Medication dose needed for general anesthesia varies widely: Some patients may require less anesthesia

"Providing general anesthesia is a delicate balance, ensuring the patient receives enough, but not more than needed," said Ana Ferreira, M.D., lead author of the study and a medical researcher in the Anesthesiology Department at Centro Hospitalar do Porto, Portugal. "Our research shows that there is no way to predict how much a patient will need. Administering the correct amount of anesthetic requires a physician anesthesiologist who has extensive knowledge of anesthesia and how to use it safely and effectively, understands the body, monitors vital functions closely and can instantly react to changes taking place. This expertise drives better outcomes and more personalized care."

Physician anesthesiologists use a combination of anesthesia medications for surgery, including one -- most commonly propofol -- to render the patient unconscious. In the study, researchers determined that the amount of propofol required to produce unconsciousness varied widely between patients and was independent of age, gender, weight or height. Close monitoring of the patient's neurological signs and brainwaves was used to determine when the correct dosage was achieved.

For the study, 126 patients were given propofol in a constant slow rate of infusion, enabling researchers to continuously monitor patient response and precisely determine when loss of consciousness occurred (e.g. not answering to name, not opening the eyes, etc.), as well as identify the exact amount of propofol required. Researchers found that there was a variation of 300 percent in the amount of propofol required to induce loss of consciousness and that more than two-thirds of the patients required less than the initial dose recommended by drug package inserts. The time needed to induce loss of consciousness varied from one minute and 22 seconds to nearly four minutes, researchers said. They also found significantly less propofol was required if pain medication (remifentanil) was given to the patient before propofol was provided, rather than after.

"We need to replace the recommendation of administering a specific amount of propofol based on a patient's weight and age with a technique that allows individualization of a patient's needs. That means administering propofol slowly at induction and monitoring the patient's response every 10 seconds to precisely identify the moment loss of consciousness occurs, identifying the amount of propofol each patient requires and then using that information to guide the infusion rate of propofol required to maintain an adequate level of anesthesia," said Pedro Amorim, M.D., co-author of the study, chief of staff of the Anesthesiology Department at Centro Hospitalar do Porto. "The time required for induction, using this method, is longer than if propofol is given based on the patient's weight and age, but less than four minutes to induce loss of consciousness is acceptable and ensures safe and effective care."