Monday, December 6, 2010

264. 4th surgery in an old dog's cheek

Surgery Report for ROY (11 Y/O mixed breed male dog)
PRE-OP
History:
Roy was presented with a malignant tumour on the Right cheek. Tumour was persistent, with ill-defined margins and had a rough 7cm circumference. It also had a history of dermatitis with multi-focal exudative pustules and papules located primarily on the proximal fore and hindlimbs, with severe scaly and crusted regions of epidermis on the caudal elbow and knee joints. Roy was otherwise eating normally.
Physical Exam (PRE-OP):
On physical examination, Roy displayed an obdunted attitude. Heart, respiratory rate and temperature were within normal limits at 102 bpm, 30bpm and 39.2degrees Celsius respectively. Peripheral perfusion seemed normal with mucous membranes being moist and pink and CRT < 2 secs. Breath was malodorous (possibility of bacterial / fungal overgrowth inside the mouth).
Treatment Plan:
Palliative and curative.
To surgically excise the malignant cheek tumour via electrocautery and check for observable metastasis to regional lymph nodes under general anaesthesia.
OPERATION
Surgical and Anaesthetic details:
Roy was not sedated prior to anaesthetic induction as there was sufficient restraint to hold him down.
Catheterization was performed via a 22G needle into his left cephalic vein for easy intravenous (IV) access before anaesthetic induction with Diazepam (0.4ml) and Ketamine (0.4ml) totaling 0.8ml IV. Roy was deemed sufficiently induced after 10minutes and surgery proceeded. Surgical site was prepped with chlorhexidine and alcohol and a transverse incision across the tumour was made via electrocautery.
The epidermis above the tumour site was undermined to relieve skin tension and provide easier excision of the tumour itself. Roy was also given an IV drip of 5% dextrose wit 0.45% NaCl to compensate for electrolyte losses and to prevent dehydration and hypovolaemia.
Care was taken not to sever the facial nerve although part of it might have been as the tumour margins were large and irregular and the base of the tumour was located deep within the facial cavity, thus requiring aggressive surgical therapy. Upon tumour excision, tumour was found to have metastasized to the bone as well as the upper gingiva. As the effects of the induction drugs weared off, gaseous anaesthesia for maintenance was administered. 5% isoflurane was administered initially and slowly decreased over the course of the surgery up to 0.2% during the muscle, subcutaneous and skin closure at the excision site. 0.1% zoletil was also administered IV during the course of the surgery as Roy was still deemed too light. After 40 minutes, tumour was partially resected and wound closure commenced so as to decrease anaesthetic risk and toxicity. Muscle, subcutaneous and skin closure was performed using 2-0 synthetic polysorb, absorbable suture for all layers. Muscle and subcutaneous layers were closed using a simple interrupted pattern while the skin layer was closed using a mattress suture pattern.
POST-OPERATION
Surgical site was washed and swiped clean with sterile saline to reduce risk of sepsis and 1ml of Tolfenamic Acid (Tolfedine) was administered IV as post-op analgesia. Roy was then placed back in his cage and equipped with an E-collar while he continued to receive the remainder of the 5% dextrose and 0.45% NaCl at maintenance rates followed by another 500ml of Hartmann’s after, also at maintenance flow rates to prevent dehydration, hypovolaemia and to maintain electrolyte balance. Blood sample was taken for CBC and biochemistry while a tumour sample was also submitted to QuestLabs for histopathology.
DRUGS USED AND PRECAUTIONS
Ketamine:
- Mode of action: Acts at the N-methyl-D-Aspartic (NMDA) receptors and blocks central sensitization. It is useful for patients with chronic pains and patients that fail to respond to conventional analgesic therapy. Can also be used (mostly in combination with other drugs such as Xylazine and Diazepam) for sedation and anaesthetic induction.
- Precautions: AVOID the use of ketamine in patients with traumatic head injury as it increases cerebral blood flow and may increase intra-cranial pressure.
Diazepam:
- Mode of action: Diazepam is a benzodiazepine that binds to a specific subunit on the gamma-aminobutyric acid (GABA) receptor at a site distinct from the binding site of the endogenous GABA molecule. Therefore it works as an allosteric modulator of GABA, enhancing its effects and provides good anxiolytic, anti-convulsant, hypnotic and amnestic properties. Used especially in the management of seizure cases.
- Precautions: IV administration of diazepam should be performed slowly, particularly when injected into the smaller veins such as the cephalic vein because of the potential of thrombophlebitis and cardiotoxicity due to the propylene glycol base.
Diazepam may cause weakness, drowsiness and loss of motor coordination. In rare cases, it may result in paradoxical excitement, unexpected aggression or unusual behavourial changes.
Zoletil
- Mode of action: Combination of 2 drugs, tiletamine and zolazepam. Tiletamine’s mode of action is similar to that of ketamine as it is a NMDA receptor antagonist and blocks central sensitization as well. Zolazepam’s mode of action is similar to diazepam as it is a pyrazolodiazepinone derivative that is structurally similar to the benzodiazepine drugs.
- Precautions: Contraindicated in animals with CNS signs, hyperthyroidism, cardiac disease, pancreatic or renal disease, pregnancy, glaucoma or penetrating eye injuries.

