Safety of Robot-Assisted Radical Prostatectomy with Pneumoperitoneum of 20 mm Hg: A Study of 751 Patients

Abstract

Background and Purpose:

Early studies describing robot-assisted radical prostatectomy (RARP) reported the use of pneumoperitoneum at a pressure of 15 mm Hg. While higher insufflation pressures (20 mm Hg) may reduce venous oozing and improve visualization, the safety of this method has not been confirmed. This study evaluates the short-term perioperative outcomes of patients undergoing RARP with insufflation pressures of 20 mm Hg.

Patients and Methods:

A single-surgeon, prospectively maintained database of patients undergoing RARP was retrospectively analyzed. Patients who underwent RARP with a pneumoperitoneum pressure of 15 and 20 mm Hg for the entire procedure were analyzed. Preoperative and postoperative hemoglobin levels and estimated glomerular filtration rate (eGFR) were compared. Complications, operative time, and estimated blood loss were also examined.

Results:

The number of patients in the experimental (20 mm Hg) and control (15 mm Hg) groups were 550 and 201, respectively. The groups were well matched with respect to age and operative time. The experimental group had a significantly smaller decrease in mean hemoglobin levels after surgery (−1.18 vs−2.13 mg/dL, P<0.0001). There was no significant difference in the eGFR on the first day after surgery (postoperative day [POD]1) (88.4 vs 85.0 mL/min/1.73m², P=0.11) or in the change in eGFR from preoperative to POD1 levels (−0.49 vs 1.54 mL/min/1.73m², P=0.18). The complication rate in the experimental group was 8.55% vs 8.46% in the control group.

Conclusion:

Pneumoperitoneum using a pressure of 20 mm Hg for RARP is safe and has no significant short-term effects on renal function and hemoglobin. Increased insufflation pressure was not associated with a higher complication rate.

Introduction

Since its introduction in 2001, robot-assisted radical prostatectomy (RARP) has become the most common surgical approach for the treatment of patients with prostate cancer in the United States.^1
–3 Compared with open radical prostatectomy, the robotic approach provides improved visualization and increased working space in the pelvis, in part because of insufflation of the peritoneal cavity with CO₂. Pneumoperitoneum, especially when combined with Trendelenburg positioning, is a physiologically complex state, with local and systemic effects on the patient.⁴ The effects of pneumoperitoneum can be attributed to both absorption of CO₂ and increased intra-abdominal pressure (IAP). The absorption of CO₂ causes hypercapnia and systemic acidosis, while increased IAP leads to increased peak airway pressures, decreased vital capacity, decreased compliance, and oliguria.⁵ These effects are dependent on both the insufflation pressure of the gas and the duration of the pneumoperitoneum.⁵

Initial descriptions of RARP techniques reported the safety and efficacy of pneumoperitoneum with insufflation pressures of 15 mm Hg.¹ A study of prolonged elevation in IAP was conducted in pigs and found that insufflation pressures greater than 15 mm Hg caused a significant decrease in cardiac output, renal vein flow, and urine output when compared with IAP less than 15 mm Hg.⁶ These changes, however, were not found to cause any permanent renal dysfunction or histological change.⁶ A study of physiologic changes during RARP with insufflation pressures of 12 mm Hg demonstrated minimal hemodynamic changes, but did reveal elevated PaCO₂ during and after the procedure.⁷

The authors' practice has been to perform RARP with insufflation pressures of 20 mm Hg throughout the procedure. The potential advantages of this higher pressure are improved visualization and reduced blood loss. The safety of this approach for RARP, however, has not been reported. One institution reported safety outcomes from 76 consecutive patients undergoing various genitourinary laparoscopic procedures,⁸ but to date there exists no published literature specifically analyzing outcomes during RARP at an insufflation pressure of 20 mm Hg. Therefore, we aim to review the data on a large, contemporary cohort of patients undergoing RARP at our institution with insufflation pressures of 20 mm Hg.

