Subnormal arterial blood pressure.
Many age-related physiologic changes affect blood pressure. Numer¬ous studies in Western countries have shown an association between age and blood pressure elevation. But paradoxically, age-related eleva¬tions in blood pressure also increase the risk of hypotension.
Baroreflex mechanisms regulate syslemic blood pressure by resist¬ing transient decreases and damping transient increases in arterial pressure. With age, baroreflex response to both hypertensive and hypo¬tensive stimuli progressively declines. Also, hypertension reduces baroreflex response. Thus, baroreflex function is most impaired in el¬derly, hypertensive patients. Signs of such impairment include in¬creased lability in blood pressure in response to daily activities and an increased response to hypolensivc stimuli, particularly medications.
The diminished baroreflex response may be caused partly by arterial stiffening, which results in damping of barorcccptor stretch and relaxa¬tion during changes in arterial pressure. Reduced adrenergic respon¬siveness by the aged heart may diminish baroreflex-mediated cardioac-celeration during hypotensive stimuli. These changes become clinically significant when common hypotensive stresses, such as postural changes, can no longer be offset by compensatory increases in heart rate or vascular resistance.
With age, cerebral blood flow declines. Risk factors for cerebrovas¬cular disease (eg, hyperiension, heart disease, diabetes mellitus, and hypcrlipidemia) further decrease cerebral blood flow. Thus, elderly pa¬tients who have such risk factors may develop cerebral ischemia from even a fairly small drop in blood pressure.
Cerebral autoregulatory mechanisms usually compensate for acute reductions in blood pressure. Curren! data suggest that autoregulation of cerebral blood flow is generally maintained with age, excepl in cer¬tain persons who have symptomatic orthostatic hypotension. Chronic hypertension, however, raises the lowest blood pressure at which autoregulation can maintain cerebral blood flow. Below this level, blood flow may decline, increasing the risk of cerebral ischemia. Al¬though an acute reduction in blood pressure may not be tolerated well by a hypertensive elderly patient, a gradual reduction, using a variety of agents, can be accomplished without compromising cerebral blood flow.

Hypovolemia, the most common cause of hypotension in the early postoperative period, results from inadequate replacement of intraoperative fluid losses, inordinate bleeding, or internal losses of fluid such as rcaccumulation of ascites or third-space losses. Third-space losses represent intravascular fluid losses caused by tissue edema, especially in the operative sile. After abdominal surgery, con¬siderable intraperitoneal hemorrhage can occur, although it may pro¬duce relatively few physical findings. The usual lest for such occult hemorrhage is to administer large amounts of blood or fluids; if blood pressure immediately rises to normal levels, followed by a rapid recur¬rence of hypotension, abdominal recxploration for bleeding is usually indicated.
The patient’s course during the operation must be reviewed, noting the anesthetics used, the estimated fluid loss, and the fluid replace¬ment. The patient’s respiratory status must be assessed as well. If the endotracheal tube is still in place, the chest is examined to make sure i he tube has not blocked a main stem bronchus or a pneumothorax has not developed. If the tube has been removed, the rate and depth of res¬pirations must be determined because reintubation may be necessary.
Drains and catheters should be examined for escaping blood.