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Spontaneous breathing and total body oxygen consumption in children recovering from open-heart surgery
J Räsänen1, K Puhakka, M Leijala
1Department of Anesthesiology, University of South Florida College of Medicine, Tampa.
Insights
Withdrawing mechanical ventilation in children post-heart surgery caused expected blood gas changes but not significant shifts in oxygen consumption (VO2). Other factors, not just respiratory effort, influence VO2, making it an unreliable measure of breathing work.
Area of Science:
- Pediatric critical care medicine
- Cardiopulmonary physiology
- Post-operative management
Background:
- Mechanical ventilation is crucial for infants and children after open-heart surgery.
- Weaning from ventilatory support requires careful monitoring of cardiopulmonary function.
- Assessing the metabolic cost of breathing is vital for successful weaning.
Purpose of the Study:
- To evaluate the impact of ventilatory support withdrawal on cardiopulmonary function, oxygen consumption (VO2), and carbon dioxide production (VCO2) in pediatric patients post-open-heart surgery.
- To determine if VO2 accurately reflects the work of breathing during weaning.
- To identify factors influencing VO2 changes during the weaning process.
Main Methods:
- Studied 25 infants and children within 7 days of open-heart surgery.
- Measured heart rate, blood pressure, blood gases, and oxyhemoglobin saturation during mechanical ventilation and spontaneous breathing with CPAP.
- Simultaneously measured VO2 and VCO2 using indirect calorimetry.
Main Results:
- Withdrawal of ventilatory support led to a significant decrease in arterial pH and an increase in PaCO2.
- Systemic blood flow improved, indicated by increased central venous oxyhemoglobin saturation during spontaneous breathing.
- Average VO2 and VCO2 did not change significantly; individual VO2 changes varied and were inversely related to body temperature and the difference between measured and expected VO2.
Conclusions:
- Factors beyond respiratory muscle oxygen uptake significantly affect total body VO2 in pediatric patients after open-heart surgery.
- Monitoring VO2 during ventilatory support withdrawal may not be a reliable indicator of respiratory work or the oxygen cost of breathing in this population.
- Further research is needed to understand the complex metabolic responses during weaning in pediatric cardiac surgery patients.
Abstract:
The effects of withdrawal of ventilatory support on cardiopulmonary function, oxygen consumption and carbon dioxide production were assessed in 25 infants and children within seven days (2.9 +/- 2.5 days; mean +/- SD) of an open heart operation, during weaning from ventilatory support. The average age of the patients was 3.4 +/- 3.5 years and weight 12.4 +/- 8.3 kg. Heart rate, blood pressure, arterial and central venous blood gas values, and oxyhemoglobin saturations were measured during controlled mechanical ventilation and during spontaneous breathing with continuous positive airway pressure. Simultaneously, VO2 and VCO2 were measured using indirect calorimetry. Withdrawal of ventilatory support effected an expected, significant decrease in arterial pH (7.42 +/- 0.10 to 7.37 +/- 0.06; p less than 0.001) and an increase in PaCO2 (34 +/- 6 to 40 +/- 5 mm Hg; p less than 0.0001), while arterial blood oxyhemoglobin saturation, heart rate, and blood pressure remained unchanged. A significant increase in central venous oxyhemoglobin saturation (67.9 +/- 11.9 to 74.8 +/- 8.3 percent; p less than 0.001) indicated improvement in systemic blood flow during spontaneous breathing. Average VO2 and VCO2 did not change significantly. A decrease in VO2 by more than 5 percent was seen in seven patients, an increase by more than 5 percent in nine, and a change within +/- 5 percent in nine patients. The change in VO2 was inversely related to the difference between measured and expected VO2 during mechanical ventilation (r = -0.73) and to body temperature (r = -0.69). The results indicate that factors other than the oxygen uptake by the respiratory muscles may have significant effects on total body VO2 in infants and children after open-heart surgery. Therefore, monitoring of VO2 during withdrawal of ventilatory support may not be an accurate indicator of respiratory work and oxygen cost of breathing in these patients.