A protocol for prospective observational study to determine if non-anaemic iron deficiency worsens postoperative outcome in adult patients undergoing elective cardiac surgery: the IDOCS study

Lachlan F Miles,David A Story,Kate L Burbury,Vanessa Pac Soo,Stephane Heritier,Sabine Braat

doi:10.1186/s13741-022-00239-2

Lachlan F Miles, David A Story + Show 4 more

Open Access

https://doi.org/10.1186/s13741-022-00239-2

Copy DOI

Abstract

BackgroundPre-operative anaemia has been associated independently with worse outcomes after cardiac surgery in adults and is often caused by absolute or functional iron deficiency. Iron deficiency is a continuum ending with anaemia, and therefore it is plausible that pre-operative early or ‘non-anaemic’ iron deficiency may also be associated with worse outcomes in patients undergoing cardiac surgery.MethodsWe have designed a prospective, observational study to determine if there is an association between non-anaemic iron deficiency and worse outcomes after cardiac surgery in adults. Patients without anaemia undergoing elective cardiac surgery will be allocated to an iron-deficient and an iron-replete group based on standard pre-operative blood tests (ferritin, transferrin saturation and C-reactive protein). The primary outcome is days alive and at home on postoperative day 30. The key secondary outcomes are days alive and at home on postoperative day 90 and readmission to acute care. Other secondary outcomes include health-related quality of life questionnaires, quality of postoperative recovery, postoperative complications, changes in haemoglobin concentration, and requirement for allogeneic blood products. The planned study sample size is 240 patients per group, which has 83% power to detect a median difference of 1.25 days in the primary outcome. The study commenced in March 2018, and recently completed recruitment, with data audit and cleaning ongoing.DiscussionThis study will be conducted using a rigorous, prospective observational design; it will provide peak bodies and clinicians with high-quality evidence concerning the associations between non-anaemic iron deficiency and patient-centred outcomes after elective cardiac surgery. Our primary and key secondary outcomes are known to have great importance to clinicians and patients alike and align with the recommendations of the StEP-COMPAC group for outcomes in prospective peri-operative research. The definition used for iron deficiency accounts for both absolute and functional iron deficiency and make use of standard pre-operative blood tests to make this determination, easing the transition of results into clinical practice. The study will be conducted in two relatively high-volume centres in a single high-income country. This limits the generalisability of study results to similar centres.Trial registrationAustralian and New Zealand Clinical Trials Registry (ACTRN12618000185268). Registered 5 February 2018.

Highlights

Pre-operative anaemia has been associated independently with worse outcomes after cardiac surgery in adults and is often caused by absolute or functional iron deficiency
Increasing attention is being paid to the continuum of iron deficiency and anaemia in patients undergoing cardiac surgery(Rössler et al, 2020; Miles et al, 2018a; Immohr et al, 2020; Piednoir et al, 2011; Hubert et al, 2019)
This is despite the observation that end-organ manifestations of iron deficiency may be present prior to anaemia becoming apparent (Favrat et al, 2014)

Summary

Introduction

Pre-operative anaemia has been associated independently with worse outcomes after cardiac surgery in adults and is often caused by absolute or functional iron deficiency. Iron deficiency is a continuum ending with anaemia, and it is plausible that pre-operative early or ‘non-anaemic’ iron deficiency may be associated with worse outcomes in patients undergoing cardiac surgery. Anaemia has been independently associated with worse outcomes after cardiac surgery (Rössler et al, 2020; Klein et al, 2016; Hogan et al, 2015; Miles et al, 2018a). In the adult patient undergoing cardiac surgery, preoperative anaemia is independently associated with increased mortality, increased hospital stay, and increased allogeneic transfusion requirement (Klein et al, 2016). It is possible that iron deficiency, in the absence of anaemia, might be associated with worse postoperative outcomes, not to the same degree as iron deficiency anaemia

Objectives

Methods

Findings

Conclusion