REFLECTIONS
As tumour was incompletely resected, the chance of recurrence is very high. Prognosis of this dog is very poor as well as it is old and there has already been evident local metastasis to bone and gingival. Distant metastasis has not been diagnosed but is possible, which will further decrease its prognosis for survival.
In my opinion, if cost is not an issue for the client, I would recommend palliative treatment with NSAIDs such as acetaminophen, aspirin, meloxicam as well as prophylactic broad spectrum antibiotics such as Trimethoprim Sulphate (TMS) or Amoxicillin Clavulanate (Amoxy-clav) along with neoplasia excision again when the tumour grows again to a clinically significant size.
As the surgery had to be aggressive, part of the facial nerve might have been severed in the process which might have resulted in the post-op excessive salivation, drooping of the lip and ear on the ipsilateral side of the lesion. Dog should also be examined for signs of nystagmus, head tilt, asymmetrical pupil size dropping of food and ataxia to further confirm the suspicion of facial nerve paresis or paralysis. Part of the sublingual and mandibular salivary glands and/or their ducts might have also been severed in the process, resulting in excessive salivation. Due to traumatic injury to the glands and/or ducts, in my opinion, I would expect the dog to develop a sialocele which would then require further surgical intervention. Diagosis of this could be confirmed with fine needle aspirate should a SOFT, palpable mass develop near the mouth region. Needle aspirate can also help differentiate a sialocele from a neoplastic process.
On a separate note, the dermatological processes should also be looked into if the client is willing. Punch biopsies should be done on the pustules and papules, centered in the middle of the biopsy specimen. Punch biopsies should also be obtained from the scaly and crusted areas AS WELL AS from the normal skin. This is to allow comparisons of the epidermis and stratum corneum of the 2 sites by the pathologist. This is done to diagnose the nature of the skin lesions and to determine an appropriate treatment plan for Roy with systemic treatment such as injectable or oral cephalosporins, enrofloxacin etc. Adjunctive therapy could include topical treatments such as Chlorhexidine gluconate (Pyohex Dermcare) shampoos as well as benzoyl peroxide (Pyoben Virbac)


Done by:
Geoffrey Yeo


COMMENTS FROM DR SING
A good report written by a 4th year Murdoch Univ student on first day of internship at Toa Payoh Vets. Interns are expected to write report of interesting cases to make them good vets as merely observing surgeries and anaesthesia during internship will not be effective in training of a vet student. In this way, veterinary surgery is brought alive to the student and hopefully, he or she will remember the case study during his final year examinations or after graduation.


