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Tag: Laboratory animals

Blood gas analysis, pt 1: why everyone needs to know about it

For those of you who have received referral histories from emergency or specialists hospitals, blood gas analysis is probably no stranger to you. For those who have never heard of them before, fear not – you are in for a treat.

In my emergency hospital, the blood gas analyser is arguably one of the most frequently used bench top lab machines, second only to centrifuge, and for good reasons…

Acid-base disturbances are common in critically ill and emergency patients, and it can help determine the severity of their condition and sometimes provide the answer. Tracking changes in blood gas parameters can provide information about the patient’s response to your interventions.

Blood gas analysis can help assess the severity of a patient’s condition and help guide your diagnostic plan.

The information gained from pulse oximetry is very limited in patients with severe respiratory compromise, and the only way to accurately assess their oxygenation and/or ventilation status is by looking at their blood gas status.

So what does the blood gas analysis actually measure?

Most blood gas panels assess the pH of the blood, partial pressure of oxygen (PO₂) and partial pressure of carbon dioxide (PCO₂). From these, the machine is able to derive the percentage of haemoglobin saturated with oxygen (SO₂), bicarbonate (HCO₃^–) concentration and base excess of the extracellular fluid (BEecf).

In most machines, they are also able to measure other parameters, such as electrolytes (Na, K, Ca, Cl), glucose and lactate.

While arterial blood gas samples are required for determining the ability of the body to oxygenate the haemoglobin, venous samples are suitable for determining the ventilation status, assessing acid base balance, electrolytes, glucose and lactate levels.

So how can this help as a point-of-care test?

As mentioned previously, blood gas analysis can help assess the severity of a patient’s condition and help guide your diagnostic plan. It can also provide a diagnosis (such as diabetic ketoacidosis, typical hypoadrenocorticism and high gastrointestinal obstructions).

The changes in these parameters over time can be essential in managing critical patients in the emergency setting; it will help guide you in developing an appropriate IV fluid therapy regime and fluid choice, address the patient’s oxygenation and/or ventilation needs, correct any electrolyte and glucose abnormalities, and – although fallen out of favour – the administration of sodium-bicarbonate therapy.

In upcoming blogs, I will teach you how to interpret the blood gas results. At the end of this, I hope everyone will incorporate blood gas analysis as their standard point-of-care test for the better assessment and management of patients.

If given the choice between a biochemistry and a blood gas panel in a critical patient, I would hands down select blood gas every time.

August 9, 2022
SNAP FeLV antigen/FIV antibody test

The past decade has seen a significant shift in the prevalence of both FeLV and FIV in most European countries. This, coupled with a better understanding of the viral dynamics of FeLV, will influence the interpretation of the results of in-house diagnostics tests of these viral infections.

FeLV is an RNA virus that undergoes classic retroviral replication that incorporates its own genes into the host genome, known as provirus. Of those infected, approximately 30% to 40% will not be able to mount an effective immune response and will become persistently viraemic (“progressors”).

The SNAP FeLV antigen/FIV antibody test.

These cats will have a high proviral load, remain persistently antigen-positive and eventually succumb to the disease. These cats have a poor prognosis, with 70% to 90% succumbing to the disease within 18 to 36 months.

The remaining infected cats will become “regressors”. These cats will be able to mount an effective immune response and, eventually, become antigen-negative; however, will still be provirus-positive as these cannot be completely eliminated.

In extremely unusual circumstances, these cats may recrudesce and become viraemic again later in life – previously known as “latent” infection – but these cases are extremely rare. Cancer and corticosteroid-induced immunosuppression is thought to be responsible in these cases.

FeLV prevalence

The prevalence of FeLV is now much lower compared to 10 to 15 years ago, with successful culling and selective breeding programmes meaning the risk of false positive results is increased.

A positive result could be because it is a true positive (FeLV-associated disease), transient positive or false positive. A much higher chance exists of a true positive within at-risk groups – young cats with lymphoma, anaemia or leukopenia, and cats with unusual infection or unexplained wasting diseases.

