What Is the Risk of Intraoperative Cerebral Oxygen Desaturation in Patients Undergoing Shoulder Surgery in the Beach Chair Position?

Abstract

Background

Previous studies have shown that intraoperative cerebral desaturation in patients undergoing shoulder surgery in the beach chair position varies widely, from 0% to 80%. To our knowledge, the risk of intraoperative cerebral desaturation is not known after all identified intraoperative modifiable physiologic parameters that influence cerebral blood flow have been controlled for.

Questions/purposes

(1) What is the risk of intraoperative cerebral desaturation during shoulder surgery with the patient in the beach chair position when patients received combined general anesthesia and an interscalene block, and what other factors associated with intraoperative cerebral desaturation can be identified? (2) Is intraoperative cerebral desaturation associated with 24-hour cognitive decline? (3) What factors are associated with intraoperative hypotension?

Methods

Between April and December 2020, 51 patients underwent elective shoulder surgery in the beach chair position at one center. Nine patients were excluded: four patients refused to participate, two patients were unable to receive an interscalene brachial plexus block, and three patients were operated on in less than 70° upright position. A total of 42 patients (aged 63 ± 10 years, of whom 52% [22 of 42] were female) were prospectively recruited into this study. Each patient was diagnosed with a rotator cuff tear and underwent arthroscopic repair in the beach chair position, which was performed in an upright position of 70° to 80°. Near-infrared spectroscopy was used to monitor regional cerebral oxygen saturation. The mean arterial pressure was monitored and controlled so that it was more than 70 mmHg in patients without hypertension and within 20% from the baseline mean arterial pressure in patients with hypertension. All patients received the standardized anesthesia protocol, which consisted of an interscalene brachial plexus block and general anesthesia. Intraoperative cerebral desaturation was defined as a decrease in the regional cerebral oxygen saturation level of more than 20% from the baseline value that lasted longer than 15 seconds after induction of anesthesia. Patients’ clinical characteristics such as age, sex, BMI, preoperative hemoglobin level, preexisting medical conditions, and continuing antihypertensive medications on the morning of surgery were analyzed to identify the association with intraoperative cerebral desaturation. We used the Montreal Cognitive Assessment to assess cognitive function at preoperative and 24 hours postoperative. Episodes of hypotension and its treatment after maximum head elevation were recorded. The patients’ clinical characteristics were analyzed to determine their association with hypotensive events.

Results

In this study, intraoperative cerebral desaturation occurred in 43% (18 of 42) of patients, and female sex was identified as an associated risk (odds ratio 4.3 [95% confidence interval 1.2 to 16.2]; p = 0.03). The median (interquartile range) duration of intraoperative cerebral desaturation was 19 minutes (5 to 38). There was no association between intraoperative cerebral desaturation and 24-hour postoperative cognitive decline (OR 0.6 [95% CI 0.1 to 2.4]; p = 0.44). Risk factors for intraoperative hypotension were a history of hypertension, regardless of whether or not the patient took antihypertensive drugs on the morning of surgery (OR 4.9 [95% CI 1.3 to 18.1]; p = 0.02), and dyslipidemia (OR 4.3 [95% CI 1.2 to 16.3]; p = 0.03).

Conclusion

The intraoperative cerebral desaturation risk in the beach chair position was high. Female sex was an intraoperative cerebral desaturation risk factor. However, there was no association between intraoperative cerebral desaturation and postoperative cognitive decline. Patients with hypertension and dyslipidemia are at risk of intraoperative hypotension after positioning. Further large-scale studies are required to identify intraoperative cerebral desaturation–associated adverse neurologic outcome.

Level of Evidence

Level II, therapeutic study.

