Identification of surgical patients at high risk of OSAS using the Berlin Questionnaire to detect potential high risk of adverse respiratory events in post anesthesia care unit

Abstract

Obstructive sleep apnea syndrome (OSAS) increases the risk of post-surgery complications. This study uses Berlin Questionnaire (BQ) to identify Chinese adult surgical patients who are at a high risk of OSAS and to determine if the BQ could be used to detect potential high risk of adverse respiratory events in the post anesthesia care unit (PACU). Results indicated that only 11.4% of the patients were considered at a high risk of OSAS. Age and body mass index are the key factors for the risk of OSAS prevalence in China and also gender specific. Furthermore, the incidence of adverse respiratory events in the PACU was higher in patients with high risk of OSAS than others (6.8% vs. 0.9%, P<0.001). They also stayed longer than others in the PACU (95±28 min vs. 62±19 min, P <0.001). Age, high risk for OSAS, and smoking were independent risk factors for the occurrence of adverse respiratory events in the PACU. The BQ may be adopted as a screening tool for anesthesiologists in China to identify patients who are at high risk of OSAS and determine the potential risk of developing postoperative respiratory complications in the PACU.

Keywords

obstructive sleep apnea / Berlin Questionnaire / Chinese surgical patients / adverse respiratory event

Introduction

Obstructive sleep apnea syndrome (OSAS) is a respiratory disorder caused by repetitive, partial, or complete obstruction of the upper airway. OSAS is characterized by episodes of breath cessation during sleep and can last for more than 10 s. Overnight polysomnogram monitoring is a standard diagnosis procedure for OSAS. However, it is expensive and has limited availability. OSAS prevalence in the general population varies according to age, gender, or body mass index (BMI) from 2% to 25% [¹,²]. A previous report shows that over 90% of Caucasians in the United States have undiagnosed OSAS because of poor awareness of OSAS, lack of routine screening preoperatively, and limited number of diagnostic sleep study facilities [³]. OSAS can cause significant morbidity and mortality under certain circumstances, including cardiovascular disorders, neurocognitive deterioration, and changes in endocrinology and metabolism [⁴,⁵].

Furthermore, a growing body of evidence indicates that OSAS is an independent risk factor for postoperative mortality and morbidity and may result in increased incidence of postsurgery complications, such as hypoxemia and respiratory, cardiac, or neurologic complications that prolong intensive care unit (ICU) or hospital stay [⁶,⁷]. Although diagnosing patients with OSAS is necessary, most surgical patients with OSAS are undiagnosed [³]. Overnight polysomnography is the gold standard for OSAS diagnosis, but it is impractical for patients prior to surgery. Therefore, identifying surgical patients who are at high risk of OSAS through a simple and easy assessment method is required to identify patients who need extra postoperative care and decrease OSAS-associated complications. As alternatives to polysomnography, the Berlin Questionnaire (BQ), STOP-Bang questionnaire, and American Society of Anesthesiologists checklist for OSAS have been employed to screen the OSAS risk with variable sensitivity and specificity [⁸–¹¹].

The BQ is often utilized in clinical practice and has been validated in primary health care, particularly in sleep clinics and surgical units in several countries, for OSAS screening [¹²–¹⁶]. The BQ has a sensitivity of 70%–90% to OSAS diagnosis and specificity of 35%–85% and has different apnea hypopnea index cutoffs and study populations [¹³,¹⁴]. The BQ contains 10 items, which are categorized into three groups, namely, Category 1 (CA1), which covers snoring and its characteristics; Category 2 (CA2), which includes daytime fatigue and its characteristics; and Category 3 (CA3), which deals with blood pressure or obesity.

Data on the OSAS prevalence among surgical patients in China is scarce, and no practical screening tool exists for OSAS and post-surgery management. The present study conducts a single-center, prospective, and observational study to establish the prevalence of patients at high risk for OSAS and postoperative complications related to the high risk of OSAS through BQ.

