Background Continuous Renal Replacement Therapies (CRRT) are the treatment of choice for critically ill children with Acute Renal Injury. Hypotension after starting CRRT is frequent but there are no studies that have analysed their incidence and importance.

Patients and methods A prospective, observational study was performed including critically ill children treated with CRRT between October 2009 and December 2013. Hemodynamic data and connection characteristics were collected before, during and 60 min after CRRT circuit connection. Hypotension with the connection was defined as a decrease in mean arterial pressure >20% from baseline and/or intravenous fluid expansion and/or if increase in vasopressors was required.

Results 161 connections in 36 children (median age 18.8 months) were analysed. 28 patients (77.8%) were in the postoperative period of cardiac surgery, 94% on mechanical ventilation and 86.1% with vasopressors. The circuit prime was discarded in 8.7% of connections, the heparinised prime was infused in 18% and the circuit was previously primed witha colloid (albumin in 77.5%) or crystalloid without heparine in 73.3%. Hypotension occurred in 49.7% of connections with a median of 5 min after the beginning. In 38.5% of the connections fluid expansion was required and in 12.4% vasopressors were increased. There was no hypotension relation to age or weight. Previous priming of the circuit reduced the frequency of hypotension to 44.6% vs. 71.4% (p = 0.004).

Conclusions Hypotension after CRRT connection is very frequent in critically ill children. Priming the circuit improves hemodynamic tolerance of the connection.