Improvement of oxygen delivery in severe hypoxaemia by a reservoir cannula

In 36 severely hypoxaemic patients (arterial oxygen tension (PaO2) less than 7.3 kPa or 55 mmHg), candidates for long-term oxygen therapy, we compared the effectiveness of three oxygen-delivery systems, the standard nasal prongs, a so-called oxygen-conserving reservoir device ("Oxymizer Pendant") and the reference pharyngeal catheter, at a preset flow rate of 2 l.min-1. After 30 min, the conserving device (OX) was at least as efficient as the pharyngeal catheter (PC) and did significantly better than the nasal prongs (NP), the mean increments in PaO2 and arterial oxygen saturation (SaO2) being, respectively, 1.1 kPa (8.1 mmHg) and 1.3% higher with OX than with NP. Twenty patients did not reach the target level of 8.6 kPa (65 mmHg) PaO2 with the nasal prongs, but the reservoir cannula allowed nine of these "refractory" patients to hit this therapeutic goal, a result indicating a clear trend towards improved immediate oxygen response. Although initially designed to spare gas, we suggest that a reservoir cannula could serve another purpose, namely to optimize oxygenation in patients treated by an oxygen concentrator. Indeed, since the oxygen flow rate cannot be reliably increased over 3 l.min-1 with the available oxygen concentrators, the reservoir device could be more effective in some selected patients whose hypoxaemia cannot be adequately corrected by standard nasal prongs.