Determinants of ICU memories and the impact on the development and trajectory of post-traumatic stress symptoms: a multicenter longitudinal cohort study

Purpose: To identify demographic and clinical determinants of memory formation in intensive care unit (ICU) patients, and determine the relationship between ICU memories and the development and trajectory of post-traumatic stress disorder (PTSD) symptoms. Methods: Adult patients (n = 426) from two Dutch University ICUs underwent a structured telephone interview using the validated ICU-Memory Tool (ICU-MT) 3 months post-ICU and were assessed for symptoms of PTSD using the Impact of Event Scale (IES-6) at 3 and 12 months post-ICU. Results: Factual memories without delusional memories were present in 47.7% (n = 203), complete ICU amnesia in 13.8% (n = 59), and delusional memories in 38.5% (n = 164) of patients. Delirium was present in 41% (n = 68) of patients with delusional memories. Using multinomial logistic regression, female sex and number of days with deep sedation were associated with ICU amnesia (aOR 1.99, 95% CI 1.04–3.81, and aOR 1.34, 95% CI 1.09–1.65, respectively), whereas delirium and length of ICU stay were associated with delusional memories (aOR 1.94, 95% CI 1.04–3.61, and aOR 1.11, 95% CI 1.02–1.21, respectively). Of 250 patients assessed at both time points, the prevalence of PTSD symptoms increased significantly over time (4.5 to 10.0%, p < 0.01), driven by a significant increase among those with delusional memories (6.7 to 18.1%, p < 0.01). In a linear mixed-effects model, delusional memories were independently linked to both 3- and 12-month symptoms of PTSD (vs. factuals, adjusted %-difference in mean IES score, 12.9%, 95% CI 2.6–24.1%, and 18.1%, 95% CI 5.2–32.5%, respectively). Conclusions: Female sex and prolonged deep sedation were associated with complete ICU amnesia, whereas a longer ICU stay and delirium were associated with delusional memories, although these memories were also common in those without delirium. Delusional memories were independently linked to the development and persistence of PTSD symptoms. Targeted interventions to mitigate memory disturbances, both during and after the ICU, may help alleviate the psychological impact of critical illness.