Dear Editor, Lung protective ventilation strategies, specifically the monitoring of plateau pressure (Pplat) and driving pressure (ΔP), are fundamental to preventing ventilator-induced lung injury (VILI). The landmark Acute Respiratory Distress Syndrome (ARDS) Network trial established the importance of limiting Pplat to less than 30 cmH2O to improve survival outcomes. 1 However, in many resource-constrained settings, older anaesthesia workstations and basic transport ventilators lack the integrated software or hardware valves required to perform an “inspiratory pause” manoeuvre. Without this function, measuring static lung compliance (Cstat) is impossible, leaving clinicians unable to optimise ventilation in complex cases. We herein describe a simple, cost-effective assembly to overcome this limitation using ubiquitous operating room supplies. For ease of reference, we have termed this device as the “ Foley-Stop Assembly” (FSA) or the “DUA” device (an acronym derived from the authors’ initials). The device utilises a standard catheter mount with an endoscopy port connected to the Y-piece of the breathing circuit. A 16 Fr two-way Foley catheter is inserted through the endoscopy port Figure 1. Distal to this, a straight connector with a gas sampling port is attached, which is connected via tubing to a handheld analog pressure manometer. In our setup, we utilised a standard endotracheal cuff pressure gauge, which has been shown in studies to provide pressure estimations within clinically acceptable limits for airway monitoring. 2 The circuit continues via a heat and moisture exchange (HME) filter to the patient. Figure 1: Photograph of the Foley-stop assembly. (A) Breathing circuit, (B) endoscopy mount, (C) straight connector with a sampling port, (D) heat and moisture exchange filter, (E) cuff pressure manometer with tubing, (F) 16 Fr Foley’s catheter. Note that the drain tube is blocked and the bulb lies proximal to the sampling port of the straight connector, (G) 50 mL syringe and (H) breathing bag, as a stand-in for patient endTo measure Pplat, the operator observes the breathing cycle. At the precise moment of end inspiration (peak pressure), the Foley balloon is rapidly inflated until complete occlusion is achieved (approximately 10 ml with our specific setup). This manual occlusion creates a static column of air distal to the blockade. A video showing the assembly of this device along with its use is uploaded as supplementary material. "href": "Single Video Player", "role": "media-player-id", "content-type": "play-in-place", "position": "float", "orientation": "portrait", "label": "Video 1", "caption": "", "object-id": {"pub-id-type": "doi", "id": "", "pub-id-type": "other", "content-type": "media-stream-id", "id": "1ᵤ0tet97o", "pub-id-type": "other", "content-type": "media-source", "id": "Kaltura"} The physiological basis for this technique relies on the equation of motion: Paw = (V̇ x Raw) + (VT/Cstat) + PEEP where Paw is the airway pressure, V̇ is the flow, PEEP is the peak expiratory pressure, and Raw is the airway resistance. 3 By manually stopping flow (V̇ = 0), the resistive pressure component drops to zero, and the manometer attached to the sampling port equilibrates to reflect the static elastic recoil pressure of the respiratory system (Pplat). We successfully tested this assembly in both volume-controlled and pressure-controlled settings. This also allows for the calculation of static compliance Cstat = VT/ (Pplat - PEEP) without advanced workstations. Although novel, we openly recognise a number of drawbacks and dangers related to this makeshift method. This approach is a proof-of-concept, and more research is required to confirm it against the most often used ventilator pause manoeuvres. At best, it should be viewed as a cost effective option in resource-constrained circumstances, rather than a replacement for normal monitoring. The operator’s ability to synchronise balloon inflation with end-inspiration is crucial to the measurement’s accuracy; early inflation indicates peak pressure, while late inflation results in a false low value. To avoid dangers such as unintended PEEP loss, circuit leakage at the endoscopic port, and persistent airway obstruction, it should be used by an experienced operator. Also, this approach should not be used in patients who have substantial airway restriction. Analog pressure gauges have poor resolution and are prone to substantial discrepancies between observers’ readings. Any potential leak in the assembly, particularly from partial occlusion, can result in a continuous underestimating of Pplat. While the assembly adds only a modest amount of dead space, this could be clinically relevant in paediatric populations or individuals with severe ARDS and hypercapnia. We believe that this technique will empower anaesthesiologists in peripheral centres to adhere to lung-protective protocols despite equipment limitations, provided it is used with caution and awareness of the physiological and mechanical caveats described. Study data availability The authors confirm that all data supporting the findings of this study (including technical specifications and the assembly process) are included within the article and its supplementary video. Further technical details are available from the corresponding author upon reasonable request. Disclosure of use of artificial intelligence (AI) -assistive or generative tools The authors confirm that no artificial intelligence (AI) -assistive or generative tools were used in the writing of this manuscript or in the production of the associated research. Author contributions UB was involved in concept, definition of intellectual content, editing, and review. DR was involved in concept, design, definition of intellectual content, literature search, manuscript preparation. AS was involved in literature search, manuscript preparation. All the authors have participated in the review, drafting and final approval of the manuscript. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
Baruah et al. (Sun,) studied this question.