A positive result in healthy cats should be considered suspicious. These cats could be regressors and should be retested 12 weeks later, where the result should become negative. Alternatively, it could be a false positive and an external lab should be used to confirm infection, preferably using an alternative method – such as DNA PCR – to test for the presence of provirus.

FIV prevalence

The interpretation of FIV test results, both in light of new disease prevalence data as well as epidemiological evidence, needs to be revised.

The prevalence of FIV in Australia is a lot higher than previously thought. In a study based on cats from the inner Sydney area, the prevalence of FIV is 16% in domestic cats with outdoor access, 21% to 25% in two feral cat colonies and up to 32% among some populations of “sick” cats (Norris et al, 2007). An owner survey revealed almost 80% of Australian cats spend some time outdoors, posing most cats at a high risk of FIV exposure.

Although no current statistics exist on the percentage of cats vaccinated for FIV, an increased vaccination rate will have a significant impact on the reliability on the results from in-house tests.

Combination test

As the name suggests, the SNAP combination FeLV antigen/FIV antibody test detects the presence of FIV antibodies. This test cannot distinguish antibodies from those naturally infected, vaccinated or derived from maternal antibody. To add to the confusion, antibodies can take anywhere between two to four weeks – and sometimes up to six months – to develop after initial infection.

To overcome this problem, PCR is needed to determine the presence of viral RNA (ELISA-positive, PCR-negative).

It should be noted the presence of FIV antibodies in naturally infected individuals is only indicative of a persistent infection. It is not correlated with the presence of immunodeficiency or diseases directly related to FIV. In fact, new epidemiological evidence shows FIV infection does not cause illness in most cats and does not seem to cause reduced lifespans.

Summary

Any cat having a FeLV-positive SNAP test result is considered to be actively shedding virus, regardless of its health status. A cat that has a FeLV-negative SNAP test means it is not viraemic, thus not shedding virus, but does not necessarily mean it is free from infection.

On the other hand, the true FIV status of a cat remains difficult to determine in-house. A positive result could mean persistently infected, maternal antibody, vaccine-induced antibody or a false positive, whereas a negative result could mean true negative, early infection or false negative.

Regardless of the result, the true relevance of the FIV status in the acute management of an otherwise healthy cat is questionable, considering the new epidemiological findings.

June 19, 2017
Don’t fear tuition fees
With the upcoming general election, the question of changing tuition fees has cropped up again.

People obsess over the fact rising tuition fees are putting poorer families off from sending their children to university. But I think they’ve got it wrong – tuition fees aren’t the problem.

Struggling with debt? Poor or middle-of-the-road people struggle because they don’t have enough “maintenance”, not because they have to pay tuition. IMAGE: pathdoc / Fotolia.

Tuition fees are only paid back once you earn enough to manage it. Therefore, they don’t affect the student in the present, while he or she is studying. Out of interest, I recently logged into my student loan repayment account and was presented with a pretty scary number.

Irrelevant

Having calculated what I’ll pay back on my starting salary, I found, to begin with, the debt will actually continue to increase because I would be paying off less than the interest that accumulates every year. That just seems ludicrous – how will I ever pay it off? The answer is I won’t. The loan is written off after 30 years; so, assuming I won’t come into a massive sum of money or win the lottery, the total owed is irrelevant.

I’m not really sure of the economics of how on earth the loan companies or government can find this sustainable, but I’m just discussing how it affects the students here.

The point is, we should ignore that big scary number of total debt and just think of it as a graduate tax. You go to university to get a good education, which should give you the knowledge and skills to get a better career or progress more quickly within that career. For that, you accept a (very small) proportion of your pay packet every month disappears into the ether of student loan repayment – and, since you don’t pay it back until you reach the threshold for repayment, it is not unaffordable.

Surviving during semesters

What is unaffordable is trying to survive at university with nothing in your bank account. Poor or middle-of-the-road people struggle because they don’t have enough “maintenance”, not because they have to pay tuition. The issue is having enough money to live off now.

