Author: Chase Doyle
New research suggests that preoperative coagulation testing can be instrumental in predicting cardiac surgery outcomes. According to a retrospective analysis of nearly 1,400 patients’ medical records, preoperative international normalized ratio (INR) is significantly associated with 30-day mortality in cardiac surgery patients. The data showed tha t for every 1-unit increase of INR, the chance of dying in 30 days after heart surgery was dramatically increased 80 times.
“An odds ratio of 80 for every 1-unit increase of INR is very significant,” said Daniel A. Barlowe, MD, MBA, a resident in the Department of Anesthesiology and Perioperative Medicine at the University of Louisville School of Medicine, in Kentucky. “Based on these results, if a patient can be stabilized in terms of coagulation without having to rush to the operating room by giving the appropriate factors or vitamin K, that extra time is worthwhile.”
As Dr. Barlowe, the lead author of the study, reported, although preoperative coagulation studies including baseline INR, prothrombin time, partial thromboplastin time, platelet number and platelet aggregation tests are routinely performed in cardiac surgery, the ability of these tests to predict clinical outcomes has remained controversial. In addition, said Dr. Barlowe, previous research by senior author Jiapeng Huang, MD, PhD, a cardiac anesthesiologist and professor at the institution, has shown that patients’ preoperative aspirin use in heart valve surgery more frequently led to reoperation due to bleeding compared with the group without aspirin.
Elevated INR and High Risk for Death
As Dr. Barlowe reported at the 2018 annual meeting of the Society of Cardiovascular Anesthesiologists (abstract 52), a higher value of preoperative INR was associated with an increased 30-day mortality rate. The odds ratio was 80.40 times higher (P=0.02) with every 1-unit increase of INR. Functional platelet number, on the other hand, had a negative association with death rate; a 1-unit decrease in functional platelet number resulted in an odds ratio of 0.99995 for 30-day mortality. The data also showed that INR was significantly associated with hospital length of stay (relative risk ratio, 1.95), while functional platelet number was only moderately associated with reoperations for bleeding.
Although preoperative INR was found to be significantly associated with cardiac surgery outcomes, researchers are still exploring the underlying causes of elevated INR.
“We understand that high INR is bad for patients undergoing heart surgery, but we don’t quite understand why the INR is high in these patients,” Dr. Barlowe said. “It could be from anticoagulants, antiplatelet medications, or it could be from poor liver function or nutritional status.”
According to Dr. Barlowe, future research will focus on finding the causative culprits for the change in INR. In the meantime, he said, preoperative coagulation testing could be incorporated into risk models to better predict cardiac surgery outcomes.
Timing Is Critical
These results underscore the vital importance of timing of cardiac surgery, said senior author Dr. Huang, as well as the value in normalizing coagulation status before operating on a patient.
“For example, if something bad happened during [a] coronary artery stent placement, and the patient has received large amounts of anticoagulant medications, is it a good idea to rushed [sic] the patient to the operating room for heart surgery?” Dr. Huang questioned. “Our data, however, suggest that we should wait until the INR and platelet functions, which are indications of the coagulation function, are back to normal.” Patients should be given fresh frozen plasma (FFP) or prothrombin complex concentrate (PPC), he continued, while waiting for the antiplatelet medications to wear off in the next few days. Overall, to circumvent these risks in the operating room, Dr. Huang emphasized the need for more prospective studies regarding preoperative coagulation parameters and clinical outcomes. “Heart surgery is high risk,” Dr. Huang concluded. “We need to be sure we’re picking the right time to do it.”
“There are risks and benefits of each modality,” Dr. Barlowe added. “If you take patients to the operating room, the obvious benefit would be fixing the cardiac pathology, but the risk would be excessive bleeding and, potentially, death, as we found out.
“However, even transfusion with FFP or PCC carries risks, such as transfusion-related acute lung injury, sepsis and volume overloads. This is why examining all these factors in a prospective study is so important.”