Carboxyhemoglobin Levels Induced by Cigarette Smoking Outdoors in Smokers.

INTRODUCTION

Non-invasive screening of carboxyhemoglobin saturation (SpCO) in the emergency department to detect occult exposure is increasingly common. The SpCO threshold to consider exposure in smokers is up to 9%. The literature supporting this cutoff is inadequate, and the impact of active smoking on SpCO saturation remains unclear. The primary objective was to characterize baseline SpCO in a cohort of smokers outdoors. Secondary objectives were to explore the impact of active smoking on SpCO and to compare SpCO between smokers and non-smokers.

METHODS

This was a prospective cohort pilot study in two outdoor urban public areas in the USA, in a convenience sample of adult smokers. SpCO saturations were assessed non-invasively before, during, and 2 min after cigarette smoking with pulse CO-oximetry. Analyses included descriptive statistics, correlations, and a generalized estimating equation model.

RESULTS

Eighty-five smokers had mean baseline SpCO of 2.7% (SD 2.6) and peak of 3.1% (SD 2.9), while 15 controls had SpCO 1.3% (SD 1.3). This was a significant difference. Time since last cigarette was associated with baseline SpCO, and active smoking increased mean SpCO. There was correlation among individual smokers' SpCO levels before, during, and 2 min after smoking, indicating smokers tended to maintain their baseline SpCO level.

CONCLUSIONS

This study is the first to measure SpCO during active smoking in an uncontrolled environment. It suggests 80% of smokers have SpCO ≤ 5%, but potentially lends support for the current 9% as a threshold, depending on clinical context.