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Barry Inhalational
Inhalational anesthetics
| Question | Answer |
|---|---|
| General Anesthesia is characterized by | altered state reversible loss of consciousness analgesia amnesia muscle relaxation |
| Three Phases of General Anesthesia | Induction Maintenance Emergence |
| Meyer-Overton Rule | Anesthetic potency correlates with lipid solubility. Implies anesthesia results from molecules dissolving at specific lipophic sites. |
| Unitary Hypothesis | Proposes all inhalational anesthetics share a common mechanism of action at the molecular level |
| Critical Volume Hypothesis | anesthesia occurs when anesthetic binding to sites on cell membrane cause an expansion of the bilayer, altering its function |
| Receptor Theory | Enhancement of GABA receptor is thought to be a target in the CNS . |
| Stage I | Amnesia occurs with induction and LOC, no pain remembrance, lightest stage, patient still feels pain |
| Stage II | Delirium with period of excitement, muscle movement, irritability, and pupils dilated, disconjugate gaze, increased RR and HR, risk of laryngospasm |
| Stage III | Surgical plane (target depth), fixed gaze of eyes, constricted pupils and no response to pain |
| StageIV | Overdose, absent or shallow RR, hypotension, profound CV compromise |
| Anesthetic depth can be monitored by | lack of movement (in non-paralyzed), RR, depth and pattern, eye signs, bp and pulse, BIS monitor |
| FGF | fresh gas flow, determined by the vaporizer and flowmeter settings |
| FI | inspired gas concentration, determined by FGF, breathing circuit volume, and circuit absorption |
| Uptake | occurs in the lungs, = [(λ) x (Q) x (PA-Pv)]/Barometric Pressure |
| Target organ of inhaled | the brain |
| FA | alveolar gas concentration, determined by uptake, ventilation, the concentration effect and second gas effect |
| Fa | arterial gas concentration, affected by ventilation/perfusion mismatch |
| The more soluble the anesthetic agent is in the blood the ________ the patient becomes anesthetized | Slower |
| The more soluble the anesthetic agent is in the blood the ____ the drug goes into the body and not the brain | More |
| Insoluble agents have a slower uptake by the blood, therefore a _____ induction | Faster |
| If CO decreases what happens to the alveolar concentration(FA) | Decreased blood flow through the lungs, less anesthetic taken up by the blood therefore the alveolar concentration increases (highly soluble agents affected more) |
| If CO increases what happens to the FA | Increase in CO, more blood travels through the lungs, thereby removing more anesthetic from the gas phase, decrease alveolar concentration and slower FA increase (for soluble agents) |
| What determines PA-Pv(Partial Pressure difference in Alveolar gas and Venous blood) | tissue solubility, tissue blood flow, arterial blood/tissue partial pressure difference |
| What is reflected by PA-Pv | tissue uptake |
| How does ventilation affect FA (Alveolar Concentration) | Decreased alveolar partial pressure caused by uptake, can be countered by increasing ventilation (also by increasing FGF or decreasing FRC) |
| Brain uptake is ______ related to the alveolar concentration (FA): the greater the concentration, the faster the uptake | Directly |
| Concentration Effect | Increasing the inspired concentration can increase alveolar concentration and also its rate of rise |
| Increasing the concentration will _____ the rate of equilibrium of the agent | Speed-up |
| Uptake _______ as tissues become saturated | Declines |
| Second Gas Effect | administration of high concentration of a first or primary gas(usually N2O) increases the rate of uptake of a second gas given at the same time |
| Ventilation/Perfusion Mismatch will | slow the rate of induction with poorly soluble agents |
| Factors that control the concentration effect also control | the second gas effect (concentration and ventilation) |
| Factors Affecting Wake Up | Agent used (more solubility=longer recovery) Length of procedure, ventilation, age, mental state, medical conditions, other medications(benzo’s, opiates, neuroleptics, intoxicants), Obesity (all agents esp. soluble dissolve and create a depot in fat) |
| Metabolism/Elimination of gases is by: | Exhalation (increasing ventilation and FGF), anesthetic circuit volume (faster if decreased), Biotransformation: cytochrome P-450(CYP), trancutaneous (insig. Amt) |
| Respiratory effects of inhaled agents | TV decreased,RR increased, Minute ventilation remains constant,Chemoreceptor response to CO2 is blunted. |
| More Respiratory effects of inhaled agents | All are great bronchodilators by direct action on smooth muscle.Good for bronchospasm. |
| Desflurane (suprane) and Isoflurane (Forane) are | pungent (irritating, may cause laryngospasm) |
| Sevoflurane(Ultane), Halothane, and Nitrous (N2O) are | non-pungent |
| CVS effects of inhaled agents | All cause myocardial depression, CO is preserved, vasodilation (decreased SVR), coronary dilators |
| Can cause initial tachycardia | Desflurane >Isoflurane can cause initial tachycardia |
| Can reduce HR | Halothane reduces HR |
