Anesthesia - 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.