When you design a fluid therapy plan, three factors come into play: the patient history, the presenting complaint and the physical exam.
What do you use as a maintenance fluid rate? How about your surgical rate? What if your patient is hypotensive? If you are unsure about what should be done, we have good news for you.
A panel of experts from the American Animal Hospital Association and the American Association of Feline Practitioners recently published fluid therapy guidelines. Remember that these are suggestions, not a new definition of standard of care for fluid therapy.
Yet these excellent guidelines are full of practical tips to improve fluid therapy protocols for sick, hypovolemic and anesthetized patients. They probably represent what most specialists would do and recommend in 2013.
What follows is not an exhaustive summary of the article, but a review of some important points, especially as they relate to the surgery world.
1 Replacement vs. maintenance fluids
When you design a fluid therapy plan, three factors come into play: the patient history, the presenting complaint and the physical exam. This information will help you determine whether there are changes in volume, content or distribution.
Changes in volume include blood loss and dehydration. Changes in content could be electrolyte imbalances. Changes in distribution encompass pleural effusion or ascites.
Patients who are not eating or drinking, but don’t have ongoing losses, hypotension or volume depletion, benefit from maintenance fluids. Patients with volume or electrolyte losses need replacement fluids.
When you use crystalloids like LRS, which are sodium rich and potassium poor, patients may become hypernatremic or hypokalemic. Periodic monitoring of electrolyte levels, for example every 24 hours, will pinpoint imbalances and help correct them.
The AAHA/AAFP guidelines suggest maintenance fluid rates of 2-3 ml/kg/h in cats and 2-6 ml/kg/h in dogs.
Depending on the patient’s needs, monitoring parameters can include:
* Physical exam findings, such as pulse quality, capillary refill time, mucous membrane color, respiratory effort, lung sounds, skin turgor and mental status.
* Basic numbers, including pulse and respiratory rate, body weight changes, urine output and blood pressure.
* Lab tests such as PCV, total solids, serum lactate, urine specific gravity, BUN, creatinine, electrolytes and blood gases.
2 Peri-anesthetic fluid therapy
When you correct ongoing losses and support cardiovascular function, you are less likely to notice hypotension and vasodilatation during anesthesia.
Giving the somewhat universal 10 ml/kg/h of IV fluids indiscriminately to all patients is not considered ideal in 2013. This high rate is not evidence-based and can lead to pulmonary edema and coagulopathies.
The guidelines suggest anesthetic fluid rates of 3 ml/kg/h in cats and 5 ml/kg/h in dogs.
Hypotension during anesthesia is often caused by inhaled anesthetic gas, so the first method to fight it should be reduction of anesthetic depth, as opposed to increasing the fluid rate.
If there is no response, the following techniques can be used—usually in the following order:
* An IV bolus of isotonic crystalloid at 3-10 ml/kg/h. It can be repeated once.
* IV administration of a colloid such as hetastarch at 1-5 ml/kg in cats and 5-10 ml/kg in dogs. Blood pressure should be monitored every three to five minutes to avoid vascular overload.
* If a normovolemic patient is still hypotensive, consider using vasopressors.
Intraoperative fluid rates over 10 ml/kg/h can be detrimental. Administration rates should be based on physiologic needs (keeping renal or cardiac disease in mind) and anticipated duration of anesthesia.
3 Fluids in the sick patient
The volume of fluids is based on whether the patient needs rehydration or volume expansion. The percentage of dehydration can be determined using these parameters:
* Mild (5 percent): minimal loss of skin turgor, semi-dry mucous membranes, normal eyes.
* Moderate (8 percent): moderate loss of skin turgor, dry mucous membranes, weak and rapid pulses, enopthalmos.
* Severe (> 10 percent): severe loss of skin turgor, tachycardia, extremely dry mucous membranes, severe enopthalmos, weak and thready pulses, hypotension, altered level of consciousness.
If patients with renal disease become oligouric or anuric, be cautious of hypervolemia.
Hypovolemic patients have signs of decreased tissue perfusion, which include abnormal mentation and CRT, cold extremities, poor pulse quality and increased heart rate.
Albumin concentration below 1.5 g/dl or total protein under 3.5 g/dl can cause hypotension secondary to reduced oncotic pressure.
Shock rates for crystalloids are 80-90 ml/kg IV in dogs, and 50-55 ml/kg in cats. However, we no longer administer the entire amount as a single bolus. Assess the patient’s fluid needs after 25 percent of the total volume has been titrated, and again after each 25 percent increment. Consider administering a colloid if no response is seen after 50 percent of the fluid volume has been given.
Hypertonic saline can also be used, especially in large patients, in which it is difficult to administer enough volume quickly, or when there is significant volume loss. Shock dose in dogs is 4-5 ml/kg and 2-4 ml/kg in cats. Effects will last for 30-60 minutes. It is important to continue crystalloid therapy simultaneously to replenish interstitial fluid losses.
When treating hypovolemia due to blood loss, colloids or blood products are more beneficial than crystalloids. The authors write: "Following 15 ml/kg of hemorrhage, even 75 ml/kg of crystalloids will not return blood volume to pre-hemorrhage levels, because crystalloids are highly redistributed.”
5 A few more pearls
* In hospitals without 24-hour care or the ability to refer to a 24-hour facility, patients may benefit from a higher IV fluid rate during the day and SQ fluids overnight.
* Use an IV pump whenever possible. When using gravity flow systems, tailor the size of the fluid bag to the size of the patient to reduce the risk of inadvertent fluid overload or death.
* The use of a T-set will allow easy IV access in patients receiving fluids. Y-ports simplify combination fluid therapy.
* "Clip and prep” before placement of IV catheters. It should be a sterile procedure. Be aware of nosocomial infections.
* Use E collars to prevent IV catheter removal by the patient.
* "The use of a potassium-containing balanced electrolyte solution does not increase blood potassium in cats with urethral obstruction.”
* When giving boluses during shock treatment, the use of a pressure bag increases the rate of fluid delivery.
* Placement of the largest size IV catheter the patient can comfortably handle is important to prevent restrictions during rapid fluid administration.
* If a patient is hospitalized on IV fluids for an extended period of time, change IV catheters and IV fluid lines after three to four days.
* Fluid therapy should not be static, or "one size fits all.” It should be tailored to each patient and periodically re-evaluated based on the patient’s needs over time.
Katie Kegerise, a certified veterinary technician in Reading, Pa., contributed to this article.