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This column is directed to my non-medical layperson readers. How does an anesthesiologist decide what dose of anesthetic to administer to a patient? You are a 100-pound, 70-year-old woman. Your son is a 200-pound, 35-year-old man. Do you both require the same doses of general anesthetic if you each need to have your gall bladder removed?
No, you do not.
Anesthesiologists use several criteria to choose the correct dose for your anesthetic.
- Your weight. All intravenous anesthetic drugs, such as hypnotics (propofol, sodium pentothal), narcotics (morphine, Demerol, fentanyl), anxiolytics (Versed, Ativan), or muscle paralyzing drugs (rocuronium, vecuronium, succinylcholine) are dosed on a milligram-per-kilogram basis. If you weigh half as much as your neighbor, if all other factors are equal, then you will receive approximately half as many milligrams of the injectable medication as she will.
- Your age. Abundant research has demonstrated the relationship between age and anesthetic effect. Youthful patients require more milligrams-per-kilogram of body weight. A teenager may require twice the dose of an 80-year-old patient.
- How stimulating the surgery is, and how much pain there will be postoperatively. A non-painful surgery, such as the repair of a small tendon in a finger, will not require large doses of narcotics or pain relievers post-operatively. A painful surgery, such as on open abdominal procedure to remove a pancreatic or liver tumor, will require more narcotics and increased doses of anesthetics. If postoperative pain is blocked by local anesthetic injection in the surgical site or by a nerve block, a patient will require less general anesthetic medications.
- The duration of the surgery. An 8-hour surgery will require a longer exposure to more anesthetic drugs than a 1-hour surgery.
- Your preoperative exposure to central nervous system depressants. All else being equal, a patient who drinks 12 beers every day will require more anesthesia than a teetotaler who never drinks. A patient who is addicted to chronic prescription painkillers will require more anesthesia than a non-addict.
Inhaled anesthetics, such as sevoflurane, desflurane, isoflurane, or nitrous oxide, are administered in standard concentrations, independent of all the above factors except the patient’s age. Inhaled anesthetics are mixed into vapor by an anesthesia machine which is connected to the your breathing system during the surgery. The anesthesia machine will usually be set to deliver either sevoflurane 1-2 %, desflurane 3 – 6 %, or isoflurane 0.8 – 1.5 %. The required concentration of these potent inhaled anesthetic decreases with age. The dose for teenager is approximately twice the dose required for a 90-year-old patient.
The most popular posts for laypeople on The Anesthesia Consultant include:
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Published in September 2017: The second edition of THE DOCTOR AND MR. DYLAN, Dr. Novak’s debut novel, a medical-legal mystery which blends the science and practice of anesthesiology with unforgettable characters, a page-turning plot, and the legacy of Nobel Prize winner Bob Dylan.
In this debut thriller, tragedies strike an anesthesiologist as he tries to start a new life with his son.
Dr. Nico Antone, an anesthesiologist at Stanford University, is married to Alexandra, a high-powered real estate agent obsessed with money. Their son, Johnny, an 11th-grader with immense potential, struggles to get the grades he’ll need to attend an Ivy League college. After a screaming match with Alexandra, Nico moves himself and Johnny from Palo Alto, California, to his frozen childhood home of Hibbing, Minnesota. The move should help Johnny improve his grades and thus seem more attractive to universities, but Nico loves the freedom from his wife, too. Hibbing also happens to be the hometown of music icon Bob Dylan. Joining the hospital staff, Nico runs afoul of a grouchy nurse anesthetist calling himself Bobby Dylan, who plays Dylan songs twice a week in a bar called Heaven’s Door. As Nico and Johnny settle in, their lives turn around; they even start dating the gorgeous mother/daughter pair of Lena and Echo Johnson. However, when Johnny accidentally impregnates Echo, the lives of the Hibbing transplants start to implode. In true page-turner fashion, first-time novelist Novak gets started by killing soulless Alexandra, which accelerates the downfall of his underdog protagonist now accused of murder. Dialogue is pitch-perfect, and the insults hurled between Nico and his wife are as hilarious as they are hurtful: “Are you my husband, Nico? Or my dependent?” The author’s medical expertise proves central to the plot, and there are a few grisly moments, as when “dark blood percolated” from a patient’s nostrils “like coffee grounds.” Bob Dylan details add quirkiness to what might otherwise be a chilly revenge tale; we’re told, for instance, that Dylan taught “every singer with a less-than-perfect voice…how to sneer and twist off syllables.” Courtroom scenes toward the end crackle with energy, though one scene involving a snowmobile ties up a certain plot thread too neatly. By the end, Nico has rolled with a great many punches.
Nuanced characterization and crafty details help this debut soar.
Click on the image below to reach the Amazon link to The Doctor and Mr. Dylan:
Learn more about Rick Novak’s fiction writing at ricknovak.com by clicking on the picture below: