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Perioperative Outcomes of Robotic-Assisted Hysterectomy Compared With Open Hysterectomy

Gali, Bhargavi MD*; Bakkum-Gamez, Jamie N. MD; Plevak, David J. MD*; Schroeder, Darrell MS; Wilson, Timothy O. MD; Jankowski, Christopher J. MD*

doi: 10.1213/ANE.0000000000001935
Patient Safety: Original Clinical Research Report
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Continuing Medical Education

BACKGROUND: Increasing numbers of robotic hysterectomies (RH) are being performed. To provide ventilation (with pneumoperitoneum and steep Trendelenburg position) for these procedures, utilization of lung protective strategies with limiting airway pressures and tidal volumes is difficult. Little is known about the effects of intraoperative mechanical ventilation and high peak airway pressures on perioperative complications. We performed a retrospective review to determine whether patients undergoing RH had increased pulmonary complications compared to total abdominal hysterectomy (TAH).

METHODS: We performed a single center retrospective review comparing the intraoperative, anesthetic, and immediate and 30-day postoperative course of patients undergoing RH to TAH, including intraoperative ventilatory parameters and respiratory complications. Patients undergoing TAH (201) from 2004 to 2006 were compared to RH (251) from 2009 to 2012. It was our hypothesis that patients undergoing RH would have increased incidence of postoperative pulmonary complications. A secondary hypothesis was that morbid obesity predicts pulmonary complications in patients undergoing RH. Complications were compared between groups using Fisher’s exact test. To account for potential confounders, the primary analysis was performed for a subgroup of patients matched on the propensity for RH.

RESULTS: A total of 351 RH and 201 TAH procedures are included. Higher inspiratory pressures were required in ventilation of the RH group (median [25th, 75th] 31 [26, 36] cm H2O) than the TAH group (23 [19, 27] cm H2O) (P < .001) at 30 minutes after incision. Peak inspiratory pressures at 30 minutes after incision for RH increased according to increasing body mass index group (P < .001). There were 163 RH and 163 TAH procedures included in the propensity matched analysis. From this analysis, there were no significant differences in cardiopulmonary complications between RH and TAH (0.6% vs 1.2%; odds ratio = 2.0, 95% confidence interval = 0.2–2.4; P = 1.00). Surgical site infection was significantly lower in the RH compared to TAH group (0.6% vs 8.6%; P < .001). Hospital length of stay was longer for those who underwent TAH versus RH (median [25th, 75th] 2 [2, 3] vs 1 [0, 2] days; P < .001).

CONCLUSIONS: There was no significant difference in perioperative complications in obese and morbidly obese women compared to nonobese undergoing RH. Patients undergoing RH had shorter hospital stays, fewer infectious complications, and no increase in overall complications compared to TAH. Higher ventilatory airway pressures (RH versus TAH and obese versus nonobese) did not result in an increase in cardiopulmonary or overall complications. We believe that peritoneal insufflation attenuates the effect of high airway pressures by raising intrapleural pressure and reducing the gradient across terminal bronchioles and alveoli. Thus, we propose that lung protective strategies for patients undergoing RH account for the markedly elevated intraperitoneal and intrapleural pressures, whereas transpulmonary airway pressures remain static. This reduced transpulmonary gradient attenuates the strain on lung tissue that would otherwise be imposed by ventilation at high pressures.

Published ahead of print April 19, 2017.

From the Departments of *Anesthesiology

Obstetrics and Gynecology

Division of Biomedical Statistics & Informatics, Mayo Clinic, Rochester, Minnesota.

Published ahead of print April 19, 2017.

Accepted for publication December 27, 2016.

Funding: Departmental and institutional.

The authors declare no conflicts of interest.

Reprints will not be available from the authors.

Address correspondence to Bhargavi Gali, MD, Department of Anesthesiology, Mayo Clinic, 200 First St SW, Rochester, MN 55905. Address e-mail to gali.bhargavi@mayo.edu.

