Table 2.

Mean estimates, standard error, interindividual variability and descriptions of component parameters in the activated partial thromboplastin time (aPTT) concentration–response model based on data from the BISTRO I patient population

Parameter	Parameter estimate	RSE (%)*	IIV (%)†	RSE of IIV (%)*	Description
BAS0 (s)	33.4	0.63	8.7‡	10.51§	Baseline aPTT at time 0 on the day of surgery
EMA0 (s)	26.9	12.45	19.9‡	33.92§	Emax at time 0 on the day of surgery
EMBA	0.102	14.41	NE	NE	Constant describing the maximum decrease in baseline aPTT over time
EC50 (ng ml−1)	94.7	17.11	38.5	40.41§	Plasma concentration at which the effect of the non linear part of the model is 50% that of Emax
SLOP (s ng−1 ml−1)	0.0509	6.68	15.2	45.22§	Constant describing the slope of the linear part of the line of regression
EMMX	0.463	12.68	NE	NE	Constant describing the maximum decrease in Emax over time
ET50 (days)	1.62	15.99	NE	NE	Time point at which baseline aPTT and Emax decreases by 50% and the effect is half that of EMBA and EMMX
Residual error (σ)	7.55*	3.53	NE	NE	Proportional error reported as coefficient of variation (CV %)

^*RSE, Residual standard error. Percentage standard error for the parameter estimates was calculated according to percentage RSE: 100% · SE/parameter estimate.

^†IIV, Inter-patient variability. Estimates of variance components (ω and σ) were converted into standard deviations by taking their square root. These are reported as coefficients of variation (% CV) after multiplying them by 100.

^‡Interpatient variability is based on values for E₀ and E_maxrather than BAS₀(initial E₀at time 0) or EMA₀(initial E_max at time 0).

^§Percentage SE is given on the variance scale; NE, not estimated.