Enrolment and baseline characteristics
A total of 202 patients who received MV with G5 were enrolled in the study (Figure 1). Thirteen patients had been ventilated with other ventilators when starting MV. One hundred and thirty-five patients (71.4%) were classified into the I-ASV success group, and 54 (28.6%) were categorized into the I-ASV failure group. In the I-ASV success group, some patients had briefly received another ventilation mode for reasons such as PCV immediately after tracheal intubation (n = 5, 3.7%), PSV for manual SBT although I-ASV revealed SBT success (n = 7, 5.2%), and a lack of medical staff experience with I-ASV (n = 9, 6.7%). Automatic control of each %MV, FIO2, and PEEP were used in 100%, 85.6%, and 14.4% of patients, respectively.
Table 1 compares the characteristics of patients in the I-ASV success and I-ASV failure groups. I-ASV failure was associated with a high APACHE II score (21 vs. 26, P < 0.0001), SOFA score (day 1) (8 vs. 11, P < 0.0001), CRRT (10.4% vs. 44.4%, P < 0.0001), use of vasopressors (day 1) (52.6% vs. 70.4%, P = 0.034), use of morphine (5.2% vs. 27.8%, P < 0.0001), use of neuromuscular blockade (4.4% vs. 25.9%, P < 0.0001), type of ICU admission (P < 0.0001) and low P/F ratio (278 vs. 167, P = 0.0003). Additionally, the duration of MV (5 vs. 10 days, P < 0.0001), length of ICU stay (6 vs. 11 days, P < 0.0001), MV after ICU (i.e.,, continued MV after ICU discharge, such as in the general ward or at a transferred hospital; 9.6% vs. 22.2%, P = 0.031), and ICU mortality (1.5% vs. 13.0%, P = 0.003) were all significantly lower in the I-ASV success group (Table 1).
Reasons for admission and MV, and severity of hypoxemia associated with I-ASV success group
The reasons for ICU admission and MV, and the severity of hypoxemia were evaluated in I-ASV success group. Notably, I-ASV success group included 94% of the patients admitted for post-elective surgery, 81.5% of those admitted for post-emergency surgery, and 55.6% of those with other medical reasons. As for the reasons for ventilation, I-ASV success was associated with central nervous dysfunction, sepsis, highly invasive surgery, and flap surgery. Regarding the severity of hypoxemia, 89.4%, 71.4%, 47.5%, and 35.0% of patients with a P/F ratio ≥ 300, 200 –300, 100 –200 and, <100, respectively, were classified into I-ASV success group (Table 1).
Annual trends regarding successful I-ASV
The number of patients who were ventilated using G5 increased annually. Among these patients, I-ASV was successful in 69.0% of patients in 2016, 72.1% in 2017, and 71.2% in 2018. Compared to patients in I-ASV failure group, those in I-ASV success group have lower APACHE II scores [19 vs. 27 in 2016 (P = 0.080), 17 vs. 23 in 2017 (P = 0.058), and 23 vs. 30 in 2018 (P < 0.0001)]. Based on the reasons for admission in 2018, 100% of those admitted for post-elective surgery, 90.6% of those admitted for emergent surgery, and 54.0% of those with other medical reasons (P = 0.0002) were classified into I-ASV success group. Regarding the severity of hypoxemia in 2018, 92.3%, 75.0%, 52.6%, and 35.7% of patients with a P/F ratio of ≥ 300, 200–300, 100–200, and < 100, respectively (P = 0.0001), were classified into I-ASV success group (Table 2).
Reasons for choosing other modes of ventilation
Figure 3 summarizes the reasons for choosing other modes of ventilation in I-ASV failure group. The main reasons included patients’ strong respiratory efforts (n = 10, 5.3%); asynchrony/tachypnoea (n = 9, 4.8%); abnormal respiratory patterns, including Cheyne-Stokes respiration and an opioid-induced respiratory pattern (n =7, 3.7%); unstable hemodynamic/metabolic acidosis (n = 5, 2.6%); severe respiratory failure/acidosis (n = 4, 2.1%); limitation of the ASV setting (n = 2, 1.1%); sensor problems (n = 2, 1.1%); other reasons (n=6, 3.2%); difficult indications (n = 9, 4.8%), such as ECMO (n = 4, 2.1%), pneumothorax (n = 3, 1.6%), one lung and hemiventilation (n = 2, 1.1%).
Multivariate analysis, ORs, and AUROC predictive of successful I-ASV
Because of the limitation of number of studied patients (n=54) in I-ASV failure group, we decided to conduct the multivariate analysis up to seven parameters which could affect the predictability of successful I-ASV (model 1). Among the seven evaluated parameters, the APACHE II score (OR: 0.92; 95% CI: 0.87– 0.96; P = 0.0006) was found to be an independent predictor of successful I-ASV. Also, we conducted the multivariate analysis with only significant variables including APACHE II and P/F ratio (model 2). As result, the APACHE II score was an independent predictor of successful I-ASV (OR: 0.92; 95%CI: 0.88-0.96; P = 0.0005). The AUROC for the APACHE II score was 0.722 (0.637–0.794, cut-off: 24 [sensitivity: 0.67, specificity: 0.65]). Although the P/F ratio was not an independent predictor of successful I-ASV, the AUROC was 0.736 (0.644–0.812, cut-off 187 [sensitivity 0.81 specificity 0.61]). (Table 3).