It’s all very well suggesting students get part-time jobs to help them pay their way through university, but that can be detrimental to the end result as it takes away time from studying and, in some degrees – such as veterinary – it becomes near impossible due to contact time and, later, rotations and clinics.

Some people do manage it, and fair play to them, but it’s certainly tough.

Stuck in the middle

IMAGE: rutchapong / Fotolia.

It’s not just the poor who struggle. In fact, the poor are better off because of means testing. It’s often the people in the middle who are stuck – those whose fates have been decided by some higher power that has ruled they’ll receive less government funding because their parents’ income means they should be able to support their children.

Wrong!

That’s okay for the rich, but for those in the middle, the family often cannot afford to stump up the difference.

What about mature students? It’s ridiculous they are still means-tested even though they could well have been living independently for years without the financial support of their parents and may not even have anything to do with them anymore.

Measured maintenance

Maintenance should not be one size fits all either. Vocational degrees, such as veterinary, require many more materials than arts degrees, for example. Over the five years of my veterinary degree, I bought:
- protective clothing (boiler suits, lab coats, wellies, waterproofs, scrubs, gloves and hospital shoes)
- equipment (a thermometer, stethoscope and dissection kit)
- books amounting to an estimated £700 (not including my laptop)
On top of that, there’s the petrol and accommodation costs of EMS placements and rotations, not to mention the fact having to do EMS in holiday time takes away the opportunity to get a summer job.

Veterinary is an expensive degree, with many applicants not quite realising how much so until they’re in too deep. So, surely maintenance grants and loans should reflect that?

The political parties are isolating young people and students for various reasons, and part of me believes it’s because they don’t understand what we want or need. We need to stop obsessing over tuition fees and ask the students themselves why they are struggling.
June 2, 2017
Under the microscope: lessons from pathology rotation

The past couple of weeks on rotation have largely consisted of looking down a microscope or performing postmortems – and despite clinical and anatomic pathology being very different, a running theme seemed to exist across both.

Image ©iStock.com/The-Tor

On the clinical pathology week, we pored over slide after slide of blood smears and cytology samples, trying to formulate differentials from minimal or no history about the case.

We muddled through a number of biochemistry profiles and attempted interpretation, often with little or nothing to go on from the submitting clinician.

Historical significance

In anatomic pathology, we were often supplied with the history, but the clinicians would not reveal the full extent until after we had formed differential lists – even then the “full” history we were given before proceeding with postmortem examination would often be scarce.

Although we would often get there in the end, or at least in the right ballpark, I think it’s safe to say the importance of a relevant history has been drummed into us for evermore.

Going forward as new graduates – far sooner than many of us would like – I don’t think we’d dare send a sample to the university lab without filling the forms out meticulously and providing a relevant history. Making an accurate interpretation that fit the clinical picture was so much easier when a few, seemingly minor points were highlighted in the history.

The write stuff

Another lesson creeping into every rotation over the year is the sheer amount of paperwork involved in veterinary medicine – be it clinical notes, postmortem reports, lab submission forms, case reports, anaesthetic records… the list goes on.

Keeping accurate records can be the difference between being sued and being able to prove your clinical judgement at the time. Most relevant to this rotation was accurate completion of lab submission forms, so samples can be correctly identified and results sent to the right place.

Accurate completion of lab submission forms is essential. Image © gamjai / Fotolia.

It sounds obvious, but the clinical pathology staff assure us the frequency of receiving samples with important information omitted is much higher than you’d think.

Out of practice

Having explored the different aspects of clinical and anatomic pathology, while dragging a lot of material from the depths of third-year knowledge, I can appreciate how quickly some skills and understanding can be lost when you don’t practise or use them regularly.

Feeling considerably rusty at the beginning of the rotation, I feel a lot more comfortable now, but can see how vets can lose their ability or confidence to make a cytological diagnosis when in practice, especially when things get busy.

