Sleep Breath DOI 10.1007/s11325-014-0971-3

ORIGINAL ARTICLE

Critical evaluation of screening questionnaires for obstructive sleep apnea in patients undergoing coronary artery bypass grafting and abdominal surgery Flavia S. Nunes & Naury J. Danzi-Soares & Pedro R. Genta & Luciano F. Drager & Luiz A.M. Cesar & Geraldo Lorenzi-Filho

Received: 28 October 2013 / Revised: 4 February 2014 / Accepted: 3 March 2014 # Springer-Verlag Berlin Heidelberg 2014

Abstract Background Obstructive sleep apnea (OSA) is an independent risk factor for complications after surgery. However, OSA remains largely under recognized, and questionnaires designed to detect OSA have shown inconsistent results. Patients with cardiovascular diseases may not present with the typical symptoms of OSA. We therefore sought to compare the performance of screening questionnaires of patients referred for coronary artery bypass grafting (CABG) versus abdominal surgery (Abd surgery). Methods We studied 40 consecutive patients referred for CABG [29 men; age 56±7 years; body mass index (BMI) 30±4 kg/m2], and 41 referred to Abd Surgery matched for age, gender, and BMI (28 men; age 56±8 years; BMI 29±

F. S. Nunes (*) : P. R. Genta : G. Lorenzi-Filho Sleep Laboratory, Pulmonary Division, Heart Institute (InCor), University of São Paulo Medical School, Av Dr Enéas Carvalho de Aguiar, 44, 05403-904 São Paulo, Brazil e-mail: [email protected] N. J. Danzi-Soares Nursing Division, Heart Institute (InCor), University of São Paulo Medical School, Av Dr Enéas Carvalho de Aguiar, 44, 05403-904 São Paulo, Brazil L. F. Drager Hypertension Unit, Heart Institute (InCor), University of São Paulo Medical School, Av Dr Enéas Carvalho de Aguiar, 44, 05403-904 São Paulo, Brazil L. A. Cesar Chronic Coronariopathy Unit, Heart Institute (InCor), University of São Paulo Medical School, Av Dr Enéas Carvalho de Aguiar, 44, 05403-904 São Paulo, Brazil

5 kg/m2). All patients were evaluated with validated questionnaires to predict OSA (STOP-Bang and Berlin), Epworth sleepiness scale (ESS) and full overnight polysomnography. Results The prevalence of OSA (apnea-hypopnea index ≥15 events/hour) in the CABG and Abd surgery groups was similar (52 and 41 %, respectively, p=0.32). The Berlin questionnaire showed similar sensitivity (67 vs. 82 %, p=0.17) but lower specificity in the CABG group (26 vs. 62 %, p=0.02). The STOP-BANG questionnaire had a high sensitivity (90 vs. 94 %, p=0.42) but low specificity (5 vs. 13 %, p=0.25) in the CABG and Abd surgery groups, respectively. Patients referred for CABG slept less (323 [285–376] vs. 378 [308–415] minutes, p=0.04) but had lower levels of daytime sleepiness than Abd surgery patients had (ESS, 6 ± 4 vs. 9± 5; p = 0.01, respectively). Conclusions Presenting clinical characteristics of OSA are modulated by the population evaluated and may affect the performance of screening questionnaires. Keywords Coronary artery bypass . Diagnostic techniques and procedures . Preoperative care . Sleep apnea . Obstructive . Surgical procedures . General Obstructive sleep apnea (OSA) is a common condition characterized by recurrent episodes of partial or complete obstruction of the upper airway during sleep [1]. OSA is now recognized as a major health problem due to the high prevalence and the multiple systemic consequences that include increased risk of cardiovascular events and mortality [2–4]. OSA has been independently associated with postoperative respiratory and cardiovascular complications [5–9]. However, OSA remains largely under recognized in the surgical population [10, 11]. Therefore, easy-to-use questionnaires, such as the Berlin

