Evaluating the impact of lateral position alterations on intraocular pressure and cerebral oxygen saturation among elderly and middle-aged patients undergoing surgery

Abstract

Objective

To assess the impact of lateral position changes on intraocular pressure and regional cerebral oxygen saturation (rScO₂) in patients undergoing surgery.

Methods

Seventy patients were categorized into the elderly and middle-aged groups, with 35 individuals in each. Apart from collecting physiological data of patients, intraocular pressure was measured using a rebound tonometer, and regional cerebral oxygen saturation levels were assessed with a cerebral oxygen monitor at ten different time points in this study.

Results

Intraocular pressure trends in both eyes were similar in both groups, peaking after two hours and then stabilizing. The intraocular pressure of the eye on the compressed side increased after lateral positioning, and this was more notable in the elderly group, indicating a significant difference (P < 0.05). The rScO₂ levels did not differ significantly between the groups (P > 0.05); however, patients in the elderly group exhibited higher mean arterial pressure (MAP) fluctuations at post-intubation (T2) and pre-turning (T8) time points compared to those in the middle-aged group, and this difference was significant (P < 0.05). In the middle-aged group, there was no correlation between MAP and changes in cerebral oxygen saturation (P > 0.05), whereas a weak correlation was present in the elderly group (P < 0.05). There was no difference in uncorrected visual acuity between the pre-admission and six hours post-surgery time points (P > 0.05).

Conclusion

The results of this study underscores the importance of proper positioning of patients, enhanced intraoperative monitoring, and safe surgical positioning practices.

Keywords

cerebral perfusion pressure elderly patients intraocular pressure rebound tonometer regional cerebral oxygen saturation surgical position

1 Background

The increase in the proportion of the aging population poses significant health challenges.¹ The decline in physiological functions with age and the prevalence of multiple chronic diseases significantly heighten the risk of perioperative neurological complications among the elderly compared to younger adults.² The brain is the organ with the highest demand for oxygen, and as part of the aging process, there is a reduction in both the cerebral blood flow and oxygen consumption in the brain.³ Variations in volume, body positioning, and anesthesia depth can easily induce hemodynamic instability, closely associated with brain hypoxia, ischemia-reperfusion injuries during surgery,⁴ and subsequent postoperative delirium and changes in cognitive functioning.⁵ Consequently, there is a growing emphasis in anesthesiology and nursing on monitoring surgical position changes that can lead to perfusion abnormalities in critical organs and postoperative ocular complications.

The Chinese Anesthesia Guidelines and Expert Consensus⁶ published in 2017 highlight the criticality of monitoring cerebral perfusion pressure among elderly patients during surgical procedures. It advocates for the use of non-invasive regional cerebral oxygen saturation (rScO₂) as an essential parameter for intraoperative monitoring. In this study, we collected baseline data on intraocular pressure and rScO₂ before and after repositioning elderly and middle-aged patients into a lateral position. Through meticulous data analysis, our aim was to investigate trends in these parameters, thereby laying a scientific foundation for devising effective and safe surgical positioning strategies to minimize postoperative complications.

2 Participants and methodology

2.1 Study participants

The study included 70 patients who underwent thoracoscopic surgery in a city hospital between February 2019 and June 2020. They were stratified into two groups based on their age, namely, the elderly and the middle-aged groups, with 35 patients in each. Individuals aged ≥ 65 years were assigned to the elderly group, while those who were younger comprised the middle-aged group, irrespective of gender. All procedures were conducted under general anesthesia using double-lumen endotracheal tubes, followed by lateral decubitus positioning. Post-surgery, patients were repositioned supine, switched to single-lumen tubes, and transferred to the intensive care unit (ICU) for continued observation after stabilizing.

The inclusion criteria were: (1) patients classified as ASA (American Society of Anesthesiologists) grades I to III; (2) patients undergoing elective thoracoscopic surgeries under general anesthesia, positioned at a 90° lateral angle, with the duration of surgery ranging from two to four hours; and (3) patients without severe metabolic, respiratory, circulatory, or infectious diseases, maintaining stable vital signs, and devoid of serious complications.

