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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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slide1

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

inhalation anesthesia
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

inhaled anesthetics
Inhaled Anesthetics
  • Isoflurane
  • Desflurane
  • Sevoflurane
isoflurane advantages
Isoflurane: Advantages
  • Minimal organ toxicity
  • Low acquisition cost
isoflurane disadvantages
Isoflurane: Disadvantages
  • Moderate blood/gas solubility
  • Moderate tissue/blood solubility
  • Slower awakening
desflurane advantages
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
desflurane disadvantages
Desflurane: Disadvantages
  • Delivered with rapid titration to high concentrations
    • - Transient sympathetic hyperactivity
  • Suboptimal for inhalation induction
    • - Pungency & airway irritability
sevoflurane advantages
Sevoflurane: Advantages
  • Recovery superior to isoflurane
  • Lack of pungency
  • Smooth mask or vital capacity induction
sevoflurane disadvantages
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
recovery characteristics
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.
slide14

Emergence and Extubation:

Desflurane vs Isoflurane, Propofol, and

Sevoflurane

review of pharmokinetics
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.
slide17
Least metabolized of the potent inhaled anesthetics and is metabolized 10-fold less than isoflurane.
  • MAC decreases with age.
slide18
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.
recovery thresholds
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

special clinical techniques and considerations
Special Clinical Techniques and Considerations
  • Low flows
  • Use with LMAs
  • Overweight - obese patients
  • Elderly patients
  • Patients that smoke or have irritable airways
low fresh gas flows
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
low flow advantages
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
cost savings
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
slide24
Alternative to mask &endotracheal intubation.

“Most important use” –> difficult or failed intubation.

LMAs
lma advantages
LMA: Advantages
  • No requirement for muscle relaxation.
  • Minimal CV response & stress response with insertion.
  • Less pollution in OR than with mask anesthesia.
lma disadvantages
LMA: Disadvantages
  • Possible aspiration of gastric contents
  • Coughing and laryngospasm
  • Difficulty positioning
  • Trauma to the airway
slide27
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.

clinical use
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.
slide29
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.

slide30

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.

airway responses
Airway Responses
  • Laryngospasm
  • Bronchoconstriction
  • Swallowing
  • Coughing
  • Cardiovascular Stimulation??
how to reduce irritation response
How to Reduce Irritation Response
  • Reduce or Eliminate the:
    • - Irritation itself
    • - Sensitivity of the receptors
    • - Physiologic response to irritation
reduce receptor sensitivity
Reduce Receptor Sensitivity
  • IV agents
  • Topical Agents
reduce physiologic response
Reduce Physiologic Response
  • Continue Inhalers
  • Deepen General Anesthesia
  • Reduce Preoperative Anxiety
smoker study
Smoker Study

Airway Responses During Desflurane Versus Sevoflurane Administration via a LMA in Smokers.

McKay RE et al. Anesthesia and Analgesia, Nov. 2006

study objective
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

slide47
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.
elderly population
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.
elderly population49
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.
slide51
Elderly Co-morbidities
  • Decrease functional reserve of all organ systems

Respiratory

  • Respiratory
  • ↓ lung volumes ↑ chest rigidity ↑ V/Q mismatching

Cardiovascular

  • ↓ CI ↓CO ↓ inotropic and chronotropic responses, ↑ systolic BP ↑ perioperative arterial hypotension
hepatorenal and immune
Hepatorenal and Immune
  • ↓40% hepatic mass by age 80 ↓ hepatic blood flow
  • ↓ rates of plasma clearance, prolonged drug effects
  • ↓ 30% renal mass by age 80 ↓ GFR

↓ renal reserve

  • ↓ immune response ↑ sepsis
metabolism body composition pharmacokinetics
Metabolism, Body Composition, Pharmacokinetics
  • ↓ Skeletal muscle mass ↑ lipid fraction
  • ↓ BMR ↓ heat production ↑hypothermia
  • ↓ metabolism 1% per year after age 30
  • ↓ Circulating plasma volume ↓ drug dosages
slide54
CNS
  • ↓ Brain mass ↓ CBF ↓ neurons that synthesize neurotransmitters
  • ↓ MAC ↓ dosage of narcotics and sedatives
  • ↑ POCD (postoperative cognitive dysfunction) with ↑ age
  • Morbidity same for GA and regional
  • POCD more subtle and needs neuropsychological testing
slide55
POCD
  • POCD present if ↓ 20% or more on psychometric tests – preop, postop

1 week + 3 mos.