Materials and methods

BQ

The BQ consists of 10 questions in three categories, namely, (1) snoring severity (one introductory question and four follow-up questions about frequency and loudness), (2) daytime somnolence (three primary questions and one subquestion about drowsy driving), and (3) history of hypertension and BMI of>30 kg/m². Age and gender were also recorded. Patients were defined as being at a high risk for OSAS if they have a score of 2 in at least two categories [¹⁷]. The original English version of the BQ was translated into Chinese by a professional medical translator and examined by sleep apnea experts from the Sleep Medicine Center of the West China Hospital. The final version in Chinese was developed and compared with original English version by experts from the Chinese Academy of Sleep Medicine to ensure that the integrity of the former.

Patients

Patients (i.e., aged>18 years, ASA I–II scheduled for elective surgery under general anesthesia, and without a history of sleep disorder) were randomly selected for 7 months (September 2009–March 2010). The purpose of the study was explained to the patients, and their written informed consent was obtained. Pregnant females, history of substance dependence, emergency surgery, psychiatric disorders, patients who admitted to the ICU after surgery, and those who were unwilling to provide a written consent were excluded from the study. The BQ survey was conducted by anesthesiologists who received in-depth training on BQ and interview techniques. All the interviews were performed on the day before surgery in the ward. The time duration of each interview was also recorded. All the patients underwent general anesthesia, which included sufentanyl 0.3–0.4 mg/kg for induction and 0.1 mg/kg per hour, 50 mg/kg midazolam, 0.2 mg/kg cisatracurium for induction and 0.05 mg/kg bolus per hour, 0.1–0.3 mg/(kg·min) remifentanil, and 1%–2% sevoflurane for maintenance. All the patients were extubated in the operating theater and transferred to PACU without oxygen. SPO₂ on admission to the PACU and length of stay in the PACU were recorded. Adverse respiratory events were recorded in the PACU, including upper airway obstruction that requires an intervention, SPO₂ less than 90% on air breath, SPO₂ less than 90% on nasal oxygen (3 L/min), and intubation. Complications during the first 24 h postoperation were also recorded.

BQ score

The questionnaire results were analyzed by two independent sleep apnea experts who have extensive expertise on the BQ score system. Complete concordance was observed between the scores from the two experts.

Statistical analysis

All statistical analyses were performed in SPSS 19.0. The differences between the variables of high-risk group and those of low-risk group were tested with c² or t-tests. A P value of<0.05 was considered statistically significant.

Results

All 1092 patients (632 males and 460 females) consented and completed the interview and survey questions. The average time of the interviews was 366 s. The average age of patients was 52.9±14.8 years, and the average BMI was 22.4±3.4 kg/m². Of the total number of patients, 621 (56.9%) had snoring symptoms, 131 (12%) showed somnolence in daytime, 190 (17.4%) had hypertension, 210 (19.2%) were overweight (BMI≥25 kg/m²), and 9 (0.8%) were considered obese (BMI≥30 kg/m²).

The BQ identified 125 (11.4%) subjects with high risk of OSAS, whereas 967 had low risk. The OSAS features were listed and those of high-risk group were compared with those of low-risk groups (Table 1). The patients in the high-risk group were approximately 10 years older (P<0.01) than those in the low-risk group regardless of gender. The former also had significantly higher BMI, prevalence of snoring, and hypertension and showed more somnolence in daytime (P<0.01) than the latter. Although more male patients belonged to the high-risk group compared with female patients, the difference was nonsignificant (P = 0.102). No difference was observed in the incidence of smoking and diabetes. The prevalence of patients in the high-risk group was 11.4%, 13.1%, 7.7%, 17.3%, 13.3%, and 9.3% in the general, cardiac-thoracic, orthopedic, otolaryngological urologic, and neurosurgery types, respectively. However, no significant difference in the surgical type between the high- and low-risk groups was observed.

