Medical procedures are some of our most common procedures. From x-rays to ultrasounds, endoscopies to feeding tube placement, chest drain placement and beyond… Our medical patients need a lot of investigations to reach a diagnosis, begin treating them, and successfully administer nursing care.

In the second part of this 2-post series on anaesthesia for medical procedures, we’ll focus on the anaesthetic considerations for some of our most common non-endoscopic procedures - diagnostic imaging procedures, feeding tube placement, bone marrow biopsies and joint taps. We’ll chat through why we perform these procedures, and what we need to think about to anaesthetise these patients safely.

Diagnostic Imaging

We perform a variety of different imaging procedures on our medical patients - X-rays of the chest, abdomen, urinary tract or joints, for example, abdominal ultrasound scans, and CT scans of the head, chest or abdomen. It’s important we know a few fundamental principles when anaesthetising patients for different imaging procedures… and these will vary depending on where we are imaging, and how.

Radiography

The thorax is probably the most common area we x-ray. We may be doing this in a patient with pre-existing respiratory disease or respiratory signs, or to look for metastasis in a patient with suspected neoplasia, or to look for evidence of aspiration in a patient with regurgitation.

The exact cause for the x-rays will influence your anaesthetic considerations - for example, are they at increased risk of hypoxia? If so, we need to think about:

• Using drugs that minimise respiratory depression

• Pre-oxygenation

• Monitoring SpO2 especially closely

• Monitoring ETCO2 to detect hypercapnia/hypoventilation

• Securing airway access as soon as possible

• Providing sufficient inspired oxygen (100% oxygen)

• Recovering the patient in a quiet, calm area with oxygen available

• Having an emergency respiratory kit on recovery if re-intubation may be required or complications are anticipated

If your vets want to get a really good look at the lungs, the best thing to do is anaesthetise these patients and take inflated views of the chest. This involves a person behind a lead screen (or dressed in lead PPE if you do not have a screen available) temporarily holding the lungs at full expansion whilst the exposure is taken. 

However, this may not be possible in all respiratory conditions, for example, patients with pulmonary bullae - as they are at increased risk of developing pneumothorax. So before you begin anaesthetising the patient, ask your vet what they’re looking for and whether they need inflated views.

Other areas we typically x-ray include the limbs in patients with immune-medial polyarthritis. These are typically taken prior to joint taps, to look for joint effusions or erosive changes. IMPA is a painful condition, with patients presenting with lameness, swollen and painful joints, and pyrexia. Anaesthesia is preferred for their investigations since repositioning and manipulation of their joints will be needed for multiple x-ray views and joint taps.

Ultrasound

Abdominal ultrasound is one of the most common procedures we perform in medicine. It tells us about the structure and function of various organs and allows us to collect samples such as FNAs, needle-core tissue biopsies, and cystocentesis samples.

In many cases, we can perform ultrasonography under sedation and it is not a painful procedure. We do need to consider, though:

• How painful the patient is - because even though the ultrasound isn’t painful itself, the patient may have abdominal pain

• How tense the patient is - as our sonographers often have to apply a lot of pressure to the abdomen, especially in larger or deep-chested patients

• Whether any samples will be taken during the ultrasound, and if so which samples.
  For example, deeper sedation is required for patients undergoing cholecystocentesis - where bile is collected from the gall bladder. This is due to the (low) risk of gall bladder rupture and bile peritonitis associated with the procedure.

• Why we are performing the ultrasound - is our patient regurgitating? Do they have a higher risk of peri-procedure regurgitation and aspiration? If so, do we need to change their sedation plan to a GA, so we can intubate and protect their airway?

CT

The use of CT is becoming more common in veterinary practices. CT provides us with 3-dimensional x-rays, taken as ‘slices’ through the patient and reconstructed in different planes. They give us much more information than a single x-ray, and we can further enhance the information we get from them by administering intravenous contrast media such as iohexol.

CT scans are commonly performed in patients with respiratory and/or nasal disease, neoplasia, and to look for anatomical defects such as portosystemic shunts, patent ductus arteriosus and ectopic ureters.

Here are a few things to think about when anaesthetising a patient for a CT:

Why are we performing the scan? What disease do we suspect is going on? And how will this change our anaesthetic plan?

