The effect of reverse Trendelenburg position on cerebral oxygenation inseptorhinoplasty

Authors

Abstract

Aim The use of reverse Trendelenburg position and controlled hypotension during septorhinoplasty can potentially impact regional cerebral oxygen saturation (rScO2). Cerebral oximetry, utilizing near-infrared spectroscopy (NIRS), allows for the monitoring of these changes and the detection of low rScO2 and tissue hypoxia. This present investigation was designed to determine the combined influences of reverse Trendelenburg positioning and controlled hypotension on rScO2 in patients undergoing septorhinoplasty.
Materials and Methods Fifty patients who underwent septorhinoplasty were enrolled in this prospective study. Regional cerebral oxygen saturation was continuously monitored using cerebral oximetry (NIRS). Participants were allocated to one of two groups based on the operating table’s position: a horizontal position (0° RTP) or a 15-degree reverse Trendelenburg position (15° RTP).
Results During the surgical procedures, rScO2 values from both the right and left cerebral hemispheres were recorded at ten distinct time points and compared between the two groups. The analysis of the collected data revealed no statistically significant differences in intergroup rScO2 values.
Discussion The implementation of the 15-degree reverse Trendelenburg position in conjunction with controlled hypotension did not result in any impairment of regional cerebral oxygen saturation during septorhinoplasty surgery.

Keywords

Introduction

Achieving a bloodless and clear surgical field is a primary goal in septorhinoplasty, with various anesthetic and surgical techniques employed to facilitate this. These methods include controlled hypotension, intranasal or oral corticosteroid administration, and the application of local injections or topical sinonasal vasoconstrictors [1]. Controlled hypotension is a frequently utilized technique to minimize perioperative bleeding, enhance surgical field visualization, reduce operative time, and decrease the incidence of surgical complications. It is typically defined by a reduction in systolic arterial pressure (SAP) to 70- 80 mmHg, maintaining mean arterial pressure (MAP) between 50-65 mmHg, or a decrease of the initial MAP by 30% [2, 3]. In addition to controlled hypotension, adopting a reverse Trendelenburg position (RTP) can also be an effective strategy [4]. RTP can decrease venous return and raise systemic vascular resistance, thereby reducing the perfusion index. Furthermore, at a 15-degree RTP, the hydrostatic pressure difference between the brain and the arm is approximately 10 mmHg, meaning a MAP of 65 mmHg measured at the arm level would equate to roughly 55 mmHg at the circle of Willis, a pressure near the lower limit of cerebral vascular autoregulation. Previous research has indicated that moderate intentional hypotension (60-70 mmHg) can lead to an increase in S-100 β levels, an early marker for brain ischemia-related changes [5]. Consequently, this study aimed to investigate the impact of perioperative controlled hypotension and RTP on cerebral oxygenation using cerebral near-infrared spectroscopy (NIRS) monitoring. NIRS offers a continuous and non-invasive method for assessing oxygen saturation in the frontal part of the brain [6]. NIRS monitoring can be performed at various anatomical sites, including the brain, kidneys, lower extremities, brachioradialis muscle, and thenar region [7, 8]. Cerebral oximetry, first described over three decades ago, has seen increased application in specialized clinical settings over the past twenty years [9]. NIRS technology operates on the Beer-Lambert law, measuring light absorption by biological tissue to determine substance concentration, with modifications to account for light scattering. In the 700- 900 nm optical window, light can penetrate skin and bone, with hemoglobin being the primary absorber. By analyzing the differential absorption of oxygenated and deoxygenated hemoglobin at two wavelengths, NIRS devices estimate tissue oxygen saturation under the probe. Unlike pulse oximeters that use subtraction algorithms for arterial saturation, NIRS devices employ similar algorithms to filter superficial signals and derive an average hemoglobin saturation in the underlying tissue. Most NIRS devices provide continuous real-time rScO2 readings [10]. NIRS can facilitate the early detection of tissue hypoxia before significant negative impacts on rScO2 [11]. The surgical position of a patient is a critical factor in interpreting rScO2 values, irrespective of the surgical procedure. Particular attention is warranted during arterial hypotension, especially in semi-Fowler’s or Fowler’s positions. In certain conditions that elevate intracranial pressure, cerebral perfusion may be reduced even with normal arterial blood pressure. Therefore, the patient’s intraoperative positioning is recognized as a factor necessitating cerebral oximetry [12]. In this study, cerebral NIRS monitoring was employed in patients undergoing septorhinoplasty. Controlled hypotension was maintained by a remifentanil infusion to achieve a mean arterial pressure of 60- 70 mmHg, aiming to minimize surgical bleeding. The study also sought to compare NIRS values between patients positioned at 0 degrees and 15 degrees RTP.

