Acidosis is common in newborn calves as a result of impaired uteroplacental gas exchange or asphyxia. Acidosis can be a life-threatening condition, depending on the severity and duration. Venous blood pH < 7.2 (measured in samples obtained during or after birth) is considered indicative of a critical situation and has been associated with a mortality rate of 33%1 to 56%2 in calves, whereas a pH < 7.0 was associated with a mortality rate of 100% in both studies.
Various buffer solutions are used for the treatment of acidosis in newborn calves.3 Solutions of NaHCO3 are the standard treatment because of the high alkalinizing potential and rapid effect.4-6,a Although hypertonic NaHCO3 solutions with osmolalities of 2,000 mOsm/L (8.4%)6,a,b and 1,190 mOsm/L (5%)5 have been used with excellent results, an isotonic solution (1.3%) is recommended for clinical use because of potential adverse effects associated with administration of hypertonic solutions.4,7-9 Administration of hypertonic NaHCO3 solution reportedly can cause hyperosmolality of the extracellular fluid, hypokalemia, and hypernatremia10 as well as hypocalcemia.8 Paradoxic acidosis attributable to hypercapnia is another potential effect,11 which can affect intracellular fluids and CSF. Bicarbonate reacts with hydrogen ions to form water and carbon dioxide. However, a further increase in carbon dioxide content, which could account for paradoxic acidosis, was not detected in newborn calves during and following treatment with 5% NaHCO3 solution.5 In a study12 of healthy anesthetized 4- to 10-day-old calves, the administration of 8.4% NaHCO3 solution at a dosage of 5 mmol/kg resulted in a transient increase in PCO2 in the arterial blood but not in the CSF. This means that hypertonic NaHCO3 solution did not lead to hypercapnia-induced acidosis in the CSF.12
The primary objective of the study reported here was to test the hypothesis that the administration of hypertonic NaHCO3 solution to acidotic newborn calves would not result in adverse changes in electrolyte concentrations and enzyme activities. A secondary objective was to determine those blood variables that would be affected by acidosis.
Materials and Methods
Animals—Forty-two newborn calves born to dairy cows at our facility were used in the study. Twenty calves were born to client-owned dams that had dystocia; forced extraction involving 1 or 2 people was used to deliver 5 calves, and the remaining 15 calves were delivered via Cesarean section, as described in another report.13 These calves had a venous blood pH < 7.2 and were treated by IV administration of NaHCO3 solution (treatment group). This group comprised 16 males and 4 females and included 8 Swiss Braunvieh, 7 Simmental, 3 Holstein-Friesian, and 2 mixed-breed calves.
Twenty-two calves born to 20 university-owned dairy cows were used as control calves (control group). Births of these calves were uneventful and did not require assistance. This group comprised 18 singleton and 4 twin calves, all of which had a venous blood pH ≥ 7.2 immediately after birth. Control calves consisted of 12 males and 10 females and included 16 Swiss Braunvieh, 5 Simmental, and 1 Holstein-Friesian calf.
Collection and analysis of samples—A blood sample was collected from each calf immediately after birth for blood gas analysis and 10, 30, 60, and 120 minutes after birth for blood gas, hematologic, and serum biochemical analyses. After collection of the initial blood sample, a brief clinical examination, which included measurement of rectal temperature and assessment of neonatal stress and asphyxia, was performed on each calf.c One liter of the dam's colostrum was fed to each calf via a nipple bottle after collection of the last blood sample.
The initial blood sample (2 mL) for blood gas analysis was collected from a jugular vein by use of a needled attached to a heparin-coated evacuated tube.e For each of the subsequent collections, 2 mL of blood was collected for blood gas analysis, 2.7 mL of blood was collected into an evacuated tube that contained calcium-EDTAf for hematologic analysis, and 4.5 mL of blood was collected into an evacuated tube without anticoagulantg for serum biochemical analysis. After the blood collection at 10 minutes after birth, calves in the treatment group were administered 5% NaHCO3 solutionh (1,190 mOsm/L) IV via an indwelling polytetrafluoroethylene-coated catheter.i The amount of NaHCO3 solution needed for infusion was determined on the basis of the body weight and base excess of each calf at 10 minutes after birth as well as the volume of distribution of bicarbonate (ie, 0.5)4,14 and was calculated by use of the following equation: mEq of NaHCO3 = body weight × (–base excess) × 0.5. Each liter of 5% NaHCO3 solution contained 0.595 mEq of bicarbonate; therefore, the calculation was used to provide the amount of bicarbonate required to fully compensate for the deficit.
