Classification of impedance spectra for monitoring ischemic injury in the gastric mucosa in a septic shock model in pigs

The disruption of the gastrointestinal mucosa plays a key role in the evolution of shock and is the motor of "multiple organ failure". This study evaluated the feasibility of identifying ischemic injury in the gastrointestinal mucosa by impedance spectroscopy, using a minimally invasive nasogastric catheter to record the impedance spectra of the gastric wall. Ischemic injury was estimated and classified from the duration and severity of ischemia as measured by gastric tonometry. Thirteen pigs (9-25 Kg) were anesthetized (pentobarbital 17 mg/kg) and subjected to septic shock induced by a continuous intravenous infusion of lipopolysaccharide (LPS, 160 μg/kg per hour). Subjects were divided into two groups: Control animals (n = 3) received no treatment but LPS. In the treated group (n =10), four hours after LPS the animals received a combination of therapies, including fluid resuscitation, catecholamines and nitric oxide synthase modulators, in order to promote changes in hemodynamic response and splachnic perfusion. A pattern recognition neural network was developed, trained and tested according to the estimated injury class. The results suggest it is feasible to identify different levels of ischemic injury from gastric impedance spectra under conditions of diverse pharmacological interventions and physiological responses, which better simulate conditions encountered in a clinical setting.