Date of Award

January 2018

Document Type

Open Access Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

Manuel Fontes

Abstract

Abstract: Coronary artery graft surgery (CABG) using a cardiopulmonary bypass (CPB)

pump to allow for stopping the heart, commonly designated as “on pump CABG” or

ONCAB, requires complete anticoagulation and is associated with significant

postoperative anemia. In addition, a reduction in postoperative platelet counts is relatively

common in large part due to heightened activation of hemostatic pathways and platelet

consumption secondary to blood passing through the CPB circuit. It has been

demonstrated that both anemia and nadir platelet counts after ONCAB are associated

with the incidence and severity of postoperative acute kidney injury (AKI). Over the past

several years, techniques have been refined for performing CABG without CPB,

commonly designated as “off pump CABG” or simply OPCAB. This approach removes

the need for anticoagulation thus potentially reducing postoperative bleeding and anemia,

and negates the effect of CPB on platelet consumption. Whether OPCAB surgery

mitigates the severity of postoperative anemia and thrombocytopenia relative to ONCAB,

however, remains unclear. Furthermore, it remains unknown if the association between

nadir platelet counts and AKI evident in ONCAB patients is present following OPCAB.

The present study was designed to test the hypotheses that: a) nadir platelet counts and

hemoglobin values, as well as bleeding and transfusion requirements differ between

ONCAB and OPCAB surgeries; b) the postoperative recovery of platelet counts and

hemoglobin values is more protracted in ONCAB vs. OPCAB; and c) that hemostatic

derangements are more closely associated with postoperative AKI in ONCAB as

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compared to OPCAB surgeries.

Methods: With IRB approval, a retrospective study from a single institution was

conducted involving 634 adult patients undergoing elective OPCAB (n=255) or ONCAB

(n=379). Data were captured for demographics, medical history, surgical characteristics,

postoperative blood loss (defined as chest tube output in the first 48 hours), hemoglobin

levels and platelet counts, and blood product transfusions. Between groups, daily median,

postoperative nadir, and discharge values for hemoglobin and platelets were compared

with nadir counts defined as the median lowest in-hospital value measured over the first 5

postoperative days and at discharge. In addition, the incidence of frank

thrombocytopenia, defined as platelet values of < 74 x 109/dL, was compared along with

the administration of packed red blood cells (RBC), fresh frozen plasma (FFP) and

platelet suspensions. AKI was defined according to KDIGO criteria, whereby

postoperative serum creatinine rise >50% or 0.3 mg/dL was indicative of injury. The

incidence of AKI was then determined for the OPCAB and ONCAB groups, both as a

whole and when subdivided into the segment of each group that was thrombocytopenic.

Results: The ONCAB and OPCAB cohorts were similar in regard to age (67 + 10 vs 67

+ 10), and male/female distribution (80/20 vs 72/28). For both groups, the median nadir

platelet values were observed on the second postoperative day and were not different

(145K vs 142K, p =0.44). Similarly, the incidence of thrombocytopenia was the same

following both OPCAB and ONCAB (5.88% vs. 5.54%) surgeries. Median nadir

postoperative hemoglobin concentration in OPCAB patients was 10.10 mg/dl and

occurred on postoperative day 2. In ONCAB patients, the median nadir postoperative

hemoglobin concentration was not different (9.90 mg/dl, p = 0.95) but occurred on

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postoperative 4. There was no difference in postoperative bleeding measured by chest

tube output between ONCAB vs. OPCAB (892 + 421 mL vs. 850 + 441 mL, p = 0.24).

The incidence of red blood cell (RBC) transfusion was comparable between groups. In

contrast, both rates of FFP (ONCAB 20% vs. OPCAB 8%; p<0.001) as well as platelet

transfusion (ONCAB 35% vs. OPCAB 10%; p<0.001) were different. Overall the pattern

of postoperative platelet recovery was comparable, with both cohorts recovering beyond

baseline values by postoperative day 5. The overall incidence of postoperative AKI was

comparable between ONCAB vs. OPCAB [33.3% (n=126) and 34.5% (n = 88)]. Patients

(combined ONCAB and OPCAB) who developed severe thrombocytopenia (n=36) had a

higher rate of AKI as compared to those with normal platelet counts (55.6% vs. 32.4%;

p=0.004). Further, intragroup analysis (ONCAB only) demonstrated a higher incidence of

AKI in those with severe postoperative thrombocytopenia as compared to patients with

“normal” platelet counts [62% (n=13) vs. 32% (n = 113); p =<0.004]. However, the same

analysis of OPCAB patients showed no difference in the incidence of AKI [47% (n =7)

vs. 34% (n=81); p = 0.31] for severe thrombocytopenia vs. normal platelet counts.

Conclusion: Our findings demonstrate that contrary to the study hypotheses, ONCAB

and OPCAB surgeries are actually similar in regard to postoperative thrombocytopenia,

anemia, bleeding, red blood cell transfusion rates, and recovery patterns for hemoglobin

and platelets. Despite these similarities, there were higher rates of FFP and platelet

transfusions in the ONCAB group. Overall, the incidence of AKI was the same when

comparing the entirety of both groups. However, in the subgroup of patients with

postoperative thrombocytopenia, patients who underwent ONCAB had a markedly higher

rate of AKI.

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