Carbon dioxide (CO₂) has long been considered, at best, a waste by-product of metabolism, and at worst, a toxic molecule with serious health consequences if physiological concentration is dysregulated. However, clinical observations have revealed that ‘permissive’ hypercapnia, the deliberate allowance of respiratory produced CO₂ to remain in the patient, can have anti-inflammatory effects that may be beneficial in certain circumstances. In parallel, studies at the cell level have demonstrated the profound effect of CO₂ on multiple diverse signalling pathways, be it the effect from CO₂ itself specifically or from the associated acidosis it generates. At the whole organism level, it now appears likely that there are many biological sensing systems designed to respond to CO₂ concentration and tailor respiratory and other responses to atmospheric or local levels. Animal models have been widely employed to study the changes in CO₂ levels in various disease states and also to what extent permissive or even directly delivered CO₂ can affect patient outcome. These findings have been advanced to the bedside at the same time that further clinical observations have been elucidated at the cell and animal level. Here we present a synopsis of the current understanding of how CO₂ affects mammalian biological systems, with a particular emphasis on inflammatory pathways and diseases such as lung specific or systemic sepsis. We also explore some future directions and possibilities, such as direct control of blood CO₂ levels, that could lead to improved clinical care in the future.

长期以来，人们一直认为二氧化碳（CO ₂）充其量是新陈代谢的废物，最坏的情况是，如果生理浓度失调，会产生严重的健康后果的有毒分子。但是，临床观察表明，“允许性”高碳酸血症（故意让呼吸中产生的CO ₂保留在患者体内）可能具有抗炎作用，在某些情况下可能是有益的。同时，在细胞水平的研究表明，CO ₂对多种多样的信号传导途径具有深远的影响，无论是来自CO ₂的影响。本身或与之相关的酸中毒。在整个生物体水平上，现在看来可能有许多生物传感系统旨在对CO ₂浓度做出响应，并根据大气或局部水平调整呼吸和其他响应。动物模型已被广泛用于研究各种疾病状态下CO ₂水平的变化，以及允许或什至直接输送的CO ₂在多大程度上可以影响患者的预后。这些发现已经在床边进行了，同时在细胞和动物水平上阐明了进一步的临床观察。在这里，我们简要介绍一下当前对CO _2的理解会影响哺乳动物的生物系统，尤其是炎症途径和疾病，例如肺特异性或系统性败血症。我们还探讨了一些未来的方向和可能性，例如直接控制血液中的CO ₂水平，这可能会在将来改善临床护理。