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The impact of demographics, chronic health status and severity of disease on outcome from mechanical ventilation: a prospective cohort study


1) To descibe the characteristics of the ICU patients undergoing prolonged mechanical ventilation (MV) and estimate its incidence. 2) To evaluate the impact of demographics, chronic health status and severity of disease on the duration of MV and on short-term mortality.


A 20 bed multidisciplinary ICU of a 650 bed tertiary university hospital.


A prospective dynamic cohort study. Impact on outcome was analyzed by univariate (attributable risk, relative risk increase and survival analysis), and multivariate analysis (relative risk of disconnection [HR] and of mortality [OR], by the Cox proportional hazards and logistic regression models).


From a whole population of 591 patients admitted to the ICU between November 1998 and October 1999, we enrolled 205 patients who received MV for more than 12 hours.


Incidence of MV 34.7%. Age 57.8 ± 1.2 years. Males 136 (66%). SAPS II scoring: 42.01 ± 1.23 (mean ± EE), APACHE II scoring: 17.78 ± 0.53 (mean ± EE), multisystem organ failure (MSOF): 1 (0–2) (median and 25–75% interquartile range), a simplified organ failure index (s–OFI): 1 (1–2) (median and 25–75% interquartile range). ICU mortality: 25.4% (52), hospital mortality: 33.7% (69). Duration of MV: 13.9 ± 2.4 days. Weaning time: 8.8 ± 2.2 days (62.3% of total ventilation time). The mean duration of MV was longer in respiratory pathology (29.6 ± 13.9 days), followed by neurologic (14.9 ± 6.3 days) and trauma (12.8 ± 1.9 days). It was longer in nonsurvivors 15.6 ± 5.1 versus 10.8 ± 1.6 days in survivors (log-Rank, P < 0.00005). ICU length of stay (LOS) 16.6 ± 2.1 days, hospital LOS 41.9 ± 3.3 days.

APACHE II (hazard ratio [HR] 0.92; 95% CI: 0.89–0.95), body mass index (HR 0.97; 95% CI: 0.93–0.99), sepsis with or without associated pneumonia (HR 0.36; 95% CI: 0.19–0.70), and ARDS (HR 0.20; 95% CI: 0.06–0.68) reduced independently the rate of disconnection from MV. Surgical vs medical category (HR 1.68; 95% CI: 1.1–2.56), and the presence of chronic respiratory disease (HR 1.71; 95% CI: 1.02–2.90) increased the rate of disconnection.

Female gender with an attributable risk of hospital mortality of 14.8% (95% CI: 1.0–28.7%), an attributable fraction in exposed population of 34.0% (95% CI: 3.8–54.8%); χ2 4.49, P = 0.034), and an adjusted odds ratio (OR) of 2.80 (95% CI: 1.22–6.41), degree of malnutrition (OR 2.80; 95% CI: 1.35–5.84), SAPS II (OR 1.07; 95% CI: 1.03–1.10), cardiac arrest on arrival (OR 34.42; 95% CI: 6.90–171.58), postoperative respiratory failure (OR 3.65; 95% CI: 1.20–11.03), and cardiac failure (OR 5.93; 95% CI: 1.56–22.48) increased hospital mortality risk, whereas age (OR 0.97; 95% CI: 0.94–0.99) decreased it.


ICU patients undergoing prolonged MV represented an important subset of the whole ICU population (one third of total admissions, half of them medical category). Prolonged MV was associated with a relatively high short-term (ICU and hospital) mortality and prolonged ICU and hospital LOS. Gender category, chronic health condition and several early-acquired clinical data successfully predicted both the duration of MV and short-term mortality. Severity scoring indexes behaved as useful tools to predict the duration of MV (APACHE II) and the risk of mortality (SAPS II). Increasing age was not necessarily associated with an adverse outcome.

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Revuelta Rabasa, P., Naranjo Jarillo, C., Jiménez Rivera, J. et al. The impact of demographics, chronic health status and severity of disease on outcome from mechanical ventilation: a prospective cohort study. Crit Care 5, P237 (2001).

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  • Mechanical Ventilation
  • Chronic Respiratory Disease
  • Prolonged Mechanical Ventilation
  • Medical Category
  • Failure Index