The pH, Po2, Pco2, base deficit, and plasma bicarbonate concentration of venous blood samples were determined by use of a blood gas analyzer.j All samples were analyzed as soon as possible; all were analyzed < 30 minutes after collection.15 The pH, PO2, and PCO2 values were corrected on the basis of the rectal temperature of each calf.
Samples of EDTA-anticoagulated blood were analyzed immediately after collection by use of an automated hematologic analyzerk; Hct, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, mean cell volume, leukocyte and erythrocyte counts, and hemoglobin concentration were determined.
Serum samples were analyzed by use of an automated analyzerl at 37°C in accordance with published guidelines.16 Concentrations of total bilirubin, urea, creatinine, sodium, potassium, chloride, total calcium, magnesium, and inorganic phosphorus and activities of GDH, AST, CK, and GGT were determined. When blood samples were collected during the night or a weekend, serum was harvested and stored at 4°C for a maximum of 36 hours until biochemical analysis.
The anion gap was calculated by use of the following equation:
The percentage change in plasma volume was calculated by use of the following equation17:
where %ΔPV is the percentage change in plasma volume, and Hct values and hemoglobin concentrations determined in samples obtained 10 (before the administration of NaHCO3 solution) and 120 minutes after birth were used in the calculations.
Statistical analysis—Data were analyzed by use of a computer software program,m and mean and SEM values were calculated. Data without a normal distribution were transformed (log base 10). Comparisons between groups at 10 (before treatment) and 120 minutes were made by use of ANOVA. Within-group comparisons of data obtained at 10 and 120 minutes and between-group comparisons throughout the entire study period were performed by use of an ANOVA for repeated measures. Differences were considered significant at P < 0.05.
Results
Animals—Mean ± SEM body weight of treated and control calves did not differ significantly (42.7 ± 1.7 kg and 40.0 ± 1.3 kg, respectively). Clinical examinations of the calves immediately after birth revealed no injuries or abnormalities. All treated and control calves were healthy when discharged with their dams at 4 hours to 4 days after parturition.
Blood gas analysis—Mean ± SEM blood pH of calves immediately after birth differed significantly (P < 0.001) between the treatment (7.12 ± 0.02) and control (7.24 ± 0.02) groups (Table 1). The 2 groups did not differ significantly with respect to PO2 at any of the sample collection times and with respect to PO2 curves over time. Immediately after birth, PCO2 was significantly (P < 0.001) higher in the treatment group (79.1 ± 2.3 mm Hg) than in the control group (64.6 ± 1.7 mm Hg). Furthermore, at 120 minutes after birth, calves in the treatment group had a significantly (P = 0.01) higher PCO2 (61.6 ± 1.0 mm Hg) than the value for calves in the control group (56.6 ± 1.2 mm Hg). However, Pco2 decreased significantly (P < 0.001) in both groups during the study. Mean bicarbonate concentration of calves in the treatment (22.7 ± 0.9 mmol/L) and control (27.0 ± 0.6 mmol/L) groups differed significantly (P < 0.001). Similarly, base excess differed significantly (P < 0.001) between the treatment and control groups (−7.6 ± 0.7 mmol/L and 0.3 ± 0.7 mmol/L, respectively).
