Anaesthesia for renal patients

Question 1

How can you prepare anaesthesia in a patient with CKD? Why is it important?

Answer 1

• Physical exam and detailed history then complete blood count (CBC), serum chemistry profile and urinalysis (at minimum, a urine specific gravity) plus the SDMA, NIBP
• These tests provide vital information (can reduce patient morbidity & mortality) by indicating a drug dose reduction is sensible
• Mild increases in [BUN] & [creatinine] may indicate severe disease
• Trends are more useful than singular measurements
• Renal patients may be dehydrated, anaemic, azotaemic, anorectic or acid-base abnormalities
• Azotaemia increases the sensitivity of anaesthetic drugs by affecting the permeability of the blood brain barrier

Question 2

What drugs do you avoid in sedation/premedication in patients with CKD?

Answer 2

Avoid phenothiazines and alpha 2 agonists in CKD
Phenothiazines (e.g. acepromazine) can cause vasodilation and subsequent hypotension that may dip below the range of autoregulation. Appropriate doses along with careful monitoring of blood pressure and treatment of hypotension is essential.

Alpha-2 adrenergic agonists (e.g. medetomidine, dexmedetomidine) are used cautiously in cats with renal disease because this class of drug has the potential to cause up to a 60 percent decrease in cardiac output. In addition, a 50 percent decrease in RBF is seen in dogs alongside an increase in GFR but no definitive evidence exists to support this in cats; however, it would be prudent to assume these mechanisms may be similar in cats as well.
* very low does dexmed - ok as avoids side effects

Question 3

What drugs should you avoid in premed in obstructed cats?

Answer 3

Alpha-2 agonists should be avoided in obstructed cats due to their diuretic effect and should be used with caution in all other cases of renal impairment if possible.

Question 4

What premeds/sedation should you use in patients with CKD?

Answer 4

Benzodiazepines (e.g. diazepam, midazolam) are well tolerated in renally impaired cats; nevertheless, this class of drugs can cause paradoxical excitement and should be used alone with caution in cats or young, healthy animals. Co-administration with an opioid is recommended.

Opioids (e.g. buprenorphine, methadone, butorphanol, morphine, fentanyl) are generally safe for renally impaired cats and their use is often beneficial. Opioid administration may help decrease the sympathetic response associated with pain and surgery, thereby minimizing renal vasoconstriction. The addition of opioids can also decrease the amount of inhalant necessary to keep the patient immobilized, avoiding unnecessary hypotension.

Question 5

What should you use to induce and maintain anaesthesia in patients with CKD?

Answer 5

Induction - Propofol, alfaxalone and ketamine - all ok, maybe avoid ketamine as metabolised by the kidneys, will last longer as longer to be metabolised)

Maintenance - use minimal amounts of inhalants, as will resuce cardiac output and cause hypotension which can cause AKI

Local anaesthesia - good idea, will allow for less inhaled anaesthesia (lidocaine and bupivacaine - longer acting)

Question 6

What are the best tips intraoperatively and post op for patients with CKD?

Answer 6

• Avoid renal vasoconstriction & GFR reduction
• Treat pain/nociception
• Locoregional anaesthesia
• IVFT continue into post op period and encourage diuresis
• Oxygen supplementation post op
• Maintain normothermia

Question 7

Should we prescribe NSAIDs long term in CKD?

Answer 7

• NSAIDs have narrow safety margins and can cause adverse effects, and this can be exacerbated by hypotension associated with anaesthesia
• In cats, CKD can affect 40% of cats >10 yrs and 80% of cats >15yrs
• Osteoarthritis is common in cats (61% of cats >6 years, up to 90% of cats aged >12 years)
• CKD and OA may co-exist in 70% of cats – and they need pain relief
• Historically NSAIDs have been contraindicated in these animals
• BUT maybe they can be used (with care) in stable CKD cats with IRIS 1 & 2 (?3)

Question 8

Why are the advantages and disadvantages of NSAIDs?

Answer 8

NSAIDs block PGs, PG function in the kidney: Cons of NSAIDs
* Prostaglandins (PG) promote vasodilation and inhibition of Na+ reabsorption, & thromboxane A2 modulates renin production and vasoconstriction
* These mechanisms are important in protecting normal kidney function during dehydration and hypovolaemia
* PG inhibition after NSAIDs could result in deleterious renal effects in susceptible patients
* Cats with pre-existing CKD could be at increased risk of renal toxicity associated with NSAID administration.

For NSAIDs:
* Improved mobility and overall QoL after NSAID pain relief may have resulted in better appetite and increased water consumption
* An alternative hypothesis was that the NSAID had a direct anti- inflammatory effect on the kidneys and stop renal functional deterioration over time