Oxygen consumption-oxygen delivery relationship in children

Area of Science:

• Pediatric critical care medicine
• Cardiopulmonary physiology

Background:

• The relationship between oxygen delivery (DO2) and oxygen consumption (VO2) is crucial in critically ill children.
• The concept of supply-dependent VO2 suggests that VO2 is limited by DO2 in certain conditions.
• This concept has been used to guide therapies such as blood transfusions and inotropic agents.

Purpose of the Study:

• To examine the relationship between VO2 and DO2 in children after cardiac surgery and in healthy children during exercise.
• To evaluate the effects of blood transfusions and adrenaline on VO2 and DO2 in children post-cardiac surgery.
• To critically assess the validity of the supply-dependent VO2 concept.

Main Methods:

• Studied 15 children post-cardiac surgery, divided into groups receiving blood transfusions or adrenaline infusions.
• Measured VO2, DO2, plasma lactate, oxygen extraction ratio, and mixed venous oxygen saturation.
• Assessed VO2 and Doppler-derived DO2 in 25 healthy children during exercise to establish a normal relationship.

Main Results:

• Blood transfusions increased DO2 but did not affect VO2 in post-cardiac surgery children.
• Adrenaline increased both DO2 and VO2 in post-cardiac surgery children, without altering oxygen extraction ratio or mixed venous oxygen saturation.
• The relationship in healthy children during exercise was described by VO2 = 0.88 x DO2 - 6.95.
• Significant measurement errors in DO2 and spontaneous variations in VO2 were observed.

Conclusions:

• Adrenaline's effect on VO2 and DO2 may reflect increased metabolic demand rather than improved perfusion.
• The study challenges the concept of supply-dependent VO2, attributing it to methodologic and measurement errors.
• The findings suggest caution against using the supply-dependent VO2 concept to justify potentially harmful therapies in pediatric patients.