ABSTRACT: This article aims to provide the veterinary nurse with a 'recap' of the anatomy and physiology of the adrenal glands, to discuss the signs, symptoms and diagnostic tests available to diagnose conditions associated with adrenal insufficiency, and to explore the treatment options available.

There will be particular emphasis on the nursing considerations of patients undergoing an adrenalectomy.

Anatomy and physiology

The adrenal glands are paired, flattened, bi-lobed organs which are located cranio- medially to the kidneys on either side of the vertebral column. They are slightly asymmetrical in position and shape. The right adrenal gland is comma-shaped and lies between the medial surface of the cranial pole of the right kidney and the lateral aspect of the vena cava.

The left adrenal gland is situated more caudally than the right, as is the kidney. It lies medially to the cranial pole of the left kidney and has fatty tissue separating it from the vena cava. The cranial portion of the left adrenal gland is broad and flat, with the caudal portion being long and narrow. The cranial portions of both adrenal glands are covered with peritoneum and the rest of the glands are surrounded by loose connective tissue and fat. The caudal pole of each gland is buried in peri-renal fat (Figure 1).

Figure 1: Anatomical position of the adrenal glands (Source: Welch Fossum, T. et al., (2002).)

The adrenal glands comprise two major divisions, which are functionally and developmentally separate: the outer cortex and the inner medulla.

These two regions on cross-section can usually be differentiated from each other as the cortex is firm and yellow in colour, whilst the medulla is softer and brown. The cortex tends to be uniform in thickness and the medulla naturally conforms to the shape of the gland.

The cortex and medulla are contained within a fibrous capsule composed of white fibrous tissue. From the capsule there are numerous septa, which penetrate the cortex dividing it into oval or oblong compartments providing a framework for the gland parenchyma.

The medulla is also split into groups of cells by the septae (Figure 2).

Figure 2: Cross-section of an adrenal gland. (Source: http://www.yardsnacker.com/wpcontent/uploads/2008/12/adrenal_gland21.jpg)

The cortex of the adrenal gland is generally split into three different layers of cells, which produce three main different groups of hormones (Table 1).

The functioning of the adrenal cortex is controlled by adrenocorticotrophic hormone (ACTH), which is secreted by the anterior pituitary gland in response to corticotrophin releasing hormone (CRH).

The adrenal medulla produces epinephrine (adrenaline) and nor-epinephrine (nor-adrenaline). The medulla releases these into the bloodstream when the sympathetic nervous system is stimulated. This increases cardiac output and the metabolic rate, which causes vasoconstriction in order to raise the blood pressure and to decrease gastrointestinal tract motility.

Common conditions

The cortex of the adrenal glands is essential to life, but the medulla is not. The main disorders associated with the adrenal glands include: Hyperadrenocorticism (Cushing’s disease) This is usually associated with excessive production (invariably caused by a corticotrophic adenoma of the pituitary gland) or over-administration of glucocorticoids and is one of the most commonly diagnosed endocrine diseases in dogs. The clinical signs typically include polydipsia, poluria, polyphagia, abdominal distension, muscle weakness or atrophy, calcinosis cutis and other skin changes, myotonia, hypertension to name but a few.

Hypoadrenocorticism (Addison’s disease) This is an uncommon condition in cats and dogs and is generally the result of immune-mediated adrenocortical destruction, resulting in underproduction of the glucocorticoids and mineral- ocorticoids (primary) or reduced ACTH secretion (secondary). Clinical signs can vary from under-perfusion and acute collapse with vomiting, diarrhoea, abdominal pain and hypothermia, to other non-specific signs making the animal generally ‘unwell’.

Phaeochromocytoma

A tumour of the chromaffin cells of the adrenal medulla. It can cause hypersecretion of the medullary hormones resulting in tachycardia, oedema and cardiac hypertrophy.

Primary hyperaldosteronism (Conn’s syndrome)

Aldosterone is the principal mineralocorticoid produced by the adrenal gland and controls the serum potassium levels. This condition is typically caused by a tumour of the zona glomerulosa of the adrenal glands and the clinical signs include hypokalaemia, hypertension or both.

Diagnostic testing

To diagnose a specific adrenal disease, dynamic function tests will be needed. These can accurately predict the site of malfunction when there is a possibility of one or more conditions.

Some examples of these tests include:

•   ACTH Response Test to diagnose canine hyperadrenocorticism and canine and feline hypoadrenocorticism.

A blood sample is taken and then a synthetic ACTH is administered. The blood sample is repeated 30 to 60 minutes later in dogs and 60 to 90 minutes later in cats. This test measures the circulating cortisol levels in the patient and its response to the ACTH injection (Figure 3).

Figure 3: Carrying out an ACTH response test. (Image courtesy of Dot Creighton.)

Low-dose dexamethasone suppression test to diagnose canine hyper- adrenocorticism and differentiate between the pituitary-dependent form of the condition and the form caused by an adrenal tumour.

A blood sample is taken before an injection of dexamethasone. Blood samples are repeated at 3 – 4 hours and 8 hours post injection. This again is measuring the cortisol levels in the patient and their response to the dexamethasone.

