Participants
Out of 29,236 hospital deliveries, 265 critically ill obstetric patients entered the ICU between January 1, 2009, and December 31, 2019, in our hospital. One hundred forty-five (54.7%) of them were treated with mechanical ventilation. Two were excluded because of death within 24 hours of the commencement of MV. Finally, one hundred forty-three patients were enrolled in this study (see Fig. 1). Among these patients, 52 (36.4%) were transferred from other hospital and all of them gave birth at our hospital. Seven (4.9%) of those patients were admitted during pregnancy and 136 (95.1%) admitted postpartum.
The median age was 31 years, and the median gestational week was 34.9 weeks. Obstetric causes made up the majority of the causes of ICU admission (62.9%, 90/143). The main obstetric cause was postpartum haemorrhage (35%, 50/143). Other obstetric causes included eclampsia or pre-eclampsia (18.9%, 27/143), puerperal infection (5.6%, 8/143), acute fatty liver of pregnancy (AFLP) (2.1%, 3/143) and others (1.4%, 2/143). Nonobstetric causes included haematological diseases (11.2%, 16/143), autoimmune diseases (5.6%,8/143), cardiovascular disease (2.1%, 3/143), neuropsychiatric diseases (4.2%, 6/143), acute pancreatitis (3.5%, 5/143), gastrointestinal perforation (3.5%, 5/143) and others (7.0%, 10/143). The median length of mechanical ventilation was 19 hours. The median length of ICU stay and hospital stay were 72 hours and 13 days, respectively. Four obstetric patients died in the hospital (2.8%) (see Table 1 and Table 2).
Table 2 Comparison of outcomes for the prolonged mechanical ventilation group and the non-prolonged mechanical ventilation group
|
Median [IQR] / no. (%)
|
|
Outcomes
|
Overall
|
PMV group
|
Non-PMV group
|
P value
|
Number
|
143
|
65
|
78
|
|
Length of ICU stay, hours
|
72(27 - 168)
|
168(99 - 312)
|
31(23 - 67)
|
<0.001
|
Length of hospital stay, days
|
13(9 - 20)
|
15(12 - 26)
|
11(8 - 16)
|
<0.001
|
Mortality
|
4(2.8%)
|
3(4.6%)
|
1(1.3%)
|
0.229
|
Abbreviation: IQR interquartile ranges, ICU intensive care unit, PMV prolonged mechanical ventilation.
Prolonged mechanical ventilation and outcomes
Sixty-five critically ill obstetric patients (45.5%) underwent PMV. The length of ICU stay (P<0.001) and hospital stay (P<0.001) were both significantly longer in the PMV group than in the non-PMV group. The mortality was very low, and there was no significant difference between the two groups (P=0.229).
Univariate analysis
Compared with non-PMV patients, PMV patients had a higher APACHE II score (P=0.008) and a larger amount of estimated blood loss during delivery (P<0.001). The incidence of AKI (P<0.001) and myocardial injury (P<0.001) was significantly higher in the PMV group than in the non-PMV group. PMV patients had significantly higher blood creatinine(P<0.001), troponin(P<0.001), TBIL (P<0.001), BNP (P<0.001), PaCO2 (P=0.012), and lactate (P=0.002) levels. The blood platelet count (P=0.026) and the arterial blood PaO2/FiO2 (P<0.001) were significantly lower in the PMV group. No significant difference in age, BMI, gestational weeks, causes of ICU admission, blood WBC count, blood albumin level, arterial blood pH, or bicarbonate was observed (see Table 1 and Table 2).
Multivariate analysis
Variables including APACHE II score, BMI, AKI, myocardial injury, TBIL, BNP, platelets, PaCO2, PaO2/FiO2, and estimated blood loss with a P value of <0.05 in the univariate analysis were identified as risk factors for PMV. We tested the multicollinearity of all the risk factors. The results showed that the largest VIF was 1.66 and the smallest tolerance was 0.60 (see Additional file 1). Therefore, we included all 10 chosen risk factors in the logistic regression model, and we found that estimated blood loss (L) (odds ratio (OR) =1.296, P=0.029), AKI (OR=4.305, P=0.013), myocardial injury (OR=4.586, P=0.012), and PaO2/FiO2 (mmHg) (OR=0.989, P<0.001) were independent risk factors for PMV in critically ill obstetric patients (see Table 3). The Hosmer-Lemeshow test showed that the fit for the logistic regression model was good (P=0.097, chi2=153.56). The ROC curve based on the predicted probability of the logistic regression is shown in Fig. 2, and the area under the curve was 0.934 (95% CI, 0.895 to 0.974). The plot of the regression coefficients is shown in Fig. 3.
Table 3 Logistic regression of prolonged mechanical ventilation and clinical variables
Variables
|
OR
|
P value
|
95% CI
|
Estimated blood loss, L
|
1.296
|
0.029
|
1.028 – 1.634
|
Myocardial injury
|
4.596
|
0.012
|
1.394 – 15.159
|
AKI
|
4.305
|
0.013
|
1.361 – 13.617
|
PaO2/FiO2, mmHg
|
0.989
|
<0.001
|
0.984 – 0.995
|
APACHE II score
|
1.080
|
0.207
|
0.958 – 1.216
|
BNP, pg/mL
|
0.999
|
0.399
|
0.999 – 1.000
|
TBIL, μmol/L
|
1.014
|
0.317
|
0.987 – 1.041
|
Platelet, ×1012/L
|
1.002
|
0.647
|
0.995 –1.009
|
Lactate, mmol/L
|
1.229
|
0.349
|
0.798 – 1.894
|
PaCO2, mmHg
|
1.040
|
0.457
|
0.938 – 1.152
|
Abbreviations: APACHE acute physiology and chronic health evaluation, AKI acute kidney injury, BNP brain natriuretic peptide, TBIL total bilirubin, PaCO2 arterial partial pressure of carbon dioxide, PaO2/FiO2 the ratio of the arterial partial pressure of oxygen and the fraction of inspired oxygen, OR odds ratio, CI confidence interval.
Nomogram
Through the logistic regression model, we built a prognostic nomogram incorporating the above independent prognostic factors for visualization and facilitation of clinical practice, as shown in Fig. 4. In this model, we transferred PaO2/FiO2 into four classes based on the Berlin definition of acute respiratory distress syndrome (ARDS) to simplify clinical practice [21].