19 Anesthetic Agents

Ideal Anesthetic Rapid and pleasant induction and withdrawal from anesthesia Skeletal muscle relaxation Analgesia High potency Wide therapeutic index Nonflammable Chemical inertness

Stages of Anesthesia Analgesia: pain abolished but consciousness retained Excitement: unconsciousness but possible unpleasant shaking, violence, and fear

Stages of Anesthesia Surgical anesthesia: progressive muscle relaxation and unconsciousness Medullary paralysis: respiratory failure and circulatory collapse

Preoperative Medications Adjuncts to surgery; preanesthetics Used to reduce anxiety, sedate, produce amnesia, increase comfort, reduce gastric acidity and volume, increase gastric emptying, decrease nausea and vomiting, reduce incidence of aspiration

Table 19-1 Preoperative Medications as Adjuncts to Surgery

Table 19-1 (continued) Preoperative Medications as Adjuncts to Surgery

Table 19-1 (continued) Preoperative Medications as Adjuncts to Surgery

General Anesthetics Affect whole body; produce unconsciousness by depressing CNS Skeletal muscle relaxation and diminished reflexes Used in combinations to smoothly and rapidly induce anesthesia and allow prompt recovery; ensure wide safety margin; and reduce side effects

Choosing Appropriate Anesthesia The choice of anesthetic drug depends on many factors, including: Patient’s general physical condition Area being operated on Anticipated length of procedure

Adverse Drug Reactions Older adults are more likely to experience adverse drug reactions than younger adults because, in general, they take more medications.

Types of General Anesthesia Inhalation anesthetics: volatile liquids or gases Intravenous anesthetics

Table 19-2 General Anesthetics Used by Inhalation

Dangers of Malignant Hyperthermia Malignant hyperthermia is a life-threatening, acute pharmacogenetic disorder that develops during anesthesia. Characterized by rapid increase in body temperature, unexplained tachycardia, unstable blood pressure, muscle rigidity, and cyanosis

Table 19-3 General Anesthetics Commonly Given by Injection

Figure 19-1A Mechanism of action of anesthetics: normal nerve conduction.

Figure 19-1B Mechanism of action of anesthetics: anesthetic blocking sodium channels.

Diabetes and Surgery The stress of surgery in diabetic patients may increase blood glucose levels. Insulin or hypoglycemic medications should be coordinated with the: Patient Surgeon Anesthesiologist

General Anesthetics: Uses Lipophilic agents that cross blood–brain barrier to close sodium channels to prevent neural conduction Used in combination to produce balanced anesthesia

General Anesthetics: Adverse Effects Common: drowsiness, weakness, or fatigue for a few days postanesthesia; fuzzy thinking, blurred vision, incoordination Other: headache, shivering, muscle pain, nausea and vomiting, sore throat, nightmares

General Anesthesia: Contraindications Contraindicated in patients who: Have received MAOIs in previous 14 days Are intolerant to benzodiazepines

General Anesthesia: Contraindications Also contraindicated in patients who have: Hypersensitivity Myasthenia gravis Acute glaucoma Increased intracranial pressure

General Anesthesia: Contraindications Also contraindicated in patients who have: Impaired cerebral circulation Alcohol intoxication Status asthmaticus Porphyrias

Local Anesthetics Used to provide regional or topical anesthesia without loss of consciousness Two groups: esters and amides

Table 19-4 Local Anesthetics

Table 19-4 (continued) Local Anesthetics

Amide Anesthetics: Uses Inhibit sodium channels, which inhibits nerve impulse transmission Used to increase patient comfort and cooperation during procedures including incision and drainage, laceration repair, biopsy, wart treatment, vasectomy, neonatal circumcision, dental procedures, childbirth, diagnostic procedures

Amide Anesthetics: Adverse Effects Toxic effects are dose related. Symptoms of toxicity: dizziness, nystagmus, restlessness, disorientation, psychosis, slurred speech, tremors, hypotension, bradycardia, cardiac arrest

Amide Anesthetics: Contraindications Contraindicated in older adults, debilitated adults, and children; pregnancy, labor, lactation, sepsis, acidosis, heart or spinal block, severe hemorrhage, hypotension and shock, hypertension, and more Local anesthetics interact with many drugs.

Amide Anesthetics: Patient Information Instruct patients to report Dizziness Disorientation Slurred speech

Mechanism of Action of Lidocaine Animation Click on the screenshot to view an animation showing the mechanism of action of lidocaine. Back to Directory

Specific Anesthetic Applications Topical anesthesia Infiltration anesthesia Field block anesthesia Nerve block anesthesia Spinal anesthesia Epidural anesthesia

Figure 19-2 Techniques for applying local anesthesia: topical (A), nerve block (B), infiltration (C), spinal (D), and epidural (E).

Topical Anesthesia Application of nerve conduction blocking agent onto tissue layer Provides anesthesia of urethra, vagina, rectum, skin Affected tissue is limited to area in contact with topical anesthesia. Cryoanesthesia: application of freezing agent

Local Infiltration Anesthesia Blocks nerves Produced by injection of anesthetic into an area Most common local anesthesia

Field Block Anesthesia Affects a single nerve, deep plexus, or network of nerves Administered in series of injections to form a wall of anesthesia around an operative field

Spinal Anesthesia Anesthetic agent is injected into subarachnoid space through a spinal needle Used for gynecological, obstetrical, orthopedic, and genitourinary surgery

Epidural Anesthesia Injection of local anesthetic into epidural space via a catheter; allows repeated infusions Anesthetic agent is slowly absorbed into cerebrospinal fluid. Used for labor and delivery