Patients and Methods

Study design

After obtaining Institutional Review Board approval at our institution, a prospectively maintained, single-surgeon database was reviewed for patients who underwent RARP between 2007 and 2012. All patients underwent RARP for localized prostate cancer by a single, high-volume surgeon. The high pressure group consisted of 550 consecutive patients (#302–#851 of personal case series) who underwent RARP with an insufflation pressure of 20 mm Hg. For comparison, 201 patients with RARP performed using the same technique and by the same surgeon (#101–#301 of personal case series) at 15 mm Hg insufflation pressure were designated as the control group.

Evaluated data points included: Preoperative, immediate postoperative, 1-day postoperative (POD1) hemoglobin (Hgb), and preoperative and postoperative creatinine levels. These creatinine measurements, along with patient age and race, were used to calculate each patient's estimated glomerular filtration rate (eGFR) using the Modification of Diet in Renal Disease study equation. Estimated blood loss (EBL), operative time, and postoperative complications were also evaluated. Categorical variables were evaluated using the Fisher exact test, and continuous variables were compared using t test with a two-tailed P value of <0.05 considered significant. All statistical analyses were performed by SPSS version 21 (IBM, Armonk, NY).

Operative technique

All patients were given preoperative antibiotic prophylaxis. Abdominal access was obtained using a Veress needle, and insufflation with CO₂ at a pressure of 15 or 20 mm Hg was initiated. Conventional insufflation was used for all cases; no AirSeal® device or other valve-free insufflation system was used. Pneumoperitoneum was maintained at the designated pressure until the urethrovesical anastomosis was completed. The IAP was then reduced to 5 mm Hg for 5 minutes to confirm the absence of significant bleeding. All patients were extubated immediately postoperatively. Prophylactic anticoagulation was not used routinely, except for one patient who had a mechanical heart valve.

Results

The demographic and perioperative clinical data for all study patients is represented in Table 1. A total of 751 patients were identified who underwent RARP from 2007 to 2012. Of these, 550 patients were included in the experimental group (20 mm Hg) and 201 patients in the control group (15 mm Hg). The groups were well matched with respect to mean age (59.0 vs 58.7 years, P=0.596) and operative time (198.5 vs 194.6 min, P=0.391).

Table 1.

Patient Demographics and Perioperative Outcomes

	15 mm Hg ^a (n=201)	20 mm Hg ^a (n=550)	P value
Clinicodemographic characteristics
Age (year)	58.7±6.5	59.7±7.0	0.09
Preoperative PSA (ng/mL)	5.97±3.60	6.44±7.69	0.40
Biopsy Gleason score
6	143 (71.5%)	294 (54.1%)	<0.001
7	42 (21.1%)	192 (35.4%)
8≤	15 (7.5%)	57 (10.5%)
Clinical stage
≤T_1c	167 (83.1%)	469 (85.1%)	0.28
≥T_2a	34 (16.9%)	82 (14.9%)
Perioperative characteristics
Operative time (minutes)	194.6±6.2	198.5±58.6	0.39
Estimated blood loss (mL)	183.1±21.1	249.5±181	<0.0001
Pelvic lymph node dissection
No	193 (96.0%)	461 (83.8%)	<0.0001
Yes	8 (4.0%)	89 (16.2%)
Preoperative eGFR^b (mL/min/1.73 m²)	83.4±17.1	88.8±20.4	0.0009
Postoperative day 1 eGFR^b (mL/min/1.73/m²)	85.0±34.2	88.4±22.0	0.11
Preoperative Hgb^c (gm/dL)	14.7±0.15	14.63±1.2	0.41
Immediate postoperative Hgb^c (gm/dL)	13.4±0.17	13.4±1.19	>0.99
Postoperative day 1 Hgb^c (gm/dL)	12.6±0.15	12.8±1.17	0.02
Change in eGFR^b:Postoperative day 1 vs preoperative (mL/min/1.73 m²)	1.54±24.8	−.49±15.39	0.18
Change in Hgb^c:Postoperative day 1 vs preoperative (g/dL)	−2.13±0.17	−1.18±1.14	<0.0001
Histopathologic characterics
Pathologic Gleason Score
6	93 (46.7%)	239 (44.2%)	0.80
7	79 (39.7%)	229 (42.3%)
≥8	27 (13.6%)	73 (13.5%)
Pathologic stage
≤pT_2c	163 (81.5%)	407 (75.2%)	0.08
≥pT_3a	37 (18.5)	134 (24.8%)
Prostate weight (g)	49.1±17.5	48.3±20.0	0.61

