The first article in the series focused on physiological and age-related changes for small animal geriatric anaesthesia. This second article will focus on an approach to anaesthesia for the geriatric patient.
Chemical restraint in everyday veterinary practice includes both sedation and general anaesthesia. The main difference between sedation and general anaesthesia is the level of consciousness: they are different levels in the spectrum of consciousness. An animal is fully conscious at one end of the spectrum where there is no sedation, and totally unconscious with general anaesthesia. Sedation can vary from mild to moderate to deep. For many veterinary procedures such as radiography and ultrasonography, deep sedation is often requested but doesn’t mean that this is the safest option.
| Sedation is not always safer than general anaesthesia! |
Pre-anaesthetic assessment
The pre-anaesthetic assessment is the first step to building any anaesthetic protocol. Every pre-anaesthetic assessment should include a thorough clinical examination and inspection of the history of the animal. Good communication between different members of the team to verify what procedures need to be performed is important before anaesthesia.
| Communication is key in pre-anaesthetic assessment! |
A thorough history should be obtained, including not only the history of the current problem of the animal but also previous or concurrent disease, any ongoing medications, reactions to any drugs, previous anaesthetic history and if there are reports of behavioural issues.
Following the history gathering, a physical examination should be performed by the person making the anaesthesia plan, even if the primary clinician has already carried one out. If the animal’s exercise tolerance is normal, then a physical exam can include thoracic auscultation, pulse assessment, mucous membrane assessment, capillary refill time, respiratory rate assessment and temperature measurement. If the animal’s exercise tolerance is poor, then it would be preferable to include further cardiopulmonary investigations such as electrocardiography, echocardiography and radiography.
Pre-anaesthetic blood tests in patients over seven years old revealed subclinical disease in almost 30 percent (Joubert, 2007). Suggested minimum blood examination should include packed cell volume (PCV), total protein, albumin, glucose, urea, creatinine, alkaline phosphatase (ALP) and alanine aminotransferase (ALT). Furthermore, if there are “red flags” from clinical examination or clinical history, then that alone can be a reason to perform pre-anaesthetic blood tests.
| Seven years old was used as the “geriatric cut-off age” by Joubert (2007) but most anaesthetists will consider patients geriatric if they are older than 80 percent of their anticipated lifespan. |
Something that should not be forgotten is that older patients usually have increased anxiety. The decreased visual and auditory acuity in combination with chronic pain from osteoarthritis can make these patients more anxious and scared in unfamiliar places. We should approach all patients, but particularly geriatric patients, patiently and gently and consider the use of anxiolytic medications if appropriate. Lower doses of anxiolytic medications are recommended in this age group.
| Handle your older patient gently! |
Premedication
Lower doses of premedication are preferred in geriatric patients as the elimination time is prolonged and older animals can have increased blood–brain barrier permeability, therefore a greater sedative effect may be achieved (Tables 1 and 2). Ideally, we would like to administer drugs with minimal cardiovascular and respiratory side effects. Opioids are commonly chosen with low doses of alpha-2 adrenergic agonists, acepromazine or benzodiazepines where appropriate, dependent on any underlying cardiac pathology. If the animal is having a painful procedure it is better to use a full mu agonist such as methadone instead of butorphanol. Benzodiazepines should not be given as a sole agent as some animals can suffer disinhibition excitement after administration.
Lower doses of premedication are preferred in geriatric patients as the elimination time is prolonged and older animals can have increased blood–brain barrier permeability, therefore a greater sedative effect may be achieved
| Drug | Dose (mg/kg) | Route of administration |
| Dexmedetomidine | 0.0005-0.002 0.005 | IV IM |
| Medetomidine | 0.001-0.003 0.005-0.01 | IV IM |
| Acepromazine | 0.005-0.01 0.01-0.02 | IV IM |
| Butorphanol | 0.2-0.3 | IV or IM |
| Methadone | 0.2-0.3 | IV or IM |
| Morphine | 0.2-0.3 | IV or IM |
| Hydromorphine | 0.05-0.1 | IV or IM |
| Buprenorphine | 0.005-0.02 | IV or IM |
| Midazolam | 0.05-0.2 | IV or IM |
| Diazepam | 0.05-0.2 | IV or IM |
| Drug | Dose (mg/kg) | Route of administration |
| Flumazenil | 0.01-0.03 | IV |
| Naloxone | 0.004-0.04 0.01-0.1 | IV IM |
| Atipamezole | Dogs: Equal volume of solution to that of medetomidine/dexmedetomidine Cats: Half volume of solution to that of medetomidine/dexmedetomidine | IM |
Pre-oxygenation
Geriatric patients should be pre-oxygenated with a face mask for five minutes before induction if that is acceptable to the animal without creating any further stress. Pre-oxygenation increases the alveolar oxygen reserve and can reduce the hypoxaemia that can occur during induction of anaesthesia.
| Pre-oxygenate if it is not stressful for the animal! |
Anaesthetic induction
Before anaesthetic induction, again if it is tolerated by the animal, the anaesthetist should attach the ECG pads and the pressure cuff to the patient.
Both propofol and alfaxalone can be used as induction agents. Regardless of the drug choice, it is important to administer them slowly and to effect starting with a dose of 1mg/kg (propofol) or 0.5mg/kg (alfaxalone). The use of co-induction with midazolam, diazepam, fentanyl or ketamine can be considered but depending on the dose all the above drugs can cause respiratory depression. Benzodiazepines can cause excitement if they are given before the induction agent.
Mask induction should be avoided as it can be stressful for the patient and causes environmental pollution.
| Give all induction drugs slowly and to effect. If there is no clinical indication for one drug over another, then use the one you are most familiar with. |
Maintenance of anaesthesia
Both isoflurane and sevoflurane can be used to maintain anaesthesia without major differences between the agents. The minimum alveolar concentration (MAC) of inhalation agents in older individuals is reduced, therefore the depth of anaesthesia should be monitored carefully and frequently, and the anaesthetist should be prepared to reduce the dialled volatile agent percentage as appropriate.
For many reasons that were explained in more detail in the first article of the series, hypoventilation and hypercapnia are more common in geriatric patients, so support of the respiratory system with the use of mechanical or manual ventilation may be required.
Finally, if there are no contraindications, such as cardiac disease, fluid therapy should be initiated during anaesthesia (usually Hartmann’s solution at a rate of 5ml/kg/h for dogs and 3 to 5ml/kg/h for cats, as suggested by the 2024 American Animal Hospital Association fluid therapy guidelines). If patients do have cardiac disease, then lower fluid therapy rates may be indicated.
Analgesia
Analgesia may be required even for simple procedures such as radiography, because of potential stiffness post-procedure due to osteoarthritis.
A multimodal analgesia approach is preferable. Non-steroidal anti-inflammatory drugs should only be administered if renal function is normal and the patient is normally hydrated and normotensive. Paracetamol can be administered in dogs. Mild to moderate increases in liver isoenzymes do not preclude administration of this drug.
If the animal will need to undergo a surgical procedure then a locoregional anaesthesia technique should be performed to be able to reduce the amount of analgesia drugs and inhalant agent during surgery.
Recovery
Geriatric patients suffer more from emergence delirium than other age groups, which can be explained by senile changes, increased blood–brain barrier permeability and increased anxiety. Therefore, for these patients it would be wise to have a sedation plan prepared in case immediate administration is needed.
Older animals are also usually more reluctant to urinate or defecate in an unfamiliar place and a full bladder can cause discomfort, so the urinary bladder should be emptied before recovery from anaesthesia.
| Empty the bladder before allowing the patient to recover. |