There has been an increasing availability and utilization of minimally invasive surgical techniques (MIST). Laparoscopic hysterectomy was first developed in the 1960s. A robotic platform for gynecologic procedures was approved by the US Food and Drug Administration in 2005. Since this time, increasing numbers of minimally invasive hysterectomies have been performed. Between 2007 and 2010, robotic procedures increased from 0.5% to 9.5% of all hysterectomies performed, whereas laparoscopic hysterectomies increased from 24.5% to 30.5%.1,2 By 2013, 191,000 robotic hysterectomies (RH) had been performed in the United States.3 Recent studies have demonstrated a reduced hospital length of stay and lower intraoperative blood loss when MIST are compared with total abdominal hysterectomy (TAH).1,4

MIST hysterectomy requires utilization of pneumoperitoneum and steep Trendelenburg for visualization of the pelvis. RH frequently requires Trendelenburg positioning of >30˚, and a patient must stay in a fixed position while the robot is docked. Although Trendelenburg position decreases pulmonary compliance and functional residual capacity5,6 and can worsen arterial oxygenation, the addition of pneumoperitoneum accentuates respiratory compromise.7 The respiratory consequences of robotic surgery include increased peak airway pressures, increased inspired-to-arterial oxygen gradient, increased arterial to end-tidal carbon dioxide gradient, and lower tidal volumes.8 These conditions could potentially result in an increase in atelectasis and postoperative respiratory complications. Literature over the past 2 decades has indicated that mechanical ventilation with lower tidal volumes might be protective of the lung in certain clinical conditions.9 Recent literature suggests that the magnitude tissue strain is the main determinant of mechanical lung injury. Transpulmonary pressure (airway pressure minus intrapleural pressure) is a measure of lung parenchymal stress. In the situation of RH, abdominal insufflation could potentially transmit pressures across the diaphragm to raise intrapleural pressures and result in reduced strain and injury of the lung.10

We performed a retrospective review to assess whether undergoing RH was associated with higher incidence of pulmonary complications compared with TAH.

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METHODS

After Mayo Clinic institutional review board approval, retrospective chart review was performed. We compared patients undergoing TAH for benign disease and low-risk stage I endometrial cancer from 2004 to 2006 to patients undergoing RH for the same indications from July 2009 to 2012 at our institution. During both study periods, standard management for low-risk endometrial cancer consisted of hysterectomy and bilateral salpingo-oophorectomy without lymphadenectomy.11 Patients were excluded if they did not provide consent for their data to be utilized for research or had additional procedures other than bilateral salpingo-oophorectomy at the same time as their hysterectomy. Robotic surgery was introduced at Mayo Clinic Rochester in December 2006. We selected the 3-year period before the introduction of RH for the TAH cohort, because the TAH procedure was standard performed in the same fashion by all gynecologic surgeons. By July 2009, RH had diffused thoroughly into the gynecologic surgery practice. To maintain consistency, our cases were performed predominantly by the same 3 surgeons for the 2 periods of chart review we performed.

Baseline demographics including age, body mass index (BMI), preoperative hemoglobin and creatinine, pulmonary and cardiac comorbidities, and American Society of Anesthesiologists (ASA) classification were abstracted. Intraoperative data collected included length of time in the operating room, length of surgery, volume of fluid and blood administration, estimated blood loss, and peak inspiratory pressures. In-hospital and 30-day postoperative complications included pulmonary (requirement for noninvasive ventilation, reintubation, pneumonia, requirement for respiratory therapy intervention, atelectasis noted in chart), cardiac (arrhythmias noted in chart or on electrocardiogram, elevated troponin, or notes documenting myocardial ischemia or infarction), and infectious complications (surgical site infection [SSI] and pneumonia). SSI was defined as wound infection documented in clinical notes requiring further wound care, antibiotics, or surgical intervention. Hospital length of stay and readmission within 30 days were also collected.

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Statistical Analysis

Table 1.

Table 1.

