Allogeneic red blood cell transfusion: Physiology of oxygen transport

Cerebral Oxygen Metabolism Before and After RBC Transfusion in Infants Following Major Surgical Procedures

OBJECTIVE

Although infants following major surgery frequently require RBC transfusions, there is still controversy concerning the best definition for requirement of transfusion in the individual patient. The aim of this study was to determine the impact of RBC transfusion on cerebral oxygen metabolism in noncardiac and cardiac postsurgical infants.

DESIGN

Prospective observational cohort study.

SETTING

Pediatric critical care unit of a tertiary referral center.

PATIENTS

Fifty-eight infants (15 after pediatric surgery and 43 after cardiac surgery) with anemia requiring RBC transfusion were included.

INTERVENTIONS

RBC transfusion.

MEASUREMENTS AND MAIN RESULTS

We measured noninvasively regional cerebral oxygen saturation and microperfusion (relative cerebral blood flow) using tissue spectrometry and laser Doppler flowmetry before and after RBC transfusion. Cerebral fractional tissue oxygen extraction and approximated cerebral metabolic rate of oxygen were calculated. Fifty-eight RBC transfusions in 58 patients were monitored (15 after general surgery, 24 after cardiac surgery resulting in acyanotic biventricular physiology and 19 in functionally univentricular hearts including hypoplastic left heart following neonatal palliation). The posttransfusion hemoglobin concentrations increased significantly (9.7 g/dL vs 12.8 g/dL; 9.7 g/dL vs 13.8 g/dL; 13.1 g/dL vs 15.6 g/dL; p < 0.001, respectively). Posttransfusion cerebral oxygen saturation was significantly higher than pretransfusion (61% [51-78] vs 72% [59-89]; p < 0.001; 58% [35-77] vs 71% [57-88]; p < 0.001; 51% [37-61] vs 58% [42-73]; p = 0.007). Cerebral fractional tissue oxygen extraction decreased posttransfusion significantly 0.37 (0.16-0.47) and 0.27 (0.07-039), p = 0.002; 0.40 (0.2-0.62) vs 0.26 (0.11-0.57), p = 0.001; 0.42 (0.23-0.52) vs 0.32 (0.1-0.42), p = 0.017. Cerebral blood flow and approximated cerebral metabolic rate of oxygen showed no significant change during the observation period. The increase in cerebral oxygen saturation and the decrease in cerebral fractional tissue oxygen extraction were most pronounced in patients after cardiac surgery with a pretransfusion cerebral fractional tissue oxygen extraction greater than or equal to 0.4.

CONCLUSION

Following RBC transfusion, cerebral oxygen saturation increases and cerebral fractional tissue oxygen extraction decreases. The data suggest that cerebral oxygenation in postoperative infants with cerebral fractional tissue oxygen extraction greater than or equal to 0.4 may be at risk in instable hemodynamic or respiratory situations.

Anemia management after acute brain injury

Anemia is frequent among brain-injured patients, where it has been associated with an increased risk of poor outcome. The pathophysiology of anemia in this patient population remains multifactorial; moreover, whether anemia merely reflects a higher severity of the underlying disease or is a significant determinant of the neurological recovery of such patients remains unclear. Interestingly, the effects of red blood cell transfusions (RBCT) in moderately anemic patients remain controversial; although hemoglobin levels are increased, different studies observed only a modest and inconsistent improvement in cerebral oxygenation after RBCT and raised serious concerns about the risk of increased complications. Thus, considering this "blood transfusion anemia paradox", the optimal hemoglobin level to trigger RBCT in brain-injured patients has not been defined yet; also, there is insufficient evidence to provide strong recommendations regarding which hemoglobin level to target and which associated transfusion strategy (restrictive versus liberal) to select in this patient population. We summarize in this review article the more relevant studies evaluating the effects of anemia and RBCT in patients with an acute neurological condition; also, we propose some potential strategies to optimize transfusion management in such patients.

Blood component transfusion in critically ill patients

PURPOSE OF REVIEW

This review summarizes the current evidence base for commonly transfused blood components with a particular focus on the nonacutely bleeding patient.

RECENT FINDINGS

There remains little definitive evidence to guide transfusion practices in the critically ill. The most rigorous evidence to guide red blood cell (RBC) transfusion practice is derived from the Transfusion in Critical Care Trial (TRICC Trial) that was published in 1999. Specific subgroups of patients may be at particular risk of the adverse effects of anemia, and require further study. There are no randomized controlled trials addressing clinically important outcomes evaluating frozen plasma, platelet thresholds, or impaired platelet activity in the critically ill.

