Changes in intraocular pressure and optic nerve sheath diameter in patients undergoing robotic-assisted laparoscopic prostatectomy in steep 45° Trendelenburg position
© The Author(s). 2017
Received: 3 November 2016
Accepted: 28 February 2017
Published: 11 March 2017
To evaluate changes in intraocular pressure (IOP) and intracerebral pressure (ICP) reflected by the optic nerve sheath diameter (ONSD) in patients undergoing robotic-assisted laparoscopic prostatectomy (RALP) in permanent 45° steep Trendelenburg position (STP).
Fifty-one patients undergoing RALP under a standardised anaesthesia. IOP was perioperatively measured in awake patients (T0) and IOP and ONSD 20 min after induction of anaesthesia (T1), after insufflation of the abdomen in supine position (T2), after 30 min in STP (T3), when controlling Santorini’s plexus in STP (T4) and before awakening while supine (T5). We investigated the influence of respiratory and circulatory parameters as well as patient-specific and time-dependent factors on IOP and ONSD.
Average IOP values (mmHg) were T0 = 19.9, T1 = 15.9, T2 = 20.1, T3 = 30.7, T4 = 33.9 and T5 = 21.8. IOP was 14.0 ± 7.47 mmHg (mean ± SD) higher at T4 than T0 (p = 0.013). Univariate mixed effects models showed peak inspiratory pressure (PIP) and mean arterial blood pressure (MAP) to be significant predictors for IOP increase. Mean ONSD values (mm) were T1 = 5.88, T2 = 6.08, T3 = 6.07, T4 = 6.04 and T5 = 5.96. The ONSD remained permanently >6.0 mm during RALP. Patients aged <63 years showed a 0.21 mm wider ONSD on average (p = 0.017) and greater variations in diameter than older patients.
The combination of STP and capnoperitoneum during RALP has a pronounced influence on IOP and, to a lesser degree, on ICP. IOP is directly correlated with increasing PIP and MAP. IOP doubled and the ONSD rose to values indicating increased intracranial pressure. Differences in the ONSD were age-related, showing higher output values as well as better autoregulation and compliance in STP for patients aged <63 years. Despite several ocular changes during RALP, visual function was not significantly impaired postoperatively.
Z-2014-0387-6. Registered 8 July 2014.
KeywordsIntraocular pressure Optic nerve sheath diameter Robotic-assisted laparoscopic prostatectomy steep Trendelenburg position
Prostate cancer is the most common cancer in men (31.9%) and the third leading cause of cancer death (11%) in Germany . Depending on the tumour entity, prostate resection is one treatment option. Robotic-assisted laparoscopic prostatectomy (RALP) is a popular and increasingly used alternative to open prostatectomy because of benefits such as minimal invasion, better short-term outcome and improved functional results [2, 3]. Actually the RALP seems to be at least equal or even superior in oncologic efficacy and complication rates compared to open prostatectomy and in 2016 any small incremental expense justifies its use [4, 5]. RALP is one of the most technically advanced treatment modalities, and its advantages include stereoscopic visualization and good manoeuvrability with 7 envelopes in the operating area. RALP requires a steep (23° to 35°) Trendelenburg position (STP) and a CO2 pneumoperitoneum. STP may lead to pathophysiological changes such as pulmonary dysfunction with formation of atelectasis and increasing airway pressure as well as ocular complications . In 2007, Weber et al.  firstly reported 2 patients with bilateral ischaemic optic neuropathy (ION) after a da Vinci robotic-assisted procedure. Lee  reported 3 patients with postoperative visual loss (POVL) after RALP, 2 of them with bilateral POVL (67%). These cases were documented in the Registry of the American Society of Anaesthesiologists (POVL) between 2006 and 2010. STP has raised concerns that prolonged elevation of venous pressure in the head may increase the risk of developing ION. However, no investigations have yet been made into intraoperative changes in intraocular pressure (IOP) and optic nerve sheath diameter (ONSD) − correlating with intracranial pressure (ICP) − and their adverse ocular effects. Almost all studies were performed by doing a 30° up to a 35° Trendelenburg position. The operative conditions get better the steeper the positioning, providing excellent intraabdominal view and probably less bleeding. The hypothesis of the study is that patients placed in steep Trendelenburg position for several hours have a high risk for ocular changes and peri- and postoperative complications.
The aim of this study was to investigate the influence of capnoperitoneum and permanent 45° STP on IOP and ONSD in patients undergoing RALP. We also analysed the influence of age, body mass index (BMI), peak inspiratory pressure (PIP), mean arterial blood pressure (MAP), duration of surgery and STP on IOP and ONSD during RALP. Perioperative and postoperative complications were also recorded.