Introduction

The beach chair position provides unique benefits for shoulder surgery, including excellent intraarticular visualization, ease of conversion to the open approach, and reduced risk of direct neurovascular trauma from positioning [9, 19]. However, this position is related to multiple concerning physiologic changes that result in hypotension, bradycardia, and especially cerebral hypoperfusion [3, 6, 14, 17]. Several case reports described cerebral ischemic complications with permanent disabilities after shoulder surgery in the beach chair position [4, 20]. Near-infrared spectroscopy is a valuable, noninvasive, real-time monitoring tool that can assess the regional cerebral oxygenation (rSO₂) level [16, 21, 22]. Even though the risk of disastrous cerebrovascular events related to the beach chair position, such as ischemic stroke, is very low (< 0.1%), this position carries a great risk of intraoperative cerebral desaturation [23]. Previous studies demonstrated that the patients who received general anesthesia in the beach chair position had diminished cerebral autoregulation [13]. Consequently, a hypotensive event, which occurred more often in anesthetized seated patients, impaired the cerebral blood flow, and potentially put the patients at a higher intraoperative cerebral desaturation risk compared with other positions [3, 15, 16].

The intraoperative cerebral desaturation risk in the beach chair position varies widely from 0% to 80%, depending on the anesthetic techniques used, definition of cerebral desaturation, and the study design [14, 16, 23]. Moerman et al. [14] reported that intraoperative cerebral desaturation in the beach chair position occurred in 80% of patients when routine anesthesia management and standard monitoring were adopted. To our knowledge, the risk of intraoperative cerebral desaturation and its associated risk factors during shoulder surgery in the beach chair position in patients who received combined general anesthesia and an interscalene block with controlled targeted mean arterial pressure and other modifiable physiologic parameters that influence cerebral blood flow are not yet known. Several studies investigated the association of intraoperative cerebral desaturation in the beach chair position and postoperative neurocognitive dysfunction, which greatly differ according to the test used and timing of the neurocognitive assessment; however, they were unable to conclude the impacts of intraoperative cerebral desaturation yet [13, 23]. A recent retrospective study revealed that preoperative interscalene brachial plexus block was an independent risk factor associated with hypotension in the beach chair position [1]. However, a combination of general anesthesia and an interscalene brachial plexus block is still a widely used anesthetic technique for shoulder surgery [10]. It is important to know which modifiable risk factors are associated with intraoperative hypotension so it can be controlled and improve the patient’s safety when these combined anesthetic techniques are used for shoulder surgery in the beach chair position.

Therefore, we asked: (1) What is the risk of intraoperative cerebral desaturation during shoulder surgery with the patient in the beach chair position when patients received combined general anesthesia and an interscalene block, and what other factors associated with intraoperative cerebral desaturation can be identified? (2) Is intraoperative cerebral desaturation associated with 24-hour cognitive decline? (3) What factors are associated with intraoperative hypotension?

Patients and Methods

Study Design and Setting

This was a prospective, observational, single-center study conducted at King Chulalongkorn Memorial Hospital, Bangkok, Thailand. The patients were prospectively enrolled in the study from April 2020 to December 2020. The patients recruited into this study were operated on by three experienced orthopaedic surgeons (none were study authors) who specialized in arthroscopic surgery. There was no difference in position preference between the surgeons; most of the patients were placed in an upright position of 70° to 80°, and their heads and necks were secured in a neutral position. Anesthetic procedures were performed by an experienced regional anesthesia team who practiced longer than 5 years and performed more than 100 interscalene brachial plexus blocks.

Participants

Inclusion criteria were patients older than 18 years of age with American Society of Anesthesiologists physical status 1 to 3 scheduled for elective shoulder surgery in the beach chair position. As per our institution’s protocol and surgeon’s preference, we performed elective shoulder surgery in the beach chair position, which places the patients in an upright position of 70° to 80°. However, if the patients were not suitable for this position, then a lateral decubitus position or reducing the degrees of upright position were considered. We excluded patients who declined to participate, those who were unable to perform a cognitive test, those who could not be monitored by near-infrared spectroscopy or the bispectral index, those who declined or could not undergo an interscalene brachial plexus block or general anesthesia, and those who planned to have surgery in an upright position less than 70° or other positions. During the study period, 51 patients were scheduled for elective shoulder surgery in the beach chair position. Six percent (3 of 51) of patients were excluded as the planned upright position was less than 70°, 8% (4 of 51) refused to participate in the study, and in 4% (2 of 51) of patients it was not feasible to perform interscalene brachial plexus block due to morbid obesity with severe obstructive sleep apnea and poorly controlled chronic obstructive pulmonary disease. Thus, a total of 42 patients were included and analyzed (Fig. 1).

