How Does Anesthesia Affect the Body?
As a physician anesthesiologist, general anesthesia is the most common type I administer on a daily basis. Different types of anesthesia—general, spinal, sedation, nerve blocks, and local numbing—affect the body in different ways. In this article, the term "anesthesia" will refer to general anesthesia.
During general anesthesia, a combination of medications is used to achieve unconsciousness, inability to feel pain, and immobility so the surgeon may operate. The effects on the body discussed here are the predominant, overall, and most usual effects. There are many exceptions and variables that change these outcomes.
The most logical way to discuss this might be to address how anesthesia affects the body from head to toe.
Effects of Anesthesia on the Brain
General anesthesia means unconsciousness is achieved and maintained.
- You are unable to respond to verbal or painful stimuli.
- Your memory for the time surrounding surgery will be interrupted.
- Some people suffer postoperative cognitive dysfunction, meaning they have longer-lasting effects on memory, mental functioning, or personality. This effect seems to occur with any type of anesthesia and is likely caused by a combination of anesthesia and the stress of surgery on the body.
- Anesthesia providers must have a more thorough understanding of each anesthesia drug and its effect on parameters such as cerebral blood flow, cerebral perfusion pressure, cerebral metabolism, and so on.
What Happens to the Mouth and Throat after General Anesthesia?
Throat: During a general anesthestic, a breathing tube or breathing mask is used to deliver oxygen and gas anesthesia. While we are gentle in placing this device, and it is made of soft plastic or rubber, the throat is very sensitive. You will likely have a dry, sore throat after surgery. This is usually relieved by cold beverages or lozenges and resolves in a few days.
Mouth: The mouth may also feel very dry after surgery. You will receive oxygen by a face mask in the recovery room. This dry flow of oxygen makes you feel dry and thirsty.
Other Concerns: One of the most common complications of general anesthesia is damage to a tooth during placement of the breathing tube. We use a special curved metal flashlight-like device to intubate. Occasionally, a tooth will be chipped or damaged in the process. This is more likely with those who have large, heavy necks, small mouths, anatomic problems with their face or jaw, or a poor overall dental condition.
How Does Anesthesia Affect the Heart?
The effects of anesthesia on the heart are varied and complex. Overall, a general anesthetic will usually decrease heart rate, blood pressure, and the strength of the heart’s pumping action. A normal heart and circulatory system will compensate quite well for this. A sick heart, however, requires much attention to the selection, dosages, and combination of anesthetic medications to avoid cardiovascular collapse.
If you have a known heart disease, symptoms of heart disease, or cardiac risk factors, you should have a full evaluation by your cardiologist before undergoing elective surgery. The results of the tests should be made available to your anesthesiologist. Unfortunately, even other physicians don’t always realize the implications of heart disease on the safe delivery of anesthesia. They will try to be helpful by providing a "clearance" note, saying "patient is cleared for surgery." This tells us only that nothing else will be done by them before surgery; it does not provide any information we can use to tailor your anesthetic to make it as safe as possible. So, in addition to the clearance note, please request results of your EKG, echocardiogram, stress test, Holter monitor, and any other cardiac testing from the past year.
Ever Wonder What Doctors See in All Those Lines and Blips on Your EKG? This Is a Bit Technical, but Gives a Good Intro:
Postoperative Risks Associated with Smoking
- Postoperative pneumonia and other pulmonary complications (including admission to the ICU for respiratory failure)
- Decreased ability to deliver oxygen to organs and body tissues
- Effects on the heart from nicotine (increased heart rate and blood pressure, heart attacks)
- Poor wound healing
Postoperative Pulmonary Complications—the Lungs and Anesthesia
Issues associated with the lungs, breathing, and oxygen delivery are often grouped as postoperative pulmonary complications (PPCs).
The depth and rate of breathing are generally decreased by general anesthesia. During your anesthetic, you will have a breathing tube or mask to deliver oxygen. With the tube, the ventilator (respirator) is often used to help you breathe. As you take over this critical function on your own at the end of surgery, you will be told to take deep breaths or cough to expand the airways. This is helpful in reducing the incidence of pneumonia and atelectasis—the lack of expansion of parts of the lungs.
If you smoke, there is conflicting data on how helpful it is to stop at various intervals before surgery. My thought is that it is important to quit anyway, so use your surgery as the motivation to do it! Ask your doctor for nicotine patches or gum well in advance of your planned operation. Eight weeks seems to give the best chance for improving most of the risk associated with smoking. If you aren't able to quit permanently, you will gain some benefit from not smoking in the 12-18 hours prior to your operation (yes, we are aware that probably isn't going to happen when you are nervous about your surgery, but we have to recommend it anyway).
Risk Factors for PPCs
Smoking, preexisting asthma, and recent airway infections increase the chances of having "reactive airways," asthma exacerbations, low oxygen levels, and pneumonia postoperatively. Patients who have obstructive sleep apnea are also more likely to have post-op pulmonary complications. Other risk factors for PPCs include advanced age, poor preoperative health, longer surgeries, more invasive surgeries, surgery of the chest and abdomen, and possibly obesity.
Liver and Kidney Function after Anesthesia
Liver: Blood flow through the liver decreases with general anesthesia. Also, many of the medications we use are metabolized, at least in part, by the liver. Most normal livers tolerate these challenges very well. If you have hepatitis or other liver disease, you should see a gastroenterologist before surgery. If your liver isn’t working well to start with, it could get worse after an anesthetic. In some cases, liver failure has followed routine surgery and anesthesia on livers that were not healthy to start with.
Kidneys: The kidneys also are susceptible to damage due to decreased blood flow. Normal kidneys will not suffer any clinical effects. Kidneys that are functioning poorly before anesthesia and surgery may very well become worse afterwards.
Bladder Retention is a Common Anesthesia Side Effect
Bladder retention after anesthesia is very common. The bladder must contract to expel urine. Through effects on the nervous system, general anesthesia decreases these contractions, leading to urinary retention (an abnormally full bladder). Usually, this is a minor, short-lived annoyance. If not resolved, bladder retention could predispose for urinary tract infections.
Why Do I Have Muscle Aches after Surgery?
In order to place the breathing tube and make the operation easier for the surgeons, a medication called succinylcholine is given to relax the muscles all over the body. Succinylcholine causes a rapid contraction of the muscles before they relax. This all-over contraction, called “fasciculation,” can make the muscles feel sore all over for a few days after surgery. In addition, for the length of the surgery, your body is immobile. Your muscles don't contract or move as they do during normal sleep. This also contributes to the feeling of stiffness and aching after surgery. Heating pads and pain medications usually treat this effectively.
For More Information
Another way to approach the study of anesthetic effects on the body would be to discuss each of the dozens of drugs used during anesthesia on each of the body systems separately. This would be tedious, complex and lengthy, and has been done in the voluminous anesthesia texts, so unless you are studying for the anesthesia board exam, it isn’t necessary. (If you are studying for the anesthesia board exams, I strongly recommend this approach, however. You will be quizzed on it extensively.)
Anesthesia has many more effects on the body and body systems, down to the cellular level. This has been a broad overview to help you understand the basics of the effects of anesthesia on the body. For more information on how you might feel after your anesthetic, my article Common Anesthesia Side Effects might be helpful.
I've given thousands and thousands of anesthetics and have had at least five general anesthetics myself, so I can attest to the fact that while these effects seem scary, they are rarely significant for most people.