Chapter 10: General Anesthetics
What is the minimal level of oxygen required for nitrous oxide fail-safe systems?
30% Nitrous oxide equipment today has built-in safety features, including a minimal concentration of 30% oxygen flow, or the machine's fail-safe system will shut off the flow of nitrous oxide
For safe administration, levels of nitrous oxide required used for patient comfort should not exceed which of the following?
50% The percentage of nitrous oxide required for patient comfort may range from 10% to 50%, with the average being 35%. At levels higher than 50%, increased adverse effects such as vomiting and loss of consciousness may occur
Modern anesthetic techniques use more rapidly acting agents than those associated with Guedel's stages. Flagg's stages reflect these agents and include all except which of the following?
Analgesia Analgesia is not included in Flagg's stages of general anesthesia. Flagg's stages describe more rapidly acting anesthetic agents than those used when Guedel's stages were developed, and they include the following:(1) Induction—all preparation and medication for the patient up to the beginning of the operation, including preoperative medications, adjunctive drugs to anesthesia, and anesthetics required for induction.(2) Maintenance—this phase begins with the patient at the depth of anesthesia sufficient to allow surgical manipulation and continues to the completion of the procedure.(3) Recovery—this phase begins with the termination of the surgical procedure and continues throughout the postoperative period until the patient is fully responsive to the environment.
All are contraindications for nitrous oxide administration except which of the following?
Anxious patients Anxiety is one of the primary indications for use of nitrous oxide conscious sedation. Any condition that interferes with the patient's ability to breathe will interfere with the efficacy of nitrous oxide. Respiration in patients with chronic obstructive pulmonary disease, such as emphysema, is driven by lack of oxygen, and the increased levels of oxygen given with nitrous oxide could interfere with their respiratory drive. Patients who are emotionally unstable may be taking psychotropic medications that could have an adverse effect
Which color is a nitrous oxide cylinder in the United States?
Blue Nitrous oxide cylinders are standardized by color coding for safety. Nitrous oxide cylinders in the United States are color-coded blue, and oxygen cylinders are green.
Which of the halogenated hydrocarbon general anesthetics requires a special vaporizer and cannot be used for induction because it induces cough and laryngospasm?
Desflurane Desflurane's low volatility requires a special vaporizer. Because of its ability to cause cough and laryngospasm, it cannot be used for induction.
Which agent would be most effective for the surgical stage of general anesthesia?
Enflurane Enflurane is one of the most commonly used volatile liquid general anesthetic agents. Midazolam and nitrous oxide are anxiolytic agents that are used adjunctively with general anesthetic agents. Levodopa is used in the treatment of Parkinson's disease.
Adverse effects of the halogenated hydrocarbon general anesthetic halothane include all except which of the following?
Hypertension Halothane has not been shown to have cause hypertension. Adverse effects include hypotension and cardiac depression. This agent sensitizes the heart to catecholamines such as epinephrine and norepinephrine, and can cause serious cardiac arrhythmias such as ventricular fibrillation. It is also linked to hepatoxicity.
Diffusion hypoxia at the end of nitrous oxide administration can be prevented by
Increasing the percentage of oxygen to 100% for 5 minutes The patient should be placed on 100% oxygen for at least 5 minutes at the termination of a procedure using nitrous oxide sedation to prevent the phenomenon known as diffusion hypoxia. The rapid outflow of nitrous oxide accompanied by oxygen and carbon dioxide can cause severe headache and other adverse effects.
Use of this halogenated hydrocarbon general anesthetic can provoke coughing but does not cause liver toxicity. Low tissue solubility allows for rapid induction and recovery, making it a useful and popular drug for general anesthetic.
Isoflurane The tissue solubility of isoflurane (Forane) is poor, which allows for rapid induction and recovery. Its odor limits induction concentration because of the potential for coughing. Because only about 15% of isoflurane is metabolized in the liver, hepatoxicity is not a problem
Which general anesthetic agent can produce dissociative anesthesia?
Ketamine Ketamine produces a state called dissociative anesthesia because it disrupts association pathways in the brain. The patient taking ketamine appears catatonic and has amnesia. Analgesia is produced without loss of consciousness.
The properties that make nitrous oxide conscious sedation popular in dental offices include all except which of the following?