•   Combined high-dose dexamethasone suppression test and ACTH response test to diagnose feline hyper-adrenocorticism.

A blood sample is taken from the patient followed by an injection of dexamethasone. A repeat blood sample is taken 4 hours later, then synthetic ACTH is given and another blood sample is repeated after one hour. Again, this test measures the circulating cortisol levels and their response to the dexamethasone first and then theACTH injections (see Mooney & Peterson, 2004, for doses and administration routes).

Having performed these tests and received the results from the labora
tory, the vet should have a definitive diagnosis and be able to progress with the treatment and management of the case, be it medical or surgical management in the form of an adrenalectomy.

Medical management would require the patient to take different medication every day to either supplement hormones which are being under-produced or suppress the overproduction of others (Table 2).

Surgical intervention would likely result in an adrenalectomy. But both carry risks and many patients will require long-term medication, even after surgery. The VN should be able to support the veterinary surgeon in helping the client understand the treatment options, their associated risks and the patient’s care in the longer term.

Pre-operative considerations

During the pre-op period, the VN will probably be asked to obtain a blood sample from the patient to run haematology and biochemistry tests and, according to the results, he or she may have to place the patient on intravenous fluid therapy (IVFT) to ensure that electrolyte and acid-base balance is restored to normal and is also stable enough to provide support throughout anaesthesia.

If the patient has been vomiting prior to surgery, the GI disturbances will contribute to the electrolyte imbalances. The vet will also check the biochemistry results for indicators of renal insufficiency in case a nephrectomy is also required.

The VN must remember that animals release protective steroids during surgery to prevent circulatory collapse and if the patient has Addison’s disease it will not be able to do this, so the vet may instruct the administration of glucocorticoid supplements before and during surgery.

If the patient is having minor surgery – a straightforward adrenalectomy – then the glucocorticoid will normally be administered intravenously before induction and intramuscularly following recovery, with a view to the patient receiving normal oral doses the day after surgery. If the patient is having major surgery and will be under general anaesthesia (GA) for a prolonged period, the vet will instruct the same protocol as above, with the addition of the surgical dose being continued for two to three days after surgery, before returning to normal oral doses.

If the patient has been diagnosed with Cushing’s syndrome, it stands a higher chance of developing pulmonary thromboembolisms, so the vet may ask the nurse to administer low-dose heparin pre-operatively. Asymptomatic urinary tract infections may also be present, so routine urinalysis – including culture and sensitivity – should be performed by the VN.

The surgical VN should also speak to the vet to establish the full clinical history of the patient as many dogs with adrenal gland insufficiencies will have concurrent illnesses that will influence the nursing care provided – conditions such as congestive heart failure and diabetes mellitus – which also make the patient a more risky anaesthetic candidate. It is also the responsibility of the surgical VN to check what premedication, antibiotics and analgesics the vet wants the patient to have prior to surgery, and then to administer them accordingly.

Intra-operative procedure

Certain anaesthetic drugs will adversely affect patients with adrenal gland insufficiencies, so the vet will avoid them! The VN should ensure the patient’s need for steroid replacements during the procedure are met, as per the vet’s instructions, and maintain normal electrolyte levels, glucose levels and renal perfusion using IVFT and supplements as required, according to serial monitoring results.

The caudal vena cava is closely associated with the adrenal glands and may even be infiltrated in cases of neoplasia, so in addition to normal monitoring protocols, vigilant monitoring of the circulatory functioning of the patient is required when the vet is manipulating and retracting this structure.

Intra-operative antibiotics may be required, especially in patients with Cushing’s syndrome, because the high levels of glucocorticoids and subsequent immunosuppression dramatically increases the chances of their developing a post-op infection and potential wound dehiscence. The VN must also remember that the intra-abdominal fat deposition and muscle wastage associated with Cushing’s syndrome may result in the patient having respiratory difficulty under GA, so intermittent positive-pressure ventilation (IPPV) may be required.

Positioning criteria

The vet will normally access the abdomen through a ventral midline celiotomy to facilitate easier visualisation and checking of the contra-lateral adrenal gland, so you must position the patient in dorsal recumbency supported by a cradle, and clip and surgically prepare the entire ventral abdomen and caudal thorax, extending to the lateral skin edges.

The technique has also been described using the paracostal, flank approach, where you have the patient in lateral recumbency with the affected side uppermost. A rolled-up towel or sandbag should be placed under cranial abdomen or caudal thorax to support the patient and make the surgery easier. You should clip and surgically prepare an area which includes the caudal thorax and cranial abdomen, extending from the dorsal midline to the ventral midline (Figure 4).

Figure 4: Paracostal incision. (Source: Welch Fossum, T. et al., (2002).

It will ultimately be the vet’s preference as to which surgical approach is to be used and for which you must prepare the patient. He or she will guide you as to the extent of the clip they require.

