Courtney Scales DipVN, NCert(Anaesth), RVN – Clinical Specialist (Anaesthesia)

Joel Huey BA (Hons) - Content Editor

Part two - You can read part one here →


Hypothermia:

Hypothermia is a common complication in patients during the anaesthesia period. Patients requiring anaesthesia for dental treatment often have procedures that are long in duration, there is frequent repositing of the patient, and they have a constant stream of cold water running over their mouth during scaling, drilling and rinsing. This often means that the patient recovers from anaesthesia with very wet fur on their head which should be dried prior to recovery. The author prefers using the hairdryer on a warm setting and separating the hair with a slicker brush, taking care not to cause hot spots which may burn the patient and taking care around the eyes with the brush. Using an absorbable barrier such as an incontinence pad with a hole in the middle for the nose and mouth to come through can prevent the patient from getting excessively wet.

Thankfully, as dental procedures are contained to the head, the anaesthetist has complete access to the rest of the patient. Active warming equipment, such as heat mats, can be used while the patient's head is positioned over a drain. Passive warming can be applied to the patient with fabric blankets, foil blankets and by insulating the extremities with baby socks or bubble wrap.

As dental procedures can be long in duration, the dental equipment should be checked prior to its use to ensure everything is in working order e.g., sufficient water supply, air compressing equipment functions. This will avoid any unnecessary troubleshooting while the patient is anaesthetised.

Aim to start patient warming methods from premedication and monitor their temperature through to recovery, while acting on trends.

Pain:

Animals display obvious behaviours when in acute pain such as crying, guarding the painful area or limping. Animals with excruciating chronic dental pain will often suffer in silence, with subtle behaviours such as inappetence, posture change, drooling, becoming head shy and pawing at their face. However, some animals may also be stoic and hide their reaction to pain. Chronic pain and inflammation can negatively impact an animal’s quality of life.

While periodontal disease doesn’t impact the metabolism of anaesthesia drugs, chronic pain and inflammatory states can cause changes in the central or peripheral nervous system, resulting in ‘wind up’ pain. Central sensitisation occurs when the spinal cord is subjected to repeated and uncontrolled painful stimuli causing excitatory neuropeptides, including substance P and glutamate, to be released. These bind to and stimulate the NMDA receptor, causing painful stimuli to be amplified. An NMDA antagonist such as ketamine can be administered to block substance P and glutamate from binding to this receptor. While the patient has altered pain processing, other drugs such as opioids and alpha-2 adrenergic agonists can become ineffective. Inflammation can also impact the effectiveness of local anaesthetic drugs (Snyder and Soukup, 2014), which are discussed below.

Almost all dental procedures that involve anything more than a scale and polish are likely to be painful. The benefits of effective pain management during anaesthesia include the ability to reduce the minimal alveolar concentration (MAC) of inhalant agents, reducing their dose-dependent side effects. If the heart rate, blood pressure and/or respiratory rate increases in response to surgical stimuli during anaesthesia, then additional intraoperative analgesia may be required. In some long dental procedures, the initial analgesic provided in the premedication may require a repeat dose e.g., methadone has a duration of action of 4-8 hours, but some patients may require analgesia from 4 hours (Kerr, 2016). Postoperative pain management promotes a smoother recovery period, patient comfort and welfare.

Multimodal analgesia should be provided when pain is anticipated. An opioid in combination with an NSAID is commonly administered to patients who are having dental procedures:

• Full mu-opioids are ideal analgesics for dental procedures as they can be titrated, are synergistic with sedatives, they have an       antagonist effect at the NMDA receptor and have a faster onset than buprenorphine, a partial mu agonist. Butorphanol is a kappa   agonist and mu antagonist and does not provide adequate analgesia in dental procedures as its effects are short-lived. Because of its lesser efficacy and short duration of action, butorphanol is not recommended as an effective analgesic for dental procedures (Mills, 2016).

• NSAIDs prevent the formation of prostaglandins by targeting the cyclooxygenase enzyme responsible for prostaglandin production.

Constant rate infusions of opioids or NMDA antagonists can be considered. They offer stable and effective analgesia in comparison to IM or IV administration of analgesia as they avoid “peaks and troughs” of drug plasma concentrations.

Adjuvant analgesics such as ketamine, gabapentin and paracetamol can be administered, if suitable. It is important to remember that ketamine preserves the laryngeal and pharyngeal reflexes, so the patient may appear to be swallowing while under anaesthesia.

A multidimensional composite pain scale should be used postoperatively, however, none are validated for dental or oral pain in small animals. The Feline Grimace Scale has been shown to be a reliable tool for pain assessment in cats undergoing dental extractions (Watanabe et al., 2020). If there is any doubt that the patient is experiencing pain, analgesia should be given, and the response assessed.

