Gastrointestinal disorders are some of the most common medical conditions we see in practice. From acute gastroenteritis to inflammatory bowel disease, intussusception surgeries or infectious diseases, we nurses are highly involved in the treatment and care of these patients.

But what about when these patients require sedation or anaesthesia? Well, there’s a lot more to consider than we might first think. In this post, we’ll explore how gastrointestinal disorders affect our anaesthetic planning and monitoring, as well as the recovery considerations for patients with GI disease.

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Let’s talk about GI disease

There are many different gastrointestinal diseases, each affecting our patients in slightly different ways. This means our anaesthetic considerations will vary a little depending on the type of GI disease present.

Here’s an example for you…

A patient who presents with acute gastroenteritis will likely be in better body condition than a patient who presents with a chronic GI disease. They may, however, be more dehydrated and have more acute acid-base imbalances requiring treatment before anaesthesia.

Compare that with a patient who has protein-losing enteropathy. This is usually caused by a combination of inflammatory bowel disease and lymphangiectasia causing protein loss through the diseased intestines. As these patients have low albumin levels, they may have a reduced circulating volume, and complications such as oedema, ascites or pleural effusion.

Both GI diseases - but causing different consequences for our patients!

General considerations

Despite this, though, there are some fundamental principles we need to consider in any patient presenting with GI disease or for a GI procedure. These include:

• Fluid balance: i.e. is dehydration and/or hypovolaemia present?

• Electrolyte imbalances: we can see abnormalities in chloride levels in vomiting patients, sodium and chloride in patients with pure water loss, and hypokalaemia in patients with anorexia (since potassium is sourced from the diet)

• Acid-base disturbances: abnormalities such as metabolic acidosis may be present in patients with diarrhoea (since bicarbonate, a base, is lost). In patients with vomiting, chloride loss can cause metabolic alkalosis, since chloride acts as an acid in the body.

• Body condition: many gastrointestinal diseases cause weight loss, either due to issues with absorption, hyporexia or anorexia, or dysphagia. Reductions in body condition score can compromise the distribution of lipid-soluble anaesthetic drugs, as well as increase hypothermia under anaesthesia

• Pain: many GI diseases result in abdominal pain. Even if the procedure to be performed is not in itself painful, your patient may be. This will impact our premedication choices.

Pre-anaesthetic considerations

The pre-anaesthetic considerations will depend on where in the GI tract the patient’s disease is, alongside other individual patient factors.

As we’ve spoken about in our fundamentals of anaesthesia post, a thorough pre-anaesthetic assessment is vital for every patient, to make a tailored anaesthetic plan for the individual. This should factor in their clinical examination findings, pain or anticipated pain levels, disease process and temperament.

Blood results should also be reviewed as part of this assessment, particularly looking for:

• Anaemia (if GI haemorrhage is present)

• Evidence of dehydration/haemoconcentration

• Hypoalbuminaemia

• Electrolyte abnormalities

These should, as far as possible, be corrected before anaesthesia begins.

Premedication drug choices typically include a sedative and analgesic in combination. Either a benzodiazepine, alpha 2 adrenergic agonist or a phenothiazine is used for sedation:

• Benzodiazepines (e.g. diazepam, midazolam) provide good sedation but no analgesia. They are useful in combination with other sedatives for anxious or aggressive patients. Alternatively, they can be used as part of a co-induction for patients who cannot have other sedatives.

• Phenothiazines (e.g. acepromazine) provide good sedation, but no analgesia. They cause vasodilation so can significantly reduce blood pressure and cardiac output, and potentially reduce gastric emptying time. They are also potent antiemetics.

• Alpha-2 adrenergic agonists (e.g. dexmedetomidine) provide good sedation and some minor analgesia. They will cause dose-dependent bradycardia and vasoconstriction and can sensitise the heart to arrhythmias. They also cause some decreased GI motility, and can cause emesis, particularly in cats.