The exclusion criteria were as follows: (1) patients with preoperative intraocular pressure > 21 mmHg, or with ocular conditions like conjunctivitis or endophthalmitis; (2) individuals with severe myopia (> −600 D); (3) those with thyroid enlargement or hyperthyroidism; (4) patients who were administered mydriatics, diuretics, or other intraocular pressure-influencing drugs in the preceding two weeks; (5) individuals with extensive systemic traumas, fractures, shock, or an Injury Severity Score (ISS) > 18; (6) patients suffering from systemic conditions such as chronic obstructive pulmonary disease (COPD), emphysema, or significant liver, renal, or heart dysfunction, and autoimmune diseases, among others.

The Ethics Committee of the institution approved this study, and all procedures adhered to the Helsinki Declaration. All participants provided voluntary, informed consent.

2.2 Methodology

2.2.1 Study methodology

After admission, patients were initially placed in a supine position and connected to monitors for observing their vital signs. After induction of general anesthesia, a double-lumen endotracheal tube was inserted, its position verified via a fiberoptic laryngoscope, and securely affixed. The patient was transitioned into the lateral decubitus position with the collaborative efforts of the circulating nurse, anesthesiologist, and surgeon, ensuring the patient's body was on its side at a 90° angle, with the operated side elevated, and the head and both lower limbs positioned at a 10- to 15-degree decline to facilitate optimal chest access for the surgery. Following the completion of the surgery, the wound dressing was applied. The angle of the surgical bed was adjusted, and the patient was assisted back into a supine position. The anesthesiologist then swapped the double-lumen tube for a single-lumen one before transferring the patient to the anesthesia recovery room or ICU for further monitoring.

2.2.2 Observational metrics and data collection techniques

Prior to surgery, medical history details of patients, including conditions like glaucoma, cataracts, high myopia, other ocular diseases, past surgeries, and medication use, were documented. Uncorrected visual acuity was assessed using Jaeger's chart upon admission and again six hours post-surgery. Vital signs were continuously monitored from the time of admission, with the patient placed in a supine posture. The EGOS-600C cerebral oxygen saturation monitor was employed (Suzhou Enginmed Co., Ltd), with the probe attached above the right eyebrow along the midline of the forehead and secured with surgical film. This system helped to measure and monitor shifts in regional cerebral oxygen saturation during the surgery once the patient's condition was stable.

Intraocular pressure for both eyes was measured using the icareTA03 handheld rebound tonometer (Shenzhen Relin Co., Ltd). A standardized protocol of six readings per eye was used, with automatic averaging of the results. Measurement procedures were exclusively performed by specially trained nursing staff from the research team to minimize human error, with the study's lead author responsible for collecting all intraocular pressure and rScO₂ data.

Data for intraocular pressure and rScO₂ were collected at ten specific time intervals: upon admission (T1), after intubation (T2), five minutes following lateral repositioning (T3), 30 min post-repositioning (T4), one hour into surgery (T5), two hours into surgery (T6), three hours into surgery (T7), prior to repositioning (T8), post-extubation (T9), and pre-discharge (T10). Additionally, continuous recordings were maintained for mean arterial pressure (MAP), heart rate (HR), arterial pulse oxygen saturation (SPO₂), total fluid balance, urine output, and any significant medications that were administered.

2.2.3 Statistical analysis methods

Data were analyzed using SPSS 20.0. Quantitative data that followed a normal distribution were presented as the mean ± standard deviation ( $\bar{x}$ ± s). Temporal data variations were examined using repeated measures analysis of variance (ANOVA). Initially, Mauchly's test for sphericity was applied; if sphericity was confirmed, the F-test from repeated measures ANOVA was utilized directly without adjusting the degrees of freedom. In instances where the assumption of sphericity was violated, the Greenhouse-Geisser correction was employed to adjust the degrees of freedom. The t-test was used for comparisons of intraocular pressure, SPO₂, rScO₂, and MAP between the compressed and non-compressed sides in both groups. Pearson correlation analysis was used to explore the relationship between MAP and rScO₂, considering a P value of < 0.05 as indicating statistical significance.

3 Results

3.1 Overview of general data

The elderly group comprised 35 patients (30 males and 5 females) with an average age of 71.69 ± 5.98 years, weight of 62.69 ± 8.05 kg, surgery duration of 4.30 ± 0.90 h, total fluid intake of 2050 ± 640.9 ml, and urine output of 364.3 ± 116.0 ml. The middle-aged group also had 35 patients (28 males and 7 females), with an average age of 40.66 ± 14.14 years and weight of 66.83 ± 13.45 kg; the surgery lasted 3.94 ± 0.65 h. No significant differences were observed between the groups (P > 0.05), thereby ensuring their comparability.

