Introduction
In contemporary clinical practice, 50–84% of patients are exposed to
excess oxygen and hyperxemia as a result of efforts to prevent or
reverse hypoxemia via various interfaces such as a nasal cannula, nasal
catheter, venturi mask and non-rebreathing mask.1-4Recently, a systematic review and meta-analysis provides high-quality
evidence that hyperoxia is life-threatening in acutely ill adults with
acute myocardial infarction, sepsis, critical illness, stroke, trauma,
cardiac arrest.5
Oxygen treatment can be divided into high-flow and low-flow systems. The
high-flow system provides a flow that is equal to or exceeds the
patient’s peak inspiratory flow and ensures a fixed
FIO2, while the low-flow system is variable due to the
entrained indoor air that dilutes the oxygen, resulting in a low
FIO2.1,2,4 The precise
FIO2 amount delivered is difficult to determine in
spontaneously breathing patients because it is influenced by the
breathing pattern, including the patient’s minute ventilation, f,
VT, inspiratory time (TI), expiratory
time (TE), functional apparatus dead space, inspiratory
flow rate, expiratory flow rate and impact of open or closed
mouth,1,2,4,6-9 particularly in patients with
respiratory failure, which manifests as hypoventilation or
hyperventilation.
Although oxygen therapy can reduce the symptoms of
hypoxemia,10 but high concentrations of oxygen cause
adverse effects such as chronic obstructive pulmonary
disease(COPD)11 and type II respiratory
failure.12 Clearly, more precise control of the
inspired oxygen concentration is very important for patients have a high
respiratory rate (f) with shallow or deep breathing in lower lung
compliance such as acute respiratory distress
syndrome,13 left ventricular
failure14 and pulmonary fibrosis15and increased airway resistance such as COPD16-18 and
asthma.19,20 The nasal cannula provides oxygen flow at
a rate of 1–5L/min,3 is the most widely used low-flow
oxygen device for adults, children and infants.1-4Modern guidelines and the literature lack much data regarding the
correlation between how much to give and breathing patterns in
respiratory failure during low-flow oxygen therapy with a nasal
cannula.1,2,6,21-26
We conducted this bench study to investigate the performance of nasal
cannula in a manikin head-test lung-ventilator system to simulate a
spontaneous breathing pattern in normal, restrictive and obstructive
lung models. To describe the effects of various VT and f
on the measured FIO2 near the carina and provide
equations to estimate FIO2 during standard nasal cannula
oxygen therapy.