Tuesday, June 2, 2015

2181. Rat anaesthesia & surgery: Mastectomy. Zoletil. A 385-gram pet rat had a 77-gram breast tumour

Tuesday, June 2, 2015.

Pet rats are rare in Singapore and therefore most vets will never encounter a case of mastectomy in a female rat. This report shares my knowledge of the anaesthetic protocol for a pet rat anaesthesia.  

The couple was prepared to take the anaesthetic risk to get the gigantic 77-gram breast tumour of the 2.5-year-old female pet rat excised. Such a huge tumour would have commandeered a large volume of blood. Removal of a gigantic 77-gram breast tumour in a 385-gram older rat meant removal of 20% of the bodyweight.  Such a loss of a large amout of body tissue could deprive the rat of a sufficient blood volume. Death could be due to hypovolaemic shock.

It was either this surgery or euthanasia. The rat was still eating but the tumour kept growing.

"After surgery, the tumour may recur," I explained this possibility of a breast cancer to the owner. However the couple decided. So I prescribed 3 days of antibiotics and pain-killer and had the rat operated today.

"The caudal superficial epigastric blood vessels must be located and ligated to prevent death from bleeding," I explained to Dr Daniel. "There will be bleeding from the tissues, but this vessel must be located and ligated."

The rat was sedated with 0.2 ml Zoletil 100 and given around 0.5% isoflurane gas maintenance. She went home 2 hours after surgery but had not wakened up yet. She was placed in a horizontal stretching position with her eyes open. She was breathing very slowly even at 2 hours after surgery although the duration of Zoletil is said to be 30 minutes to 2 hours. So, I thought this could be a "touch and go" case. The owner did not want histology of the 77-gram breast tumours.

Anaesthetic protocol used in this rat for mastectomy

Date: Tuesday, June 2, 2015.

Patient admitted at 10 am. No food and water for the past 12 hours. Surgery at 3 pm.

2.5-year-old female rat
Bodyweight: 385 grams
Active, eating, not obese
Gigantic breast tumours left mammary glands, growing larger from 7 months ago
Surgery: mastectomy

1. Pre-surgical analgesia and antibiotics
Three days of the NSAID meloxicam and antibiotic enrofloxacin (baytril) given orally at home. Meloxicam at 1 mg/kg PO or SQ 30 minutes before surgery and every 24 hours after surgery is advocated by some vets. Enrofloxacin is given at 5-20mg/kg SQ once daily or 50-200 mg/L in the drinking water is advised by some vets.

No food 12  hours before surgery in this rat. Some vets say that food with-holding is not necessary as the rat does not vomit and water is to be freely available before anaesthesia.  

2. No premedication with atropine at 0.05 mg/kg SQ was done in this case. Atropine before induction is said to decrease bronchial and salivary secretion and protect the heart from vagal inhibition.

2.1 Induction was with Zoletil 100 IM at 50-75 mg/kg for rats.   In this case, 50mg/kg was selected as the rat is considered old (life span said to be 3 years). The amout rate was given 0.2ml IM.
2.2 Zoletil is said to be safe, permits smooth recovery, does not cause cardio-vascular depression or affect kidney funcions. It is safe for use in pregnant dogs and cats. No cumulative toxicity or effects on the kidneys if given top-up by IM for maintenance. Zoletil does not provide good analgesia. Onset was 3-5 minutes.  Isoflurane gas was used in this rat via a face cone. 

3. Isoflurane + oxygen gas via face cone at 5% and then mainly 0.5% (1-3%) for maintenance and to effect. Intubation was not done.

3.1  A precision vaporiser which delivers controlled levels of isoflurane gas mixed with oxygen was used.

4. Post-surgical analgesic was NSAID meloxicam oral. No injection of Opioids with buprenorphine preferred. Zoletil has mild analgesic effect and adequate pain management is given using NSAID or Opioid. Indications of pain in the rat are decreased food and water intake and locomotor activity, horizontal stretching (rat horizontal on the ground), twitching and withering. Zoletil provides a smooth recovery. 

4.1 For post-surgical pain control, some vets advocate the use of opioid buprenorphine 0.05 mg/kg SQ or opiod + NSAID like carprofen.
4.2 No post-surgical injections of opioids or opioid + NSAID in this rat
4.3 NSAID meloxicam oral was continued with good outcome of the rat eating and active within 24 hours after surgery.

No post-surgical fluid therapy with lactated Ringers or during anaesthesia in this case. Some vets advise Ringer's lactate at 5ml/kg/hour

5. Indicators of pain in rats are:
5.1  Vocalisation - rarely reported unlike in dogs..
5.2  Horizontal stretching (rat horizontal on the ground).
5.3 decreased food and water intake or movement.
5.4 withering and twitching

This rat went home 2 hours after surgery. The rat was placed in the horizontal stretching position in a container to bring home. She was breathing very slowly.

Warm water in plastic bag heating of the body was advised. Quiet and dark room to recover


Jun 2, 2015 3 pm mastectomy. Rat goes home at 6 pm. Still in horizontal stretching position and breathing rate is around 20/min. Eyes open.

