Outcome from mechanical ventilation.

The prognostic assessment of patients requiring mechanical ventilation has two important aspects. Firstly, it has sound therapeutic implications, derived from a better understanding of the factors influencing outcome. Secondly, it has important ethical implications, in helping to identify the patients who are not likely to benefit from mechanical ventilation. In these patients, the use of mechanical ventilation would only add to their discomfort, prolong suffering, and also add useless costs, at a time when health care resources are becoming limited [1, 2]. In this issue of the Journal, JIMENEZ et al. [3] evaluated the outcome of 118 patients, 76 being ventilated for more than 72 h. Thirty three (28%) of these patients died. In the population studied, the best predictors of outcome were the number of associated complications and the degree of severity of the disease, as assessed by the simplified acute physiology score (SAPS), the degree of hypoxaemia, and the age of the patients. A logistic regression analysis revealed that the exclusion of the oxygenation index and the age did not reduce the prognostic assessment, indicating that the degree of global impairment was the major determinant of outcome. One should emphasize that the study by JIMENEZ et al. [3], like those of others [4–8], included a mixture of underlying diseases, and the prognosis may be different in adult respiratory distress syndrome (ARDS), chronic obstructive pulmonary disease (COPD) and in other diseases. The present study included more than one third of postsurgical and traumatized patients, whose prognosis is known to be good [8], and only 8% of patients with ARDS. This can account for the Intensive Care Unit (ICU) mortality rate of only 28%, whilst this mortality rate was usually around 50% in other studies [4, 6, 8]. In patients with ARDS, the degree of hypoxaemia, and especially its time course, is an important prognostic factor [9–11], even though death is less commonly due to refractory hypoxaemia than to multiple organ failure [12]. However, ARDS is a heterogeneous syndrome, and the fatality rate also depends on the underlying problem. For instance, mortality is much higher when ARDS is due to sepsis than when it is due to fat embolism or aspiration of gastric content [13]. It is clear that the prognosis is related more to the degree of lung impairment in patients with COPD with other causes of respiratory failure [13]. Incidently, there have recently been very few reports on the outcome from mechanical ventilation in COPD patients, and it would be interesting to see whether changes in ventilatory management (especially the use of noninvasive mechanical ventilation) have influenced the outcome. The study by JIMENEZ et al. [3] is in agreement with previous studies, indicating that the prognosis in patients requiring mechanical ventilation is determined by three major factors: 1. The cause of mechanical ventilation. It is clear that the outcome is poorer in patients who are ventilated after prolonged cardiopulmonary resuscitation than in patients with transient postoperative failure or with drug intoxication [8, 14–16]. 2. The number of organs failing and the number of complications [4, 13]. Application of a severity index like the SAPS score has been sometimes, but not always [17], found useful. 3. The age and the degree of physiology reserve. Several studies [6, 8, 15, 18–20], but not all [4, 14], identified age as an important factor. A low serum albumin level [7], or the presence of cachexia [17], as signs of altered functional status have also been recognized as indicators of poor prognosis. Once mechanical ventilation is initiated, the prognosis may also be related to its duration. For instance, SPICHER and WHITE [8] found that only 39% could be discharged from ICU when the duration of mechanical ventilation exceeded 10 days. A recent study indicated that prolonged mechanical ventilation may not be associated with a greater ICU mortality but with a greater one year mortality rate [21]. One should indeed emphasize that success of weaning from mechanical ventilation, ICU survival, and long-term survival represent three different aspects. Roughly one half of the ICU survivors will be alive one year later. For instance, STAUFFER et al. [15] observed a successful weaning in 67% of patients, an ICU survival of 61%, a hospital survival of 50%, and a survival rate one year later of only 30%. Similarly, ELPERN et al. [6] reported that one half of their patients died in the first year after discharge. In patients ventilated for 10 days or more SPICHER and WHITE [8] observed an acute survival of 39%, and one year survival of 29%. DAVIS et al. [1] reported a hospital survival of 44% and a 2 yr survival of 28%. What are the clinical implications of these observations? Let us return to the two aspects outlined initially. In terms of therapeutic implications, it appears that fatal cases are more commonly related to extrapulmonary than to pulmonary factors. This strongly suggests that mechanical ventilation is less a form of treatment than a EDITORIAL