Median Effective Analgesic Concentration of Local Anesthetic
The illustration of sequence of successful and failed blocks is in figure 2. The linear model estimator led to an EC50 of 0.129 %, the linear-logarithmic model resulted in an EC50 value of 0.142 %, the exponential regression gave an EC50 of 0.113%, and the centred isotonic regression (a nonparametric method) yielded an EC50 of 0.115%(see Figure 2). The 95% confidence intervals for the 3 parametric models (linear, linear-logarithmic and exponential) were 0.103%, 0.359%; 0.112%, 0.347%; and 0.108%, 0.343%, respectively(Table 2) and they showed similar fitted probabilities within the range of the ED50, and the 95% confidence intervals from these models successfully covered all observed data. Table 2 also showed the results of residual standard deviations for goodness of fit of each model. The exponential regression has the least residual standard error (0.2243) among the all models.