  • Contributing factors - ↑ age, type and ↑ length of surgery, pre-existing brain disease, ↓ educational level, medication, anemia, “lyte” imbalances, sepsis, length of hospital stay
  • Incidence – 26-40%, at 3 months in the elderly, ↑with ↑ age over 75
slide56
“The target organ for anesthetic drugs is the brain. It was assumed that their effects did not outlast their pharmacologic action and target organ restored to previous state once agent eliminated” – “Not True”

Silverstein et al. Anesthesiology March 2007

slide57
“Cognitive dysfunction is common in adult patients of all ages at hospital discharge after major non-cardiac surgery, but only the elderly (aged 60 yr or older) are at significant risk for long-term cognitive problems. Patients with POCD are at increased risk of death in the first year after surgery.”

Monk et al. Anesthesiology, Jan. 2008

recovery of elderly patients
Recovery of Elderly Patients
  • More rapid early recovery of elderly patients from prolonged anesthesia of more than two hours duration is significantly faster after desflurane.

Heavner et al. Br J Anesthesia 2003; 91: 502-6

  • Patients receiving desflurane reported faster recovery from anesthesia due to a faster washout than sevoflurane but an earlier and more intense perception of pain after surgery.

Iannuzzi et al. Minerva Anesthesiol 2005; 71:147-55

emergence
Emergence
  • Less Desflurane needs to be released from tissues & eliminated from body at end of long case due to its low solubility
    • - More rapid emergence & return of cognitive function.
    • - More rapid return to wakefulness and dexterity skills.
    • Juvin et al. Emergence of elderly patients from prolonged desflurane, isoflurane or propofol anesthesia. Anesth Analg. 1997; 85:647-651.
emergence with desflurane
Emergence with Desflurane
  • SpO2 values significantly better
  • Sedation significantly less pronounced at 30 minutes & 120 minutes
  • Improved patient morbidity
slide61

“Desflurane Anesthesia After Sevoflurane Inhaled Induction Reduces Severity of Emergence Agitation in Children Undergoing Minor Ear-Nose-Throat Surgery Compared with Sevoflurane Induction and Maintenance”

Mayer, et al, Klinikum Ludwigshafen, Germany

Anesthesia & Analgesia, February 2006

study objective62
Study Objective

To evaluate the influence of desflurane maintenance after sevo induction versus sevo induction and maintenance on emergence agitation in pediatrics undergoing ear, nose, and throat surgery.

overall methods
Overall Methods
  • Randomized, single blind study, N =38, children age 1 yr to 7 yr.
  • Premedication with midazolam 30 min prior to surgery.
  • Mask induction-8% sevo in N2O (50%) and oxygen (50%).
  • Children randomly received sevo (1.0 MAC, n=19) or des (1.0 MAC, n=19) for maintenance of anesthesia.
overall methods cont d
Overall Methods (cont’d)
  • Blinded observer recorded time to extubation, duration of exposure to volatile anesthetics, and surgery time. Same observer recorded degree of agitation in a time interval from 10 min to approx. 30 min after admission to PACU.
  • Groups were similar in surgery time (25 min) and anesthesia time (57 min.)
three most significant results
Three Most Significant Results
  • Time to tracheal extubation was much shorter with desflurane maintenance than sevo maintenance (5.4 min. vs. 13.4min. – p<0.05).
  • Modified Aldrete scores were higher on arrival to PACU with desflurane patients than with sevoflurane patients (8 vs. 7 – p<0.05),
  • A new, validated measure for emergence delirium, the Pediatric Anesthesia Emergence Delirium (PAED) showed significant advantages for desflurane patients over sevoflurane patients (6[--15] vs 12 [2-20]).
conclusion
Conclusion

Maintenance of anesthesia with desflurane after mask induction with sevoflurane resulted in less severe agitation with faster emergence times.

Although time of PACU stay did not differ significantly, a more rapid immediate recovery from anesthesia could be an additional benefit in a busy operating room.

overweight patient
Overweight Patient
  • Overweight - Obesity increases the risks of anesthesia & surgery
  • Morbid obesity defined as twice IBW (100% over)
  • Risk factors related to organ systems increase proportionally with obesity
    • - Physiologic changes occur in
    • pulmonary, cardiovascular, hepatic,
    • renal, GI, endocrine, & metabolic as
    • obesity increases
statistics
Statistics
  • In 2000, 38.8 million American adults met classification of obesity.
    • - NHANES: estimate 64% U.S. adults either
    • overweight or obese, 1999-2000.
  • Increased obesity rates in every subgroup in U.S. population.
  • Children 6-19 yrs.: increased obesity

-13-14% between 1970’s to 1990’s &

increased hospital costs to $127M/year.