Data were summarized using mean ± standard deviation or median (interquartile range [IQR]) for continuous variables and frequency counts and percents for categorical variables. To assess whether patient factors were potentially associated with the choice of technique, univariate analyses were performed to compare baseline patient characteristics including age, BMI, ASA status, and preoperative comorbidities between the TAH and RH groups using the two-sample t-test, or rank sum test, for continuous variables and Fisher’s exact test for categorical variables. To account for potential confounders, the primary analysis assessing differences between TAH and RH techniques was performed using a propensity matched sample. To obtain this sample, logistic regression was used to calculate propensity scores for RH using all variables listed in Table 1. Patients who underwent TAH and RH were matched 1:1 on the logit of the propensity score using a caliper of 0.2 standard deviation units. Standardized mean differences after propensity score adjustment were obtained for each covariate to assess the effectiveness of the propensity score to control for confounding of the observed variables. To assess whether outcomes differed according to obesity, supplemental analyses were performed to compare outcomes across groups defined according to BMI (≤29.9, 30.0–39.9, ≥40.0 kg/m2) using the Kruskal-Wallis test for continuous variable and the Cochrane-Armitage test for categorical variables. In all cases, 2-sided tests were performed with P < .05 used to denote statistical significance. Analyses were performed using SAS version 9.3 (SAS Institute Inc, Cary, NC). This manuscript adheres to the applicable Equator guidelines. The sample size for this investigation was determined by the number of patients undergoing TAH and RH during the respective study periods. For the outcome of any complication, assuming a complication rate of 20% in those undergoing TAH, the sample size for our propensity matched analysis provides statistical power (2-tailed, α = .05) of 82% to detect an odds ratio of 0.40 when assessing whether patients undergoing RH have a lower complication rate than patients who undergo TAH.

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RESULTS

Baseline Patient Demographics

A total of 201 patients underwent TAH and 351 underwent RH during the study periods. BMI was significantly higher in patients undergoing RH (P < .002). Age, ASA Physical Status Classification, pre-existing comorbidities, and hemoglobin level were not significantly different between the groups (Table 1). Propensity scores were available for 351 patients undergoing RH and 198 of those undergoing TAH. From these, a matched sample of N = 163 patients per group was obtained. Characteristics of the propensity matched sample are also presented in Table 1.

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Intraoperative Characteristics

The length of surgery was significantly longer in RH compared to TAH (median 149 minutes [IQR 117, 193] vs 117 minutes [IQR 94, 141], P < .001). Estimated blood loss was significantly higher among those who underwent TAH (200 mL [IQR 100, 300]) compared to RH (100 mL [IQR 50, 150]); P < .001).

Peak inspiratory pressure at 30 minutes after incision was available for 34.3% in the TAH group and 96% of the RH group secondary to updates in our electronic intraoperative record between these time periods. Based on available data, significantly higher inspiratory pressures were required in ventilation of the RH group (median 31 cm H2O [IQR 26, 36]) than the TAH group (23 cm H2O [IQR 19, 27], P < .001) at 30 minutes after incision. Similarly, peak inspiratory pressures at 2 hours after incision were significantly higher in the RH group (27 cm H2O [IQR 17, 35] vs 18 [IQR 7, 23] cm H2O, P < .001).

The volume of crystalloid administration was significantly different between the groups (TAH median 2.43 L [IQR 1.89, 3.05] RH 2.21 L [IQR 1.70, 2.76], P = .002). There was no difference in administration of red blood cells or colloid between TAH and RH intraoperatively (Table 2). None of the patients received platelets, cryoprecipitate, or fresh frozen plasma intraoperatively.

Table 2.

Table 2.

In all cases, intraoperative differences between TAH and RH were consistent when the analyses were performed using the propensity matched subset.

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Impact of BMI on Ventilator Pressures

Table 3.

Table 3.

Table 4.

Table 4.

Peak inspiratory pressures at 30 minutes after incision for RH increased according to increasing BMI group: nonobese (BMI <29.9 kg/m2) had a median 27 cm H2O (IQR 23, 31), obese (BMI 30.0–39.9 kg/m2) had a median 35 cm H2O (IQR 30, 37), and morbidly obese (BMI ≥40.0 kg/m2) had a median 38 cm H2O (IQR 35, 40) (P < .001) (Table 3). At 2 hours after incision, peak inspiratory pressures in RH diminished but remained significantly higher in obese and morbidly obese BMI categories with the highest pressures noted in those who were morbidly obese (P < .001). Among the 69 patients who underwent TAH with peak inspiratory pressure data available, the impact of BMI on peak inspiratory pressure at 30 minutes after incision was as follows: nonobese had a median 19 cm H2O (IQR 17, 23), obese with median 28 cm H2O (IQR 24, 39), and morbidly obese with median 28 cm H2O (IQR 26, 32) (P < .001) (Table 4). There was no difference in peak inspiratory pressures at 2 hours after incision.