Fig. 1.

Flow diagram showing patient recruitment.

Preoperatively, the participants’ demographic data such as age, sex, BMI, American Society of Anesthesiologists physical status, history of smoking, preexisting medical conditions, and current medications were recorded. Baseline cognitive function was assessed by using the Montreal Cognitive Assessment (Thai version) [25]. For patients with hypertension, their usual medications were continued on the morning of surgery except for those taking angiotensin-converting enzyme inhibitors and those taking angiotensin receptor blockers.

Patients’ Demographics and Baseline Factors

In the study population, the mean age was 63 ± 10 years, 52% (22 of 42) were female, 55% (23 of 42) had hypertension, and 21% (9 of 42) had diabetes. Seventy-one percent (30 of 42) of the patients had American Society of Anesthesiologists physical status Class 2. Baseline mean arterial pressure, oxygen saturation, and hemoglobin levels were 93 ± 9 mmHg, 98% ± 1%, and 13 ± 1 g/dL, respectively. The mean height of head elevation, which was measured perpendicularly from tragus to the midpoint of the blood pressure cuff, was 34 ± 5 cm. Seventy-one percent (30 of 42) of patients had more than 12 years of education, and the baseline preoperative Montreal Cognitive Assessment score was 24 ± 4 (Table 1). All patients were diagnosed with a rotator cuff tear and underwent arthroscopic repair in the beach chair position performed by three arthroscopic orthopaedic surgeons.

Table 1.

Demographics data and clinical characteristics of the patients

Characteristic	Value
Age in years	63 ± 10
Female, %	52 (22 of 42)
BMI, kg/m2	25 ± 4
ASA physical status
1	19 (8 of 42)
2	71 (30 of 42)
3	10 (4 of 42)
Underlying disease
Hypertension	55 (23 of 42)
Beta-blockers	22 (5 of 23)
Calcium channel blockers	57 (13 of 23)
ACEIs, ARBs	61 (14 of 23)
Diabetes mellitus	21 (9 of 42)
Dyslipidemia	48 (20 of 42)
Cerebrovascular disease	2 (1 of 42)
Previous myocardial infarction	5 (2 of 42)
Pulmonary disease	5 (2 of 42)
Smoking history	5 (2 of 42)
Baseline hemodynamic variables
MAP, mmHg	93 ± 9
SBP, mmHg	133 ± 14
DBP, mmHg	74 ± 9
HR, mmHg	71 ± 11
SpO2, %	98 ± 1
Cerebral oxygenation
Baseline rSO2 in room air	58 ± 8
rSO2 after induction (FiO2 = 0.5)	62 ± 12
rSO2 after maximum head elevation	57 ± 9
Hemoglobin, g/dL	13 ± 1
Education
< 6 years	17 (7 of 42)
6-12 years	12 (5 of 42)
> 12 years	71 (30 of 42)
Baseline preoperative MoCA score	24 ± 4
Operation time in minutes	76 ± 33
Anesthesia time in minutes	132 ± 44
Head elevation time in minutes	97 ± 37
Total crystalloid, mL	607 ± 203
Blood loss, mL, median (IQR)	10 (5-50)
Endtidal-Desflurane, %	5 ± 1

Data presented as mean ± SD or % (n), unless otherwise noted; IQR = interquartile range; ACEIs = angiotensin converting enzyme inhibitors; ARBs = angiotensin II receptor blockers; MAP = mean arterial pressure; SBP = systolic blood pressure; DBP = diastolic blood pressure; HR = heart rate; SpO₂ = pulse oximetry; rSO₂ = regional cerebral oxygenation; FiO₂ = fraction of inspired oxygen; MoCA= Montreal Cognitive Assessment.

