How often do you anaesthetise patients with liver disease?

We see patients with liver diseases very frequently. From young puppies and kittens in for portosystemic shunt investigations to our crispy older cats with inflammatory liver disease, we nurses anaesthetise them all.

Because the liver is vital in metabolising anaesthetic agents, we must be very careful when anaesthetising certain liver disease patients. The risk of anaesthetic complications is high in patients with liver dysfunction, including:

• Slow or impaired metabolism of anaesthetic agents

• Delayed anaesthetic recovery

• Hypoglycaemia

This is going to impact the drugs we use, and the way we monitor and recover these patients.

And that’s exactly what we’ll be chatting about in this post. By the end, you should know exactly what your anaesthetic considerations are for different liver disease patients, and how to monitor and care for them confidently.

Let’s quickly look at our liver

Before we get into our anaesthetic considerations, I’m going to take you on a (very short) trip back to A&P. Why? Because to appreciate what complications we could see when anaesthetising liver disease patients, we need to understand what our liver does.

What does our liver do?

The liver is responsible for several vital functions in the body, including:

• Forming plasma proteins

• Forming clotting factors

• Converting ammonia to urea for elimination

• Conjugating bile

• Storing glucose

• Producing cholesterol and triglycerides

How does it do this?

These functions are made possible by the dual blood supply the liver receives, from both the hepatic portal vein and hepatic artery. 

70-75% of its blood supply is deoxygenated blood from the portal vein, containing waste products and metabolites from the GI tract. This blood is essentially detoxified by the liver before entering the vena cava and returning to the heart. 

The remaining 25-30% of the liver’s blood supply is oxygenated blood from the hepatic artery. Since less than a third of the liver’s blood supply is oxygen-rich, our hepatocytes are especially susceptible to hypoxic injury.

Several factors can also reduce blood flow to the liver. These include:

• Hypotension

• High mean airway pressures (e.g. during IPPV)

• Excessive sympathetic nervous system stimulation

We as veterinary nurses need to consider this when anaesthetising our liver disease patients, since hypotension and apnoea are common.

What about when there’s liver disease?

The first thing to say regarding liver disease is that there is a big difference between liver disease and liver dysfunction. And this is important to consider when anaesthetising our liver patients.

Patients with increased liver enzymes but no signs of liver dysfunction have no specific anaesthetic requirements. They are not in liver failure, so can still metabolise anaesthetic drugs, for example.

What do I mean by this?

Well, injury to our hepatocytes will cause enzymes like ALT and AST to leak from those damaged liver cells into the bloodstream. But those patients may still have a liver that’s able to perform all of those vital functions we discussed earlier in this post - metabolising waste products, forming urea and storing glucose, for example.

Compare this to a patient with a portosystemic shunt. These patients have an additional vessel causing some of the blood from the GI tract to bypass the liver, rather than flow through the portal vein. This means the liver doesn’t receive the blood supply it needs to develop fully, and our anaesthetic drugs circulate in the body longer since blood flow to the liver is impaired.

So what’s the take-home message when anaesthetising liver disease patients?

Not every liver disease causes liver dysfunction, and patients who only have increased liver enzymes generally do not require specific anaesthetic considerations - such as avoiding medications metabolised by the liver.

If you have a patient with liver failure or dysfunction, that’s the patient who needs significant changes to their anaesthetic plan.

Pre-anaesthetic considerations

Fluid, electrolyte and acid-base balance

Patients with liver diseases often present with changes to their fluid and acid-base balance, affecting their anaesthetic risk level. We see this both due to the liver’s impaired ability to form plasma proteins like albumin - which is responsible for maintaining oncotic pressure) and due to the anorexia/hyporexia that our liver disease patients often present with.

Before anaesthesia, a complete assessment of hydration and perfusion should be performed, including assessment of:

• Skin tent

• MM dryness/moistness

• Eye position (e.g. how sunken the globe is)

• Acute bodyweight change

• Heart rate

• Pulse quality

• MM colour

• Capillary refill time

• Blood pressure

• Demeanour/mentation

Fluid therapy should be administered at an appropriate rate as required.

