1 Introduction
Mechanical ventilation (MV) is a commonly used mode of support in the intensive care unit (ICU). The reported rate of MV varies widely between studies, likely due to variations in the clinical characteristics of the admitted patients (e.g., age or whether medical or post-surgical admission), availability of facilities, and definition of MV (in particular, the minimum duration of MV required for inclusion in the analysis). For example, a 28-day international study including 361 ICUs from Spain, France, Canada, Argentina, England, and the USA found that the rate of MV was 32.9% in patients admitted to the ICU,[1] [2] [3] [4]
The reported in-hospital mortality rate in patients given MV in the ICU ranges from 23% to 51%.[1,2,5–10] [11] [12] [3]
The prognosis of patients receiving MV is influenced by many factors, including age, Acute Physiology And Chronic Health Evaluation (APACHE) II score (or other measure of functional status), severe sepsis, acute lung injury (ALI), acute respiratory distress syndrome (ARDS), acute renal, cardiovascular or hepatic failure, and requirement for neuromuscular blockers or vasopressors.[1,2,5,13] 2 /FiO2 ) ratio <200, and chronic pulmonary diseases were independently associated with ICU mortality.[12] [3] [3,12]
The aim of this retrospective cohort study was to investigate the factors affecting the prognosis of patients who were treated with MV in the ICU of Beijing Geriatric Hospital between January 2006 and December 2017.
2 Patients and methods
2.1 Study design and patients
This retrospective cohort study was conducted at Beijing Geriatric Hospital (Beijing, China), a tertiary hospital managed by the Beijing Hospital Administration Bureau. Beijing Geriatric Hospital has an 8-bed ICU managed by full-time ICU directors and staffed by 5 physicians and 15 nurses.
The inclusion criteria for this study were: admitted to the ICU of Beijing Geriatric Hospital between January 2006 and December 2017; received invasive MV with establishment of an artificial airway (endotracheal intubation) via the mouth, nose, or tracheotomy; and age >16 years. The exclusion criteria were: data required for the analysis were missing from the medical records; pregnancy; and treatment discontinued by the patient.
The indications for invasive MV at our hospital included: deterioration in clinical condition after active treatment of the underlying disease; disturbance of consciousness; severe abnormal respiration, such as respiratory rate >35 to 40 breaths/min or <6 to 8 breaths/min, abnormal respiratory rhythm, or weak/absent spontaneous breathing; blood gas analysis suggested severe disorders of ventilation and oxygenation (PaO2 <50 mmHg, progressive increase in PaCO2 , and progressive acidosis). The relative contraindications for invasive MV included: pneumothorax or mediastinal emphysema that had not been drained; pulmonary bullae or cysts; inadequate treatment of hypovolemic shock; severe pulmonary hemorrhage; and tracheoesophageal fistula. There were no absolute contraindications to MV.
All medical interventions were performed with the informed consent of the patient or his/her family members. The Institutional Ethical Committee of Beijing Geriatric Hospital approved this study. Informed consent for inclusion in the study was waived as the study was retrospective and anonymized.
2.2 Collection of clinical data
The following data were obtained from the medical records: age; sex; reason for ICU admission; APACHE II score[14] [15] [16] [17] [18] [19] [20]
2.3 Statistical analysis
Data analysis was performed using SPSS 17 (SPSS Inc., Chicago, IL). All measurement data were tested for normality. Normally distributed continuous variables are expressed as mean ± standard deviation and were compared between groups (survivors vs non-survivors) using Student t test. Non-normally distributed continuous variables are presented as median (interquartile range [IQR]) and were compared between groups using the Mann–Whitney U test. Categorical variables are expressed as number (percentage) and were compared between groups using the chi-squared test or Fisher exact test (for small sample sizes). In a stratified analysis based on patient age (<65 years and ≥65 years), multivariate logistic regression was performed to identify variables independently associated with mortality. Significant variables in the univariate analysis were included in the multivariate logistic regression analysis (using the enter method), but variables showing multicollinearity were excluded from the final logistic regression model. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated. A P -value <.05 was considered statistically significant.
3 Results
3.1 Baseline characteristics of the study participants
From January 2006 to December 2017, 916 patients were treated with invasive MV in the ICU of our hospital. Eleven patients were excluded due to missing data (n = 4) or discontinuation of treatment (n = 7). Therefore, 905 patients were included in the final analysis (Fig. 1 ).