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and STOP-Bang, have been developed for OSA screening in the clinical and surgical population [12, 13], and recent guidelines have recommended OSA screening during perioperative management [14, 15]. The performance of screening questionnaires may differ depending on the population studied [16, 17]. Differences in presenting symptoms of OSA may vary among specific populations and may explain in part the variable performance of these questionnaires. For instance, there is growing evidence that the typical daytime symptoms associated with OSA may not be present in patients with cardiovascular disease, including heart failure [18], stroke [19], and hypertension [20]. Moreover, the specificity of screening questionnaires may be impaired in groups of patients with an extremely high prevalence of diseases like hypertension that when present are considered a positive domain suggestive of OSA. We therefore hypothesized that the clinical characteristics of OSA and performance of screening questionnaires depend on the population studied. To this end, we assessed the clinical characteristics and the performance of screening questionnaires (Berlin and STOP-Bang) of patients referred for coronary artery bypass grafting (CABG) versus patients with nonvascular abdominal surgery (Abd surgery) in a tertiary University Hospital who were carefully matched for the main risk factors for OSA, including age, gender, and body mass index (BMI). The rationale to study those two groups was that patients with lower prevalence of cardiovascular disease (and in particular coronary artery disease) would present a different symptoms associated with OSA. Abdominal surgery was chosen because it aggregates a frequent category of surgery.

Methods Patients We studied consecutive patients referred for CABG to the Heart Institute (InCor)—University of São Paulo Medical School. The exclusion criteria were as follows: age 70 years, BMI >40 kg/m2, left ventricular ejection fraction ≤45 %; renal failure (serum creatinine >2 mg/dl), untreated hypothyroidism, recent cancer diagnosis (in the last 5 years), liver failure, and previous stroke. We excluded patients older than 70 years because the clinical presentation of OSA may be distinct in this population. We were willing to exclude major underlying clinical conditions that could (at least in theory) change or perhaps modulate symptoms associated with OSA. Patients with low ejection fraction were excluded in order to avoid central sleep apnea. Patients referred for elective Abd surgery due to gallstones or inguinal hernia was recruited from the Hospital das Clinicas—University of São Paulo Medical School. The groups were matched to the CABG patients for gender, age (±5 years), and BMI (±2 kg/m2). Patients with a

previous history of heart disorders (including coronary artery disease, congestive heart failure, or arrhythmia) were excluded from the Abd surgery group. All patients provided written informed consent before participating in the study, and the local ethics committee approved the study protocol (#168/06). Study protocol Clinical and biochemical evaluation Body weight was measured using a digital scale while subjects were wearing lightweight clothing. Height was determined with subjects barefoot. Both height and weight were measured during the screening visit. BMI was determined using the formula: weight (kg)/height (m2). Abdominal circumference was measured with a soft tape on standing subjects midway between the lowest rib and the iliac crest. Neck circumference was determined at the cricothyroid membrane level. Two blood pressure recordings were obtained from the right arm with the patient in a sitting position after 15 min of rest at 5-min intervals, and their mean values were registered. All patients from the CABG group underwent echocardiography and left ventricular ejection fraction determination as previously described [21] as part of their preoperative evaluation. Fasting blood samples were drawn for determination of glucose, total cholesterol, low-density lipoprotein (LDL-c), high-density lipoprotein (HDL-c), triglycerides (TG), and hemogram. Metabolic syndrome was defined according to the Adult Treatment Panel (ATP) III [22]. The definition of dyslipidemia (DLP) was based on the National Cholesterol Education Program updates of the ATP III. Two different criteria were used according to this panel [22, 23]. For patients in the CABG group, DLP was considered present if LDL-c ≥100 mg/dl or if the subject was using cholesterol-lowering medications, and/or HDL-c 3 to 4 times/week). Category 3 is defined as positive by the presence of hypertension or a body mass index ≥30 kg/m2. To be considered at high risk for OSA, a patient has to be positive in at least two symptom categories [12].

