Two cases of anaesthesia for resection of a bladder tumour are described using the diode laser technique guided by abdominal ultrasound.
The main objective of the anaesthetic protocol is to produce the necessary analgesia to avoid nociception and the resulting hemodynamic repercussions. Thus, epidural anaesthesia with lidocaine is used.
Local anaesthetics block the entry of sodium into nerve fibres preventing depolarization and the transmission of nerve impulse.
By blocking the transmission there is no nociception derived from the surgical procedure and hemodynamic responses such as the increase in blood pressure, heart rate, respiratory rate and drop in cardiac output with the consequent reduction in tissue perfusion-oxygenation do not occur.
The inhibition of nociception also reduces the expired fraction of isoflurane (% FeIso) and prevents the administration of analgesic drugs.
Lidocaine was administered as it has an action period of 1.5-2 hours1. This is the approximate procedure’s duration and the animals may wake up without motor block and feel more comfortable during the postoperative period. As it was a urinary bladder surgery, morphine was not administered since it can cause urinary retention2.
The two cases presented mild hypotension, probably caused by the sympathetic blockade because of the epidural anaesthesia. This was controlled with continuous infusion of dopamine.
With this anaesthetic protocol the objective was met, the animals had no nociceptive responses to the surgical stimulus and both had good recoveries.
The surgical technique used is a minimally invasive technique, but both cystoscopy3 and cystotomy are painful procedures.
In the case of the female cat, the laser could be introduced through the urethra and act directly on the bladder tumour without the need for laparotomy and cystotomy.
In the case of the male, being the urethra very narrow and unable to pass the laser, it was accessed through the alba line and an incision was made in the bladder to introduce the laser and reach the tumour.
CLINICAL CASES DESCRIPTION
Case 1 is a 7-year-old and 4 kg British cat female with azotaemia and atrophy or degeneration of the right kidney. Case 2 is a 13-year-old European cat male and 3.7 kg with mild anaemia and azotaemia. Both cases were diagnosed with a bladder tumour.
In both cases, tumour excision is performed using the endoscopy diode laser technique guided by ultrasound to ensure the integrity of the bladder wall.
Both are classified as ASA III.
The anaesthetic protocol was adapted to the character of the animal.
The cat received fluid therapy with Lactated Ringer solution administered 24 hours prior to surgery.
Intravenous sedation was performed with methadone (0.1 mg/kg) and alfaxalone (1 mg/kg), it was pre-oxygenated with a mask for 5 minutes and the induction was done with alfaxalone (0.6 mg/kg) and midazolam (0, 1 mg/kg).
It was maintained with isoflurane with FeIso between 1.4-0.42%.
The cat wasn’t gentle, so we had to administer dexmedetomidine (2 µg/kg) with methadone (0.2 mg/kg), midazolam (0.1 mg/kg) and alfaxalone (1 mg/kg) all in the same syringe and intramuscular.
Induction was performed with alfaxalone (1 mg/kg) and midazolam (0.1 mg/kg) after pre-oxygenate for 5 minutes.
FeIso remained between 0.99-0.42%.
In both cases a good sedation and induction was achieved. For intubation, 0.1 mL of 2% lidocaine was applied to the arytenoid cartilages and a PVC tube with a low-pressure balloon of 3.5 mm internal diameter was introduced.
To provide analgesia of the lumbosacral area, a sacrococcygeal epidural with 2% lidocaine was performed with the doses recommended in felines by Otero & Portela4 and considering the toxic intravenous dose in cats; 1 mL and 0.7 mL were administered respectively.
Sacrococcygeal epidural was performed to avoid subdural injection because in cats the dural sac extends to the first sacral vertebra.
The epidural space was located by the neurostimulation guided technique that allows to differentiate the position of the needle with an efficiency of 100%. The needle is inserted between S3 and Cd1 until it crosses the yellow ligament, the contraction response of the muscles of the middle and distal thirds of the tail at a current of 0.5 mA (1 Hz and 0.1 ms)5 indicates the correct position of the needle in the epidural space.
The monitored parameters, capnography, electrocardiogram, oxygen saturation and temperature remained stable.
The fluid therapy was maintained with Lactated Ringer between 3-5 mL/kg/h.
30 minutes after the start of anaesthesia, the mean arterial pressure (MAP) dropped to values below 60 mmHg and systolic blood pressure (SBP) to 85 mmHg. Then, fluid therapy was increased to 5 mL/kg/h and FeIso was reduced, but it was not enough, and the MAP decreased to 51 mmHg and the PAS to 79 mmHg, so dopamine was administered to maintain it in values greater than 60 mmHg of PAM and 90 mmHg of PAS.
The anaesthesia time was 1 h 50 min and the final temperature was 36.4 °C.
The parameters monitored, capnography, electrocardiogram, oxygen saturation remained stable.
The fluid therapy was maintained with Lactated Ringer between 3-5 mL/kg/h.
35 minutes after the start of anaesthesia, the MAP dropped to 54 mmHg and the SBP to 73 mmHg. Then, the FeIso was reduced to 0.7%, but it was not enough, and the MAP decreased to 47 mmHg and the PAS to 69 mmHg, so dopamine was administered to normalize the values.
The temperature dropped to 33.7 °C; in this case the procedure was percutaneous and the serum that entered the urine bladder wet the animal. It was kept with electric blanket for small animals and the introduced serum was heated, but it was not enough to maintain normothermia.
The anaesthesia time was 2 h 05 min.
Both cases had mild hypotension that was resolved with continuous infusion of dopamine.
Blood pressure was measured with an HDO oscillometric method that overestimates low blood pressure values and underestimates high and medium diastolic blood pressure values in anesthetized cats6.
The main objectives of the anaesthetic-analgesic protocol that were to produce analgesia for the surgical procedure and to use low % FeIso were met.
The analgesia was adequate since it was not necessary to administer intraoperative analgesics.
FeIso remained at very low levels to avoid the hypotensive effect of isoflurane, since they are long-lasting procedures.
Even though, the two cases presented mild hypotension, which could be caused by the sympathetic block produced by epidural anaesthesia, which was controlled with continuous infusion of dopamine.
In conclusion, we believe that the anaesthetic protocol was adequate to meet the proposed objectives.
The animals had no nociceptive responses to the surgical stimulus and had good recoveries.
Case 2 recovered the temperature by administering hot air and maintaining it with an electric blanket and adequate room temperature.
- Steven M. Fox: Pain Management in Small Animal Medicine. Taylor & Francis Group. 2014; 331
- Tania Duke-Novakovski, Marieke de Vries, Chris Seymour: Manual de anestesia y analgesia en pequeños animales. BSAVA 2017, pàg. 245.
- Clarke K W, Trim C M, Hall L W. Veterinary anesthesia. Saunders Elsevier, 11th edition, págs. 466-468. 2014.
- Pablo E. Otero, Diego A. Portela: Anestesia Regional en animales de compañía: anatomía para bloqueos guiados por ecografía y neuroestimulación. (1ª) Ciudad Autónoma de Buenos Aires, Inter-Médica, 2017 pàg 296
- Pablo E. Otero, Diego A. Portela: Anestesia Regional en animales de compañía: anatomía para bloqueos guiados por ecografía y neuroestimulación. (1ª) Ciudad Autónoma de Buenos Aires, Inter-Médica, 2017 pàg 392
- Mark J. Acierno, Diana Seaton, Mark A.Mitchell, Anderson da Cunha, Agreement between directly measured blood pressure and pressures obtained with three veterinary-specific oscillometric units in cats. Journal of the American Veterinary Medical Association, August 15, 2010, Vol. 237, No. 4, Pages 402-406