3.2 Comparison of uncorrected visual acuity pre- and post-surgery

There were no significant differences in the uncorrected visual acuity between measurements taken after admission (pre-surgery) and six hours post-surgery (P > 0.05).

3.3 Changes in intraocular pressure at various time points for the non-compressed and compressed sides

The intraocular pressure in the non-compressed side among patients of both groups remained stable or exhibited a slight decrease, indicating minimal impact. However, there was a significant increase in the intraocular pressure on the compressed side, suggesting that obstructed venous return on the compressed side may contribute to elevated intraocular pressure subsequent to changes in body position.

Comparative analyses at identical time points across the two groups revealed no significant disparities in intraocular pressure changes in the eyes on the non-compressed side, indicating comparable baseline intraocular pressure levels between the two groups. Conversely, notable differences were observed in the changes in intraocular pressure in the compressed side, suggesting that structural changes in the eyes of patients in the elderly group resulted in consistently higher baseline intraocular pressure values compared to those in the middle-aged group. The significance of monitoring intraocular pressure during surgery lies in the meticulous monitoring of increasing intraocular pressure trends, enabling timely adjustments in positioning of the head and reduced application of pressure to mitigate postoperative visual risks. Details are presented in Table 1.

Table 1.
Comparison of intraocular pressure changes between non-compressed and compressed sides at different time points (mmHg, $\bar{x}$ ± s).

At the

During During During Before Supine Time of

Admission Intubation surgery surgery surgery turning position Discharge

Groups (T1) (T2) 5 min(T3) 30 min(T4) (T5) (T6) (T7) (T8) (T9) (T10)

Non-compressed side

Elderly group 18.55 ± 2.49 14.75 ± 2.99 17.84 ± 2.78^a 18.89 ± 2.86^a 20.07 ± 2.35^a 20.35 ± 2.54^a 20.07 ± 2.31^a 19.61 ± 2.09 18.52 ± 2.63^a 17.70 ± 2.40

Middle-aged group 18.40 ± 1.92 15.50 ± 2.12 16.30 ± 2.31 17.17 ± 2.41 17.76 ± 2.60 18.20 ± 2.60 17.93 ± 2.07 18.40 ± 2.24 16.91 ± 2.63 16.53 ± 2.35

T-value −0.151 0.751 −1.543 −1.714 −2.311 −2.154 −2.140 −1.211 −1.617 −1.171

P-value 0.999 0.583 0.004 0.000 0.000 0.000 0.000 0.053 0.002 0.070

Compressed side

Elderly group 18.17 ± 2.06 14.57 ± 2.81 19.27 ± 2.76^a 21.37 ± 1.41^a 22.35 ± 1.41^a 22.59 ± 0.89^a 22.62 ± 0.88 22.42 ± 0.71 18.56 ± 1.90 17.49 ± 1.85

Middle-aged group 18.79 ± 2.24 15.56 ± 2.20 17.74 ± 1.69 19.31 ± 1.79 20.78 ± 1.89 21.39 ± 1.64 21.53 ± 1.60 21.76 ± 1.47 18.25 ± 1.95 16.89 ± 2.21

T-value 0.620 0.997 −1.523 −2.051 −1.566 −1.200 −1.086 −0.660 −0.305 −0.591

P-value 0.647 0.079 0.000 0.000 0.000 0.015 0.039 0.561 0.995 0.707

										At the
Non-compressed side
Elderly group	18.55 ± 2.49	14.75 ± 2.99	17.84 ± 2.78^a	18.89 ± 2.86^a	20.07 ± 2.35^a	20.35 ± 2.54^a	20.07 ± 2.31^a	19.61 ± 2.09	18.52 ± 2.63^a	17.70 ± 2.40
Middle-aged group	18.40 ± 1.92	15.50 ± 2.12	16.30 ± 2.31	17.17 ± 2.41	17.76 ± 2.60	18.20 ± 2.60	17.93 ± 2.07	18.40 ± 2.24	16.91 ± 2.63	16.53 ± 2.35
T-value	−0.151	0.751	−1.543	−1.714	−2.311	−2.154	−2.140	−1.211	−1.617	−1.171
P-value	0.999	0.583	0.004	0.000	0.000	0.000	0.000	0.053	0.002	0.070
Compressed side
Elderly group	18.17 ± 2.06	14.57 ± 2.81	19.27 ± 2.76^a	21.37 ± 1.41^a	22.35 ± 1.41^a	22.59 ± 0.89^a	22.62 ± 0.88	22.42 ± 0.71	18.56 ± 1.90	17.49 ± 1.85
Middle-aged group	18.79 ± 2.24	15.56 ± 2.20	17.74 ± 1.69	19.31 ± 1.79	20.78 ± 1.89	21.39 ± 1.64	21.53 ± 1.60	21.76 ± 1.47	18.25 ± 1.95	16.89 ± 2.21
T-value	0.620	0.997	−1.523	−2.051	−1.566	−1.200	−1.086	−0.660	−0.305	−0.591
P-value	0.647	0.079	0.000	0.000	0.000	0.015	0.039	0.561	0.995	0.707