The average age and BMI of the female patients were relatively close to those of the male patients in the high-risk group, suggesting that age is not gender specific. However, the prevalence of hypertension and smoking among the female patients was significantly lower than those of the male patients (P = 0.017; Table 2). No difference was observed in the occurrence of diabetes between the female and male patients in the high-risk group. The prevalence of surgical patients with high risk of OSAS increased with age in the male and female patients. However, the prevalence in the female patients only increased in the age group of≤70 years and had a slight drop after the age of 70 years (Fig. 1). The prevalence of patients with high risk of OSAS was more remarkable among male patients than among female patients in the age groups younger than 50 years old, but the number decreased among male patients in the age group between 51 and 70 years.

The prevalence of high risk in CA1 (severe snoring), CA2 (daytime somnolence), BMI, and hypertension were stratified with age and sex (Fig. 2). The distribution of high risk in CA1 (severe snoring) was most remarkable in female patients aged 50–60 years and male patients aged 60–70 years. The prevalence of high risk in CA1 in the age groups of 50–60 and 60–70 years was significantly higher among the female patients relative to those among the male patients (P<0.05). The prevalence of high risk in CA2 (daytime somnolence) was apparent in both genders in the age groups of 50–60 and 60–70 years. The risk was also higher among the female patients compared with that among the male patients in these two age groups. The BMI increased with age among the female patients aged 40–70 years, whereas the BMI increased with age for the male patients aged>50 years old. The BMI values of the female patients were significantly higher compared with those of the male patients in the age groups of 50–60 and 60–70 years (P<0.05). The prevalence of hypertension also increased with age in both genders.

Among the patients in the high-risk group, the incidence of hypoxemia on admission to the PACU was 8%, which was significantly higher than those in the low-risk group (1.2%, P<0.001). Moreover, adverse respiratory events, which were defined as hypoxemia (SPO₂ less than 90% with breathing room air) or upper airway obstruction that requires an intervention (i.e., jaw thrust, oral, or nasal airway tube support), occurred more frequently in the high-risk group than in the low-risk group (6.8% vs. 0.9%, P<0.001). Multiple regression analysis results showed that age, high risk for OSA, and smoking were independent risk factors for the occurrence of adverse respiratory events in the recovery room (Table 3). Furthermore, the length of stay in the PACU was longer in the high-risk group (95±28 min) than that in the low-risk group (62±19 min; P<0.001). However, no difference was observed between the two groups in terms of pulmonary complication, stroke, or other diseases in the first 24 h postoperation (2.1% vs. 1.9%, P = 0.875).

Discussion

This study shows that the prevalence of Chinese patients with high risk of OSAS was generally 11.4%, with a gender-specific prevalence of 12.8% for male patients and 9.6% for female patients. These figures represent the number of patients at a high risk of OSAS identified by the BQ. The OSAS risk among the surgical patients was higher compared with that in the general population, which was reported at 5.7% for males and 2.4% for females [¹⁸]. The higher potential risk of OSAS in adult surgical patients compared with that in the general population is consistent with the results of previous studies conducted mostly on Caucasians in Western countries [¹⁹]. However, the prevalence in the Chinese population appears to be much lower compared to that in the population in the Western countries. Lockhart et al. [¹⁹] revealed that the prevalence of undiagnosed surgical patients at risk for OSAS was 24.1% by the BQ, 16.7% by the STOP questionnaire, and 41.6% by the STOP-BANG questionnaire. Another study employed the apnea risk evaluation system OSAS screening questionnaire, which combines the features from the BQ, Flemons’ Index, and Epworth sleepiness scale. Its results indicated that the prevalence of undiagnosed surgical patients at risk for OSAS is 23.7%–24% of the selective surgery patients. The patients at high risk for OSAS was 24% by the BQ [20]. In the STOP questionnaire, 27.5% of the patients were at high risk of OSAS [¹⁷]. Agrawal [²¹] reported that 24.5% of the subjects were at high risk for OSAS with the STOP BANG questionnaire. The difference in the risk percentage between our study and the previous studies may be explained by the BMI cutoff value in the BQ. The BMI cutoff value in the BQ was calculated by relying on the data from the Caucasian populations and is generally higher than those from the Chinese population. The BMI cutoff value for the Chinese is 24 kg/m² for overweight individuals and 28 kg/m² for obese individuals. This BMI cutoff may cause an underestimation of the prevalence of OSAS in the surgical population in China. However, the patients in the high-risk group have signature characteristics (i.e., male, elderly with high BMI and high prevalence of snoring, somnolence in daytime, and hypertension), which are consistent with the results of previous studies [⁴,¹⁹].

