Persistent Inflammation, Immunosuppression and Catabolism after Severe Injury or Infection

Abstract

Starting in the 1990s, reports describing chronic critical illness emerged under a va- riety of descriptive terms including the “neuropathy of critical illness”, “myopathy of critical illness”, “intensive care unit (ICU)-acquired weakness” and most recently “post-ICU syndrome”. These reports largely originated from medical ICUs that in- cluded individuals with a wide variety of admission diagnoses, most common of which was acute exacerbation of chronic disease. These patients required prolonged mechanical ventilation and were often discharged to long-term care facilities. Given the clinical heterogeneity of this patient population, the underlying pathophysiology of chronic critical illness has remained ill-defined. However, with recent improved implementation of evidence-based ICU care, the epidemiology of multiple organ failure (MOF) has evolved. Early hospital mortality has decreased substantially and the incidence of late onset MOF deaths in the ICU has largely disappeared. As a re- sult, protracted low grade MOF has become a common cause of chronic critical illness. Based on substantial laboratory and clinical research data, the Persistent, Inflammation, Immunosuppression and Catabolism (PICS) paradigm was proposed as a mechanistic framework in which to explain the increased incidence of chronic critical illness in surgical ICUs, which we believe represents the next major chal- lenge in surgical critical care. The purpose of this review is to provide a historic perspective of the epidemiologic evolution of MOF into PICS, discuss the long- term outcomes of chronic critical illness and PICS and review the mechanisms that can induce PICS.