- 15% between 1999 to 2000.

www.cdc.gov/nccdphp/dnpa/obesity/trend

obese co morbidities
Obese Co-morbidities

Respiratory System

  • ↓ Chest wall and lung compliance
  • ↓ FRC ↓ VC ↓ TLC VQ mismatch

↑ hypoxemia

  • OSA (>75% in obese patients), use CPAP in hospital

Cardiovascular System

  • ↑blood volume ↑ CO ↑ LVH ↑CAD ↑BP
slide71
GI System

↑ gastric volume (up to 75% greater), delayed gastric emptying

  • ↑ reflux
  • ↑ hepatic fatty infiltrates

Renal and Endocrine

  • Loss of nephron function ↓ GFR
  • Impaired glucose tolerance ↑ type II diabetes mellitus (>80%)
slide72
Airway
  • Limitations of movement of cervical spine
  • Excessive tissue folds in mouth and pharynx
  • Short, thick neck, thick submental fat pad

Pharmacology

  • ↑ VD for lipophilic drugs unchanged VD for poorly lipophilic drugs
slide73
Emergence and Recovery Characteristics of Desflurane vs. Sevoflurane in Morbidly Obese Adult Surgical Patients

Strum et al, Anesth Analg 2004; 99: 1848 -53

study74
Study
  • Patients BM1>35, PS II & III
  • Undergoing gastrointestinal bypass via open laparotomy
  • Epidural catheter placed prior to induction
  • 1 MAC for each agent until end of surgery
  • Emergence, recovery (Aldrete scores), 02 saturation, pain scores and PONV were assessed.
results
Results

Emergence and Immediate Recovery Times After Discontinuation of Volatile Anesthetics in the Two Anesthetic Groups

results cont d
Results (cont’d)
  • Patients given desflurane left OR significantly sooner (26.3 min. vs. 35.8 min.)
  • Higher Alrete scores upon PACU arrival (8.1 vs. 7.1)
  • Greater oxyhemaglobin saturation (97% vs. 94.8%)
  • No difference in PACU or hospital stays or in PONV or VAS scores between the two patients groups.
conclusion77
Conclusion

The present study demonstrates that morbidly obese patients anesthetized for more than three hours recover significantly more rapidly after desflurane anesthesia than after sevoflurane anesthesia.

slide78
Airway Reflexes Recover More Rapidly After Desflurane Than After Sevoflurane Anesthesia

Rachel Eshima McKay, M.D. and

Warren R. McKay, M.D.

Department of Anesthesia and Perioperative Care

University of California, San Francisco

Abstract, 2004

study design
Study Design
  • Protective airway reflexes measured after anesthesia with desflurane vs. sevoflurane.
  • The return of protective upper airway reflexes was measured by an ability to swallow 20 ml of water and not cough when swallowing is attempted.
  • An LMA was placed, lubricated with ky gel.
  • Measurements were taken exactly 2 min., 14, 22, and 30 minutes after patient opened eyes to command.
slide80
“Eshima concludes that the awakening from anesthesia to the point of the ability to respond to commands does not necessarily predict the resumption of protective airway reflexes.”
slide81
Eshima further concludes that the recovery of protective upper airway reflexes is delayed more after sevoflurane than after desflurane anesthesia.
slide82
Two minutes after responding appropriately to command, each patient was asked to swallow 20 mL of water. All patients given desflurane could swallow water without coughing or drooling, but less than half the patients given sevoflurane could do so.
recovery from desflurane
Recovery from Desflurane
  • Low tissue solubility
  • Predictable and rapid recovery
  • Reduction in postoperative hypoxemia
  • Increase in patient mobility

Juvin et al. Postoperative recovery after desflurane, propofol or isoflurane anaesthesia among morbidly obese patients. Anesth Analg. 2000; 91:714-719.

advantages of desflurane
Advantages of Desflurane
  • Less respiratory depression
    • - Improved ventilation; less hypoxia
      • Less chance for reintubation
    • - Less chance for post-obstructive pulmonary edema
  • Less risk for aspiration
  • Less window for nausea
  • Less OR time (decrease expensive))
discharge
Discharge
  • Quicker wake-up
  • Quicker discharge
  • Less expense to patient & insurance

company

  • More active the next day

Mahmoud et al. Desflurane or sevoflurane for gynaecological day-case anaesthesia with spontaneous respiration? Anaesthesia. 2001; 56:171