In the face of increasingly complex intensive care interventions and an aging population, the prevention of long-term IMV is one of the great challenges in modern intensive care medicine. Our aim was to identify risk factors for long-term ventilation early after initiation of invasive mechanical ventilation. Using data from more than 7.500 inpatient hospitalisations, we identified a set of risk factors that can be assessed in the first four days after intubation. Drawing on the knowledge of a consulting multiprofessional team and a systematic literature review [8], we examined a wide range of different factors in exploratory analyses. This approach allowed us to identify multiple previously unknown risk factors, but also favourable conditions with respect to subsequent invasive long-term IMV. In contrast with the literature [2, 10, 11], age did not play a role in our anaysis. As outlined in previous studies, COPD [2, 11, 12], evidence of previous dependence on a ventilator invasive or noninvasive [2, 13], colonisation with multidrug-resistant pathogens [14] and cerebral infarction [15] were confirmed as risk factors in our study population. Other risk factors not previously described include medical history, preexisting conditions, admission diagnoses, resource prescriptions, and procedures performed within the first 96h after initiation of IMV.
Unexpectedly, nursing home accommodation immediately before hospitalisation was a prognostically favourable factor, which can best be explained by the fact that the treating intensivists performed a thorough pre-selection of these patients with regard to the general prognosis before initiating IMV. Among admission diagnoses, thyroiditis, eating disorders, rheumatic mitral valve disease and acute pancreatitis were identified as risk factors for subsequent long term IMV. In the case of thyroiditis, hypothyroidism, which often develops during the course of the disease, probably plays a role. However, both hyperthyroidism [16] and hypothyroidism [17][15] can affect respiratory function through muscle weakness. In the context of eating disorders, in addition to general cachexia-related muscle weakness, hypophosphatemia [18] may also be play a role, as indicated by a small study on the effect of serum phosphorus concentration on ventilatory weaning [19]. Rheumatic mitral valve disease is the most common valvular heart disease [20] and can lead to heart failure via tricuspid regurgitation, which in turn is a known risk factor for long-term ventilation [20].
Pre-existing dementia and previous placement of a dialysis fistula, as well as peritonitis, cardiac arrhythmias, and pulmonary or abdominal metastases as admission diagnoses turned out to be favourable factors with respect to subsequent long-term ventilation. The association of known dementia with delirium [21] in the context of acute hospitalisation may have led to the administration of more sedative medications and, via this, to an increase in the duration of ventilation, but without requiring subsequent long-term ventilation. In the case of the above-mentioned admission diagnoses, both cardiac arrhythmias and peritonitis are causally treatable diseases, which allows termination of ventilation after successful completion of treatment. The same is true for patients with a dialysis fistula; here, the likely pathogenesis of respiratory failure is volume overload, which can be rapidly corrected. With regard to metastases and dementia, we assume a selection bias; usually, only patients with a very favourable prognosis are admitted to an intensive care unit in this situation [22].
Of the operations and procedures studied within the first 96h initiation of IMV were particularly procedures that indicate a pulmonary cause of the need for ventilation found to be risk factors, such as bronchoscopy or computed tomography of the chest. Also, the early tracheostomy, which was associated with a very high risk, is certainly an indicator that the treating physicians already suspected prolonged weaning. Patients with particularly complex prolonged ICU courses were also at increased risk for long-term ventilation, indicative of the use of Extracorporeal lung assist (ECLA) or extracorporeal membrane oxygenation (ECMO), positioning therapy, transfusion of plasma components or coagulation factors. The use of a chest tube as a further risk factor indicates either a pre-existing pulmonary condition or complications related to barotrauma or iatrogenesis [23]. In addition, procedures suggestive of leading neurological problems such as cerebral spinal surgeries, cerebrospinal fluid system surgeries, or cranial imaging were also predictors for unfavourable outcomes. In contrast, radical cervical lymphadenectomy, or autologous blood collection and transfusion, usually as part of elective surgery, showed a favourable prognosis with respect to subsequent long-term ventilation. The combination of all identified risk factors makes it possible to assess the prognosis with regard to subsequent long-term ventilation in the first days of intensive medical care with an acceptable predictive accuracy. The predictive value of this model, could be confirmed based on a subsequent validation cohort. Strengths of this model are the large number of patients, the validation in a later cohort and the 30-day follow-up.
Despite the steadily increasing number of long-term ventilated patients, the associated individual suffering and the high costs for the health care systems, there are only a few studies that have dealt with the determination of risk factors of invasive ventilation [8].
One of the largest studies on ventilatory weaning by Béduneau et al, the WIND study, provides a multicentre population of 2,729 ventilated patients and identified age, Sequential Organ Failure Assessment (SOFA) Score at admission, duration of MV before the first separation attempt and medical admissions as risk factors for weaning failure. However, the study did not aim to identify risk factors but to describe the weaning process, according to a new operational classification [10]. Two smaller studies from China with 302 and 343 patients investigated risk factors for prolonged mechanical ventilation and weaning failure and found age > 74 years and COPD as well as Glasgow Score and PaCO2 (at the beginning of the first spontaneous breathing trial) as risk factors [12, 24]. The most comprehensive study dealing with weaning failure is the study by Windisch et al. It is a retrospective analysis of a German weaning registry, here the data of 11.424 patients transferred to a specialised weaning centre were examined, the need to continue with invasive ventilation was most strongly associated with the duration mechanical ventilation prior to transfer from the ICU, a low body mass index, pre-existing neuromuscular disorders and advanced age [2].
The current WEAN SAFE study also examined factors associated with weaning failure. Demographic factors independently associated with weaning failure included older age, weakened immune system and frailty. Critical illness-related factors associated with weaning failure were severity of critical illness as measured by the SOFA score, cardiac arrest or a non-traumatic neurological event as the reason for admission to the ICU, pre-existing limitations of care, and the degree of respiratory dysfunction (respiratory rate and lower partial pressure of arterial oxygen relative to FiO2) and ventilatory support (dynamic driving pressure and PEEP) used at the time of the first disconnection attempt. Among the potentially modifiable factors, the presence of deep sedation levels at the time of the first weaning attempt was associated with weaning failure; and the time interval between the development of weaning criteria and the first weaning attempt was independently associated with weaning failure [6]. In addition to consistent and timely implementation of weaning attempts when weaning criteria are met, we need models that allow us to identify high-risk patients as early as possible.
Limitations
The main drawback of our study includes the use of data on health care services designed for reimbursement with all the associated problems [25] as well as the fact that only data from a statutory health insurance fund was used. Data that was not available but might also be predictive is for example social support in the home setting or if outpatient specialised health support is available.