing and Retzius Sparing approaches have been associated with better functional outcomes and therefore these are important confounders.¹³

Outcomes

Outcome data included intraoperative characteristics (EBL, operating time, injury to other pelvic structures, anaesthetic complications) and postoperative complications (Clavien-Dindo grading), post-anaesthesia care unit (PACU) admissions (planned and unplanned) and readmissions to hospital.

Oncological outcomes included positive surgical margins (PSM), postoperative PSA persistence (defined as PSA ⩾0.1 ng/mL at 3 months) and biochemical recurrence (defined as PSA ⩾0.2 ng/mL at any time).

Continence outcomes included early (0–3 months) and late (3–12 months) continence outcomes defined by patient reported 24-hour pad usage, and rates of referral for artificial urethral sphincter surgery.

Statistical analysis

Data analysis was carried out using Microsoft Excel (version 16.94 for Mac) with the Real Statistics add-on (Release 9.4). Quantitative data was analysed using the Mann–Whitney U test, and categorical data was analysed using the chi-square test, or Fisher’s exact test for small sample sizes (where expected values were 5 or less). A two-tailed p value of <0.05 was considered statistically significant.

Results

Baseline patient and cancer characteristics

Median BMI was 27.7 kg/m² in the BMI <35 kg/m² group, and 36.3 kg/m² in the BMI ⩾35 kg/m² group. There were <5 patients with BMI ⩾40 kg/m² (Table 1).

Table 1.

Baseline patient and cancer characteristics.

Parameter	BMI ⩾35 kg/m² (n = 50)	BMI <35 kg/m² (n = 186)	p value*
Age, years, median (IQR)	62 (57–66)	64 (59.2–69.0)	0.041
BMI, kg/m², median (IQR)	36.3 (35.5–37.6)	27.7 (25.1–30.0)
ASA Grade, n (%)
ASA 2	30 (60)	169 (91)	<0.001
ASA 3	20 (40)	17 (9)
Charlson Comorbidity Index, n (%)
0	<5	<5	0.13
1	6 (12)	33 (18)
2	22 (44)	73 (39)
3 +	19 (38)	78 (42)
Comorbidity, n (%)
Heart disease (ischaemic, structural or valvular)	<5	14 (7.5)	1
Arrhythmia	<5	11 (5.9)	1
Hypercholesterolaemia	14 (28)	39 (21)	0.3
Hypertension	36 (72)	81 (44)	<0.001
Venous thromboembolism	<5	<5	0.3
Diabetes	11 (22)	27 (15)	0.2
Respiratory disease	7 (14)	23 (12)	0.8
Renal disease	<5	6 (3.2)	0.2
Liver disease	<5	<5	0.07
Thyroid disease	<5	7 (3.4)	1
Neurological disease	<5	11 (5.9)	1
Obstructive sleep apnoea	6 (12)	5 (2.7)	0.01
Clinical Staging, n (%)
T2	41 (82)	131 (70)	0.1
T3	9 (18)	55 (30)
Membranous urethral length, mm, median (IQR) (98% complete)	14 (12–15)	16 (14–18)	0.003
Gland weight, g, median (IQR)	53 (41–65)	45 (36–56)	0.03
Preoperative PSA, ng/mL, median (IQR)	5.9 (4.4–7.9)	6.8 (4.7–10.7)	0.05
Preoperative (Biopsy) Gleason Score, n (%)
6	<5	<5	0.8
7	39 (78)	154 (83)
8	<5	10 (5.4)
9	5 (10)	18 (9.7)

BMI: body mass index; ASA: American society of anaesthesiologists; PSA: prostate-specific antigen.

p values calculated using Mann–Whitney U test for continuous and chi-square or Fisher’s exact test for categorical variables.

Patients with BMI ⩾35 kg/m² were younger (median age 62 years compared to 64 years in BMI <35 kg/m², p = 0.03), were more likely to be ASA 3 instead of ASA 2 (p < 0.001) and had a higher incidence of HTN (p < 0.001) and OSA (p = 0.013) compared to those with BMI <35 kg/m².

