Oxygen extraction ratio: A valid indicator of myocardial metabolism in anemia

Acute Normovolemic Hemodilution: A Critical Evaluation of Its Safety and Utility in Pediatric Patients

“…Numerous studies and reviews have documented the hemodynamic and oxygenation safety of ANH in adults and in baboon and canine models of normovolemic hemodilution. 11,17,[20][21][22][23][24][25] Troponin I, a very sensitive marker of myocardial damage, for example, was undetectable in adult patients undergoing hemodilution to 20% during major orthopedic surgery. 26 Transesophageal echocardiographic hemodynamic monitoring did not demonstrate any hemodynamic compromise in diastolic and systolic myocardial function in normal adult volunteers undergoing normovolemic hemodilution to 8 g/dL (hematocrit of 24%).…”

“…While nonspecific measurements such as mixed venous oxygen saturation, plasma lactate and physiological monitoring are useful, such measurements may not adequately reflect the effect of decrease oxygen delivery to individual organs with different oxygenation thresholds. 41,42 Although animal studies can be relied on to ascertain specific organ safety (as was initially used to ascertain safety in the early clinical assessment of hemodilution 20,23,24,43 ), these are no substitutes for actual organ specific oxygen delivery measurement in children; however, it is unlikely, given the vulnerability of children as research subjects, that such studies will be forthcoming.…”

Practical management of anticoagulation, bleeding and blood product support for cardiac surgery part two: Transfusion issues

“…In animal models, coronary lactate production occurs at a haemoglobin level of 35 g/L. 39 In a coronary stenosis model, this occurred at a haemoglobin of 60-70 g/L. 40,41 A large randomised controlled study of 838 critically ill patients compared a restrictive transfusion strategy (transfusing when Hb < 70 g/L) with a more liberal strategy (Hb < 100 g/L).…”

Preoperative haemodilution

“…It is important to realize that the systemic oxygen delivery at rest normally exceeds the oxygen requirements two to five times (20,23). In drastic haemodilution, almost incompatible with metabolic stability (below loyo), systemic oxygen extraction is around 50% (24). There is thus a safety margin in oxygen transport.…”

“…When the systemic oxygen delivery is decreasing, oxygen extraction becomes increasingly important to meet tissue demands. In patients (25) and animals (24), an increase in arterial lactate, as a possible indicator of anaerobic metabolism, takes place at haematocrits around or below 10%. Several animal studies, dealing with survival during extreme haemodilution (see 17), indicate that haematocrits just below 10% may be compatible with life.…”