Anaemia and Desaturation in Anaesthesia

Pathophysiology and Clinical Impact

In healthy adults with normal haemoglobin levels breathing ambient air, the delay between onset of apnoea and arterial oxygen desaturation (SpO2 <90%) is 1-2 minutes, which can be extended to 6-8 minutes with pre-oxygenation 1
Anaemia reduces the oxygen-carrying capacity of blood, which directly impacts the oxygen reserves available during periods of apnoea 1
Patients with anaemia have reduced functional residual capacity (FRC) of oxygen, leading to more rapid desaturation during periods of apnoea 1
The risk of arterial oxygen desaturation is directly proportional to the severity of anaemia 2
The American Society of Anesthesiologists recommends investigating and treating anaemia preoperatively whenever possible, especially before elective procedures 2

Cardiovascular disease significantly increases the risk of complications from anaemia-related desaturation 2
Obesity and pregnancy (from second trimester) reduce functional residual capacity, further accelerating desaturation in anaemic patients 1
Age greater than 55 years is a consistent predictor of desaturation during procedural sedation 4
Pre-oxygenation is crucial in anaemic patients to maximize oxygen reserves and delay onset of desaturation 1
Effective pre-oxygenation is achieved when end-tidal oxygen fraction (FeO2) is greater than 90% 1
The American Heart Association recommends continuous monitoring with pulse oximetry for early detection of desaturation 5

In cardiac surgery, markers of adequate oxygen delivery such as lactate, cerebral near infrared spectroscopy values, and central venous oxygen saturation should be monitored 6
For children with anaemia who are critically ill, haemodynamically stable and not bleeding, maintaining a haemoglobin >70 g/l is recommended 6
Investigate and treat anaemia preoperatively whenever possible, especially before elective procedures, as recommended by the British Journal of Anaesthesia 2
Implement patient blood management strategies throughout the perioperative period, as recommended by the Anaesthesia society 6