Page 589 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

576 FLUID THERAPY

to the tissues. 56 This may be of particular benefit to the a heart rate of 180 bpm, weak femoral pulses, and the feet
animal in shock. These contradictory findings in acidosis are cold. The respiratory rate is 60 breaths/minute. On
make it difficult to determine if restoring a normal pH is auscultation no murmurs or arrhythmias are heard and
beneficial. In addition there is concern that bicarbonate no abnormal breath sounds are evident.
therapy is itself associated with adverse effects. The few On presentation, flow by oxygen is provided and a
clinical trials of bicarbonate therapy for the treatment cephalic venous catheter is placed. Blood work collected
of acidemia in human medicine have had disappointing at the time of catheter placement reveals the following:
results. 19,92,93,144
Bicarbonate combines with hydrogen ions in the extra­
Measured Reference
cellular fluid to form carbonic acid, which rapidly is
Parameter Value Range
convertedinto carbon dioxide and water in the presence
of carbonic anhydrase. Hydrogen ions and bicarbonate
pH 6.911 7.34-7.38
cannot readily cross the cell membrane so they are some­ PvCO 2 mm Hg 45.6 40-46
what trapped in the extracellular fluid space. In contrast PvO 2 mm Hg 32.7 49-67
the carbon dioxide formed as a result of bicarbonate ther­ HCO 3 mEq/L 9.5 22-24
apy rapidly diffuses into cells and causes intracellular aci­ SBE mEq/L 21.2 2to0
dosis. 12 To avoid this the patient must increase alveolar Glucose mg/dL 133 65-112
ventilation substantially to prevent elevations in blood Lactate mmol/L 19 <2.5
PCO 2 . This is challenging for the compromised patient, Packed cell volume % 70 37-55
such as one in circulatory shock, and paradoxical intracel­ Total protein g/dL 3.5 5.4-7.1
lular acidosis following bicarbonate therapy can occur. 128
In addition the drop in ionized calcium associated with A severe lactic acidosis without respiratory
alkalinization and the hypertonicity of sodium bicarbon­ compensation is evident with hemoconcentration and
ate can also have adverse effects. There are only two small, hypoproteinemia.
prospective, randomized clinical trials in human medicine Rapid administration of 2000 mL of lactated Ringer’s
evaluating the role of sodium bicarbonate in the therapy solution via a pressure bag and 300 mL of 6% hetastarch is
of lactic acidosis. 19,92 No difference in cardiovascular per­ provided. Following this the perfusion parameters have
formance could be identified in these studies following improved; the mucous membranes are still pale, capillary
therapy and there was a significant drop in ionized refill time is approximately 2 seconds, heart rate is 150
calcium associated with therapy. Although the role of bpm, and the femoral pulses are assessed as being stron­
sodium bicarbonate therapy in lactic acidosis remains ger. Another 1000 mL of lactated Ringer’s solution and
somewhat controversial, there is unanimous agreement another 200 mL of hetastarch is given rapidly. The perfu­
that identification and treatment of the underlying cause sion parameters at this time are greatly improved
for lactic acidosis is the first and foremost important although the heart rate remains elevated.
step. 6,12 Only after aggressive resuscitation efforts have Following initial resuscitation, a full physical examina­
been made should bicarbonate therapy be considered. tion reveals abdominal pain. There is hemorrhagic gelati­
The 2008 Surviving Sepsis guidelines recommend that nous diarrhea evident on rectal examination. A dose of
sodium bicarbonate should not be administered to hydromorphone IV is given at this time, following which
patients with a lactic acidosis unless the pH is less than the heart rate drops to 120 bpm. A second venous blood
7.15. 26 The role of sodium bicarbonate in patients with sample is evaluated, which reveals a resolution of the lactic
a pH less than 7.15 is uncertain because of the lack of acidosis, PCV of 58%, and a total protein of 3.2 g/dL. An
studies evaluating this question. Some authors in the ongoing fluid plan of 1 mL/kg/hr of 6% hetastarch and
human literature advise against bicarbonate therapy at 200 mL/hr of lactated Ringer’s with appropriate potas­
any pH. 6,48 Sodium bicarbonate is contraindicated in sium chloride supplementation is instituted.
patients with volume overload such as congestive heart
failure or in patients with ventilatory compromise. CASE 1 - Case Notes
This dog presented in severe circulatory shock with signs
suggestive of vasoconstriction. Given the signalment, the
CASE EXAMPLES absence of any previous history of heart disease, and no
murmur or arrhythmia detected, cardiogenic shock was
CASE 1: Hypovolemic Shock
considered unlikely and the diagnosis of hypovolemic
A 2-year-old male neutered Labrador weighing 30 kg is shock was made. The severe lactic acidosis supports the
presented collapsed. There is no history of trauma, toxin physical examination findings of severe shock. The lack
ingestion, or previous medical problems. On presentation of respiratory compensation is likely secondary to central
the dog is found to be severely obtunded, has very pale nervous system depression as a result of poor brain perfu­
mucous membranes, a capillary refill time of 4 seconds, sion. The very high PCV in combination with the low