A preoperative dose has a clock of its own. If absorption is still underway when anesthesia starts, a blood sample drawn at the end of a short operation can contain more midazolam than an earlier sample from the same patient.
A Swiss observational study administered 7.5 mg of oral midazolam before elective general anesthesia and collected plasma at induction and at the end of surgery. Five of 22 evaluable patients in the short-procedure group had higher concentrations at the end. None of the 24 evaluable patients in the longer-procedure group showed that pattern. Four enrolled patients had no detectable midazolam in either sample and were excluded.
Use the administration timestamp, the specimen collection time and the formulation together. Two samples establish the direction of change between those times. They do not locate the actual peak or show how alert a patient was at discharge. The cohort included women aged 20–60 and used one oral dose, so its observed frequency cannot be transferred to intravenous dosing or to every surgical population.