This single-centre, prospective and nonrandomised study was approved by the local institutional review board (Protocol no. 14-101-0107) and registered at the local Centre for Clinical Studies (Z-2014-0387-6. Registered 8 July 2014). Informed consent was obtained from 51 patients scheduled for elective prostatectomy at the Department of Urology in Regensburg. All patients were recruited between January 2015 and August 2015. Main exclusion criteria were pre-existing eye disease (diabetic retinopathy, glaucoma and retinal detachment), history of eye surgery, age >80 years, BMI >40, American Society of Anaesthesia (ASA) physical status > III, known cardiac insufficiency and pulmonary hypertension.
Anaesthesia protocol and surgical technique
Measurements of intraocular parameters and the optic nerve sheath diameter
Time points of IOP and ONSD measurements
Time points of measurements
Patient awake in supine position before induction of anaesthesia
20 min after induction of general anaesthesia in supine position
After insufflation of the abdomen with CO2 in supine position
After 30 min in 45° Trendelenburg position with the abdomen still insufflated with CO2
Control of Santorini’s plexus in 45° Trendelenburg position with CO2 still insufflated
Anaesthetised before awakening in supine position
Registration of postoperative (visual) complications
Postoperative all patients were observed in the recovery room, 8 h later on the ward and the next day and received a clinically visual and perimetric examination.
Due to the exploratory nature of this study and the lack of a primary endpoint with expectable effect sizes, no sample size calculation was performed a priori. To get robust effects in a feasible amount of time, we decided to include about 50 patients into this study. To analyse the influence of the variables age, BMI, intravenous infusion, PIP and MAP on IOP and ONSD, linear mixed models were used. These models account for correlated measurements within each patient because of several time points. Each variable was analysed in a separate model, containing time as an additional factor. The covariance structure between the time points was set to autoregressive. Effect estimates of significant variables are presented as slopes (effect on IOP and ONSD per one unit change of the variable) with corresponding 95% confidence intervals. All reported p values are two-sided, and a p value of 0.05 is considered the threshold of statistical significance. Because of the explorative nature of this study, no adjustment for multiple testing was done. Data were analysed with the software SAS 9.4 (SAS Institute Inc., Cary NC).
Patient demographics and operative variables
Duration of surgery (min)
Duration of 45° Trendelenburg position (min)
Intravenous infusion during operation (ml)
Individual and surgical influences on IOP during RALP
Individual and operational influences on ONSD during RALP
Neither ocular nor neurological complications were observed in the recovery room, 8 h later on the ward and the next day. One patient experienced perioperative cardiac ischemia; reporting angina symptoms in the recovery room he received postoperative coronary angiography with stent implantation due to significant coronary stenosis.
In this study, we examined the changes in IOP and ONSD between supine and STP during RALP. The combination of STP and capnoperitoneum during RALP has a pronounced influence on IOP and, to a lesser degree, on ICP. IOP was directly correlated with increasing ventilation pressure and MAP. However, no ocular or cerebral pressure-related complications occurred in our study population.
Changes in IOP during RALP
The mean baseline IOP of our awake patients was 19.9 mmHg; thus, it was slightly higher than in other studies (18.0 mmHg, 14.9 mmHg), which may depend on the fact that we measured IOP with a rebound tonometer without topical anesthesia in the awake patient [12, 13]. Induction of anaesthesia in supine position decreased the mean IOP from 19.9 to 15.9 mmHg. The ocular hypotensive effect of anaesthetics has been known for many years and may counteract IOP increases induced by RALP . IOP is significantly more reduced by propofol than by volatile anaesthetics [15, 16]. During RALP, the mean IOP more than doubled between T1 and T4 (15.9 to 33.9 mmHg) in this study, and the highest IOP value measured was 59.6 mmHg. Awad et al.  also reported that the mean IOP was 5 mmHg lower after induction of anaesthesia and had increased almost threefold (10.7 to 29.0 mmHg) in STP at the end of surgery. This mean was on average 13 mmHg higher than pre-anaesthesic values. In another study, the mean IOP had increased after induction of anaesthesia from 9.8 mmHg to 24.2 mmHg at the end of STP .
Molloy found that baseline IOP and duration of surgery were the only factors predicting increased IOP . In our study, age, BMI, duration of surgery and STP did not affect IOP, but MAP and PIP showed a direct relationship and significant effect on IOP. However, respiration in terms of lung protective ventilation or hypotension is hardly feasible when using STP. One way of reducing IOP could be a variation in the Trendelenburg position to avoid extreme IOP increases. Raz et al. applied a modified Z-TP during RALP and found a significant positive effect on patient neuro-ocular safety by lowering intraocular pressure without any negative effects on surgery. Increased IOP can also be reduced by drugs . In a study by Molloy et al., 32.5% of patients undergoing lengthy laparoscopic surgery in STP had an IOP higher than 40 mmHg . Treatment with dorzolamide-timolol eye drops significantly reduced elevated IOP.
On the basis of this study, we were able to quantify the changes in IOP throughout the procedure. We therefore concluded that patients treated with robotic prostatectomy reach IOP levels comparable to those observed in patients with glaucoma. However, possible adverse ocular effects as a consequence of IOP changes have not yet been investigated. In our study, no patient experienced ischaemic optic neuropathy after RALP clinically represented by scotoma or significant visual loss.