STOP-Bang The STOP-Bang questionnaire is composed of eight questions related to snoring (S), tiredness (T) during daytime, observed apnea (O) during sleep, high blood pressure (P): (STOP), and BMI, age (a), neck size (n) and gender (g): (Bang). The STOPBang questionnaire was validated in a variety of surgeries, including general, obstetric, and urological [13].

Epworth sleepiness scale The Epworth sleepiness scale (ESS) was used to evaluate subjective excessive daytime sleepiness. Briefly, the patient rates the probability of dozing of 0 to 3 in eight different conditions, and a score above 10 points suggests excessive daytime sleepiness [24].

Sleep study All participants underwent standard full overnight polysomnography prior to surgery that included electroencephalography (C3/A2, C4/A1, O1/A2, O2/A1), electrooculography, submental and anterior tibialis electromyography, pulse oximetry, measurements of airflow (thermistor and nasal pressure), body position detector, snoring detector, and measurements of rib cage and abdominal movements during breathing (XactTrace)—(EMBLA Medical Devices, Broomfield, CO, USA). Apnea was defined as complete cessation of airflow for at least 10 s. Hypopnoea was defined as a significant reduction (≥50 %) in respiratory signals for at least 10 s associated with oxygen desaturation of >3 % or if the event was associated with an arousal [25]. The apneahypopnoea index (AHI) was calculated as the total number of respiratory events (apneas plus hypopnea) per hour of sleep. Due to the high-expected prevalence of OSA, we only considered patients with moderate to severe OSA (AHI ≥15 events/h) as we have previously described for high-risk population [26].

Statistical analysis The expected prevalence of OSA in the group was 40 %. The difference in sensitivity and specificity to detect OSA

according to the surgical group was unknown, and this was a convenience sample. Continuous variables are presented as mean±SD or median (interquartile range), and groups were compared using the Student’s t test or Mann–Whitney test when appropriate. Categorical variables are expressed in contingency tables including frequency distribution (n) and proportion (%) and were compared using chi-square statistics or Fisher’s exact test. McNemar’s test was used to test for the differences in sensitivity and specificity of Berlin and StopBang questionnaires within CABG and Abd surgery groups. Finally, p values 5 is shown in Fig. 1 because the significance of mild OSA is still being determined and future studies may demonstrate its relevance. The sleep structure characteristics of the patients according to the surgical group are presented in Table 2. Despite having significantly lower total sleep time, patients in the CABG group had significantly lower ESS than patients in the Abd surgery group had (6±4 and 9±5, p=0.008) (Fig. 2).

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Abd surgery (n=41)

p value

Male, n (%) Age, year BMI, kg/m2 Neck circumference, cm Abdominal circumference, cm Systolic blood pressure, mmHg Diastolic blood pressure, mmHg Questionnaires for OSA STOP-Bang positive, n (%)

29 (73) 56±7 30±4 40±4 103±14 138±22 85±14

28 (68) 56±8 29±5 39.0±4 101±12 151±20 94±16

NA NA NA 0.671 0.701 0.010 0.007

37 (93)

36 (88)

0.712

Berlin positive ESS ESS ≥10, n (%) Comorbidities Smoking, n (%) Hypertension, n (%) Diabetes mellitus, n (%) Dyslipidemia, n (%) Metabolic syndrome, n (%) Metabolic profile Fasting glucose, mg/dl Total cholesterol, mg/dl LDL-c, mg/dl HDL-c, mg/dl Triglycerides, mg/dl Drugs Statins ß-Blockers

28 (70) 6±4 8 (21)

23 (56) 9±5 18 (44)

0.195 0.008 0.033

5 (13) 33 (83) 16 (40) 39 (98) 33 (83)

5 (13) 24 (60) 5 (13) 21 (58) 21 (60)

0.184 0.026 0.005

Critical evaluation of screening questionnaires for obstructive sleep apnea in patients undergoing coronary artery bypass grafting and abdominal surgery.

Obstructive sleep apnea (OSA) is an independent risk factor for complications after surgery. However, OSA remains largely under recognized, and questi...
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