Posttraumatic stress disorder in survivors of acute lung injury: evaluating the Impact of Event Scale-Revised

Abstract

Background: Survivors of acute lung injury (ALI) and other critical illnesses often experience substantial posttraumatic stress disorder (PTSD) symptoms. However, most questionnaires have not been validated against a PTSD diagnostic reference standard in this patient population. Hence, in the current study of survivors of ALI, we evaluated the Impact of Events Scale-Revised (IES-R), a questionnaire measure of PTSD symptoms, against the Clinician-Administered PTSD Scale (CAPS), the current state-of-the-art PTSD diagnostic reference standard, which also provides a quantitative assessment of PTSD symptoms.

Methods: We evaluated the IES-R questionnaire vs the CAPS diagnostic interview in 60 of 77 consecutively recruited survivors of ALI from two prospective cohort studies of patients 1 to 5 years after ALI.

Results: The IES-R total score (range: 0.0-3.2) and the CAPS total severity score (range: 0-70) were strongly related (Pearson r=0.80, Spearman ρ=0.69). Using CAPS data, eight of the 60 patients (13%) had PTSD at the time of assessment, and an additional eight patients had partial PTSD (total prevalence, 27%). In a receiver operating characteristics curve analysis with CAPS PTSD or partial PTSD as criterion variables, the area under the curve ranged from 95% (95% CI, 88%-100%) to 97% (95% CI, 92%-100%). At an IES-R threshold of 1.6, with the same criterion variables, sensitivities ranged from 80% to 100%, specificities 85% to 91%, positive predictive values 50% to 75%, negative predictive values 93% to 100%, positive likelihood ratios 6.5 to 9.0, negative likelihood ratios 0.0 to 0.2, and efficiencies 87% to 90%.

Conclusions: The IES-R appears to be an excellent brief PTSD symptom measure and screening tool in ALI survivors.

Figure 1.

Convergence of two measures of PTSD symptoms in the last week before interview: the IES-R total score vs the CAPS total severity score. Lines indicate the slope and 95% CI of a fitted linear regression line; Pearson r = 0.80 (P < .0005) and Spearman ρ = 0.69 (P < .0005). CAPS = Clinician-Administered PTSD Scale; IES-R = Impact of Events Scale-Revised; PTSD = postraumatic stress disorder.

Figure 2.

Receiver operating characteristics (ROC) curve for the IES-R total score (test variable) vs CAPS (criterion variable, eight of 60 patients). The area under the ROC curve is 95% (95% CI, 88%-100%). See Figure 1 legend for expansion of abbreviations.

Figure 3.

Flow diagram of the diagnostic accuracy of an IES-R total score threshold ≥ 1.6 using CAPS PTSD as the criterion variable. See Figure 1 legend for expansion of abbreviations.