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Inhalation Anesthesia

Anesthetic Considerations Using Potent Inhaled Anesthetics: Desflurane Rapid Emergence & Economic Advantages Ann Briggs, MS, CRNA Loyola University Medical Center Department of Anesthesia Maywood, IL. Inhalation Anesthesia. Depth of anesthesia determined by concentration of anesthetic in CNS

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Inhalation Anesthesia

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  1. Anesthetic Considerations Using Potent Inhaled Anesthetics: Desflurane Rapid Emergence & Economic AdvantagesAnn Briggs, MS, CRNALoyola University Medical CenterDepartment of AnesthesiaMaywood, IL

  2. Inhalation Anesthesia • Depth of anesthesia determined by concentration of anesthetic in CNS • Concentration of individual gas in mixture of gases proportionate to partial pressure or tension • Important factor influencing transfer of anesthetic from lungs to arterial blood is solubility

  3. Inhaled Anesthetics • Isoflurane • Desflurane • Sevoflurane

  4. Isoflurane: Advantages • Minimal organ toxicity • Low acquisition cost

  5. Isoflurane: Disadvantages • Moderate blood/gas solubility • Moderate tissue/blood solubility • Slower awakening

  6. Desflurane: Advantages • Precise control of anesthetic concentration • Rapid elimination & recovery regardless of anesthetic duration • Safe with use of low flows • Cost-competitive with low flows

  7. Desflurane: Disadvantages • Delivered with rapid titration to high concentrations • - Transient sympathetic hyperactivity • Suboptimal for inhalation induction • - Pungency & airway irritability

  8. Sevoflurane: Advantages • Recovery superior to isoflurane • Lack of pungency • Smooth mask or vital capacity induction

  9. Sevoflurane: Disadvantages • Slower than desflurane in speed of recovery • Potential for renal injury due to production of compound A & inorganic fluorides • - Renal insufficiency: creatinine >1.5 mg/dl • Minimum low flow rate of <1 L/min not recommended • Exposure to 1 or <2 L/min FGF not to exceed 2 MAC-hours • Precautions in pediatric cases – reported associated cases of seizures • Canister fires

  10. Recovery Characteristics • Early recovery indicators: • Time to eye opening • Time to orientation • Late recovery indicators: • Ready to leave recovery room • Ready to go home • 24 hour post recovery: • Full activity next day • Mahmoud NA, et al: Desflurane or Sevoflurane for gynaecological day-case anaesthesia with spontaneous respiration? Anaesthesia. 2001.

  11. Solubility in Blood

  12. Intraoperative Management

  13. Metabolism of Inhaled Agents

  14. Emergence and Extubation: Desflurane vs Isoflurane, Propofol, and Sevoflurane

  15. Intraoperative Management

  16. Review of Pharmokinetics • Most insoluble of the potent inhaled anesthetics. • A blood: gas partition coefficient of 0.42, similar to that of nitrous oxide (0.47). • Sevoflurane is greater than 50% more soluble in the blood than desflurane, with a blood: gas partition coefficient of 0.69. • Desflurane also has the lowest blood, fat and lean tissue solubilities of all potent inhaled anesthetic agents.

  17. Least metabolized of the potent inhaled anesthetics and is metabolized 10-fold less than isoflurane. • MAC decreases with age.

  18. Switching from isoflurane to desflurane at the end of a case does not improve time to awakening. • Bis monitoring reduces inhaled anesthetic usage 30-38% with more rapid awakening and increased ability for fast-tracking. • Overall, the use of desflurane has many advantages in fast-track anesthesia.

  19. Recovery Thresholds • MAC – Awake is 0.3 MAC • Threshold for cognitive impairment is 0.1 MAC • Does full recovery occur at 0.05 MAC? • For the patient maintained at 1 MAC, 95% decreament is needed to attain full recovery Eger EI II, Schafer SL Anesth Analg 2005; 101: 688-696

  20. Special Clinical Techniques and Considerations • Low flows • Use with LMAs • Overweight - obese patients • Elderly patients • Patients that smoke or have irritable airways

  21. Low Fresh Gas Flows • Low inflow administration can be defined as fresh gas flows of less than half the alveolar minute volume • Low flow anesthesia is an inhalation technique in which a circle system with absorbent is used with fresh gas inflow ranging from: • - 500 ml/min • - 1 L/min or less • - 3 L/min or less