Our study also determines that the prevalence of female patients aged<50 years in the high-risk group was relatively low, and this patients are younger than the general female population in a previous study [¹⁸]. The risk increases significantly with those aged>50 years and is higher than male surgical patients in the same age range. This finding is consistent with a previous study, which shows that menopause can be another significant risk factor for sleep apnea in females [²²]. The average age of menopausal women in China is 49 years [²³]. The distribution of the prevalence in the high-risk group varied with different age groups, thereby confirming that age is a strong risk factor for OSAS in surgical patients, particularly among male patients. The risk continuously rises as age increases. However, the OSAS risk among female patients decreases with those aged over 70 years. The prevalence in the high risk of OSAS among female and male surgical patients is significantly higher than that of the general population who aged over 50 years old. We believe that our findings on the effect of age on the OSAS risk can become an essential consideration for anesthesiologists for pre- and post-surgery care for patients over the age of 50 years old.

The OSAS prevalence is also affected by different surgeries. The incidence is 71% in bariatric surgery [²⁴] and 33% in medically refractory epilepsy patients that require surgical intervention [²⁵]. It is also high among patients who underwent intracranial tumor excision [²⁶]. Our study results show that the incidence of patients with high-risk OSAS differs among operations (i.e., 17.3% prevalence with ENT surgery and 9.3% in neurosurgery), but these were statistically similar. Why different surgeries result in changes in the OSAS risk remains unclear, but this result can be attributed to the characteristics of patients.

Our study also establishes that hypoxemia incidence after PACU admission and occurrence of adverse respiratory events in the PACU are significantly high in patients at high risk of OSAS. OSAS has been described as an independent risk factor for postoperative hypoxemia, respiratory complications, cardiac complication, neurological complication, and unplanned intensive care [²⁷]. However, minimal evidence exists that can describe the respiratory complications of high-risk patients in the PACU. Early respiratory complications in the immediate postoperative period can lead to increased morbidity and mortality. Therefore, our findings show that the preoperative screening of high-risk OSAS patients by the BQ has important clinical significance by reminding the anesthesiologists to provide special care for these patients. This scenario can then lower the incidence of hypoxemia and respiratory complications.

Several limitations should be considered in our study. No patient in this study underwent a polysomnography, so the sensitivity and specificity of the BQ for OSAS among Chinese adult surgical patients remains undetermined. Moreover, the morbidity and mortality rate of the patients postsurgery was not investigated and analyzed, which lowers the accuracy of the BQ in predicting post-surgery morbidity and mortality. A large prospective cohort study is essential to the design and assessment of BQ as a screening tool for OSAS in surgery units in China. A standard screening tool for OSAS has not been established in presurgery units around China. Owing to a significantly large number of patients who are administered in surgery units each year, a solid assessment is urgently required. Our results assessed the capability of BQ to predict OSAS risk in China for the first time. Although the diagnosis and management of heart and lung diseases for the surgical patients have been routinely checked in the preoperative period, OSAS risk should also be included in the checklist prior to surgery [²⁵]. Our results also support the introduction of the assessment of OSAS risk by Chinese anesthesiologists to detect potential OSAS-associated complications in certain patient groups during pre- and postsurgical management.

Therefore, our study confirms the feasibility of the BQ in OSAS screening for patients who will undergo general anesthesia and surgery. The patients determined to be at high risk for OSAS by the BQ have increased incidence of adverse respiratory events in PACU. The BQ may be a practical screening tool for anesthesiologists in China to prevent perioperative complications associated with OSAS.

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