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Tuesday, May 21, 2013
The choice of a particular anesthetic technique is normally a decision made by the anesthesiologist, taking into account the type of surgery and the condition of the patient, as well as the needs and preferences of both the patient and the surgeon.
General anesthesia provides unconsciousness so that the patient does not feel, see, or hear anything during a surgical procedure. The anesthetic medications are given through an intravenous (IV) line or as a breathing gas, and patients are monitored by an anesthesia provider - an anesthesiologist (MD), or a certified registered nurse anesthetist (CRNA) or anesthesia assistant under appropriate supervision.
The state of decreased consciousness achieved during general anesthesia reduces, or eliminates completely, the observed response to a painful stimulus, like a surgical knife. The responses that are blocked are not only muscle movements, but also reactions of the so-called autonomic nervous system - like increased heart rate and blood pressure, and sweating. During general anesthesia we believe that pain, as such, is not felt. In many cases, drugs with pain-killing properties, such as morphine, are used as part of the "mix" of anesthetic drugs. Paralyzing drugs are often given to make sure the muscles do not naturally contract which would make surgery difficult. The muscles of breathing then also become paralyzed and therefore an artificial airway must be inserted and breathing achieved with a machine - a mechanical ventilator.
The anesthesiologist or anesthetist monitors the patient very closely throughout the entire procedure with a variety of sophisticated monitors as well as with close "hands-on" observation with the human senses.
Anesthesia must be maintained until the surgical procedure is over. Recovery from anesthesia occurs through removal of the anesthetic from the brain and, ultimately, the body. The gases are removed from the body mainly by breathing them out, and the intravenous drugs by the action of the liver and kidneys. The action of the paralyzing drugs is usually be ended by giving other "reversal" drugs. After waking up from anesthesia, patients are usually transferred to a recovery area where they are monitored closely by specially trained nurses. After certain major surgeries, patients may be taken to an intensive care unit for recovery.
Some patients may experience nausea and vomiting afterwards. Other after-effects or problems that can occur after general anesthesia include sore throat, tooth damage, headache, drowsiness or dizziness.
Severe problems or even death can occur with general anesthesia but are rare.
Depending on the surgery and the type of anesthesia used, many patients may be able to go home within a few hours. It is important however that any patient who has had anesthesia has a responsible adult companion to provide an escort home and care at home for the first 24 hours or so after surgery.
Sedation techniques include mild, moderate and deep sedation. A variety of other terms are used, such as "monitored anesthesia care" (MAC), "conscious sedation" and "twilight sleep". These techniques differ from general anesthesia in that patients are more responsive to painful stimuli, are able to breathe more easily without the assistance of a breathing tube or ventilator, and show less effect on the heart and blood pressure.
Sedation techniques usually involve:
Because sedation usually entails the administration of lower doses of anesthetic drugs than with a general anesthetic, the recovery period tends to be shorter. The drugs that are used affect one's ability to remember the procedure, but periods of awareness can occur.
There is no fixed dose of anesthetic agent that produces a particular effect in all patients. A particular patient's response depends on age, weight, sex, general state of health or disease, genetic factors, drug interactions, and other factors. Because there is this degree of unpredictability a patient undergoing sedation may on occasion experience the effects associated with general anesthesia. The anesthesiologist must be able to provide support for the airway (such as a breathing tube), breathing (such as a mechanical ventilator) and the heart and blood pressure (such as a resuscitation drugs). This is known as the ability to "rescue" and is one of the main reasons why sedation is risky when undertaken by unqualified hospital personnel or lay people.
In this form of anesthesia, so-called "local" anesthetic medications are injected to numb the nerves that supply sensation to the operated-on body part. Lidocaine, and the old "Novocain" (procaine) are examples of local anesthetics.
The nerves are "blocked", meaning that they cannot transmit their signals during the time the anesthetic is active.
Regional anesthesia relies on the anesthetic drug being placed in exactly the right part of the body, close to the nerve, or bundle of nerves, or the spinal cord. Anesthesiologists use two main kinds of technology to assist in the location of the nerves. Ultrasound equipment can provide good images of many superficial nerves, and via the monitor the anesthesiologist can observe the local anesthetic as it is injected. Nerve stimulators pass small amounts of electrical current through a needle causing any nerve that is in proximity to conduct impulses to muscles, and specific patterns of muscle contraction that identify the needle as being in the right position. It is also possible to achieve regional anesthesia simply through sound applied knowledge of human anatomy. If good positioning is not achieved, the regional anesthesia will not work well or may not work at all. General anesthesia may then be necessary.
Other problems that can occur with regional anesthesia include, temporary or permanent nerve injury (rare), headache, backache, infection, reactions to the medication ("toxicity") or allergic reactions. Severe problems are as uncommon as with general anesthesia but can occur.
Epidural anesthesia is a form of regional anesthesia in which a narrow tube, (also called a catheter) is placed in the epidural space in your back. The epidural space is a part of the spinal canal that is in close contact with nerves. By injecting anesthetic medication into this space, the spinal nerves are numbed. An epidural requires the insertion of a special needle into the back. The epidural needle can be inserted with very little discomfort by an experienced practitioner, using local anesthesia to numb up the skin and tissues of the back. When the needle is in place, the epidural catheter is threaded through the needle and the needle is then removed.
Spinal anesthetic is an alternative to the epidural technique. A special needle is inserted in the lower part of the back, and anesthetic medication is injected through the needle directly into the fluid that bathes the spinal nerves. The needle is then removed. No catheter is involved.
The effects of spinal and epidural anesthesia, and of other regional anesthesia techniques, are very similar - they temporarily block nerves, so that pain is not felt. As well as blocking sensation, these anesthesia techniques usually also decrease the ability to move part of the body. As the medication wears off, the affected parts recover both sensation and movement.
Sedation is often given along with regional anesthesia to provide comfort but some patients, with the assent of anesthesiologist and surgeon, may choose to remain completely awake during regional anesthesia and surgery.
This technique is the use of local anesthetic at the surgery site. By definition, there is no anesthesiologist providing sedation and monitoring the patient, who is therefore completely conscious.
The local anesthetic agent is applied either on the surface of the skin or via injection. Sometimes a drug such as epinephrine (adrenaline) is administered so that the blood flow to that area of the body is reduced. This allows the anesthetic drug to remain in effect in the area longer.
Local anesthesia is a good option when surgery is very minor and the patient does not mind being fully awake during the procedure. The patient is normally able to get up and go home without escort, although the effects of the local anesthetic itself can take up to a few hours to wear off.
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Last Reviewed: Oct 05, 2010
Gareth S Kantor, MD
Assistant Professor of Anesthesiology
School of Medicine
Case Western Reserve University