Table 4

Models exploring the effect of 4 h net fluid balance on the trajectory of glucose-corrected sodium

Model 1Model 2Model 3Model 4
Intercept variablesUreaUreaUreaUrea
PCO2PCO2PCO2PCO2
GroupGroupGroup
Trajectory variablesTime0.5Time0.5Time0.5Time0.5
Time2Time2Time2Time2
Trajectory interactionsGroup × time0.5Net fluid balance × time0.5Group × time0.5
Group × time2Net fluid balance × time2Group × time2
Group × net fluid balance × time0.5Group × net fluid balance × time0.5
Group × net fluid balance × time2Group × net fluid balance × time2
AIC2037.72057.22045.22048.2
  • A series of exploratory models is shown, examining the effect of 4 h net fluid balance on glucose-corrected sodium. The effects include: (1) intercept, how the independent variables influence glucose-corrected sodium at time zero (presentation to hospital); (2) trajectory, the relationship between glucose-corrected sodium and time; and (3) interaction effects, interacting variables that may alter the trajectories in (2). Model fit is quantified by the Akaike Information Criterion (AIC), with smaller values indicating a better fit. All models are adjusted for baseline urea and PCO2. Model 1 is the ‘reference model’ from table 3, quantifying the effect of the oedema-defined groups on corrected sodium. Model 2 ignores the oedema group classification and examines the role of 4 h net fluid balance on corrected sodium trajectory. Models 3 and 4 examine whether fluid balance affects the three oedema-based groups in different ways (a higher order interaction). The lowest AIC (best model fit) is for model 1, demonstrating that inclusion of fluid balance does not improve model fit.

  • PCO2, partial pressure of dissolved carbon dioxide at hospital presentation. Group refers to: controls, early and late onset cerebral oedema.