In patients with liver dysfunction, there is controversial evidence surrounding the use of Lactated Ringer’s (Hartmann’s) solution. This is due to reports that lactate accumulation can result, as lactate is metabolised in the liver.

However, lactate accumulation is not typically observed in liver dysfunction patients. In addition, other organs such as the kidneys often compensate for this, by utilising more lactate.

Hepatic encephalopathy

Patients with severe liver dysfunction or conditions such as portosystemic shunts also often present with hepatic encephalopathy (HE). This is where the toxins that would usually be cleared by the liver accumulate in the circulation, ultimately causing neurological signs.

Clinical signs such as ataxia, depression, circling, head-pressing and seizures are common in HE patients. Where these signs are seen, ammonia levels should be checked, and a lactulose retention enema administered to quickly reduce circulating ammonia levels.

Hypoglycaemia

Since the liver is responsible for storing glucose, hypoglycaemia is a risk in patients with liver dysfunction. At-risk patients should have their glucose levels measured before anaesthesia, and regularly during GA.

Where hypoglycaemia is present, a dextrose infusion is administered. This can quickly and easily be prepared by nurses using the following guide:

[quote]

To make a 2.5% solution, you need 0.05ml of 50% glucose for every 1ml of fluid in the bag

To make a 5% solution, you need 0.1ml of 50% glucose for every 1ml of fluid in the bag

NB. You need to remove this volume of fluid first before replacing it with glucose, to keep the percentages correct!

[end quote]

Anaesthetic agents

Arguably the biggest consideration in anaesthetising liver disease patients is which medications to use.

In patients with liver dysfunction (e.g. failure or portosystemic shunt patients) we want to avoid medications metabolised by the liver - since the dysfunctional liver will be less efficient at this. This means that many of our anaesthetic agents will have a prolonged duration of action.

Sedatives

Acepromazine, benzodiazepines and alpha-2 adrenoreceptor agonists are metabolised by the liver. 

Ideally, these medications should be avoided - perhaps except alpha-2s, since they are short-acting and can be reversed.

If alpha-2s are used, they should be used at low doses (starting at 0.5 mcg/kg of dexmedetomidine or 1 mcg/kg of medetomidine, and increasing to effect).

Analgesics

Some opioids, such as morphine, are highly dependent on hepatic blood flow, and will have decreased clearance where hepatic blood flow is reduced.

However, analgesia should not be withheld in a painful patient. Certain liver conditions, such as inflammatory liver diseases, biliary tract obstructions or following biliary surgery, are incredibly painful and these patients will often require potent opioids.

Ideally, in patients with liver dysfunction, lower doses should be used initially (in case prolonged effects are seen due to decreased metabolism). Top-up doses can then be administered depending on the patient’s pain scores.

Non-steroidal anti-inflammatories (NSAIDs) can be used in patients with increased liver parameters, provided there is no liver dysfunction. If liver function is impaired, these medications should not be administered.

Induction agents

All injectable induction agents are metabolised by the liver. However, propofol is partially metabolised by other tissues, such as the kidneys and lungs - so is preferred.

Maintenance agents

All inhalant anaesthetic agents will cause dose-dependent vasodilation, reducing cardiac output and arterial blood pressure. This will, in turn, reduce hepatic blood flow.

Both isoflurane and sevoflurane are safe choices in patients with liver disease, provided that arterial blood pressure is measured regularly and mean arterial pressure (MAP) is kept above 60-70mmHg throughout anaesthesia.

Monitoring

So we’ve assessed our patient, and selected and administered our anaesthetic plan. But what do we need to think about when monitoring anaesthetised liver patients?

In addition to routine anaesthetic monitoring, areas to keep a particularly close eye on include:

• Temperature

• Arterial blood pressure

• Blood glucose levels

Temperature

Many of our liver disease patients have reduced body condition, especially portosystemic shunt patients due to their young age, small size and poor growth.