Mean ± SEM values for blood gas analysis and rectal temperature in 22 untreated control calves (venous blood pH immediately after birth, ≥ 7.2) and 20 acidotic calves (pH immediately after birth, < 7.2) treated by IV infusion of 5% NaHCO3 solution.
| Variable | Group | 10 minutes after birth (before treatment) | 120 minutes after birth (after treatment) |
|---|---|---|---|
| pH | Control | 7.27 ± 0.01a,A | 7.32 ± 0.01c,B |
| Treated | 7.10 ± 0.02b,A | 7.28 ± 0.01d,B | |
| Po2 (mm Hg) | Control | 29.2 ± 1.2C | 26.3 ± 1.0D |
| Treated | 33.5 ± 3.7 | 25.9 ± 1.2 | |
| Pco2 (mm Hg) | Control | 61.6 ± 1.1a,A | 56.6 ± 1.2e,B |
| Treated | 78.1 ± 2.2b,A | 61.6 ± 1.0f,B | |
| Bicarbonate (mmol/L) | Control | 26.8 ± 0.5a | 27.5 ± 0.4 |
| Treated | 22.1 ± 1.0b,A | 27.6 ± 1.0B | |
| Base excess (mmol/L) | Control | 0.6 ± 0.7a,C | 1.6 ± 0.5D |
| Treated | −8.4 ± 1.2b,A | 0.3 ± 1.1B | |
| Rectal temperature (°C) | Control | 39.4 ± 0.1A | 38.1 ± 0.1c,B |
| Treated | 39.9 ± 0.1A | 38.5 ± 0.1d,B |
Within a variable, values differ significantly (a,bP < 0.001, c,dP < 0.05, and e,fP = 0.01 [ANOVA for repeated measures]) between groups.
Within a row, values differ significantly (A,BP < 0.001 and C,DP = 0.01 [ANOVA for repeated measures]) between time periods.
NaHCO3 treatment—Calves in the treatment group received a mean ± SEM of 286.4 ± 29.5 mL (range, 45 to 500 mL) of 5% NaHCO3 solution. Depending on the amount administered, duration of the infusion varied from 3 to 12 minutes. For the 120-minute study period, there were significant (P < 0.001) differences between the treatment and control groups for all 3 blood gas variables. At 120 minutes after birth, blood pH of calves in the treatment group was still significantly lower (7.28 ± 0.01) than that of calves the control group (7.32 ± 0.01; Figure 1). However, at 120 minutes after birth, bicarbonate concentration and base excess did not differ significantly between the groups (Figure 2).
Mean ± SEM blood pH in 22 untreated control calves (venous blood pH immediately after birth, ≥ 7.2; diamonds) and 20 acidotic calves (pH immediately after birth, < 7.2; squares) treated by IV infusion of 5% NaHCO3 solution. The period during which the NaHCO3 solution was infused is indicated (black bar).
Citation: American Journal of Veterinary Research 68, 8; 10.2460/ajvr.68.8.850
Mean ± SEM blood pH in 22 untreated control calves (venous blood pH immediately after birth, ≥ 7.2; diamonds) and 20 acidotic calves (pH immediately after birth, < 7.2; squares) treated by IV infusion of 5% NaHCO3 solution. The period during which the NaHCO3 solution was infused is indicated (black bar).
Citation: American Journal of Veterinary Research 68, 8; 10.2460/ajvr.68.8.850
Mean ± SEM blood pH in 22 untreated control calves (venous blood pH immediately after birth, ≥ 7.2; diamonds) and 20 acidotic calves (pH immediately after birth, < 7.2; squares) treated by IV infusion of 5% NaHCO3 solution. The period during which the NaHCO3 solution was infused is indicated (black bar).
Citation: American Journal of Veterinary Research 68, 8; 10.2460/ajvr.68.8.850
Bilirubin, urea, and creatinine concentrations—Immediately after birth, the mean bilirubin concentration was significantly higher in calves of the treatment group than that in calves of the control group (6.6 and 4.1 Mmol/L, respectively). During the study period, the bilirubin concentration increased significantly in both groups, but the concentrations did not differ at 120 minutes (Table 2).
