The main objective of this study is to improve our knowledge on the pharmacodynamic, pharmacokinetic, and pharmacogenetic relationships of morphine administered to relief severe postoperative pain. The analysis will encompass the efficacy (acute during titration and subacute during the first 24 hours) and adverse effects of morphine. Our purpose is also to better characterize the age- and sex-related differences which probably markedly differ between the two periods (acute vs sub acute).