Normal Oxygen Delivery (DO2) Values
Normal oxygen delivery (DO2) in healthy adults is approximately 950-1150 mL/min or 520-720 mL/min/m² when indexed to body surface area.
Understanding DO2 Calculation
DO2 is calculated using the equation: DO2 = CaO2 × Q, where CaO2 is arterial oxygen content and Q is cardiac output 1. The arterial oxygen content depends primarily on hemoglobin concentration and oxygen saturation, with minimal contribution from dissolved oxygen 1.
Normal DO2 Values in Clinical Context
Absolute Values
- Normal DO2: Approximately 950-1150 mL/min in a typical 70 kg adult
- Indexed DO2 (DO2I): 520-720 mL/min/m² when normalized to body surface area
Clinical Thresholds from Guidelines
During cardiopulmonary bypass, the 2024 EACTS/EACTAIC/EBCP guidelines recommend maintaining DO2 >280-300 mL/min/m² during normothermic conditions to improve clinical outcomes 1. For transfusion decisions during bypass, DO2 should be maintained >273 mL/min/m² 1.
In critically ill patients, there is ongoing debate about "supranormal" DO2 targets. Some evidence suggests targeting DO2I >600 mL/min/m² may reduce mortality in certain populations 2, 3, though this remains controversial 4, 5.
Critical DO2 Threshold
The critical DO2 - below which tissue oxygen consumption becomes supply-dependent - appears to be quite low in healthy individuals. Research in conscious healthy volunteers demonstrated that DO2 can decrease to 7.3 mL O2/kg/min (approximately 511 mL/min in a 70 kg person) without evidence of inadequate systemic oxygenation 6. This represents roughly 50% of normal DO2 values.
Clinical Monitoring Approach
Rather than targeting arbitrary DO2 values, monitor markers of adequate tissue oxygenation 4, 5:
- Mixed venous oxygen saturation (SvO2): Target >70% (or >65% for central venous saturation) 4
- Lactate levels: To detect tissue hypoxia 4
- Oxygen extraction ratio: Should normalize when DO2 is adequate 3
The most important principle is that normalizing SvO2 when it is low is more clinically relevant than achieving arbitrary absolute DO2 values 5, 4.
Important Caveats
DO2 depends on three components: hemoglobin concentration, oxygen saturation, and cardiac output 1, 4. Simply increasing oxygen saturation in a patient already at 90% will only increase DO2 by approximately 10%, whereas correcting anemia or low cardiac output produces much greater improvements 1.
A normal or high SvO2 does NOT exclude tissue hypoxia, particularly in septic patients where oxygen extraction may be impaired 4. Approximately 23% of septic patients have elevated lactate despite ScvO2 >70% 4.
Age matters: Patients >75 years may not benefit from aggressive DO2 augmentation to supranormal levels and may have lower oxygen extraction ratios, suggesting potential overtreatment 3.