Mean ± SEM values for serum biochemical analysis in 22 untreated control calves and 20 acidotic calves treated by IV infusion of 5% NaHCO3 solution.
| Variable | Group | 10 minutes after birth (before treatment) | 120 minutes after birth (after treatment) |
|---|---|---|---|
| Total bilirubin (μmol/L)* | Control | 4.1(3.9, 4.4)c,A | 9.1(8.5, 9.6)B |
| Treated | 6.6(5.9, 7.4)d,A | 10.4(9.2, 11.8)B | |
| Urea (mmol/L) | Control | 3.5 ± 0.3 | 3.6 ± 0.3 |
| Treated | 3.9 ± 0.3 | 4.0 ± 0.4 | |
| Creatinine (μmol/L)* | Control | 374.1(337.3, 416.0)A | 337.3(305.5, 372.4)B |
| Treated | 251.2(191.9, 328.9) | 306.0(285.8, 329.6) | |
| GDH (U/L) | Control | 2.7 ± 0.3c,A | 4.3 ± 0.4B |
| Treated | 4.4 ± 0.6d | 4.8 ± 0.6 | |
| AST (U/L)* | Control | 13.3(12.9, 13.7)a,A | 20.2(19.4, 21.0)a,B |
| Treated | 23.4(22.1, 24.8)b,A | 33.7(31.6, 36.1)b,B | |
| CK (U/L)* | Control | 69(59, 79)A | 173(141, 213)e,B |
| Treated | 133(107, 164)A | 297(247, 358)f,B | |
| GGT (U/L)* | Control | 12.9(11.9, 13.9)E | 19.1(15.7, 23.2)F |
| Treated | 12.9(11.5, 14.4) | 12.6(11.2, 14.1) | |
| Sodium (mmol/L) | Control | 146.6 ± 0.6 | 146.2 ± 0.3c |
| Treated | 145.3 ± 0.8A | 147.8 ± 0.7d,B | |
| Potassium (mmol/L) | Control | 5.4 ± 0.1 | 5.3 ± 0.1 |
| Treated | 5.5 ± 0.1 | 5.2 ± 0.2 | |
| Chloride (mmol/L) | Control | 104.1 ± 0.9e | 104.2 ± 1.0a |
| Treated | 99.6 ± 1.1f,E | 98.2 ± 1.3b,F | |
| Calcium (mmol/L) | Control | 2.93 ± 0.04 | 2.95 ± 0.03c |
| Treated | 3.09 ± 0.07A | 2.78 ± 0.06d,B | |
| Magnesium (mmol/L) | Control | 1.02 ± 0.04C | 1.00 ± 0.04D |
| Treated | 1.05 ± 0.04A | 0.94 ± 0.04B | |
| Inorganic phosphorus (mmol/L) | Control | 2.22 ± 0.07A | 2.03 ± 0.05B |
| Treated | 2.40 ± 0.11A | 1.99 ± 0.08B |
Data were transformed (log base 10) for analysis; values in parentheses represent minimum and maximum of back-transformed SEM.
Within a row, values differ significantly (P < 0.05 [ANOVA for repeated measurements]) between time periods.
See Table 1 for remainder of key.
At 10 and 120 minutes after birth, there were no significant differences between the 2 groups with respect to urea and creatinine concentrations (Table 2). However, in calves of the control group, there was a significant (P < 0.001) decrease in the mean creatinine concentration from 10 to 120 minutes after birth (374.1 and 337.3 Mmol/ L, respectively).
Mean ± SEM base excess in 22 untreated control calves and 20 acidotic calves treated by IV infusion of 5% NaHCO3 solution. See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 68, 8; 10.2460/ajvr.68.8.850
Mean ± SEM base excess in 22 untreated control calves and 20 acidotic calves treated by IV infusion of 5% NaHCO3 solution. See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 68, 8; 10.2460/ajvr.68.8.850
Mean ± SEM base excess in 22 untreated control calves and 20 acidotic calves treated by IV infusion of 5% NaHCO3 solution. See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 68, 8; 10.2460/ajvr.68.8.850
Enzyme activity—Ten minutes after birth, GDH and AST activities were higher in calves of the treatment group than in calves of the control group (Table 2). In calves of the treatment group, the activities of AST and CK increased significantly between 10 and 120 minutes after birth. In the control calves, the activities of all 4 measured enzymes increased significantly between 10 and 120 minutes after birth. During the study period, significant differences existed between the 2 groups for curves of the activities of GDH, AST, and GGT.
