How Much PEEP Does High Flow Deliver via Tracheostomy? A Literature Review and Benchtop Experiment

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.

High‐flow via a tracheostomy tube and speaking valve during weaning from mechanical ventilation and tracheostomy

“…A low, but potentially beneficial, CPAP effect has been found for HFT nasal cannula 22 . In comparison, the HFT‐T CPAP effect is modest, while still helpful during the weaning process 17,19 . The present study's benchtop experiments confirmed no or very little pressure support by HFT‐T‐OWV.…”

“…The absence of flow through the OWV and tracheostomy tube for maximum pressure measurements was confirmed by keeping the tracheostomy tube tip below the water surface of a filled container (Figure 2). If flow occurred, bubbles would be visible, and the tip of the tube moved deeper under water 19 . Pressure was measured after the adapter's side holes, before the OWV.…”

Fluid dynamic assessment of positive end-expiratory pressure in a tracheostomy tube connector during respiration

“…PEEP attained by high-flow oxygen therapy using a tracheostomy tube in tracheostomized patients has been shown to have various clinical benefits [ 8 , 35 ]. Although the relationship between the magnitude of EEP and inflow rates was previously investigated experimentally using high-flow tracheostomy [ 24 , 38 ], it was still unknown whether simple geometrical changes in tracheostomy tube connectors, including the stenosis rate and inlet angles, could potentially generate PEEP. Since it is thought that PEEP is a consequence of the balance between connector fluid flow and lung mechanical responses, the 3D CFD of airflow in the connector during respiration under boundary conditions will be useful to understand the mechanical conditions necessary for PEEP generation.…”

“…Furthermore, HFNC can decrease the work of breathing and also enhance neuroventilatory drive [ 35 ]. More recently, benchtop experiments were performed with a high-flow tracheostomy circuit, and the so-called potential PEEP, defined as the blow-off pressure of the open gas delivery system, was approximately 0.3–0.9 cmH 2 O (≈ 29.4–88.3 Pa) for an inflow rate of 40–60 L/min [ 38 ].…”

Home High-Flow Therapy in Patients with Chronic Respiratory Diseases: Physiological Rationale and Clinical Results

“…When comparing HFT delivered through a nasal cannula (nHFT) vs. via a tracheal interface (tHFT), tHFT seems to generate even less distending pressure. In a bench trial, Thomas et al demonstrated that tHFOT generates a potential PEEP of 0.3 cmH 2 O, 0.5 cmH 2 O, and 0.9 cmH 2 O when the flow is set to 40 L/m, 50 L/m, and 60 L/m, respectively [ 47 ]. In line with these findings, tHFOT produces lower tracheal mean and peak expiratory pressure when compared to nHFT [ 48 ].…”