Preliminary experimental outcomes of induced hypercapnia in treatment of obstinate singultus

Our team found that abolishing the venous-arterial CO₂ gradient can cease singultus (hiccups), in which the CO₂ pressure in blood reaches no less than 50 mmHg. In order to precisely investigate the target level as a preliminary study, we made a combination gas consisting of 10% CO₂ and 90% O₂ to generate the conditions instantly and safely.

Thirty-five cases consisting of 26 patients with long-term chronic singultus were treated using the gas. The group consisted of 21 males and 5 females with mean singultus duration of 8.0±13.1 years. A standard oxygen mask was used for delivery of the gas to the patients, and patients breathed in the gas until they felt relief. The duration of the procedure was measured from the beginning to the point at which singultus ceased. A blood test was performed to measure the partial pressure of CO₂ in venous blood at the point at which singultus ceased.

Singultus ceased in all patients in a mean time of 5.3±1.5 minutes, with complete recurrence observed in two cases. The mean partial pressure of CO₂ in the venous blood at the point the singultus stopped was 60.8±6.8 mmHg. No life-threatening complications were found in any patient.

One of the definitive conditions for ceasing singultus is acute CO₂ retention in the body, the target of which is around 60 mmHg of CO₂ in venous blood. We believe that targeting acute hypercapnia can always stop singultus, although further neuroscientific investigation is necessary to reveal the physiological mechanism.