Nitrous Oxide Determination in Postmortem Biological Samples: A Case of Serial Fatal Poisoning in a Public Hospital

Quantitative determination of nitrous oxide in human blood by HS-GC-MS: forensic application of two fatal poisoning cases

Nitrous oxide (N2O), also known as laughing gas, has a euphoric effect and is becoming increasingly popular as a recreational inhalant drug. Deaths caused by recreational nitrous oxide abuse are rare, but may still occur. Although some methods for the quantification of N2O by GC-MS have been reported, elimination of carbon dioxide interference and the choice of a suitable internal standard remain current limitations to accurate N2O quantification. Here, a validated method using headspace-gas chromatography-mass spectrometry (HS-GC-MS) is described that allows the quantification of N2O in human blood samples: sodium hydroxide is used to remove carbon dioxide, and n-pentane is chosen as a suitable internal standard. Collectively, the validation results show a good linear relationship of N2O in blood within the concentration range of 0.02 ∼ 0.5 mL/mL and an LOD of 0.005 mL/mL. Subsequent application of the validated method to two real mortality cases due to N2O intoxication provided reference values for blood concentrations in forensic cases. Other biological specimens (gaseous samples and tissues) of the deceased were also analyzed to demonstrate that the deaths were caused by asphyxia due to the inhalation of N2O.

Nitrous oxide abuse direct measurement for diagnosis and follow-up: update on kinetics and impact on metabolic pathways

Recreational use of nitrous oxide (N2O) has become a major health issue worldwide, with a high number of clinical events, especially in neurology and cardiology. It is essential to be able to detect and monitor N2O abuse to provide effective care and follow-up to these patients. Current recommendations for detecting N2O in cases of recreational misuse and consumption markers are lacking. We aimed to update current knowledge through a review of the literature on N2O measurement and kinetics. We reviewed the outcomes of experiments, whether in preclinical models (in vitro or in vivo), or in humans, with the aim to identify biomarkers of intoxication as well as biomarkers of clinical severity, for laboratory use. Because N2O is eliminated 5 min after inhalation, measuring it in exhaled air is of no value. Many studies have found that urine and blood matrices concentrations are connected to ambient concentrations, but there is no similar data for direct exposure. There have been no studies on N2O measurement in direct consumers. Currently, patients actively abusing N2O are monitored using effect biomarkers (biomarkers related to the effects of N2O on metabolism), such as vitamin B12, homocysteine and methylmalonic acid.

Driving under the influence of nitrous oxide - A retrospective study of HS-GC-MS analysis in whole blood

Since 2020, our lab has received blood samples from traffic cases involving suspicion of driving under the influence of nitrous oxide (N2O). While N2O analysis by gas chromatography (GC) has been around for decades, quantitative results in blood from drivers have been only scarcely reported. We present a three-year (2020-2022) retrospective study of N2O from traffic cases in Eastern Denmark with suspected involvement of N2O intake. Whole blood samples from traffic cases were analysed for N2O using headspace-GC-MS. Freshly made calibration curves and additions of xenon gas as an internal standard were used for calculation of N2O concentrations. Positive samples have been defined as having concentrations greater than 0.1 mL N2O/L blood. Over a three-year period, we have tested 62 traffic case blood samples for the presence of N2O. Despite the technical challenges associated with the analysis of N2O, we have found N2O in 52 of the samples. Calculated concentrations were in the range 0.1-48 mL N2O/L blood, which are similar to the few cases previously found in the literature.

Nitrous Oxide Abuse: Clinical Outcomes, Pharmacology, Pharmacokinetics, Toxicity and Impact on Metabolism

The recreational use of nitrous oxide (N2O), also called laughing gas, has increased significantly in recent years. In 2022, the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) recognized it as one of the most prevalent psychoactive substances used in Europe. Chronic nitrous oxide (N2O) exposure can lead to various clinical manifestations. The most frequent symptoms are neurological (sensitive or motor disorders), but there are also other manifestations like psychiatric manifestations or cardiovascular disorders (thrombosis events). N2O also affects various neurotransmitter systems, leading to its anesthetic, analgesic, anxiolytic and antidepressant properties. N2O is very challenging to measure in biological matrices. Thus, in cases of N2O intoxication, indirect biomarkers such as vitamin B12, plasma homocysteine and plasma MMA should be explored for diagnosis and assessment. Others markers, like oxidative stress markers, could be promising but need to be further investigated.

Lethal nitrous oxide (N2O) intoxication during surgery: the contribution of immunohistochemistry in identifying the cause of death: a case report

BACKGROUND

Nitrous oxide (N2O) is a gas used in medicine for its analgesic, anxiolytic and amnesic properties. It is a drug considered safe if adequately administered. In the literature, accidental N2O-related deaths are rare. They are mostly related to inhalation of this substance for recreational and autoerotic purposes; rarely are reported deaths due to incorrect administration of medical gas in anesthesia. The diagnosis of death from acute N2O intoxication is complex and is generally an exclusion diagnosis: the macroscopic and microscopic post-mortem signs are entirely nonspecific. Furthermore, the circumstantial data are not always supportive and can even be confusing, mainly if the death occurred inside a hospital.

CASE PRESENTATION

We describe a particular case of death from acute nitrous oxide poisoning in a hospital environment, of a Caucasian male of 72-years-old. The intoxication occurred during a minimally invasive vascular surgery due to an incorrect assembly of the supply lines of medical gases (O2 and N2O). The identification of the cause of death resulted from the analysis of circumstantial data, macroscopic and microscopic autoptic findings, and immunohistochemical investigations based on the search for antibodies anti E-selectin, P-selectin, and HIF 1-α.

CONCLUSION

Although not pathognomonic of asphyxiation by N2O, the latter molecules are a valid and early marker of hypoxic insult. Therefore, in concert with all other findings, it may constitute valid support for the forensic pathologist to ascertain the cause of death in case of suspected intoxication by N2O.

Nitrous oxide intoxication: systematic literature review and proposal of new diagnostic possibilities

Background

Nitrous oxide (N2O), also called “laughing gas,” is the most commonly used inhalation anesthetic in dentistry. The N2O is no longer used, because of the long-term neurologic and cardiovascular sequelae. Due to its sedative and euphoric properties, N2O is often used for recreational use or in some erotic activities. Accidental deaths are mainly associated with the uses of N2O: death can occur from sudden cardiac arrhythmia or, most commonly, acute asphyxiation due to hypoxia. This paper aims to study the literature concerning deaths due to N2O intoxication and highlight pathological findings useful for diagnosis when the crime scene investigation does not reveal any evidence.

Materials and methods

The authors conducted the literature search by PubMed and Scopus databases, searching for articles from 1 January 1970 to 1 March 2020 using the key terms: “Nitrous oxide,” “Laughing gas,” “Hypoxic damage,” “Nitrous oxide anesthesia,” and “Nitrous oxide death.”

Results and discussion

A total of 244 articles were collected. Only 26 articles were included in the systematic review. Most of the deaths from intoxication are due to asphyxiation; the diagnosis is often difficult and immunohistochemistry could be helpful. Nitrous oxide increases the intracellular adhesion molecule expression, E- and P-Selectin (markers of the early inflammatory response), and HIF-1 α (indicative of oxidative stress during ischemia-reperfusion).

Conclusion

The macroscopic and microscopic signs of N2O intoxication are non-specific, but N2O has been proven to cause hypoxic damage to the brain. The suspicion of the presence of the gas in the environment should guide the pathologist. Tissue analyzes provide important information; immunohistochemical stains can confirm hypoxic damage through the use of markers such as HIF-1 α, E-Selectin, and P-Selectin.