End-expiratory lung volume assessment using helium and carbon dioxide in an experimental model of pediatric capnoperitoneum.

BACKGROUND: Capnoperitoneum during laparoscopy leads to cranial shift of the diaphragm, loss in lung volume and risk of impairedgas exchange. Infants are susceptible to these changes and bedside assessment of lung volume during laparoscopy might assist with optimizing the ventilation. Thus, the primary aim was to investigate the monitoring value of a continuous end-expiratory lung volume (EELV) assessment methodbased on CO2 dynamics (EELVCO2 )in a pediatric capnoperitoneummodel by evaluating the correlation and trending ability against heliumwashout (EELVHe ). METHODS: Intra-abdominal pressure (IAP) was randomly varied between 0, 6 and 12 mmHg with CO2 insufflation, while positive end-expiratory pressure (PEEP) levels of 3, 6 and 9 cmH2 O were randomly applied in eight anesthetized and mechanically ventilated chinchilla rabbits. Concomitant EELVCO2 and EELVHe and lung clearance index (LCI) were obtained under each experimental condition. RESULTS: Significant correlations were found between EELVCO2 and EELVHe before capnoperitoneum (r=0.85, p<0.001), although increased IAP distorted this relationship. The negative influence of IAP was counteracted by the application of PEEP 9, which restored the correlation between EELVCO2 and EELVHe and resulted in 100% concordance rate between the methods regarding changes in lung volume. EELVHe and LCIshowed a curvilinear relationship, and an EELVHe of approximately 20mlkg(-1) , determined with a receiver operating characteristic curve, was associated with near-normal LCI values. CONCLUSION: In this animal model of pediatriccapnoperitoneum, reliable assessmentofchanges inEELV based on EELVCO2 requires an open lung strategy, defined as EELV above approximately 20 mlkg(-1) .