Low Flow Anesthesia with Desflurane

Low Flow Anesthesia with Desflurane: 

Low Flow Anesthesia with Desflurane รศ.นพ.เทพกร สาธิตการมณี ภาควิชาวิสัญญีวิทยา คณะแพทยศาสตร์ มหาวิทยาลัยขอนแก่น

Flow Technique Nomenclature: 

Flow Technique Nomenclature High Flow 2 L / min Low Flow 1 L / min Minimal Flow 500 mL / min Metabolic (closed) 250 mL/min

ข้อดีของ Low flow anesthesia: 

ข้อดีของ Low flow anesthesia Economic Environmental & Personal health Conservation of heat and humidity

Requirement : 

Requirement Qualified personnel Low flow anesthetic machine Accurate fresh gas delivery (Accurate and consistent settings, accurate readability) Very low leakage of the system (must not exceed 100 mL/min) Monitor Standard : EKG, pulse oximeter, NIBP, capnography Option : gas monitor

Uptake of gas during anesthesia: 

Uptake of gas during anesthesia Oxygen uptake equal to oxygen consumption estimate 250 mL/min Nitrous oxide uptake (N 2 O is not metabolised) defined solely the alveolar-arterial partial pressure difference V O 2 = 10 x BW (kg) 3/4 (mL/min) V N 2 0 = 1000 x t -1/2 (mL/min)

Uptake of gas during anesthesia: 

Uptake of gas during anesthesia Inhalation anesthetic agent VA N = f x MAC x l B/G x Q x t -1/2 (ml/min) (Lowe Formula) V AN = f x MAC x l B/G x Q x t -1/2 (ml/min)

Uptake of gas during anesthesia: 

Uptake of gas during anesthesia

Oxygen concentration with reduced fresh gas flow: 

Oxygen concentration with reduced fresh gas flow During Low Flow Anesthesia (1.0 L/min) Oxygen concentration shall be increased to 50 vol.% At least to 40 vol % Minimal Flow Anaesthesia (0.5 L/min) Oxygen concentration shall be increased to 60 vol.% O 2 300 mL/min + N 2 O 200 mL/min

Pharmacokinetic and pharmacodynamic properties of different inhalation anesthetics: 

Pharmacokinetic and pharmacodynamic properties of different inhalation anesthetics

Time constant: 

Time constant The time constant is the duration to reach 63% of the intended fresh gas flow concentration in the breathing system T = V S / V D System 5 L ,FGF 0.5 L/min >> T = 10 min System 5 L ,FGF 1.0 L/min >> T = 5 min 2 x T it will have reached 86.5% and after 3 x T about 95%

Procedure : Standard: 

Procedure : Standard Induction by IV or inhalation Initial phase lasting 10-20 min with high flow Initially setting a high fresh gas concentration Stepwise reducing the fresh gas flow rate 2 L/min after the initial 5 minutes 1 L/min after 10 minutes 0.5 L/min after 15 minutes MAC is additive when using N 2 O MAC bar equal to 1.7-2.0 MAC

Procedure : Simplified: 

Procedure : Simplified Induction by IV or inhalation Initial phase : 2-3 min O 2 1 L/min + N 2 O 1 L/min + Desflurane 12% www.youtube.com search: “ desflurane low flow ” part (1/3)

Procedure : Simplified: 

Procedure : Simplified Maintenance phase : after 2 min O 2 300 mL/min + N 2 O 200 mL/min + Desflurane 5% (exp. conc. Des 3.5%) www.youtube.com search: “ desflurane low flow ” part (2/3)

The difference between fresh gas and expired gas of Desflurane: 

The difference between fresh gas and expired gas of Desflurane

Procedure : Simplified: 

Procedure : Simplified Emergence phase Switch desflurane vaporizer to “0” O 2 flow 6 L/min Disconnect Y-connector from ET Flush O 2 to wash out anesthetic gases from anesthetic circuit Reversal drugs administration and ventilate the patient Extubate according to criteria www.youtube.com search: “ desflurane low flow ” part (3/3)

Nitrous Oxide: 

Nitrous Oxide Reduction of supplementary opioids and anesthetics Rapid wash-in and wash-out Shortens time required for mask induction Stabilizes cardiocirculatory function Prevents from intraoperative awareness

Contraindications for Nitrous Oxide: 

Contraindications for Nitrous Oxide Air in tissues or hollow spaces Bowels distended by gas, bowel obstruction Increased intracranial pressure Vitamin B12 deficiency Immunodeficiency, bone marrow depression

Further arguments not to use nitrous oxide: 

Further arguments not to use nitrous oxide Early pregnancy, in-vitro-fertilisation Severe PONV in patient's history Reduction of the work place load with N 2 O Ecological arguments: ozone destruction and green house effect

Special precaution: 

Special precaution Hypoxemia Gas volume deficiency High gas humidity Exhaustion of the absorbent Minimal Flow Anesthesia with a fresh gas flow of 0.5 L/min increases the consumption of soda lime about fourfold

Monitoring for Safe Performance of Low Flow Anesthesia: 

Monitoring for Safe Performance of Low Flow Anesthesia Inspiratory oxygen concentration Airway pressure and/or minute volume Anesthetic agent concentration in the circuit Expiratory CO 2 -concentration

Limitations and Contraindications: 

Limitations and Contraindications Not suitable for the following procedures Short term anesthesia with a face mask Procedures with imperfectly gas-tight airways (i.e. bronchoscopies with a rigid bronchoscope) Unsatisfactory equipment with a high gas leakage : uncuffed ETT in children High metabolic state : thyroid storm, high fever Inadequate monitoring (i.e. malfunction of the oxygen measuring device)

Absolute contraindications: 

Absolute contraindications Malignant hyperthermia Absolute contraindications for the use of the rebreathing techniques Soda lime exhaustion Failure of the oxygen monitor (unless pure oxygen is used as carrier gas) Failure of the anesthetic agent monitor

Cost of Desflurane: 

Cost of Desflurane

Cost of Desflurane: 

Cost of Desflurane FGF ( lpm ) 4% 6% 8% 0.5 145 218 290 1.0 290 436 580 2.0 580 872 1160 บาท / ชั่วโมง ราคาเหมาจ่าย กรมบัญชีกลาง 450 บาท / ชั่วโมง เปิด 12% ที่ 2 lpm 3 นาที = 90 บาท

Slide 25: 

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