97 Transportation of oxygen(DO2)

Oxygen delivery (DO₂): formula, normal values, the oxygen delivery chain and causes of reduced delivery.

Oxygen delivery (DO₂) is the amount of oxygen carried to the tissues by the arterial blood each minute. It depends on three links in a chain: how well the lungs load oxygen onto haemoglobin (saturation), how much haemoglobin the blood contains, and how much blood the heart pumps (cardiac output). Oxygen is essential for producing ATP by oxidative phosphorylation, so it must be delivered reliably to every active cell; when delivery falls below what the tissues need, cells switch to anaerobic metabolism, lactate rises and organs can be damaged. In this application the value also reflects the function of the systemic and pulmonary circulation, heart, liver and gut.

Oxygen transportHaemodynamicsShock

FormulaDO₂ = CO × CaO₂ × 10

Arterial O₂ content1.34 × Hb × SaO₂ + 0.003 × PaO₂

Adult at rest≈ 1000 mL/min

Indexed (DO₂I)≈ 500–600 mL/min/m²

Figure 1. Oxygen delivery depends on lung oxygenation, haemoglobin concentration and cardiac output. At rest the tissues use only about a quarter of the oxygen delivered.

Calculation and measurement

DO₂ (mL/min) = cardiac output (L/min) × [1.34 × Hb (g/dL) × SaO₂ + 0.003 × PaO₂ (mmHg)] × 10

Almost all oxygen is carried bound to haemoglobin; dissolved oxygen contributes very little at normal pressures. The reference measurement requires invasive cardiac output monitoring (thermodilution or the Fick method) and an arterial blood gas.

Causes of reduced oxygen delivery

Low cardiac output: heart failure, cardiogenic shock, bleeding and dehydration, arrhythmias
Low haemoglobin: anaemia of any cause
Low saturation: lung disease, hypoventilation, high altitude; abnormal haemoglobin (carbon monoxide, methaemoglobin)

In high-risk surgical patients, an oxygen debt (inadequate delivery for the body's needs) was associated with organ failure and death, which is why oxygen delivery is closely monitored in intensive care.

Seek emergency care

for breathlessness with confusion, bluish lips, cold clammy skin, chest pain or fainting.

References

Dunn JO, Mythen MG, Grocott MP. Physiology of oxygen transport. BJA Educ. 2016;16(10):341–348.
Shoemaker WC, Appel PL, Kram HB. Role of oxygen debt in the development of organ failure, sepsis, and death in high-risk surgical patients. Chest. 1992;102(1):208–215. doi:10.1378/chest.102.1.208

This article is for general information and does not replace a consultation with a doctor. Measurements must be interpreted by a physician together with symptoms and other tests.

Published on 5 May 2024