MONITORING THE IV FLUID THERAPY PATIENT AMY NEWFIELD, CVT, VTS (ECC)
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4 IS YOUR PATIENT URINATING? Urine output should be monitored. In patients where kidney disease is suspected or patients that are down, urinary catheters should be placed to accurately account for urine production as well as to keep animals clean. In both dogs and cats 1-2ml/kg/hr of urine should be produced if the patient is not on fluids. If the patient is on fluids then the total volume you are giving into the patient should ideally be urinated out. If a cat is on 20ml/hr of fluids, it should urinate out about 20ml/hr. You can place non-absorbent litter boxes in cages with cats and quantify the urine; you can catch the urinations of canine patients in a bowl for quantification. 5 PHYSICAL EXAM Patients receiving fluid therapy should be minimally given a full physical exam ever 4-6 hours. Mucous membrane color should be assessed. A pale or white color to the mucous membranes may indicate vasoconstriction and decrease perfusion, which generally indicates increasing fluid rates. This same color could also mean anemia where an increase in fluid rate is not necessarily indicated. Dark red or injected mucous membranes may indicate fever or sepsis, but may also indicate high blood pressure which can occur from fluid overload. Normally, blood will refill the capillary bed in 1-2 seconds. A slow return to color (>2 seconds) supports vasoconstriction which often occurs because of a decrease in effective circulating volume. Increased heart rates (greater than 160bpm in the dog and greater than 220 bpm in the cat) generally occur from a compensatory response due to
a decrease in cardiac output. In some cases, however, increase in heart rate can occur from fluid overload. Increases in heart rate can also occur from pain, fear, excitement, and tachyarrhythmias. Palpating a pulse is not just to get a heart rate. It is important to feel a pulse to feel the overall stroke volume of the circulatory system. Feeling a moderate to strong pulse would be normal. Feeling a weak to thready pulse supports decreased stroke volume and peripheral vasoconstriction. Feeling a bounding and fast pulse supports circulatory overload, but may also occur during times of severe dehydration, hyperdynamic shock, anemia, etc. The patient’s temperature is also important. A decrease in temperature indicates peripheral vasoconstriction as is often the response to a decrease in circulating effective volume. Increases in temperature generally cause the fluid requirements for the patient to increase simply because more fluid loss is expected. 6 BLOODWORK Packed cell volume (PCV) and total solids (TS) should be monitored once daily for patients receiving fluid therapy. In general, total solids that remain above 8.0 g/dl, dehydration should be suspected. Dehydration can also be suspected in patients with PCV about 45% in cats and 55% in dogs. Aggressive fluid therapy dilution can be seen in both the PCV and TS readings. A patient that came in with a PCV of 45% and a TS of 8.5 g/dl could have a PCV of 33% and a TS of 4.8 g/dl once hemodilute.
Lactate builds up the tissues and blood as a result of inadequate oxygen available to tissue which can be caused by tissue hypoperfusion somewhere in the patient. Increases in lactate can be seen because of shock, sepsis, renal failure, liver disease and even toxins. Lactate can be measured using a simple hand- held device similar to a blood glucose machine. Under a value of 2.5 mmol/L is normal. It is important to normalize lactate concentrations. In some cases, increases in lactate may be the only indication that hypoperfusion still exists. In several human studies, decreasing serum lactate levels during resuscitation was associated with improved survival. If lactate levels are elevated more aggressive fluid therapy is likely warranted. 7 BLOOD PRESSURE Generally speaking, arterial hypotension, ideally assessed by the mean arterial pressure less than 60 mmHg or by a Doppler with a systolic less than 80 mmHg usually warrants more aggressive fluid therapy. Normalization of blood pressure (MAP 80-100 mmHg or systolic between 110- 140 mmHg) is usually the goal of fluid therapy. If blood pressure is high then fluid overload may be considered. 8 CONCLUSION It is important to understand how to appropriately monitor your patient. Monitoring all parameters provides a better picture of the patient’s fluid
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