Figure 1: Flow chart showing enrolment of the study participants. ICU = intensive care unit, MV = mechanical ventilation.
The baseline characteristics of the study participants are shown in Table 1 . The 905 patients (610 men, 67.4%) had a median age of 78 (IQR, 69.5–83) years and an average APACHE II score of 27.3 ± 8.9. The survivor group included 585 patients (388 men, 66.3%) with a median age of 77 (IQR, 67–83) years and an average APACHE II score of 25.6 ± 8.4, and the non-survivor group consisted of 320 cases (222 men, 69.4%) with a median age of 78 (IQR, 72–83) years and an average APACHE II score of 30.6 ± 8.9. The retrospective analysis of data spanned 12 years, but there were no significant differences in mortality rate between the various years. The age range of the patients admitted to the ICU in our hospital was 17 to 98 years, with most patients aged ≥61 years old. There was no significant difference in age between the survivor group and non-survivor group (Table 1 ).
Table 1: Clinical characteristics of the study participants.
Compared with the survivor group, the non-survivor group had a significantly higher APACHE II score (P < .001), a longer duration of MV (P = .009), higher rates of ICU admission for shock (P = .002), or malignant cancer (P = .035), a lower rate of ICU admission after surgery (P < .001), higher rates of MV given for shock (P = .002) or CPR (P < .001), a lower rate of MV given for a surgical reason (P < .001), a lower rate of successful weaning from MV (P < .001), and higher rates of nosocomial infection in the ICU (P < .001), VAP (P < .001), CLABSI (P = .003), AKI (P < .001), RRT (P < .001), septic shock (P < .001), invasive hemodynamic monitoring (P < .001), and blood transfusion (P < .001; Table 1 ).
3.2 Multivariate logistic regression analysis of factors associated with mortality in the ICU
Based on the univariate analysis (Table 1 ), the following factors were entered into the multivariate logistic regression analysis: APACHE II score, duration of MV, ICU admission for shock, ICU admission for malignant cancer, ICU admission after surgery, MV given for shock, MV given for CPR, MV given after surgery, successful weaning from MV, nosocomial infection in the ICU, AKI, RRT, septic shock, invasive hemodynamic monitoring, and blood transfusion. VAP and CLABSI were excluded from the analysis because they exhibited significant multicollinearity with nosocomial infection. In patients aged <65 years (Table 2 ), factors independently associated with higher odds of death in the ICU were APACHE II score (OR: 1.108; 95% CI: 1.021–1.202; P = .014), nosocomial infection in the ICU (OR: 6.618; 95% CI: 1.065–41.113; P = .043), AKI (OR: 17.302; 95% CI: 2.728–109.735; P = .002), and invasive hemodynamic monitoring (OR: 10.051; 95% CI: 1.362–74.191; P = .024), whereas factors independently associated with lower odds of death in the ICU were MV for CPR (OR: 0.122; 95% CI: 0.016–0.924; P = .042), duration of MV (OR: 0.993; 95% CI: 0.988–0.998; P = .008), successful weaning from MV (OR: 0.012; 95% CI: 0.002–0.066; P < .001), and RRT (OR: 0.039; 95% CI: 0.005–0.324; P = .003). In patients aged ≥65 years (Table 3 ), factors independently associated with higher odds of death in the ICU were APACHE II score (OR: 1.062; 95% CI: 1.030–1.096; P < .001), nosocomial infection in the ICU (OR: 2.427; 95% CI: 1.359–4.334; P = .003), septic shock (OR: 2.017; 95% CI: 1.153–3.529; P = .014), and blood transfusion (OR: 1.939; 95% CI: 1.174–3.202; P = .010), whereas factors independently associated with lower odds of death in the ICU were duration of MV (OR: 0.999; 95% CI: 0.999–1.000; P = .043) and successful weaning from MV (OR: 0.027; 95% CI: 0.015–0.047; P < .001).
Table 2: Multivariate logistic regression analysis of factors independently associated with mortality in 167 patients aged <65 years who received invasive mechanical ventilation in the intensive care unit.
Table 3: Multivariate logistic regression analysis of factors independently associated with mortality in 738 patients aged ≥65 years who received invasive mechanical ventilation in the intensive care unit.