Mean±standard deviation for continuous variable and Count (percent) for categorical variable.

mmHg=millimeters of mercury pressure.

eGFR=estimated glomerular filtration rate.

Hgb=hemoglobin.

PSA=prostate-specific antigen; eGRF=estimated glomerular filtration rate; Hgb=hemoglobin.

The experimental group had significantly higher biopsy Gleason scores, but clinical stage, pathologic Gleason scores, and stage were not significantly different between groups (Table 1). The experimental group had a significantly higher proportion of patients who underwent pelvic lymph node dissection (PLND) (16.2% vs 4.0%, P<0.0001); however, PLND in this cohort was not associated with a significant difference in postoperative Hgb or EBL (data not shown).

Mean EBL was significantly greater in the experimental group compared with the control group (249.5 vs 183.1 mL, P<0.0001). The experimental group, however, had a higher mean Hgb on POD1 (12.8 vs 12.6, P=0.02, Table 1) and a smaller decrease in mean Hgb levels from preoperative to POD1 time points compared with the control group (−1.18 vs −2.13 mg/dL, P<0.0001). One patient in each group needed blood transfusion postoperatively. The overall complication rate in the experimental group was 8.55% versus 8.46% in the control group (nonsignificant).

The mean eGFR was calculated for the study cohorts preoperatively and at POD1. Mean eGFR was significantly greater in the experimental group than in the control group preoperatively (P=0.0009). There was no significant difference in the mean eGFR on POD1 (88.4 experimental vs 85.0 control, P=0.113) or in the change in mean eGFR from preoperative to POD1 levels (-0.49 vs 1.54 mL/min/1.73m², P=0.181).

A total of 47 (8.55%) complications were identified in the experimental cohort and 17 (8.46%) in the control group; the rate of complications was not statistically significant between groups. A comparison of the surgical complication rates is represented in Table 2. There is no significant difference in the severity of complications between the groups. Specific complications are listed in Table 3. One patient in each group needed postoperative transfusion. The lone transfusion in the experimental group occurred in a patient who needed perioperative anticoagulation with heparin and Lovenox because having a mechanical heart valve. No deep vein thrombosis, stroke, or pulmonary embolism occurred in either group of patients. There were no cardiac or pulmonary complications in either cohort of patients. No patients in this study needed a reduction of the insufflation pressure during the procedure.

Table 2.

Comparison of Surgical Complication Rates Using Clavien-Dindo Classification

Frequency	15 mm Hg (n=201)	20 mm Hg (n=550)
Surgical complications: N (%)
No	184 (91.5)	503 (91.5)
Yes	17 (8.5)	47 (8.5)
Clavien surgical complications: N (%)
I	9 (4.5)	32 (5.8)
II	0	1 (0.2)
IIIa	0	2 (0.4)
IIIb	9 (4.0)	12 (2.2)
IVa	0	0
Major surgical complication≥3a: N (%)
No	193 (96.0)	536 (97.5)
Yes	8 (4.0)	14 (2.5)

Table 3.

