Aintree University Hospital - Measuring Exhaled Carbon Monoxide - Does Breath Alcohol Cross React?

Carboxyhaemoglobin (COHb) is the key measure of exposure to carbon monoxide (CO) used by researchers and clinicians. The gold standard means of measuring COHb is by taking a blood sample. However, this can be off-putting to potential subjects in laboratory studies. It is also logistically difficult in community studies, and introduces a time delay in clinical environments such as busy emergency departments (COHb degrades rapidly and the result can normalise by the time a blood test is taken).

Measurement of exhaled CO is a rapid way of measuring CO exposure without the need for blood tests. These tests are widely used in smoking cessation and antenatal clinics, but they are known to be affected by alcohol on the breath (alcohol cross-reacts with the sensor and is mistakenly read as CO).

Alcohol is excreted via the lungs for up to 24 hours after drinking so this is a problem in both community studies and clinical use in emergency departments, where a significant proportion of the population will have drunk in the previous day. The aim of this study is to measure exhaled CO and breath alcohol in volunteers before, during and after a period of drinking a controlled amount of alcohol.

The data will be used to quantify the effect of alcohol on the apparent CO level and mathematical modelling will be undertaken to better understand the effect and to calculate a correction factor for this monitor. This will lead to future studies which will aim to validate the correction factor by measuring the COHb calculated by the device with blood COHb levels.