Increased 90-Day Mortality in Spontaneously Breathing Patients With Paraquat Poisoning: In Addition to Disease Severity, Lung Strain May Play a Role*

Objectives: 1) To evaluate the prognostic roles of quantitative CT and pulmonary function tests and 2) to assess the association of dynamic strain and ventilation heterogeneity during unassisted spontaneous breathing with 90-day survival in patients with paraquat poisoning. Design: Prospective study. Setting: A university hospital ICU. Patients: One-hundred spontaneously breathing patients with paraquat poisoning without mechanical ventilation. Interventions: A standardized treatment protocol. Measurements and Main Results: Blood samples were collected to measure the plasma paraquat concentration upon arrival. CT scans at suspended inspiration and pulmonary function tests were performed at day 5. The weight of the poorly aerated lung compartment as a percentage of total lung weight (%Wpoor) was exponentially transformed, generating a new variable, Exp(%Wpoor/15). The functional residual capacity that was determined by helium dilution was used to calculate the dynamic strain (tidal volume/functional residual capacity by helium dilution method). Respiratory system reactance at 5 Hz was used as a marker of ventilation heterogeneity. Exp(%Wpoor/15) (adjusted hazard ratio, 2.58; 95% CI, 2.021-3.296; p < 0.001) was most strongly associated with mortality, such that neither blood paraquat concentration nor Pao(2) provided any additional prognostic information. The ratio of residual volume to total lung capacity as a percentage of the predicted value (adjusted hazard ratio, 1.041; 95% CI, 1.026-1.057; p < 0.001) was the only variable that added prognostic value to Exp(%Wpoor/15). While controlling for Exp(%Wpoor/15) and percentage of predicted residual volume/total lung capacity, increases in dynamic strain (adjusted hazard ratio, 2.041/0.1 U; 95% CI, 1.283-3.248; p = 0.003) and/or decreases in respiratory system reactance at 5 Hz (adjusted hazard ratio, 1.19/0.1 U; 95% CI, 1.03-1.386; p = 0.02) were independently associated with increased 90-day mortality. Conclusions: In patients with paraquat poisoning, Exp(%Wpoor/15) and percentage of residual volume/total lung capacity are independent prognostic indicators. Higher dynamic strain and increased ventilation heterogeneity during unassisted spontaneous breathing were associated with worsened survival independent of Exp(% Wpoor/15) and percentage of residual volume/total lung capacity.