Baltimore, MD, USA: Lippincott Williams & Wilkins, 2012. End-tidal and arterial carbon dioxide gradient in serious traumatic brain injury after prehospital emergency anaesthesia: a retrospective observational study. The PaCO2-ETCO2 gradient in pre-hospital intubations of all aetiologies from a single UK helicopter emergency medicine service 2015–2018. Hibberd O, Hazlerigg A, Cocker PJ, et al. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. In such situations, arterial measurement may be more appropriate.Īcute Respiratory Distress Syndrome Network, Brower RG, Matthay MA, et al. This is particularly relevant for traumatic brain injury, where high carbon dioxide can lead to raised intracranial pressure, whilst low carbon dioxide can lead to cerebral ischaemia. Given that in unstable patients, the gradient is more significant than previously thought and that there is a lack of a predictable relationship, the ETCO 2 is not a suitable stand-in for the PaCO 2 where pH or PaCO 2 requires precise control. Moreover, a correlation has only been moderate, meaning there is variation between the levels, making it difficult to predict the difference in the gradient. This has been observed to result in patients with high or low CO 2 being misclassified as having normal CO 2. More recent studies have demonstrated the gradient in unstable patients exceeds the expected difference of 0.5 kPa (3.8 mmHg). However, in the presence of ventilation-perfusion mismatch, acid-base disturbance, and haemodynamic instability, this difference may increase. These guidelines are based upon evidence which has been extrapolated from healthy individuals, often in the controlled setting of an operating theatre. Can the PaCO2- ETCO2 gradient be predicted?Ĭurrent guidance recommends an ETCO2 of 4.0–4.5 kPa (30.0–33.8 mmHg) as a stand-in for a low-normal PaCO 2 with an expected difference of 0.5 kPa (3.8 mmHg).
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