INTRODUCTION: Carbon dioxide angiography may be an alternative for IVC filter placement.
CASE PRESENTATION: 60 y/o African American female was diagnosed with pulmonary embolism by CT after one week of progressive shortness of breath. She had negative duplex dopplers of the lower extremities . Anti coagulation was initiated and the patient was discharged home. Upon leaving, she fell and sustained a fracture of the right distal fibula which was casted. She was readmitted for open repair of her fracture and to manage anticoagulation. Her past medical history was significant for diabetes mellitus, hypertension, hyperlipidemia and gout. Her physical exam was notable for a morbidly obese female, resting comfortably. Her temperature was 37.4, BP 160/70, pulse 74, respiratory rate 19, and oxygen saturation 94% on 2L NC. Notable exam findings included Mallampati 4 airway and pedal edema with her right leg in a removable cast with chronic venous stasis change. Laboratory data suggests chronic carbon dioxide retention and renal insufficiency with values of 36 and 1.8 respectively: ABG 7.32/pCO2 80/pO2 75. Multiple surgeries were planned with recurrent need to interrupt anticoagulation. Her ABG was suggestive of OHS and potentially OSA. The recommendations included retrievable IVC filter, nocturnal BiPAP and outpatient sleep study. Interventional radiology placed an IVC filter using carbon dioxide angiography secondary to her renal disease. She did not receive any sedation. Post procedure she was obtunded on 100% NRB with an ABG: 7.14/pCo2 greater than 100, p02 120. She was intubated with a diagnosis of hypercapnic respiratory failure secondary to carbon dioxide angiography.
DISCUSSION: Carbon dioxide has been used since the 1960s for IVC filters. The carbonic anhydrase catalyzes carbon dioxide and water to form carbonic acid which subsequently dissociates into hydrogen ions and bicarbonate. The bicarbonate moves quickly into the plasma where it dissolves. The reverse process occurs to release carbon dioxide into the lungs. Large IVC injection and selective pulmonary artery injections into rats demonstrated no gas in the pulmonary vein suggesting that even massive volumes are eliminated in one pass through the lungs. The advantages to carbon dioxide angiography are that it is non-toxic, invisible, highly compressible, non viscous, buoyant and rapidly absorbed. There is no allergic potential and no renal toxicity thereby it is ideal for complex cases requiring larger amounts of contrast. Additionally, collateral arteries are better demonstrated, arteriovenous shunting can be observed in tumors and AV malformations and minute amounts of bleeding can be visualized. Carbon dioxide use specifically for IVC filter placement is indicated only if contrast contraindicated. More numerous and selective injections are required as the right renal vein as a posterior structure does not readily fill with carbon dioxide and an IVC thrombus may go undetected. Additionally, the use of carbon dioxide in patients with respiratory compromise is debated secondary to the theoretical risk of exacerbating carbon dioxide retention. Therefore, it is recommended to decrease the volume and increase the time interval for injection. Most centers do not have a protocol and follow the dictum “as much as we need.” “Carbon dioxide should not be a problem unless a patient….cannot respond with increased ventilation.”
CONCLUSIONS: In a morbidly obese patient with baseline hypercarbia/hypoventilation the additional carbon dioxide load introduced during carbon dioxide angiography resulted in hypercarbic respiratory failure secondary to the patient’s inability to respond to the increasing carbon dioxide load with increased ventilation. Carbon dioxide as a contrast agent holds promise for complicated procedures and patients who could not otherwise have contrast but there are no sizeable human trials to demonstrate safety. There are no standard protocols at this time although many institutions are developing guidelines to regulate speed and amount of carbon dioxide is administered.
Reference #1 Hawkins,Caridi, Carbon Dioxide (CO2) digital subtraction angiography: 26 year experience at the University of Florida. European Radiology. 1998;8: 391-402
Reference #2 Shaw,Kessel, The current status of the use of carbon dioxide in diagnostic and interventional angiographic procedures. Cardiovascular Interventional Radiology. 2006; 29: 323-331
Reference #3 Hawkins et al, Carbon dioxide in angiography to reduce the risk of contrast-induced nephropathy. Radiol Clin N Am, 2009; 47: 813-825
DISCLOSURE: The following authors have nothing to disclose: Kelly Newton
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