For example, if you think your patient has a portosystemic shunt, this will significantly impact the drugs we use, the monitoring we include (e.g. by adding the need for blood glucose monitoring), and our concerns for recovery (since many anaesthetic agents are metabolised by the liver, leading to prolonged recovery in shunt patients). These patients are often also much smaller, and younger, so hypothermia is a more significant concern.

Are you scanning the chest? If so, you’ll likely need to induce apnoea to examine the lungs properly. 

CT scans take anywhere from 15-90 seconds to complete, depending on the area you’re scanning and the settings you’re using. So if your patient is breathing at a rate of 30 breaths/minute and you’re doing a 60-second scan, every 2 seconds the lungs will move.

This means there will be a lot of movement artefact on your scan - limiting the vet’s ability to interpret the images. 

To counteract this, we usually hyperventilate our patients (via IPPV) to drop their ETCO2 on purpose. This reduces their respiratory drive and induces a temporary period of apnoea. The apnoea only lasts for a short period whilst the scan is performed, and as their ETCO2 increases, they begin ventilating spontaneously again.

However, like our inflated chest x-rays, this is not appropriate in all patients. Severe respiratory disease, pneumothorax patients and patients at risk of a pneumothorax may not be candidates for this, so discuss with the vet beforehand and decide as a team if apnoea is required.

Are you giving contrast?

Contrast media such as iohexol or iopamidol is used to highlight areas of increased blood flow, such as tumours, or highlight blood vessels during a scan. However, its use is not without risk. Hypersensitivity reactions, changes in pulse rate, blood pressure, respiratory rate, twitching and arrhythmias are reported, though severe reactions are rare.

As nurses, we need to monitor our patients for signs of contrast reaction both during their anaesthetic and in recovery. In addition, we need to ensure that we’ve checked renal function recently since contrast agents can be nephrotoxic. A period of intravenous fluid therapy is administered after the patient recovers, to help ‘flush’ the contrast through the kidneys and avoid renal injury. 

Feeding Tubes

Some of our anaesthetic considerations will change depending on the type of feeding tube we’re placing, and how we’re placing it.

For example - nasal feeding tubes may be able to be placed consciously, or with mild sedation. I personally like the patient to be only sedated enough to facilitate the placement of nasal tubes, since we want them to be able to swallow the tube! If they are too asleep, I find it is easier for the tube to inadvertently enter the trachea.

An oesophagostomy tube, gastrostomy tube or jejunostomy (though J tubes are VERY rarely placed now) tube will require general anaesthesia for placement.

The first thing to think about when anaesthetising a patient for feeding tube placement is how long they have been anorexic, and what’s driving the anorexia.

I can’t stress enough that our medical patients are not healthy patients undergoing elective procedures - we’re doing this because they are ill. And this will change their anaesthetic plan.

Pay close attention to:

• Hydration status, fluid, acid-base and electrolyte balance. Hypokalaemia is common with anorexia, and dehydration will be a risk in patients who have not been drinking enough, or consuming enough water via their food, for example.

• Renal and hepatic function - if kidney or liver disease is causing anorexia, this has the potential to affect how we monitor these patients and the drugs we use.

• GI disease - if the patient has a chronic GI disease, we may see changes to albumin levels impacting things like fluid balance and blood pressure. We may also have patients in poor body condition, increasing our risk of hypothermia under anaesthetic.

If you’re placing an oesophagostomy tube, you’ll need to ensure your ET tube is very well tied in and connected. There is an increased risk of the tube becoming dislodged when placing an O tube, since the vet (or nurse!) will be placing forceps through the mouth into the oesophagus, and then pushing the O tube down into the oesophagus manually.

If you’re placing a gastrotomy tube, you’ll need to think about how this is being placed. We have 2 options - surgically, or endoscopically. Surgical G tube placement will require an ex-lap, significantly increasing the pain associated with the procedure, and changing our analgesic choices. We’ll also have higher risks of hypothermia, for example, from the large clipped and scrubbed area, and the open abdomen.

Endoscopic (PEG) tube placement carries similar considerations to upper gastrointestinal tract endoscopy.

