Respiratory function testing is safe in patients with abdominal aortic aneurysms

According to a former US politician ‘‘There are known knowns . . .There are known unknowns . . .But there are also unknown unknowns . . . ’’ This phrase is also apt in the respiratory function laboratory. One particular ‘‘known unknown’’ is the safety of respiratory function testing (RFT) in patients with abdominal aortic aneurysms (AAAs). Abdominal aortic aneurysm affects approximately 4% to 7% of men and 1% to 2% of women older than 65 years of age. Aneurysms >5.5 cm diameter in men and >5.0 cm in women are at significant risk of rupture and are considered for elective repair unless major contraindications exist. Respiratory function testings are recommended in the preoperative assessment of patients with AAA to reduce the morbidity and mortality associated with elective AAA repair. However, performing RFTs in patients with large (>6 cm) aneurysms is a potential contraindication because of concern of AAA rupture. An important reason for the persistence of this concern is a lack of data on the safety of performing RFTs in patients with AAA. We conducted a retrospective observational study of patients who had undergone preoperative RFTs for infrarenal nonruptured AAA between October 2008 and March 2014 in our institution. Patients’ hard copy medical records and electronic discharge summaries were reviewed. The study was approved by the Gold Coast Hospital and Health Service Human Research Ethics Committee (HREC/13/QGC/129). We identified 56 patients who had undergone RFTs during their AAA preoperative assessment. Median age was 73 years (range: 55-83), and 14% were women. The median size of the AAA was 6 cm (range 5-13 cm). Spirometry was performed in all 56 patients, diffusion capacity was performed in 29 (52%) patients, and lung volumes were measured in 26 (46%) patients. Chronic obstructive pulmonary disease was found in 43 (77%) patients, among whom 20 (36%) patients had mild (forced expiratory volume in 1 second [FEV1] 80% predicted), 15 (27%) patients had moderate (FEV1 50%-79% predicted), and 8 (14%) patients had severe (FEV1 30%-49% predicted) disease. Importantly, there were no reported early or late complications following RFTs. Three patients declined to perform lung volume testing because of concern about their AAA size (size of the AAA was 7 cm in 2 patients and 5.5 cm in 1 patient). In all, 45 (80%) patients underwent operative intervention for the AAA (open AAA repair in 29 patients and endovascular aneurysm repair in 16 patients). The median time between a patient performing RFT and undergoing operative intervention for the AAA was 41 days (range 3-353 days). At the end of the study, 7 (13%) had died, and the median time of the death since performing RFT was 138 days (range 60-1286 days). Among the 7 patients who died, 3 patients had surgical intervention for the AAA and died within 30 days of surgery due to postoperative complications. Our study demonstrates the safety of performing RFTs even in patients with large AAAs. Additionally in a recent study, 188 patients with large AAAs (>5.5 cm) underwent preoperative spirometry and cardiopulmonary exercise testing, implying that spirometry can be safely performed in patients with large AAAs. Although our contribution to global geopolitics has been negligible, we think the results of our study contribute to the burden of proof that RFTs are safe even in patients with large AAAs and make it one of the ‘‘known knowns.’’