Note: Repeated measures ANOVA for both groups: Compressed Side F_time = 174.2, F_group = 6.819, F_interaction = 6.671; all P < 0.05. Non-Compressed Side F_time = 30.46, F_group = 9.551, F_interaction = 4.934; all P < 0.05. 1 mmHg = 0.133 KPa; ^a indicates comparison with the middle-aged group, P < 0.05.

(1) The pattern of intraocular pressure change is consistent across both groups, reaching a peak at 2 h (T6) and maintaining a stable state thereafter. After returning to the supine position (T9), the intraocular pressure of both eyes gradually returns to the baseline values at admission.

(2) The intraocular pressure of the eyes on the compressed side is higher than that of the non-compressed side in the T3 to T8 time points for patients in both groups, with a statistically significant difference (P < 0.05).

(3) The intraocular pressure of the eyes on both the compressed and non-compressed sides among patients in the elderly group is higher than those in the middle-aged group throughout the T3 to T10 time points, with a statistically significant difference (P < 0.05). After intubation (T2), the reduction in intraocular pressure among patients in the elderly group is less than those in the middle-aged group, with a statistically significant difference.

The curves illustrating the intraocular pressure changes for the compressed and non-compressed sides at various time points for both groups are presented in Figure 1, with the blue curve representing the middle-aged group and the red curve representing the elderly group. Analysis of this curve graph revealed the following observations: 1) Intraocular pressure values in the elderly group were generally elevated compared to those in the middle-aged group. This elevation may have stemmed from age-associated modifications in eye structure and function, leading to higher baseline intraocular pressure values on both the compressed and non-compressed sides. 2) While the middle-aged group exhibited certain intraocular pressure effects that may have been due to body positional changes and other factors, the variation in intraocular pressure between the eyes on the compressed and non-compressed sides in the elderly group was less pronounced, possibly indicating adaptive changes in the eye structure among the elderly. 3) Despite the overarching trend of higher intraocular pressure in the elderly group relative to the middle-aged group, individual variances persisted within each group. 4) The data in this study provided a comparison of intraocular pressure changes under both compressed and non-compressed conditions across middle-aged and elderly groups, with a preliminary exploration of the relationship between intraocular pressure, age, and external pressure factors. The insights from our results can serve as a valuable point of reference for both medical research and clinical applications.

Figure 1.

Curve illustrating changes in intraocular pressure on the non-compressed and compressed sides among patients in the elderly and middle-aged groups at different time points.

3.4 Changes in SPO₂, rScO₂, and MAP

The variations in SPO₂, rScO₂, and MAP across different time points for patients in both groups are presented in Table 2.

Table 2.
Comparison of SPO₂, rS_cO₂, and MAP between the two groups at different time points (% and mmHg, $\bar{x}$ ± s).

At the

During During During Before Supine Time of

Admission Intubation surgery surgery surgery turning position Discharge

Groups (T1) (T2) 5 min(T3) 30 min(T4) 1 h (T5) 2 h (T6) 3 h (T7) (T8) (T9) (T10)

SPO₂

Elderly group 97.63 ± 2.31 99.40 ± 0.55 99.46 ± 0.42 99.03 ± 0.34 98.77 ± 1.13 99.66 ± 0.24* 99.69 ± 0.18 99.69 ± 0.12 99.66 ± 0.18 99.77 ± 0.15

