Ex vivo detection of recreational consumed nitrous oxide in exhaled breath

Abstract

The increasing use of recreational nitrous oxide ([Formula: see text]O) in the Netherlands and its link to traffic accidents highlights the need for reliable detection methods for law enforcement. This study focused on ex vivo detection of [Formula: see text]O in exhaled breath and examining its persistence in the human body. Firstly, a low-cost portable infrared based detector was selected and validated to detect [Formula: see text]O in air. Then, the influence of interferents and conditions potentially influencing the analysis were evaluated including relative humidity, ethanol, acetaldehyde and [Formula: see text]. Subsequently, [Formula: see text]O breathing dynamics were evaluated in vitro and ex vivo. Initially, a lung simulator was used to model respiratory mechanics and [Formula: see text]O decay, revealing detectable [Formula: see text]O levels up to 90 min after exposure. In the final part of this study, a controlled single and double dose of [Formula: see text]O gas was administered to 24 volunteers in an operating theatre. The presence of [Formula: see text]O in exhaled breath of the volunteers was analysed using infra red spectroscopy every 12-15 min. Our results show that [Formula: see text]O was detectable in exhaled breath for a minimum of 60 min post-administration and revealed a window of detection to potentially measure [Formula: see text]O for law enforcement and forensic purposes.

Fig. 1

(a) Statistics retrieved from the Dutch National police, showing the prevalence of laughing gas related traffic accidents from 2019–2023. (b) The recreational dosing method and schematic depictions of the in vitro and ex vivo models used in this study. (c) The detection methodology used to detect O in exhaled breath.

Fig. 2

Mean O concentration as measured by the G200 O analyzer of O standards prepared using the gas generation set-up. RH = relative humidity.

Fig. 3

(a) Concentration O in the exhaled air of the lung simulator versus time for varying air refresh ratios (ARR). The O concentration with an ARR of 0.10 first shows a steep decline ( min) between 0–30 min, after 30 min the decline is less steep ( min). The lines are fits using the linear series gas redistribution model. (b/c) The corresponding half-lifes of (a) for different ARR. The O concentration in the lung simulator is described by a fast gas-exchange process min (b) and a slower timescale min (c).

Fig. 4

O concentrations found in the ex vivo study at different time intervals. The individual measurements of the single-dose and double-dose are binned in time-steps of 20 min. The blue and grey lines are a fits with min (single dose) and min (double dose).

Fig. 5

(a) Schematic setup of the Michigan Instruments Dual Adult Lung Simulator. The interior of the lung simulator consists of elastomer bellows. The lifting movement of the frame of the elastomer bellows generates a negative pressure in the lung, this allows a controlled mechanical ventilation with =100–1800 mL at breaths per minute. (b) The linear series two-compartment gas redistribution model. represents the lumping of homogeneous alveoli, and is the volume present in the trachea up to the upper respiratory tract. The initial O concentration is assumed to be homogeneously distributed in and with concentration . After inhalation, the concentration of O redistributes: the exhalation is controlled by a linear exhalation parameter , the gas-exchange between the alveoli and the upper respiratory tract is modeled using . The ambient concentration is assumed to be zero .