NATIONAL HARBOR, MD. – Angiotensin receptor blockade on the morning of a major orthopedic surgery was associated with a tripling in the risk of acute kidney injury – a link probably driven by the drugs’ association with perioperative hypotension, a retrospective analysis has found.
"Our study does support the idea of withholding beta-blockers on the morning of these major procedures," Dr. Eileen Hennrikus reported at the annual meeting of the Society of Hospital Medicine.
Extant literature has confirmed a link between beta-blockers and hypotension in connection with cardiovascular surgery, but not orthopedic surgery. Dr. Hennrikus, of the Milton S. Hershey Medical Center, Hershey, Penn., examined the link in patients undergoing elective spine fusions, total hip or total knee replacement – procedures typically associated with greater blood loss than cardiovascular surgeries.
She used retrospective data from 922 patients who had undergone any of the three surgeries during 2010. Induction hypotension was defined as a systolic blood pressure of 80 mm Hg for at least 10 minutes within a half hour of anesthesia induction. Intraoperative hypotension was defined as a systolic blood pressure of 80 mm Hg for at least 10 minutes during maintenance anesthesia. The measure of acute kidney injury was an increase in serum creative of at least 0.3 mg/dL, or a 50% increase over preoperative levels.
Of the entire cohort, 37% (343) patients received their prescribed angiotensin receptor blocker or angiotensin converting enzyme inhibitor on the morning of their surgery. The incidence of induction hypotension was significantly greater in those patients in patients who took the medication than in those who did not (12% vs. 6.7%; OR 1.93). Acute kidney injury was also significantly more common among those who had the medications, however (8% vs. 2%; OR 5.4). Intraoperative hypotension was not significantly different between the groups.
Dr. Hennrikus conducted a multivariate analysis to further tease out the relationship between the medications and acute kidney injury. The regression controlled for age, medical comorbidities (diabetes, coronary artery disease, hypertension, and congestive heart failure), body mass index, medications (diuretics, beta-blockers, calcium channel blockers, general anesthesia-induction agents, and vasopressors), and blood loss.
After adjustment for all of those factors, angiotensin blockade conferred a threefold increase in the risk of acute kidney injury (OR 2.97). Although in the primary analysis, intraoperative hypotension had not been significantly associated with the drugs, it more than doubled the risk of kidney injury the risk (OR 2.6) in the multivariate analysis.
The model also revealed something of a surprise, Dr. Hennrikus said: Body mass index was an independent risk factor for acute kidney injury. For every 5 kg/m2 increase in BMI, the risk increased by 29% (OR 1.29).
Acute kidney injury exerted its own influence over hospital length of stay and mortality. The length of stay was significantly longer in patients who had kidney injury (6. days vs. 3 days). Two-year mortality was also significantly higher (6% vs. 2%).
Neither Dr. Hennrikus nor her coinvestigators reported having any financial conflicts.