Postoperative pain
Posted by admin on November 18th, 2009The elderly are more tolerant of and philosophical about pain than younger adults (see Ch. 12). Because of changes in neu¬ral pathways, the elderly may actually be less aware of pain. As a re¬sult, patient-controlled analgesia, in which patients control their own IV narcotic delivery, may be less effective. Patient-controlled analgesia should be monitored closely because an elderly patient may become confused and disoriented from the narcotic.
Many elderly patients have a compromised response to drugs, partic¬ularly narcotics, that can lead to prolonged or exaggerated effects (see Ch. 21). Because of their sensitivity to narcotic side effects, the elderly also tend to experience hallucinations and disorientation, making post¬operative management more difficult. Thus, when it comes to manag¬ing postoperative pain with narcotics, the adage “a little goes a long way” is apropos.
Ch. 27 Surgery: Preoperative, Intraoperative, and Postoperative Care 335
Fluid and electrolyte imbalance: Managing fluids and electrolytes is difficult because the capacity to maintain homeostasis is reduced in the elderly. A relatively narrow margin exists between loo little and too much fluid in the treatment of these patients. Proper fluid replacement can be determined only by close monitoring. Initially, a rough estimate can be made, but it should be followed by a definitive plan, which can then be modified to optimize blood pressure, pulse, and urine output.
For several days after an operation, the body normally retains water and sodium in response to increased aldosterone and antidiuretic hor¬mone. Therefore, excessive fluid administration should he avoided in an elderly patient whose cardiovascular function is reduced. Enough fluid should be given to provide for urine output of 0.5 ml ,/kg/h or about 30 mL/h to replace insensible fluid losses and to replace other measured or estimated external losses. In the early postoperative period, all this fluid is usually given IV.
When external losses are not great, fluid requirements for 24 h usu¬ally range from 1500 to 2500 niL. Considerably more fluid may be needed, however, if excessive third-space sequestration of fluids oc¬curs—eg, as happens with distended bowel or inflamed subcutaneous tissues from burns. Precautions should be observed in these cases be¬cause Ihe sequestered fluid usually is mobilized on the third to fifth postoperative days. Central venous pressure, pulmonary wedge pres¬sure, and urine output provide further guidance for fluid management.
The amount of insensible fluid loss is relatively constant, usually averaging 600 to 900 mL daily. This amount may rise to 1500 mL daily with hypermetabolism, hyperventilation, or fever. Insensible loss usu¬ally is replaced with 5% D/W.
After a few postoperative days, fluid overload is no longer a danger, and about I L of fluid daily is needed to replace ihe urine volume re¬quired to excrete Ihe catabolic end products of metabolism. The urine volume usually is not replaced on a milliliter-for-milliliter basis be¬cause an output of 2 to 3 L on a given day could represent fluids given during the surgical procedure or excessive fluid administration. Gas¬trointestinal losses, which are usually isotonic or slightly hypotonic, arc replaced with 0.9% sodium chloride solution. When the estimated loss is slightly above or below isotonicity, appropriate adjustments can be made in the daily water intake. Maintenance fluids should be admin¬istered at a steady rate over 24 h.
Electrolyte replacement must include 40 mF.q/L/day of potassium lo replace urine losses and about 20 mEq/L to replace gastrointestinal losses. Inadequate potassium replacement may prolong postoperative ileus: if hypokalemia is not corrected, resistant metabolic alkalosis may develop. Calcium and magnesium also may be replaced if serum values warrant.
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