Conscious sedation, otherwise known as alert anesthesia or moderate sedation, is a black box in more ways than one, says Dr. John Dombrowski, an anesthesiologist in private practice and president of the D.C. Society of Anesthesiologists.
“Most people learn about it only 10 minutes before they go to sleep,” he says — hardly enough time to absorb much information, especially when the patient is facing a colonoscopy for the first time. Moderate sedation commonly is used for procedures that use an optical instrument called an endoscope for viewing inside the body.
“Most people are so overwhelmed by the whole event, they won’t ask anything,” he says.
For many patients, the terminology is as confusing as the experience itself because it involves an amnesia-producing drug that prevents them from remembering anything about the medical procedure they have just undergone.
They quite literally feel “in the dark” until they wake up. They may then be told — horrors — how cooperative and chatty they were. Being conscious enough to be able to respond to verbal commands but not conscious enough to control reactions sounds contradictory, which is why the American Society of Anesthesiologists is at pains to clarify the treatment and sensations.
The formal definition from the ASA is “a drug-induced depression of consciousness during which patients respond purposefully to verbal commands, either alone or accompanied by light tactile stimulation. No interventions are required to maintain patient airway, and spontaneous ventilation is adequate. Cardiovascular function is usually maintained. Reflex withdrawal from a painful stimulus is not considered a purposeful response.”
So-called general — as opposed to local or regional — anesthesia has four levels, each controlled by different drugs chosen and monitored by a physician or a specially trained nurse.
“Minimal [sedation] is when we can talk. Moderate is where you receive drugs that decrease anxiety but allow you to respond,” explains Dr. Robert Parker, chairman of the Department of Anesthesiology at Washington Hospital Center. “When you move into deep sedation, people tend to become less responsive, and with general sedation, you don’t respond at all.”
Procedures employing moderate sedation also include cardiac catheterization and an upper gastrointestinal endoscopy, he says.
The levels are not strictly defined and can vary from patient to patient, depending on the person and the drug used, according to Dr. Jeffrey Gross, professor of anesthesiology and pharmacology at the University of Connecticut School of Medicine in Farmington.
“Minimal is like taking Valium at home or like what a dentist may give you to fill a cavity. Moderate is when a patient may drowse off but can be stimulated by calling his name. With deep sedation, a patient will wake up, but only by doing something painful to arouse them. Under general, even if what you do is painful, the patient won’t wake up.”
The drugs are given intravenously for greater impact.
“With a pill, absorption can be erratic,” Dr. Gross says. “Pills only get absorbed over a period of time, so that a patient can still be absorbing [a drug] even after the procedure is over.”
Patients don’t get to pick the type of anesthesia they prefer or even the particular anesthesiologist in attendance. Specialists in this branch of medicine work from a chart detailing the patient’s physical condition and medical profile to decide what type and amount of drug to use and then observe resulting reactions of the heart and lungs to make any necessary adjustments.
“There is not a single anesthetic without a problem or a potential one,” Dr. Dombroski states.
The drugs involved are a combination of an anxiety-reduction agent and a painkiller, each with somewhat predictable but varying effects on the body. They are a potent mixture, often referred to as a “cocktail,” with a one-two effect that act on different receptor sites in the brain.
Demerol is commonly used to relax a patient and dull or kill any pain. Alternately, the patient might be given fentanyl, a synthetic narcotic that resembles opium. The amnesia drug of choice is Versed, the trade name for a generic chemical agent known as midazolam related to the more familiar Valium, which was developed in the 1960s. Versed has been around since the 1970s.
Propofol, a newer and more potent version of the amnesia drug, was introduced in the early 1990s. It is metabolized even faster in the body without any hangover effect.
“If used in lower doses, it can put a patient in moderate or conscious sedation,” Dr. Gross says, “but the problems are that it is easy for a patient to slide into a state of general anesthesia, and it is a wicked depressant of breathing. …You might have decreased blood pressure and even cardiac arrest.”
The critical part of anesthesia is the amnesia because “people don’t want to remember the procedure,” says Dr. Dombrowski, explaining its mechanism as “a lock-and-key format. The key fits into the lock that prevents the brain from laying down a memory.”
A crude comparison, he says, is that of a person who drinks to excess — “You are conscious when you are drinking, but Sunday morning, you say, ‘I don’t remember anything.’ That is one component of anesthesia, one pillar of the building block you should be able to count on.”
Every drug has the possibility of depressing the central nervous system, says Dr. Dombrowski, adding propitiously enough that the symbol for his profession is the lighthouse — “always looking vigilant.”
To help forestall any problems, an instrument called a pulseoximeter is attached to the patient’s finger on a clip to measure the amount of oxygen in the blood as an indicator of breathing capacity. A pulseoximeter can be placed on the finger or on the ear lobe — wherever light can shine through. “Basically you look to see whether the patient is getting enough oxygen by changes in color. If the blood gets too blue, showing lowered amounts of oxygen, an alarm will sound,” Dr. Gross says.
“There is a wide spectrum about how people respond,” Dr. Parker offers. “You can sometimes say the elderly will need less anesthesia because you tend to handle drugs differently as you get older because you tend to have decreased metabolism and certain drugs’ effects get magnified.”
Usually, all safety measures have been followed and the blissfully unaware patient wakes up 30 to 45 minutes later with no memory of the event. With the IV line removed, he is able to stand up and even talk over matters with his doctor before going home.
“We have succumbed to our own successes,” Dr. Dombrowski says. “When anesthesia was first developed in the early 1800s, 50 percent [of patients] died because of the anesthesia. The [mortality] rate now is one in 250,000. People say, ‘It’s a miracle’— meaning the anesthetic itself.”