Effects of erythrocytes, bicarbonate, temperature and albumin on in vitro ionized calcium variations with pH.
Using a heart lung machine as an in vitro model, the relation between ionized calcium (cCa2+) and pH has been shown to depend on several variables such as erythrocytes, temperature and albumin as well as the total calcium and bicarbonate concentrations. The respiratory acid-base disturbances were simulated by changing the gas flow between 1.0 and 2.41 min-1 by adding CO2, to the machine at a concentration of 0 to 17%. When pCO2 was used to alter pH, cCa2+ varied from 0.16 mmol l-1 per pH unit to 0.52 mmol l-1. The regression slope of cCa2+ on pH was made steeper by decreasing erythrocyte volume fraction and by increasing temperature and the concentrations of HCO3, calcium or albumin. The metabolic acid-base alterations were produced by HCl or NaHCO3 at a constant gas flow, cCA2+ changes per pH unit were 0.70 mmol l-1 in plasma and 1.04 mmol l-1 in whole blood. The different results found in plasma and in erythrocyte fluids may be explained by their different buffering capacity. Haemoglobin may buffer hydrogen ions, and the formation of HCO3- is catalysed by carbonic anhydrase from the red cells.
Kancir
C B
CB
Department of Anaesthesia, Odense University Hospital, Denmark.
Petersen
P H
PH
Madsen
T
T
D000136:Acid-Base Equilibrium; D000418:Albumins / Q000502:physiology*; D001639:Bicarbonates / Q000032:analysis*; D002118:Calcium / Q000032:analysis* / Q000097:blood; D004912:Erythrocytes / Q000502:physiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008955:Models, Cardiovascular; D013696:Temperature
D000418:Albumins; D001639:Bicarbonates; D002118:Calcium