Locoregional anaesthesia:

Utilising locoregional anaesthesia techniques contributes to a balanced anaesthesia protocol and a multimodal analgesia plan. Local anaesthetic drugs prevent the transmission of painful stimuli from reaching the central nervous system. The use of locoregional anaesthesia improves anaesthetic safety because the MAC is decreased (Grubb and Lobprise, 2020a) and it can result in lower postoperative pain scores compared to patients that do not receive one (Aguiar et al., 2014).

It is important to consider that when local nerve blocks are performed for surgical extraction of teeth, they are less effective in regions of tissue infection (Grubb and Lobprise, 2020b). This is due to local inflammation of the tissue, which changes the tissue pH, reducing the drug's efficacy and effect (Snyder and Soukup, 2014). As some nerves may have multiple branches that are potentially not desensitised, local nerve blocks should not be relied upon as the only analgesia for dental surgery.

Different local anaesthetic drugs can be used depending on practice preference and the needs of the patient. Drugs include lidocaine, bupivacaine, mepivacaine and ropivacaine. While these different drugs have published durations of action, they may have prolonged action when injected in the dental foramen, with bupivacaine being reported to exceed 24 hours in one study (Snyder et al., 2016). Drugs can be added to the local anaesthetic to prolong its duration of action, including buprenorphine and adrenaline (Snyder et al., 2016) (Lanz, 2003).

Doses and toxicity should be considered for all individual local anaesthetics, especially as patients may need multiple nerve blocks in a single treatment. There are recommended volumes of infiltration (Lantz, 2003):

• Cats 0.2–0.25ml per site

• Dogs 0.25, 0.5, or 1ml per site for small, medium and large dogs, respectively

Accurate and detailed knowledge of the neuroanatomy of the oral cavity is necessary when preparing to perform local nerve blocks, especially as some blood vessels run alongside the nerve. Prior to injecting the local anaesthetic drug, the syringe should be aspirated to ensure intravascular injection does not occur. Intravascular injection and nerve damage are common complications with locoregional techniques. Listed below are common nerve blocks that can be performed in dental and oral surgery:

 • Mental nerve block (Figure 1) – This nerve block desensitises the teeth rostral to the mental foramen if the needle is advanced caudally into the canal, which can be difficult to achieve in cats and small dogs, otherwise only the buccal soft tissues and lower lip are desensitised.

 • Mandibular nerve block (Figure 2)– This nerve block desensitises the mandibular teeth rostral to the block and the skin over the lower lip. It can be performed intra- or extraoral.

 • Maxillary nerve block (Figure 3) – This nerve block captures the maxillary nerve before it enters the infraorbital canal and desensitises the upper teeth and lip, nose, maxilla and hard and soft palates. It can be performed intra- or extraoral.

 • Infraorbital nerve block (Figure 4) – this nerve is where the maxillary nerve exits the infraorbital canal. Depositing the local anaesthetic drug at the foramen does not provide dental analgesia as it is a sensory nerve to the nose and upper lip. To desensitise teeth with this block, the needle must be inserted into the infraorbital canal, which may cause nerve damage with poor technique.

When performing an infraorbital nerve block, care should be taken regarding accidental globe penetration in cats and brachycephalic breed of dog, who have a short infraorbital canal. Globe penetration can be avoided by not advancing a needle further than 2–3 mm into the canal and directing the needle ventrally not dorsally towards the globe. Accidental globe penetration can also occur in the intraoral approach to the maxillary nerve block in cats (Perry et al., 2014).

Accident globe penetration in a brachycephalic

When performing a local nerve block, the patient may respond due to the acidic nature of the local anaesthetic, causing an increase in the heart rate, respiratory rate and even patient movement. This can confirm that the drug has been administered to the correct location. However, if the patient does not react, it does not correlate to the local anaesthetic being placed in the wrong location as the patient’s anaesthesia depth may impact this (Snyder and Soukup, 2014).

When administering local anaesthetics through a small gauge needle, administer the volume slowly as exerting pressure at a fast velocity can cause tissue damage (Snyder and Soukup, 2014).

Self-trauma due to inadvertent anaesthesia of the tongue is anecdotally mentioned in the veterinary literature, however, to the author's knowledge, has not been reported or published in scientific journals. This occurs when the local anaesthetic drug is deposited too far medially and caudally when performing a mandibular nerve block (which has 3 branches), and when the lingual and mylohyoid branches of the mandibular nerve are desensitised instead of the inferior alveolar nerve (Milella and Gurney, 2016).

