Critical Oxygen Delivery in Conscious Humans Is Less Than 7.3 ml O2· kg−1· min−1

Abstract

A decrease in DO2 to 7.3+/-1.4 ml O2 x kg(-1) min(-1) in resting, healthy, conscious humans does not produce evidence of inadequate systemic oxygenation. The critical DO2 in healthy, resting, conscious humans appears to be less than this value.

Subcutaneous Po2 as an index of the physiological limits for hemodilution in the rat

“…However, successful case reports of extreme hemodilution indicate a wide margin between current practice and more extensive, but still safe, hemodilution (11,17). This disparity could be reduced by accurate and continuous information about tissue oxygenation during hemodilution (34). More use of hemodilution and an improved cost-to-benefit ratio are realistic potential outcomes if a reliable physiologically relevant end point can be developed to prevent the onset of dangerous tissue hypoxia as O 2 -carrying capacity is reduced (36).…”

“…However, at Hct Ͻ20%, it is well recognized clinically that blood pressure needs to be supported, usually with colloid infusions (33)(34)(35). Furthermore, a universally applicable "critical Hct," below which O 2 supply becomes insufficient for tissue needs during hemodilution, has not been identified (36,61,64).…”

Anemia and Transfusions in Surgical Patients: Current Concepts and Future Directions

“…Packed red blood (SvO 2 : venous oxygen saturation), and (2) an increase of CO. The latter can be well tolerated by healthy subjects [20,21], but patients without sufficient cardiac reserve, particularly the elderly, may not be able to employ this compensatory mechanism. Moreover, increases in stroke volume and heart rate to raise CO are accompanied by increases in myocardial oxygen consumption, potentially exacerbating pre-existing compromised flow dynamics, thus leading to ischemia, and possibly explaining the higher rate of cardiac complications and death in anemic patients.…”

Acute Normovolemic Hemodilution in Cardiac Surgery

“…In healthy volunteers and awake patients undergoing major abdominal surgery, moderate to severe hemodilution is associated with a 10-20% increase in systemic O 2 consumption that was mainly related to this increased myocardial oxygen demand. 11,24,25 In dogs, myocardial O 2 consumption more than doubles when the hematocrit is reduced to about 10%. 26 In these conditions, coronary vasodilatation is nearly maximal.…”

“…43 Acute administration of negative inotropic agents like anti-arrhythmic drugs or β-blocking agents will also reduce the cardiac output response to ANH. 25,44 In the postoperative period, tolerance of patients with altered myocardial function will closely depend on the potential recovery of their cardiac function and, again, on the level of metabolic demand.…”