These agents are paired with an appropriate analgesic, depending on the patient’s pain levels and the procedure to be performed. Most opioids will reduce gastrointestinal motility, with more potent analgesics (e.g. full mu agonists) having a more significant effect than partial agonists.

Oral disease

Patients with oral diseases e.g. neoplasia or dysphagia may be at an increased risk of airway obstruction, increasing their risk of hypoxaemia and aspiration. Intubation can be challenging, so before anaesthesia, a plan should be made for this.

Options include using stylets or urinary catheters to intubate the patient, and then feeding an ET tube over the top, or considering tracheostomy if needed.

Where airway obstruction is a risk, patients should be pre-oxygenated and SpO2 monitored closely before and throughout induction.

Oesophageal disease

Patients with oesophageal disease often present with regurgitation, increasing their risk of perianaesthetic regurgitation and aspiration. These patients may require additional medications as part of their anaesthetic plan, such as:

• Antiemetics e.g. maropitant

• Prokinetics e.g. a metoclopramide CRI during the procedure

• Proton pump inhibitors e.g. omeprazole, if there is any evidence of oesophagitis/ulceration 

Sedation should be avoided in patients with oesophageal disease. Since these patients are at risk of aspiration, we need to protect their airways - so general anaesthesia and intubation are vital.

Gastric and small intestinal disease

Considerations for patients with gastric and small intestinal disease depend on the procedure to be performed. For example, a patient with a duodenal foreign body will require more potent analgesia than a patient with chronic enteropathy undergoing an upper GI tract endoscopy.

We need to balance the anticipated pain level, and our patient’s temperament, with the effects on GI motility and nausea we can see with different analgesic and sedative agents, tailoring our drug plan to the individual.

Specific gastrointestinal diseases come with their own monitoring and care considerations - a great example of this is gastric dilation-volvulus (GDV). Anaesthetising GDV patients would be an entire post in itself - for now, if you want to know more about managing these patients specifically, I suggest you read this article.

Large intestinal and rectal disease

Individual protocols for patients with large intestinal and/or rectal disease should be created based on the individual patient, their pain level, their disease process, fluid/electrolyte/acid-base balance and temperament (as should all of our patients, really!)

Patients with anal sac neoplasia often have paraneoplastic hypercalcaemia, causing polyuria and polydipsia and increasing the risk of dehydration. If this is present, rehydration with 0.9% saline (since this does not contain calcium) is required prior to anaesthesia or sedation. Hypercalcaemia has potential renal and/or cardiovascular effects, so this should be corrected before anaesthesia begins.

Patients with gastrointestinal haemorrhage or bleeding rectal masses may be haemodynamically unstable, requiring correction before anaesthesia or sedation begins.

Induction and maintenance considerations

Induction

The most common choices for anaesthetic induction in gastrointestinal disease are propofol and alfaxalone, as either standalone agents or in combination with a benzodiazepine, depending on the individual patient and their premedication protocol.

After induction, airway access should be secured as quickly as possible, with the cuff appropriately inflated. This should ideally be performed using a manometer if possible, to ensure a sufficient seal has been established without overinflating and damaging the trachea. The ET tube should always be checked for leaks before volatile agents are started.

As discussed, patients with GI disease are at higher risk of perianaesthetic regurgitation, so aspiration or fluid or material is an important consideration. After the patient has settled under anaesthetic, the cuff should be checked again as further muscle relaxation may occur, allowing leaks to form around the ET tube.

Maintenance

Both inhalation (isoflurane or sevoflurane) and intravenous agents (propofol/alfaxalone CRIs) are appropriate choices for maintenance in patients with GI disease.

However, we need to note that all of these medications can decrease the lower oesophageal sphincter pressure/tone to varying degrees, potentially impacting the incidence of regurgitation under anaesthesia.

Monitoring

Abdominal/gastric distension can impair cardiac function and ventilation by pressing on the diaphragm and affecting venous return to the heart. This can be seen in patients with conditions such as GDV, or in patients where the stomach is inflated (e.g. during gastrointestinal endoscopy). Due to the impact this has on both ventilation and cardiac output, monitoring of end-tidal CO2, oxygen saturation and blood pressure is indicated throughout anaesthesia.