Materials and Methods

Following approval from the Malatya Tutgut Özal University Clinical Research Ethics Committee (2022/52), fifty patients scheduled for septorhinoplasty were included. Exclusion criteria comprised individuals under 18 or over 50 years of age, those with an American Society of Anesthesiologists (ASA) physical status classification more than 2, a history of cerebrovascular disease, chronic obstructive pulmonary disease, asthma, peripheral artery disease, central nervous system disease, congestive heart failure, liver disease, kidney disease, diabetes mellitus, alcohol or drug dependence, and a history of allergy to anesthetic drugs. No premedication was administered. Upon arrival in the operating room, patients were subjected to standard monitoring, including a 3-lead electrocardiogram, non-invasive blood pressure, peripheral oxygen saturation, and regional cerebral oxygen saturation (rScO2) using an INVOS 5100C oximeter (Somanetics, Covidien, Minneapolis, USA), with baseline values recorded. Anesthesia induction involved intravenous administration of 1.5 mg kg-1 lidocaine, 2 mg kg-1 propofol, and 2 µg kg-1 fentanyl, followed by 0.6 mg kg-1 rocuronium for muscle relaxation. After intubation, a goniometer was placed near the patient’s head, and the operating table was adjusted to the assigned angle for each group: either the horizontal 0-degree position or the 15-degree RTP. Controlled hypotension was maintained throughout the procedure with an intravenous remifentanil infusion at a dose of 0.25-0.5 µg kg-1 min-1, targeting a mean arterial pressure of60-70 mmHg. The remifentanil infusion was to be discontinued if the mean arterial pressure decreased by more than 30% from baseline. Throughout the intubation period, peripheral oxygen saturation, mean arterial pressure, heart rate, left and right cerebral regional oximetry (rScO2) values, and end-tidal carbon dioxide were continuously recorded. Postoperatively, patients were extubated and transferred to the recovery unit.
Statistical Analysis
Data were indicated as mean ± standard deviation, median (min-max), and count (percent). The Shapiro-Wilk test was used to assess conformity to normal distribution. Statistical analyses were performed using appropriate tests, including the Pearson chi-square test, independent sample t-test, and Mann-Whitney U test. A p-value less than 0.05 was statistically significant. Datum analysis was performed using IBM SPSS Statistics 26.0.
Ethical Approval
This study was approved by the Ethics Committee of Malatya Tutgut Özal University (Date: 2022-10-22, No:2022/52).

Results

This present investigation comprised a total of 50 patients. Demographic data are indicated in Table 1. Indicating no significant differences between the 15° RTP group (17 female, 7 male) and the 0° RTP group (21 female, 5 male) in terms of age, height, weight, or Body Mass Index (BMI). Comparisons of peripheral oxygen saturation, mean arterial pressure, heart rate, left and right cerebral regional oximetry (rScO2) values, and end-tidal carbon dioxide values between the groups revealed significant differences during specific phases of surgery: Heart Rate (p 0.006*), Pulse Saturation (p 0.013*), and End Tidal CO2 (p 0.010**) at the ‘Starts of Surgery’ phase; Pulse Saturation (p 0.003) and End Tidal CO2 (p 0.0049) during ‘Surgery 1’; End Tidal CO2 (p 0.001) during ‘Surgery 2’; and Mean Arterial Pressure (p 0.0027) and End Tidal CO2 (p 0.001) during ‘Surgery 3’. When examining Regional Cerebral Oximetry (rScO2) values, no significance was observed among the groups at any stage (Table 3). Cerebral Oximetry Values of the Groups are shown in Figure 1. Specifically, rScO2 monitoring of both right and left hemispheres across ten different time points showed no statistically significant intergroup differences.