Study Interventions and Monitoring

All patients received the standardized anesthesia protocol, which was an interscalene brachial plexus block combined with general anesthesia. Intraoperative monitoring included electrocardiography, noninvasive blood pressure measurement using a cuff placed on the nonoperative upper arm, pulse oximetry, capnography, bispectral index, and cerebral oxygen saturation.

We used near-infrared spectroscopy (Adult SomaSensor probe, INVOSTM 5100) to monitor rSO₂, and baseline values were obtained while the patient breathed in room air without sedation. Probes were applied bilaterally at the frontotemporal area 1 cm above the eyebrow. We used the bispectral index (Quatro Sensor probe, Vista) to monitor anesthesia depth.

After the baseline rSO₂ value was obtained, an experienced anesthesiologist performed an ultrasound-guided interscalene brachial plexus block using 0.33% bupivacaine, 15 mL (50 mg of bupivacaine). General anesthesia was then induced with 1.5 mg/kg to 2.5 mg/kg of propofol, 0.1 mg/kg to 0.2 mg/kg of cisatracurium, and/or 1 mcg/kg to 2 mcg/kg of fentanyl. The airway was secured with an endotracheal tube; anesthesia was maintained with desflurane in the air with a fraction of inspired oxygen of 50%. The bispectral index was maintained between 40 and 60. Ventilation was controlled with a tidal volume of 8 mL/kg, and the respiratory rate was adjusted to keep the end-tidal carbon dioxide level between 35 cmH₂O and 40 cmH₂O. The noninvasive mean arterial pressure was monitored in the nonsurgical arm every 5 minutes and was maintained above 70 mmHg in patients without hypertension or within 20% from the baseline mean arterial pressure in those with hypertension [18]. All hypotension episodes were recorded and treated with fluid administration, inotrope, or vasopressor at the discretion of the attending anesthesiologist. Reversal agents were 0.02 mg/kg to 0.07 mg/kg of neostigmine and 0.2 mg of glycopyrrolate per 1 mg of neostigmine.

After the baseline rSO₂ value was obtained, the rSO₂ level was continuously monitored until the participant was transferred to the postanesthesia care unit. All data were recorded electronically in real time. Intraoperative cerebral desaturation was defined as a decrease in rSO₂ of more than 20% from a baseline value and longer than 15 seconds after induction of general anesthesia. Each desaturation episode was counted as one episode until rSO₂ returned above the threshold.

Twenty-four hours postoperatively, the patient’s cognitive function was assessed by using the Thai version of the Montreal Cognitive Assessment. All perioperative complications, such as pressure sores, skin irritation, and especially focal neurologic deficits, were explored and recorded.

Primary and Secondary Study Outcomes

Our primary study goal was to identify the intraoperative cerebral desaturation risk in the beach chair position after patients had received combined general anesthesia and an interscalene block and when known intraoperative modifiable physiologic parameters that influence cerebral blood flow had been controlled and targeted.

Our secondary study goals explored the risk factors associated with intraoperative cerebral desaturation, the association between intraoperative cerebral desaturation and 24-hour postoperative cognitive decline, and the risk factors associated with hypotension after positioning.

Bias

Since the study sample size was quite small, the results of secondary outcomes might be different in a larger-scale study primarily intended to detect those outcomes.

All patients in this study were diagnosed with rotator cuff injury and underwent only arthroscopic repair. Because of surgical concerns, the surgeons planned that some patients would be in an upright position of less than 70° during the surgery, and they were excluded from the study. The intraoperative cerebral desaturation risk may differ in other procedures that have longer operation time and more blood loss, which may affect cerebral oxygen delivery. Even though obesity and severe pulmonary diseases were not primarily in our exclusion criteria, two patients with these conditions were not included in this study because there was a concern of respiratory complications from interscalene brachial plexus block.

Ethical Approval

This study was approved by the institutional review board of the Faculty of Medicine, Chulalongkorn University (number 153/2020), and registered in the Thai Clinical Trial Registry (registration number TCTR20200407004). Written informed consent to participate in the study was obtained from all of the patients.

