Evaluation of five oxygen delivery devices in spontaneously breathing subjects by oxygraphy

Abstract

SummaryOxygen supply systems may be divided into constant and variable performance systems. As the variable performance systems are widely used, it is relevant to investigate the variation in performance between devices and the influence of oxygen supply on the inspired oxygen fraction. Data were collected from 10 healthy volunteers during the use of one constant performance system and four variable performance systems at different gas flows and inspired oxygen fractions. A thin sampling catheter was placed in the nasopharynx to allow the measurement of the end-tidal oxygen fraction. When oxygen was supplied to variable performance systems, end-tidal oxygen fraction values measured in this way varied less and were more easily quantifiable than inspired oxygen fraction. End-tidal oxygen fraction was used to calculate inspired oxygen fraction. With the variable performance systems, inspired oxygen fraction varied considerably between subjects whereas a constant and equal rise was found for each subject with the fixed performance system. A large nasal catheter was capable of delivering the highest inspired oxygen fraction, whereas the Venturi mask delivered the most precise inspired oxygen fraction. We found oxygraphy useful in the interpretation of measurements made in patients receiving unknown inspired fractions of oxygen.

BTS guideline for oxygen use in adults in healthcare and emergency settings

“…The performance and variation of nasal cannulae for medium-concentration oxygen therapy is broadly similar to that of the simple face mask, both in laboratory experiments230 464 and in clinical practice 457–459 466 467. One study suggested that the saturation was lower with nasal cannulae than with simple face masks in a subgroup of men following abdominal surgery 467.…”

“…Chart 2 shows a suggested scheme that allows the oxygen level to be adjusted upwards or downwards in gradual increments depending on a patient's clinical progress (see also sections 11.3.6 and 11.3.7). Venturi masks were previously recommended for low-concentration oxygen therapy because they deliver a more reliable oxygen concentration than nasal cannulae or variable flow masks 230. They can also be combined with a humidifier system when necessary (see section 10.2.3).…”

“…However, there is wide variation in patients' breathing patterns so the same flow rate of nasal oxygen may have widely different effects on the blood oxygen and carbon dioxide levels of different patients. Nasal cannulae at 1–4 L/min can have effects on oxygen saturation approximately equivalent to those seen with 24–40% oxygen from Venturi masks 230 463. The actual concentration of oxygen delivered (FiO 2 ) cannot be predicted and so cannot be used if a calculation of A–a gradient is required.…”

“…The oxygen concentration continues to rise up to flows above 6 L/min. Some patients may experience discomfort and nasal dryness at flows above 4 L/min, but they can be well tolerated (see section 10.2.5) 230 464. Although one might expect mouth breathing to reduce the efficiency of nasal cannulae, the majority of studies have shown that mouth breathing results in either the same inspired oxygen concentration or a higher concentration, especially when the respiratory rate is increased 464.…”

Performance of oxygen delivery devices when the breathing pattern of respiratory failure is simulated*

“…There is a range of devices by which oxygen may be administered in differing concentrations [3]. Delivered F I O 2 depends on the balance between the oxygen flow rate and the patient's inspiratory flow rate, the presence of a reservoir from which entrainment occurs, the presence of an expiratory pause [4] which allows a pharyngeal reservoir of oxygen to build up, and whether the oxygen is delivered by face mask or nasal cannulae.…”