Erroneous radial artery pressure reading during dissection of the right internal mammary artery.

Erroneous radial artery blood pressure reading occurred during asymmetrical chest wall retraction required for internal mammary artery dissection, used for coronary artery bypass grafting. The most likely cause was subclavian artery compression. It is advised to insert a catheter in the contralateral radial artery when the internal mammary artery is going to be dissected. When bilateral internal mammary arteries are used, a femoral artery catheter should be inserted.