Unique infrared thermographic profiles and altered hypothalamic neurochemistry associated with mortality in endotoxic shock

Abstract

Neonatal sepsis results in significant morbidity and mortality, but early detection is clinically challenging. In a neonatal rat model of endotoxic shock, we characterised unique infrared thermographic (IRT) profiles in skin temperature that could identify risk of later mortality. Ten-day old rats were placed in a thermally stable isolette and IRT images of cranial (T_CR), scapula (T_SC) and rump (T_RU) skin temperature were obtained continuously for 8 h following an intraperitoneal injection of lipopolysaccharide (LPS) or saline. LPS resulted in ∼74 % mortality (designated as non-survivors, LPS_NS) between 4.5 and 7.5 h post-injection. LPS_NS and survivors of LPS (LPS_S) rats displayed hypothermic tendencies with T_CR, T_SC and T_RU decreasing at ∼80–100 min (T_80–100) post-injection. Compared to LPS_S rats, however, the hypothermia of LPS_NS rats occurred slightly earlier (T₈₀), was more severe, and failed to recover. The T_CR, T_SC and T_RU of LPS_S rats fully recovered by 4 h (T₂₄₀) post-injection. In separate rats, hypothalamic microglia and extracellular matrix (ECM) expression at T₂₄₀ post-injection were increased in putatively identified LPS_NS rats (but not LPS_S rats) and negatively correlated with IR temperatures. IRT could be a useful early identifier of infants at risk of death from endotoxic shock, which may be related to early failure of central nervous system (CNS) thermogenic mechanisms mediated by unique hypothalamic changes in inflammatory (microglia) and ECM neurochemistry.