Many surgical patients spend time in an intensive care unit and on the wards. Medication errors are one of the most frequent causes of preventable harm in ICU and wards, and occur predominately in the dispensing and administration phases. Despite a plethora of publications and studies of medication errors in these locations, significant differences in definitions, study methods, and local workflows lead to remarkable differences in the rates of error reported. Increasing number of medications per patient, nurse to patient ratios, and patient age contribute to medication errors in the ICU. Pediatric ICUs tend to have higher rates of error, and this often is due to mis-calculation of a dilution or a weight based dose. On the wards, administration errors are common, especially when exact timing is expected for a given administration. Prescribing errors are often the result of lack of knowledge, whether related to diagnosis or medication; administration errors are more frequently skill based errors such as slips or lapses.

Surgical patients undergo multiple transitions of care, from home to the operating room, to a recovery unit to a ward, and so on. Each transition poses a risk of medication error if the current medications are not reconciled or managed appropriately in the new phase of care. Home medications may be suspended, stopped, substituted for, or need to be continued, often in the face of changing preoperative guidelines. Admission and discharge medication reconciliations are at high risk for inaccuracies and for mis-information for the patient as well as the patient's primary provider. Intraoperative medication management is largely but not exclusively, under the control of the anesthesiologist, who serves as the sole agent for the prescription, dispensing, preparation, administration, documentation and monitoring of the anesthetic medications. Common errors include syringe or vial swaps, omissions (e.g., no redosing of antibiotics), wrong route, wrong dose, and even wrong choice of medication. Medication errors occur in approximately every 2 anesthetics, most are of little to no harm, but each has the potential for significant injury. Medication errors also can be made by a surgeon or OR nurse; communication failures between care team members often contribute.