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Maintenance with Alfaxan
Following induction, anaesthesia may be maintain with an inhalation agent or for the dog and cat with intravenous Alfaxan 44, 53, 54
Maintenance
Maintenance of anaesthesia following induction with Alfaxan can be achieved through either a transition to an inhalational agent such as isoflurane or sevoflurane, or with the use if intravenous Alfaxan.
Transition to inhalational maintenance
Should only occur only once endotracheal intubation completed and the patient has stable alveolar ventilation (i.e. no apnoea).
Successful maintenance relies on a number of factors including the choice of volatile agent, the breathing system used and the flow rate.
Transition to maintenance with intravenous Alfaxan
Dogs and cats may be maintained under anaesthesia with intravenous Alfaxan following induction. The use of a syringe driver is recommended to administer Alfaxan slowly, however small, regular doses can also be used to maintain anaesthesia if a syringe driver is unavailable.
See below for maintenance dose rates.
Monitoring
Good monitoring is a combination of traditional (relying on one’s senses) and modern monitoring equipment. Multi-parameter monitoring is the ideal but never rely upon equipment alone.
Key considerations for monitoring include: Anaesthetic depth, ventilation, the cardiovascular system and body temperature. 44, 53, 54
Record Keeping
It is important to keep good records of any anaesthetic and specifically designed monitoring charts are ideal for this.
Look out for trends during the anaesthetic as these are more important than one off values. The charts make for easier hand overs and post op planning and allow the whole team to see when other medications were administered and at which dose.
Essential Equipment
Obviously your senses – sight, touch, hearing and smell are essential and you will need a thermometer, a pen and a stethoscope (ideally an oesophageal one).
The Cardiorespiratory System During the Maintenance Phase
It is important to continuously monitor the heart rate and rhythms well as other parameters linked to the CR system:
- Does the patient have an appropriate HR for its age, species and type of premed administered (e.g. α2 agonist)?
- What is the pulse rate and quality? Peripheral pulse is preferred to femoral as it gives a better indication of blood pressure.
- Is the pulse synchronised with the heart beat?
- Are the mucous membranes a healthy colour with an appropriate capillary refill time?
- What is the hydration status? Has blood loss occurred? Is hypovolaemia expected?
- What is the respiratory rate and effort? Is there any apnoea? Does the patient require ventilation? Check the ET tube is not occluded.
Temperature
The ideal range for an animal under anaesthesia is between 36.5°C and 38.5°C for the dog and cat – this should be checked continuously via a probe or every 30 minutes as a minimum. It is important to maintain temperature body temperature to prevent delayed recoveries.
Many drugs given during premedication can affect the thermoregulatory centre and/or cause peripheral vasodilation, as can induction and volatile agents.
Other risk areas include if the patient is in a cold kennel, is wet and / or stationary and following surgery which has required open body cavities.
Capnography
Important part of the monitoring process which measures:
- Cellular metabolism
- Circulation
- Ventilation
- Gaseous exchange
- Equipment issues
- Some possible complications
- ET tube obstruction
- Exhausted soda lime
- Impending cardiac arrest
Blood Pressure
Maintenance of blood pressure ensures adequate renal perfusion and therefore aids homeostasis
Mean Arterial BP gives information on the overall driving blood pressure and tissue perfusion. In cats and dogs maintain MAP at >60mmHg minimum, ideally >80mmHg.
Vasodilation results in hypotension and many of the drugs associated with anaesthesia will cause vasodilation.
Pulse Oximetry
Measures oxygen saturation of haemoglobin. The sensor is placed on depigmented extremities with a pulsatile capillary bed (e.g. tongue, digits) and the pulse rate is displayed.
Aim for oxygen saturation levels of above 90% (Ideally >95%)
Electrocardiogram
Provides information about the electrical activity of the heart, and is often used to determine the cause of arrhythmias. Avoid using ECGs alone with no other monitoring equipment.Other
Check airway pressure gauge on ventilators are set appropriately to avoid barotrauma.
Puppies and kittens are prone to hypoglycaemia. Ensure regular checks of blood glucose are performed and suitable treatment is available should it be required.
Alfaxan Maintenance Dose
Cat Maintenance Dose
| Un-Premedicated | Premedicated |
| Dose for constant rate infusion | |
| 10 – 11 mg/kg/hour | 7 – 8 mg/kg/hour |
| 0.16 – 0.18 mg/kg/min | 0.11 – 0.13 mg/kg/min |
| 0.016 – 0.018 >mL/kg/min | 0.011 – 0.013 mL/kg/min |
| Bolus dose for each 10 minutes maintenance | |
| 1.6 – 1.8 mg/kg | 1.1 – 1.3 mg/kg |
| 0.16 – 0.18 mL/kg | 0.11 – 0.13 mL/kg |
Dog Maintenance Dose
| Un-Premedicated | Premedicated |
| Dose for constant rate infusion | |
| 8 – 9 mg/kg/hour | 6 – 7 mg/kg/hour |
| 0.13 – 0.15 mg/kg/min | 0.10 – 0.12 mg/kg/min |
| 0.013 – 0.015 >mL/kg/min | 0.010 – 0.012 mL/kg/min |
| Bolus dose for each 10 minutes maintenance | |
| 1.3 – 1.5 mg/kg | 1.0 – 1.2 mg/kg |
| 0.13 – 0.15 mL/kg | 0.10 – 0.12 mL/kg |