37 | How to confidently care for a pheochromocytoma patient as a vet nurse

PodcastEndocrine
Written By Laura Jones

Ever heard of a pheochromocytoma before?

 

Nor had I before I walked into referral… but in all honesty, they’re some of the riskiest cases we see. These can be scary, especially regarding surgery - and we’ll chat about why later in today’s episode. For now, though, let’s look at what a pheo is, and the impact these have on our patients.

What is a pheochromocytoma?

A pheochromocytoma is an adrenal tumour - specifically, it’s a tumour of the adrenal medulla. When we chatted all about Cushing’s and Addison’s in episodes 32 and 33, we spoke about the adrenal cortex - which is responsible for releasing hormones like cortisol and aldosterone.

The medulla, however, is the neuroendocrine heart of the adrenal gland. It releases adrenaline and noradrenaline, our ‘fight or flight’ hormones.

A pheochromocytoma is a rare tumour of a particular type of cell in the adrenal medulla called ‘chromaffin’ cells. These release catecholamines - those fight-or-flight hormones. They’re more commonly seen in dogs, are very rare in cats, and are usually diagnosed in older patients, with males more commonly affected than females. 

The tumour usually affects just one adrenal gland and is locally invasive, often large, and slow-growing. They can cause a thrombus to form in the neighbouring vena cava, and the tumour will be metastatic in around ¼ of cases. Common sites of metastasis include:

  • Liver

  • Lung

  • Pancreas

  • Lymph nodes

  • Spleen

  • Heart

  • Kidney

  • Bone

  • CNS/spinal cord

Extra-adrenal tumours have rarely been reported in other tissues, including the heart. 

The tumour cells sporadically release adrenaline and noradrenaline, usually stimulated by blood flow, direct pressure, chemicals, or medications.

These catecholamines cause hypertension and tachycardia, vasoconstriction and increased smooth muscle tone, mydriasis and alternations in hepatic glucose uptake. 

What signs do we see in a patient with a pheochromocytoma?

Clinical signs are usually vague and intermittent unless a hypertensive crisis is seen.

The crisis is associated with the release of adrenaline and/or noradrenaline, causing hypertension, tachycardia, weakness and collapse episodes.

Other clinical signs include:

  • Panting

  • Agitation

  • Syncope

  • PUPD (Most common)

  • Lethargy (Most common)

  • Vomiting

  • Inappetence (Most common)

  • Anxiety

  • Weight loss

  • Anorexia

So, how do we diagnose a pheochromocytoma?

Diagnosing a pheo can be challenging and is usually achieved using a combination of blood pressure measurement, bloodwork, urine analysis and diagnostic imaging.

Let’s start with blood pressure.

Because these patients often experience hypertension, blood pressure measurement is an important diagnostic tool. Many patients have hypertension, though normal blood pressure does not exclude the condition.

And what about bloodwork?

Routine biochemistry and haematology rarely show specific changes, but they are important prior to anaesthesia and surgical treatment, particularly to assess general health and bleeding risk.

An ACTH stimulation or low-dose dexamethasone suppression test may be performed to rule out a tumour of the adrenal cortex rather than the adrenal medulla.

Then there’s urine analysis.

Routine urine analysis is usually not helpful in diagnosing pheochromocytoma, but a specialised urine test can be used to detect catecholamine metabolites in urine. This test, known as urine metanephrine testing, is often performed in patients with suspected pheochromocytoma but requires careful sample handling and preparation.

Samples must be acidified to a pH of 3-4 by adding acid to a fresh urine sample and then submitted to the laboratory for analysis as soon as possible.

What about imaging?

Diagnostic imaging is a vital tool in investigating pheochromocytomas. CT is the modality of choice since it allows us to detect the primary tumour, determine the degree of vascular invasion, and screen for metastases.

Radiography is usually less useful for detecting an adrenal mass; alternatively, abdominal ultrasound can be used to visualise an adrenal lesion and define its infiltration into local vessels or other organs. If indicated, it can also be used to collect guided aspirates, though this is risky because any time the mass is stimulated, it can cause the sudden release of catecholamines.

So you’ve diagnosed your patient. What’s next? How do we treat them?

Initial treatment is medically achieved for at least 2 weeks to stabilise the patient prior to surgery (or permanently in the case of inoperable masses).

Medical management

Medical treatment is achieved with phenoxybenzamine. This is a beta-1 and beta-2 receptor antagonist, which blocks the response to catecholamines. It expands the patient’s extracellular volume, normalises blood pressure, and reduces intraoperative hypertensive episodes. 

Studies have shown that starting medical treatment before surgery lowers perioperative mortality rates. However, we do need to be careful that patients don’t develop hypotension on treatment since the tumour tends to cause peaks of hypertension rather than sustained hypertension.

Alongside administering phenoxybenzamine, clients should be instructed to surround their pet with a stress-free environment and avoid intense or strenuous exercise to minimise catecholamine release.

Surgical management

Once our patient has been stabilised, they’ll undergo a unilateral adrenalectomy +/- caudal vena cava venotomy as needed to remove the tumour and any metastatic lesions or thrombi present.

This is a challenging surgery and a challenging anaesthetic since handling the tumour can cause massive catecholamine release. Where this happens, patients can develop sudden severe tachycardia, hypertension and potentially fatal cardiac arrhythmias.

This surgery also carries a high haemorrhage risk, so have blood products on hand and ensure you’ve blood-typed your patient and assessed their coagulation times and platelet levels beforehand.

After surgery, these patients require intensive care and monitoring.

What about nursing care?

During the initial diagnostic period, our nursing focus is on the careful management of hypertension, accurate blood pressure measurement, and monitoring for those hypertensive crisis or collapse episodes.

The majority of our nursing care is during surgery and in recovery. Under anaesthesia, these patients require careful monitoring. Placing an arterial catheter is recommended to facilitate direct blood pressure measurement. The patient should also have a central venous catheter or multiple IV catheters, including a rescue line or emergency line, that can be easily reached at all times during a hypertensive/tachycardic crisis under GA.

A continuous ECG should also be placed and assessed throughout the anaesthetic for any cardiac arrhythmias. Antiarrhythmic and antihypertensive medications should be given as needed, and careful communication between the surgeon and anaesthesia team is vital - we should know if the surgeon is about to handle the tumour, for example, to ensure we have emergency drugs on hand.

In recovery, our nursing attention turns to ICU care and monitoring. We’ll monitor ECG and blood pressure frequently for the first 24 hours and then reduce the intensity of our monitoring as needed, alongside providing general nursing care.

So that’s my guide to managing patients with pheochromocytomas! Though these tumours are rare, we do see them, and given the associated risks, it’s vital that we understand what they are and how we can safely manage them as nurses. This includes careful monitoring, creating a stress-free environment, and intensive care alongside general nursing.

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That’s it for this episode. Thanks again for listening, and I’ll see you next time! In the meantime, keep up the great nursing care.

Did you enjoy this episode? If so, I’d love to hear what you thought - screenshot it and tag me on Instagram (@vetinternalmedicinenursing) so I can give you a shout-out and share it with a colleague who’d find it helpful!

Thanks for learning with me this week, and I’ll see you next time!

References and Further Reading

Laura Jones
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