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Postoperative Complications

Aside from SSI, postoperative complications in the first 30 days were not found to differ significantly between groups (Table 5). There were no significant differences in pulmonary, cardiac complications, or readmissions. Of note there were few cardiac or pulmonary complications. None of the patients in either group required reintubation. Atelectasis was reported in only 0.9% in RH and 1.0% in TAH. Only 2 patients (1 in each group) developed pneumonia. Cardiac ischemia was reported in 0.3% in RH and 1.0% in TAH groups. Arrhythmias were also similar in both groups (0.9% RH and 2% TAH, P = .264), and electrocardiographic changes (P = .106) were not significantly different between the groups. Readmission within 30 days was not found to differ significantly between the 2 groups. There were no significant differences in the overall postoperative complication rate among BMI groups in either RH or TAH (Tables 3 and 4).

Table 5.

Table 5.

The overall 30-day SSI rates were significantly higher in the TAH group compared to RH (all patients: 8.5% vs 1.4%, odds ratio [OR] = 0.2; 95% confidence interval [CI], 0.1–0.4, P < .001; propensity matched samples: 8.6% vs 0.6%, OR = 0.1, 95% CI = 0.0–0.5, P < .001) (Table 5). Length of stay was longer for those who underwent TAH compared to RH (all patients: median [IQR] 3 [2, 3] days vs 1 [1, 1] day,P < .001; propensity matched: 2 [2, 3] days vs 1 [0, 2] days, P < .001) (Table 2).

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DISCUSSION

Our study found few differences in the perioperative and immediate postoperative outcomes of women undergoing RH compared to TAH at our institution. We affirmed our hypothesis that there is decreased blood loss, shorter length of hospital stay, and reduced SSI rates among those undergoing RH compared with TAH. However, we found no difference in pulmonary complications despite the requirement for higher peak airway pressures for intraoperative ventilation for the RH group. In addition, there was no increase in respiratory or overall complications in obese and morbidly obese patients, although significantly higher peak inspiratory pressures were needed to ventilate these patients compared with patients who were not obese.

RH required higher peak inspiratory pressures compared with TAH. However, there were no statistically significant differences in postoperative pulmonary complications including pneumonia, atelectasis, or respiratory issues noted at 30 days. Lung protective strategies (low-tidal volume of approximately 6 cc/kg ideal body weight and maintenance of plateau pressure below 30 cm H2O) have been advocated for in the setting of intraoperative mechanical ventilation.12,13 More recent evidence points to the importance of driving pressure (positive end-expiratory pressure subtracted from plateau pressure) as having the greatest effect on outcome in patients with acute respiratory distress syndrome.12 Each 7-cm H2O increase in driving pressure was associated with increased odds of death by 1.3 to 1.5. In addition, increased driving pressure is associated with postoperative pulmonary complications.13

Our patients, in particular the obese and morbidly obese patients, were ventilated with high peak airway pressures (>30 cm H20). In patients with normal lung compliance, high peak airway pressure correlates with higher plateau pressure. Because most of our patients had no known preexisting pulmonary disease, we assume their lung compliance was normal. Therefore, the driving pressure required for ventilation in these patients was likely higher than would be consistent with lung protective strategies. Thus, patient positioning in fixed, steep Trendelenburg and peritoneal insufflation in RH can make the implementation of recommended guidelines challenging, if not impossible.

Lung protective strategies aim to minimize stress across the lung (transpulmonary pressure). It may be that the true stress placed on our patient’s lungs was less than what was indicated by the peak airway pressures. Although airway pressures were significantly elevated during RH, their transpulmonary pressures (alveolar pressure minus pleural pressure) may have been attenuated by the peritoneal insufflation required for RH. To achieve surgical exposure, the abdominal cavity can be inflated to pressures as high as 20 cm H20. These pressures would be transmitted transdiaphragmatically, reduce transpulmonary pressure, and attenuate the stretch otherwise imposed by positive pressure ventilation on terminal bronchioles and alveoli.

This may explain why the increased pressures for patients undergoing RH in our study did not lead to a detectable increase in perioperative respiratory complications. Also, despite the fact that some of our patients had underlying pulmonary disease (10% with asthma, chronic obstructive pulmonary disease, and pulmonary hypertension), none developed an acute lung injury after RH. In light of these data, we propose that lung protective strategies for patients undergoing RH account for the markedly elevated intraperitoneal and intrapleural pressures, whereas transpulmonary airway pressures remain static.

