Postoperative Hematocrit and Adverse Outcomes in Pediatric Cardiac Surgery Patients: A Cross-Sectional Study From the Society of Thoracic Surgeons and Congenital Cardiac Anesthesia Society Database Collaboration.

Study type: A retrospective cross-sectional study

Methods: The Society of Thoracic Surgeons Congenital Heart Surgery Database (STS-CHSD) and Congenital Cardiac Anesthesia Society Database Module (2014-2019) were accessed. These are databases of congenital and paediatric cardiac surgical operations in North America. Multivariable logistic regression models, adjusting for covariates in the STS-CHSD mortality risk model, were used to assess the relationship between postoperative haematocrit and primary outcomes of operative mortality or any major complication. Operations after which the oxygen saturation is typically observed to be < 92% were classified as cyanotic and ≥ 92% as acyanotic.


  • 27,462 index operations were included, with 4909 (17.9%) being cyanotic and 22,553 (82.1%) acyanotic.
  • The median [25th percentile, 75th percentile] hematocrit on arrival to the ICU in the cyanotic group was 40.7 [36.6, 45.0] percent vs 36.0 [32.0, 40.0] percent in the acyanotic group.
  • Operative mortality occurred more often in the cyanotic versus the acyanotic group, 5.5% vs 1.3%. Major postoperative complications were more common in the cyanotic versus the acyanotic group, 30.3% vs 11.9%.
  • For cyanotic patients, each 5% incremental increase in haematocrit over 42% was associated with a 1.31-fold (95% confidence interval [CI], 1.10-1.55; P = 0.003) increase in the odds of operative mortality and a 1.22-fold (95% CI, 1.10-1.36; P < 0.001) increase in the odds of a major complication.
  • For acyanotic patients, each 5% incremental increase in hematocrit >38% was associated with a 1.45-fold (95% CI, 1.28-1.65; P < 0.001) increase in the odds of operative mortality and a 1.21-fold (95% CI, 1.14-1.29; P < 0.001) increase in the odds of a major complication.
  • Secondary outcomes were clinical complications, duration of mechanical ventilation and hospital length of stay.

Take Home Message

  • High hematocrit on arrival to the intensive care unit (ICU) is associated with increased operative mortality and major complications in pediatric patients following cardiac surgery.
  • No association was observed between medium range haematocrit values, defined as 36% to 42% in the cyanotic group and 32%-40% in the acyanotic group, and adverse outcomes.


  • Is there any recent research, evidence or study on a similar question?
    1. High haematocrit targets have generally been favoured in congenital cardiac surgery, but concerns remain about the association between high haematocrits and the association with morbidity and mortality in paediatric postcardiac surgical patients.
    2. Recent reviews of paediatric intensive care data showed similar clinical outcomes can be achieved with more conservative transfusion triggers.
    3. Recent research from prospective observational studies on paediatric postcardiac surgical patients finds that transfusion practices vary greatly between centres and that transfusion triggers vary between and within acyanotic and cyanotic patient groups.
    4. Blood transfusions have been associated with increased risk of infection, length of ICU and hospital stay, duration of mechanical ventilation, and mortality in the paediatric population.
    5. This study is novel as it examines haematocrit as a marker of the target for transfusion which has been less studied than transfusion trigger.
    6. The tolerable upper limit of the haematocrit in the paediatric postcardiac population is poorly defined.


  • What are the strengths of the study?
    1. The novelty of the study is the focus on haematocrit as the target of blood transfusion, rather than targets for transfusion triggers or outcomes of transfusion vs no transfusion.
    2. Surgical procedures were classified into “acyanotic” vs “cyanotic” based on the expected circulatory physiology, as clinically this is a primary consideration affecting transfusion triggers in the paediatric cardiac surgery population.
    3. The study is of a large scale (27,462 cases) which adds to the knowledge in this area.
    4. Relevant preoperative and postoperative factors were appropriately included in the multiple regression modelling.


  • What are the limitations of the study?
    1. It is a retrospective cross-sectional study, and as such is prone to bias and can identify associations but not causation.
    2. Additional studies will be needed to understand the optimal haematocrit at the time of ICU admission.


  • Is the study applicable to our practice or to our population?
    1. The results are applicable to our paediatric cardiac surgery population.
    2. The results show there is a threshold range for haematocrit values, beyond which, the overall risk of major complications or operative mortality increases linearly.


Reviewed by Dr Bojana Stepanovic