Neurological Patients for Nonneurosurgeries

Anesthetic Considerations ( Table 47.1 )

A few issues must be addressed in the patients with AD. Patients with severe cognitive dysfunction are incapable of giving proper history and consent, so caregivers should be involved in preoperative assessment and preparation. In advanced stage, patients with AD might be disoriented and uncooperative, and make regional anesthesia more difficult. Anesthesia becomes even more challenging in these patients due to interactions of the drugs used for its treatment with the anesthetic agents and the adverse effects of anesthetic agents on the disease progression.

Effect of Disease on Anesthesia

These patients are at high risk for postoperative confusion and delirium due to preexisting cognitive impairment. Sedative premedications should be carefully prescribed as these patients are more sensitive to sedative drugs and further increment in mental confusion can occur. Increased sensitivity is attributed to age-related changes in body composition and physiology, causing altered pharmacokinetics and pharmacodynamics of the drugs. There is smaller initial volume of distribution, relative increase in body fat, lower serum albumin, and age-related decline in renal function, which necessitate smaller doses for sedative–hypnotic agents. Other factors that can precipitate delirium; including cerebral hypoxia or hypoperfusion, endocrine or ionic imbalances, postoperative pain, sepsis, and bowel or bladder distention, should be avoided. Use of certain medications such as high-dose steroids, neuroleptics, benzodiazepines, ketamine, tertiary anticholinergics, opioids, histamine H ₂ blockers, and droperidol can also precipitate delirium.

Various medications used for the treatment of AD interact with the anesthetic agents. Cholinesterase inhibitors have been reported to prolong the action of succinylcholine and remifentanil, and may cause resistance to nondepolarizing neuromuscular blockers (NMBs). The patients taking monoamine oxidase inhibitors can develop profound pressor effect after administration of both indirectly and directly acting sympathomimetic drugs. If the patient is receiving antidepressants and psychotomimetic drugs preoperatively, there can be exaggerated effect of anxiolytic and sedative agents. So, the patient’s drug chart must be reviewed to avoid severe drug interactions due to polypharmacy.

The requirements for both volatile and intravenous anesthetic agents decline progressively with age. Elderly patients have altered responses to regional anesthesia. The dose of local anesthetic for subarachnoid block, to achieve the same level of sensory blockade, is lesser than the healthy indiviuals. The sensitivity of CNS to the depressant effects of general anesthetic agents is aggravated by severe cortical atrophy and synaptic loss. Hence, lower dosages of sedative and hypnotic agents are required, and the emergence from general anesthesia may be slow.

Effect of Anesthetic Agents on Disease Progression

In the same manner, anesthetic agents also affect the course of this disease. The experimental and animal studies showed that the general anesthetic agents and some perioperative events enhance the molecular mechanisms associated with AD. The use volatile anesthetic agents and hyperventilation increase the amyloid beta levels, and hypothermia leads to profound phosphorylation of tau (τ) protein. The clinical significance of such experimental studies is unclear. The data from retrospective studies fail provide any convincing evidence for an association between anesthetic exposure and the subsequent risk for development of AD. There is no single “best” anesthetic agent or technique for the patients with AD.

To summarize, the goals of anesthetic management of patients with AD are to avoid drug interactions, postoperative delirium, and the drugs and physiological conditions that can aggravate the disease and careful selection of anesthesia technique to maintain hemodynamic stability.

Anesthetic Considerations

Perioperative challenges of the patient with PD include maintenance of perioperative drug therapy that leads to potential adverse drug interactions, and various other systemic derangements associated with the disease ( Table 47.2 ). Our goal is to prevent the aggravation of symptoms and to maintain the hemodynamics. Perioperative stress can also worsen the disease.

Effect of the Disease on Anesthetic Agents

The short half-life of levodopa (about 90 min) makes its even brief interruption undesirable. Drug interactions might lead to malignant syndrome, characterized by hyperthermia, akinesia, altered consciousness, muscle rigidity, and autonomic dysfunction. Hence, the drug interruption should be brief, and if patients are not able to take oral drugs then intravenous levodopa with carbidopa should be used. Bioavailability of levodopa decreases significantly in patients with gastroparesis as it undergoes first-pass metabolism after absorption from stomach.

Effect of Anesthetic Agents on the Disease

Various agents being used perioperatively can affect the disease course of PD. Volatile anesthetic agents affect dopaminergic circuitry in the brain, but their effect on PD is not known. These agents have been successfully used during deep brain stimulation with intraoperative electrophysiological monitoring. Propofol has both excitatory and inhibitory effects and produces both dyskinesias and ablation of resting tremor, and has also been used successfully during deep brain stimulation surgery. Dexmedetomidine does not interfere with motor symptoms and appears to be safe. Ketamine has a potential of interactions with levodopa due to its sympathomimetic effects. Drugs acting on dopamine receptors (butyrophenones and phenothiazines) can exacerbate PD and should be avoided. In patients with deep brain stimulation coil implanted, the neurostimulator should be switched off during magnetic resonance imaging. In these patients if cautery is required intraoperatively then bipolar mode should be used, and the leads and generator should not be placed in the path from surgical site to the ground plate.

Regional anesthesia is advantageous over general anesthesia, as the side effects of general anesthetic agents can be avoided. Besides this, oral levodopa can be continued preoperatively, during surgery and in early postoperative period, if required. During regional anesthesia the pharyngeal and laryngeal reflexes are intact or at least same as baseline, so chances of aspiration are lesser. The major disadvantage of regional anesthesia is the difficulty in positioning the patient.

To summarize, the patients with PD are associated with multisystem derangements that leads to increased risk of perioperative morbidity and mortality. Our anesthetic goal should be to avoid any drug that can decrease the level of dopamine, and the drugs that interact with anesthetic agents.

Anesthetic Considerations ( Table 47.3 )

The literature on anesthetic management for a patient with HD is derived mostly through the case reports and by theoretical complications as per patient’s symptoms.