Ron Hines DVM PhD
Your Pet’s Capillary Refill Time = CRT
This very simple but very informative test (CRT) is one your veterinarian will often perform on your dog and cat during a health-related office visit. It is an examination of the pink portions of your pet’s gums. Physicians also find the CRT test to be a very useful indicator of circulation wellbeing. They will generally pinch your fingers or toes. (read here)
When judging circulation, the first thing your veterinarian looks for is color. Dogs and cats that are anemic have pale gums. The gums of cats and dogs that are receiving too little oxygen are often a “muddy” grayish color as well. That observation is usually followed by a finger pressed firmly against your pet’s gum surface. When the finger pressure is released, the pink color will spring back (return). How long it takes the pink color to return is your pet/s capillary refill time (CRT). It should be less than two seconds (preferably less than 1.5 seconds).
How fast the gum capillaries (tiny blood vessels) of your dog and cat refill with blood after that finger pressure is removed depends on how well its peripheral perfusion is performing. (read here) But it is also a good indication of how well blood is circulating throughout your pet’s entire body. It is a crude, old, but still very useful test. It is best used to confirm your veterinarian’s general impression as to the seriousness of your pet’s health issue. When CRT time is overly long, your pet’s pulse taken in the groin or neck is usually weaker than it should be as well. It is also quite likely that when your veterinarian listens to your pet’s heart through his/her stethoscope, heart rate, rhythm and beat abnormalities will be present.
The longer the CRT (time), the more serious and worrisome the problem. Heart issues and shock are the most common causes of prolonged CRT time.
All three tests help your veterinarian gauge the adequacy of your dog and cat’s blood flow. All pets with extended CRT times are not delivering sufficient oxygen to their tissues (= tissue hypoxia). Many serious cases need to be placed in a high oxygen environment asap.
Some Reasons Why Your Dog Or Cat’s Capillary Refill Time Might Be Increased: (Take longer)
Besides heart issues, long CRT times are often due to a decrease in your pet’s blood volume. The four common causes for that are dehydration, shock (hypovolemic shock), traumatic blood loss or internal bleeding.
Dehydration that prolongs CRT can be due to things like heat stroke, prolonged fever, inability to drink fluids or the excessive fluid loss resulting from diarrhea and/or vomiting.
Hypovolemic shock has many causes. Some are toxic, some are infectious, some are allergic (e.g. anaphylaxis). Some are traumatic, as after a car accident and/or blood loss. In all of them, your pet’s pulse will also be weak, its respiration will usually rapid and shallow and its heart rate often increased. When dehydration is the underlying cause of a prolonged CRT, your pet’s gums tend to be dry and their skin, when pulled upward, will be slow to spring back to its normal position.
Another common cause of increased CRT time are problems related to your cat or dog’s heart. It could be due to the slowly progressive congestive heart failure so common in older dogs, or a sudden cardiomyopathy that occurs in midlife in cats and in dogs. In all forms of heart disease, the problem is the pet’s loss of its ability to maintain blood flow (decreased peripheral perfusion). Another common cause in dogs is the presence of large numbers of mature heartworms.
Medication overdoses can also cause an abnormal slow heart rhythm (bradycardia) leading to an increase in CRT time. Some of the drugs that have that ability to do that are beta blockers like atenolol (Tenormin®) and propranolol (Inderal®), calcium channel blockers like diltiazem (Cardizem®), digoxin (Lanoxin®, Cardoxin®), pimobendan (Vetmedin®), various narcotics as well as insecticide poisoning of the organophosphate type.
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