April 2023 - Surgical Critical Care

April 2023
EAST Monthly Literature Review

"Keeping You Up-to-Date with Current Literature"
Brought to you by the EAST Manuscript and Literature Review Committee

This issue was prepared by EAST Mentoring Committee Members Emily A. Grimsley, MD, and Jennifer To, DO.


Thank you to Haemonetics for supporting the EAST Monthly Literature Review.


In This Issue: Surgical Critical Care

Article 1 reviewed by Emily A. Grimsley, MD and Jennifer To, DO
Association between Length of Storage of Transfused Packed RBC Units and Outcome of Surgical Critically Ill Adults: A Subgroup Analysis of the Age of Blood Evaluation Randomized Trial. Lehr AR, Hebert P, Fergusson D, Sabri E, Lacroix J. Crit Care Med. 2023 Mar 1;51(3):e73-e80.

Article 2 reviewed by Emily A. Grimsley, MD and Jennifer To, DO
Hemoglobin Concentration Impacts Viscoelastic Hemostatic Assays in ICU Admitted Patients. Roh DJ, Chang TR, Kumar A, Burke D, Torres G, Xu K, Yang W, Cottarelli A, Moore E, Sauaia A, et al. Critical Care Medicine. 2023 Feb 1;51(2):267-278.

Article 1
Association between Length of Storage of Transfused Packed RBC Units and Outcome of Surgical Critically Ill Adults: A Subgroup Analysis of the Age of Blood Evaluation Randomized Trial. Lehr AR, Hebert P, Fergusson D, Sabri E, Lacroix J. Crit Care Med. 2023 Mar 1;51(3):e73-e80.

The Age of Blood Evaluation (ABLE) trial compared the outcomes of fresh (< 7 days old) versus standard issue red blood cell (RBC) transfusions in critically ill patients and found no differences in mortality or complications between the two groups. This study refuted prior claims that older RBC units were associated with worse clinical outcomes secondary to increased inflammatory mediators. Clinicians, however, continued to question the effects of older RBCs in surgical patients. As anemia in surgical patients is multifactorial from blood loss, coagulopathy, cytokine inhibition, hemodilution, and iatrogenesis, these patients tend to require more blood product and transfusions than medical critically ill patients. Prior studies have also suggested that surgery patients have higher risks of adverse outcomes than their trauma and critically ill counterparts. This study by Lehr et al. evaluated a subset of the original ABLE patients admitted to the ICU following a major surgical procedure (elective and urgent cases). Notably, trauma patients were excluded. Similar to the original trial, baseline characteristics, comorbidities, number of RBC transfusions, and transfusion reactions were collected. Intention-to-treat was utilized. Primary outcome was all-cause 90-day mortality. Secondary outcomes were in-ICU, in-hospital, and 6-month mortality, in addition to rates of organ failure, infection, need for hemodynamic or renal support, length of stay and length of ventilator support.

They included 320 surgical ICU patients, who were randomized to two groups: fresh blood n=172; standard blood n=148. Baseline patient characteristics did not differ for the two groups. Baseline hemoglobin was similar between fresh and standard groups (7.9±1.6 and 7.8±1.1g/dL, respectively). Average length of RBC storage for the fresh blood group was 7.2±6.4 vs. 20.6±8.4 days for the standard group (p<0.0001). There was no difference in mortality nor complications (ARDS, heart failure, MI, DVT/PE, nosocomial infection, transfusion reaction, and multi-system organ dysfunction) between the two groups. The results of this study are consistent with the results of the ABLE study. Demographics and transfusion requirements were similar in both studies suggesting that the conclusions of the ABLE study can also be applied to surgical critically ill patients. These results are also consistent with studies involving surgical patients as well as other subgroups. Their small sample size is a limitation and larger studies are needed to confirm these results, though their structure of a multicenter RCT and homogeneity between the fresh and standard groups gives significant strength to their results. Given a strong study design and agreement with existing literature, there appears to be no benefit to moving towards a fresh-blood-only approach.
 

Article 2
Hemoglobin Concentration Impacts Viscoelastic Hemostatic Assays in ICU Admitted Patients. Roh DJ, Chang TR, Kumar A, Burke D, Torres G, Xu K, Yang W, Cottarelli A, Moore E, Sauaia A, et al. Critical Care Medicine. 2023 Feb 1;51(2):267-278.

Rotational thromboelastometry (ROTEM) and thromboelastography (TEG) have become commonplace in the assessment of coagulopathy in the bleeding patient. However, studies have demonstrated lower hemoglobin (Hgb) concentration is associated with paradoxical hypercoagulable ROTEM/TEG results. This paradoxical finding is thought to be due to an in-vitro (in-laboratory) testing artifact. Given the growing reliance on ROTEM/TEG to guide transfusions in the bleeding patient, it is critical to further evaluate this paradoxical hypercoagulability in this vulnerable population.  The authors sought to assess the clinical relevance of lower Hgb concentrations on ROTEM/TEG results in ICU patients. This was a prospective observational cohort study of patients admitted to the ICU with diagnosis of a spontaneous primary intracranial hemorrhage (ICH). All adult patients with baseline Hgb and baseline ROTEM/TEG results were included in the study. Trauma patients, those who received transfusions prior to viscoelastic testing, or patients with baseline coagulopathy were excluded. Patients were divided into three cohorts: 1) ICH and ROTEM (n=39), 2) ICH and TEG (n=239), 3) non-ICH surgical ICU patients with pre-operative ROTEM (n=121). All patients were managed according to American Heart Association treatment protocols. The primary outcomes were ROTEM/TEG coagulation kinetics and clot strength. Secondary outcomes were the other ROTEM/TEG parameters. A separate in-vitro study was performed to assess the change in viscoelastic assay tracings with change in Hgb. Standard coagulation profiles were also performed on these samples to ensure PT, aPTT, and fibrinogen levels were unchanged.

The authors found no correlation between Hgb and coagulation time (ROTEM)/R time (TEG), however there was a positive correlation between Hgb and coagulation kinetics (ROTEM clot formation time, r=0.46; TEG K time, r=0.49; both p≤0.01), an inverse correlation between Hgb and clot propagation (alpha angle; ROTEM r=-0.66; TEG r=-0.48; both p<0.0001), and clot strength (ROTEM maximum clot firmness r=-0.52; TEG max amplitude r=-0.40, both p<0.01). In-vitro sample dilution showed that with decreasing Hgb, there were faster coagulation kinetics and greater clot strength, though these results were not significant. There were no significant associations between Hgb and PT, aPTT, or platelet count. There was a moderate inverse relationship between fibrinogen and Hgb, but this effect was not significant in mixed-model analyses, leaning towards an overall lack of effect. Overall, these findings suggest that lower hemoglobin concentrations may have an artifactual effect on viscoelastic assay testing results in ICU patients. ROTEM/TEG results may appear normal in patients with low hemoglobin even if they are mildly hypocoagulable. Further studies are needed to validate these results as well as evaluate the need to correct this artifact. This study highlights the important need to scrutinize ROTEM/TEG results in the setting of anemia, particularly in the bleeding patient.