Middle-aged group 97.83 ± 1.71 99.03 ± 0.95 99.09 ± 0.74 98.51 ± 1.03 98.40 ± 1.48 98.63 ± 1.29* 99.40 ± 0.14 99.17 ± 0.61 99.03 ± 0.77 99.71 ± 0.28

rScO₂

Elderly group 60.86 ± 0.77 60.88 ± 0.93 60.63 ± 1.21 61.19 ± 0.77 61.34 ± 1.03 60.83 ± 0.74 61.64 ± 0.38 60.32 ± 0.67 60.82 ± 0.79 60.63 ± 1.75

Middle-aged group 60.88 ± 0.76 60.90 ± 0.89 60.66 ± 1.19 61.24 ± 0.73 61.38 ± 1.01 60.88 ± 0.77 61.66 ± 0.35 60.32 ± 0.66 60.81 ± 0.80 60.64 ± 1.72

MAP

Elderly group 94.54 ± 14.32 65.63 ± 12.97* 82.34 ± 8.01 82.37 ± 8.06 85.74 ± 8.06 85.20 ± 9.05 84.57 ± 7.71 84.11 ± 7.12* 88.63 ± 8.20 87.80 ± 7.87

Middle-aged group 92.74 ± 9.81 88.66 ± 13.75* 83.80 ± 10.58 80.97 ± 12.68 80.71 ± 8.10 82.51 ± 8.54 82.69 ± 8.29 103.20 ± 7.30* 83.17 ± 10.07 85.62 ± 9.54

										At the
SPO₂
Elderly group	97.63 ± 2.31	99.40 ± 0.55	99.46 ± 0.42	99.03 ± 0.34	98.77 ± 1.13	99.66 ± 0.24*	99.69 ± 0.18	99.69 ± 0.12	99.66 ± 0.18	99.77 ± 0.15
Middle-aged group	97.83 ± 1.71	99.03 ± 0.95	99.09 ± 0.74	98.51 ± 1.03	98.40 ± 1.48	98.63 ± 1.29*	99.40 ± 0.14	99.17 ± 0.61	99.03 ± 0.77	99.71 ± 0.28
rScO₂
Elderly group	60.86 ± 0.77	60.88 ± 0.93	60.63 ± 1.21	61.19 ± 0.77	61.34 ± 1.03	60.83 ± 0.74	61.64 ± 0.38	60.32 ± 0.67	60.82 ± 0.79	60.63 ± 1.75
Middle-aged group	60.88 ± 0.76	60.90 ± 0.89	60.66 ± 1.19	61.24 ± 0.73	61.38 ± 1.01	60.88 ± 0.77	61.66 ± 0.35	60.32 ± 0.66	60.81 ± 0.80	60.64 ± 1.72
MAP
Elderly group	94.54 ± 14.32	65.63 ± 12.97*	82.34 ± 8.01	82.37 ± 8.06	85.74 ± 8.06	85.20 ± 9.05	84.57 ± 7.71	84.11 ± 7.12*	88.63 ± 8.20	87.80 ± 7.87
Middle-aged group	92.74 ± 9.81	88.66 ± 13.75*	83.80 ± 10.58	80.97 ± 12.68	80.71 ± 8.10	82.51 ± 8.54	82.69 ± 8.29	103.20 ± 7.30*	83.17 ± 10.07	85.62 ± 9.54

Note: * indicates P < 0.05 when compared to the middle-aged group.

(1) There is no statistically significant difference in cerebral oxygen saturation changes between the two groups at any time point.

(2) Patients in the elderly group show higher and statistically significant fluctuations in MAP when compared to the middle-aged group at the post-intubation (T2) and pre-turning (T8) time points.

SPO₂: This suggests that patients in both groups maintained good oxygenation throughout the surgery without significant decreases in oxygen saturation levels, implying a minimal impact of the surgical procedure on respiratory function.

rScO₂: There were no notable differences in rScO₂ levels during surgery between patients in the elderly and middle-aged groups, indicating comparable efficiency in cerebral oxygen supply among patients in both groups.

MAP: After intubation (T2), there was a significant decrease in the MAP among patients in the elderly group, likely due to anesthetic administration. As the surgery progressed, MAP levels gradually increased, returning to near baseline, suggesting the recovery of circulatory function in elderly patients during surgery.

Despite some fluctuations, the physiological parameters of both groups stayed within normal ranges throughout the surgery, affirming the stability of the surgical process.