Patients with BMI ⩾35 kg/m² had a significantly lower median MUL (14.0 mm vs 15.5 mm, p = 0.004) and greater median gland weight in (53 g vs 45 g, p = 0.038).

There was no difference in other baseline patient or cancer characteristics including Charlson Comorbidity Index, clinical staging, preoperative PSA or preoperative (biopsy) Gleason Score.

Perioperative anaesthetic and surgical management

A significantly higher proportion of patients with BMI ⩾35 kg/m² were reviewed by the High-Risk PAC anaesthetist (54% vs 31% p = 0.002) and discussed at the high-risk MDT (34% vs 11%, p < 0.001) (Table 2).

Table 2.

Perioperative and surgical management.

Parameter	BMI ⩾35 kg/m² (n = 50)	BMI <35 kg/m² (n = 186)	p value*
Patients discussed in High-Risk MDT, n (%)	17 (34)	20 (11)	<0.001
Patients reviewed in High-Risk PAC, n (%)	27 (54)	57 (31)	0.002
Primary operating surgeon, n (%)
Consultant	36 (72)	150 (81)	0.2
Fellow	14 (28)	36 (19)
Pelvic lymph node dissections, n (%)	5 (10)	12 (6.5)	0.3
Retzius sparing, n (%)	9 (18)	102 (55)	<0.001
Nerve sparing, n (%)
None	15 (30)	49 (26)	0.9
Unilateral	14 (28)	53 (29)
Bilateral	21 (42)	84 (45)

MDT: multidisciplinary team meeting; PAC: pre-operative assessment clinic.

p values calculated using chi-square or Fisher’s exact test for categorical variables.

A smaller proportion of patients with BMI ⩾35 kg/m² received Retzius Sparing surgery (18% vs 56%, p < 0.001). There was no difference in the grade of the primary operating surgeon (consultant vs fellow undergoing supervised training where >50% steps were performed by the fellow), rates of pelvic lymph node dissection or nerve sparing.

Surgical and anaesthetic outcomes

Operation data revealed a significantly higher median operating time (206 minutes vs 190 minutes, p = 0.035), median EBL (300 mL vs 200 mL, p = 0.004) and incidence of blood transfusion in patients with BMI ⩾35 kg/m² (p = 0.009, however incidence <5 in both groups). There was no difference in the rates of intraoperative surgical complications (Table 3).

Table 3.

Perioperative surgical, anaesthetic, oncological and continence outcomes.

Parameter	BMI ⩾35 kg/m² (n = 50)	BMI <35 kg/m² (n = 186)	p value*
Operating time, minutes, median (IQR)	206 (176–238)	190 (158–224)	0.035
Estimated blood loss, mL, median (IQR)	300 (158–500)	200 (100–350)	0.004
Length of stay, days, median (IQR)	2 (1–2)	1 (1–2)	0.1
PACU admissions, n (%)	15 (30)	13 (7.0)	<0.001
Unplanned PACU admissions, n (%)	<5	<5	1
Unplanned re-admissions, n (%)	<5	9 (4.8)	0.48
Intraoperative anaesthetic complications, n (%)
Difficult intubation	0	<5	1
Ventilatory difficulties or desaturation	7 (14)	5 (2.7)	0.004
Arrhythmia	0	<5	1
Epistaxis	<5	0	0.2
Intraoperative surgical complications, n (%)
Minor damage to other pelvic structures	<5	6 (3.2)	0.7
Patients requiring perioperative blood transfusion	<5	<5	0.03
Postoperative complications by Clavien-Dindo Grade, n (%)
Grade 1	<5	10 (5.4)	0.5
Grade 2	6 (12)	15 (8.1)
Grade 3 +	0	<5
Margins, n (%)
Positive > 3 mm	<5	5 (2.7)	0.8
Positive <3 mm	11 (22)	33 (18)
Negative	38 (76)	148 (80)
Pathological staging, n (%)
pT2	32 (64)	117 (63)	0.9
pT3	18 (36)	69 (37)
PSA persistence (⩾0.1 ng/mL) at 3 months, n (%) (87% complete)	7 (16)	45 (28)	0.1
Any detectable PSA postop, n (%) (63% complete)	6 (21)	40 (34)	0.2
Biochemical Recurrence (> 0.2 ng/mL), n (%) (63% complete)	<5	8 (6.7)	1
Continence at 0–3 months (1 pad or fewer), n (%) (96% complete)	26 (57)	113 (63)	0.4
Continence at 3–12 months (1 pad or fewer), n (%) (77% complete)	31 (80)	120 (84)	0.5
Referrals for AUS, n (%) (70% complete)	<5	<5	0.1

PACU: post-anaesthesia care unit; PSA: prostate-specific antigen; AUS: artificial urinary sphincter.

p values calculated using Mann–Whitney U test for continuous and chi-square or Fisher’s exact test for categorical variables.

