THE ASSOCIATION BETWEEN ANAEMIA WITH OR WITHOUT IRON DEFICIENCY STATUS AND PHYSICAL EXERCISE CAPACITY BEFORE CARDIAC SURGERY

K.W.D. Yau¹, M.J. Underwood², G.M. Joynt¹, A. Lee¹

Background: Preoperative anaemia is associated with poorer clinical outcomes and higher healthcare costs in patients undergoing cardiac surgery. Iron deficiency is a common cause of anaemia. Low preoperative physical capacity is also associated with adverse postoperative outcomes and may be associated with preoperative anaemia or iron deficiency. This sub-study is part of an ongoing quasi-experimental study exploring the prevalence of anaemia and iron deficiency before cardiac surgery, and examines the potential benefits of preoperative intravenous iron therapy on exercise capacity and postoperative outcomes.

Purpose: The objective of this sub-study was to assess the association between anaemia/iron deficiency and physical exercise capacity in patients before elective cardiac surgery.

Methods: A prospective cohort study at a university hospital in Hong Kong was conducted from July 2018 to June 2020. Haemoglobin, ferritin, transferrin saturation and C-reactive protein concentrations were measured. Anaemia/iron deficiency status was classified into four groups (Group A: Anaemia with iron deficiency; Group B: Anaemia without iron deficiency; Group C: No anaemia but with iron deficiency; Group D: No anaemia or iron deficiency) before surgery. Physical capacity was estimated using the 6-minute walk test (6MWT) with peak oxygen update (VO_{2 peak}) estimation based on the parameters obtained during test, and was compared with that using the Chinese Veteran Specific Activity Questionnaire (CVSAQ). Multiple regression was used to determine the association between disease status groups and physical capacity measures, adjusting for age, gender, obesity (BMI ≥25 kg.m^-2) and frailty (Clinical Frailty Scale ≥4).

Results: Of the 113 patients, there were 79 (69.9%) males, 76 (67.3%) frail participants and 54 (47.8%) were obese. The median (IQR) age was 64 (58-69) years. There were 11 (9.7%), 25 (22.1%), 6 (5.3%) and 71 (62.8%) patients in Groups A, B, C and D respectively. Disease status was associated with total distance walked (P=0.009) and estimated VO_{2 peak} (P=0.014), but not with age-adjusted estimated physical capacity from CVSAQ (P=0.134). Anaemic patients (Groups A+B) had shorter mean total distance walked (-38.4, 95%CI: -62.8 to -14.0 metres) and lower estimated mean VO_{2 peak} (-0.9, 95%CI: -1.5 to -0.2 ml.kg^-1.min^-1) than non-anaemic patients (Groups C+D). Compared to the reference (Group D) where the mean total distance walked was 395 (95%CI: 380-410) metres, Group B patients had shorter mean total distance walked (351, 95%CI: 330-372 metres)[P=0.001]. Group B patients had lower estimated mean VO_{2 peak} (11.0, 95%CI: 10.5-11.5 ml.kg^-1.min^-1) than the reference group (12.1, 95%CI: 11.6-12.6 ml.kg^-1.min^-1)[P=0.003].

Conclusion(s): Anaemic patients demonstrated lower objectively measured physical capacity than those who did not have anaemia. Those without iron deficiency (Group B) also demonstrated lower objectively measured physical capacity than those who did not have anaemia or iron deficiency (Group D). Because of small patient numbers in Groups A and C, additional associations with physical exercise capacity were inconclusive.

Implications: Anaemia is a potential target for preoperative optimisation, however anaemia without iron deficiency is rarely treated with iron supplementation. Physiotherapists who have an emerging role in preoperative risk screening and management shall aware that its strong association with reduced physical capacity and alternative interventions may be needed for these patients.

Funding, acknowledgements: The trial is supported by the Department of Anaesthesia and Intensive Care, The Chinese University of Hong Kong

Keywords: Cardiac surgery, Anaemia, Physical capacity

Topic: Service delivery/emerging roles

Did this work require ethics approval? Yes

Institution: The Chinese University of Hong Kong

Committee: Joint CUHK-New Territories East Cluster Clinical Research Ethics Committee

Ethics number: 2018140