Intervertebral disk disease (IVDD) is a very common disorder and it’s probable that you’ll be responsible for the anesthesia for an affected patient during your technical career. Knowing how to better induce, position, and recover patients with disk disease is important to reduce worsening of their condition. For the purposes of this article, we will focus on Hansen’s type I and type II disk disease. Understanding the etiology of these specific conditions will allow for improved anesthetic management and patient outcome.
The intervertebral disk is made up the annulus and the nucleus pulposus. The annulus is a multi-layered ligament made up of collagen layers. The nucleus pulposus is the highly hydrated central portion of the disk. Degenerative changes cause both annulus and nucleus to become less hydrated. The weakened annulus becomes prone to bulges or tears. In Hansen’s type I, the annulus tears and the nucleus ruptures in to the spinal cord. In Hansen’s type II, the annulus bulges up into the spinal cord but does not tear. Hansen’s type I is commonly found in younger animals (ages 2-6 years). Breeds such as Dachshunds, Basset hounds, French bulldogs, Pekingese, and Beagles are at high risk of disk degeneration by the age of 9 months with clinical signs appearing by the age of 3. Hansen’s type II disk is usually found in older pets ages 8-10 with breeds such as German Shepherds and Labrador Retrievers being most common. Regardless of the type of IVDD, as the disk dehydrates, it becomes less able to absorb everyday concussive forces. Additional pressure added to the spine may result in worsening of disc disease. Clinical signs of IVDD include pain, limb weakness, ataxia, and paralysis.
Now that we know a little about IVDD, we can use that to properly sedate and anesthetize these patients for their ultimate safety and comfort. The main goal during anesthesia is to prevent further injury to the spine. This can be achieved by proper handling and maintaining spinal cord perfusion. Premedication will usually include an opioid for pain management, plus or minus agents with sedative or anxiolytic properties. IM injections can be painful, can provoke agitation and are best avoided in pets with spinal disease.
During induction, it is best to use IV rapid induction techniques to avoid struggling. Using an opioid, such as fentanyl, along with a benzodiazepine will help to decrease the amount of induction agent used and help preserve cardiac function. Intubation of dogs with cervical injuries can be done in lateral recumbency to avoid over flexion or over extension of the neck. A laryngoscope should be used for visualization of the larynx which will avoid unnecessary trauma or intubation into the esophagus. During maintenance of anesthesia, intermittent positive pressure ventilation (IPPV) is recommended to ensure normal C02 levels as surgical position and anesthetics can cause respiratory depression. In patients with known cervical disk disease, make sure their head and neck are in a neutral position. This can be done by adding towels or pillows under their head. In patients with thoracolumbar disk disease, avoid any curving or twisting of the spine if possible.
Monitoring should include ECG, blood pressure measurement, temperature, capnography, and pulse oximetry. Multi-modal analgesia will help reduce the amount of inhalant needed and help support appropriate blood pressure. We recommend intraoperative CRI’s with opioids (fentanyl or hydromorphone), ketamine, and lidocaine. Intravenous fluids help to maintain proper profusion and help replace volume in cases of hypovolemia. Temperature monitoring is important to maintain proper tissue perfusion, metabolic stasis, and brain function. Warming can be provided in a variety of ways. We recommend circulating warm air, fluid line warmers, and warm water blankets.
During recovery of the patient, it is important to continue the administration of analgesics to provide a calm and controlled recovery from anesthesia. In some cases, microdoses of dexmedetomidine may be needed for patients that are anxious or stressed. Minimizing struggling and or dysphoria is important as twists and curves in the spine can lead to worsening disk disease. Keeping the kennel well-padded for the patient is important for patient comfort. Use of a no-slip mat can also provide comfort and decrease the risk of a slip injury. Avoid the use of collars and/or neck leads when possible; a harness is best for patients affected with disk disease.
As a veterinary technician our patient’s comfort is our main goal. Whether sedating for imaging, anesthetizing for a surgical procedure or providing postoperative patient care, knowledge of basic nursing techniques for dogs with disk disease will help us in our day to day practice and ensure that our patients are well cared for.