Specific equipment

Besides the standard operative packs, you will need to have some additional pieces of equipment ready for the surgery. These include:

•   a range of sizes of artery forceps (some of the vessels and structures are very small and delicate, so some Halstead mosquito forceps would be appropriate)

•   a self-retaining abdominal retractor (such as a Balfour, Figure 5)

Figure 5: Balfour abdominal retractor

•   malleable retractors with moistened sponges on the end to retract abdominal structures (Figure 6), or any other hand-held retractors, such as Langenbeck or Morris retractors (Figure 7).

Figure 6: Malleable retractors

Figure 7: Morris retractor

•   Rampley sponge-holding forceps (Figure 8).

Figure 8: Rampley sponge forceps

•   a strong, slowly absorbed suture material, because patients with Cushing’s disease, for example, may suffer delayed healing, especially if steroid administration is required peri-operatively.

•   electrocautery would be useful for intra-operative haemostasis.

Post-operative considerations

Many veterinary operations are performed to cure a problem or condition. However, once an adrenalectomy has been performed, it is not the whole solution to the patient’s problem or the end of the concerns. Typically the patient’s hydration status, electrolyte balance and acid-base balance must be monitored and corrected appropriately using IVFT and supplements, and pain levels need to be assessed and analgesics given. These patients are already at risk of delayed wound healing because of the nature of their condition .

If they have had a bilateral adrenalectomy, patients will have a permanent deficiency in the production of adrenal hormones, such that they will require life-long supplementation of glucocorticoids and/ or mineralocorticoids. Administration of these will be the responsibility of the pets’ owners and will test their commitment to their animal, so they must be informed of it before they agree to surgery.

The owners will also need to be informed about the risk of the animal suffering an Addisonian crisis post-operatively if the oral supplementation is inadequate, and they should be told what signs to look out for should their animal be developing the crisis – general malaise, inappetence, decompensation and other associated clinical symptoms.

Clients should also be informed that an Addisonian crisis can be fatal if not detected; and that, in some circumstances – such as if their animal goes into crisis overnight – they may find it dead in the morning. We do not want to panic the owners, but death is a potential reality and they need to know that if it does happen on it is not anyone’s fault.

If the patient has had a unilateral adrenalectomy, then steroid supplements will be required in the post-op period until the other adrenal gland is functioning correctly. This is usually confirmed by using an ACTH stimulation test. This is essential because sometimes the other adrenal gland can become atrophied. 

As previously mentioned, pulmonary thromboembolism development is a real possibility in these patients and it is life-threatening. The patient needs to be monitored closely for sudden or severe respiratory distress, as this is the main clinical symptom. In some cases it may be necessary to perform a lung perfusion scan to detect areas of hypoperfusion indicative of the presence of a thromboembolism.

The VN must support the patient’s actual problem by providing it with strict cage rest, oxygen therapy, anticoagulants and thrombolytic agents under the direction of the vet. The major potential problem to then bear in mind when administering anticoagulants and thrombolytic medications is the possibility of haemorrhage, so the VN should monitor the patient’s PCV every two hours, and prepare a blood transfusion in case it is needed.

The VN must not neglect the standard post-op care checks either and requirements including correcting hypothermia, routine wound checks (remember the increased chance of dehiscence) and good nutrition!

Main complications associated with adrenalectomy

•   Haemorrhage

•   Fluid and electrolyte disturbances

•   Pancreatitis

•   Wound infection

•   Delayed wound healing

•   Thromboembolism

Homecare advice and support

It is most certainly the responsibility of the VN to make sure owners are aware of their job in the life-long management of their pets at home. This should be done by discussing the medications they need to administer and how to administer them, the clinical symptoms associated with a deterioration in the animal’s condition, and making sure they come back in for regular check-ups either with the VN or the vet.

It would be advisable to write an information leaflet to be given out to the owners, which details the relevant facts about their pet’s condition, the surgery that has been performed, why life-long medication is required, what the clinical symptoms of deterioration are and why they are significant, and then also a section that specifically relates to their animal and what you have asked them to do at home.

Remember each animal and case is unique, and you should create a homecare plan for the owners according to the patient’s needs – maybe a daily checklist for them or simple chart or diary for them to complete and bring with them at each visit.

Further reading

HOTSTON MOORE, A. (ed) (1999) BSAVA Manual of Advanced Veterinary Nursing. BSAVA, Gloucester

MARTIN, C. and MASTERS, J. (2006) Textbook of Surgical Nursing. Oxford, Elsevier

MOONEY, C. T. and PETERSON, M. E. (2004) BSAVA Manual of Canine and Feline Endocrinology. BSAVA Gloucester.

WELCH FOSSUM, T. et al., (2002) Small Animal Surgery 2nd Edition. St Louis. Mosby

Author

Claire Bloor BSc (Hons) RVN PGCE Cert VN (Dent) C-SQP MBVNA MifL

Claire graduated in 2003 with a 1st class BSc(Hons) degree in veterinary nursing. She worked in mixed practice and then as a dental nurse whilst teaching part-time. Claire took up a fulltime lecturing position at Myerscough College in 2006 and teaches primarily the higher education courses and advanced nursing diploma.

• VOL 25 • No4 • April 2010 • Veterinary Nursing Journal