| CNS effects of inhalationals | increased CBF (autoregulation of CBF impaired), increased ICP d/t CBF and hypercapnea |
| EEG changes due to inhaled agents | decreased Amplitude, increased Latency |
| All volatile anesthetics cause this potential OB problem | Uterine Relaxation |
| Intraoperative Awareness risk factors | age, gender, substance abuse/use, underlying medical conditions, ALSO Paralytic use, Type of surgery Poor Machine maintenance, estimated at 0.15% |
| Renal risk factors induced by inhaled agents | renal function usually returns to normal after stopping anesthesia (dose dependent decreases in renal blood flow, GFR, Urine output), Sevo potentially produces Compound A which is renal toxin |
| Compound A | produced by degradation of Sevoflurane by strong bases found in CO2 absorber, increase probability for low flow rates or dried out CO2 absorbents, and greater than 2MAC hours of sevo with FGF<2L |
| Liver problems associated with inhaled agents | Halothane may cause a transient increase in LFT’s, Halothane hepatitis |
| MAC | alveolar concentration at one atmosphere of an inhalational agent at which 50% of patients do not move in response to skin incision or similar noxious stimuli |
| Why is the Alveolar concentration used as the measure of anesthetic concentration | because the partial pressure in the aveolus quickly equilibrates with that in the blood and brain because of the brains high blood flow |
| How is MAC related to potency? | MAC is INVERSELY related to POTENCY |
| What is ED95 | ED95= 1.2- 1.3 MAC of any volatile anesthetic has been found to prevent movement in 95% of patients |
| What is MAC awake | MAC of volatile anesthetic at which a patient will open their eyes (0.3-0.4 MAC) |
| What is MAC BAR | concentration required to block adrenergic responses to nociceptive stimuli (1.5-2.0 MAC) |
| MAC for loss of recall | 0.5 MAC |
| Factors that increase MAC | Hyperthermia, Drugs that increase CNS catecholamine levels (monoamine oxidase inhibitors, tricyclic antidepressants, acute cocaine use,Infants (6-12 months),Hypernatremia, chronic ethanol abuse |
| Factors that decrease MAC | Hypothermia, Preoperative medications (benzos, opiods), and IV anesthetics (lidocaine, ketamine), Neonates and the elderly (6% per decade), Pregnancy, Alpha-2 agonists, acute alcohol ingestion, hyponatremia, |
| Factors that have no efect on MAC | Duration and Gender, Anesthetic metabolism, Thyroid gland dysfunction,Hyper/Hypokalemia, PaCO2 15-95 mm HgPaO2 above 38Blood pressure above 50 mm Hg |
| Signs of MH | Increased ETco2, increased heart rate and temperature (late sign) |
| What is MH | The release of excessive calcium from the sarcoplasmic reticulum(SR), Fulminant HYPERMETABOLIC (fevers), induced by volatile anesthetics, succinylcholine, |
| Halothane | contains thymol preservative, non-pungent, soluble (BG coefficient= 2.5), halothane hepatitis, sensitizes the myocardium (↑ dysrhythmias), faster elimination that isoflurane d/t greater biotransformation |
| ISOFLURANE(Forane) | Advantages: cheap, soluble-slow to leave pt , coronary steal, Solubility-high residual at end of case, pungent (can’t be used for gas induction) Blood:Gas coefficient= 1.4 MAC:1.2, minimal cerebral dialation |
| Isoflorane may be a good choice for pt with | Increased ICP |
| DESFLURANE(Suprane) | Insoluble, fastest on and off, low residual at end of case, patient more awake, pungent, SNS stimulation (↑ HR), can’t be used for induction, careful irritable airways, BG coefficient 0.42 MAC 6.0, potential Carbon monoxide with dry CO2 absorbers |
| Desflurane(suprane) neg side effects | increased HR (espec, with rapid increase in []) airway irritation, potential for Carbon monoxide release with dry CO2 absorbers, increases ICP |
| SEVOFLURANE(Ultane) | non-pungent, good for fast induction (1-3min), less SNS activation, quicker wakeup, Compound A and absorber fires are potential problems, Blood:Gas coefficient= .65 MAC:2.0 |
| Sevoflurane is a good | bronchodilator |
| Nitrous Oxide (N2O) | Only inorganic,colorless, pleasant smell, non-pungent, non-explosive, non-flammable, usually used with inhaled or with O2, Blood:Gas coefficient= 0.47,No good for induction, minimal CV effects,NOT a MH trigger, increased RR,decreased TV, okay for OB, |
| Which Inhaled is okay for use during OB? | N2O |
| Side Effects of Nitrous oxide | slight myocardial depression usually offset by the SNS(increased endogenous catecholamines)Increased RR, decreased TV, reduced ventilatory response to hypoxia, mild increase is ICP |
| N2O problem during emergence | diffusion hypoxia, correct by using more O2 at end of case |
| Contraindications of Nitrous | Major drawback is the diffusion of N2O into closed air Avoid N2O use in bowel cases/obstruction, pnuemothorax/blebs, venous air emboli, middle ear surgery, some eye surgeries, Pulm HTN |
| Toxicity of Nitrous | N2O inhibits methionine synthetase by oxidizing the cobalt in Vit B12 and can result in bone marrow depression, spontaneous abortions in women working in the OR/dental offices (Unproven) |
Created by:
dupy6
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