Intraoperative Hypoxemia from Compression of the Right Pulmonary Artery Caused by a Sternal Retractor (2008)

A 55-yr-old man presented to an outside hospital with an acute myocardial infarction. Within 24 h, he was transferred to our institution where he was scheduled for coronary artery bypass grafting. A preoperative transthoracic echocardiogram was unremarkable and showed an ejection fraction of 51%. His medical history was negative for any underlying pulmonary diseases. After induction of general anesthesia and sternotomy, the surgeon proceeded to place an internal mammary artery (IMA) sternal retractor, specifically, a Delacroix-Chevalier™ (Delacroix-Chevalier, Paris, France) asymmetric sternal retractor, and take down the left IMA (Fig. 1).1 Per the surgeon’s request, the patient’s tidal volumes were reduced from 600 to 500 mL to facilitate a more optimal visual field. Total minute ventilation was maintained. Six minutes later, the patient’s arterial blood pressure (BP) steadily declined and was accompanied by profound hypoxemia (Spo2 declined to the mid-60s) when the systolic BP decreased below 125 mm Hg. The patient was placed on 100% Fio2 and manually ventilated until his saturations slowly returned to the 90s. Simultaneously, his BP was treated with ephedrine and we reconfirmed placement of the endotracheal tube with a fiberoptic bronchoscope. This pattern was repeated three times over the next several minutes. An associated decline in end-tidal carbon dioxide (25–16 mm Hg) and a small increase in the pulmonary artery pressures (31–39/20–29) were noted. A transesophageal echocardiography (TEE) probe was inserted and demonstrated preserved left and right ventricular function and chamber sizes, no patent foramen ovale or shunt, no intracardiac mass or thrombus, but a very small compressed right pulmonary artery (RPA) (Fig. 2, Video clip 1; please see video clip available at www.anesthesia-analgesia.org).Figure 1.: Picture of a Delacroix-Chevalier™ sternal retractor in use in another patient. As shown, this retractor provides exposure through both downward pressure on the right hemisternum and elevation of the left hemisternum.Figure 2.: Midesophageal ascending aortic short axis view by transesophageal echocardiography color flow Doppler showing flow across the compressed right pulmonary artery (RPA). AO = aorta; MPA = main pulmonary artery.On inspection, the right side of the IMA sternal retractor appeared to have slipped and was angled down significantly into the mediastinum. Within 5 minutes of the initial TEE examination, take down of the IMA was completed and the sternal retractor repositioned. Repeat TEE examination now showed a normal caliber RPA (Fig. 3, Video clip 2; please see video clip available at www.anesthesia-analgesia.org). The rest of the surgical procedure proceeded uneventfully.Figure 3.: Midesophageal ascending aortic short axis view by transesophageal echocardiography color flow Doppler showing flow in the uncompressed right pulmonary artery (RPA). AO = aorta; MPA = main pulmonary artery.Compression of the RPA has often been cited in the literature.2–6 However, we were unable to find a report of external compression by an IMA sternal retractor as presented in this case. Other reported causes of intraoperative compression of the pulmonary artery include TEE probe insertion in a pediatric case,2 aortic aneurysm,3 an aneurysm from a saphenous vein graft,4 fibrous mediastinitis,5 and tumor.6 Potential causes of intraoperative hypotension and hypoxia also include acute myocardial infarction, acute pulmonary edema, pulmonary embolus, right endobronchial intubation, tracheal/lung mass, and patent foramen ovale with right to left shunting. In this case, these possibilities were excluded by both the fiberoptic bronchoscope and TEE. With compression of the RPA, pulmonary perfusion was decreased. The decrease was mild enough for oxygenation and cardiac output to be maintained at higher perfusion pressures but significant enough to be affected by declines in systolic BP below 125 mm Hg. Basal short axis views are useful for assessing the anatomy of the right ventricular outflow tract including the pulmonary artery. As seen in Figure 3, a standard view of the main and right pulmonary arteries is the midesophageal ascending aortic short axis view at the level of the aortic valve. It shows the main pulmonary artery at the level of its bifurcation. Anatomically, the main pulmonary artery branches into the left pulmonary artery (LPA) and RPA. The RPA can be traced for a distance of several centimeters while the LPA starts to give off its branches after a short distance from the bifurcation. Unlike the latter, the RPA can be seen from its origin when using the midesophageal ascending aortic short axis view. The LPA is obscured by the left mainstem bronchus that lies between the former and the esophagus. This can explain why it is not seen in this view. Intraoperative TEE was valuable in helping to determine a major contributor to this patient’s hemodynamic alterations and in excluding other potential causes already mentioned. Presumably, the use of other style retractors that are suspended above the patient, such as the Pittman™ (MN Scientific Instruments, Minneapolis, MN) or Rultract™ (Rultract, Cleveland, OH) retractors, would have avoided this complication. Anesthesiologists and surgeons alike should be aware of this rare contributor to hypotension with associated hypoxemia during the intraoperative period, especially when a Delacroix-Chevalier™ sternal retractor is being used. TEE should be readily available to help in evaluating and treating possible causes of such alterations.