Anesthesia Flashcards
Define anesthesia.
A reversible state of CNS depression where the patient is in an amnestic state resulting in the loss of response to external stimuli and pain.
What are the five benefits of anesthesia?
- Sedation and reduction of anxiety.
- Lack of awareness and amnesia.
- Skeletal muscle relaxation.
- Suppression of undesirable reflexes.
- Analgesia.
None of the currently available anesthetic agents when used alone can achieve all of these desired effects well.
What are the factors that we should consider when selecting anesthetic agents?
- Status of the patient’s organ systems.
- Concomitant use of drugs.
What are the considerations for the cardiovascular system in the selection of anesthetic agents?
Anesthetic agents can suppress cardiovascular function to varying degrees, necessitating treatment with vasoactive substances.
This is especially important in patients with coronary artery disease (CAD), heart failure (HF), dysrhythmias, valvular disease, and other cardiovascular diseases (CVD).
How do inhaled anesthetics affect the respiratory system?
Inhaled anesthetics depress the respiratory system by reducing the ventilatory response to increased levels of CO2 in the blood.
They also act as bronchodilators and are classified based on whether they are pungent (airway irritants) or non-pungent anesthetics.
What is the impact of anesthetics on the liver and kidneys?
Some anesthetics are hepatotoxic and nephrotoxic, with the release of fluoride, bromide, and other metabolites of halogenated hydrocarbons potentially affecting these organs.
Which patients should be cautious with anesthesia due to nervous system concerns?
Patients with epilepsy, myasthenia gravis, neuromuscular disease, and compromised cerebral circulation should avoid anesthesia or require careful selection of the anesthetic agent.
What are the risks of administering anesthesia during pregnancy?
Certain anesthetics can harm the pregnant individual and the fetus.
For example, nitrous oxide may cause aplastic anemia, and benzodiazepines have been associated with oral clefts and floppy baby syndrome (temporary hypotonia).
What is the role of muscle relaxants in anesthesia?
Muscle relaxants, such as NMJ blockers and curares, are used to facilitate intubation during anesthesia.
How do H2 blockers contribute to the anesthetic process?
H2 blockers like famotidine and ranitidine are used to reduce gastric acidity, which is important during anesthesia.
What is the purpose of benzodiazepines (BZs) in anesthesia?
Benzodiazepines, such as midazolam and diazepam, are used for their anxiolytic effects and to facilitate amnesia.
How do barbiturates assist in anesthesia?
Barbiturates aid in sedation and facilitate smooth induction of anesthesia. When administered concurrently, they also lower the dose of anesthetic required to maintain the desired level of surgical anesthesia.
What is the role of non-opioids and opioids in anesthesia?
Non-opioids like acetaminophen and celecoxib or opioids like fentanyl, are administered for their analgesic properties.
Why are antihistamines used in the context of anesthesia?
Antihistamines are used to prevent allergic reactions during the administration of anesthesia.
How does a serotonin antagonist like ondansetron serve in anesthesia?
Ondansetron is a serotonin antagonist used to prevent postoperative nausea and vomiting.
What is the role of anticholinergic drugs in anesthesia?
Anticholinergic drugs, such as glycopyrrolate, are used to prevent bradycardia and the secretion of fluids into the respiratory tract during anesthesia.
What is a potential downside of coadministering multiple drugs with anesthesia?
Coadministration can enhance undesirable anesthetic effects such as hypoventilation.
What is the induction stage of anesthesia?
Induction is the period from the onset of administration of the potent anesthetic until the development of effective surgical anesthesia.
What is the induction stage of anesthesia?
Induction is the period from the onset of administration of the potent anesthetic until the development of effective surgical anesthesia.
What is the purpose of the maintenance stage in anesthesia?
Maintenance is the phase that provides sustained surgical anesthesia during the procedure.
What happens during the recovery stage of anesthesia?
Recovery is the period after the discontinuation of anesthesia until consciousness and protective physiologic reflexes are regained.
How is anesthesia induction usually initiated in adults, and what is its onset time?
Anesthesia induction is normally initiated with an IV anesthetic like propofol, which produces unconsciousness within 30-40 seconds after injection.
