If you are due to have a colonoscopy, you may have questions about the procedure as well as what type of anesthesia will be used.

A colonoscopy is a procedure in which a doctor examines your large intestine (also called your colon) to look for and remove growths that could be precancerous or cancerous. 

During the procedure, a doctor explores the colon with a colonoscope, which is a thin, flexible tube with a video camera attached to it. This instrument helps doctors look for growths such as polyps or tumors as well as inspect for inflammation, bleeding and ulcers. 

According to Ira G. Rock, MD, director of Out of Operating Room/Endoscopy Anesthesiology in the Department of Anesthesiology at Yale Medicine, there are two kinds of anesthesia used during colonoscopies. If you have conscious sedation, it is usually administered by the doctor who performs your colonoscopy. If you undergo general anesthesia (also known as full or deep sedation), you can expect to be monitored by a credentialed anesthesiologist and nurse anesthetist.

At Yale Medicine, anesthesiologists caring for patients who want deep sedation for their colonoscopy typically use a drug called propofol. “It is a short-acting anesthetic that has the advantage of wearing off relatively quickly,” Dr. Rock explains. Propofol works quickly; most patients are unconscious within five minutes. "When the procedure is over and we stop the intravenous drip, it generally takes only 10 to 15 minutes before he or she is fairly wide awake again.”

Propofol is considered safe and effective for most patients, but there are some side effects that need to be considered. The drug may lower blood pressure and cause slower breathing. If you have very low blood pressure or heart and/or breathing problems, your doctor may advise against using propofol for your colonoscopy.

Dr. Rock says that 95 percent of patients are able to tolerate propofol well. "In 5 percent of cases, out of concern for the patient’s safety, we opt for conscious sedation instead,” he notes.

Your doctor will give you advice on how to prepare for your colonoscopy well in advance of your procedure. You can expect to have restrictions regarding the food you can eat and liquids you can drink the day before. You will also be given instructions on how to empty your colon. “For anesthesia purposes, we typically require patients to avoid any solid food for at least eight hours and any clear liquids for at least two hours before the procedure," says Dr. Rock.

On the day of your procedure, an anesthesiologist and nurse anesthetist meet with you to review your medical history and vital signs. If they identify any potential problems, your doctor will discuss making an alternative plan such as using conscious (light) sedation instead of general anesthesia during your colonoscopy, or rescheduling it for another time.

For patients in good health, whose heart and blood pressure are working normally and who are breathing well, the anesthesiologist will attach an intravenous drip to the arm. This helps to make sure that the drug flows correctly and consistently into the vein. Within a few minutes, the patient is asleep, and the doctor then begins the colonoscopy. 

According to Dr. Rock, many people are surprised when they wake up and learn their procedure is over. "Patients may not even notice that they have gone out," he says. 

Most colonoscopies take between 30 minutes and an hour to complete. During the procedure, the anesthesiologist and nurse anesthetist work together to ensure that the patient’s vital signs, especially blood pressure and breathing rate, remain in a safe range.

“We’re constantly watching what’s going on,” Dr. Rock says. “In very rare cases, if a patient’s blood pressure dips too low, we may adjust the dose of the anesthesia accordingly or treat the patient with additional medication to improve blood pressure.”

According to Dr. Rock, Yale Medicine's anesthesiologists are highly focused on patients' safety as well as their comfort. 

“Every patient undergoing anesthesia for colonoscopy here has an anesthesiologist and/or nurse anesthetist looking after them during the procedure," he says. 

In cases where an anesthesiologist is simultaneously supervising several nurse anesthetists, each patient will have a dedicated nurse anesthetist who is caring only for him or her. “We work to ensure we know everything we can about a patient’s medical condition, so that we can tailor an anesthetic and dose that is perfect for that patient," says Dr. Rock.