Bone Marrow Biopsies

Bone marrow aspiration and biopsy is a common procedure in anaemic, thrombocytopenic and/or neutropenic patients. There are a few things to think about when caring for patients undergoing this procedure:

• Cardiovascular status. Is our patient transfusion dependent? If so, they will be hypovolaemic and have reduced oxygen-carrying capacity. This will significantly impact anaesthetic risk and needs to be corrected prior to/during the procedure. We will typically start blood products before the anaesthetic if needed, and begin the procedure either once the transfusion is complete, or after a significant portion of the transfusion has been given.

• Pain. Bone marrow biopsies are painful! Get good analgesia on board in the premedication, and utilise local anaesthetic techniques. In our bone marrow patients, the nurses draw up and aseptically administer lidocaine at the biopsy site. We instil the lidocaine directly against the bone, then withdraw the needle to infiltrate the subcutaneous tissues overlying the site.

• Vascular access. There are a few sites we can use for bone marrow sampling - usually the proximal humerus (if they’re right-handed usually the left humerus is used), iliac crest, or proximal femur. The site will be manipulated a lot during the procedure, so avoid placing intravenous catheters in the limb to be used. If your patient already has an IV in the leg to be used, it may be advisable to place a second catheter in another site before the procedure begins. That way, if you need to give emergency medications during the anaesthetic, you don’t need to worry about your catheter becoming dislodged.

Joint Taps

We’ve already touched on managing IMPA patients when we discussed limb x-rays. After we’ve imaged their joints, we’ll need to collect samples of their synovial fluid for cytology and culture to confirm our diagnosis. Here are a few things to think about in these patients:

• Pain. IMPA can be a very painful condition. We’re then going to manipulate their limbs a lot to radiograph them and collect synovial fluid. Deep sedation or general anaesthesia is indicated, with good analgesic agents as part of the patient’s premed.

• Avoiding NSAIDs. Though useful for managing their pyrexia and providing additional analgesia, if a diagnosis of IMPA is made, our patient will need steroids. This means NSAIDs are out - so we’ll need to think of alternative ways to provide multimodal analgesia. In dogs, we often use paracetamol - so this may be an option for you to discuss with the vet.
  

So those are my top considerations for anaesthetising or sedating medical patients for common procedures! 

Regardless of what you’re doing with your patient, make sure you consider their disease process and why we’re performing the procedure required. Speak to your vet about what the procedure will involve, and if there are any specific risks for your particular patient - for example, whether you can inflate the lungs for chest x-rays or not. And lastly, think about all the common complications we see in our medical patients - dehydration, hypovolaemia, electrolyte abnormalities and pain, to name a few - and the impact these will have on your anaesthetic plan.

Do you frequently anaesthetise patients for medical procedures? DM me on Instagram and let’s chat about it!

References

1. Harvey, J. W. 2004. Bone marrow aspiration biopsy. Online. Clinician’s Brief. Available from: https://www.cliniciansbrief.com/article/bone-marrow-aspiration-biopsy 

2. Scarabelli, S., Cripps, P., Rioja, E. and Alderson, B. 2016. Adverse reactions following administration of contrast media for diagnostic imaging in anaesthetised fogs and cats: a retrospective study. Veterinary Anaesthesia and Analgesia, 43 (5), pp. 502-510.

3. Schiborra, F. 2017. Percutaneous ultrasound-guided cholecystocentesis: Complications and association of ultrasonographic findings with bile culture results. Online. Available from: https://livrepository.liverpool.ac.uk/3059347/1/Manuscript%20final.pdf

4. Specht, A. and Guarino A. 2019. Canine Immune-Mediated Polyarthritis: Meeting the Diagnostic and Therapeutic Challenges. Online. Today’s Veterinary Practice. Available from: https://todaysveterinarypractice.com/internal-medicine/canine-immune-mediated-polyarthritis-meeting-the-diagnostic-and-therapeutic-challenges/

5. Veterian Key, 2017. Anaesthesia for patients with respiratory disease or airway compromise. Online. Available from: https://veteriankey.com/anesthesia-for-patients-with-respiratory-disease-andor-airway-compromise/