Descriptions of Surgical Complications

Frequency, N (%)	15 mm Hg (n=201)	20 mm Hg (n=550)
Urinary retention	7 (3.5)	25 (4.5)
Bladder neck contracture	4 (2.0)	7 (1.3)
Hernia	2 (1.0)	1 (0.2)
Wound dehiscence	1 (0.5)	0
Rectal injury	1 (0.5)	2 (0.4)
Wound infection	1 (0.5)	0
Ileus	0	6 (1.1)
Lymphatic drainage	0	2 (0.4)
Lymphocele	0	1 (0.2)
Transfusion	1 (0.5)	1 (0.2)
Corneal abrasion	0	1 (0.2)
Hemorrhage	0	1 (0.2)
Total	17 (8.46)	47 (8.55)

Discussion

We compared a large cohort of contemporary patients who underwent RARP with insufflation pressure of 20 mm Hg with a similar cohort using an insufflation pressure of 15 mm Hg. Pneumoperitoneum can improve visualization by reducing bleeding but has many potential physiologic side effects. Major complications of pneumoperitoneum can include both cardiovascular (gas embolism, bradycardia, arrhythmia) and pulmonary (hypercarbia, pneumothorax) sequelae, among others. The 550 patients in the experimental cohort had a complication rate of 8.55%, but without any major cardiac or pulmonary complications. The control group had a similar overall complication rate of 8.46%.

Oliguria is a common finding in laparoscopy⁴ and thought to be from both compression of renal parenchyma and renal vasculature.⁹ The long-term sequelae of elevated insufflation pressures are not known. In this study, while the experimental group had a higher baseline eGFR preoperatively, there was no significant difference in the eGFR between groups postoperatively. The change in eGFR from preoperative baseline was not significantly different between groups.

One benefit of increased insufflation pressure is thought to be improved visualization as a result of less venous oozing in the operative field. Whether a significant amount of bleeding is prevented by higher insufflation is unknown. Paradoxically, in our study, the EBL was significantly greater in the experimental group despite higher insufflation pressures. More importantly, however, both POD1 Hgb (12.8 vs 12.6 g/dL, P=0.016) and the change in Hgb from baseline (−1.18 vs−2.13 g/dL, P<0.0001) significantly favored the experimental group, suggesting that there may be a true effect of higher insufflation pressures in minimizing blood loss during RARP.

While we cannot conclusively explain the finding of a higher EBL in the experimental group, the current results suggest that EBL may not be a reliable indicator of small differences in intraoperative bleeding and that the postoperative Hgb values represent a more objective measure of blood loss during the procedure. In addition, higher postoperative Hgb and a smaller decrease from baseline are seen in our experimental cohort despite the significantly higher rate of PLND in that group.

This study compares two large and contemporary cohorts of patients who underwent RARP with high-pressure (20 mm Hg) and standard (15 mm Hg) pneumoperitoneum by a single surgeon. There are several limitations to this study. First, long-term oncologic outcomes and complications are not included in this report. Invasive monitoring was not used in this study to assess the physiologic effects of high-pressure pneumoperitoneum. The outcomes of the study are from a single surgeon at a single institution and may not be generalizable to other surgeons at other institutions.

Finally, there is the possibility of confounding because of a learning-curve effect in this cohort, because the 201 RARP performed in the control group were performed immediately before the 550 RARP cases that comprise the experimental group. All 751 cases, however, took place after the surgeon's first 100 independent RARP procedures as well as a laparoscopic/minimally invasive urology fellowship. In addition, the EBL was significantly lower in the former than in the latter group.

Conclusion

A randomized, controlled, and blinded trial would be the ideal method to thoroughly characterize the benefits and risks of elevated insufflation pressure, especially given the noted differences in EBL and change in Hgb. Given the widespread use and safety of RARP at insufflation pressures of 15 mm Hg, however, the potential benefits of such a randomized, controlled trial may be outweighed by the financial and opportunity costs of such an undertaking.

Instead, we propose that the currently available data are sufficient to justify the use of 20 mm Hg insufflation pressure at appropriate times during RARP and in the context of an ongoing communication with anesthesia staff. Such an adjustment may be of use to surgeons during difficult portions of the procedure or in particularly difficult cases to improve visibility. Overall, the current findings demonstrate that 20 mm Hg pneumoperitoneum pressure can be safely used in a large, contemporary cohort of patients.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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