Being able to send samples to the experts is a major advantage, but I think, as new grads, we should at least have a quick look down the microscope and make a provisional call to be confirmed by the lab, rather than just sending samples straight off.

January 30, 2017
Needle aspirate subcutaneous masses

Cytology of a mast cell tumor from a Labrador retriever at a magnification of 1,000x. Image by Joel Mills [GFDL, CC-BY-SA-3.0 or CC-BY-SA-2.5-2.0-1.0], via Wikimedia Commons.
Fine needle aspiration (FNA) is a valuable tool in subcutaneous skin masses.

We have all had those lumps that, on palpation, you are sure are lipomas (being soft, freely mobile and slow growing). Indeed, the vast majority are just such benign problems – however, it is worth aspirating them to be sure.

Felt like lipoma

We recently had a case in a nine-year-old Labrador with a soft subcutaneous mass the owner had been aware of for a month. It felt just like a lipoma.

On checking the lump again two weeks later, this had got noticeably bigger. FNAs of the mass revealed the presence of a mast cell tumour.

Following excision with good 3cm margins, the Lab went on to make a full recovery.

June 20, 2016
Festive threats to four-legged family members

Now well into December, and getting ever closer to Christmas, there will be an abundance of “goodies” around the house that are not so good for the four-legged family members.

Jordan advises colleagues to ensure clients keep an eye on their pets during the festivities. Image: © Freeimages/s22k.

Most owners are aware of the dangers of chocolate and so are likely to rush down to the vet on Boxing Day when their Labrador has broken into the tin of Heroes – but what other festive dangers are there that owners are not so clued up on?

Pudding

The festive favourite Christmas pudding, while enjoyable for us, can be lethal for pets. It is the raisins, currants and sultanas that may lurk within that are poisonous.

While the mechanism of toxicity is poorly understood, we know it can cause acute kidney failure in dogs.

The treatment protocol for poisoning by raisins, etc, is similar to general suspected poisoning with an unknown agent: give an emetic (to make the animal vomit), an adsorbent (for example, activated charcoal) and supportive care (IV fluids) to protect the kidneys for a few days.

Antifreeze

Ethylene glycol, more commonly known as antifreeze, is extremely toxic to pets, with consumption of tiny amounts resulting in crystal formation in the kidneys, and so acute renal failure. Antifreeze smells and tastes sweet, so pets are often attracted to it. For this reason, it is best for owners to ensure it is kept in a secure container, well away from pets.

Early symptoms include neurological signs, such as wobbliness, twitching, seizures and depression. As the poisoning progresses, the animal will have cardiac and respiratory signs, such as increased heart and respiratory rate. It’s vitally important owners look out for these signs if their pets have had any possible access to antifreeze (for example, if they’ve got into the garage or if a cat has been missing for a few days and potentially been locked in someone’s shed).

The antidote for ethylene glycol poisoning is ethanol, because it replaces ethylene glycol as a substrate for the enzyme that breaks it down into toxic products. More specifically, lab-grade ethanol is best.

Sweetener

Xylitol is a sugar-free sweeter that is used in chewing gum, cakes and sweets, particularly diabetic foods. Xylitol causes insulin release in the body, resulting in hypoglycaemia and, later, liver damage.

Symptoms include vomiting and signs of hypoglycaemia: lethargy, weakness, collapse and, if it progresses, seizures and coma. Unlike ethylene glycol, there isn’t a specific antidote, but supportive care, including fluids and liver protectants, is vital. The prognosis for xylitol toxicity is good if the animal’s hypoglycaemia is corrected quickly, so it is essential for owners that suspect this to contact their vet immediately. If you’re trying to determine whether xylitol is in a product, it is often listed as a food additive, code E967.

Decorations?

And don’t forget the potential foreign body too – if the cat has been playing with the tinsel and managed to swallow some or the dog has ingested a few tasty looking baubles.

Enjoy the festive season, but advise owners to keep an eye on their pets this Christmas.

December 15, 2015