Electrolyte concentrations—At 10 minutes after birth (ie, before treatment), the concentrations of sodium, potassium, calcium, and magnesium did not differ significantly between calves of the 2 groups, but the chloride concentration was significantly lower in calves of the treatment group (Table 2). At 120 minutes after birth, the concentrations of sodium, chloride, and calcium differed significantly between the 2 groups. During the study period, potassium concentrations did not differ significantly within and between groups. At 120 minutes after birth, the concentration of sodium (P < 0.05) was significantly higher and concentrations of chloride (P < 0.001) and calcium (P < 0.05) significantly lower in the treatment group, compared with those in the control group.
Curves of the sodium and chloride concentrations of the 2 groups differed significantly (P < 0.001; Figure 3). In calves of the treatment group, the sodium concentration increased markedly between 10 and 30 minutes after birth (ie, during and immediately following administration of the NaHCO3 solution).
Mean ± SEM concentrations of sodium (squares) and chloride (triangles) in 22 untreated control calves (solid lines) and 20 acidotic calves treated by IV infusion of 5% NaHCO3 solution (dashed line). See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 68, 8; 10.2460/ajvr.68.8.850
Mean ± SEM concentrations of sodium (squares) and chloride (triangles) in 22 untreated control calves (solid lines) and 20 acidotic calves treated by IV infusion of 5% NaHCO3 solution (dashed line). See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 68, 8; 10.2460/ajvr.68.8.850
Mean ± SEM concentrations of sodium (squares) and chloride (triangles) in 22 untreated control calves (solid lines) and 20 acidotic calves treated by IV infusion of 5% NaHCO3 solution (dashed line). See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 68, 8; 10.2460/ajvr.68.8.850
Curves of the calcium and magnesium concentrations of the 2 groups differed significantly (P < 0.001 and 0.05, respectively). In the treatment group, the calcium concentration decreased during the infusion of NaHCO3 solution from 3.09 ± 0.07 mmol/L to 2.77 ± 0.06 mmol/L and remained at that concentration for the remainder of the study period. In the control group, the calcium concentration fluctuated little. Curves of the phosphorus concentration of the 2 groups did not differ significantly.
Hematologic analysis—At 10 minutes after birth, calves of the treatment group had higher leukocyte counts and lower values for mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration than did control calves (Table 3). Curves of the Hct, hemoglobin concentration, and leukocyte counts differed significantly (P < 0.001) between the 2 groups.
Mean ± SEM values for hematologic analysis and the anion gap in 22 untreated control calves and 20 acidotic calves treated by IV infusion of 5% NaHCO3 solution.
| Variable | Group | 10 minutes after birth (before treatment) | 120 minutes after birth (after treatment) |
|---|---|---|---|
| Hct (%)* | Control | 37 (36, 38)C | 38 (37, 39)c,D |
| Treated | 36 (34, 38)A | 33 (31, 35)d,B | |
| Hemoglobin (g/dL) | Control | 12.59 ± 0.39C | 12.67 ± 0.40e,D |
| Treated | 11.42 ± 0.55A | 10.78 ± 0.59f,B | |
| Erythrocyte count (X 106 cells/μL) | Control | 8.71 ± 0.22C | 8.92 ± 0.25c,D |
| Treated | 10.33 ± 2.02 | 7.93 ± 0.40d | |
| Leukocyte count (X 103 cells/μL) | Control | 11.07 ± 0.54e | 11.26 ± 0.53 |
| Treated | 14.65 ± 1.08f,A | 11.41 ± 0.94B | |
| Mean corpuscular hemoglobin (pg) | Control | 14.35 ± 0.21e | 14.32 ± 0.18c |
| Treated | 13.53 ± 0.21f | 13.53 ± 0.24d | |
| Mean corpuscular hemoglobin concentration (g/dL) | Control | 32.71 ± 0.17a | 32.96 ± 0.17e |
| Treated | 31.05 ± 0.38b,A | 31.88 ± 0.32f,B | |
| Mean corpuscular volume (fl) | Control | 44.00 ± 0.56 | 43.41 ± 0.62 |
| Treated | 43.58 ± 0.70A | 42.71 ± 0.73B | |
| Anion gap (mmol/L)*† | Control | 22.13(21.23, 23.07)a,C | 19.63(19.01, 20.28)a,D |
| Treated | 28.64(27.48, 28.85)b,E | 26.49(25.06, 27.99)b,F |
Anion gap was calculated as (sodium concentration + potassium concentration) – (chloride concentration + bicarbonate concentration).
