What's causing your pet's digestive upset?
Sally was a sad dog: she's been vomiting for two days, and her owner was worried about her. My job as her vet was to discover the cause.
The digestive system is one of the busiest parts of the body: food goes in, and waste goes out, continually. It's essential that the system works effectively, and if something goes wrong, signs of illness are often very visible. The challenge for vets is to work out what exactly is causing the problem: a wide range of different causes can cause a similar outcome: vomiting, diarrhoea, constipation, or in some cases, weight loss. So how do vets discover the underlying cause?
The first stage of any diagnostic process is always detailed history-taking. Before even looking at the animal, it's important to listen carefully to everything the owner has to report about what's been happening. What are the signs of illness that the owner has noticed? Vomiting, diarrhoea, or weight loss? How long has it been going on for? Is the animal eating and drinking normally? What are they normally fed on? Have they eaten anything unusual recently (such as the remains of a take-away meal)? Could they have been scavenging? This discussion can take five or ten minutes, and the information often provides the key to discovering what's going on.
The second step is to physically examine the animal. Every vet has their own standard way of doing this, systematically checking every part of the patient to ensure that nothing is missed. My approach is to start at the tip of the nose and work back to the tip of the tail. Everyhing is examined, noting anything that veers from the normal. What is the general demeanor of the animal? Happy, sad, excited or dull? Are the gums moist, wiht a healthy pink colour? Does the skin feel normal or are there signs of deydration? Are there any enlarged lymph nodes around the body? Does the abdomen feel normal when poked and prodded? Are there any internal lumps or bumps? Using a stethoscope, does the chest and abdomen sound normal? Does the animal have a normal temperature? Sometimes an internal examination needs to be done, and this gives useful information about the faeces: is there any blood in it?
The third step is to take samples from the animal to try to learn more about their internal metabolism. Three types of samples may be collected: blood, urine and faeces.
The blood sample is most important: this can be analysed - often in an in-house laboratory, with instant results.
The simplest blood test is the so-called Packed Cell Volume: this tells the vet about the level of dehydration of an animal, a common and serious complication of many digestive diseases. A badly dehydrated animal needs to be given immediate intravenous fluids to bring their hydration level back to normal. If there's no significant dehydration, it's often possible to treat the animal at home rather than needing hospitalisation.
Other blood tests include red and white blood cell counts and measurements of a wide range of biochemicals, including enzymes, which inform the vet about the internal functions of the intestines, liver, pancreas, kidneys and other organs. The results of these tests are crucial: this is often how a vet is able to make a definitive diagnosis about the underlying problem.
A urine sample may seem like a strange request when dealing with a digestive problem, but it can provide useful extra information about a pet's state of hydration, as well as other clues about kidney function.
A faeces sample is less useful than you might think: this tends to be needed only on rare occasions for more complex illnesses. The sample may be sent off to the external laboratory for full analysis and to be cultured: some serous causes of digestive problems (like Salmonella) can only be identified by such tests.
In many cases, the collection of samples from the animal is sufficient to make a full diagnosis of the cause, but sometimes, the next stage is needed: diagnostic imaging. This uses modern technology to visualise the internal structures of an animal. The two methods that are most commonly used are xrays and ultrasound. CAT and MRI scans are possible in theory, but are only rarely used, in long term, serious illnesses such as cancer.
X-rays are the equivalent of black and white photos of the internal organs: they provide useful information in cases like obstructions caused by ingested foreign bodies. You can actually see many objects, like stones, on x-rays, and while other objects (like sponges) may be invisble on x-rays, there are gas patterns that can strongly suggest that something is causing an obtruction.
Ultrasound allows vets to see more of the precise structure of the inside of the abdomen, and it's a moving picture, like a video. This allows far more detailed analysis of what's going on.
Sally, the vomiting dog, needed a full work up to discover why she was vomiting. It turned out that she'd swallowed a corn-on-the-cob husk that had become lodged in her intestines. A vague shadow was visible on the x-ray, and ultrasound confirmed it. She needed an operation, but here's the good news: it saved her life.