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Lung mechanics and airway pressure transmission in infants after open heart surgery
Insights
Positive airway pressure can improve lung mechanics in infants after heart surgery. Moderate pressure optimization is needed, but wide pressure transmission requires careful hemodynamic monitoring.
Area of Science:
- Pediatric Critical Care
- Cardiothoracic Surgery
- Respiratory Physiology
Background:
- Infants undergoing open heart surgery often experience altered lung mechanics.
- Positive airway pressure (PAP) is used to support ventilation, but its effects on infant lung mechanics require evaluation.
Purpose of the Study:
- To assess the impact of positive airway pressure on lung mechanics in infants post-cardiac surgery.
- To determine airway pressure transmission into the intrathoracic space in this population.
Main Methods:
- Airway and intrathoracic pressures were recorded during stepwise lung inflation in 17 infants (first year of life) undergoing open heart surgery.
- Lung and chest wall compliance were calculated in 11 patients with cuffed tracheal tubes.
Main Results:
- Lung inflation with 2.5 ml/kg above functional residual capacity improved lung compliance in 7/11 infants, requiring 4-11 cm H2O airway pressure.
- Higher inflation volumes (10 ml/kg) did not further improve mechanics.
- Intrathoracic pressure transmission averaged 47% (range 33-61%) at 10-15 cm H2O airway pressure.
Conclusions:
- Moderately elevated airway pressure optimizes lung distensibility in most infants after open heart surgery.
- A 50% pressure transmission is a reasonable clinical assumption, but the wide range necessitates careful hemodynamic monitoring during positive pressure ventilation.
Abstract:
To evaluate the effects of positive airway pressure on lung mechanics and airway pressure transmission into the intrathoracic space, airway and intrathoracic pressure were recorded during stepwise lung inflation in 17 infants undergoing open heart surgery during the first year of life. Eleven of the 17 patients had cuffed tracheal tubes allowing calculation of lung and chest wall compliance. In 7 of these 11 patients, lung inflation to 2.5 ml/kg above functional residual capacity produced an improvement in initially low lung compliance. This volume increment required elevation of airway pressure by 4-11 cm H2O above ambient. Further lung inflation to 10 ml/kg did not effect an improvement in lung mechanics. In the remaining patients, initial lung compliance was high and remained unchanged throughout the range of lung inflation. Transmission of pressure into the intrathoracic space averaged 47 +/- 9% (mean +/- SD) and ranged from 33% to 61% when airway pressure was 10-15 cm H2O. The results indicate that the use of moderately elevated airway pressure is required to optimize lung distensibility in most infants immediately after open heart surgery. When evaluating circulatory effects of elevated airway pressure, assumption of a 50% pressure transmission is appropriate for clinical purposes. However, the observed wide range of pressure transmission warrants careful hemodynamic monitoring during continuous positive pressure breathing.