See Tables 1 and 2 for remainder of key.
Anion gap and change in plasma volume—At 10 minutes after birth, anion gap of calves in the treatment group was significantly (P < 0.001) higher (mean, 6.51 mmol/L) than that of calves in the control group (Table 3). After NaHCO3 treatment, the value for the groups remained different until the end of the study period.
In calves of the treatment group, mean ± SEM plasma volume increased by 12 ± 3% between 10 and 120 minutes after birth. This value differed significantly (P < 0.001) from the value for the control group, in which mean plasma volume decreased by 6 ± 2%.
Discussion
The administration of NaHCO3 solution is a standard treatment in calves with acidosis and is aimed at restoration of the bicarbonate concentration, which is decreased in animals with acidosis.3,18,b,n Immediately after birth, calves may have varying degrees of metabolic or respiratory acidosis. Although the metabolic component of acidosis is ameliorated by the administration of bicarbonate, the respiratory component is not. This was exemplified in our study via the effect on the base excess, which is a major index of metabolic or strong ion acidosis.19 In calves of the treatment group, the administration of NaHCO3 solution resulted in a pronounced increase in the base excess (from −8.4 ± 1.2 mmol/L before to 2.7 ± 0.8 mmol/L immediately after treatment; Figure 2). During the same period, pH increased from 7.10 ± 0.01 to 7.27 ± 0.01 (Figure 1). Thus, NaHCO3 treatment led to base excess and pH values within 30 minutes after infusion that required at least 6 hours for untreated acidotic calves to attain in another study.6,n This means that treatment with hypertonic NaHCO3 solution shortened the period of life-threatening acidosis that may affect neonatal calves. Rapid correction of acidosis is critical in calves with a pH < 7.2n because their risk of fatality is higher during the first 48 hours after birth, compared with that for calves with a pH > 7.2.1,2
Because of the potential adverse effects of hypertonic NaHCO3 solution, the use of an isotonic solution has been recommended.4,7-9,18-20 Hypertonic NaHCO3 solutions have been used in some studies,5,a,n and adverse effects, at least those that could be monitored via blood gas variables, were not detected. In another study,12 the effect of a hypertonic (2,000 mOsm/L) NaHCO3 solution on acid-base variables in arterial blood and CSF and on Hct, total protein, hemoglobin, and various electrolyte values was investigated in healthy, anesthetized 4- to 10-day-old calves. The calves were monitored for 60 minutes after administration of the hypertonic NaHCO3 solution. In that study, the Hct and sodium concentration differed between treated and control calves, with the sodium concentration increased by 5 mmol/L in treated calves. In the study reported here, the mean sodium concentration in treated calves increased by a maximum of 3 mmol/L, which could arguably have been attributable to the sodium in the treatment solution. In both the treatment and control groups, the sodium concentration remained within the reference range for nontreated neonatal calves.21,22 Similarly, chloride concentrations of the treated calves were within the reference range, although they decreased from a relatively low concentration of 99.6 ± 1.1 mmol/L before treatment to 97.0 ± 1.3 mmol/L after treatment. The reason for this decrease was believed to be attributable to dilution or displacement of chloride by bicarbonate ions.10 We cannot explain the reason that the chloride concentration in the control calves was > 103.0 mmol/L and thus outside the reference range.21,23
The curves of inorganic phosphorus and magnesium concentrations of the 2 groups were approximately parallel throughout the study period, although the magnesium concentration, similar to the calcium concentration, decreased slightly as a result of treatment. This was believed to be attributable to dilution. In contrast, the potassium concentration was not affected by the degree of acidosis or infusion of the hypertonic NaHCO3 solution. Overall, the concentrations of all electrolytes that were measured were within published reference ranges.23,24
