3.3.3 Mucous membranes
Abnormal mucous membrane colour is a non-specific and insensitive indicator of cardiac dysfunction. However, some horses in low-output heart failure will have pallor or peripheral cyanosis and animals with right to left shunts such as tetof Fallot may have central cyanosis. Evidence of anaemia may be accompanied by a physiological ('haemic') murmur and a high cardiac output. Injected mucous membranes are found in some animals with endocarditis or severe systemic disease.
Capillary refill time (CRT) is also an insensitive indicator of peripheral perfuand can even appear to be normal in a recently dead animal! However, CRT should be assessed in all cases. It may be increased in high-output conditions such as febrile illnesses, or decreased with low-output failure, hypotension or shock. It can be a valuable indicator for monitoring the effects of drug treatment.