Can nitrous oxide be administered effectively by nasal cannula? A preliminary report

Area of Science:

• Anesthesiology
• Respiratory Physiology

Background:

• Nasal cannulas are commonly used for oxygen delivery.
• Predicting inspired gas concentrations is crucial for effective patient management.

Purpose of the Study:

• To predict the inspired concentrations of nitrous oxide (N2O) when administered with oxygen via nasal cannula.
• To evaluate the efficacy of nasal cannula delivery for N2O/O2 mixtures.

Main Methods:

• A mathematical model was developed based on established methods for calculating inspired oxygen fraction (FiO2).
• Assumed physiological parameters included tidal volume (500 ml), respiratory rate (20 breaths/min), inspiratory time (1 sec), expiratory time (2 sec), and anatomic reservoir volume (50 ml).
• Calculations considered cannula flow rate and the fraction of N2O delivered.

Main Results:

• Calculated FiO2 values for oxygen alone matched existing data.
• Estimated inspired N2O fraction (FiN2O) was directly proportional to cannula flow rate and N2O fraction.
• At a maximum total flow of 6 L/min with 70% N2O, the estimated FiN2O was only 0.21, with a corresponding FiO2 of 0.23.

Conclusions:

• The maximum achievable FiN2O using a nasal cannula is limited to 0.21.
• This limitation is observed even with a 6 L/min flow of 70% N2O, given the defined respiratory parameters.
• Nasal cannula delivery may not be optimal for achieving higher inspired concentrations of nitrous oxide.