SUMMARY

As all blood components have some level of risk, the general approach to transfusion should be one of minimization. For the nonacutely bleeding critically ill patient, a RBC transfusion trigger of 70 g/l is clinically acceptable. For patients at potentially higher risk of adverse effects related to anemia such as those with septic shock, severe and/or acute ischemic heart disease, or brain injury, a higher threshold (80-90 g/l) may be considered. There is insufficient evidence to recommend specific thresholds for transfusion of frozen plasma or platelets in the critically ill.

Intraoperative transfusion threshold and tissue oxygenation: a randomised trial

BACKGROUND AND OBJECTIVES

Transfusion with allogeneic red blood cells (RBCs) may be needed to maintain oxygen delivery during major surgery, but the appropriate haemoglobin (Hb) concentration threshold has not been well established. We hypothesised that a higher level of Hb would be associated with improved subcutaneous oxygen tension during major spinal surgery.

MATERIALS AND METHODS

Fifty patients aged 18 years or older scheduled for spinal fusion with instrumentation were included and randomised to receive RBCs at either a Hb concentration of 7·3 g dL(-1) (restrictive group) or a Hb concentration of 8·9 g dL(-1) (liberal group) (Registration no.: H-C-2009-072). Oxygen tension was measured with a polarographic electrode placed subcutaneously over the left deltoid muscle. The primary endpoint was subcutaneous oxygen tension at the time most patients were still undergoing surgery.

RESULTS

Forty-eight patients were included in the intention-to-treat analysis; 25 patients in the restrictive group and 23 patients in the liberal group. The median change in subcutaneous oxygen tension 60 min after surgical incision was -0·79 and -0·75 kPa in the restrictive and the liberal groups, respectively (P = 0·78). No significant difference was found in the lowest subcutaneous oxygen tension; -2·07 vs. -1·95 kPa in the restrictive and the liberal groups, respectively (P = 0·85).

CONCLUSION

A Hb concentration transfusion threshold of 8·9 g dL(-1) was not associated with a higher subcutaneous oxygen tension during major spinal surgery than a threshold of 7·3 g dL(-1), but the trial was compromised by methodological difficulties.

Red blood cell transfusion in the critically ill patient

Red blood cell (RBC) transfusion is a common intervention in intensive care unit (ICU) patients. Anemia is frequent in this population and is associated with poor outcomes, especially in patients with ischemic heart disease. Although blood transfusions are generally given to improve tissue oxygenation, they do not systematically increase oxygen consumption and effects on oxygen delivery are not always very impressive. Blood transfusion may be lifesaving in some circumstances, but many studies have reported increased morbidity and mortality in transfused patients. This review focuses on some important aspects of RBC transfusion in the ICU, including physiologic considerations, a brief description of serious infectious and noninfectious hazards of transfusion, and the effects of RBC storage lesions. Emphasis is placed on the importance of personalizing blood transfusion according to physiological endpoints rather than arbitrary thresholds.

Red blood cell transfusion for infants with single-ventricle physiology

The purpose of this study was to assess how red blood cell (RBC) transfusions impact hemodynamic parameters in infants with single-ventricle lesions. This was a retrospective chart review. The setting was a pediatric cardiac intensive care unit at a tertiary care children's hospital. Fifty-nine patients <1 year of age with single-ventricle physiology who received a blood transfusion between December 2007 and April 2009 were analyzed. They received a total of 183 transfusions. Exclusion criteria included transfusions given within 72 h of cardiac surgery or transfusions given to patients with active bleeding. There were no interventions. The study population was divided into terciles based on pretransfusion hemoglobin (Hgb) concentration. The pretransfusion Hgb concentration in group A was 7.8 to 12.3 gm/dl, in group B was 12.4 to 13.2 gm/dl, and in group C was 13.3 to 15.7 gm/dl. Heart rate, blood pressure, arterial saturation, and cerebral near-infrared spectroscopy (cNIRS) values before transfusion, as well as at 1, 2, 4, 8, and 12 h after transfusion, were collected. There was significant improvement in diastolic blood pressure, arterial saturation, and cNIRS in group A after 12 h. Transfusions given in group B also resulted in improvement in diastolic blood pressure and arterial saturation, with less robust response of cNIRS. In group C, only arterial saturation values increased significantly. RBC transfusions can improve hemodynamics and markers of oxygen delivery in infants with single-ventricle physiology, but further studies are needed to determine an optimal Hgb level in this population. Interventions to increase Hgb above this level may be of limited benefit.