An RVN can perform oral local nerve blocks under the supervision of a veterinary surgeon, however, they are unable to perform dental extractions that require the use of dental instruments.

Recovery:

The postoperative recovery period is a high-risk period; 47% of dogs and 61% of cat fatalities occurred during this time and half of them within the first 3 hours. Respiratory complications were identified as a common cause. The CEPSAF study concluded that greater patient care is needed in the recovery period, and this can easily be managed with continued patient monitoring and observation (Brodbelt, et al., 2008).

Prior to recovery, the oral cavity should be checked with a laryngoscope or other light source to ensure there is no debris that could be aspirated after extubation. It may be beneficial to position the patient with their nose facing down so that any foreign material can drain from the mouth. In dogs, the ETT should be removed once there is a strong swallowing reflex. The ETT can be left partially inflated for extubation as this will pull forward any foreign material that may have accidentally made its way into the airway. In cats, extubation should be performed with the cuff deflated when there is a strong pinna reflex (ear twitch) or if they have a strong palpebral blink.

Cats have a strong laryngeal reflex, causing immediate closure of the glottis and vocal cords. Airway obstruction can occur in cats in the recovery period due to laryngospasm and oedema, and is commonly seen after dental procedures. A laryngospasm is usually self-limiting and can be managed by extending the head and neck forward while providing flow-by oxygen. If there is a sustained laryngospasm causing cyanosis or oxygen saturation of <90%, the patient may need to be re-anaesthetised, and the larynx desensitised again.

Inadequately controlled pain in the recovery period is considered a postoperative complication and must be managed appropriately (Mosing, 2016). Pain scoring with a validated system should be performed every 30 minutes during the recovery period, before and after analgesia is administered (Kata et. al., 2015). When performing a pain score in the recovery period, it is important to factor in if the patient is too sedated to respond appropriately, as sedation does not equal adequate analgesia.

Conclusion:

There are specific considerations for patients undergoing dental procedures that are potentially overlooked as they may be perceived differently from other surgical procedures, such as soft tissue and orthopaedic surgeries.

It is also important to highlight that the benefits of any dental procedures performed under general anaesthesia can be short-lived unless there is effective home care. This can be promoted through RVN-lead dental clinics, providing client education and demonstrations of tooth cleaning. This straightforward and inexpensive nursing care promotes regular veterinary visits, which strengthens the practice bond with the client.

Burtons Veterinary Equipment Key Dental Anaesthesia Products:

Burtons Veterinary Equipment manufacture and provide a large range of dental and anaesthesia equipment with some of the key machines being industry famous. Think VETair dental machines and the Burtons Adaptable anaesthesia machine. Below are just a few of the products that are linked to this article. You can view the complete range here: Anaesthesia Category / Dental Category

The Burtons VETair Classic retains all the key industry leading features of its predecessor the original VETair, but now comes with an in-built oil-free compressor, lowering lifetime maintenance cost by removing the need for oil changes. It has been designed to incorporate the same technology as Burtons large oxygen concentrators, a clever combination of spring-mounted components and delay timer tech softens the inertia of starting and stopping the pump, irradicating the well-known issue of noisy, oil free compressors and leaving you with a gentle and quiet environment for stress-free dental procedures.

The VETair classic still boasts its robust, easy-to-clean Burtons Lifetime stainless steel frame with its three-station control unit for high and low speed hand pieces, as well as a three-way syringe for your water/air/mist. It is also surprisingly compact, with direct connection to your dental scaler thanks to its onboard water supply, concealed internal storage drawer, cable tidy’s and four-way power socket for all your accessories attached. When not in use, the fully mobile unit can be neatly stored under your knee space tub table and secured by its lockable wheels.

Our Low Dead Space Adapters allow a side stream capnography line to be directly attached, reducing apparatus dead space.

Although often required, attachments used between a patient and a breathing system can lengthen the apparatus dead space and contribute to the rebreathing of expired gases, especially when the fresh gas flow is not adequate. Heat and moisture exchangers can also increase this.

Burtons CarbonTech Heat Mats feature a new generation of technology that is specifically designed for even heat distribution. This works by delivering a low contact heat temperature whilst directly transferring the energy necessary for warming the patient, meaning no heat is stored within the blanket and therefore reducing the risk of hot spots and burns. The material used ensures ultimate comfort for the patient, as well as allowing some flexibility in how they are used. The target temperature is reached within just 5 minutes of switching on. These mats are available in two sizes, ideal for operating tables and patient kennels. 

Download this PDF to test your knowledge on dental anaesthesia

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References

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