HOW LONG DOES GENERAL ANESTHESIA LAST?

“I’m going to have surgery to have my gall bladder out. How long will the anesthesia last?”

The query “How long does general anesthesia last?” is a common question before surgery. Modern anesthetics wear off quickly after surgery, but the answer to your question is “It depends.” It depends on: (1) which drugs were administered, (2) the length of the anesthetic time, (3) the type of surgery you had, (4) how much pain you have following the surgery, and (5) how healthy you are.

Let’s look at each of these factors:

  • WHICH DRUGS WERE ADMINISTERED.

The main classes of general anesthetic drugs are intravenous (IV) and inhalational.

IV DRUGS. The most common IV drugs include propofol and narcotics. 

Propofol is a hypnotic drug that renders people unconscious in seconds. A single dose of propofol wears off quickly, within minutes, because the molecules of propofol redistribute throughout the body, to wherever the bloodstream takes the propofol. Organs such as the brain, heart, liver, and kidneys receive high blood flow. Muscle and fat receive less blood flow. If propofol is continuously infused into your IV by a pump or a drip, propolol levels can remain nearly constant. When the infusion is stopped, the propofol concentration in the bloodstream drops, and the drug redistributes back from the brain, heart, live, and kidneys into the bloodstream once again. As the propofol concentration in the brain drops, you begin to awaken. When a propofol infusion is stopped, for most patients, within 10-15 minutes the propofol concentration in the bloodstream will decrease to 10-20% of its previous concentration. Intravenous anesthesia is well discussed in the textbook Miller’s Anesthesia, Ninth Edition, Chapter 23.

SEE ABOVE: For a bolus of propofol at time 0, the concentration peaks in less than one minute, and drops below the Therapeutic range by 8 minutes, meaning the patient will awaken.

Fentanyl is the most common IV narcotic used in surgery in the United States. Narcotics blunt pain, but will not keep you asleep unless administered in very high doses. When fentanyl or any IV narcotic is administered, its blood level is at its highest immediately, and then the blood concentration decreases just like propofol did, by redistributing throughout the rest of the body.

SEVOFLURANE VAPORIZER

INHALATIONAL DRUGS. Sevoflurane is the most commonly used potent inhalational anesthetic. Sevoflurane has both a quick onset and a quick offset time when ventilated into or out of your body. When your surgery ends, your anesthesiologist will turn off the sevoflurane in your inhaled gas mixture, and 90% of the sevoflurane is typically ventilated away in the first 10-15 minutes. Inhalational anesthesia is well discussed in the textbook Miller’s Anesthesia, Ninth Edition, Chapter 20.

Per the left graph, 80-90% of sevoflurane or N2O concentration is exhaled after 10 minutes time

Nitrous Oxide (N2O) is a commonly used anesthetic gas of modest potency. By itself, N2O cannot produce a general anesthetic. It is typically used in a concentration of 50%, as an adjunct to sevoflurane or narcotics. The advantages of N2O are that it is inexpensive, it wears off quickly, and it has a reliable safety record. Dentists sometimes use N2O to bring on inhaled sedation when they are doing office procedures such as filling a cavity.

Balanced anesthesia: Most general anesthetics include balanced doses of propofol, sevoflurane and a narcotic. How fast you wake at the end of your general anesthetic after a surgery depends on the sum total of how much propofol, sevoflurane, fentanyl (or other narcotic) you were given. Higher drug doses –> slower wakeup. Lower drug doses –> faster wakeup.

  • THE LENGTH OF THE ANESTHETIC TIME.

If you have a brief thirty-minute anesthetic to repair a tendon defect in your hand, you’ll wake up quickly, because the doses of the IV and inhalational drugs discussed above will be lower than if you had an eight-hour surgery.

  • THE TYPE OF SURGERY YOU HAD.

Surgeries differ in terms of the amount of anesthetic required. A colonoscopy, for example, is technically not a surgery, but rather an endoscopic examination of the inside of your colon. There is no incision, there is usually only moderate discomfort, and there is no significant postoperative pain. The only anesthetic required may be an infusion of propofol alone, and when that infusion is stopped, you’ll wake in 5 minutes. In contrast, if you have an open heart surgery, such as coronary artery bypass grafting (CABG), the anesthetic plan may be to keep you asleep for several hours after the surgery in the ICU, or even overnight, while your heart, lungs, blood pressure, and temperature recover from the surgery. For the gall bladder excision surgery you’re scheduled for, the typical anesthetic and surgery duration is about two hours. The anesthetic plan would be to turn off the IV and inhaled anesthetic drugs at the conclusion of the surgery, leaving just enough narcotic concentration in your bloodstream so you will awaken with excellent pain control. The duration of this wakeup from when the anesthetics are turned off until you are awake and talking will be 10 – 20 minutes for most patients.

  • HOW MUCH PAIN YOU HAVE AFTER THE SURGERY.

Some surgeries do not hurt. For example, a small breast biopsy is relatively painless. In contrast, an intraabdominal operation such as removal of a portion of your colon will cause much more pain in the hours and days following surgery. Even though 90% of the propofol and sevoflurane will wear off in the first two hours after abdominal surgery, you’ll require ongoing doses of narcotics such as morphine or Dilaudid to be comfortable. Ongoing narcotics cause sedation, and you’ll be sleepy for the duration of time that you require IV narcotics for pain relief.

  • HOW HEALTHY YOU ARE.

All else being equal, patients with normal heart and lung function, and normal body weight, will awaken sooner than patients with decreased heart function, decreased lung function, and/or obesity.

***THE ROLE OF LOCAL ANESTHETICS***

One last topic is the role of local anesthetics to speed anesthetic wakeup and recovery. Local anesthetics such as lidocaine, ropivicaine, or bupivacaine can be injected via needles to effect pain relief. There are several ways this can be done:

  1. Local infiltration of the anesthetic into the skin incision, into the joint if you’ve had an arthroscopy, or into the tissues surrounding the surgical site. Local infiltration directly decreases pain in that region, and therefore decreases the amount of general anesthesia drugs needed or narcotic drugs needed. 
  2. Spinal or epidural blocks, administered by the anesthesiologist into the low back, cause the loss of sedation in the abdomen, pelvis, and lower extremities. This directly decreases pain, and therefore decreases the amount of general anesthesia drugs or narcotic drugs needed. 
  3. Ultrasound directed regional nerve blocks administered by the anesthesiologist, can effect numbness in a shoulder, upper extremity, knee, leg, or foot enervated by a specific nerve. This decreases the amount of general anesthesia drugs or narcotic drugs needed. 

Some examples of how long it takes to wake up, if you’re healthy, after general anesthesia for common procedures:

Colonoscopy                                                    5 minutes

Knee arthroscopy                                            5-10 minutes

Tonsillectomy                                                  5-15 minutes

Breast augmentation                                      10-15 minutes

Abdominal/flanks liposuction                        10-15 minutes

Rhinoplasty/nose surgery                               10-15 minutes

Laparoscopic abdominal surgery                  10-20 minutes

Total knee/hip replacements                         10-20 minutes

Brain surgery/craniotomy                              15-25 minutes

Open heart surgery                                        2 – 12 hours

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