Why are IV anesthetics often used for induction?
IV anesthetics are preferred for their rapid onset and the ability to control the depth of anesthesia quickly.
How is anesthesia induction performed in children without IV access?
Inhalation induction is used with non-pungent agents such as halothane or sevoflurane to induce general anesthesia in children without IV access.
How is anesthesia commonly maintained, and why?
Anesthesia is commonly maintained with the administration of volatile anesthetics, which offer good control over the depth of anesthesia.
Why are IV anesthetics used during induction not typically used for maintaining anesthesia?
IV anesthetics used during induction usually have a short duration of action and cannot maintain the anesthetic activity for a long time.
What underlines the recovery process from anesthesia?
Redistribution from the site of action, rather than metabolism of the anesthetic, plays a major role in the recovery process.
What characterizes Stage I of anesthesia?
Stage I is known as the analgesia stage, where pain sensation is diminished.
What is stage II of anesthesia, and how can it be managed?
Stage II is known as the excitement stage. To shorten this stage, a rapid-acting agent like propofol is given intravenously before inhalation anesthesia is administered.
What is crucial about managing stage III of anesthesia?
Stage III is known as surgical anesthesia. Continuous careful monitoring is required to prevent progression to stage IV.
What is stage IV in anesthesia and why is it critical to avoid?
Stage IV is characterized by medullary paralysis, severe depression of the respiratory and vasocenters, which can lead to coma and death, hence it must be avoided.
What factors determine the rate of transfer of anesthetic agent from alveoli to arterial blood and from arterial blood to the brain?
The rate of anesthesia is positively affected by the anesthetic concentration in inspired air and negatively affected by the anesthetic solubility in blood. Pulmonary blood flow has a complex effect; it has a negative impact on the induction speed for soluble agents due to uptake by the blood, but positive for insoluble agents. Pulmonary ventilation positively influences the rate of anesthesia.
How does the concentration of anesthetic in the inspired air affect the induction of anesthesia?
Increasing the concentration of anesthetic in the inspired air leads to a higher alveolar anesthetic concentration, which increases the rate of transfer into the blood, and consequently, speeds up the rate of induction of anesthesia.
What is the blood:gas solubility coefficient and how does it affect anesthesia induction and recovery?
The blood:gas solubility coefficient defines the relative affinity of an anesthetic for blood compared to air. Agents with low blood solubility have a low blood:gas solubility coefficient, leading to rapid alveolar concentration increase, quick equilibration with the blood and brain, rapid induction, and recovery. Agents with higher solubility have slower induction and recovery.
How is solubility in blood ranked according to the blood:gas solubility coefficient for common anesthetics?
The ranking from highest to lowest solubility coefficient is:
halothane > enflurane > isoflurane > sevoflurane > desflurane > nitrous oxide.
How does an increase in cardiac output affect the induction of anesthesia in terms of pulmonary blood flow?
An increase in cardiac output leads to increase pulmonary blood flow, which removes more anesthetic agent from the alveoli. This reduces the rate of increase in arterial tension of the anesthetic, thereby slowing down the induction process.
How do changes in minute ventilation affect the induction of anesthesia with insoluble and soluble agents?
For insoluble agents in the blood, changes in minute ventilation have little influence on induction since the alveolar concentration is always high. However, for soluble agents, increased minute ventilation significantly raises alveolar tension, thereby affecting induction.
What is the primary use of inhalation anesthetics?
Inhalation anesthetics are mainly used for the maintenance of anesthesia after induction with an IV agent.
What types of inhalation agents are commonly used?
Common inhalation agents include gas anesthetics like nitrous oxide, and liquid volatile anesthetics such as halothane, sevoflurane, desflurane, and isoflurane.
How can the depth of anesthesia be adjusted during maintenance?
The depth of anesthesia can be rapidly altered by changing the inhaled concentration of the drug. Increasing anesthetic concentration increases the transfer of the drug to the blood.
What should be considered due to the therapeutic index of inhalation anesthetics?
Inhalation anesthetics have a very narrow therapeutic index, generally from 2 to 4, which means they should be monitored carefully.
Are there antagonists for inhalation anesthetics?
