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What should we consider when anaesthetising the geriatric patient?

Anaesthesia for the geriatric patient

As our patients live longer we are challenged with undertaking anaesthesia in more geriatric animals. A patient is considered to be geriatric when in the last 25% of their expected life span and they frequently present for anaesthesia with comorbidities that require additional consideration.

Considerations

Alteration in patient anatomy and physiology may affect the pharmacology of drugs administered as part of anaesthesia. Thinking about how these changes may affect anaesthesia allows the clinician to plan a suitable protocol. Anaesthesia should always be planned on an individual basis, and the geriatric patient is no different.

The following important considerations will assist the clinician when planning anaesthesia in the geriatric patient;

  • Reduction in muscle mass, therefore less sites available for intramuscular injection, less support and protection for joints and bony prominences
  • Reduction in body fat, therefore less insulation and reduced protection over bony prominences
  • Organ function
    • Reduced cardiac reserve leads to a reduction in cardiac output. This along with an inability to maintain blood vessel tone and therefore auto regulate blood pressure, results in an increased risk of hypotension.
    • Reduction in the functional residual capacity (FRC) of the lungs, with an increased risk of atelectasis during anaesthesia and postoperative respiratory complications such as inability to maintain oxygen saturation (SpO2).
    • Hepatic metabolism and excretion of drugs may be altered and drug binding may also be changed by hypoproteinaemia. There is a reduced ability to maintain blood glucose levels.
    • Renal blood flow (RBF) reduction may lead to lowered renal clearance and prolong the duration of action of drugs used. Reduced renal capacity may also leave the geriatric patient less able to cope with dehydration and haemorrhage. Fluid therapy planning and lower tolerance for haemorrhage should be factored into the anaesthetic protocol.
    • Age related reduction in central nervous system function may lead to unexpected effects of drugs administered during the peri-anaesthetic period, such as dysphoria and confusion. Minimum alveolar concentration (MAC) of the inhalational agents decreases with age and the depressant effects of other drugs are likely to be increased, leading to complications such as a prolonged recovery and excessive depth of anaesthesia.
  • Temperature regulation is disrupted by drug administration and further impaired by reduced muscle mass, reduced hepatic function and central nervous system function ageing. Prevention and treatment of hypothermia is essential.
  • Comorbidities such as osteoarthritis may compound problems associated with positioning during anaesthesia, gaining IV access and tracheal intubation. Good analgesia is essential to minimise discomfort and may be necessary even if a non-painful procedure, such as diagnostic imaging is planned.
  • Increased stress levels and anxiety on admission to the clinic may increase the risk of dehydration and pain. When appropriate this should be discussed with the client and medication used to minimise stress prior to admission.

Pre-anaesthesia preparation

The ability to detect subclinical disease not evident on physical examination will provide the clinician with additional useful information. Performing pre-anaesthetic blood testing is advised in all dogs over 8 years of age. There is currently no evidence based on the geriatric feline patient but the same may apply in cats over 10 years of age.

If blood work has been performed recently and there is no change in clinical status then PCV, TP and electrolyte measurement prior to anaesthesia may be considered (PCV, TP and electrolyte measurement provides information on hydration status, red cell mass and any electrolyte abnormalities). If a patient presents with previously undocumented disease or a change in health status then repeating full blood work prior to anaesthesia is advisable. Of most importance when interpreting blood work is not to ignore abnormal values.  It may therefore be useful to perform pre-anaesthetic blood testing and any other diagnostics on a day prior to admission to ensure time for appropriate therapy or further diagnostics prior to anaesthesia and to avoid having to delay planned procedures on the day itself.

Fluid therapy

Intravenous fluid therapy during the peri-anaesthetic period aims to maintain intra-vascular volume, hydration status and maintain patency of IV access. Choice and administration rate of fluid therapy may vary depending on the individual and any electrolyte abnormalities, but in most cases Hartmanns solution is an appropriate initial choice. Fluid therapy should be continued post-operatively until the patient is completely recovered, ideally until eating and drinking. This is extremely important in the geriatric patient at increased risk of dehydration.

Protocol selection

Lower doses of sedative and opioid analgesic drugs should be used in premedication so as to allow their effect and duration of action to be assessed. Acepromazine has a relatively long duration of action which maybe further prolonged in the geriatric patient. The alpha-2 agonists may prove useful, if no contraindication is present, as their effect and duration of action is dose dependent and they may be antagonized.  If sedation is necessary then a low dose should be used, which can always be repeated prior to recovery if necessary. Full mu agonist opioids such as methadone are most appropriate for a surgical procedure because they are more easily ‘topped up’ if additional analgesia is required. This is more difficult to achieve with a partial agonist. For non-surgical procedures, an agonist-antagonist such as butorphanol often provides excellent sedation (although poor analgesia), either alone or in combination with a sedative. If a patient is particularly calm then an opioid alone may be sufficient for premedication. Again, a sedative can always be administered into the recovery period if necessary.

