Gas Exchange during Controlled Ventilation in Children with Normal and Abnormal Pulmonary Circulation

Abstract

R, NIKLASSON L, DREFELDT B. Gas exchange during controlled ventilation in children with normal and abnormal pulmonary circulation: a study using the single breath test for carbon dioxide. Anesth Analg 1986;65:645-52. Carbon dioxide single breath tests (SBT-COJ were obtained during anesthesia and controlled ventilation in 42 children about to undergo thoracic surgery. The tests were obtained with a computerized system based on the Servo ventilator. The system made on-line corrections for compressed volume, apparatus deadspace, and rebreathing. Children with normal pulmonary circulation had excellent gas exchange with high Pao, values, a mean alveolar deadspace fraction (VoalviVTalv) of 0.10, and a gently sloping phase 111 of SBT-CO,. Children with pulmonary hyperperfusion (left to right shunting) due to an atrial septal defect or a ventrical septal defect had significantly lower Paoz values, steeper phase 111 slopes, and a greater spead of values for VualvlV?'alv. Children with pulmonary hypoperfusion due to pulmonary stenosis in combination with intracardiac right to left shunting had extremely low Pao, values, and "adult" values for V,alviVTalv. They required increased ventilation to maintain CO, homeostasis. In the pooled material, the airway deadspace was strongly correlated to height, weight, and age. The airway deadspace was unaffected when tidal volume was increased by 37%, and ventilatory frequency simultaneously reduced by 30%, a maneuver that left alveolar ventilation unchanged. This is probably because an endinspiratory pause was used; when frequency is reduced the length of the end-inspiratory pause increases, allowing proximal diffusion of the alveolarlfresh gas interface.Many children presenting for cardiovascular surgery have lesions that affect perfusion of the lung. A patent ductus arteriosus (PDA) will give rise to a small to moderate degree of pulmonary hyperfusion, i.e., left to right (L-R) shunt. Greater degrees of L-R shunt can be seen with an atrial septal defect (ASD) or a ventricular septal defect (VSD), the latter often giving rise to pulmonary hypertension. In these, arterial oxygenation is only moderately reduced.When pulmonary stenosis (PS) occurs as an isolated defect, the circulation is normal or hypokinetic, but PS combined with an intracardiac right to left (R-L) shunt gives rise to pulmonary hypoperfusion with hypoxemia. In transposition of the great arteries (TGA), both the pulmonary and systemic circulations may be hyperkinetic, but the large R-L shunt may Part of this work has been presented in abstract form. Br J Anaesth 1985;57817-8.

Pulmonary Deadspace and Postoperative Outcomes in Neonates Undergoing Stage 1 Palliation Operation for Single Ventricle Heart Disease*

“…Vd/Vt was lower in the BTS group when compared with that in the RV-PA group at all time points. Fletcher et al (9) reported high Vd/Vt (0.41) in patients with pulmonary hypoperfusion. Although Vd/Vt values decreased over the early postoperative period, a large difference in arterial to end-tidal CO 2 (thus Vd/Vt) remained at the time of extubation from mechanical ventilation.…”

“…Vd/Vt is increased in parenchymal lung disease and in diseases that alter lung perfusion. Children with congenital heart disease (CHD) characterized by either pulmonary hypoperfusion or cyanosis have been shown to have higher Vd/Vt, and higher Vd/Vt has been shown to prolong duration of mechanical ventilation and length of hospitalization after cardiac surgery for CHD (9,10). Children with congenital heart disease (CHD) characterized by either pulmonary hypoperfusion or cyanosis have been shown to have higher Vd/Vt, and higher Vd/Vt has been shown to prolong duration of mechanical ventilation and length of hospitalization after cardiac surgery for CHD (9,10).…”

Sudden decrease in end-tidal carbon-dioxide in a neonate undergoing surgery for type B interrupted aortic arch

“…However, in patients with CHD, there exist large gradients between the PaCO 2 and the end-tidal exhaled alveolar gas carbon-dioxide (P ET CO 2 ). [2,3] In patients with cyanotic CHD, the difference is related to both increases in dead space ventilation and intracardiac venous admixture, whereas in patients with acyanotic CHD, the PAH resulting from the increased pulmonary blood flow may cause a greater ventilation perfusion mismatch resulting in increased PaCO 2 -P ET CO 2 gradients. [4] This difference may be further exaggerated in anesthetized and paralyzed patients with PAH due to atelectasis and increase in dead space ventilation.…”

Anaesthesia for thoracic surgery in children

“…Therefore patients undergoing this procedure are frequently premature, ventilator‐dependent neonates in whom there is an increase in pulmonary relative to systemic blood flow. This causes increased lung water with a consequent decrease in lung compliance ( 74) and impaired V/Q matching ( 75). Surgical access is through a left thoracotomy, and the duct can normally be visualized with minimal lung retraction.…”