Study objective Elevated arterial lactate levels are closely related to morbidity and mortality in various patient categories. In the present retrospective study, the relation between arterial lactate, partial pressure of carbon dioxide (Pco₂) and pH was systematically investigated in patients who visited the emergency department (ED) with psychogenic hyperventilation.

Methods Over a 5-month period, all the patients who visited the ED of a university hospital with presumed psychogenic hyperventilation were evaluated. Psychogenic hyperventilation was presumed to be present when an increased respiratory rate (>20 min) was documented at or before the ED visit and when somatic causes explaining the hyperventilation were absent. Arterial blood gas and lactate levels (reference values 0.5–1.5 mmol/l) were immediately measured by a point-of-care analyser that was managed and calibrated by the central laboratory.

Results During the study period, 46 patients were diagnosed as having psychogenic hyperventilation. The median (range) Pco₂ for this group was 4.3 (2.0–5.5) kPa, the pH was 7.47 (7.40–7.68) and the lactate level was 1.2 (0.5–4.4) mmol/l. 14 participants (30%) had a lactate level above the reference value of 1.5 mmol/l. Pco₂ was the most important predictor of lactate in multivariate analysis. None of the participants underwent any medical treatment other than observation at the ED or had been hospitalised after their ED visit.

Conclusions In patients with psychogenic hyperventilation, lactate levels are frequently elevated. Whereas high lactates are usually associated with acidosis and an increased risk of poor outcome, in patients with psychogenic hyperventilation, high lactates are associated with hypocapnia and alkalosis. In this context, elevated arterial lactate levels should not be regarded as an adverse sign.