@article {Shastrie000886, author = {Lisha Shastri and Benedict Kj{\ae}rgaard and Stephen Edward Rees and Lars Pilegaard Thomsen}, title = {Changes in central venous to arterial carbon dioxide gap (PCO2 gap) in response to acute changes in ventilation}, volume = {8}, number = {1}, elocation-id = {e000886}, year = {2021}, doi = {10.1136/bmjresp-2021-000886}, publisher = {Archives of Disease in childhood}, abstract = {Background Early diagnosis of shock is a predetermining factor for a good prognosis in intensive care. An elevated central venous to arterial PCO2 difference (∆PCO2) over 0.8 kPa (6 mm Hg) is indicative of low blood flow states. Disturbances around the time of blood sampling could result in inaccurate calculations of ∆PCO2, thereby misrepresenting the patient status. This study aimed to determine the influences of acute changes in ventilation on ∆PCO2 and understand its clinical implications.Methods To investigate the isolated effects of changes in ventilation on ∆PCO2, eight pigs were studied in a prospective observational cohort. Arterial and central venous catheters were inserted following anaesthetisation. Baseline ventilator settings were titrated to achieve an EtCO2 of 5{\textpm}0.5 kPa (VT = 8 mL/kg, Freq = 14 {\textpm} 2/min). Blood was sampled simultaneously from both catheters at baseline and 30, 60, 90, 120, 180 and 240 s after a change in ventilation. Pigs were subjected to both hyperventilation and hypoventilation, wherein the respiratory frequency was doubled or halved from baseline. ∆PCO2 changes from baseline were analysed using repeated measures ANOVA with post-hoc analysis using Bonferroni{\textquoteright}s correction.Results ∆PCO2 at baseline for all pigs was 0.76{\textpm}0.29 kPa (5.7{\textpm}2.2 mm Hg). Following hyperventilation, there was a rapid increase in the ∆PCO2, increasing maximally to 1.35{\textpm}0.29 kPa (10.1{\textpm}2.2 mm Hg). A corresponding decrease in the ∆PCO2 was seen following hypoventilation, decreasing maximally to 0.23{\textpm}0.31 kPa (1.7{\textpm}2.3 mm Hg). These changes were statistically significant from baseline 30 s after the change in ventilation.Conclusion Disturbances around the time of blood sampling can rapidly affect the PCO2, leading to inaccurate calculations of the ∆PCO2, resulting in misinterpretation of patient status. Care should be taken when interpreting blood gases, if there is doubt as to the presence of acute and transient changes in ventilation.}, URL = {https://bmjopenrespres.bmj.com/content/8/1/e000886}, eprint = {https://bmjopenrespres.bmj.com/content/8/1/e000886.full.pdf}, journal = {BMJ Open Respiratory Research} }