EFFECT OF SHORT-TERM HYPERVENTILATION ON IONIZED SERUM-CALCIUM

Background and objective: Paraesthesias and carpopedal spasms on hyper ventilation are explained by a reduction in ionised serum calcium (ISC ). We tested whether 5-minute hyperventilation changes the concentrati on of ISC. Subjects and method: Arterial blood samples were obtained v ia 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 bre athing and considered adequate when the end-expiratory pCO(2) had fall en to 2.5 kPA within the first minute and remained below this level du ring the remaining 4 minutes. These criteria were met in nine of the t en patients. The ISC concentration was measured with an ion-selective electrode, the pH, p(a)CO(2) and bicarbonate levels with an autoanalys er. Results: Paraesthesias of the fingers and hand occurred in nine of the volunteers, carpopedal spasma in seven. Despite a definite rise i n pH from 7.39 +/- 0.02 to 7.75 +/- 0.045, the concentration of ISC di d not change significantly during the hyperventilation. Conclusion: Pa raesthesias and carpopedal spasms which occur during hyperventilation are not caused by a fall in ionised serum calcium in arterial blood.