Fig. 11.1
A patient treated with transnasal insufflation (TNI)
Several studies have shown that TNI improves oxygenation, increases end-inspiratory lung volume, reduces airway resistance, increases functional residual capacity, and flushes nasopharyngeal dead space (thus reducing CO2 rebreathing) [4].
The nasopharynx facilitates the humidification and warming of inspired gases through contact with its large surface, but this generates an appreciable resistance to the gas flow. However, TNI minimizes the inspiratory resistance of the nasopharynx by providing a nasopharyngeal gas flow that matches or exceeds the patient’s peak inspiratory flow. The resulting change in resistance translates into a decrease in resistive work of breathing (WOB) [4].
Parke et al. [5] measured airway pressure during TNI at 30, 40, and 50 l/min in healthy individuals with both open and closed mouth. They found a positive linear relationship between the flow imposed and airway pressure. In patients recovering from cardiac surgery, a mean positive airway pressure of 2.7 cmH2O was measured with a flow of 35 l/min with the mouth closed. In healthy individuals, TNI generated a flow-dependent median positive expiratory pressure of 7.4 cmH2O at 60 l/min with the mouth closed [6]. However, a large interpatient variability was reported, probably due to differences in air leak around the outer part of the nasal cannula and the wide variability in the size of the nostrils. A smaller leak may create an increased resistance to expiration, resulting in higher nasopharyngeal pressure and, therefore, in an increased positive end-expiratory pressure (PEEP) effect [5]. Although this mechanism is particularly effective in neonates, it could also be potentially useful in adult patients.
Moreover, by delivering humidified air, TNI may prevent drying of the airway, thus avoiding the consequent inflammatory response and improving mucociliary function, and could facilitate the clearance of secretions and reduce the formation of atelectasis. Finally, conditioning (warming) of the gas mixture administered can also minimize airway constriction, resulting in a reduction of WOB, which may help to maintain effective delivery of oxygen to the lungs [4].
11.2.3 TNI in Children with OSA
CPAP is the most effective treatment option for children with OSA who are not eligible for surgical interventions (adenotonsillectomy is the treatment of choice when there is adenoid or tonsil hypertrophy), whose parents refuse adenotonsillectomy, or who have residual OSA after surgery. However, as mentioned, adherence to CPAP is relatively low. Accordingly, a large number of children remain untreated [4].
The use of TNI in children with OSA may offer several advantages. First, the patient interface is a nasal cannula, which is less bulky than a nasal mask and avoids facial compression. Accordingly, it might be better tolerated by children during sleep. Moreover, TNI could represent a therapeutic option even more effective than CPAP in children who showed a suboptimal response to the latter. McGinley et al. [7] assessed the effect of TNI (20 l/min of air), compared with CPAP, on upper airway obstruction in 12 children, aged 10 ± 1 years, with mild to severe OSA (2–36 events/hour), by measuring the inspiratory duty cycle and the apnea-hypopnea index (AHI) (namely, the rate of obstructive events per hour of sleep) during both rapid eye movement (REM) and non-REM sleep. They found that the improvements in AHI with TNI were similar to those with CPAP in most of the children. These results appear to be better than those previously shown in adult OSA patients [5]. A possible explanation is that TNI may be generally more effective in increasing pharyngeal pressure in children than in adults because of the relatively larger size of the nasal cannula as compared with the size of the nostrils. Alternatively, the slight increase in pharyngeal pressure might increase lung volume to a greater extent in children than in adults because of higher chest wall and lung compliance, particularly during REM sleep (when the chest wall musculature is hypotonic).
The improvement in AHI in children receiving TNI suggests that the increases in inspiratory airflow and tidal volumes provided by this technique may be sufficient to prevent hypoxia and/or arousals. If these data are confirmed by larger investigations, the implications for the management of sleep-disordered breathing in children could be significant.
11.2.4 TNI in Adults with OSA
TNI has also been used in adult patients with OSA (see Fig. 11.1). McGinley et al. [8] assessed its efficacy in 11 patients with mild-to-severe obstructive apnea–hypopnea syndrome. TNI reduced the overall AHI by 63.2 % (from 28 ± 5 to 10 ± 3 per hour, p < 0.01), and some improvement in the AHI was observed in each subject. In a larger study, TNI was shown to reduce the respiratory disturbance index (RDI), namely the mean number of episodes of apnea, hypopnea, and respiratory event-related arousal per hour of sleep, below a clinically acceptable threshold (10 events/hour) in approximately one-quarter of the 56 patients who required CPAP. Overall, RDI decreased by 31 % (from 22.6 ± 15.6 to 17.2 ± 13.2 events/hour, p < 0.01) [3].
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