Anesthesia

ANESTHESIA

"My diseases are an asthma and a dropsy and, what is less curable, seventy-five."

—Samuel Johnson.

Over 40 percent of all surgical procedures in the United States are performed on patients over age sixty-five, a remarkable statistic given that those over sixty-five comprise only 13 percent of the U.S. population. Elderly patients are more likely than their younger counterparts to suffer serious medical complications such as a heart attack, pneumonia, or kidney failure during or after an operation, further compounding the impact that caring for elderly patients has on the medical system.

Basics of anesthesia

There are three broad categories of anesthesia: local anesthesia, regional anesthesia, and general anesthesia. Local and regional anesthesia involve the injection of a drug, such as lidocaine or bupivacaine, that soaks into the nerves and blocks the electrical signals from traveling down the nerves. With local anesthesia the drug is injected under the skin in the area of the surgery where the nerves are diffusely spread about in the tissue, whereas in regional anesthesia the drug is injected next to large, discrete nerves traveling to the surgical area. For example, when injected at the right location in the armpit, the arm can be made completely numb, allowing surgery to proceed without the patient feeling any pain. A spinal anesthetic involves placing the needle between the vertebrae into the spinal sac. The drug then reaches the nerves that go to the lower half of the body, making the patient numb from approximately the upper abdomen down. An epidural anesthetic is similar to a spinal, only the needle is placed outside the spinal sac, and, typically, a catheter is inserted (and the needle removed). An advantage of the catheter is it is easier to give subsequent injections.

A general anesthetic renders the patient unconscious during surgery. Most often, unconsciousness is rapidly achieved by injecting a large dose of a sedative, such as pentothal or propofol. Since the drug wears off quickly, it is immediately followed by a gas anesthetic to keep the patient asleep. During surgery, narcotic painkillers may be used to reduce the amount of gas being used, and to get a head start on the pain control that may be required after surgery. Sometimes drugs that paralyze the muscles must also be used to facilitate the operation.

During the use of any anesthetic, the patient's vital signs are watched carefully and continuously. The electrical activity of the heart (electrocardiogram) is displayed on a monitor (see Figure 1); blood pressure is measured every few minutes with an automated machine; and the oxygen level in the arterial blood is measured via a device that clips to a finger. During a general anesthetic a machine will measure the concentration of the gas anesthetic, as well as the level of carbon dioxide coming from the lungs. Careful monitoring is important because all anesthetics can lower blood pressure, depress breathing, and impair many of the body's defense mechanisms. The amount of anesthetic given the patient must therefore be continuously adjusted to match the conditions present during surgery.

The unique challenge of the elderly patient

Aging decreases the ability of every organ system in the body to withstand stress, including those associated with surgery and anesthesia. Stress begins in surgery with the combined effects of the anesthetic and surgical trauma. After surgery, the patient faces a potentially long period of recovery from that trauma, as well as the stress of pain. Chronic diseases such as stroke, heart disease, diabetes, or high blood pressure also compromise the body's ability to withstand stress and make the patient more vulnerable to complications such as a heart attack, pneumonia, kidney failure, or even death. Aging has its greatest adverse impact on older patients who also have medical illness. Among healthy people, the risk of complications from anesthesia and surgery increases only slightly with age. Among people with multiple chronic medical conditions, however, risk dramatically increases with age. The challenge to the care of elderly patients lies in tailoring the anesthetic to the patient's medical illnesses as well as taking into account the effect of age on the responses to the anesthetic. In all phases of anesthetic care, everything is done with an eye to reducing the likelihood that complications will occur.

Preoperative assessment

Before a patient has surgery, it must be determined that the expected benefits of the surgery outweigh the risks. With a healthy patient, this decision is usually straightforward; but this determination is more difficult for an elderly patient with multiple medical problems contemplating a high-risk surgery. Sometimes it is useful to get other specialists involved in order to perform more sophisticated tests that will better define the extent of the disease. Such testing may lead to therapy aimed at improving the medical status of the patient in order to decrease the risk of the surgery. For example, a patient with poorly controlled asthma might benefit from a few days of steroids to bring the asthma under control. With the current trend of performing as many surgeries as possible on an outpatient basis, many patients now go to preoperative clinics where their medical history and current condition can be assessed and further evaluation or treatment initiated well in advance of the scheduled surgery.

Intraoperative management

Virtually all anesthetic drugs have more pronounced effects on elderly patients. Drug effects typically last longer in older adults because metabolism (elimination of the drug from the body) slows with age. A given dose of a drug usually has a greater effect on older patients because higher initial blood levels are achieved than in young patients, thereby permitting more drug to enter the brain. In some cases the older brain is also more sensitive to the drug. In consequence, elderly patients usually receive small doses, and whenever possible drugs are used that possess a short duration of action.