No antagonists exist for inhalation anesthetics.
What are the general safety features of inhalation anesthetics?
Inhalation anesthetics are generally nonflammable and nonexplosive, with the exception of ether.
How do inhalation anesthetics affect cerebrovascular resistance?
Inhalation anesthetics decrease cerebrovascular resistance, which leads to increased perfusion of the brain.
What effect do inhalation anesthetics have on bronchial smooth muscle and how is this beneficial?
Inhalation anesthetics can cause bronchodilation, which can be particularly useful for patients with wheezing and status epilepticus.
How is the potency of inhaled anesthetics defined?
The potency of inhaled anesthetics is defined as the minimum alveolar concentration (MAC).
How is MAC expressed, and what does it indicate?
MAC is usually expressed as the percentage of gas in a mixture required to achieve anesthetic immobility. It indicates the concentration needed to prevent movement in response to surgical incision in 50% of subjects.
What is the relationship between MAC and the potency of anesthetics?
A smaller MAC value indicates a more potent anesthetic (such as sevoflurane, isoflurane, and halothane), while a larger MAC indicates a less potent agent (such as nitrous oxide).
How does lipid solubility affect the potency of an anesthetic?
The more lipid-soluble an anesthetic is, the higher the fat:gas partition coefficient and the lower the MAC value, which corresponds to higher potency.
What factors can increase MAC, making the patient less sensitive to anesthetics?
Factors that increase MAC include hyperthermia and increased CNS catecholamines (due to drugs like ephedrine and amphetamine). Chronic ethanol abuse can also increase MAC.
What factors can decrease MAC, making the patient more sensitive to anesthetics?
Factors that decrease MAC include increased age, hypothermia, pregnancy, sepsis, acute ethanol intoxication, concurrent administration of IV anesthetics, and α-2 adrenergic receptor agonists like clonidine and dexmedetomidine.
What is the primary effect of intravenous anesthetics on the induction of anesthesia?
Intravenous anesthetics cause the rapid induction of anesthesia.
Is there a specific receptor identified for the action of general anesthetics?
No specific receptor has been identified as the locus of general anesthetic action.
What are the main targets for inhalation anesthetic action?
The main targets for inhalation anesthetics are 1) increasing the sensitivity of GABA receptors to GABA, 2) increasing the activity of glycine receptors in the spinal motor neurons, and 3) blocking the excitatory postsynaptic currents of the nicotinic and glutamate receptors.
What are the key characteristics of Halothane as an anesthetic?
Halothane is a prototype anesthetic that is non-explosive and allows for rapid induction and quick recovery compared to previous anesthetics, despite having a high blood:gas partition coefficient which generally leads to slower induction and recovery than the newest anesthetics.
What are the therapeutic uses of Halothane?
Halothane is used as a potent anesthetic often coadministered with nitrous oxide, opioids, or local anesthetics due to its relatively weak analgesic properties. It causes uterine and skeletal muscle relaxation (useful in obstetric when uterine relaxation is indicated) and is a bronchodilator and non-pungent, making it suitable for patients with airway problems.
Why is Halothane considered suitable for children?
Halothane is considered suitable for children due to its low hepatotoxicity in the pediatric population and its pleasant odor which makes administration easier.
What are the pharmacokinetics and potential hepatotoxic effects of Halothane?
Halothane is metabolized to tissue-toxic hydrocarbons like trifluoroethanol and bromide ions, which can cause hepatic necrosis. Symptoms of this include anorexia, nausea, vomiting, and possible signs of hepatitis. Therefore, Halothane anesthesia should not be repeated at intervals of less than 2-3 weeks to avoid such effects.
What are the cardiac effects associated with Halothane use?
Halothane can cause myocardial depression, leading to reduced cardiac output and hypotension. It also has vagomimetic effects that can cause atropine-sensitive bradycardia and may sensitize the heart to arrhythmias.
What is malignant hyperthermia and how is it related to Halothane?
Malignant hyperthermia is a life-threatening condition characterized by severe muscle contraction, increased skeletal muscle oxidative metabolism, and an overwhelming increase in body temperature, which can lead to death if not treated immediately. It can be triggered by Halothane.