Discussion

A primary concern regarding the use of controlled hypotension in septorhinoplasty is its potential adverse effect on cerebral oxygenation. The addition of RTP has also raised concerns about further compromising cerebral oxygen delivery. This study investigated the combined influence of controlled hypotension and RTP on brain oxygenation and found no deterioration in cerebral oxygenation as indicated by NIRS monitoring in either group. Bleeding in septorhinoplasty typically originates from the nasal mucosa’s capillary network, and nasal blood flow is influenced by arterial blood flow, vascularization, and venous pressure [13, 14]. Persistent, albeit minor, bleeding from the nasal mucosa can significantly impair visualization within the confined nasal cavity. Our study aimed to assess the impact of interventions employed to reduce such bleeding on cerebral oxygenation during RTP. Previous studies by Gan et al. and Hathorn et al. demonstrated that 15° or 20° RTP can substantially facilitate surgical visualization [3, 15]. Our findings align with this, as we observed no significant difference in rScO2 values between the 0° and 15° RTP groups under controlled hypotension. In a study involving patients undergoing controlled hypotension in the beach chair position, a 25% rate of cerebral desaturation events (CDEs) was reported, with CDEs associated with negative postoperative neurocognitive test outcomes. This highlights the potential utility of brain oximetry in preventing adverse neuropsychiatric outcomes during functional endoscopic sinus surgery [16]. NIRS has also proven beneficial in assessing cerebral tissue oxygen levels in patients undergoing cardiac surgery, hypotensive anesthesia, and prolonged RTP positioning. Beyond surgical contexts, NIRS is increasingly used to evaluate brain oxygenation during critical events such as cardiac arrest [17]. Cerebral oximetry assesses average regional tissue oxygenation through the frontal cortex, functioning similarly to pulse oximetry by analyzing the ratio of oxygenated to deoxygenated hemoglobin based on light transmission [18]. NIRS provides quantitative and qualitative data on total tissue oxygen and deoxyhemoglobin, reflecting oxygen supply and demand, whereas pulse oximetry focuses solely on arterial hemoglobin [19]. Near-infrared (NIR) light, typically between 700 and 850 nm, is used in clinical NIRS applications. This spectral range maximizes the distinction between oxygenated and deoxygenated hemoglobin and minimizes interference from other chromophores. The influence of myoglobin on NIRS measurements of tissue oxygenation is generally considered minimal [20, 21]. Yang et al. in their study on endoscopic sinus surgery, utilized remifentanil infusion for controlled hypotension (MAP 65-75 mmHg) and found that while 15° RTP improved surgical clarity, rScO2 remained unaffected by varying RTP degrees [22]. Our study corroborates these findings, showing no significant difference in rScO2 between horizontal and 15° RTP. Zhang et al. reported a minimal decrease (around 5%) in rScO2 compared to baseline when MAP was reduced by 30% during endoscopic sinus surgery, with decreases in rScO2 correlating with reduced MAP [23]. Shear et al. found that controlled hypotension within the 55-65 mmHg range did not affect rScO2 in pediatric patients, and Salman et al. noted that esmolol-induced controlled hypotension did not impact rScO2 during myomectomy [24, 25].

Limitations

Limitations of this investigation include its single-center study, relatively small patient sample size, and the absence of postoperative mental state assessments.

Conclusion

The application of RTP in septorhinoplasty patients undergoing controlled hypotension did not result in a significant difference rScO2 among the groups. However, given the uncertainty surrounding postoperative cognitive function, it is advisable to closely monitor blood pressure and avoid profound hypotension while considering the circulatory effects of advanced RTP on the circle of Willis.

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