Institutions looking to reduce their incidence of acute kidney injury (AKI) after cardiac surgery should consider following the lead of researchers at the Johns Hopkins University School of Medicine, in Baltimore. Their goal-directed protocol was associated with a reduced incidence of the sometimes devastating adverse event within 72 hours of surgery, prompting them to suggest that colleagues consider adopting similar initiatives.
“We were looking at our institution’s rate of acute kidney injury, and found that they were no lower than anywhere else in the country,” said Viachaslau Barodka, MD, assistant professor of anesthesiology. “In fact, they were maybe a bit higher than the natural average. This was unacceptable to us, so we formed a working group to see what we can do to improve on this outcome in our adult cardiac surgery population.”
With that in mind, the researchers built a multidisciplinary team comprising anesthesiologists, surgeons, nephrologists, the ICU team and perfusionists at the institution. Once the team was formed, the researchers discussed their practice and consulted the literature for modifiable factors associated with cardiopulmonary bypass that might affect AKI risk after cardiac surgery. This work led to the development of the protocol (Table), which was implemented as a quality improvement measure in cardiac surgery patients at the institution in 2015.
|Table. Goal-Directed Perfusion Guidelines|
|Minimize CPB circuit volume||Use 3/800 instead of 1/200 tubing if possible for venous line Position CPB circuit closer to operating room table|
|Avoid “stress” on kidneys||Avoid mannitol in CPB prime|
|Avoid hypovolemia||Avoid RAP or ensure <10% decrease in mean arterial pressure or NIRS if using RAP Return all CPB perfusate to patient|
|Ensure tissue oxygenation||Maintain oxygen delivery >300 mL oxygen per minute per m2 body surface area|
|Monitor NIRS data to maintain at baseline|
|Reduce inflammatory cytokines and coagulation factor consumption||Use hemoconcentrator and zero-balance ultrafiltration Use heparin drip on CPB|
|Avoid splanchnic vasoconstriction||Minimize phenylephrine use; increase CPB flow first if possible|
|Limit rapidity of rewarming||Rewarm no faster than 1° C every 5 minutes Maintain temperature differential between arterial and venous blood <3° C|
|CPB, cardiopulmonary bypass; RAP, retrograde autologous priming; NIRS, near-infrared spectroscopy|
With the protocol established, the investigators then set out to determine its efficacy. To that end, they compared data from 88 cardiac surgery patients in whom the protocol was used with 88 matched controls using propensity scoring across 15 variables. The primary and secondary outcomes of the analysis were the incidence of AKI and the mean rise in serum creatinine within the first 72 hours after cardiac surgery. The two groups of patients were similar across all variables, including mean age and preoperative glomerular filtration rate. Nevertheless, controls received more mean phenylephrine on cardiopulmonary bypass (2.1 vs. 1.4 mg; P<0.001) and had a lower mean nadir oxygen delivery (241 vs. 301 mL oxygen per minute per m2; P<0.001).
New Protocol Proves Effective
“As expected, we saw a fairly significant reduction in postoperative acute kidney injury,” Dr. Barodka told Anesthesiology News.
Indeed, as reported at the 2017 annual meeting of the Society of Cardiovascular Anesthesiology (abstract SCA206), the incidence of AKI was found to be 23.9% in controls, significantly more than the 9.1% in patients who were treated using the goal-directed protocol (P=0.008). Furthermore, the incidences of stages 1, 2 and 3 AKI were 19.3%, 3.4% and 1.1% in controls, compared with 5.7%, 3.4% and 0% in the protocol patients. Control patients also exhibited a larger median percentage increase in creatinine from baseline (27% vs. 10%; P<0.001).
Yet as encouraging as these results may be, it was not always easy to convince practitioners to adopt the proposed protocol. “There were several staff members who said they didn’t think our current practice was a problem and wanted to continue the way we always had,” Dr. Barodka said. “Others thought it was a great idea. So in this case we found that the best strategy was to adopt the protocol with the providers who were open to the change, then share our results to show everyone the improvement,” he said. “When the rest of the team saw our results, they also started demanding the new protocol. And that’s how practice changes.”
Other institutions considering adopting similar measures would be best served to begin the process by exploring their own practices and outcomes, he added. “The No. 1 intervention to improve outcomes is awareness,” he described. “So if you want to improve acute kidney injury, you need to know what your rate is right now, and monitor it accordingly. Then you need to assemble multidivisional groups to look at your practice and the available literature, and go from there.”
James A. DiNardo, MD, professor of anesthesia at Harvard Medical School and the Francis X. McGowan, Jr., MD Chair in Cardiac Anesthesia at Boston Children’s Hospital, thought that the study will help pave the way toward what may ultimately become a regular part of clinical practice. “The authors have, for the most part, done an admirable job of assembling an evidence-based, goal-directed perfusion protocol,” Dr. DiNardo commented. “This study is an excellent first step in what hopefully will be the evolution of a well-devised, goal-directed protocol into conventional care.”