Background Approximately half of all children admitted to PICU in the United Kingdom are infants (under 1 year of age). We perceive that the length of PICU stay for infants is increasing over time.

Aims To describe the following trends in infants, in our institution:

• Crude numbers of proportions of PICU admission

• Length of PICU stay (LOS)

• Mortality rate, up to two years of age

Methods Single centre multi-disciplinary PICU, retrospective analysis of prospectively collected anonymised data of all PICU admissions from PICU database, between 1 September 1995 and 31 August 2015 (20 years). Infant admission was defined as age ≤365 days at PICU admission. Long-stay was defined as cumulative PICU stay of ≥28 days.

Results Of 19,140 patients (23,306 admissions; 139,434 bed-days), 8647 patients (11,954 admissions) were infants at the time of admission. The proportion of infant admissions (mean 51%, range: 47–56%) and bed-days (60%, range: 52–66%) remained sTable. However, the mean length of stay per infant increased on average by 0.3 days/year (5.4 ± 6.8 to 11.5 ± 11.9 days; r²= 0.8; p < 0.001), compared to a smaller increase for the whole population (4.7 ± 5.6 to 9.6 ± 12 days; 0.2 days/year; r²=0.7; p < 0.001). We observed a smaller but significant increase in the median LOS (3 to 5 days; 0.06 days/year; r²=0.6; p < 0.001]. 540 infants (6.2%; 1,642 admissions) were long-stays. 238 of them died before their second birthday (44%). This was significantly higher than the mortality rate of short-stays [1,170 deaths in 8,107 patients (10,322 admissions); 14%; p < 0.001]. The proportion of infant long-stays and PICU infant bed-days have both increased over the study period (5% to 13%, p < 0.001; and 14% to 38%, p < 0.001, respectively). Although the annual mortality rate for long-stays has decreased (33% to 15%, p = 0.02), the overall in-PICU rate during this study period for long-stays was significantly higher than short-stays (47% vs. 15%, p < 0.001).

Conclusions There is a steady trend towards increasing LOS for all infants over the last two decades in PICU. Long-stays are also increasing and they have a significantly higher mortality compared to overall infant and PICU population.