Indexing haemodynamic variables in young children

Background: Haemodynamic studies in children are rare and most studies have included few subjects in the youngest age group. Haemodynamic variables need to be indexed to establish a reference of normality that is valid in all populations. The traditional way to index haemodynamic variables with body surface area (BSA) is complicated in young children due to its non-linear relationship with body weight (BW). We examined several haemodynamic variables in children by indexing them with BSA and BW. Methods: A single-centre, observational cohort study comparing non-indexed and indexed haemodynamic variables in children undergoing heart surgery (divided into three weight groups: 1-5 kg, >5-10 kg and >10-15 kg). Results: A total of 68 children were included in this study, mean age 11.1 months ± 11.1 month (range 0 to 43 months). All haemodynamic variables, cardiac output (CO), stroke volume (SV), total end-diastolic volume (TEDV), central blood volume (CBV) and active circulation volume (ACV), increased with weight without indexing (P <.05). Indexing variables with BW produced a more linear relationship for all haemodynamic variables between weight groups than BSA. The mean BSA-indexed haemodynamic values were CI_BSA 3.5 ± 1.1 L/min/m² and SVI_BSA 27.3 ± 8.9 ml/min/m². The mean BW-indexed haemodynamic values were CI_BW 180 ± 50 ml/min/kg and SVI_BW 1.34 ± 0.38 ml/kg. Blood volume variables indexed with BW were TEDV_BW 12.0 ± 2.8 ml/kg, CBV_BW 21.3 ± 6.6 ml/kg and ACV_BW 70.3 ± 15.2 ml/kg. Conclusions: Indexing haemodynamic variables with BW produces a more appropriate body size-independent scale in young children than BSA. Summary statement: In this study, we studied indexing of haemodynamic variables and estimation of blood volumes in young children undergoing corrective heart surgery using an indicator dilution technology.