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Monitoring adequacy of ventilation by capnometry during thoracotomy in dogs
A E Wagner1, J S Gaynor, C I Dunlop
1Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins 80523, USA.
Objective:
To determine whether end-tidal partial pressure of carbon dioxide (PETCO2) was a reliable estimate of PaCO2 in dogs undergoing thoracotomy.
Design:
Case series.
Animals:
18 dogs that underwent thoracotomy.
Procedure:
PaCO2 and PETCO2 were measured shortly after induction of anesthesia, while dogs were breathing spontaneously; 5 minutes prior to initial skin incision, while dogs were receiving intermittent positive-pressure ventilation (IPPV); 5, 30, and 60 minutes after the thoracic cavity was opened, while dogs were receiving IPPV; and after the thoracic cavity was closed and evacuated, when dogs were again breathing spontaneously. For each period, arterial-end-tidal difference in partial pressure of carbon dioxide (PaCO2-PETCO2) was compared with PaCO2-PETCO2 for the preceding period.
Results:
Significant changes in PaCO2-PETCO2 from one period to the next were not detected except when values obtained 5 minutes after the thoracic cavity was opened were compared with values obtained 5 minutes before incision. The PaCO2-PETCO2 was not constant for individual dogs.
Clinical Implications:
PETCO2 was not a reliable indicator of adequacy of ventilation during thoracotomy in these dogs, because it differed greatly from PaCO2, and PaCO2-PETCO2 was not consistent.