Allan Williamson

DVM, MS, Dipl. ACVAA
Dr Williamon
Veterinary Specialist
Anesthesiology
Dr Williamon

At a Glance

Practicing Since:

2013

Board Certified:

ACVAA 2017

Specialties Include:

Anesthesia and Analgesia

My Pets:

Jerry

Dr. Allan Williamson earned his DVM degree from Ontario Veterinary College, following which he stayed on an additional year as a small animal intern. He then completed a combined Master’s of Science and residency program in anaesthesia and analgesia at the Virginia-Maryland College of Veterinary Medicine in Virginia. After spending a year as a clinical instructor at University of Wisconsin-Madison, he returned to Ontario to join the Anaesthesia team at the 404 VERH. He has a special interest in anaesthetic equipment and locoregional anaesthesia.

When not at work he enjoys fencing, cycling and spoiling his cat rotten.

Education
BSc (Hons), McMaster University, Hamilton, ON – (2009)
DVM, Ontario Veterinary College, Guelph, ON – (2013)
MS, Virginia Tech, Blacksburg, VA, USA – (2017)

Advanced Clinical Training
Small Animal Rotating Internship, Ontario Veterinary College, Guelph, ON – (2013-2014)
Residency in Anesthesia and Pain Management, Virginia-Maryland College of Veterinary Medicine – (2014-2017)

Publications:
Oxygen Concentrators

Oxygen Concentrators

Objective: A review of oxygen concentrators, their maintenance and use

Authored by: A. Williamson

Published: Veterinary Anesthetic and Monitoring Equipment. Oct 2018

Isoflurane minimum alveolar concentration sparing effects of fentanyl in the dog

Isoflurane minimum alveolar concentration sparing effects of fentanyl in the dog

Objective: To characterize the isoflurane-sparing effects of a high and a low dose of fentanyl in dogs, and its effects on mean arterial pressure (MAP) and heart rate (HR).

Study design: Prospective, randomized crossover trial.

Animals: Eight healthy male Beagle dogs weighing 12.1 ± 1.6 kg [mean ± standard deviation (SD)] and approximate age 1 year.

Methods: Dogs were anesthetized using isoflurane and minimum alveolar concentration (MAC) was determined in duplicate by the bracketing method using an electrical stimulus on the tarsus. Animals were administered fentanyl: low dose (33 μg kg-1 loading dose, 0.2 μg kg-1 minute-1) or high dose (102 μg kg-1 loading dose, 0.8 μg kg-1 minute-1) and MAC was re-determined (MACISO-F). Blood was collected for analysis of plasma fentanyl concentrations before administration and after MACISO-F determination. All values are presented as mean ± SD.

Results: Isoflurane MAC (MACISO) was 1.30 ± 0.23% in the low dose treatment, which significantly decreased to 0.75 ± 0.22% (average MAC reduction 42.3 ± 9.4%). MACISO was 1.30 ± 0.18% in the high dose treatment, which significantly decreased to 0.30 ± 0.11% (average MAC reduction 76.9 ± 7.4%). Mean fentanyl plasma concentrations were 6.2 and 29.5 ng mL-1 for low and high dose treatments, respectively. MAP increased significantly only in the high dose treatment (from 81 ± 8 to 92 ± 9 mmHg). HR decreased significantly in both treatments from 108 ± 25 to 61 ± 14 beats minute-1 with the low dose and from 95 ± 14 to 42 ± 4 beats minute-1 with the high dose.

Conclusions and clinical relevance: Fentanyl administration resulted in a dose-dependent isoflurane MAC-sparing effect with bradycardia at both doses and an increase in MAP only at high dose. Further evaluation is needed to determine the effects of fentanyl on the overall cardiovascular function.

 

Authored by: Williamson AJ, Soares JHN, Pavlisko ND, McAlister Council-Troche R, Henao-Guerrero N

Published: Vet Anaesth Analg. 2017 Jul;44(4):738-745

Cardiovascular and respiratory effects of two doses of fentanyl in the presence or absence of bradycardia in isoflurane-anesthetized dogs

Cardiovascular and respiratory effects of two doses of fentanyl in the presence or absence of bradycardia in isoflurane-anesthetized dogs

Objective: To compare the cardiopulmonary effects of low and high doses of fentanyl before and after the correction of bradycardia in isoflurane-anesthetized dogs.

Study design: Prospective, randomized crossover trial.

Animals: Eight healthy male Beagle dogs weighing 11.1 ± 1.3 kg [mean ± standard deviation (SD)] and aged approximately 1 year.

Methods: The dogs were anesthetized with isoflurane [1.3 × minimum alveolar concentration (MAC)] on two occasions and fentanyl was administered intravenously; either low-dose fentanyl, loading dose (33 μg kg-1) and infusion (0.2 μg kg-1 minute-1) or a high-dose, loading dose (102 μg kg-1) and infusion (0.8 μg kg-1 minute-1). Cardiopulmonary variables were measured at three time points in equipotent isoflurane concentrations (1.3 MAC): before fentanyl administration (ISO), during fentanyl-induced bradycardia (ISO-F) and after administration of glycopyrrolate normalized heart rate (ISO-FNHR). Data are mean ± SD.

Results: Heart rate and cardiac index (CI) decreased and systemic vascular resistance index (SVRI) increased at ISO-F in both treatments. Bradycardia and vasoconstriction at ISO-F were greater in high than in low-dose fentanyl (42 ± 7 versus 57 ± 15 beats minute-1 and 3457 ± 1108 versus 2528 ± 968 dyne second cm-5 m-2), respectively. Oxygen delivery index (DO2I) decreased only during high-dose fentanyl. CI and DO2I were higher in both treatments at ISO-FNHR than at ISO-F; however, they were higher only during the high-dose fentanyl than at ISO. SVRI was higher at ISO-F than at ISO and ISO-FNHR in both treatments, and was higher at ISO-F in the high than in the low-dose treatment.