The strong ion model describes the acid-base equilibrium by use of the predominant strong anions and cations19 and helps to exemplify the difference between acidosis in a newborn calf and acidosis in a diarrheic calf. The latter is characterized by an increased lactate concentration, hyponatremia, and hyper- or normochloremia with a resulting increase in the strong ion difference.25,26 In contrast, electrolyte concentrations are within the reference ranges in acidotic neonates, and the acidosis, other than the respiratory component attributable to carbon dioxide, is caused by unidentified strong ions. In neonates, this is L-lactate that originates from anaerobic metabolism.27 Therefore, characterization of the metabolic component of acidosis in neonates is feasible by use of the anion gap because its magnitude is not substantially influenced by alterations in electrolyte concentrations.
Significant differences in the activities of GDH and AST were detected between calves of the 2 groups. In control calves of the study reported here, activities were similar to those described in other studies of GDH° and AST.28 In contrast, calves of the treatment group had GDH and AST activities that were increased by 60% and 52%, respectively. In cattle, both enzymes are considered specific for the liver and indicative of hypoxic conditions29,30 and increases in their activities can reflect a severe or prolonged hypoxic insult to the liver. The GDH activity was similar in both groups at 2 hours after birth. The activity of AST also increased in the control calves, although this was later than in the treated calves. Possibly, this was attributable to hypoxia during the late portion of stage II labor in calves in which acidosis was minimal.
An increase in the activity of CK in cattle is most commonly caused by muscle damage. At 10 minutes after birth, CK activity in the treated calves was almost twice that of the control calves; however, the variations were large and the difference not significant. The increase in the CK activity during the study period in both groups was believed to reflect muscle trauma during birth.
Of the hematologic variables, only the leukocyte counts, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration differed between the 2 groups at 10 minutes after birth, although only the difference in leukocyte counts was considered clinically important. Comparable increases in leukocyte numbers in neonatal calves have been attributed to stress-induced secretion of glucocorticoids and catecholamines21,31; increased concentrations of adrenaline and noradrenaline have been detected in severely acidotic newborn calves after birth.22 In the study reported here, the leukocyte counts were similar in the 2 groups at 120 minutes after birth. At that time, treated calves had a lower Hct and erythrocyte count than the control calves, and because there was no evidence of hemorrhage, an increase in the plasma volume was assumed to be the cause. Changes in the plasma volume were calculated for both groups by use of the Hct and hemoglobin concentration, which is a method that has been evaluated in humans17 and calves.9,32 The decrease of 6% in plasma volume in the control calves could have been caused by redistribution of fluid from the intravascular to the interstitial space. Clinically normal calves have extremely high concentrations of catecholamines immediately after birth, but they decrease within 30 minutes.22 Presumably, the high adrenaline and noradrenaline concentrations cause peripheral vasoconstriction, which will be reversed when the concentrations decrease, resulting in improved peripheral and splanchnic perfusion and fluid redistribution into the interstitium. In contrast, the treated calves in the study reported here had an increase in the plasma volume of 12%, which was comparable to an increase of 15% in calves with experimentally induced acidosis that were treated with hypertonic (8.4%) NaHCO3 solution in another study.12 In that study, the plasma volume decreased within 30 minutes after treatment but remained higher than the initial volume. The authors considered the improved tissue perfusion and oxygenation following the infusion of hypertonic NaHCO3 solution to be beneficial effects of the increased plasma volume and other favorable cardiovascular variables, such as a decrease in systemic vascular resistance. We believe that these beneficial effects were also evident in the treated calves of our study.