Anaesthetic records revealed an increased incidence of documented ventilatory difficulties and desaturation in patients with BMI ⩾35 kg/m² (14% vs 2.7%, p = 0.004), with no abandoned procedures and without a significant difference in any other anaesthetic complication.

Postoperative data revealed a significantly higher rate of PACU admissions for patients with BMI ⩾35 kg/m² (30.0% vs 7.0%, p < 0.001); however, there was no significant difference in the incidence of unplanned PACU admissions. There was also no difference in the median LOS, rates of unplanned readmissions or number of Clavien-Dindo grade 1, 2 or 3+ complications.

Oncological outcomes

Oncological data showed no difference in the rates of positive margins, PSA persistence at 3 months, biochemical recurrence or detectable postoperative PSA at any time (Table 3).

Continence outcomes

Despite significantly lower MUL and rates of Retzius Sparing, there was no difference in early or late continence rates, or rates of referral for artificial urinary sphincter surgery (AUS) between the two BMI groups (Table 3).

Discussion

Our data demonstrates that with careful patient selection and optimisation using our high-risk preoperative services, the BMI ⩾35 kg/m² cohort achieved outcomes comparable to the BMI <35 kg/m² cohort.

From an anaesthetic perspective, although patients with BMI ⩾35 kg/m² were younger, they had higher ASA grades, reflecting more poorly controlled comorbidities. HTN and OSA rates were significantly higher in the BMI ⩾35 kg/m² group. There was no significant difference in the Charlson Comorbidity Index scores between the two groups, though this scoring system does not account for HTN or OSA.

The age difference may reflect the MDT selection process; within those with BMI ⩾35 kg/m², younger patients are more likely to be offered RARP due to better functional status, exercise tolerance and fewer comorbidities. Furthermore, younger patients derive greater long-term benefit from RARP over radiotherapy, given the long-term risk of radiation-associated malignancies, and evidence suggesting improved cancer-specific survival with RARP in patients under the age of 65.^14,15 Consequently, the risks of RARP may be more acceptable in younger patients.

Intraoperatively, ventilatory difficulties, including high airway pressures and desaturation, were more common in patients with BMI ⩾35 kg/m², though no postoperative respiratory complications occurred. Abdominal obesity reduces functional residual capacity after induction of anaesthesia, pneumoperitoneum and steep Trendelenburg positioning, promoting atelectasis and ventilation–perfusion mismatch. Anaesthetic records indicate intra-abdominal pressure was reduced or Trendelenburg flattened to improve ventilation; this was balanced against surgical exposure, although pressure adjustments were not standardised, varying by patient, surgeon and stage of surgery.

RARP in patients with obesity is technically challenging due to increased intra-abdominal fat restricting visibility and working space.¹⁶ Our data showed increased operating times (206 minutes vs 190 minutes) and EBL in the BMI ⩾35 kg/m² group (300 mL vs 200 mL); however, rates of blood transfusions were too low to draw conclusions. There was no selection bias of cases according to the level of experience of the primary operating surgeon.

Postoperatively, although a significantly greater proportion of patients with BMI ⩾35 kg/m² were admitted to the PACU, there was no difference in the incidence of unplanned admissions, suggesting appropriate planning at pre-assessment for enhanced postoperative care. This enables earlier detection of complications and facilitates interventions such as early mobilisation and optimisation of analgesia, reducing postoperative morbidity, mortality and LOS.¹⁷ Accordingly, there was no significant difference in inpatient LOS, rates of postoperative complications, or unplanned readmissions once discharged from hospital.

