Helium poisoning: new procedure for sampling and analysis

Abstract

An increasing number of suicidal asphyxiation with a plastic bag with inert gases, and in particular helium (He), have been reported from numerous countries over the last decade. These cases are differently managed and lead to different and variable interpretations. Based on the twelve last cases analysed in the laboratory and on the review of the most recent literature about this topic, updated autopsy guidelines for sampling have been proposed regarding to the samples choice and analytical challenges required by the gaseous state of this substance. Biological samples from airways (lungs lobe) followed by brain and cardiac blood are the best matrices to take during the autopsy to diagnose He exposure. Gaseous samples from trachea, pulmonary bronchi, gastric and cardiac areas are also recommended as alternative samples. The anatomical site of sampling must be carefully detailed, and to this end, forensic imaging constitutes a beneficial tool. Even if He detection is sufficient to conclude to He exposure, He concentrations in samples may be related to He exposure conditions (duration, breathing rate, etc.). A quantification in biological samples could be helpful to document more precisely the case. He concentrations in gaseous samples are reported up to 6.0 µmol/mL (tracheal gas), 2.4 µmol/mL (pulmonary gas), 0.64 µmol/mL (cardiac gas) and 12 µmol/mL (gastric gas). He concentrations in solid/liquid samples are reported up to 28 µmol/g (lungs) and 0.03 µmol/g (cardiac blood). The other matrices usually sampled during autopsy such as urine, peripheral blood, liver, fat matter and kidney appear as not relevant.

Suicidal deaths due to helium inhalation

“…Tsujita et al [47] demonstrated that hydrogen gave the highest intensity and the good shape of helium peak as compared to argon or nitrogen as a mobile phase. It was also suggested and confirmed by Varlet et al [44] to use hydrogen as a carrier gas to obtain the best selectivity and sensitivity of the method. According to the available literature data, volatile substances are analyzed under isothermal conditions [3,10,20,36,37,[44][45][46][47].…”

“…Due to the physical properties of helium (gas), the only methods enabling its separation are variants of gas chromatography (GC), e.g., GC with headspace analysis. The most commonly used detectors are mass spectrometers (MSs) [3,10,20,[44][45][46][47] and thermal conductivity detectors (TCDs) [36][37][38]48]. However, Tsujita et al [47] pointed out the poor selectivity and sensitivity for helium detection by GC-TCD.…”

“…Many researchers [3,10,20,36,37,49] propose use of nitrogen as the mobile phase in cases of testing for helium. Malbranque et al [45], Musshoff et al [46], Varlet et al [44], and Tsujita et al [47] used hydrogen as the carrier gas in their analyses. Tsujita et al [47] demonstrated that hydrogen gave the highest intensity and the good shape of helium peak as compared to argon or nitrogen as a mobile phase.…”

“…According to the available literature data, volatile substances are analyzed under isothermal conditions [3,10,20,36,37,[44][45][46][47]. In the case of MS detection, the preferred detection mode is selected ion monitoring (SIM) [3,10,20,[44][45][46][47]. Table 3 shows the methods used to detect helium in autopsy specimens, and their qualitative and quantitative results.…”

“…The test was carried out by puncturing the heart chambers with a syringe containing a small amount of water and then aspiring the content of the chamber. Similarly, Varlet et al [44] considered postmortem computed tomography as a useful tool in cases of suspected deaths due to helium gas embolism.…”