Monitoring in Thoracic Surgery

Intraarterial Catheterization

Most practitioners routinely place an intraarterial catheter in thoracic surgery. For mediastinoscopic exams, a right-sided catheter will help monitor for brachiocephalic artery compression (but has the disadvantage of not working as well when this occurs); a left-sided catheter functions continuously, but if placed a right-sided pulse oximetry probe should be placed, as it will assist in pointing out brachiocephalic artery compression. For thoracotomies, the radial artery catheter should be in the dependent arm, as it can then assist in the recognition of axillary artery compression (due to an inadequate chest roll).

Another important reason for intraarterial catheterization is the ability to draw frequent ABGs. SpO2 is inadequate in thoracic surgery because at high saturations, it becomes insensitive – knowledge of PaO2 is important, as it gives on a sense for the margin of safety (a patient with 400 mm Hg on FiO2 of 1.0 will not likely desaturate during OLV, whereas a person at 200 mm Hg likely will). It is important to develop a habit of checking an ABG at the same time following initiation of OLV – Miller recommends 20 minutes. This will allow the anesthesiologist to develop a sense for who is moving towards true desaturation during OLV (overall incidence is 1-10%).

Central Venous and Pulmonary Artery Catheterization

Indications are no different than in other operations, however in these cases the internal jugular vein is the preferred placement site, as the external jugular vein often kinks during lateral decubitus positioning and a pneumothorax associated with a subclavian placement can be disastrous during one lung ventilation. While many centers routinely monitor CVP in thoracic cases, it is commonly believed that CVP readings are not reliable in an open-chest, laterally-positioned patient. [Miller’s Anesthesia, 7th ed. 2009. p 1832]

Note also that the PA catheter is most commonly placed in the R lower lobe – in R lung or lobe resections, the PA catheter needs to be directed into the L lung. Intentional direction of the PA catheter into the L lung can be achieved 50% of the time by placing the patient in the R lateral position (R-side down, L-side up) [Parlow JL et al. J Cardiothorac Vasc Anesth 6: 202, 1992]. If the PA catheter is thought to have migrated into the operative lung, it must be withdrawn prior to vascular clamping. Because of these risks, plus others known to be associated with PA catheters, as well as the belief that cardiac output may not be reliable in a laterally-positioned open-chest one-lung-ventilated patient, the risk-benefit profile of a PA catheter is less favorable in thoracic surgery patients than in other patient populations. [Miller’s Anesthesia, 7th ed. 2009. p 1832]

Transesophageal Echocardiography

Generally not routine in most thoracic procedures, although is commonly used during lung transplantation. That said, there have been reports of tumor identification and/or description of important anatomic characteristics (ex. invasion of the heart, compression of the PA) using TEE [Manguso L et al. Chest 93: 144, 1988; Pothoft G et al. Pneumologie 446: 111, 1992; Neustein SM et al. Can J Anaesth 40: 664, 1993]. Also, 9% of patients given 15 cm H2O PEEP (ex. during OLV) will show a PFO, which TEE can detect – these patients may desaturate during OLV, and TEE can help diagnose why. One particular disadvantage of TEE in thoracic surgery is its relative inability to quantitatively image the RV.