Is obstructive sleep apnoea associated with hypoxaemia and prolonged ICU stay after type A aortic dissection repair? A retrospective study in Chinese population

This retrospective study was conducted in 252 consecutive patients with acute or chronic TAAD (either anterograde or retrograde subtype) who underwent total arch replacement between January 1 and December 31, 2018, at the Beijing Anzhen Hospital. TAAD was diagnosed using computed tomographic angiography in all the patients.

Patients would be excluded from this study due to one of the following conditions:

A total of 124 patients completed the sleep test and 83 of them had complete sleep data and answered the STOP-BANG questionnaire [17]. These 83 patients were included in the final analysis (Fig. 1).

OSA was diagnosed via completing sleep test within 90 days following surgical procedure. Nox T3 devices (Nox Medical, Reykjavík, Iceland) were used to perform the sleep tests, and an acceptable sleep test should contain a total sleep time > 5 h. Recorded electrodes included nasal pressure transducers, thoracic and abdominal plethysmography, cardiac pulse, snoring, body position, activity, and percutaneous oxygen saturation.

According to the detection of a nasal airflow transducer, apnoea was defined by breath cessation or ≥ 90% airflow drop that lasted longer than 10 s, while hypopnea was verified by at least 30% decline in airflow that lasted longer than 10 s and was accompanied by a 3% decrease in oxygen saturation. Apnoea hypopnea index (AHI) was defined as the sum of apnoea and hypopnea per hour. OSA was diagnosed when the AHI was 15/h or more, and severe OSA was defined by an AHI greater than 30/h. Hypoxaemia during sleep was determined by the average oxygen saturation, the nadir nocturnal oxygen saturation, the percentage of time with oxygen saturation of < 90%, and the oxygen desaturation index (i.e., oxygen saturation drop by ≥ 3% per hour). Daytime sleepiness was calculated using the Epworth Sleepiness Scale (ESS) [18].

Although not accepted as a diagnostic tool, the STOP-BANG score was completed [17] routinely on admission. Patients were assessed by answering “yes” or “no” to eight questions related to major subjective and objective manifestations of OSA. The sum of scores ranged from 0 to 8, and a modified STOP-BANG score of ≥ 4 was considered a high risk of OSA [19]. The consistency of the STOP-BANG score with the objective sleep test was calculated.

The indications and techniques of TAAD repair in our centre have been described in detail previously [20]. Briefly, it is performed under cardiopulmonary bypass with selective antegrade cerebral perfusion and involves deployment of a stented vascular graft into the descending aorta via hypothermic circulatory arrest, followed by total arch replacement using a four-branched graft.

The duration of cardiopulmonary bypass, cross-clamp, antegrade cerebral perfusion, and the entire procedure as well as the amount of packed red blood cells transfused during surgery were collected. To evaluate the severity of the patients’ perioperative desaturation, arterial blood was drawn 2 h before and 6 h after the surgical procedure, and the blood gas was assessed on-site promptly.

Preoperative and postoperative oxygenation indices (OIs) were calculated as the ratio of arterial partial oxygen/inspired oxygen fraction at 2 h before and at 6 h after the surgery. Preoperative or postoperative hypoxaemia was defined as an OI of < 200 mmHg [21, 22]. Postoperative complications, a composite endpoint, included sepsis, pulmonary infection, cardiac dysfunction, acute renal failure, re-exploration for bleeding, surgical site infection, stroke, postoperative delirium, paraplegia or paralysis and gastrointestinal bleeding. Systolic blood pressure (BP) of ≥ 130 mmHg or diastolic of ≥ 80 mmHg were regarded as uncontrolled BP [23] Prolonged ICU stay was defined as a ≥ 72 h stay in the ICU for any reason [24].