Statistical Analysis

In this study, we used the infinite population proportion formula to calculate the sample size; Jeong et al. [11] reported that the intraoperative cerebral desaturation risk, defined as a decrease of rSO₂ of more than 20% from the baseline value for more than 15 seconds, was 41%. When we used a 95% CI and a Type I error of 0.05, and an acceptable error was set to 0.15, 42 patients were needed for this study to detect the risk of intraoperative cerebral desaturation as previously defined. The statistical analysis was performed with SPSS Statistics, version 26.0 (IBM Corp). Normal distribution was tested using the Shapiro-Wilk test. For descriptive statistics, numbers and percentages were used for categorical data, the mean with SD was used for continuous data with a normal distribution, and the median with IQR was used for continuous data with a skewed distribution. A binary logistic regression analysis was used to identify risk factors associated with intraoperative cerebral desaturation, 24-hour postoperative cognitive decline, and intraoperative hypotension and are presented as ORs and 95% CIs. A p value less than 0.05 was considered statistically significant.

Results

Intraoperative Cerebral Desaturation Risk in the Beach Chair Position

The risk of intraoperative cerebral desaturation in this study was 43% (18 of 42). The median (interquartile range) duration of intraoperative cerebral desaturation was 19 minutes (5 to 38). The median (range) number of intraoperative cerebral desaturation events was 1 (1 to 3) episode per procedure, and the desaturation event usually occurred approximately 20 minutes after the maximum head elevation was reached (Fig. 2). Female sex was a risk factor associated with intraoperative cerebral desaturation (Table 2).

Fig. 2.

This graph shows intraoperative cerebral desaturation events in 18 patients; rSO₂ = regional cerebral oxygenation.

Table 2.

Risk factors for ICD by binary logistic regression

Variable	ICD group (n = 18)	Non-ICD group (n = 24)	OR (95%CI)	p value
Age in years	65 ± 7	61 ± 12	1.0 (0.9-1.1)	0.29
Female	13	9	4.3 (1.2-16.2)	0.03
BMI, kg/m2	25 ± 5	25 ± 4	0.9 (0.8-1.1)	0.85
Hemoglobin, g/dL	13 ± 1	14 ± 2	0.6 (0.4-1.1)	0.08
Hypertension	11	12	1.6 (0.5-5.4)	0.48
Continue antihypertensive medication	9	6	3.0 (0.8-11.1)	0.09
Diabetes mellitus	5	4	1.9 (0.4-8.5)	0.39
Pulmonary disease	1	3	0.4 (0.1-4.3)	0.46
Head elevation, cm	33 ± 4	35 ± 5	0.9 (0.8-1.1)	0.24
Fasting time in hours	11 ± 2	11 ± 2	1.0 (0.8-1.4)	0.82
Total crystalloid, mL	650 ± 190	575 ± 210	1 (0.9-1.01)	0.24
Blood loss, mL	25 (5-50)	10 (5-50)	1.02 (0.9-1.05)	0.10

Data presented as mean ± SD, number, or mean (interquartile range); ICD = intraoperative cerebral desaturation; OR = odds ratio.

Intraoperative Cerebral Desaturation Episodes and Cognitive Decline

There was no association between intraoperative cerebral desaturation and cognitive decline at 24 hours postoperatively (OR 0.6 [95% CI 0.1 to 2.4]; p = 0.44). Fourteen percent (6 of 42) of patients had postoperative cognitive decline (Table 3). All six patients who had 24-hour postoperative cognitive decline had at least one episode of hypotension intraoperatively. The only risk factor for postoperative cognitive decline was education of less than 6 years (OR 10.5 [95% CI 1.3 to 83.5]; p = 0.02) (Table 4). No patients had focal neurologic deficits postoperatively.

Table 3.

24-hour postoperative cognitive decline

MoCA difference	ICD group (n = 18)	NonICD group (n = 24)
0	16	20
-1	2	2
-2	0	2

MoCA = Montreal Cognitive Assessment; ICD = intraoperative cerebral desaturation.

Table 4.