From a functional perspective, continence outcomes were similar across both groups despite lower rates of Retzius Sparing and lower MUL in the high BMI group, both confounders associated with reduced continence rates.^18,19 Another potential confounding factor is age, with younger patients generally having improved continence outcomes²⁰; however, the small difference (median age 62 vs 64) is unlikely to be clinically significant in this regard. Oncological outcomes were also comparable, though these are influenced by surgical volume and experience and may not be applicable to smaller volume centres.²¹

It should be noted that although BMI correlates with subcutaneous adipose tissue, it is less strongly associated with visceral adipose tissue (VAT), which can increase operative difficulty, and has been independently linked to increased comorbidity risk.²² Accordingly, we plan to adopt practical methods to assess VAT in outpatient clinical settings and incorporate these measures into future evaluations.

Overall, these findings support the principle that RARP can be safely performed in select patients with BMI ⩾35 kg/m², provided certain criteria are met. Surgical experience maintains comparable functional and oncological outcomes despite the technical challenges of raised BMI. Our High-Risk PAC provides anaesthetic expertise, continuity of care and appropriately predicts those who may benefit from enhanced postoperative care,²³ reducing the risk of perioperative complications. The High-Risk MDT facilitates shared decision-making on whether RARP is feasible, and the necessary pre-optimisation required, with future plans for a preoperative weight loss programme, which has been associated with reduced surgical complication rates.^24,25

Limitations

There are several limitations of this service evaluation. The median BMI in our BMI ⩾35 kg/m² group was 36.3 kg/m² (interquartile range (IQR): 35.5–37.6 kg/m²), with <5 patients having BMI ⩾40 kg/m². Therefore, conclusions cannot be drawn about the safety of RARP in patients with BMI ⩾40 kg/m².

In addition, rare cases in which significant intraoperative ventilatory difficulties prevented the completion of surgery in high BMI patients were not captured, as they occurred outside of the 2-year evaluation window.

Some follow-up data was incomplete due to follow-up conducted in local hospitals in other regions. We also did not collect data on pre-RARP baseline continence, as stress incontinence is rare preoperatively in patients with prostate cancer, and erectile function was not assessed.

Finally, we recognise the potential for selection bias in our study, as we compared a carefully selected group of patients with BMI ⩾35 kg/m² with an unselected lower BMI cohort.

Conclusion

Our data supports RARP as a safe and feasible option for treatment of prostate cancer in a well-selected and optimised cohort of patients with BMI ⩾35 kg/m². We propose that key elements of delivering a safe RARP service for patients with a high BMI are surgical expertise within a high-volume centre, pre-assessment by anaesthetists with experience in high-risk cases and a joint surgical and anaesthetic approach to preoperative decision-making via an MDT.

Footnotes

Conflicting interests

The authors declare that there is no conflict of interest.

Funding

The authors received no financial support for the research, authorship and/or publication of this article.

Ethical considerations

Ethical approval was not sought for this study as it was conducted as a service evaluation and registered with the UCLH departmental Audit and Quality Improvement Registry. Approval for publication was obtained from the UCLH Caldicott Guardian and Information Governance Department prior to submission.

Informed Consent

Informed consent was not sought from individual patients as this study was conducted as a service evaluation. Patients who had enrolled in the National Data Opt-Out were removed from the data prior to publication, and all published data is fully anonymised as per UCLH Information Governance guidance.

Consent to participate

NA.

Consent for publication

NA.

Data availability statement

The data supporting this article may be available upon request to the corresponding author, subject to approval by the UCLH Information Governance Department.

Guarantor

C.G.

Author contributions

CG designed the study, defined the patient selection and medical optimisation protocols, developed the inclusion and exclusion criteria, supervised data collection and revised the initial draft of the manuscript, addressed the editors’ comments, and wrote the final version of the manuscript. Y.P., C.G. and E.D. were involved in designing the data collection methodology. Y.P., E.D. and J.R. collected the data. Y.P. performed the statistical analysis of the data. Y.P. and E.D. researched literature and wrote the first draft of the manuscript. All authors reviewed and edited the manuscript and approved the final manuscript.

ORCID iDs

Yuhan Peng

Carmen Gore

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