Fluid Therapy Can Be Lifesaver If Done Right:
When done properly, fluid therapy can make a world of difference in the health of a pet.
January 17, 2011
By Jessica Tremayne
How Much Fluid:
With fluids, most criticalists use (30 x BW in kg) + 70 per day, or 132 x BW0.75 per day for dogs and 70 x BW0.75 per day for cats. All of these give the answer in ml per day. Other formulas, such as 2 ml/kg/hr, 40-60 ml/kg/day and 1 ml/lb/hr are all used. “Multiple fluid rate formulas can be used,” says Amy Butler, DVM, Dipl. ACVECC, of Ohio State University. “There is no one correct maintenance fluid calculation. Every patient will have different fluid requirements.”
Butler says the requirements of a patient suffering from renal insufficiency are likely to be higher than those of a patient with hyperadrenocorticism, who in turn would have higher requirements than an otherwise healthy patient. Commitment to one formula isn’t as important as continued assessment of the patient after fluid administration. “When calculating a fluid rate, the dehydration maintenance rate and ongoing losses are the first considerations,” Butler says. “A rate of 100-180 ml/kg/day is often used for young animals. Patients with renal or endocrine disease will likely need higher maintenance fluid rates.”
Time to Reassess:
Continuing to monitor the patient on fluids is important when deciding the next move in fluid therapy. “The patient should be assessed at least once daily to make sure the fluid therapy plan is meeting the patient’s needs,” Butler says. “Increased skin turgor, dry mucous membranes, thirst or weight loss are signs that the patient is not receiving enough fluids. Very frequent urination in a patient with normal kidneys, weight gain, chemosis and pulmonary crackles are signs that the patient is receiving too much fluid. “The bottom line is to pick a fluid rate based on calculation, but then titrate to effect.”
Watch for Anemia:
Not giving IV fluids to anemic patients is another fluid therapy misstep.
“Many clinicians are afraid to give IV fluids to anemic animals out of fear that they will bring down the PCV,” Butler says. “Even if the plasma volume is expanded and PCV decreases, the total number of red blood cells remains the same. If the patient is showing signs of poor perfusion or shock, giving IV fluids will improve tissue perfusion and tissue oxygen delivery.”
Dehydrated patients and those in shock should be stabilized before anesthesia or a surgical procedure. “Aliquots of the shock dose should be given until signs of shock have improved,” Butler says. “Anesthesia decreases the body’s compensatory responses to hypovolemia, so it is important that hypovolemia be resolved prior to surgery. If the patient is severely dehydrated, perfusion will be compromised, especially once those compensatory mechanisms are removed under anesthesia. “Provide adequate fluid rates during anesthesia using 5-10 ml/kg of isotonic crystalloids. However, patients with excessive losses may require more fluids.”
In severe cases, administration of too much fluid can cause pulmonary or interstitial edema, but not giving enough fluid also has consequences. “Too little fluid can result in tissue hypoperfusion,” says Wayne E. Wingfield, DVM, Dipl. ACVS, Dipl. ACVECC, of Colorado State University. “Continued dehydration, renal failure and hypovolemic shock, even death, can occur.”