Risk factors for 24-hour postoperative cognitive decline

Variable	Postoperative cognitive decline (n = 6)	No postoperative cognitive decline (n = 36)	OR (95% CI)	p value
At least one episode of ICD	2	16	0.6 (0.1- 2.4)	0.44
At least one episode of hypotension	6	18	N/A	0.99
Education level
< 6 years	3	4	10.5 (1.3-83.5)	0.02
6-12 years	1	4	3.5 (0.3-48.0)	0.35
> 12 years	2	28	Reference	> 0.99

ICD = intraoperative cerebral desaturation; OR = odds ratio.

Risk Factors for Intraoperative Hypotension

Risk factors for intraoperative hypotension were a history of hypertension, regardless of whether or not the patient took antihypertensive drugs on the morning of surgery (OR 4.9 [95% CI 1.3 to 18.1]; p = 0.02), and dyslipidemia (OR 4.3 [95% CI 1.2 to 16.3]; p = 0.03) (Table 5). Fifty-seven percent (24 of 42) of the patients had at least one episode of hypotension after positioning. To achieve the targeted mean arterial pressure, 23 of 24 patients received ephedrine (6 ± 13 mg), and three patients received norepinephrine (7 ± 4 mcg) to raise the mean arterial pressure. Among the patients who had intraoperative hypotension, 11 of 24 patients developed intraoperative cerebral desaturation after the hypotension episode. There was no association between intraoperative hypotension and intraoperative cerebral desaturation (OR 1.3 [95% CI 0.4 to 4.6]; p = 0.65).

Table 5.

Risk factors for intraoperative hypotension by binary logistic regression

Variable	Intraoperative hypotension (n = 24)	No intraoperative hypotension (n = 18)	OR (95% CI)	p value
Age in years	64 ± 8	61 ± 12	1.0 (0.9-1.1)	0.29
Female	14	8	1.8 (0.5-6)	0.37
BMI, kg/m2	26 ± 4	24 ± 3	1.2 (0.9-1.4)	0.10
Hemoglobin, %	14 ± 2	13 ± 1	1.3 (0.8-2.1)	0.34
Chronic hypertension	17	6	4.9 (1.3-18.1)	0.02
Continue antihypertensive medication	12	3	5.0 (1.1-21.9)	0.03
Discontinue antihypertensive medication	12	2	8 (1.5-42.7)	0.01
Diabetes mellitus	5	4	0.9 (0.2-4.0)	0.91
Dyslipidemia	15	5	4.3 (1.2-16.3)	0.03
Fasting time in hours	11 ± 2	11 ± 2	0.9 (0.7-1.3)	0.82
Head elevation, cm	34 ± 5	33 ± 5	1.0 (0.9-1.2)	0.64
Total crystalloid, mL	640 ± 220	560 ± 180	1.0 (0.9-1.1)	0.24
Blood loss, mL	10 (5-30)	30 (5-50)	0.9 (0.9-1.1)	0.24

Data presented as mean ± SD, number, or median (interquartile range); ICD = intraoperative cerebral desaturation; head elevation = distance perpendicularly measured from tragus to midpoint of blood pressure cuff; OR = odds ratio.

Discussion

Regardless of the fact that combined general anesthesia and an interscalene brachial plexus block predispose seated patients to hypotension and subsequently cerebral hypoperfusion, this technique is still widely performed as the mainstay for shoulder surgery [1, 12, 13]. Previous studies showed a very wide range of intraoperative cerebral desaturation risk in this position; also, none of the studies controlled all known intraoperative modifiable physiologic parameters that influence cerebral blood flow and used this combined anesthetic technique [16, 23, 27]. Moreover, in the Enhanced Recovery After Surgery (ERAS) era, with more advanced arthroscopic surgical techniques, intraoperative cerebral desaturation is still problematic, and its association with postoperative neurocognitive decline, which may affect the patient’s recovery, is not yet concluded [13, 23].

Limitations

There are some limitations to this study. The study sample size was quite small. We did not have enough power to investigate other secondary outcomes such as risk factors for early postoperative cognitive dysfunction, which occurred less frequently than intraoperative cerebral desaturation. Most patients in this study had American Society of Anesthesiologists physical status Class 2, and only one patient had a history of cerebrovascular disease. Hence, the number of comorbidities in the presence of a neurological disease may affect the intraoperative cerebral desaturation risk.

