[The effect of short-term hyperventilation on the concentration of ionized serum calcium]

Abstract

Background and objective: Paraesthesias and carpopedal spasms on hyperventilation are explained by a reduction in ionised serum calcium (ISC). We tested whether 5-minute hyperventilation changes the concentration of ISC.

Subjects and method: Arterial blood samples were obtained via a small plastic catheter introduced into the femoral artery of ten healthy male volunteers (mean age 33 years) before, during and after 5 minutes of hyperventilation, which was achieved by deep and rapid breathing and considered adequate when the end-expiratory pCO2 had fallen to 2.5 kPA within the first minute and remained below this level during the remaining 4 minutes. These criteria were met in nine of the ten patients. The ISC concentration was measured with an ion-selective electrode, the pH, paCO2 and bicarbonate levels with an autoanalyser.

Results: Paraesthesias of the fingers and hand occurred in nine of the volunteers, carpopedal spasms in seven. Despite a definite rise in pH from 7.39 +/- 0.02 to 7.75 +/- 0.045, the concentration of ISC did not change significantly during the hyperventilation.

Conclusion: Paraesthesias and carpopedal spasms which occur during hyperventilation are not caused by a fall in ionised serum calcium in arterial blood.