Hypothermia also slows drug metabolism, which is something we especially want to avoid in patients with liver dysfunction - since they’re already at a high risk of this!

Our liver dysfunction patients should have ideally continual temperature monitoring via an oesophageal or rectal temperature probe; if this is not available, then the patient’s temperature should be measured every 5 minutes.

Warming should begin before anaesthesia to prevent heat loss, and insulation materials used in addition to active heating sources.

Arterial blood pressure

Maintaining hepatic perfusion is important in patients with liver disease since the liver receives little oxygenated blood, and many of our anaesthetic agents (propofol and volatile agents, for example) cause dose-dependent vasodilation.

Blood pressure should be monitored regularly and any hypotension should be managed by:

• Decreasing volatile agent concentrations if possible

• Administering additional analgesia to facilitate volatile agent reduction

• Managing any hypovolaemia with a fluid bolus

• Administering medications such as ephedrine or glycopyrrolate to increase blood pressure +/- heart rate as required

Blood glucose

Blood glucose levels should be checked regularly in any patient at risk of hypoglycaemia during anaesthesia.

This generally includes assessment before anaesthesia, following induction, and every 30-60 minutes throughout. Hypoglycaemia should be managed as previously discussed, by administering a dextrose infusion (+/- boluses as required).

Recovery

We know that, regardless of disease process, between 47-60% of all anaesthetic-related deaths in dogs and cats occur during recovery. This means that careful monitoring during recovery is vital - especially in patients with liver dysfunction, who will often have delayed clearance of their anaesthetic drugs.

In addition to general monitoring of heart rate, respiratory rate, blood pressure, temperature and mentation, blood glucose checks should continue in recovery until normoglycaemia is maintained since hypoglycaemia can also increase recovery time.

Monitoring in recovery can be de-escalated as the patient becomes more alert, ambulatory and normothermic.

Any reversible medications (e.g. dexmedetomidine) should be antagonised; where significantly delayed recovery persists, opioids may be reversed with naloxone, provided the patient is not painful (or alternative analgesia plans have been made).

Intravenous access should be maintained in these patients until they are fully recovered, to allow the administration of reversal agents, fluid therapy and emergency medications in recovery as required. Additionally, many patients will require ongoing treatment, or require emergency venous access - for example, in a portosystemic shunt patient at risk of seizures.

So there you have it - my top considerations for anaesthetising patients with liver disease! The main thing to remember? There is a big difference between ‘just’ having increased liver enzymes and liver dysfunction - and it’s our dysfunction patients who have the most specific anaesthetic management considerations!

The drugs we give these patients and our monitoring considerations are especially important, as is recovery. We know these patients will often have a delayed recovery as they can’t metabolise these drugs normally - so keep an especially close eye on them as they recover!

What protocols do you use in your liver patients? DM me on Instagram and let me know!

References

1. AAHA, 2020. Liver disease [Online] AAHA. Available from: https://www.aaha.org/aaha-guidelines/aaha-anesthesia-guidelines-for-dogs-and-cats/anesthesia-with-comorbidities/liver-disease/

2. De Vries, M. 2011. Anaesthesia and Liver Disease: When’s Time to Start to Worry? [Online] Vet Times. Available from: https://www.vettimes.co.uk/app/uploads/wp-post-to-pdf-enhanced-cache/1/anaesthesia-and-liver-disease-when-time-to-start-to-worry.pdf

3. Grubb, T, et al. 2020. 2020 AAHA Anaesthesia and Monitoring Guidelines for Dogs and Cats [Online] AAHA. Available from: https://www.aaha.org/globalassets/02-guidelines/2020-anesthesia/anesthesia_and_monitoring_guidelines_final.pdf

4. Mama, K. and Rezende, M. 2015. Anaesthesia in Hepatic Disease [Online] Clinician’s Brief. Available from: https://www.cliniciansbrief.com/article/anesthesia-hepatic-disease

5. Merrill, L. 2012. Small Animal Internal Medicine for Veterinary Technicians and Nurses. Iowa: Wiley-Blackwell.