The human gut microbiome in critical illness: disruptions, consequences, and therapeutic frontiers

Abstract

With approximately 39 trillion cells and over 20 million genes, the human gut microbiome plays an integral role in both health and disease. Modern living has brought a widespread use of processed food and beverages, antimicrobial and immunomodulatory drugs, and invasive procedures, all of which profoundly disrupt the delicate homeostasis between the host and its microbiome. Of particular interest is the human gut microbiome, which is progressively being recognized as an important contributing factor in many aspects of critical illness, from predisposition to recovery. Herein, we describe the current understanding of the adverse impacts of standard intensive care interventions on the human gut microbiome and delve into how these microbial alterations can influence patient outcomes. Additionally, we explore the potential association between the gut microbiome and post-intensive care syndrome, shedding light on a previously underappreciated avenue that may enhance patient recuperation following critical illness. There is an impending need for future epidemiological studies to encompass detailed phenotypic analyses of gut microbiome perturbations. Interventions aimed at restoring the gut microbiome represent a promising therapeutic frontier in the quest to prevent and treat critical illnesses.

Keywords: Critical illness; Dysbiosis; Fermented foods; Gut; Microbiome.

Fig. 1.

The vital role of the gut microbiome in maintaining health. The gut microbiome plays a crucial role in normal physiological processes, including regulating metabolism, supporting immunity, and fermenting non-digestible fibers to produce SCFAs. It also protects against pathogens, synthesizes vitamins, aids wound healing, and preserves intestinal homeostasis. Alterations in its composition can influence the functions of remote organs such as the brain, lungs, and liver.

Fig. 2.

Common therapeutic interventions in critical care medicine that promote gut microbiome dysbiosis. These standard medical practices can substantially reduce gut microbial diversity, predispose ICU patients to infections like C. difficile, select for antibiotic-resistant strains, and potentially result in complications such as muscle loss and an elevated risk of sepsis. This highlights the need for a balanced approach to patient care to prevent inadvertently compromising the gut health of the patient.

Fig. 3.

Alterations in the gut microbiome can significantly influence both the progression of disease and the trajectory of recovery in critically ill patients. Those with critical illnesses often exhibit diminished gut microbiome compositions in the ICU, a result of both the underlying disease and the treatments administered. Notably, these microbiome shifts can affect distant organ systems via the gut-brain, gut-lung, and gut-liver axes. Therapeutic interventions designed with the gut microbiome in mind, such as the inclusion of fermented foods, might offer promise in restoring gut health and aiding recovery from critical illnesses and post-intensive care syndrome.