As per our institution’s protocol and surgeons’ preference, most elective shoulder surgeries are usually in the beach chair position, which placed the patients in an upright position of 70° 80°. There were only a few patients who were operated on in other positions, so it is difficult to compare the intraoperative cerebral desaturation risk to the beach chair position. It is possible that other centers may have been more selective about using the beach chair position or placed patients in a lesser degree of uprightness, hence, the intraoperative cerebral desaturation risk may be different. Moreover, in our study, shoulder surgery was performed by three experienced orthopaedic surgeons. In other settings where there are several surgeons, the surgical techniques, position preference, blood loss and operative time may vary and affect the intraoperative cerebral desaturation risk.

Intraoperative Cerebral Desaturation Risk in the Beach Chair Position

We recognize that despite an attempt to control and monitor multiple physiologic parameters that influence cerebral perfusion, including end-tidal carbon dioxide, anesthesia depth, neck position, and especially the mean arterial pressure of the nonsurgical arm, the intraoperative cerebral desaturation risk was still high. However, when compared with a previous rSO₂-blinded observational study that investigated the intraoperative cerebral desaturation risk during routine anesthesia management and used the same intraoperative cerebral desaturation definition as our study, the intraoperative cerebral desaturation risk in our study was much lower [14]. The intraoperative cerebral desaturation event usually occurred approximately 20 minutes after the maximum head elevation was met (Fig. 3). Salazar et al. [24] also reported that the mean time to onset of the initial intraoperative cerebral desaturation was 8 minutes after positioning, which contrasts with a previous report that the intraoperative cerebral desaturation event usually occurs immediately after positioning [3, 14]. Cautious monitoring of factors that might affect cerebral perfusion and oxygenation, especially mean arterial pressure, should be made during this period. The reason why an intraoperative cerebral desaturation event usually happens at this particular time remains unclear. Our hypothesis is that cerebral autoregulation might not be impaired yet in the first period after induction. If blood pressure can still be maintained, during the period which cerebral autoregulation is not yet impaired, then an intraoperative cerebral desaturation event should not develop immediately after positioning. Further studies should investigate the timing of when cerebral autoregulation starts to become impaired while in the beach chair position to confirm this hypothesis.

Fig. 3.

This graph shows MAP and rSO₂ intraoperatively in patients who had cerebral desaturation; MAP = mean arterial pressure; rSO₂ = regional cerebral oxygenation.

Female sex was a risk factor associated with intraoperative cerebral desaturation in our study. Gilotra et al. [8] also studied intraoperative cerebral desaturation risk factors during shoulder surgery in the beach chair position. Among all four reported intraoperative cerebral desaturation patients, three were female. In addition, we observed that continuing to take antihypertensive medications, such as calcium channel blockers and beta-blockers during the morning of surgery, similar to other procedures in a non–beach chair position, may be an intraoperative cerebral desaturation risk factor. Trentman et al. [26] reported that preoperative use of antihypertensive medication was associated with an increased incidence of hypotension in patients who underwent shoulder surgery in the beach chair position. To our knowledge, there has been no evidence of an association between intraoperative cerebral desaturation events and taking antihypertensive drugs preoperatively. Although we did not find use of antihypertensive medication on the morning of surgery to be a risk factor, it could be that this was because of our study’s small size. A large well-designed study may be able to answer this question and change our current practice on continuing preoperative antihypertensive medication for specific positions, like the beach chair.

Intraoperative Cerebral Desaturation Episodes and Cognitive Decline

For cognitive function, there was no association between intraoperative cerebral desaturation and postoperative cognitive decline. Salazar et al. [24] also studied the impact of intraoperative cerebral desaturation on postoperative cognitive decline using Repeatable Battery for the Assessment of Neurophysiological Status (RBANS) and found no association either in composite score or any of the subindices between intraoperative cerebral desaturation and postoperative neurocognitive function. Laflam et al. [13] compared the beach chair position with lateral decubitus position and reported that patients in the beach chair position had lower cerebral oxygen saturation; nevertheless, there was no difference in brain injury biomarker levels and composite neurocognitive outcome. However, the sample size in our study was quite small, so the power may not have been enough to detect such an association. Aside from that, we did not assess patients’ cognitive function beyond 24 hours postoperatively, so we do not know the long-term neurocognitive impact of intraoperative cerebral desaturation. We recommend that a future study with a larger sample size and a longer follow-up period should be conducted to assess the neurocognitive impact of intraoperative cerebral desaturation postoperatively.

