This study was designed to determine the association between AHI and. We found that with the 5-unit increase of AHI, the incidence of DMV was significantly higher. The secondary outcome showed that AHI, age, and Mallampati classification were independent factors of DMV. Indeed, AHI was shown to be highly related to DMV. Normally, the most widely used definition of DMV was by Han et al, which was described as “inadequate, unstable, or requires two providers” with or without muscle relaxant. Impossible mask ventilation was defined as the inability to mask ventilate with or without muscle relaxant. In this study, we rated mask ventilation according to Langeron et al as “the inability of an unassisted anesthesiologist to maintain oxygen saturation >92%, as measured by pulse oximetry, or to prevent or reverse signs of inadequate ventilation during positive-pressure mask ventilation under general anesthesia”.
Numerous previous studies on the prediction and treatment of DMV (difficult mask ventilation) concluded that Age>55, BMI >26 kg/m2, presence of beard, edentulousness, and snoring are 5 independent factors related to DMV . In addition, neck radiotherapy, neck circumference, male gender, Mallampti grade, and severely limited jaw protrusion are known as the risk factors for DMV [2, 4, 10]. Among these studies, one of the independent factors of DMV is a history of snoring (Patients were asked if they were habitual snorers or not) . Although OSA is very common, the majority of patients presenting to the operating room with OSA have not previously been diagnosed and lacked self-awareness of this condition. In this study, all patients underwent PSG preoperatively, which could provide detailed diagnoses of OSA and validate the accuracy of patient’s self-reported history of snoring/choking for air during sleep. In conclusion, the PSG result was clinically more reliable than a declared history of snoring, as provided by the patients.
From a previous study, higher age, higher BMI, greater neck circumference, male gender, and higher Mallampati score were significantly correlated with a high risk of OSA. Concurrently, these overlapping risk factors were also related to DMV [2-4, 10]. It was found that patients with OSA had a three to four-fold higher risk of difficult intubation or mask ventilation, or both, compared to non-sleep apnea patients. However, most previous studies used diagnosed OSA as the primary outcome. While PSG is the diagnostic standard of OSA, one of its important parameters is AHI, which is calculated by adding all apneas and hypopneas and then dividing by total sleep time. An AHI of 15 or more events per hour, or five or more events per hour in the presence of symptoms or cardiovascular comorbidities, is the diagnostic criteria for OSA[11, 12]. In this study, AHI was used as a new continuous measurement for DMV that provided more information the simple presence or absence of diagnosed OSA.
Normally, a conventional PSG examination is time-consuming and complicated to perform, requiring a minimum of 22 wires attached to the patient. With the development of home sleep testing devices, patients are more likely to accept and enjoy certain conveniences, as in this study. The portable PSG consisted of continuous recording with three sensors (respiratory effort belt, cannula and noninvasive pulse oximetry). Among the 200 patients, only 21 patients didn’t have the PSG report due to inadequate time of measuring and feeling discomfort during the PSG testing. Concurrently, other parameters such as oxygen desaturation and heart rate during the night might further aid decision making for anesthesiologists.
As for the Chinese population, there was a limited number of articles on mask ventilation. Relatively, most of the trials were from the European and US populations. Furthermore, there were fewer bearded Chinese patients to consider, as well was differences in head and facial structures.
For the secondary outcome, age, AHI and Mallampati score were three significant, independent factors for the DMV. Most DMV evaluations consist of questionnaires which are time consuming for anesthesiologists to complete and score. Additionally, it is unclear which predictive method is easier to perform and reliable for use in clinical settings. In our study, we demonstrated a possible solution that efficiently utilizes portable PSG, which, combined with AHI outputs, age, and Mallampati scores, can a predict patient’s risk of DMV. Moreover, these three factors remained objective compared to the subjective answers extracted from questionnaires. Certain predictive models mutually benefit both the patient and anesthesiologist by saving time, avoiding recall bias, raising patient’s satisfaction score, and providing a pre-liminary assessment of potential OSA in otherwise undiagnosed patients.
Once limitation of the study was the relatively small sample size (n=159). To explore further applications of AHI in DMV patients, we will need to study larger patient populations. Also, our study focused on Chinese patients, which are ethnically different from other global populations. A larger, more versatile sample would be desirable for further study to demonstrate the effectiveness of our predictive model. Meanwhile, some of the patients reported an uncomfortable experience while they were sleeping during the PSG testing. Future models of PSG equipment should be developed to improve certain concerns from patient’s perspective.