  22. Low Flow: Advantages • Provides a more economical delivery of anesthesia • - Lower cost • Reduced heat loss • Maintenance of humidification & temperature • - Decreased shivering • Decreased release of anesthetic to the environment • - Limits atmospheric pollution

  23. Cost Savings • The cost-effective way to use inhaled anesthetics is to reduce gas flow rates during maintenance phase. • IL/min (or less) for desflurane • 2L/min for sevofurane

  24. Alternative to mask &endotracheal intubation. “Most important use” –> difficult or failed intubation. LMAs

  25. LMA: Advantages • No requirement for muscle relaxation. • Minimal CV response & stress response with insertion. • Less pollution in OR than with mask anesthesia.

  26. LMA: Disadvantages • Possible aspiration of gastric contents • Coughing and laryngospasm • Difficulty positioning • Trauma to the airway

  27. LMA The most common problems encountered with insertion or tolerance of the LMA are due directly to inadequate depth of anesthesia – regardless of the anesthetic agent in use.

  28. Clinical Use • Gradually increase the delivered desflurane concentration of 1% (at 4-6 l/min flow rate) every few breaths until desired anesthetic depth is reached; then may switch to low flow for maintenance. • Desflurane concentrations of less than 6% rarely produce clinical manifestations of airway irritation or sympathetic stimulation, especially if adjuncts are used.

  29. There is an incorrect perception that there is a difference in ease of use between desflurane and sevoflurane when utilizing an LMA. • At MAC or lower none of the potent inhaled anesthetics have significant irritant effects. • In unmedicated patients, 5.4% desflurane does not produce breath holding, coughing, laryngospasm or increased secretions yet allows the insertion of an oral airway. * The incidence of coughing during anesthetic maintenance while using a LMA is minimal and does not differ among the anesthetics commonly used for anesthesia, including propofol.

  30. Figure 1. The incidence of coughing during anesthetic maintenance during use of an LMA is minimal and does not differ among the anesthetics commonly used for anesthesia. % of Patients Coughing During Anesthesia While Breathing Through a Laryngeal Mask Airway (differences not significant) Data for desflurane and isoflurane are from Ashworth and Smith. Data for sevoflurane are from Tang et al. Both of these references supplied the data for propofol.

  31. Desflurane/Sevoflurane

  32. Recovery Characteristics

  33. Sevoflurane/Desflurane(The Day After)

  34. Conclusions

  35. Observations

  36. Patients that Smoke or have Irritable Airways

  37. Airway Responses • Laryngospasm • Bronchoconstriction • Swallowing • Coughing • Cardiovascular Stimulation??

  38. How to Reduce Irritation Response • Reduce or Eliminate the: • - Irritation itself • - Sensitivity of the receptors • - Physiologic response to irritation

  39. Reduce Receptor Sensitivity • IV agents • Topical Agents

  40. Reduce Physiologic Response • Continue Inhalers • Deepen General Anesthesia • Reduce Preoperative Anxiety

  41. Study

  42. Method

  43. Observations

  44. Recent Studies Utilizing LMAs

  45. Smoker Study Airway Responses During Desflurane Versus Sevoflurane Administration via a LMA in Smokers. McKay RE et al. Anesthesia and Analgesia, Nov. 2006

  46. Study Objective Study tested whether the use of a more pungent anesthetic (desflurane) would result in a higher rate of coughing, breath holding, laryngospasm or desaturation among patients who smoke. Average pack years smoked: 25 years

  47. In summary, in patients who smoke, the incidence and severity of respiratory complications during maintenance of anesthesia delivered via an LMA are modest but occur more than in non-smokers. For either smokers or non-smokers, the incidence does not differ for desflurane vs. sevofluane. Initial recovery is more rapid with desflurane.

  48. Elderly Population • Elderly (> 65 years) population is the fastest growing demographic segment in the U.S. • In 2000, 4.2 million aged > 85 years old, a 30% increase since 1990. • 75-84 years old number 12.4 million, more than a 20% increase since 1990.

  49. Elderly Population • Aging increases the probability of requiring a surgical procedure. • - 12% likelihood 45-60 years old. • - >21% in those aged > 65 years old • Perioperative mortality increases with age. • - Steep increases observed after age 75 • years.

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