When the anti-Xa level was 0.3-0.7IU/mL, the majority of samples from infants demonstrated a supra-therapeutic APTT, whilst adults tended to have a sub-therapeutic APTT. This may lead to under anticoagulation in infants or over anticoagulation in adults with risk of bleeding if APTT is used to monitor UFH. These results further strengthen existing evidence of the limitation of APTT in monitoring UFH. Discordance of APTT and anti-Xa level in adults and children may be due to elevation of fibrinogen level.

Objectives: To ascertain: i) the frequency of thrombocytopenia and heparininduced thrombocytopenia (HIT), ii) positive predictive value (PPV) of the pre-test probability score (PTPS) in identifying HIT iii) clinical outcome of HIT in adult patients receiving veno-venous (VV)-extracorporeal membrane oxygenation (ECMO) or veno-arterial (VA)-ECMO, compared to cardiopulmonary bypass (CPB). Design: A single-centre, retrospective, observational cohort study from January 2016 to April 2018 Setting: Tertiary referral centre for cardiac and respiratory failure Patients: Patients who received ECMO for >48hrs or had CPB during specified period Interventions: None. Measurements and Main Results: Clinical and laboratory data were collected retrospectively. PTPS and HIT testing results were collected prospectively. Mean age (standard deviation) of the EMCO and CPB cohorts were 45.4 (±15.6) and 64.9 (±13), p< 0.00001. Median duration of CPB was 4.6 [2-16.5] hrs compared to 170.4 [70-1008] hrs on ECMO. Moderate and severe thrombocytopenia were more common in ECMO compared to CPB throughout (p<0.0001). Thrombocytopenia increased in CPB patients on day 2 but was 4 normal in 83% compared to 42.3 % of ECMO patients at day 10. Patients on ECMO also followed a similar pattern of platelet recovery following cessation of ECMO. The incidences of HIT in ECMO and CPB were 6.4% (19/298) and 0.6% (18/2998) respectively p<0.0001). There was no difference in prevalence of HIT in patients on VV-ECMO (9/156, 5.7%) vs VA-ECMO (11/142, 7.7%), p=0.81. The PPV of the PTPS in identifying HIT in patients post-CPB and on ECMO were 56.25% (18/32) and 25% (15/60) respectively. Mortality was not different with (6/19, 31.6%) or without (89/279, 32.2%) HIT in patients on ECMO, p=0.79. ConclusionsThrombocytopenia is already common at ECMO initiation. HIT is more frequent in both VVand VA-ECMO compared to CPB. PPV of PTPS in identifying HIT was lower in ECMO patients.HIT had no effect on mortality.

In this prospective, single‐centre observational study of 30 patients undergoing cardiopulmonary bypass (CPB), the effect of unfractionated heparin (UFH), CPB surgery and protamine sulphate on complement and on post‐operative blood loss were assessed. Although C3 and C4 levels decreased significantly immediately following the administration of UFH, C3a, C5a, Bb fragment and SC5b‐9 remained unchanged. During CPB, C3 and C4 continued to fall whilst both alternative and classical pathways activation markers, Bb, C3a, C5a and SC5b‐9 increased significantly. Protamine sulphate had no effect on classical pathway components or activation markers but decreased alternative pathway activation marker Bb. Over the 12–24 h post‐surgery, both classical and alternative pathway activation markers returned to baseline, whilst C3 and C4 levels increased significantly but not to baseline values. Total drain volume 24 h after the surgery showed a moderate inverse correlation with post‐protamine C3 (r = −0.46, p = 0.01) and C4 (r = −0.57, p = 0.0009) levels, whilst a moderate positive correlation was observed with post‐protamine C3a (r = 0.46, p = 0.009), C5a (r = 0.37, p = 0.04) and SC5b‐9 (r = 0.56, p = 0.001) levels but not with Bb fragment (r = 0.25, p = 0.17). Thus, inhibition of complement activation may be a therapeutic intervention to reduce post‐operative blood in patients undergoing CPB.