Abstract
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.
