Total carbon dioxide value and pH were higher in pericardial fluid than in arterial blood in 11 patients undergoing open-heart surgery, while calcium, phosphorus, and total protein levels were lower, and sodium, potassium, chloride, and urea nitrogen levels were the same. The findings are consistent with rapid diffusion of carbon dioxide and slow equilibration of bicarbonate across the pericardial membranes.
Hutchin P, Nino HV, Suberman R. Electrolyte and Acid-Base Composition of Pericardial Fluid in Man. Arch Surg. 1971;102(1):28-30. doi:10.1001/archsurg.1971.01350010030007