Abstract
Background High flow tracheostomy (HFT) is a commonly used weaning and humidification strategy for tracheostomised patients, but little is known as to how much PEEP or mechanical benefit it offers. Patient anatomy and device characteristics differentiate it from high flow nasal cannula and the physiological effects observed. Objectives (1) To review the available literature on the effects of HFT on airway pressure and indices of gas exchange. (2) To quantify PEEP generated by a HFT circuit. Methods A randomised benchtop experiment was conducted, with a size 8 uncuffed Portex tracheostomy connected to an Optiflow™ with Airvo 2™ humidifier system. The tracheostomy tube was partially immersed in water to give rise to a column of water within the inner surface of the tube. An air fluid interface was generated with flows of 40 L/min, 50 L/min, and 60 L/min. The amount of potential PEEP (pPEEP) generated was determined by the distance the water column was pushed downward by the flow delivered. Findings. Overall 40 L/min, 50 L/min, and 60 L/min provided pPEEP of approximately 0.3 cmH2O, 0.5 cmH2O, and 0.9 cmH2O, respectively. There was a statistically significant change in pPEEP with change in flows from 40–60 L/min with an average change in pPEEP of 0.25–0.35 cmH2O per 10 L/min flow (p value <0.01). Interpretation. HFT can generate measurable and variable PEEP despite the open system used. The pPEEP generated with HFT is minimal despite statistically significant change with increasing flows. This pPEEP is unlikely to provide mechanical benefit in weaning patients off ventilatory support.
Highlights
Introduction and AimHigh flow nasal cannula (HFNC) has become a mainstay of treatment in adult and paediatric ICU/HDU settings in the past decade [1]
TM TM tached to an Optiflow with Airvo 2 humidifier system with oxygen connected through a wall outlet. e tracheostomy tube was partially immersed in the beaker to 3 centimetres by hand to give rise to a column of water within the inner surface of the tube. e apparatus was stabilised by a sturdy flat level table
Measurements were recorded 1 minute after the initiation or change in flow; this was done to allow the system to equilibrate to the change in flow and to avoid error. e potential PEEP (pPEEP) generated was measured by two independent observers with the help of a line gauge for accuracy. e observers were blinded to the amount of flow during each reading, and the recorder was blinded to the measurement of pPEEP. e measurements were verbally relayed to the recorder by the two observers, and an average of the two readings was documented for accuracy
Summary
Introduction and AimHigh flow nasal cannula (HFNC) has become a mainstay of treatment in adult and paediatric ICU/HDU settings in the past decade [1]. HFNC has shown to improve respiratory mechanics and oxygenation by delivering up to 3–6 cm H2O of PEEP and increasing FRC by augmenting pulmonary airway pressures [2]. High flow tracheostomy (HFT) is a common therapy utilised in delivering mechanical and physiological support to critical care patients. Akin to HFNC, mechanical support with HFT targets the lost PEEP, Critical Care Research and Practice previously offered by the upper airway. High flow tracheostomy (HFT) is a commonly used weaning and humidification strategy for tracheostomised patients, but little is known as to how much PEEP or mechanical benefit it offers. Patient anatomy and device characteristics differentiate it from high flow nasal cannula and the physiological effects observed. E pPEEP generated with HFT is minimal despite statistically significant change with increasing flows. HFT can generate measurable and variable PEEP despite the open system used. e pPEEP generated with HFT is minimal despite statistically significant change with increasing flows. is pPEEP is unlikely to provide mechanical benefit in weaning patients off ventilatory support
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