Capnodynamic determination of effective pulmonary blood flow and end expiratory lung volume : studies in children and paediatric animal models

Sammanfattning: Dynamic capnography is a haemodynamic and respiratory monitoring technique enabling continuous cardiac output (Effective Pulmonary Blood Flow, COEPBF) and end expiratory lung volume (Effective Lung Volume, ELV) assessment in mechanically ventilated subjects. The method utilizes variations in exhaled CO2, implemented via periods of deliberate changes in the respiratory pattern. The method has been validated against high precision reference methods in animal experiments. Data from these studies have pointed to a potential use also in children, a patient group suffering from the lack of reliable and easy accessible cardiac output/functional residual capacity (CO/FRC) monitoring methods. We have validated dynamic capnography in a series of paediatric clinical studies and experimental models. COEPBF was tested for agreement of absolute values and ability to detect change against suprasternal Doppler, COSSD, in anaesthetized children and against transpulmonary flow probe, COTS, in a porcine model mimicking the clinical study. COEPBF was also tested for the same qualities, against COTS and CO2 Fick (COFick) in a model of hypoxia induced pulmonary hypertension in piglets. The respiratory parameter ELV was examined for consistency against helium wash out in a paediatric rabbit model of CO2-induced pneumoperitoneum. In addition to this, the same protocol was used to determine the PEEP level associated with most favorable conditions for preservation of lung homogeneity and CO2 clearance. COEPBF showed good agreement and trending ability when compared to COTS and COFick in the experimental setting. In the clinical study, COEPBF performed in the expected way. The reference method COSSD exhibited operator dependent qualities and appeared less reliable than COEPBF. Absolute values and changes in FRC could be monitored adequately by ELV, provided the application an adequate PEEP. The adequate PEEP level was also associated with optimal preservation lung homogeneity and CO2 removal, thus suggesting the use higher level of PEEP during laparoscopy. Dynamic capnography appears to be a reliable and accurate method for continuous CO and FRC monitoring and is a promising concept for future studies.