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Changes in respiratory mechanics in children undergoing cardiopulmonary bypass
C J Lanteri1, S Kano, A W Duncan
1Division of Clinical Sciences, Princess Margaret Hospital, Perth, Western Australia.
Insights
Increased pulmonary blood flow (PBF) in children with congenital heart defects significantly worsens respiratory mechanics. Surgical correction using cardiopulmonary bypass (CPB) improved these mechanics post-surgery, indicating a net benefit.
Area of Science:
- Pediatric Cardiology
- Respiratory Physiology
- Thoracic Surgery
Background:
- Congenital heart malformations frequently cause abnormal pulmonary hemodynamics, impacting respiratory mechanics.
- Cardiopulmonary bypass (CPB) during corrective surgery can lead to lung atelectasis, further impairing lung function.
Purpose of the Study:
- To investigate the impact of pulmonary blood flow (PBF) on respiratory mechanics in pediatric patients.
- To evaluate if surgical correction benefits outweigh CPB-induced lung compromise.
Main Methods:
- Studied 23 children (2-120 months) undergoing cardiac surgery.
- Measured respiratory mechanics (dynamic and static elastance, resistance) before and after CPB.
- Utilized pulmonary-to-systemic blood flow ratio as an index of PBF.
Main Results:
- Increased PBF correlated with significantly elevated dynamic and static lung elastance and resistance (220-330% predicted).
- No correlation was found between mean pulmonary artery pressure (MPAP) and respiratory mechanics.
- Post-CPB, dynamic elastance and resistance normalized in patients with increased PBF.
Conclusions:
- Elevated PBF significantly impairs respiratory mechanics in children with congenital heart defects.
- Surgical correction, despite CPB, leads to improved respiratory mechanics post-operatively.
Abstract:
Congenital heart malformations are often associated with altered pulmonary hemodynamics. Lesions associated with increased pulmonary blood flow (PBF) or increased mean pulmonary artery pressure (MPAP) may in turn alter respiratory mechanics. Surgical correction of these cardiac defects frequently involves the use of cardiopulmonary bypass (CPB), during which the lung may be partially or completely atelectatic for lengthy periods, further compromising lung mechanics. The aims of this study were to document the effect of PBF on respiratory mechanics in children and to determine whether the detrimental effects of CPB were outweighed by the potentially positive effects of the corrective surgery. Twenty-three children (2-120 mo) undergoing surgery were studied while anesthetized, paralyzed, and mechanically ventilated. Pulmonary to systemic blood flow ratio was used as an index of PBF. Seventeen children had lesions associated with increased PBF (group 1), while six had decreased or normal PBF (group 2). Respiratory mechanics were measured just before the commencement of CPB and within approximately 2 h after the cessation of CPB, with the chest closed. Dynamic elastance (Ers,dyn) and resistance (RRS) were calculated from flow, volume (V), and pressure (Pao) measurements, using multiple linear regression with a volume-dependent single compartment model. Static elastance (ERS,st) was calculated from Pao and V measurements obtained when deflating the lung in steps from a maximal Pao of 30 cm H2O. ERS,dyn, ERS,st, and RRS increased significantly with increasing PBF to 220-330% predicted. There was no correlation between MPAP and respiratory mechanics. After CPB, ERS, dyn and RRS fell to normal levels in group 1.(ABSTRACT TRUNCATED AT 250 WORDS)