Presenter: Becky Robinson BVSc MVetMed DipECVAA FHEA MRCVS RCVS Recognised Specialist in Veterinary Anaesthesia
Fluid therapy is a subject area where I spend a lot of time clutching my head, never quite knowing which text book I should take heed of when trying to work out the correct fluid therapy for my sick patient. With the apparent limitless and sometimes contradictory advice dispensed on this topic it can at times just seem easier to assume ‘a one fit fixes all solution’ which in my case would mean administering Hartmann’s at twice maintenance.
This of course works well in many cases but last week’s webinar led by Becky Robinson emphasised the importance of not viewing fluid therapy as a benign process and understanding there can be serious consequences if each individual case is not considered carefully. As Becky stated ‘fluid therapy is a pharmacological intervention and should be treated and monitored as one’.
Becky did however acknowledge that there are a large number of different fluid types available to us, and can completely understand why many vets would like a ‘complete idiot’s’ guide to the use of fluids which offers a simple and intelligent approach without compromising patient care. This is exactly what was on offer within Becky’s webinar, which at first detailed the physiological aspects of fluids therapy and the main types of fluids available to vets which included isotonic, hypotonic and hypertonic crystalloids as well as synthetic, semisynthetic and natural colloids.
General rules for fluid therapy were then outlined by Becky who advised always replacing like with like, always replacing volume for volume and always replacing at a similar rate at which the fluid was lost. ‘Replacing like with like’ was the first of Becky’s rules and she offered a number of examples of the types of fluids which could potentially be lost. For example, whole blood is lost through haemorrhage, extra cellular fluid can be lost through conditions such as diarrhoea and diuresis, protein rich extracellular fluid can be lost through pleural effusions and protein losing conditions and finally pure water can be lost through primary water deprivation or an elevated respiratory rate.
I am pleased to say Becky advised that the use of Hartmann’s solution is one of the most appropriate balanced extracellular fluid replacer which is why my fall back option of utilising Hartmann’s has usually been effective. There are however exceptions where Hartmann’s is not always the most appropriate choice and these include patients with persistent vomiting, hypernatraemia, cerebral oedema, severe hypovolaemia and hypoproteinaemia. Becky outlined other types of fluids available for these conditions and why each fluid type would be appropriate in each case.
The volume of fluid delivered should always be based on supplying a patient’s daily needs, replacing ongoing losses and ensuring all fluid deficits are replaced. There are now some much debated figures for maintenance values in the dog and cat which currently stand at 2-3mls/kg/hr in the cat and 2-6mls/kg/hr in the dog with larger dogs being at the lower end of this requirement and smaller dogs and neonates being at the higher end. Anaesthetic fluid rates were also discussed within this webinar and Becky explained that the traditional anaesthetic rate of 10mg/kg/hr has now been disputed with studies demonstrating that either too high or too low a fluid rate during anaesthesia can lead to a high number of complications. A recent review now suggests more appropriate rates of around 3ml/kg/hr in the cat and 5ml/kg/hr in the dog. Becky also discussed administering rapid IV boluses of isotonic crystalloids for hypovolaemic patients at a rate of 10-20mls/kg. Colloids or hypertonic saline can also be used at rates of 2-5ml/kg or 4-7 ml/kg respectively in the dog.
Becky ended this webinar by discussing the importance of monitoring all patients being administered fluid therapy. Regular assessments should be performed by checking heart rate and respiratory rate, checking PCV, total solids and lactate and finally measuring urine output which should be 1-2mls/kg/hr. This level of monitoring is essential in order to prevent any potential side effects such as pulmonary oedema from developing. It also acts to remind us that fluid therapy is a pharmacological intervention, and last week’s webinar offers a fresh look at how, why and when we should be administering fluid therapy to our patients, and perhaps even more importantly, when to stop.
The Stethoscope (MRCVS)