Conclusions and clinical relevance: An overall improvement in cardiovascular function of dogs anesthetized with equipotent isoflurane doses (1.3 MAC) was observed after the treatment of bradycardia only with the high-dose fentanyl.

Authored by Williamson AJ, Soares JH, Henao-Guerrero N, Council-Troche RM, Pavlisko ND

Published Vet Anaesth Analg. 2018 Jul;45(4):423-431

The effect of two doses of fentanyl on chest wall rigidity at equipotent doses of isoflurane in dogs

The effect of two doses of fentanyl on chest wall rigidity at equipotent doses of isoflurane in dogs

Objective: To evaluate the effect of two doses of fentanyl upon chest wall rigidity of dogs anesthetized at equipotent doses of isoflurane [1.3 minimum alveolar concentration (MACISO) of each dose of fentanyl].

Study design: Prospective crossover randomized study.

Animals: A group of eight male Beagle dogs, approximately 1 year old and weighing 12.1 ± 1.6 kg (mean ± standard deviation).

Methods: The dogs were anesthetized with isoflurane and instrumented for the measurement of esophageal pressure (PESO), flow (V˙) and volume (V). Chest wall elastance (ECW) was estimated by multiple linear regression of the model. PESO(t) = V˙(t) × RCW + V(t) × ECW + EEPESO where t is time, RCW is chest wall resistance and EEPESO is end-expiratory PESO. Chest wall compliance (CCW) was calculated as 1/ECW and normalized to the body weight of each dog (mL cmH2O-1 kg-1). Anesthesia was maintained at 1.3 MACISO for at least 15 minutes and CCW recorded (CCW-ISO). The dogs were randomly assigned to the lower fentanyl dose [loading dose (33 μg kg-1) and infusion (0.2 μg kg-1 minute-1)] or the higher fentanyl dose [loading dose (102 μg kg-1) and infusion (0.8 μg kg-1 minute-1)]. After 60 minutes of fentanyl infusion, CCW was recorded for each dose (CCW-FENT). During fentanyl infusion, the dogs were maintained at equipotent doses of isoflurane (1.3 MACISO for each fentanyl dose). A two-way analysis of variance followed by a Bonferroni test was used to compare CCW-ISO and CCW-FENT in both treatments and CCW-FENT between treatments. A p value <0.05 was considered significant.

Results: Neither of the fentanyl doses decreased CCW and there was no difference in CCW-FENT between doses.

Conclusions and clinical relevance: Fentanyl at the studied doses did not result in chest wall rigidity in dogs anesthetized with equipotent doses of isoflurane (1.3 MACISO).

Authored by: Soares JH, Henao-Guerrero N, Pavlisko ND, Williamson A, Giannella-Neto A

Published: Vet Anaesth Analg. 2019 May;46(3):360-364

Ultrasound-guided catheterization of the femoral artery in a canine model of acute hemorrhagic shock

Ultrasound-guided catheterization of the femoral artery in a canine model of acute hemorrhagic shock

Objective: To describe a technique for gaining ultrasound-guided access to the femoral artery in an experimental model of acute hemorrhagic shock in anesthetized dogs.

Case series summary: Five healthy, purpose-bred adult male intact Beagles were enrolled in a respiratory mechanics study under general anesthesia. Upon completion of the primary study a hypovolemic state was induced by blood removal to achieve a mean arterial pressure ≤ 55 mm Hg. Dogs were positioned in dorsal recumbency with the hind limb extended caudally. An ultrasound probe was applied to the medial aspect of the hind limb and positioned in the transverse orientation so that the femoral artery was visualized in its short axis. The artery was identified by lack of compression and presence of visible pulsation. The probe was rotated 90° into the longitudinal orientation such that the artery was visualized in its long axis. Under ultrasound guidance a 19-gauge introducer needle was advanced into the lumen of the femoral artery. Using a modified Seldinger technique the needle was removed and a catheter was placed in the femoral artery. Correct placement of the catheter was verified by observation of the characteristic arterial blood pressure waveform. Upon completion of the study dogs were humanely euthanized. The femoral artery was successfully catheterized in 4/5 dogs and a hematoma was reported in 1/5 dogs.

New or unique information provided: Ultrasound-guided femoral artery catheterization is feasible on anesthetized dogs with concurrent acute hemorrhagic shock.

Authored by:  Pavlisko ND, Soares JHN, Henao-Guerrero NP, Williamson AJ

Published: J Vet Emerg Crit Care (San Antonio). 2018 Nov;28(6):579-584
See our departments

Anesthesiology

The Anesthesiology Service at the 404 Veterinary Emergency and Referral Hospital provides comprehensive care for our patients that require surgery or diagnostics under heavy sedation or anesthesia. Our specialized team is dedicated to providing exceptional care before, during and after their procedure. Each patient is carefully evaluated, and their anesthetic protocol is tailored to their specific needs, based on their health conditions, personality, level of pain and many other factors. We do our best to minimize risks and ensure our patients are as comfortable as possible during their hospital stay, using the latest in technology to help monitor and treat them.

Our specialized staff is highly trained, and all sedated or anesthetized cases are overseen by one of our board-certified anesthesiologists, who work alongside each of our departments. We also provide telephone consultation to local general practitioners in dealing with both routine and urgent matters.

 
For more information on the American College of Veterinary Anesthesia and Analgesia, please here.

404 Veterinary Emergency and Referral Hospital

510 Harry Walker Parkway South

Newmarket, ON L3Y 0B3

Main: 905-953-1933

Fax: 905-953-8845

Hospital Hours:

    Mon-Sun: Open 24 hours

Referral Hours:

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