Careful consideration should be given to the route of administration of drugs. Reduced muscle mass may make IM injections painful as well as the necessity to reduce the volume that may be safely injected at a single site. Care should be taken to avoid touching the needle against the periosteum, as this may exacerbate pain and lead to haemorrhage. In a patient with significant subcutaneous adipose tissue, poor absorption is likely if the drug remains within fat. Where possible the IV route should be utilised, this will ensure use of minimum effective dosing and make the effect and time to onset more reliable.

Premedication

It is important to allow premedication sufficient time to take effect, even if given by the IV route. The patient should be housed in a calm, quiet area, were possible following premedication and be wrapped in a blanket or if small then placed in an incubator. This will minimise heat loss during this period. It is recognised to be much easier to maintain body temperature, rather than re-warming an already hypothermic patient, particularly important in the geriatric patient with reduced muscle mass. Use of a safety checklist prior to induction of anaesthesia will focus the clinical team on the patient and planned procedure and assist in minimising risk.

Induction of anaesthesia

The drug selected for induction of anaesthesia is probably less important than the method of its use. The induction agent should be administered IV slowly, to effect, enabling tracheal intubation. The respiratory depressant effects of the IV induction agents are dose related and therefore can be minimised if the agent is injected slowly to allow for sufficient circulation time for its full effect. Mask induction of anaesthesia is not recommended.

Maintenance

Similar to induction of anaesthesia, the inhalational agent chosen for the maintenance period is probably less important. More importantly, the appropriate adjustment of vaporiser setting according to depth of anaesthesia, therefore minimising the adverse effects will likely result in the best outcome. The main adverse effects observed with the inhalational agents are respiratory depression and vasodilation, resulting in hypotension, both of which are dose dependent.

Intra-operative analgesia

Good provision of intra-operative analgesia is essential, with the aim to reduce inhalational anaesthesia requirements and therefore adverse effects such as vasodilation and hypoventilation. Options for analgesia during a surgical procedure include local anaesthetic techniques, additional opioids (such as methadone or fentanyl; bolus administration or by infusion) ketamine and lidocaine (recommended in dogs only). As previously mentioned additional analgesia may be required during a non-surgical procedure due to patient conformation and positioning.

Monitoring during anaesthesia

Continuous monitoring of patient status is an important aspect of patient safety during any anaesthetic. The combination of a suitably trained person having direct contact with the patient and the addition of electronic monitoring tools will increase anaesthetic safety and aid to detect any abnormalities before they become a problem.

Fluid therapy

Current recommendations suggest an initial rate of 4-5ml/kg/h (dogs) and 3-4ml/kg/h (cats) in the healthy patient during anaesthesia. This should be modified according to patient requirements. Situations where this requires alteration include, cardiac disease, lung disease, renal disease, dehydration and hypotension during anaesthesia. If fluids need to be restricted due to lung or cardiac disease, particular care should be taken with the hypotensive patient not to overload the circulatory system. Crystalloid fluids are the most commonly used type during anaesthesia, of which Hartmanns solution, a balanced electrolyte solution has the most appropriate properties for use in many situations.

Recovery

The recovery period should be considered just as important as any other part of the process of anaesthesia. Careful monitoring should aim to address the following points:

  • Continuous monitoring until the patient has their trachea extubated and can maintain sternal recumbency
  • Regular monitoring until body temperature is over 37oC
  • The bladder should be checked before the patient regains consciousness and emptied if required. A full bladder is one of many reasons for a rapid recovery from anaesthesia
  • Pain should be assessed on a regular basis and analgesia provided as required. Where pain scoring is not utilised additional analgesia should be provided into the recovery period where necessary to ensure a smooth recovery. This will also help to reduce a rapid awakening from anaesthesia
  • Fluid therapy should be continued at an appropriate rate (depending on any relevant disease) until the patient is fully recovered and eating and drinking
  • Soft, comfortable bedding should be provided to minimise discomfort associated with lying in a kennel
  • Nursing care to ensure the patient is assisted to urinate and defaecate when necessary, e.g. following orthopaedic surgery
  • Consideration should be given to whether any monitoring equipment is required in the initial recovery phase, e.g. a patient with lung disease may benefit from pulse oximetry to ensure adequate oxygen saturation and supplementary inspired oxygen should be administered, e.g. by face mask

Summary

Careful pre-clinical examination, identification of risk factors and consideration of anaesthetic risks will improve safety in the geriatric patient. Good preparation and planning are key to successful anaesthesia in this part of the veterinary population.

Article by
Carl Bradbrook
BVSc CertVA DipECVAA MRCVS

Originally published: Thursday, 20th June 2019

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