3.5 Relationship between mean arterial pressure and cerebral oxygen saturation

The Pearson correlation analysis indicated no significant relationship between MAP and cerebral oxygen saturation changes in the middle-aged group (r-value = -0.04217, P > 0.05). A weak correlation was observed between MAP and changes in cerebral oxygen saturation in the elderly group (r-value = 0.1122, P < 0.05), as depicted in Figure 2.

Figure 2.

Correlation between mean arterial pressure and changes in cerebral oxygen saturation among patients in the middle-aged and elderly groups.

4 Discussion

4.1 Surgical position adjustments notably influence intraocular pressure

4.1.1 The lateral position exerts a notable influence on intraocular pressure by impeding venous return in the eye on the compressed side, negating the height differential between the eyeball and the heart, thereby impacting changes in intraocular pressure

Surgical positioning exerts a significant effect on intraocular pressure.⁷ Cross-sectional studies⁸ have revealed a distinctive evolution in intraocular pressure responses to varying surgical positions over the course of surgery. Early findings by Friedland⁹ indicated that changes in body position result in blood redistribution within the choroidal vessel bed due to variations in choroidal vessel filling, contributing to increased intraocular pressure. Additionally, the autoregulation capacity of human choroidal blood flow is limited, influenced not only by the eyeball's perfusion pressure but also by MAP and intraocular pressure, rendering choroidal circulation particularly vulnerable to systemic changes.¹⁰

It has been observed that in a lateral position, the intraocular pressure in the eyes affected by positioning does not remain constant; the pressure in the compressed eye significantly exceeds that in the non-compressed eye, likely due to differential surrounding pressures impacting venous return.¹¹ The extent to which the relative height difference between the heart and each eye in lateral positions affects intraocular pressure in compressed and non-compressed eyes warrants further investigation.

The results of this study revealed congruent trends in intraocular pressure in both eyes of patients in both groups were evident, showing a gradual increase with changes in body position, peaking at two hours (T6), and subsequently stabilizing. After shifting from the lateral back to the supine position (T9), intraocular pressures in both eyes gradually reverted to baseline levels recorded at the time of admission (T1). Between T3 and T8, the intraocular pressure in the eyes on the compressed side in patients of both groups was consistently higher than on the non-compressed side, with a statistically significant difference (P < 0.05). This substantiates that intraocular pressure changes vary with alterations in body position. The lateral position significantly impacts intraocular pressure and barring pathological conditions, the fluctuation in intraocular pressure remains within a reasonable range.

4.1.2 The impact of head position and angle on ocular perfusion pressure and intraocular pressure

Wang et al.¹² investigated the effects of different head elevations (30 degrees higher and lower than the trunk, and level with the center of the thoracic vertebrae at 0 degrees) on intraocular pressure in patients with primary open-angle glaucoma (POAG) positioned laterally. Their findings indicated that eyes positioned lower exhibited consistently higher intraocular pressure compared to those positioned higher, with intraocular pressure diminishing as the head was elevated. Similar outcomes have been validated in animal research,¹³ showing an increase in intraocular pressure with the head in lower positions.

The blood supply to the eye is via the ophthalmic artery, which is the initial intracranial branch of the internal carotid artery,¹⁴ capable of autonomously adjusting to changes in ocular perfusion pressure.¹⁵ Certain positions that involve extension, compression, suspension, weightlessness,^16,17 or stretching of the neck may disrupt blood perfusion to the neck. In the current study, the lateral decubitus position required for surgery involved positioning the body on its side at a 90° angle, with the head and leg boards slightly declined (10 to 15 degrees) to facilitate access to the chest for surgery. It is critical during such positioning to maintain the alignment of the cervical spine and use a head pillow to elevate the neck, thereby preventing neck suspension. Adjustments in body position during surgery should be executed with caution to avoid excessive pulling or twisting that might alter the angle of the head and consequently affect neck blood perfusion and intraocular pressure.

4.2 Rapid increase and slow recovery of intraocular pressure in elderly patients

The results of this study indicate that intraocular pressure levels in the eyes on both the compressed and non-compressed sides among patients in the elderly group were consistently higher than those in the middle-aged group during time points T3 to T10, with a statistically significant difference (P < 0.05). Additionally, curve graphs distinctly showed that the baseline intraocular pressure levels of patients in the elderly group were higher than those in the middle-aged group at all time points.