Although the volume of intraoperative fluid resuscitation needed was higher in those undergoing TAH compared to RH (mean 2.56 L vs 2.31 L with P = .002), the clinical significance of <250-mL volume difference is likely negligible. Consistent with previous studies, estimated blood loss was higher in the TAH group.14–16

Postoperative complications were not found to differ significantly between the 2 groups, except for an SSI rate of 8.5% in the TAH group compared to 1.4% in the RH group. Historical data at our institution from 1999 to 2008 showed a 9.9% incidence of SSI. A more recent study demonstrated the ability to reduce the relative risk of SSI by 82.4% with the use of an SSI reduction bundle.17 A retrospective study from our institution found obesity to be a risk factor for SSI.18 Previous reports have also shown a significantly lower SSI rate in minimally invasive approaches.14,15,19

Obese and morbidly obese patients did not have a higher incidence of postoperative complications in this study. This finding appears to be novel. For example, Mahdi et al20 performed a single-institution retrospective study comparing women with morbid obesity with those who were not obese undergoing surgery for endometrial cancer and found significantly more surgical and infectious postoperative complications in the morbidly obese. However, they also identified that morbidly obese women were less likely to undergo minimally invasive surgery. Thus, clinical decision-making may have introduced bias.

Concern has been raised as a result of the increased cost of RH compared with laparoscopic hysterectomy, vaginal hysterectomy, and TAH.1,4,21,22 Because of both increased cost associated with and unique skills involved in performance of RH, it has not become an approach recommended by the American Association of Gynecologic Laparoscopists as a standard alternative to TAH.23 Recent studies have shown benefits of RH include a significant decrease in perioperative complications such as SSI and hospital length of stay compared with TAH.11,24 Additionally, a meta-analysis of 22 studies comparing RH, TAH, and laparoscopic hysterectomy found significant decreases in blood loss, incidence of SSI, and length of hospital stay with RH compared to TAH.25 This suggests that RH is a useful and beneficial alternative minimally invasive technique to TAH. Our study confirms these findings.

Strengths of our study include the fact that all procedures were performed by the same surgeons during these study periods, limiting variability that may be seen with a less cohesive surgical practice. Data regarding postoperative events were available for all patients, and events up to 30 days were available for nearly all patients.

Our study does have limitations. This is a single-center and retrospective study that carries the inherent limitations associated with both aspects. Electronic medical record documentation changed during the study period from which the TAH group was identified, and this affected the volume of certain data points, including intraoperative ventilator data. This limited ventilator data to specific parameters without documentation of plateau pressure or tidal volume based in ideal body.

We found no difference in short-term respiratory outcomes with use of higher airway pressures needed for ventilation intraoperatively during RH, even in obese and morbidly obese patients. This is unexpected considering that lung protective strategies were not used and suggests that RH is an attractive approach for obese and morbidly obese women, despite the challenges that may arise with intraoperative ventilator management.

Because this was a single-center retrospective study, more data regarding management and outcomes of obese and morbidly obese patients will help clarify how to best manage intraoperative ventilation for RH. Further study will be needed to determine if there are optimal ventilatory strategies for the intraoperative period.

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DISCLOSURES

Name: Bhargavi Gali, MD.

Contribution: This author helped with the contribution/design, critical revisions, final approval, and accountability of work.

Name: Jamie N. Bakkum-Gamez, MD.

Contribution: This author helped with the contribution/design, critical revisions, final approval, and accountability of work.

Name: David J. Plevak, MD.

Contribution: This author helped with the contribution/design, critical revisions, final approval, and accountability of work.

Name: Darrell Schroeder, MS.

Contribution: This author helped with the contribution/design, critical revisions, final approval, and accountability of work.

Name: Timothy O. Wilson, MD.

Contribution: This author helped with the contribution/design, critical revisions, final approval, and accountability of work.

Name: Christopher J. Jankowski, MD.

Contribution: This author helped with the contribution/design, critical revisions, final approval, and accountability of work.

This manuscript was handled by: Richard C. Prielipp, MD.

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