Constable Peter D, Stämpfli Henry R, Navetat Hérve, Berchtold Joachim, Schelcher François
Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, Urbana, IL 61802, USA.
J Vet Intern Med. 2005 Jul-Aug;19(4):581-9. doi: 10.1892/0891-6640(2005)19[581:uoaqsi]2.0.co;2.
Acid-base abnormalities are frequently present in sick calves. The mechanism for an acid-base disturbance can be characterized using the strong ion approach, which requires accurate values for the total concentration of plasma nonvolatile buffers (A(tot)) and the effective dissociation constant for plasma weak acids (K(a)). The aims of this study were to experimentally determine A(tot), K(a), and net protein charge values for calf plasma and to apply these values quantitatively to data from sick calves to determine underlying mechanisms for the observed acid-base disturbance. Plasma was harvested from 9 healthy Holstein-Friesian calves and concentrations of quantitatively important strong ions (Na+, K+, Ca2+, Mg2+, Cl-, L-lactate) and nonvolatile buffer ions (total protein, albumin, phosphate) were determined. Plasma was tonometered with CO2 at 37 degrees C, and plasma P(CO2) and pH measured over a range of 15-159 mm Hg and 6.93-7.79, respectively. Strong ion difference (SID) was calculated from the measured strong ion concentrations, and nonlinear regression was used to estimate values for A(tot) and K(a) from the measured pH and P(CO2) and calculated SID. The estimated A(tot) and K(a) values were then validated using data from 2 in vivo studies. Mean (+/- SD) values for calf plasma were A(tot) = 0.343 mmol/g of total protein or 0.622 mmol/g of albumin; K(a) = (0.84 +/- 0.41) x 10(-7); pK(a) = 7.08. The net protein charge of calf plasma was 10.5 mEq/L, equivalent to 0.19 mEq/g of total protein or 0.34 mEq/g of albumin. Application of the strong ion approach to acid-base disturbances in 231 sick calves with or without diarrhea indicated that acidemia was due predominantly to a strong ion acidosis in response to hyponatremia accompanied by normochloremia or hyperchloremia and the presence of unidentified strong anions. These results confirm current recommendations that treatment of acidemia in sick calves with or without diarrhea should focus on intravenous or PO administration of a fluid containing sodium and a high effective SID.
酸碱平衡异常在患病犊牛中很常见。酸碱平衡紊乱的机制可以用强离子方法来描述，这需要血浆非挥发性缓冲剂的总浓度（A(tot)）和血浆弱酸的有效解离常数（K(a)）的准确值。本研究的目的是通过实验确定犊牛血浆的A(tot)、K(a)和净蛋白电荷值，并将这些值定量应用于患病犊牛的数据，以确定观察到的酸碱平衡紊乱的潜在机制。从9头健康的荷斯坦-弗里生犊牛采集血浆，测定定量重要的强离子（Na+、K+、Ca2+、Mg2+、Cl-、L-乳酸）和非挥发性缓冲离子（总蛋白、白蛋白、磷酸盐）的浓度。在37℃用CO2对血浆进行血气平衡处理，分别在15 - 159 mmHg和6.93 - 7.79的范围内测量血浆P(CO2)和pH。根据测得的强离子浓度计算强离子差（SID），并使用非线性回归从测得的pH和P(CO2)以及计算出的SID估计A(tot)和K(a)的值。然后使用两项体内研究的数据对估计的A(tot)和K(a)值进行验证。犊牛血浆的平均（±标准差）值为：A(tot) = 0.343 mmol/g总蛋白或0.622 mmol/g白蛋白；K(a) = (0.84 ± 0.41)×10(-7)；pK(a) = 7.08。犊牛血浆的净蛋白电荷为10.5 mEq/L，相当于0.19 mEq/g总蛋白或0.34 mEq/g白蛋白。将强离子方法应用于231头有或无腹泻的患病犊牛的酸碱平衡紊乱表明，酸血症主要是由于低钠血症伴正常氯血症或高氯血症以及存在未识别的强阴离子导致的强离子酸中毒。这些结果证实了目前的建议，即治疗有或无腹泻的患病犊牛的酸血症应侧重于静脉内或口服给予含钠且有效SID高的液体。
