Monitoring tidal volumes when using the Ventrain® emergency ventilator

Abstract

The Ventrain® emergency ventilation device allows active inspiration and expiration through transtracheal catheters or the lumen of an airway exchange catheter. This single-use handheld device is manually operated and driven by an external pressurized oxygen source. The Ventrain® may be used to ventilate patients with acomplete or pending upper airway obstruction reducing the risk of barotrauma due to the possibility of active expiration. However tidal volumes (V T) applied and withdrawn with the Ventrain® can only be controlled by visual inspection of chest movements; V T monitoring is not provided. Excessive inspiratory volumes or air trapping due to insufficient expiration may remain clinically undetected until pulmonary trauma and/or cardio-respiratory deterioration occur. Active expiration itself carries the risk of overwhelming lung deflation with the formation of atelectasis. Thus, an inspiratory and expiratory tidal volume monitor is urgently required. The aim of this study was to evaluate efficacy and precision of the Florian respiratory function monitor (RFM) to monitor in- and expiratory V T administered by the Ventrain® emergency ventilation device through asmall cannula to the ASL5000 test lung (ASL). In an in-vitro setting the RFM was used with its neonatal flow sensor to monitor inspiratory and expiratory V T applied by the Ventrain® emergency ventilation device through a2mm internal diameter (ID) transtracheal catheter to the ASL. Driving flows of 6, 9, 12 and 15l min(-1) were chosen to vary tidal volumes at aconstant respiratory rate of 15min(-1) and an I:E ratio of 1:1. Experiments were repeated five times with two flow sensors. An initial set-up calibration run was performed to calculate abias correction factor for inspiratory and expiratory V T measured by the RFM. This bias correction factor was used to simulate acorrection of the in the RFM programmed linearization table. In asecond, identical setting the experiments were repeated five times with two flow sensors. V T measured by the adjusted RFM were compared with those obtained from the ASL5000 in this second run and the percentage differences were calculated. Bland Altman analysis was used to investigate the agreement of inspiratory or expiratory VT measured by both methods (ASL and RFM). Calculation of the mean of differences between both methods is given as bias and the 95 % agreement interval as precision. Tidal volumes measured by the ASL ranged from 140 to 675ml. The percentage correction factor was 16.27 % (2.60 %) during inspiration for V T ranged from 0 to 700ml and 11.51 % (2.56 %) during expiration for V T of 0 to 225ml, 7.41 % (2.94 %) for VT 226 to 325ml and 5.35 % (3.57 %) for TV e >325ml. Inspiratory and expiratory tidal volumes measured by the adjusted RFM demonstrated apercentage deviation (mean [SD]) of 2.59 % (1.86 %) during inspiration and 1.66 % (1.14 %) during expiration when compared with the ASL5000. Bias (precision) of the Bland Altman plot for the adjusted RFM is 2.05ml (23.20) during inspiration and 4.62ml (10.40) for expiration. The tested respiratory function monitor using hot-wire anemometer technology has the potential to monitor tidal volumes applied by the Ventrain®. With the software thus adapted, the RFM measures precise inspiratory and expiratory tidal volumes within common technical tolerance. This could help perform adequate patient ventilation with Ventrain® and reduce the potential risk of patient trauma.