Aging, coupled with the progression of senescence, induces various changes in the vascular structure of the human eye, including a marked decrease in capillary count and retinal thickness, along with alterations in macular blood flow density and structure.¹⁸ Consequently, the elderly are more susceptible to perfusion abnormalities following alterations in the position of the body, anesthesia depth, and the loss of blood and fluids. These conditions can lead to obstructed venous return, causing a rapid surge and a gradual decrease in intraocular pressure.

4.3 Relationship between MAP and cerebral oxygen saturation changes

In this study, the Pearson correlation analysis revealed a weak correlation between MAP and changes in cerebral oxygen saturation among patients in the elderly group (r value = 0.1122, P < 0.05), underscoring the interconnectedness of the cardiovascular and cerebrovascular systems. A decline in cardiac output can significantly impact cerebral function.³ It has been demonstrated that the risk of central nervous system complications during the perioperative period of cardiothoracic surgery is considerably higher than in other surgical procedures.¹⁹

Brain tissue is particularly vulnerable to ischemia and hypoxia,^20,21 and elderly patients have a heightened risk in this regard, predisposing them to severe complications. The aging process and effects of anesthesia reduce the neuroprotective reserves of elderly patients, increase their sensitivity to drugs, and diminish the autoregulatory ability of cerebral vessels, potentially leading to insufficient SPO₂ levels. Age-related reductions in myocardial blood flow reserve, heightened arteriosclerosis, ventricular hypertrophy, and diminished baroreceptor reflex sensitivity can cause more pronounced blood pressure fluctuations in elderly patients. Factors such as the administration of anesthetic agents, fluid loss, surgical interventions, and maneuvers involving neck traction and extension can influence vital organ perfusion, creating disparities in rScO₂. Consequently, the meticulous monitoring of cerebral oxygen saturation during surgery is critical.

4.4. Surgical positioning and observations during surgery

4.4.1 Pre-Positioning assessment

Prior to positioning the patient, operating room nurses should perform a comprehensive evaluation that should include any history of cardiovascular and cerebrovascular diseases, cervical rigidity, prior neck surgeries and neck mobility, existing eye conditions such as glaucoma, cataract, and severe myopia, and the use of specific medications by the patient.

4.4.2 Aspects to be considered during surgery

The decision and process of positioning that patient should be a team effort by the surgical staff, with the aim of placing the patient in a comfortable and secure posture, striving to keep the spine and limbs naturally aligned as much as is feasible.

Post-positioning and subsequent to any positional adjustments made, meticulous attention should be paid to ensure that the alignment of the patient's cervical spine and head is in a straight line, avoiding any inadvertent dragging, pulling, or tugging.

It is crucial to handle the patient's head with care, ensuring that the head is not left unsupported while avoiding excessive stretching or rotation of the neck. The head should be maintained in a neutral position throughout the surgery and softly cushioned with a pillow to prevent direct compression of the eye on the compressed side by any firm objects.

Monitoring intraocular pressure and changes in cerebral oxygen saturation during the operation is of paramount importance. Evidence suggests that the downward tilt angle of the head should not surpass 35 degrees, especially for elderly patients and those with severe myopia.¹⁶ Sustained elevated intraocular pressure can result in postoperative ocular complications, necessitating timely notifications to the surgical team. Therefore, monitoring intraocular and cerebral perfusion pressure changes during the entire surgery is advisable, if feasible.

It is equally crucial to avoid external ocular compression. The surgical team must be vigilant and proactively prevent actions that can induce pressure, such as the manipulation of the face mask by the anesthesiologist, incorrect placement of surgical tools near the patient's head that may compress the eye, inadvertent squeezing of the patient's head by medical personnel during the course of the surgery, and movements like adjusting or twisting the patient's head that could exert pressure.

Maintaining hemodynamic stability is significant in the perioperative care of elderly patients. Monitoring vital signs, fluid balance, and rScO₂ throughout the surgery is essential. Compliance with fluid replenishment and medication orders is crucial to prevent significant variations in blood pressure. Surgical nurses should carefully adjust the angle of the surgical bed to ensure optimal blood supply to the patient's head and essential organs.

4.4.3 Postoperative follow-up

A detailed handover with the ward nurse at the patient's bedside must be ensured. This should include discussing the particulars of the surgery and any specific surgical positioning that was employed during the procedure while jointly inspecting for signs of eye compression, conjunctival edema, and other ocular anomalies.

