Flashcards in Care of the anaesthetised animal and intra-operative support Deck (46):
What are the main side effects associated with anaesthesia?
- CVS and respiratory depression
- Obtunded homeostatic mechanisms (baroreceptor reflex, hypoxic, pulmonary vasoconstriction, thermoregulation)
What physiological variables should be measured? 6
- BP - arterial and CVP
- Haemoglobin oxygen saturation (pulse oximetry)
- Inspired and expired gas concentrations
- Temperature - core and periphery
- Urine - output and S.G.
- Blood (longer surgeries) - haem, biochem, electrolytes, blood gases (arterial and venous)
What does O2 delivery depend on? 2
CO and oxygen content
Arterial PO2 < 60 mmHg or SpO2 <90%
Why may hypoxaemia occur? 6
- decreased FiO2
- V/Q mismatch
- cardiovascular depression
- increased O2 demand (pyrexia, increased BMR)
What is the normal range of CO2?
Why may hypercapnia (increased CO2) occur?
- rebreathing of exhaled gas
- increased BMR
Why is hypercapnia bad? 6
- cardiac arrhythmias
- increased ICP
- CV depression (v. high levels)
- respiratory acidosis.
How can you help hypoxaemia and hypercapnia?
- check anaesthesia depth
- check airway
- increase FiO2
- ensure no CO2 rebreathing
- ventilate with IPPV
- consider using Albuterol (Ventolin) in horses
T/F: intrapleural pressure remains negative throughout the respiratory cycle
True - this negative pressure is necessary for the normal 'thoracic pump' and CO.
What happens to intrapleural pressure during IPPV?
Intrapleural pressure remain about zero throughout the respiratory cycle.
Decreased venous return --> decreased CO (worse with high pressures, long inspiratory time, hypovolaemic animals and HF)
What is the guideline tidal volume with IPPV?
What are the guidlines for IPPV?
Inspiratory: expiratory ration (I:E ratio)
Peak inspiratory pressure (PIP)
Positive end-expiratory pressure (PEEP)
RR = 10-20bpm
I:E ratio = 1:2 - 1:3
ETCO2 = 35-45mmHg
PIP = <5 cmH20
What are the aims of cardiovascular support? 2
maintain tissue perfusion (or at least CO)
What causes reduced CO?
- Extremes of HR and rhythm disturbances
- Poor SV (low preload, poor contractility, high afterload)
At what point should you interfere with bradycardia (SA and equine)?
Causes - bradycardia - 6
- high vagal tone
- electrolyte and acid/base disturbances (esp high K+)
- drugs (potent mu-agonist opioids, a2 agonists)
- response to hypertension (baroreflex)
Tx - bradycardias and bradyarrhythmias
***atropine and glycopyrrolate, both IV)
- check parameters and GA depth
- remember a2 agonists --> bradycardia
- beware increased ICP (head trauma)
At what point should you interfere with tachycardia (SA and equine)? 5
- high circulating catecholamines
Tx - tachycardia and tachyarrhythmias
- check paramenters and GA depth
- rule out/treat underlying cause
What should you do if an AV block develops?
Define cause if possible
Atropine (M-R antagonist) or glycopyrrolate (anti-cholinergic)
How common is it to develop AF with anaesthesia?
Name 2 ventricular arrhythmias
VPCs and VT
Name 2 atrial arrhythmias
AV block and AF
Describe VPCs due to anaesthesia
can occur singly or in runs, or as VT which may be paroxysml.
When do you treat ventricular arrhythmias under GA?
IF HAEMODYNAMICALLY SIGNIFICANT: assess pulse (quality and rate, BP, SpO2, MM colour and CRT).
How would you treat ventricular arrhythmias?
Lidocaine = first choice (2-4mg/kg slow IV bolus in dog/horse, or 0.25-0.75mg/kg IV bolus in cats). THEN FOLLOW with a CRI at 10-100microg/kg/min.
Broadly, how do you treat underlying hypovolaemia/hypotension?
- reduce depth of anaesthesia
- give IV fluids (bolus if necessary)
What is the most common fluid to give during anaesthesia?
Crystalloids (unless it is a v. short procedure) as there is a relative hypovolaemia
Which crystalloid is most commonly given during GA?
Depends on nature of deficit but CSL most common (balanced, v similar to plasma). Common rate is 5ml/kg/hour. May need rapid bolus in an emergency.
When do you give colloids during GA?
If TP < 35g/l or if better intravascular filling is needed.
What fluids can be given during GA?
- plasma (low TP or if clotting factors required)
- Fresh Whole Blood (FWB)
- Packed RBCs (PRBCs)
- Human Serum Albumin (HSA)
What is the blood volume for a dog?
What is the blood volume for a cat?
What fluids do yo give if there is up to 10% blood volume loss?
What fluids do yo give if there is 10-25% blood volume loss?
What fluids do yo give if there is >25% blood volume loss?
What fluids do yo give if PCV < 10g/dL?
Blood or PRBCs
What inotrope is most commonly given to small animals?
What inotrope is most commonly given to equines?
Action - dopamine
Acts selectively on DA-R at low concentrations but at higher concentrations also acts on a1 and B1 receptors (2-10microg/kg/min) --> positive inotropic effect.
Action - dobutamine
Acts mainly on B1-Rs. Effects on A1 and B2 receptors in peripheral vasculature tend to cancel out so overall is positively inotropic with minimal effect on vascular resistance. Only mild chronotropic and less arrhythmogenic than dopamine. Dose 0.5-10microg/kg/min
What effect does hypothermia have on GA? 6
- reduces anaesthetic requirement (5% MAC reduction for every degree lost)
- alters pharmacokinetics and pharmacodynamics --> prolonged recovery
- increased blood loss --> increases clotting times
- shivering increases O2 demand in recovery
- increases surgical wound infection incidence
How can a patient's temperature be supported?
- rebreathing circuits
- heat and moisture exchangers (HMEs)
- warmed fluids
- room temperature
- warm lavage of body/cavities
What is the Cushing reflex?
increased ICP suggesting impending death due to head trauma. 2 main signs are increased BP and bradycardia (baroreflex). Also respiratory changes if not ventilated.