End-tidal carbon dioxide in critically ill patients during changes in mechanical ventilation

R. A. Hoffman, B. P. Krieger, M. R. Kramer, S. Segel, F. Bizousky, H. Gazeroglu, M. A. Sackner

Research output: Contribution to journalArticlepeer-review

Abstract

Values of end-tidal CO2 (PET(CO2)) approximate Pa(CO2) in spontaneous breathing normal subjects and in stable patients receiving mechanical ventilatory support (MVS). Because marked inequality of ventilation/perfusion ratios in critically ill patients might affect this correlation, we assessed changes of PET(CO2) in predicting changes in Pa(CO2) (ΔPa(CO2)) and changes in minute ventilation (ΔV̇e) in this patient population. Twenty consecutive intubated patients 38 to 89 yr of age (mean, 70 yr) with respiratory failure while receiving MVS with indwelling arterial lines were studied. Settins on the mechanical ventilator were varied for frequency and tidal volume, and after a minimum of 5 to 10 equilibration, Pa(CO2) and PET(CO2) were measured. Vt and V̇e were recorded from the digital indicator of the pneumotachygraphy within the mechanical ventilator and corrected for compression volume in the respirator circuit. A total of 116 simultaneous measurements were performed. PET(CO2) correlated well with Pa(CO2) (r = 0.78, p < 0.001). The 95% confidence interval for the mean difference in Pa(CO2)-PET(CO2) was 4.0 ± 0.97 mm Hg. However, ΔPET(CO2) (measured from baseline) did not correlate as well with ΔPa(CO2) (r = 0.58, p < 0.001). In four patients, the trend in their PET(CO2) during changes in mechanical ventilation were in the opposite direction from trend in their Pa(CO2). Thus, many critically ill patients, who cannot be preidentified, have an inconstant Pa(CO2)-PET(CO2) gradient with changes of ventilation. Utilization of PET(CO2) as a noninvasive monitoring sutbstitute for trends in Pa(CO2) in critically ill patients may be misleading despite establishing an initial Pa(CO2)-PET(CO2) relationship.

Original languageEnglish
Pages (from-to)1265-1268
Number of pages4
JournalAmerican Review of Respiratory Disease
Volume140
Issue number5
DOIs
StatePublished - 1989
Externally publishedYes

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