Hyperoxic ventilation enables hemodilution beyond the critical myocardial hemoglobin concentration

Area of Science:

• Cardiovascular Physiology
• Anesthesiology
• Critical Care Medicine

Background:

• Anemic hypoxia can cause significant physiological stress, indicated by ECG changes.
• Hyperoxic ventilation (HV) with 100% oxygen (FiO2 1.0) can reverse these ECG changes and prolong survival.
• The precise gain in anemia tolerance and hemoglobin (Hb)-equivalent of HV in this context remain unquantified.

Purpose of the Study:

• To quantify the increase in anemia tolerance provided by HV in anemic hypoxia.
• To determine the hemoglobin-equivalent value of HV during severe anemia.

Main Methods:

• Nine anesthetized pigs underwent hemodilution under normoxia (FiO2 0.21) until ECG changes indicated ischemia.
• HV (FiO2 1.0) was initiated, and animals were further hemodiluted until ECG changes reappeared.

Main Results:

• HV improved ECG readings in all animals experiencing anemic hypoxia (Hb 2.3 g/dL).
• HV permitted an additional blood exchange of 14 mL/kg before ECG changes recurred at a lower Hb of 1.2 g/dL.

Conclusions:

• HV enhances myocardial oxygenation, creating a safety margin and increasing tolerance to anemia.
• The Hb-equivalent of HV in anemic hypoxia is approximately 1 g/dL.