Desflurane concentrations and consumptions during low flow anesthesia

Area of Science:

• Anesthesiology
• Pharmacology
• Medical Engineering

Background:

• Desflurane, a volatile anesthetic, is known for its low solubility and high cost.
• Low fresh gas flow (FGF) techniques are often employed with desflurane to improve cost-effectiveness.
• A key challenge with low FGF is the potential for discrepancies between delivered, inspired, and end-tidal anesthetic concentrations.

Purpose of the Study:

• To quantify desflurane concentrations at various points within the anesthesia circuit.
• To investigate the impact of different FGF rates on desflurane concentration accuracy.
• To evaluate the relationship between vaporizer settings and measured concentrations under varying FGF conditions.

Main Methods:

• A crossover study involving 30 adult patients (ASA PS I-II) was conducted.
• Fresh gas flow rates of 0.5, 1, and 2 L/min were randomly applied, maintaining FiO2 at 0.3.
• Desflurane vaporizer settings aimed for a 5% end-tidal concentration (FeDES), with inspired (FiDES) and delivered (FdDES) concentrations measured.

Main Results:

• Delivered desflurane concentration (FdDES) was consistently higher than inspired concentration (FiDES) across all FGF rates.
• FdDES was significantly higher at 0.5 L/min FGF compared to 1 and 2 L/min.
• The ratio of end-tidal to delivered concentration (FeDES/FdDES) was lowest at 0.5 L/min FGF, indicating greater discrepancy.

Conclusions:

• An FGF of 2 L/min offers no significant advantage over 1 L/min in terms of delivered desflurane concentration accuracy.
• Lower FGF rates, particularly 0.5 L/min, require vaporizer adjustments to compensate for increased discrepancies between delivered and end-tidal concentrations.
• Careful monitoring and potential adjustments are necessary when using low FGF techniques with desflurane to ensure accurate anesthetic delivery.