Abstract
Background: High velocity nasal insufflation (HVNI) is a form of respiratory support that provides flows that are believed to be in excess of a patient’s inspiratory and expiratory flows. In the last decade, a proliferation of high-flow nasal cannula devices and dosing recommendations (L/min) has been introduced into the clinical setting without consideration of mechanism of action. The high velocity nasal flow facilitates a well-described mechanism of improving ventilatory efficiency by way of eliminating carbon dioxide traditionally stacked in anatomical deadspace of the upper airway.
Methods: Following IRB approval, a prospective, randomized trial of three different flows (low 0.2, medium 0.3, and high 0.4 L/kg/min PBW) HVNI at 0.21 FIO2 were used to evaluate ventilation efficiency of normal subjects by measuring minute ventilation (MV) (ExSpiron) at rest and during light exercise (increase the heart rate of subjects by 25%) on a stationary bike to mimic tachypneic patients in respiratory distress. Transcutaneous CO2 (Sentec) was used to standardize the specific minute ventilation (mL/kg) to a CO2 of 40 mm Hg.
Results: In 12 normal subjects the application of low to high HVNI resulted in a 17%, 25% and 27% reduction in minute ventilation respectively from baseline. Figure 1. During light exercise the application of HVNI resulted in an increase in MV from baseline of 9% (high), 11% (med) and 19% (low). Figure 2.
Conclusions: At rest the application of 0.2-0.4 L/min PBW of HVNI appears to eliminate upper airway deadspace improving respiratory efficiency enough to reduce MV. However, during light exercise, the application of HVNI does not appear to improve respiratory efficiency enough to result in a decrease MV from baseline.
Figure 1 represents the standardized specific MV in L/min of PBW during rest by flow category.
Figure 2 represents the standardized specific MV in L/min of PBW during light exercise by flow category.
Footnotes
Commercial Relationships: None
Support: This study was funded in part by an unrestricted research grant by Vapotherm.
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