Changes in the ONSD during RALP
In this study, the ONSD did not significantly exceed the initial value (maximum rise 3.4%, 0.2 mm). Another study reported that the ONSD increased by 12.5% (0.6 mm) during CO2 pneumoperitoneum and STP for 20 patients undergoing RALP . Chin et al. also found a significant increase in the ONSD (0.6 mm) between supine and STP in 21 patients . The basic value of the ONSD in this study was 5.88 mm. In their review, Soldatos et al.  determined 5.7–6.0 mm as the cut-off value of the ONSD that provides the best accuracy for predicting intracranial hypertension (ICP >20 mmHg). For patients with severe brain injury (subarachnoid haemorrhage, intracranial hematoma or stroke) was showed that an ONSD threshold of 5.2 mm or 5.86 mm as a predictor for ICP >20 mmHg proved to be an attractive combination of sensitivity (94 and 95%) and specificity (76 and 79%) [24, 25]. In the aforementioned studies by Kim  and Chin , the initial values for the ONSD were 4.5 and 4.8 mm, which may indicate a difference between Korean and European patient populations. Another reason for the increased initial value for the ONSD in our study could be PEEP-triggered ventilation. PEEP increases intra-thoracic pressure. The venous backflow from the brain resulting in increased ICP may explain the above average baseline value. In general, ONSD changes depend on individual patient characteristics and body position. Fichtner et al. reported an ONSD reduction of about 0.53 mm from supine to upright position for patients with orthostatic headache . During RALP, the ONSD rose above 6.0 mm, which suggests elevated ICP (Fig. 6). In addition, Whiteley et al. found a direct correlation between increased ONSD values and MAP . We did not observe any influence of MAP in our study. The non-significant increase in the ONSD may be due to the effect of PEEP and non-linearity of ONSD elasticity . The impact of a slight increased ONS remains after RALP unclear and is probably not of clinical importance.
However, we found an age-related difference (median 63 years) in the changes in the ONSD during RALP. Younger patients had a significantly higher baseline ONSD under mechanical ventilation, suggesting higher elasticity of the dura mater. Over the course of STP (T3 to T4), the ONSD decreased in younger patients, which may indicate better adaptability of the ONSD or intracranial pressure, respectively (Fig. 7).
Limitations of the study
Because of logistic preoperative constraints, we did not measure the ONSD prior to intubation. Neither ocular nor neurological complications were observed in our defined cohort. Larger prospective studies with RALP are required to further evaluate the relationship between STP and permanent ocular changes and to make recommendations regarding the prevention and treatment of increased intraoperative IOP.
In conclusion, we found that IOP and ONSD increased significantly in a time-dependent way in patients undergoing RALP in 45 ° STP. IOP doubled and the ONSD rose to values indicating slight increased intracranial pressure, but no patient reported visual impairment or at worst POVL. We observed age-related differences in the ONSD with a higher initial value and better autoregulation in STP for younger patients. RALP is associated with significant measurable ocular changes, namely an increase of IOP and ONSD.
American Society of Anaesthesia
Body mass index
Ischaemic optic neuropathy
Mean arterial blood pressure
Optic nerve sheath
Optic nerve sheath diameter
Positive end-expiratory pressure
Peak inspiratory pressure
Postoperative visual loss
Robotic-assisted laparoscopic prostatectomy
Steep Trendelenburg position
We would like to thank the bon Optic Vertriebsgesellschaft mbH and particularly its representative Mr Heidinger for providing the rebound tonometer for this study free of charge.
The study did not receive any extramural funding.
Availability of data and materials
All data generated or analysed during this study are included in this published article and are available from the corresponding author on reasonable request.
SB: Ethics approval, study design, data collection and analysis, drafted the manuscript and reviewed it for important intellectual content; MH: Idea for study, study design, patient recruitment, data collection and reviewed the manuscript for important intellectual content; FS: data collection and interpretation, and reviewed the manuscript for important intellectual content; FZ: data analysis and reviewed the manuscript for important intellectual content; CB: data analysis and reviewed the manuscript for important intellectual content; PF: data collection and analysis, reviewed the manuscript for important intellectual content; MB: made acquisitions and interpret of data and reviewed the manuscript for important intellectual content; SD: made acquisitions and interpret of data and reviewed the manuscript for important intellectual content; BG: helped interpret the data and reviewed the manuscript for important intellectual content; HH: helped interpret the data and reviewed the manuscript for important intellectual content; MP: Idea for study, study design, data collection, patient recruitment and reviewed the manuscript for important intellectual content. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Consent for publication
Ethics approval and consent to participate
This study was approved by the local institutional review board of the University of Regensburg (Protocol no. 14-101-0107). After a detailed explanation written informed consent was obtained from 51 patients scheduled for elective prostatectomy at the Department of Urology in Regensburg.
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