Maintenance of a stable blood pressure is also more difficult with older patients. Blood pressure is the product of cardiac output (the amount of blood the heart pumps to the body per minute) and vascular resistance (how hard it is for blood to flow through the blood vessels). Vascular resistance is partly controlled by the brain. Aging is associated with increasing stimulation of the blood vessels by the brain and therefore vascular resistance increases with age. During anesthesia that stimulation is lost. Consequently, the vascular resistance decreases more than in a young adult and takes the blood pressure down with it. Furthermore, aging decreases the body's ability to resist changes in blood pressure, making changes in blood pressure due to external forces such as blood loss during surgery less opposed, and therefore more dramatic. Fortunately, modest swings in blood pressure, whether up or down, are usually well tolerated by almost every patient. Nevertheless, the control of blood pressure generally requires more direct manipulation by the anesthesiologist when caring for elderly patients.

The lungs are another area of great concern. Aging diminishes the transfer of oxygen to the blood, and anesthesia worsens this problem. Elderly patients are therefore likely to need extra oxygen for a longer period of time after surgery to prevent the risk of having periods of low blood-oxygen levels. Aging also increases the likelihood that portions of the lungs will compress and make the lungs more prone to pneumonia. The reflexes in the mouth and upper windpipe protect against regurgitated stomach contents from entering the trachea and damaging the lungs. These protective reflexes also diminish with age, again making the older patient at higher risk of low blood-oxygen levels or pneumonia. Deep breathing and coughing out secretions that accumulate in the lungs are important maneuvers done by the patient to help prevent low blood oxygen or pneumonia.

Although it is a controversial area, there is suspicion that surgery somehow causes blood to clot more easily. This tendency might be a good thing at the site of the surgery, but it may also lead to clots forming at diseased areas of the arteries that supply blood to the heart or brain. If so, such clots could lead to a heart attack or to a stroke. Prevention of such complications is a major area of current research.

Postoperative care

Surgery, especially operations where the chest or abdomen is opened, creates a significant stress to the patient that continues for at least several days after the surgery. Besides problems such as pneumonia or a heart attack, older patients are particularly prone to becoming confused within a day or two of surgery. Although the confusion almost always goes away, the condition may leave the patient in a more debilitated state for a long time thereafter, and thus requiring longer hospitalization and perhaps even nursing home care on discharge from the hospital. Patients may also suffer a potentially permanent decline in mental abilities in association with surgery. Prevention of these phenomena is an important area of current research.

Anesthesiologists have been particularly involved with preventing complications by helping to provide better pain control after surgery. A popular method of pain control is the administration of morphine via a pump controlled by the patient. Within certain safety limits, a small dose of morphine is given each time the patient pushes a button. Narcotics such as morphine have side effects, however, such as itching, nausea, and sedation. In part to avoid these problems, non-narcotic drugs have been gaining popularity. For surgery on the arms or legs, the use of long-lasting local anesthetics can safely extend the anesthetic for up to a day after surgery. Through mechanisms not yet fully understood, this technique may reduce the amount of pain experienced even after the local anesthetic has worn off.

Another option for pain relief after surgery is provided by the epidural catheter described previously. By administering a low concentration of both a local anesthetic and a narcotic through the catheter, excellent pain control can be achieved without affecting the patient's brain, allowing the patient to breathe more deeply and cough more easily, thereby helping to prevent pneumonia. Good pain control may also diminish the risk of other problems, such as a heart attack. The exact role of pain control with epidural catheters is still unclear, but it appears that complications can be reduced in high-risk (often elderly) patients.

Conclusion

The anesthetic care of the elderly patient is complex and demanding because of the effects of aging on organ function, plus the greater likelihood of chronic disease with increased age. Greater attention must be afforded such patients, beginning with the evaluation and optimization of the patient's medical status. The anesthetic requires close attention to detail, and, in selected patients, special techniques may be useful in lowering the risk of complications.

G. Alec Rooke

See also Pain Management; Revascularization: Bypass Surgery and Angioplasty; Surgery in Elderly People.

BIBLIOGRAPHY

Liu, S.; Carpenter, R. L.; and Neal, J. M. "Epidural Anesthesia and Analgesia—Their Role in Postoperative Outcome." Anesthesiology 85 (1995): 1474–1506.

Mcleskey, C. H., ed. Geriatric Anesthesia. Baltimore, Md.: Williams & Wilkins, 1997.

Moller, J. T.; Cluitmans, P.; Rasmussen, L. S.; et al. "Long-Term Postoperative Cognitive Dysfunction in the Elderly: ISPOCD1 Study." Lancet 351 (1998): 857–861.

Morgan, G. E., and Mikhail, M. S. Clinical Anesthesia, 2d ed. New York: Lange Medical Books/McGraw-Hill, 1996.

Muravchick, S. Geroanesthesia. St. Louis, Mo.: Mosby, 1997.

Rooke, G. A. "Autonomic and Cardiovascular Function in the Geriatric Patient." Anesth Clin NA 18 (2000): 31–46.

Tiret, L.; Desmonts, J. M.; Hatton, F.; and Vourc'h, G. "Complications Associated with Anesthesia—A Prospective Survey in France." Canadian Anaesthetists' Society Journal 33 (1986): 336–344.

ANEURYSM, ABDOMINAL AORTIC

See Vascular disease

ANNUAL CHECK-UP

See Periodic health examination