Positioning the patient so the thorax is slightly elevated (if possible) can be useful to reduce pressure on the diaphragm if deflation of the stomach is not possible at that moment.

Where ventilation (and therefore gaseous exchange) is significantly impaired, mechanical ventilation may be indicated.

Some gastrointestinal diseases are associated with cardiac arrhythmias (e.g. GDVs, patients with severe electrolyte disturbances) - so an ECG should be placed and assessed throughout anaesthesia for any changes in heart rhythm. 

Recovery considerations

Nursing considerations and monitoring requirements in recovery will vary depending on the individual patient, their GI disease, and their ASA status.

Severely unwell patients should receive intensive nursing monitoring and care in recovery, including ongoing monitoring of blood pressure, temperature and ECG (to detect any cardiac arrythmias).

Patients with GI disease should receive regular fluid assessments in recovery, with careful monitoring of:

• Hydration parameters: skin turgor/tenting, eye position, tackiness or moistness of mucous membranes, acute bodyweight changes

• Perfusion parameters: heart rate, pulse quality, blood pressure, mucous membrane colour, capillary refill time, temperature and mentation

Electrolyte and acid-base disturbances are common and patients should be monitored for associated signs (e.g. muscle weakness or neck ventroflexion associated with hypokalaemia).

Pain assessment is a vital nursing consideration in recovery, especially in patients with abdominal pain or following gastrointestinal surgery. Pain assessments should be performed regularly using a validated pain scoring tool, and appropriate analgesia administered - balancing pain with nausea and GI motility.

In most patients, non-steroidal anti-inflammatories are avoided, since they can inhibit the effects of gastroprotective COX enzymes. Their use should be avoided in patients who are dehydrated, hypovolaemic, have evidence of gastrointestinal ulceration or haemorrhage, or have ongoing gastrointestinal signs. We also need to avoid their use in patients where IBD is likely, since we will often treat these patients with steroids.

Summary

Gastrointestinal disorders are common in dogs and cats, and with these, we often see complications such as anorexia, dehydration, weight loss, electrolyte and acid-base disturbances. Each of these will impact the preparation, administration and monitoring of these patients under anaesthetic, so a thorough pre-GA assessment is vital.

We should correct as many of these abnormalities as we can before anaesthesia or sedation begins, and monitor our patients closely during and after the procedure.

Specific anaesthesia considerations exist for patients with oropharyngeal diseases, certain gastric and/or small intestinal diseases, and some large intestinal/rectal diseases. These include oral neoplasias where airway obstruction is a risk and oesophageal disease patients where regurgitation and aspiration is a significant concern. Other disorders such as GDV, gastrointestinal foreign bodies, bleeding rectal masses and anal sac adenocarcinomas have their own specific anaesthetic considerations.

Do you anaesthetise many GI patients in your practice? What else do you consider when preparing for these cases? DM me on Instagram and let me know - I can’t wait to see what you think!

References

1. Adams, J. G., Figueiredo, J. P. and Graves, T. K. Gastrointestinal and endocrine system. In: Grimm, K. A., Lamont, L. A., Tranquilli, W. J., Greene, S. A., and Robertson, S. A. eds. Veterinary Anaesthesia and Analgesia, the 5th edition of Lumb and Jones. Iowa: Wiley-Blackwell, pp. 641-680.

2. Bondy, P. J. and Wortinger, A. 2012. Gastrointestinal. In: Merrill, L. ed. Small animal internal medicine for veterinary technicians and nurses. 1st ed. Iowa: Wiley-Blackwell, pp 193-261.

3. Figueiredo, J. P., and Green, T. A. 2015. Gastrointestinal disease. In: Snyder, L. B. C. and Johnson, R. A. eds. Canine and Feline Anesthesia and Co-Existing Disease, 1st ed. Iowa: Wiley-Blackwell, pp. 93-115.