Jun 3, 2015  6.30 pm.  Dr Sing Kong Yuen: "Is yr pet rat ok after op?"

Jun 3, 2015  6.45pm    Owner: "Yes she is okay now. Started eating since this early morning (18 hours post surgery) and now running places"

Dr Sing Kong Yuen: "Thanks. Continue medication for the next 4 days only."

CHALLENGES on Jun 4, 2015
Bit of dressing covering stitches. Start to bite stitch. Advise e-collar or replace plaster every time it got taken out by the rat for nest 10 days.
No running around. Place in a tank.

For premedication, a "single shot" injection of Zoletil causes less stress to the rat than multiple injections to reduce the dosage of isoflurane gas.

Some vets advocate atropine SC in premedication to prevent bradycardia.

Some vets advocate the following for mice:
isoflurane 4-5% + 0.8 - l L/min for induction and 1-3% + 0.8 - 1 L/min for maintenance
palpebral reflex to assess the depth of anaesthesia

For post-operative pain prevention, pre-surgical injection of NSAID (e.g. meloxicam 1 mg/kg SC 30min pre-surgery and q 24hr. I gave oral meloxicam for 3 days before surgery.  Some vets give Opioid like bupreorphine 0.05-0.1mg/kg SC q 12 hours.

Antibioitics can be enrofloxacin  5-20mg/kg q 24hr  or 50-200mg/L drinking water
or trimethorprim sulpohonamides 15-30mg/kg PO, SC, IM q 12hr
or gentamicin  5-10mg/kg SC
local anaesthetic on surgical wound injection or gel

oxygen-enriched environment, quiet, dark room
infra-red lamps, heating pads after and during surgery
ocular ointment to prevent corneal drying and damage


Jun 8, 2015

The young lady brought her rat for check up as she is worried about the big wound.
"It is very hard to put an e-collar on the rat as well as the hamster," I said. "They will try to pull it out and get stressed."

The rat weighed 306 grams on 6 days after mastectomy but weighed 385 grams with the tumour of 78 grams before mastectomy. Pre-op weight of 385 - 78 was 307 grams. So, it was good news as the rat was back to normal. Otherwise she would lose weight. 

The career lady showed me a video of a swelling where the stitches had been one day ago. It would be a haematoma. Some pink plasma seeped out. Now it is a gap as the two stitches had been bitten off.

Over 20 pieces of big round stools were in the carrier indicating that the rat was normal as she would not eat if she was infected. This was good news.

What are my advices?

1. There was no need to re-stitch as the rat may bite the stitches off. The rat may die under anaesthesia as she is older being 2.5 years old. A rat is said to live around 3-5 years.

2. An Elizabeth collar is not acceptable to the rat. She will be stressed getting it off. In any case, the wound will heal by granulation.  
3. Get a bigger plaster dressing to cover the wound instead of two smaller ones.

4. Clean the wound twice a day with chlorhexidine but rinse off the wash with clean warm water and dry the wound.

5. Antibiotics oral -  baytril and painkiller meloxicam for 2 days. Wait 4 days and repeat if needed.

Day 1  Jun 2, 2015     mastectomy

Jun 3, 2015  6.30 pm
Dr Sing: Is you pet rat ok after op?

Owner: Yes, she is okay now. Started eating since this early morning and now running places.
Dr Sing: Thanks.

Jun 4, 2015  7.44am
Dr Sing: Give medicine for the next 4 days
Owner: Thanks Dr. Will continue to give her medicine for another 2 days. The wound is quite dry. But she does chew a bit of the stitches off
Dr Sing: Need to make an elizabeth collar with thin cardboard paper to wear around the neck for 7 days at least. No running around.  E-collar similar to what dogs wear. Do it before you go to work.

Owner: Will keep her in the tank and won't let her out. 

Dr Sing: Or bring her to office.

Owner: Oh yah I saw that in the internet. Will make her one.

                  8.22 am
Dr Sing: Or tape wound with human dressing for wound protection. Urgent to do it before you go out.

That's what we did yesterday with a plaster but it came off this morning.

                 8.24 am
Dr Sing: Need to keep replacing it for 10 days.  Pl email video of stitched area.  99pups@gmail.com

Owner: Sure I will.

Sat Jun 6, 2015        5.22 pm
Dr Sing: How is the patient?

Sunday Jun 7, 2015  10.57 am
O:  Hi. Pixie has a lump just to the left of the incision. She eats and drinks okay and still very active. Am wondering if it's water retention or internal bleeding. Will send you the video of it via email now.
                                  11.38 am  
Dr Sing:   Some bleeding in the area.

O: There was some pink trace of blood but the wound looks dry and neat.

Dr Sing: The rat should be Ok.
O: Hi, she pulled off the stitches. There's an open wound now. But not bleeding though. Will bring her in the morning


Monday Jun 8, 2015. Inspection of the rat at Toa Payoh Vets

The fancy rat had an open wound as two stitches were taken out by the rat. Not serious. Advised bigger plaster and cleaning wound daily.  No need to re-stitch.  The wound will heal by granulation.

UPDATE Sunday Jun 14, 2015  6.18 am 
As I write this report, no news from the owner is good news.




Rat analgesics

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