The patient must be revisited six hours after surgery to evaluate the recovery of vision. In the event of the detection of any ocular abnormalities, an immediate consultation with the ophthalmologist must be scheduled, and follow-up observations must be maintained vigilantly.

5 Limitation

There are some limitations in this study. Due to the selection of specific surgical types and the study conducted in special Settings, the sample size is limited, which may affect the universality and repeatability of the results. The relationship between intraoperative changes in IOP and surgical position will continue to be further studied to provide scientific data for patient position safety.

6 Conclusion

In conclusion, the results of this study affirm that changes in surgical positioning of patients significantly influence intraocular pressure and cerebral oxygen saturation, and diverse patterns in these two variables were observed throughout the surgical procedure. It is imperative to closely monitor blood perfusion and hemodynamic changes in critical organs during the surgical care of elderly patients. Comprehensive assessments prior to surgery, cohesive team efforts for correct positioning of the patient for surgery, and intensified monitoring of vital organ perfusion during surgery are indispensable to preclude any procedures that may compress the eye. Postoperative protocols should include comprehensive handovers, subsequent evaluations, and assessments of ocular recovery. Future investigations with larger samples and incorporating multi-center data are essential for in-depth explorations of the effects of surgical positioning on blood perfusion and for creating a scientific foundation for the establishment of guidelines for efficacious surgical positioning.

Footnotes

Abbreviations

Acknowledgements

The Icare tonometer and brain oxygen monitor used in this study were supported by Shenzhen Ruilin Pharmaceutical Co., Ltd. and Suzhou Aeqin Biomedical Electronics Co., LTD., and I would like to express my deep gratitude through this article.

Ethics approval and consent to participate

This study was conducted with approval from the Ethics Committee of Beijing Tongren Hospital, Capital Medical University (No. TRECKY2016-016). This study was conducted in accordance with the declaration of Helsinki. Written informed consent was obtained from all participants.

Authors’ contributions

Conception and design of the research: Wei Wang.

Acquisition of data: Wei Wang, Ying-Ying Sun.

Analysis and interpretation of the data: Wei Wang, Ying-Ying Sun, Chun-Hua Xi.

Statistical analysis: Chun-Hua Xi.

Obtaining financing: None.

Writing of the manuscript: Wei Wang.

Critical revision of the manuscript for intellectual content: Wei Wang.

All authors read and approved the final draft.

Funding

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

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

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										At the
					During	During	During	Before	Supine	Time of
	Admission	Intubation			surgery	surgery	surgery	turning	position	Discharge
Groups	(T1)	(T2)	5 min(T3)	30 min(T4)	(T5)	(T6)	(T7)	(T8)	(T9)	(T10)
Non-compressed side
Elderly group	18.55 ± 2.49	14.75 ± 2.99	17.84 ± 2.78^a	18.89 ± 2.86^a	20.07 ± 2.35^a	20.35 ± 2.54^a	20.07 ± 2.31^a	19.61 ± 2.09	18.52 ± 2.63^a	17.70 ± 2.40
Middle-aged group	18.40 ± 1.92	15.50 ± 2.12	16.30 ± 2.31	17.17 ± 2.41	17.76 ± 2.60	18.20 ± 2.60	17.93 ± 2.07	18.40 ± 2.24	16.91 ± 2.63	16.53 ± 2.35
T-value	−0.151	0.751	−1.543	−1.714	−2.311	−2.154	−2.140	−1.211	−1.617	−1.171
P-value	0.999	0.583	0.004	0.000	0.000	0.000	0.000	0.053	0.002	0.070
Compressed side
Elderly group	18.17 ± 2.06	14.57 ± 2.81	19.27 ± 2.76^a	21.37 ± 1.41^a	22.35 ± 1.41^a	22.59 ± 0.89^a	22.62 ± 0.88	22.42 ± 0.71	18.56 ± 1.90	17.49 ± 1.85
Middle-aged group	18.79 ± 2.24	15.56 ± 2.20	17.74 ± 1.69	19.31 ± 1.79	20.78 ± 1.89	21.39 ± 1.64	21.53 ± 1.60	21.76 ± 1.47	18.25 ± 1.95	16.89 ± 2.21
T-value	0.620	0.997	−1.523	−2.051	−1.566	−1.200	−1.086	−0.660	−0.305	−0.591
P-value	0.647	0.079	0.000	0.000	0.000	0.015	0.039	0.561	0.995	0.707