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Literature Review

Comparison of Two Different Red Blood Cell Transfusion Thresholds on Short-Term Clinical Outcomes of Patients Undergoing Aortic Surgery with Deep Hypothermic Circulatory Arrest

Wang Y, Ji H. J Cardiothorac Vasc Anesth. 2016;30(5):1163-1166.

Reviewers: Igor Zhukov, MD1

  1. Emory University, Atlanta, GA
Background

Transfusion thresholds and the impact of transfusion during various surgical and nonsurgical patient care encounters is a continuously evolving topic. It appears that the expansion of evidence is mounting against the practice of liberally transfusing patients, citing at a minimum negligible benefits, while some authors openly caution of the possibility for harmful outcomes to patients. Confounded by surgical complexities, this topic remains a fruitful field for both research and discussion.

Methods

This is a retrospective study, evaluating a cohort of 74 patients undergoing aortic surgery under deep hypothermic circulatory arrest (DHCA), performed at a single academic center. Patients underwent their care by one of two surgical teams, consisting of a surgeon, anesthesiologist, and perfusionist. The patient also had differing transfusion thresholds based on hemoglobin values: 8g/dl vs 10g/dl, respectively. These constraints were used during the cardiopulmonary bypass (CPB) and at separation from bypass. ICU care was similar for both groups, with minimum hemoglobin value set at 8g/dl, and transfusion was tailored based on the patient’s clinical status.  

Blood and blood product use was compared among the two groups, as well as various 30-day morbidity and mortality metrics. The two groups’ demographic and surgical variables were well-matched, with the exception of longer bypass time and cross clamp time in the restrictive group 171 ± 39 min vs 152 ± 43 min and 99 ± 30 min vs 72 ± 20 min, respectively. The lowest DHCA nasopharyngeal temperature also was statistically different (21.5 vs 19.3 0C) between the restrictive and liberal groups.

Results

The liberal group received more packed red blood cell (PRBC) transfusion intra- and perioperatively: 5.9 ± 4.3 vs 2.6 ± 2.8 (P=.00) and 8.5±6.9 vs 3.9±4.8 (P=.001) units, respectively. Platelets usage also was statistically higher in the liberal transfusion group: 2.3 ± 0.5 vs 1.8 ± 0.7 (P=0.001). Curiously, the use of prothrombin complex concentrate was doubled in the restrictive group: 870 ± 372 units, as compared to 341 ± 534 units (P=.000) in the liberal transfusion group.

No difference was observed between groups with respect to 30-day mortality: 3/40 (7.5%) in restrictive group vs 2/34 (5.9%) in liberal group (P=1.000). In the morbidity category, 24-hour urine output was higher in a liberal transfusion group (4401 ± 1265 ml vs 3793 ± 1247 ml). Other morbidity metrics, such as the need for re-exploration, dialysis rates, infection rate, stroke, duration of mechanical ventilation, ICU and hospital length of stay, and chest tube outputs all were not statistically different among the two groups.

Discussion

Authors note that a definite major limitation of this study is its retrospective and observational nature. Also, it appears that not only were the groups potentially mismatched by virtue of having two completely different surgical teams, but also there was a significant procedural mismatch in the duration of the bypass and cross-clamp, both of which are implicated in increased need for transfusion.1-2

Finally, it can be argued that the power of this study is insufficient to draw serious conclusions regarding the effects of transfusion thresholds on the primary outcome, mortality, least to make any implications of the secondary outcome surrogates of morbidity in these patients undergoing complex surgery under DHCA conditions. Indeed, even in a very recent trial analyzing a substantially larger number of patients under randomized-controlled conditions, the uncertainty of patient benefit from restrictive transfusion strategy once again persisted.3

As much as this cliché is unnecessary, only a multicenter collaboration and potentially a meta-analysis of high-quality randomized data can, in my opinion, change the current approach to transfusion.

References
  1. Williams JB, Phillips-Bute B, Bhattacharya SD, et al. Predictors of massive transfusion with thoracic aortic procedures utilizing deep hypothermic circulatory arrest. J Thorac Cardiovasc Surg. 2011;141(5):1283–1288.
  2. Hajjar LA, Vincent JL, Galas FR, et al. Transfusion requirements after cardiac surgery: the TRACS randomized controlled trial. JAMA. 2010;304(14):1559-1567.
  3. Murphy G, Pike K, Rogers C, et al. Liberal or Restrictive Transfusion after Cardiac Surgery. New Engl J Med. 2015;372(11):997-1008.