1997 OPEN FORUM Abstracts
PRELIMINARY ANALYSIS: PREDICTING ARTERIAL CO2 IN POST OPERATIVE CORONARY ARTERY BYPASS PATIENTS.
John Emberger BS RRT, Herbert Patrick MD, Department of Pulmonary Care, Thomas Jefferson University Hospital, Inc, Philadelphia PA
Background: Endtidal CO2 (ETCO2) monitoring is commonly used on ventilated patients in acute care, yet ETCO2 is not relied upon for precise data. Main factors affecting PaCO2-ETCO2 gradient (Pa-ETCO2) for intubated patients are deadspace and airway obstruction. If coronary artery bypass (CABG) patients have stable deadspace and no acute airway obstruction, Pa-ETCO2 may remain relatively constant for each sequential arterial blood gas (ABG) while the patient is intubated. Hypothesis: We wanted to analyze the change in Pa-ETCO2 of sequential ABG's for intubated CABG patients. Methods: We prospectively studied post-op CABG patients with ETCO2 monitoring and collected ABG results for a one month period. Copies of ETCO2 waveforms were also collected and analyzed. Pa-ETCO2 was calculated for each ABG. The change in Pa-ETCO2 ([delta]Pa-ETCO2) was calculated for each pair of sequential ABG's on each patient. Duration between sequential ABG's was uncontrolled (range: 2 to 21 hours). Only patients with "normal" (not obstructive) ETCO2 waveforms were analyzed (waveforms that have expiratory plateau). Results: Fourteen CABG patients had "nomal" waveforms and were included in the study. A total of twenty six pairs of sequential ABG's were identified and included.
Data from 14 CABG patients having sequential pairs of ABG's:
n Avg ± Std Dev
PaCO2, torr 52 36.81 ± 6.47
ETCO2, torr 52 28.44 ± 5.94
Pa-ETCO2 of each ABG, torr 52 08.37 ± 2.96
[delta]Pa-ETCO2 of each pair of
sequential ABG's, torr 26 00.27 ± 1.80
Conclusions: The average Pa-ETCO2 fluctuates by 8.37 ± 2.96 torr in this population of CABG patients with normal ETCO2 waveforms. However, in this group of patients, the average [delta]Pa-ETCO2 of sequential ABG's in each individual patient only fluctuated 0.27 ± 1.8 torr. These results show that with each PaCO2, the next PaCO2 could be predicted within 0.27 ± 1.8 torr without an ABG drawn. These results could help to safely decrease utilization of ABG's for this population of patients.