The following is additional information for my record and to share my knowledge with other vets

HISTORY
Previous handling of the case including anaesthesia and surgery are documented at:
1. http://www.toapayohvets.com/surgery/20100618cheek_tumour_old_dog_electrosurgery_ToaPayohVets.htm

2. http://www.asiahomes.com/singaporetpvet/dogs/20100690emergency_anaesthetic_death_cheek_tumours_old_dog_excision_ToaPayohVets.htm

On this 4th surgery case study, the submandibular and popliteal lymph nodes of the dog are enlarged to around 1 cm in diameter. The mouth was very painful and the dog has poor appetite till painkillers are given. The owner gave rimadyrl tablet earlier and the dog did not feel any pain and therefore ate canned food.

PRE-OPERATION
The Miniature Schnauzer, male, 12 years old was operated 3 times. The cheek tumour was malignant and recurs within a month. It keeps growing bigger and has spread to the bones and gums now. The owner had declined cytotoxic drugs or euthanasia and expected the old dog not to die on the operating table. She was informed that this was a high risk anaesthetic case. She wanted the surgery to be postponed on Sunday as she felt that nursing would be better on Monday. So, the dog was operated on Monday.

Prior to this 4th surgery, the dog was on 2 days of IV drips, baytril and metronidazole IV as the mouth was smelly due to the large infected cheek tumour. On the day of the surgery (Monday, Dec 6, 2010 at 2 pm), the bad breath was 90% absent.

PAIN-KILLERS
Sufficient pain must be given during surgery and post-operation. The dog was whining
1. during surgery at times when the IV general anaesthetic of ketamine 0.4 ml and diazepam 0.4 ml in one syringe, totally 0.8 ml. Initially at 0.4 ml of the mixture was given via the IV cathether. This was insufficient analgesia for this 10-kg dog.

2. Isoflurane gas 5% was given for less than one minute by mask when the dog whines during the surgery. "Intubation is not practical," I told my assistant who asked for an endotracheal tube. "The cheek tumour is too large and the tube would be obstructing the excision and view." I got a small mask (usually for cats) and supplied gas at the nose level. It was effective. The tongue remained pinkish, the intern practised on taking the heart rate which was normal. Maintenance dose varies from 5% to 0.2% to effect.

3. Zoletil 100 at 0.1 ml IV was given towards the 30th minute of surgery as the dog was whining when isoflurane gas was reduced considerably. The dog stopped whining within a few seconds.

4. Tolfedine 4% at 1.0 ml given IV towards the completion of surgery as the dog was whining in pain as he had waken up at the 45th minute when the last stitching was done. I supervised the intern to give the injection IV via the IV set. "Not direct injection," I stopped him. "Stop the IV flow first, inject and continue the IV drip".
Within 60 seconds, the dog stopped whining in pain and for the next 12 hours after surgery. This shows that Tolfedine acts effectively.


NOTES: The intern was told that the IV flow must be stopped by rolling down the control wheel before injection of the drug. He asked whether there was another solution to inject the remaining drug and was told there was none - in human IV anaesthesia, another syringe with saline of 2 ml would be injected to flush in the remaining small amount of drug in the needle of the first syringe which is removed first.

FACIAL NERVE
The intern was asked to identify the large 3-mm wide white nerve seen between the right eye and the commissure of the lips, above the cheek muscle. He said it would be the trigeminal nerve.

HISTOPATHOLOGY
The intern was asked to send the greyish white fatty-like tumour for histopathology.

BLOOD TEST 2 DAYS BEFORE SURGERY
TELEPHONE FROM THE OWNER. The young lady phoned me and was told the good news that the dog was OK. Another bottle of IV drip of Hartmann's solution would be given. Metronidazole and 0.1 ml of dexamethasone IV would be in the drip. The dog would be on immunosuppressive drug.

BLOOD TEST 2 DAYS BEFORE THE SURGERY. I asked the intern to comment on the report. The total WBC was 25 (very high). The platelet count was above normal.Why? I asked him to comment in his report.


CONCLUSION
It is too early to know whether this dog will survive post-operation as it is only 14 hours post-op. Dogs do die post-op too.

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