Infrared end‐tidal CO₂ measurement does not accurately predict arterial CO₂ values or end‐tidal to arterial P, gradients in rabbits with lung injury

Abstract

End-tidal PCO2 (PETCO2) measurements from two commercially available neonatal infrared capnometers with different sampling systems and a mass spectrometer were compared with arterial PCO2 (PaCO2) to determine whether the former could predict the latter in mechanically ventilated rabbits with and without lung injury. The effects of tidal volume, ventilator frequency and type of lung injury on the gradient between PETCO2 and PaCO2 (delta P(a-ET)CO2) were evaluated. Twenty rabbits were studied: 10 without lung injury, 5 with saline lavage and 5 with lung injury by meconium instillation. Paired measurements of PETCO2 by two infrared capnometers and a mass spectrometer were compared to PaCO2. In the rabbits without lung injury, the values from the infrared capnometers and mass spectrometer correlated strongly with PaCO2 (r > or = 0.91) despite differences in the slopes of the linear regression between PETCO2 and PaCO2 and in delta P(a-ET)CO2 (P < 0.05). Values from the mainstream IR-capnometer more closely approximated the line of identity than the regression between the sidestream IR-capnometer values or the mass spectrometer and PaCO2, but tended to overestimate PaCO2. The delta P(a-ET)CO2 was similar at all tidal volumes and ventilator frequencies, regardless of capnometer type. In the rabbits with induced lung injury, while there was a positive correlation between the slopes of the regression between PETCO2 and PaCO2 for both capnometers (r > or = 0.70), none of the regression slopes approximated the line of identity. The delta P(a-ET)CO2 was greater in rabbits with injured than noninjured lungs (P < 0.05). The delta P(a-ET)CO2 was similar among capnometers regardless of tidal volume, ventilator frequency, or type of lung injury. The 95% confidence interval of plots PaCO2 against PETCO2 was large for rabbits with injured and noninjured lungs.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation of end tidal and arterial carbon dioxide levels in critically Ill neonates and children

“…Previous studies reported an influence of both VI and P/F ratio on correlation of PaCO 2 and EtCO 2 , but we found only P/F ratio to be useful in assessing the effect of severity of lung disease on this relationship. [1213] There were several limitations that could have affected the result of this study. Probably, the sample size was not large enough to reveal the influence of VI on relationship; the role of dynamic compliance and oxygenation index as indicators of severe lung disease was not analyzed; effect of cointerventions such as surfactant therapy and time of suctioning the ET tube before the measurement was not taken into consideration; and co-existing conditions that could have adversely affected PaCO 2 and EtCO 2 relationship like shock/persistent hypotension were not excluded.…”

Accuracy of a New Low-flow Sidestream Capnography Technology in Newborns: A Pilot Study

“…These findings suggest that the primary pathophysiologic process was impaired compliance as opposed to decreased dead space ventilation consistent with recent data that acquired surfactant deficiency or dysfunction plays a significant role in these patients. 26 The descending slope and angle of the capnogram represent the inspiratory phase of ventilation, known as Phase III. We found a significant increase in the descending slope and angle when comparing mechanically ventilated newborns with and without lung disease.…”

The correlation and level of agreement between end-tidal and blood gas pCO2in children with respiratory distress: a retrospective analysis

“…In patients with significant pulmonary disease, it is generally believed that EtCO 2 values will not accurately reflect blood gas pCO 2 because of ventilation-perfusion mismatch, increased dead space, and/or increased shunt fraction. [ 18 - 21 ] In fact, a number of studies have demonstrated the inaccuracy of capnography in intubated and non-intubated patients with pulmonary disease. [ 20 , 22 - 25 ] However, most of these studies focused on patients with severe lung disease or used technology that is now considered out of date.…”