In this study, all patients who had postoperative cognitive decline had intraoperative hypotension. However, a recent metanalysis of a non–beach chair position found that there was no correlation between intraoperative hypotension and the risk of postoperative cognitive dysfunction [5]. Additional studies should explore the association between intraoperative hypotension and postoperative cognitive dysfunction in the beach chair position, where cerebral circulation might be impeded. The risk factor for postoperative cognitive decline in this study was education of less than 6 years. However, this result should be cautiously interpreted because education status could confound the cognitive test performance [7]. Further investigations using a set of cognitive tests, rather than one single test, could improve the sensitivity and specificity in detecting the postoperative cognitive decline and its associated risk factors.

Risk Factors for Intraoperative Hypotension

A history of hypertension and dyslipidemia were associated with increased odds that the patients would have an intraoperative hypotensive episode. A recent cohort analysis for the risk factors of intraoperative hypotension in non–beach chair surgery also found that history of hypertension is one of the independent risk factors that increase the risk of intraoperative hypotension [2]. Choi et al. [1] conducted a retrospective analysis of 420 patients who underwent shoulder surgery in the beach chair position. They reported a 59% (248 of 420) risk of a hypotensive event after beach chair positioning, and they found multiple risk factors were associated with hypotensive event, including history of hypertension. Two independent risk factors associated with intraoperative hypotension reported in this study were preoperative interscalene brachial plexus block and being older than 62 years of age. In our study, all patients received preoperative interscalene brachial plexus block and the mean age was 63 years, yet the risk of intraoperative hypotension was still quite similar. An additional prospective study with a larger sample size is needed to identify risk factors associated with hypotension and strategies to prevent this undesired event.

At present, there are several proposed hypotheses on blood pressure management to prevent cerebrovascular insults in the beach chair position [13, 15]. Most anesthesiologists use the “waterfall concept,” which corrects the blood pressure from gravitational effects to reflect the perfusion pressure in the brain [15]. In this study, we used the blood pressure management protocol recommended by the Shoulder and Elbow Society of Australia [18]. The average height of head elevation was 33 cm. For this study, the minimum mean arterial pressure in the nonsurgical arm that was acceptable was 70 mmHg, so the estimated mean arterial pressure at tragus, which reflects cerebral perfusion pressure, was as low as 45 mmHg. Therefore, a higher threshold for treating hypotension should be considered. However, in arthroscopic surgery, where surgical exposure is limited and easily impeded by blood, an attempt to increase the mean arterial pressure to prevent cerebral hypoperfusion should be weighed against the risk of bleeding that might obscure the surgical view and may further decrease cerebral oxygen delivery. Thus, cerebral oxygenation monitoring may have an essential role in maintaining the minimum mean arterial pressure, which allows for both adequate cerebral oxygenation and minimal bleeding.

Conclusion

With an attempt to control many known intraoperative physiologic parameters that affect cerebral perfusion, nevertheless, the incidence of intraoperative cerebral desaturation was high, and female sex was a risk factor associated with intraoperative cerebral desaturation. Vigilant monitoring of cerebral circulation is mandated in the beach chair position, especially in the first 20 minutes after positioning when intraoperative cerebral desaturation usually occurs. However, the risk of postoperative cognitive decline was low and was not associated with intraoperative cerebral desaturation. Patients with history of hypertension and dyslipidemia carry a greater risk of intraoperative hypotension in the beach chair position. Careful hemodynamic management should be considered in this patient group. Further study with a larger sample size should be considered to investigate adverse neurologic outcomes associated with intraoperative cerebral desaturation.