Geriatric Neuroanesthesia

Introduction

The world is getting grayer as a result of the improvements in technology and health care facilities. The burden of disease has increased with the mean age of the population as has the stress on overstretched health care resources the world over. As a greater number of older patients (>65 years) come for a greater variety of neurosurgical diseases and surgeries, it becomes imperative to understand the interplay between the aged brain, the neurosurgical stress, and the anesthetic drugs.

Implications of Surgical Stress and Anesthesia on the Elderly

Age as a number may not affect to a great extent the basal functions of the various organ systems in the body. What is affected, however, is the ability of these organ systems and physiologic processes to respond to and compensate for the stress and physiologic upheavals associated with surgery and anesthesia. The functional reserve of the aging body system is no longer capable of buffering the insults of disease and treatment as efficiently as in its younger days.

The Framingham Heart Study has documented a linear relationship of blood pressure with age, increasing from 30 to 84 years. The changes in the control mechanisms and mechanics of the various organ systems are responsible for a majority of the “unexpected” perioperative events in response to surgery and anesthesia in the geriatric patient. The important physiologic changes with age are listed in Table 38.1 . These changes in the cardiopulmonary, renal, and neuroendocrine systems make tachycardia, hypotension, hypoxia, hyponatremia, hypercarbia, confusion, delirium, and abnormal fluid electrolyte balance occur more often than in younger patients.

Table 38.1

Physiologic Changes in the Geriatric Patient Affecting Anesthesia

Organ System	Associated Change	Pathophysiology
Cardiovascular	1. Hypertension of aging	a 50–75% decrease in arterial stiffness b. Decr. beta receptor responsiveness c Incr. SVR 25% d. Incr. Sympathetic activity
	2. Incr. conduction defects	a. Fibrosis and fatty infiltration
	3. Incr. risk of CHF and hypotension	a. Stiff hypertrophic ventricles b. Decr. heart rate variability and response to catecholamines c. Decr. passive ventricular filling, impaired SV buffering to changes in circulating volume
	4. Incr. susceptibility to ischemia
Pulmonary	1. Reduced hypoxic response 2. Rapid desaturation 3. Incr. risk of postoperative atelectasis 4. Retained secretions	a. Thoracic stiffness b. Decr. skeletal muscle mass; atrophy of respiratory muscles c. Decr. ciliary function and efficacy of cough d. 5–10% decr. in RV per decade e. 1–3% decr. in FRC per decade f. Incr. CV, equals FRC by 40 years age g. Incr. VQ mismatch
Neurologic	1. Incr. confusion and delirium 2. Incr. falls, poor balance	a. Central and peripheral neurologic degeneration b. Decr. in gray matter, neurotransmitter synthesis, complex neuronal connections; incr. demyelination in brain and spinal cord c. Decr. ability to assimilate complex multiple neuronal inputs d. Decr. proprioception, spinal cord reflexes, visual and auditory function, skeletal muscle innervation
Renal	1. Poor perioperative fluid electrolyte homeostasis (perioperative dehydration and hypotension) 2. Postoperative metabolic acidosis 3. Perioperative acute renal failure	a. 10% per decade decrease in RBF after 50 years age b. Loss and sclerosis of nephrons c. Decr. GFR d. Poor renal excretion of acid e. Incr. susceptibility to low CO, hypotension, surgical stress, pain, sympathetic stimulation and nephrotoxic drugs

CHF , congestive heart failure; CO , cardiac output; CV , closing volume; Decr. , decreased; FRC , functional residual capacity; Incr. , increased; SVT , systemic vascular resistance; VQ , ventilation perfusion.

Neurosurgical Concerns Unique to the Elderly

By virtue of surviving longer with greater age-related comorbidities, drugs, and disabilities, the elderly patient may present to neurosurgery for a variety of indications ranging from tumor, trauma, cerebrovascular accident (CVA), spinal cord stenosis, metastatic disease, etc. There is dearth of data regarding the morbidity and mortality rates for neurosurgical procedures in the elderly patient, which makes clinical decision making and prognostication difficult. In a recent retrospective study, Chibbaro et al. analyzed their geriatric neurosurgical surgeries over the past 25 years and found a progressive increase in the proportion of neurosurgical cases in elderly patients with a drop in the mortality. The length of stay of these patients in the hospital, however, remained significantly higher than that of their younger counterparts.

Preoperative Assessment for Geriatric Neurosurgery

Preoperative assessment serves three major purposes: to examine and assess if the patient’s physiology can withstand the surgical stress associated with the suggested surgery (or an alternative), to determine whether/which medical intervention is indicated prior to proceeding, and to decide on the most appropriate anesthetic and surgical intervention for the patient. The geriatric patients are prone to certain unique risks like delirium, aspiration, falls, malnutrition, and delay in rehabilitation after surgery. Risk stratification from information available through population studies, history taking, and physical examination should be supplemented with results of laboratory tests and functional examination. Preoperative optimization strategies must be decided upon in the preoperative assessment.

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