Long period of onset and recovery Nitrous oxide has low blood solubility, which allows rapid onset and quick recovery. It is popular in dental offices because of its analgesic and anxiolytic properties, ease of administration, and the retention of consciousness and protective reflexes
All of these drugs are used as part of balanced general anesthesia except which of the following?
Long-acting barbiturates Balanced general anesthesia uses several agents to help the patient pass smoothly into general anesthesia and decrease adverse effects. The ultrashort-acting barbiturates combined with nitrous oxide and oxygen are used to move the patient easily from stage I to stage III, skipping stage II. Volatile inhalation anesthetics are then administered to produce profound general anesthesia
What is the major disadvantage to using opioids as adjunctive drugs to general anesthesia?
Prolonged respiratory depression The most serious disadvantage of opioids as adjunctive drugs to general anesthesia is prolonged respiratory depression, which can lead to death if the patient is not carefully monitored. Miosis, abuse potential, and decreased gastrointestinal motility are additional, less serious adverse drug effects.
Which general anesthetic agent is unrelated to any other general anesthetic and has the advantage of allowing patients to "feel better" and ambulate sooner than with other agents?
Propofol Propofol is a general anesthetic agent that is unrelated to any other general anesthetic and has the advantage of allowing patients to "feel better" and ambulate sooner than with other agents. It is an IV anesthetic that has a rapid onset and duration of about 5 minutes. It is also used for IV sedation and for induction and maintenance of balanced anesthesia. Enflurane and halothane are both classified as volatile liquid anesthetics. Ketamine is chemically related to phencyclidine (PCP) and produces analgesia without loss of consciousness. Morphine is an opioid that is used as an adjunctive drug to general anesthetic
Intravenously administered general anesthetics include all classifications of central nervous system depressants except which of the following?
Prostaglandin inhibitors Prostaglandin inhibitors are a class of analgesics, not general anesthetic agents. Opioids, ultrashort-acting barbiturates, and benzodiazepines are central nervous system depressants that are used for induction and short periods of general anesthesia
Which is the limiting complication of the intravenous use of barbiturates?
Repeated dosing leads to prolonged recovery The intravenous use of barbiturates as an adjunct to general anesthesia is limited because repeated dosing of these drugs can greatly prolong the patient's recovery
All are important components of general anesthesia except which of the following?
Respiratory paralysis Respiratory paralysis would result in patient death, so is not a desired component of general anesthesia. The goals of surgical anesthesia are loss of consciousness, adequate muscle relaxation, good patient control, and pain cessation
Guedel's stages and planes of anesthesia describe changes that occur during anesthesia. Which stage can be uncomfortable for the patient, when emesis and incontinence may occur?
Stage II Stage II is the excitement or delirium stage of general anesthesia, beginning with loss of consciousness and associated with involuntary movement and sympathetic stimulation. Tachycardia, hypertension, emesis, and incontinence can occur. Having a rapid and smooth passage through stage II into stage III (i.e., surgical anesthesia) is important for patient comfort.
Guedel's stages and planes of anesthesia describe changes that occur during anesthesia. Which stage is absolutely contraindicated because of severe respiratory depression leading to possible death?
Stage IV Stage IV is characterized by respiratory and circulatory failure; if this stage is not immediately reversed, the patient will die. Stage I analgesia is characterized by analgesia or reduced pain sensation. The patient is conscious and responsive. Stage II delirium or excitement begins with unconsciousness and is associated with involuntary movement and excitement. Stage III surgical anesthesia is the stage during which most major surgery occurs.
The potency of general anesthetic inhalation agents is measured by the blood/gas partition coefficient. The less soluble the anesthetic is in the body tissues, the more rapid the onset and recovery will be.
The first statement is false; the second statement is true. The solubility of a general anesthetic is measured by the solubility in the blood. Drugs that are highly soluble in the blood have an increased induction and recovery time. The potency of an anesthetic agent is measure by the minimal alveolar concentration of an anesthetic at 1 atmospheric pressure.
The chronic abuse of nitrous oxide can induce neuropathy. These conditions include vision and hearing problems.
The first statement is true; the second statement is false. Chronic nitrous oxide abuse can cause nitrous-induced neuropathy symptoms, including numbness and paresthesias of the hands and legs that progresses to more serious neurologic symptoms with continued abuse. Liver and kidney problems have also been associated with nitrous oxide abuse
