Figure 1 shows the enrollment, exclusions and patients available for analysis among 16316 patients admitted into the PACU from January 1, 2015 to December 31, 2015. Finally, 14,604 patients were analysed whose basic data are shown in Table1. Of all the patients, 40.6% were males, and 59.4% were females, with ages of 50.1 ± 14.6 years. Their BMI averaged 24.2± 3.7 kg/m2. Patients with a high ASA grade were usually transferred to the ICU for further treatment after surgery; in this study, a higher proportion of patients had ASA grades of I (45.7%) or II (50.8%). All patients were given general anaesthesia using inhaled anaesthetics, intravenous anaesthetics, opioids, neuromuscular blocker and muscle relaxant antagonist. Tracheal intubation was the main method of airway management (78.27%), followed by laryngeal mask airway (20.93%). The three most common surgical sites are the head and neck (34.4%), abdomen (28%), and pelvis (9.1%). A few patients had preoperative respiratory disease (2.61%), such as chronic obstructive pulmonary disease (COPD), asthma, obstructive sleep apnea hypopnea syndrome(OSAHS), lung infection, interstitial lung disease, pleural effusion, and pulmonary bullae.
When hypoxemia was defined as SpO2 ≤ 95%, the overall incidence of hypoxemia was 21.83% (3188 patients). When hypoxemia was defined as SpO2 ≤ 90%, the overall incidence of hypoxemia was 2.79% (408 patients). Patients were divided into a hypoxemia group and a non-hypoxemia group for between-group comparison.
We performed multivariate regression analysis of the risk factors in hypoxemia and non-hypoxemia patients as SpO2 ≤ 95% and SpO2 ≤ 90% respectively. For this analysis, age, BMI, ASA classification, surgical site, and intraoperative position were multivariate categorical variables; and the reference group for each variable was 18–34-year old (age), BMI<25 kg/m2 (BMI), ASA I (ASA classification), superficial site (surgical site), and supine (intraoperative position). The results are shown in Table2 and Table3.
When hypoxemia was defined as SpO2 ≤ 95%, multivariate regression analysis showed that age and BMI were closely related to the incidence of hypoxemia, especially in elderly patients over 50-year old (50–64 years old, OR = 1.63, 95%CI:1.43–1.87; ≥65 years old, OR = 1.92, 95%CI:1.65–2.23) and people with BMI ≥25kg/m2(25≤BMI<28, OR = 1,75, 95%CI:1.59–1.92; BMI≥28, OR = 2.48, 95%CI:2.24–2.75). Other risk factors were ASA grades of II (OR = 1.2, 95%CI:1.09–1.31) and III (OR = 1.32, 95%CI:1.07–1.63), thoracic surgery (OR = 1.37, 95%CI:1.10–1.71). No significant correlation was observed between the incidence of hypoxemia and intraoperative position.
When hypoxemia was defined as SpO2 ≤ 90%, risk factors were age(≥65 years old, OR = 1.80, 95%CI:1.21–2.68), BMI (25≤BMI<28, OR = 1.55, 95%CI:1.22–1.9; BMI≥28, OR = 1.87, 95%CI: 1,43–2.4), limbs surgery(OR = 1.71, 95%CI:1.02–2.85), and thoracic surgery (OR = 2.69, 95%CI:1.51–4.7). No significant correlation was observed between the incidence of hypoxemia and intraoperative position.