Background and aims Microcirculation is usually indirectly evaluated in the critical patient. The aim of the study is to analyse if Sidestream Darkfield (SDF) microscopy allows routine evaluation of sublingual microcirculation.

Methods Prospective observational study. All patients admitted to a PICU during 3 months were included. Sublingual microcirculation was evaluated the first day (T1) and between the second and third day of admission (T2). On patients not evaluated reason was recorded. Comparison between evaluated patients (ME) and those without evaluation (WE) was performed.

Results 105 patients were included (37.1% after cardiac surgery and 30.5% with respiratory disease). Microcirculation was evaluated in 18 patients (17.1%). Microcirculation was not evaluated due to respiratory failure or absence of collaboration in 74.3% at T1 and in 59% at T2, due to the absence of trained staff in 3.8% (T1) and 4.8% (T2), and due to PICU discharge (T2) in 21.9%.

There was no difference between groups in age (ME 3.2 ± 3.5 vs WE 4.8 ± 5.3 years), weight (ME 13.4 ± 8.2 vs WE 19.4 ± 17.7 kg), days with mechanical ventilation (ME 4.1 ± 7.8 vs WE 2.8 ± 8.3), or days with vasoactive drugs (ME 2.2 ± 4.9 vs WE 3 ± 5.6). The incidence of intubation at admission (72.2%) and the length of PICU stay (18.1 ± 17 days) were significantly higher in ME than in WE (15.3% and 5.4 ± 6.9 days) (p < 0.001).

Conclusions Routine evaluation of microcirculation using SDF microscopy in the critical patient is a feasible technique, especially in sicker critically ill children. Its use is hindered by the absence of collaboration and presence of respiratory failure.