4 Discussion
In this study, we investigated the factors associated with ICU mortality among patients with a median age of 78 years given MV in the ICU of our hospital in Beijing. The main findings of the analysis were that APACHE II score, successful weaning and nosocomial infection in the ICU were independent risk factors for ICU mortality in patients receiving MV.
APACHE II score is currently the most widely used method of severity scoring in the critically ill and an important parameter used to evaluate the prognosis of patients in the ICU. It is generally believed that APACHE II score is positively correlated with the mortality rate of critically ill patients, with a higher APACHE II score indicative of a poorer health status and a worse prognosis. Consistent with our findings, previous studies have reported that APACHE II score (or an alternative disease severity score) was associated with mortality in patients treated with MV in the ICU.[1–3,5,12] [21] [22] [21,22] [1–3,5,12]
It was discovered over 20 years ago that failure to wean patients with MV was an independent risk factor for increased risk of death.[23] [24] [25] [26] [27] [28]
Compared with those in general wards, patients admitted to an ICU have a higher risk of hospital-acquired infections.[29] risk factor for hospital mortality even after adjustment for APACHE II or Sequential Organ Failure Assessment scores and age.[30] [31] [32] [33] Enterobacter and Pseudomonas ,[34] [35] [36] [37] [38] [39]
Although the reason for ICU admission, reason for MV, AKI, RRT, septic shock, hemodynamic monitoring, and blood transfusions were excluded from the final regression model in this study, all 7 of these indexes were related to prognosis in the univariate analysis. Age was not a significant factor in the univariate analysis, indicating that it was not predictive of prognosis in our patients who received MV. Previous research found that although older age decreased the rate of successful weaning in patients undergoing prolonged MV, age was not the dominant factor predicting outcomes.[40] [40] [41] [42] [5] [43]
AKI is one of the most common organ dysfunctions seen in patients in the ICU, and its incidence and mortality rate have increased year-on-year.[44] [45] [46] [47] [48] [49] [50] [51]
Sepsis occurs when the host response to infection causes organ dysfunction.[20] [20] risk factor for mortality in elderly patients receiving MV in the ICU.
In the current study, the rate of blood transfusion also differed between survivors and non-survivors in the univariate analysis, and blood transfusion was significantly associated with mortality in patients aged ≥65 years. This indicates that blood transfusion may be a risk marker for increased mortality in elderly patients given MV in the ICU. A previous study found that ICU mortality and 28-day mortality were higher in patients who received transfusion therapy, even in patients with similar levels of organ failure.[52]
Our study identified successful weaning as a very strong predictor of survival both in patients aged <65 years and those aged ≥65 years. However, it was notable that the duration of MV was significantly associated with reduced mortality, albeit very weakly. This would be inconsistent with previous studies showing that a longer duration of MV was associated with a reduced rate of successful weaning and a higher mortality rate.[53] [54] [55]
Of course, our study has some limitations. This was a retrospective study, so there is a possibility of information or/and selection bias. Since this was a single-center study, the underlying disease types were limited, and the generalizability of the findings is not known. In addition, the analysis may have been influenced by unknown confounding factors that affected prognosis. It is hoped that a multicenter, randomized controlled study with a large sample size will be carried out in the near future to better clarify the factors affecting the prognosis of patients receiving MV in the ICU.
In conclusion, this study identified several factors that were independently associated with the survival of patients treated with MV in the ICU, including APACHE II score, successful weaning, and nosocomial infection. Therefore, weaning from MV as early as possible and preventing the occurrence of nosocomial infection are important approaches to improving the prognosis of patients given MV in the ICU.
Acknowledgments
The authors thank Professor Bin Du, Medical Intensive Care Unit, Peking Union Medical College Hospital, Beijing, People's Republic of China for his rigorous revision of the article.
Author contributions
Conceptualization: Jianfeng Liang.
Data curation: Jianfeng Liang.
Formal analysis: Zhiyong Li, Haishan Dong.
Investigation: Haishan Dong.
Methodology: Chang Xu.
Project administration: Jianfeng Liang.
Resources: Zhiyong Li.
Supervision: Haishan Dong, Chang Xu.
Validation: Zhiyong Li.
Writing – original draft: Jianfeng Liang.
Writing – review & editing: Chang Xu.
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