Treatment with NaHCO3 solution can affect the oxygen-hemoglobin dissociation curve. In calves with diarrhea, infusion of NaHCO3 solution led to a left shift of the oxygen equilibrium curve and, hence, to a reduced amount of oxygen released from hemoglobin into tissues.33 Possible reasons for this are lower inorganic phosphorus concentrations, lower PCO2, and lower body temperature in diarrheic calves (compared with values in healthy calves), which are all associated with an increase in oxygen bound to hemoglobin.34 However, these factors were not detected in calves of the study reported here. On the other hand, the markedly higher PCO2 and lower chloride concentration in the treated calves at 10 and 120 minutes after birth are factors that favor the release of oxygen from hemoglobin into tissues. In the treated calves of our study, the venous Po2 remained at a constant value after treatment, in contrast to diarrheic calves of another study33 in which there was an increase in Po2.
A limitation of the study reported here may have been the lack of a control group consisting of acidotic calves that did not receive treatment. However, because the study population included client-owned patients, we decided that such a control group was not justified. Nevertheless, the potential adverse effects of hypertonic NaHCO3 solutions mentioned in the literature, especially those relating to electrolyte concentrations, were not detected in our study. Potassium and calcium concentrations were not affected by treatment, and the sodium concentration increased only transiently and remained within the reference range of 145 ± 7.6 mmol/L.23 Analysis of our findings, in combination with those of another study,12 clearly reveals that the administration of a 5% NaHCO3 solution in acidotic calves has no adverse effects. This treatment should be safe. Furthermore, it should be practical because of the small infusion volume.
ABBREVIATIONS
| NaHCO3 | Sodium bicarbonate |
| GDH | Glutamate dehydrogenase |
| AST | Aspartate transaminase |
| CK | Creatine kinase |
| GGT | γ-Glutamyltransferase |
Richter BR. Prognostische Aussagekraft arterieller gegenüber venöser Blutgasparameter im wiederholten Messrhythmus hinsichtlich des Schweregrades des neonatalen Atemnotsyndroms beim Kalb. Dr Med Vet thesis, Ambulatorische und Geburtshilfliche Veterinärklinik, University of Giessen, Giessen, Germany, 2005.
Berchtold J. Untersuchungen zur Diagnose und Behandlung systemischer Azidosen bei Kälbern. Dr Med Vet thesis, Klinik für Klauentiere und Institut für Veterinär-Physiologie, Freie Universität Berlin, Berlin, Germany, 1998.
Born E. Untersuchungen über den Einfluss der Schnittentbindung auf die Vitaliät neugeborener Kälber. Dr Med Vet thesis, Klinik für Geburtshilfe und Gynäkologie des Rindes, Tierärztliche Hochschule Hannover, Hannover, Germany, 1981.
18-gauge × 1.5-inch, 1.2 × 40 mm, Terumo, Leuven, Belgium.
Monovette 05.1147.020, Sarstedt, Sevelen, Switzerland.
Monovette 05.1167.001, Sarstedt, Sevelen, Switzerland.
Monovette 05.1727.001, Sarstedt, Sevelen, Switzerland.
Natriumbikarbonat 5%, Cantonal Apothecary, Zurich, Switzerland.
Surflo, 18-gauge, 1.3 mm × 5.1 cm, Terumo, Leuven, Belgium.
Rapidlab 248, Bayer Diagnostics, Zurich, Switzerland.
Cell-Dyn 3500, Abbott, Baar, Switzerland.
Cobas Integra 700, Roche Diagnostics, Rotkreuz, Switzerland.
StatView, version 5.1 for Windows, SAS Institute Inc, Cary, NC.
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Reinhardt H. Normwerte diagnostisch bedeutsamer Serumenzyme bei Kälbern und Ferkel in den ersten Lebensstunden und -tagen. Dr Med Vet thesis, Gynäkologische und Ambulatorische Tierklinik, University of Munich, Munich, Germany, 1977.
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