Central Venous vs Arterial Blood Gas and CO2 Gap in Critically Ill Patients With and Without Diabetes

Frequent monitoring of acid-base status, ventilation, and tissue oxygenation is essential for managing critically ill patients in the intensive care unit (ICU). While arterial blood gas (ABG) analysis is considered the standard method for these evaluations, maintaining arterial catheters carries risks of complications, such as thrombosis, hematoma, and infection. Central venous blood gas (CVBG) analysis offers a safer alternative because central venous catheters are already routinely placed for patient care. Additionally, the venous-to-arterial carbon dioxide difference (CO2 gap) serves as an indicator of systemic blood flow and tissue perfusion. However, patients with diabetes mellitus often present with underlying microvascular alterations, endothelial changes, and metabolic variations that might alter tissue perfusion and peripheral gas exchange. This study aims to assess the correlation and agreement between central venous and arterial blood gas parameters, as well as evaluate the diagnostic accuracy of the CO2 gap, in diabetic versus non-diabetic critically ill patients. A total of 100 adult ICU patients (50 diabetic and 50 non-diabetic) with pre-existing central venous and arterial lines will be enrolled. Paired blood samples will be drawn simultaneously to compare blood gas values and calculate the CO2 gap without altering standard clinical treatment.

Inclusion Criteria: * Adult patients aged 18 years and older * Critically ill patients admitted to the intensive care unit (ICU) * Patients with indwelling central venous catheter and arterial line placed for routine clinical management * Written informed consent obtained from the patient or legal next of kin Exclusion Criteria: * Known severe peripheral vascular occlusive disease affecting line placement * Use of a pulmonary artery catheter (mixed venous blood line) instead of a standard central venous catheter positioned at the superior/inferior vena cava junction * Refusal of the patient or legal representative to participate in the study * Patients younger than 18 years of age