Pulmonary thrombo-embolism

Pulmonary thrombo-embolism is also associated with a decrease in PETCO₂ as is in pulmonary air embolism.  Breen et al,¹ in an animal study, found that PETCO₂ decreases when right pulmonary artery (RPA) was occluded in anesthetized, ventilated, thoracotomized dogs.  By 1 min after RPA occlusion, CO₂ volume exhaled per breath decreased from 9.3(2.8) to 7(2.6) ml and end-tidal CO₂ decreased from 28.7(4.2) to 21.8(3.3) mm Hg. During the ensuing 70 min, VCO₂/breath increased back to baseline but PETCO₂ was still 13% less than baseline.  Both PaCO₂ (41.5(1.7) to 55.1(8.1) mm Hg) and PvCO₂ (48.2(1.9) to 62.8(6.5) mm Hg) steadily increased and approached equilibrium by 45 min of RPA occlusion. Cardiac output did not significantly change. The increased PaCO₂ was not detected by PETCO₂ which remained decreased due to increased alveolar dead space consequent to RPA occlusion. Breen et al² further showed in another study that intraoperative monitoring PETCO₂ can be used to monitor resolution of pulmonary embolus. Resolution of embolus results in progressive increases in PETCO₂ measurements. 

1. Breen PH, Mazumdar B, Skinner SC.  How does experimental pulmonary embolism decerase CO₂ elimination? Respir Physiol 1996;105(3):217-24.

2. Breen PH, Mazumdar B, Skinner SC.  Carbon dioxide elimination measures resolution of experimental pulmonary embolus in dogs.  Anesth Analg 1996;83(2):247-53.