Normally distributed continuous variables verified by Shapiro–Wilk test are expressed as mean ± standard deviation (SD), and were compared using the Student’s t test. Median and interquartile range (IQR) were used for skewed variables, which were compared using the Wilcoxon test. Categorical variables are expressed as a number (percentage), and were compared using the Pearson’s chi-square test or the Fisher’s exact test. The kappa coefficient was calculated to evaluate the agreement between the preoperative STOP-BANG questionnaire score and postoperative sleep test in the diagnosis of OSA. Adjusted odds ratios (OR) and 95% confidence intervals (CI) were estimated from the multivariate logistic model to determine the relationship between the explanatory variables of preoperative hypoxaemia, OSA and AHI stratification, and response variables of postoperative hypoxaemia and prolonged ICU stay. Covariates included in the adjusted model were age, sex, and body mass index (BMI), which were the confounding variables considering their relevance to both OSA and aortic dissection [25, 26]. A receiver-operating characteristic (ROC) curve was constructed to determine the optimal cut-off of postoperative OI that could predict prolonged ICU stay based on the value yielding the best combination of sensitivity and specificity. Statistical analysis was performed using SPSS 18.0 for Windows (SPSS Inc., Chicago, IL), and a two-tailed p-value of < 0.05 was considered statistically significant.

This study enrolled 83 patients (66 [79.5%] men, 74 [89.2%] acute and 76 [91.6%] anterograde TAAD). Among these, the diagnosis of OSA was confirmed by sleep test in 41 patients (49.4%). Modified STOP-BANG score of ≥ 4 to predict OSA also demonstrated high consistency with the objective sleep test (golden standard) (Kappa = 0.42, p < 0.001). Besides having significantly higher scores of ESS and STOP-BANG, patients with OSA were more likely to have uncontrolled hypertension than those without OSA (95.1% vs. 78.6%, p = 0.026) (Table 1).

Of the entire cohort, 56 patients developed postoperative hypoxaemia (67.5%) and 22 patients (26.5%) had prolonged ICU stay (> 72 h). Patients with OSA vs. patients without OSA, were more likely to have incidence of postoperative hypoxaemia (83.0% vs. 52.4%, p = 0.003) and composite postoperative complications (75.6% vs. 52.4%, p = 0.028), and showed significantly longer intubation time (24.6 h vs. 22.4 h, p = 0.026) and ICU length of stay (54.0 h vs. 28.5 h, p = 0.007) after surgery (Table 2). As shown in Fig. 2, the ICU length of stay was significantly longer in patients with an AHI of > 30/h than in those with an AHI of < 15/h (62.0 h vs. 28.5 h, p = 0.008).

Multivariate analysis (adjusted for age, sex, and BMI) showed that preoperative hypoxaemia and OSA were associated with postoperative hypoxaemia. Patients with an AHI > 30/h had significantly higher odds of developing postoperative hypoxaemia vs. patients with an AHI < 15/h (OR 3.28, 95% CI 1.14–10.10, p = 0.028) (Table 3).

With an overall area under the curve of 0.72 (95% CI 0.60–0.84; p = 0.002) (ROC analysis showed that a postoperative OI of 133.25 was the optimal cut-off value for predicting prolonged ICU stay (sensitivity: 63.6%; specificity: 75.4%; accuracy: 48.3%) (Fig. 3). When taken as a continuous variable, for every unit decrease in postoperative OI, the risk of prolonged ICU stay would be increased by 1% (OR 1.01; 95% CI 1.00–1.02, p = 0.008).

OSA was shown to be associated with prolonged ICU stay (unadjusted OR 3.84; 95% CI 1.32–11.17, p = 0.010; adjusted OR 4.05; 95% CI 1.27–12.90, p = 0.018) (Table 3). Furthermore, compared to an AHI of < 15/h, an AHI of > 30/h (severe OSA) was also identified to be associated with prolonged ICU stay (OR 5.46; 95% CI 1.66–19.49, p = 0.005), which persisted following adjustments for confounding variables (OR 5.60; 95% CI 1.59–21.75, p = 0.009) (Table 3).