Background: A major contributor to unfavorable outcome after traumatic brain injury (TBI) is secondary brain injury. Low brain tissue oxygen tension (PbtO2) has shown to be an independent predictor of unfavorable outcome. Although PbtO2 provides clinicians with an understanding of the ischemic and non-ischemic derangements of brain physiology, its value does not take into consideration systemic oxygenation that can influence patients' outcomes. This study analyses brain and systemic oxygenation and a number of related indices in TBI patients: PbtO2, partial arterial oxygenation pressure (PaO2), PbtO2/PaO2, ratio of PbtO2 to fraction of inspired oxygen (FiO2), and PaO2/FiO2. The primary aim of this study was to identify independent risk factors for cerebral hypoxia. Secondary goal was to determine whether any of these indices are predictors of mortality outcome in TBI patients. Materials and Methods: A single-centre retrospective cohort study of 70 TBI patients admitted to the Neurocritical Care Unit (NCCU) at Cambridge University Hospital in 2014-2018 and undergoing advanced neuromonitoring including invasive PbtO2 was conducted. Three hundred and three simultaneous measurements of PbtO2, PaO2, PbtO2/PaO2, PbtO2/FiO2, PaO2/FiO2 were collected and mortality at discharge from NCCU was considered as outcome. Generalized estimating equations were used to analyse the longitudinal data. Results: Our results showed PbtO2 of 28 mmHg as threshold to define cerebral hypoxia. PaO2/FiO2 found to be a strong and independent risk factor for cerebral hypoxia when adjusting for confounding factor of intracranial pressure (ICP) with adjusted odds ratio of 1.78, 95% confidence interval of (1.10-2.87) and p-value = 0.019. With respect to TBI outcome, compromised values of PbtO2, PbtO2/PaO2, PbtO2/FiO2, and PaO2/FiO2 were all independent predictors of mortality while considered individually and adjusting for confounding factors of ICP, age, gender, and cerebral perfusion pressure (CPP). However, when considering all the compromised values together, only PaO2/FiO2 became an independent predictor of mortality with adjusted odds ratio of 3.47 (1.20-10.04) and p-value = 0.022. Conclusions: Brain and Lung interaction in TBI patients is a complex interrelationship. PaO2/FiO2 seems to be a major determinant of cerebral hypoxia and mortality. These results confirm the importance of employing ventilator strategies to prevent cerebral hypoxia and improve the outcome in TBI patients.

中文翻译：

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肺损伤是创伤性脑损伤中脑缺氧和死亡率的预测因子。

背景：颅脑外伤（TBI）后不良结果的主要原因是继发性脑损伤。脑组织低氧张力（PbtO2）已被证明是不良预后的独立预测因子。尽管PbtO2使临床医生了解脑生理的缺血性和非缺血性紊乱，但其价值并未考虑会影响患者预后的全身性充氧。这项研究分析了TBI患者的大脑和全身氧合以及许多相关指标：PbtO2，部分动脉氧合压（PaO2），PbtO2 / PaO2，PbtO2与吸入氧分数（FiO2）的比率以及PaO2 / FiO2。这项研究的主要目的是确定脑缺氧的独立危险因素。次要目标是确定这些指标中的任何一项是否是TBI患者死亡率预后的指标。材料和方法：对2014-2018年在剑桥大学医院神经重症监护室（NCCU）入院并接受包括侵入性PbtO2在内的高级神经监测的70名TBI患者进行了单中心回顾性队列研究。收集了333份PbtO2，PaO2，PbtO2 / PaO2，PbtO2 / FiO2，PaO2 / FiO2的同时测量值，并考虑了NCCU出院时的死亡率。广义估计方程用于分析纵向数据。结果：我们的结果显示PbtO2为28 mmHg作为定义脑缺氧的阈值。当调整颅内压（ICP）的混杂因子（调整后的优势比为1.78、95％置信区间（1.10-2.87）和p值= 0.019）时，PaO2 / FiO2被发现是脑缺氧的强大且独立的危险因素。关于TBI结局，PbtO2，PbtO2 / PaO2，PbtO2 / FiO2和PaO2 / FiO2的折衷值都是死亡率的独立预测因子，但需单独考虑并调整ICP，年龄，性别和脑灌注压力（CPP）的混杂因素）。但是，当一起考虑所有折衷值时，只有PaO2 / FiO2成为死亡率的独立预测因子，调整后的优势比为3.47（1.20-10.04），p值= 0.022。结论：TBI患者的脑与肺相互作用是一个复杂的相互关系。PaO2 / FiO2似乎是脑缺氧和死亡率的主要决定因素。这些结果证实了采用呼吸机策略预防脑缺氧并改善TBI患者预后的重要性。