Effect of cardiac output changes on exhaled carbon dioxide in newborn piglets.

INTRODUCTION: International neonatal resuscitation guidelines recommend that correct tube placement should be confirmed by clinical assessment and exhaled CO2 detection. Absence of exhaled CO2 after intubation suggests oesophageal intubation, non-aerated lungs, low tidal volume delivery, or low cardiac output. The relationship between changes in cardiac output and exhaled CO2 in neonates is unknown. The aim of the study was to determine if changes in cardiac output affect exhaled carbon dioxide in a porcine model of neonatal resuscitation.

METHOD: Term piglets (n=5) aged 3-4 days were anesthetised, intubated, instrumented and exposed to normocapnic hypoxia. Exhaled CO2 was continuously measured using a flow sensor (Respironics NM3(®)). Pulmonary artery blood flow, a surrogate for cardiac output was measured using an ultrasonic flow probe (Transonic(®)). A semi-quantitative CO2-detector (Pedi-Cap(®)) was placed between the tracheal tube and flow sensor to assess colour change at changing levels of cardiac output.

RESULTS: Median (IQR) pulmonary artery blood flow significantly decreased from 177 (147-177)mL/kg/min at baseline to 4 (3-26)mL/kg/min during hypoxia (p=0.02). Exhaled CO2 remained similar throughout the experiment, 47 (41-47)mmHg at baseline vs. 40 (38-41)mmHg at the end of the hypoxia (p=1.00). Additionally, at each time point, colour change at the Pedi-Cap(®) was observed.

CONCLUSION: A significant decrease in cardiac output was not associated with changes in exhaled CO2 or failure to achieve a Pedi-Cap(®) colour change.