High flow nasal oxygen therapy (HFNO) brings several physiological benefits that differ from conventional low flow nasal oxygen therapy (LFNO). HFNO provides positive end expiratory pressure (PEEP), constant fraction of inspired oxygen, pharyngeal dead-space washout and also improves mucocilliary clearance. This oxygen delivery system has been increasingly used in clinical practice, especially in postextubation patients.1
Patients who had at least one of the following factors: older than 65 years, Acute Physiology and Chronic Health Evaluation II score higher than 12 points on extubation date, body mass index higher than 30 Kg/m2, inadequate secretion management, difficult or prolonged weaning, and more than one comorbidities, including heart failure as primary indication for mechanical ventilation, moderate to severe chronic obstructive pulmonary disease, airway patency problems or prolonged mechanical ventilation, were at high risk for extubation failure.2 In these patients, HFNO was not inferior to noninvasive ventilation for prevention of postextubation respiratory failure and reintubation. Moreover, Hernandez et al.3 demonstrated that HFNO significantly decreased the reintubation rate within 72 hours after extubation in patients at low risk for extubation failure, compared with LFNO.
One of the important advantages of HFNO in postextubation patients is allowance for patients to eat and drink orally without interruption of therapy. However, there is a lack of evidence supporting the safety of HFNO regarding to the risk of aspiration during oral intake.
During the postextubation period, the risk of aspiration increases due to several conditions such as postextubation dysphagia, incoordination between swallowing and breathing, and feeding intolerance.
The incidence of postextubation dysphagia varies from 3 to 62% and this condition shares the common risk factors with postextubation respiratory failure, such as advanced age, prolonged intubation and preexisting congestive heart failure. Moreover, postextubation dysphagia leads to aspiration pneumonia, prolonged hospitalization, increased cost of medical treatment and mortality.4
According to the coordination between swallowing and respiration, breathing ceases briefly during swallowing by inhibition of respiration at neural control centers in the brainstem and closure of the upper airway.5 In healthy adults, swallowing usually begins during the expiration and then respiration resumes with continuation of expiration after swallowing. Thus, the most common pattern of swallowing-breathing relationship is exhale–swallow–exhale or E swallow, followed by inhale–swallow–exhale or I-E swallow, which regards as one of the airway protective mechanisms. (Fig. 1) In addition, the alteration of this coordination, namely inhale–swallow–inhale or I swallow, and exhale–swallow–inhale or E-I swallow, also appears with the lower percentages in the healthy adults.
From the previous studies, the incidence of aspiration was associated with the increase in percentages of I and E-I swallows, which commonly occurred in elderly and patients with cerebrovascular, Parkinson’s and chronic obstructive pulmonary diseases5,6 Although many studies have investigated the alteration of swallowing and breathing coordination in many populations, the information in the postextubation patients remains limited.
Few studies examined the effect of airway pressure on the swallowing and breathing coordination. Samson et al. demonstrated that bronchopulmonary receptor stimulation by nasal continuous positive airway pressure (nCPAP) in lamps reduced the frequency of swallowing and altered the patterns of swallowing-breathing relationship during continuous water infusion. The changes in this relationship during continuous infusion under nCPAP, particularly a decrease in swallowing during inspiration (I and E-I swallows), might decrease the risk of aspiration.7
In addition, Hori et al. demonstrated the effect of bi-level positive airway pressure (BiPAP) on the coordination between respiration and swallowing in 22 healthy volunteers. They found that the occurrence rate of inspiration after swallow was greater in those with BiPAP, compared with the control and CPAP conditions.8
Corley et al. showed that HFNO increased end expiratory lung volume and airway pressure.9 Therefore, HFNO might stimulate the bronchopulmonary receptor and change timing of swallowing in relation to respiratory phases.
In recent years, researchers have become increasingly interested in the effect of HFNO on the swallowing function. However, there was the only research investigating in the healthy population.
Sanuki et al. demonstrated that HFNO reduced the swallowing latency time in healthy volunteers. Nevertheless, the timing of swallowing during continuous infusion of water for one minute was not different between HFNO and LFNO periods.10
Up to our knowledge, no study had looked specifically at the effect of HFNO on the relationship of swallowing and breathing during the postextubation period. The present study was firstly designed to compare the swallowing-breathing coordination during continuous water infusion between HFNO and LFNO therapy in the postextubation patients.