Intraoperative Support and Care Flashcards
17.2.14
What are the two main forms of side effects associated with anaesthesia? Give examples of the latter.
- Cardiovascular and respiratory depression
2. Obtunded homeostatic mechanisms: baroreceptor reflex, hypoxic pulmonary vasoconstriction, thermal regulation
Define Homeostasis
The ability of an animal to maintain physiological stability in the face of constantly changing environmental factors which may be internal or external
In which species is cardiovascular and respiratory depression most marked?
Horses
What factors influence the extent to which homeostatic mechanisms are Obtunded during anaesthesia?
Depth, drugs used, underlying health status
What is the hypoxic pulmonary vasoconstriction reflex?
Blood diverted to oxygenated areas of the lungs (cf. all other organs in the body.)
Outline three things to be aware of regarding the general care of an anaesthetised animal.
- Positioning - especially thin and arthritic animals. Minimise ischemia to extremities.
- Nursing care - moving the animal carefully etc.
- Eye and tongue moistening
What physiological variables can be measured during anaesthesia?
- breathing: rate, depth, character
- heart: rate and rhythm
- pulse: rate, rhythm, sync with heart beat?
- blood pressure: arterial and central venous
- haemoglobin oxygen saturation (pulse oximetry)
- inspired/expired gas concentrations.
- temperature: core and periphery
- urine output and specific gravity *
- blood: haematology (PCV, Hb, TB, platelets, coag times) biochem, electrolytes, blood gases (arterial and venous) *
- why is urine output an unreliable variable to measure during surgery?
^ADH leads to vUrine output (something to do with drugs?)
*In which type of surgeries are blood has analyses particularly useful?
Chest surgeries
Equine surgery
In blood transfusions, why may electrolyte imbalances occur?
Citrate anticoagulant is also transfused - this binds with Ca2+ -> v[Ca2+]
What is the main aim of anaesthesia? How is this calculated?
Maintain tissue oxygen delivery.
Oxygen delivery = arterial oxygen content x cardiac output
What basic parameters should you check if experiencing difficulties?
A airway
B breathing
C circulation
When may respiratory support be required?
Maintain blood oxygen content by avoiding
- hypoventilation
- hypoxeamia
- hypercapnia
Define hypoxeamia.
Arterial PO2 < 60mmHg
SpO2 < 90%
What may cause hypoxeamia?
vFiO2 Hypoventilation V/Q mismatch CV depression Anaemia (does NOT affect PO2/SpO2, therefore hypoxia NOT hypoxeamia) Increased O2 demand eg. Pyrexia or ^BMR
Define hypercapnia.
Blood CO2 should be 35-45mmHg
What may cause hypercapnia?
Hypoventilation
Rebreathing exhaled gas
^BMR
V/Q mismatch(?)
What does hypercapnia lead to?
Tachycardia Hypertension Cardiac arrythmias Increased intracranial pressure CV depression at very high levels Respiratory acidosis
How can cases of hypercapnia and hypoxeamia be treated?
Check anaesthetic depth isn't too deep Check airway Increase FiO2 if possible Ensure no rebreathing Ventilate using IPPV * Consider using albuterol (Ventolin) in horses (bronchodilator)
What is IPPV?
Intermittent positive pressure ventilation
What causes inspiration and expiration?
INTRAPLEURAL PRESSURE REMAINS NEGATIVE THROUGHOUT THE CYCLE# *
Inspiration: expansion of the thorax generates negative intrapleural pressure
Expiration: intrapleural pressure rises as thorax contracts
- why is negative thoracic pressure necessary?
Thoracic pump and cardiac output normal function
What are the negative effects of IPPV?
Intrapleural pressure remains > 0 throughout cycle
Decreased venous return through thoracic pump -> vCO *
- In which scenarios are the negative effects of IPPV worst?
High pressures/long inspiratory times
Hypovoleamia
Heart failure
What are the guideline values for IPPV?
Tidal volume: 10-15ml/kg
Rate: 10-12 breaths/min
Inspiratory:expiratory ratio (I:E) 1:2 or 1:3
End tidal CO2 35-45mmHg
Peak inspiratory pressure (PIP): <5cmH2O*
- when is PEEP used?
During thoracotomy
To prevent atelectasis
What measure is used in lieu of CO?
Blood pressure
What factors may reduce CO?
Extremes of HR
Disturbance of rhythm
Poor SV: Low preload (poor ventricular filling)/poor myocardial contractility/High after load (high vascular resistance)
What order should CV support be administered?
- Attend problems with HR/rhythm
- Treat underlying hypovoleamia/hypotension
- reduce depth of anaesthesia
- give IV fluids (bolus if necessary)
- inotropes/vasopressors
What effect do most anaesthetic agents have on vascular tone?
Vasodilators
Define bradycardia
SA: <26bpm
Which heart rate irregularity is most common during anaesthesia?
Bradycardia
What may cause bradycardia?
High vagal tone (esp. If pulling something in abdomen)
Electrolyte and acid/base disturbance esp ^K+
Hypothermia -> vBMR
Drugs (opioids - mu ag; a2 ag)
Response to hypertension
Bradyarrythmias
How can bradycardia and bradyarrythmias be treated?
Check monitored parameters and anaesthetic depth
Decrease a2 age as they cause bradycardia
Raised intracranial pressure can be a cause - BEWARE!
Anticholinergics to ^HR
eg. atropine 0.02-0.04mg/kg IV
eg. glycopyrrolate 0.005-0.01mg/kg IV
Define tachycardia
Smallies HR>180
Equine HR>50bpm
Outline causes of tachycardia during anaesthesia.
^catecholamines* hyperthermia (rare) aneamia drugs (sympathomimetics/parasympatholytics) tachyarrhythmias
*What may cause an increase in levels of circulating catecholamines? Which is most common and how may it be rectified?
Pain
Hypoxia, hypercapnia
Hypotension, hypovoleamia - most common eg. due to dehydration, give fluids, as a bolus if necessary
How are tachycardia or tachyarrythmias treated?
Check monitored parameters
Check anaesthetic depth
Rule out/treat underlying cause
What are the two types of SV arrythmias?
- AV block - usually secondary, especially seen with a2 ags (^BP->vHR, baroreceptor response) define cause if possible, give atropine or glycopyrrolate.
- Atrial fibrillation (unusual)
What will be seen on the capnograph if the heart stops?
Decreases due to lack of CO2 to remove.
In what two ways may ventricular arrythmias occur?
Singly or in runs
Ventricular tachycardia - may be paroxysmal
When would ventricular arrhythmias be treated?
Determine cause and treat it (eg. Hypercapnia/hypoxia/electrolyte imbalance)
Treat if heamodynamically significant *
*How can heamodynamic problems during anaesthesia be diagnosed?
Pulse rate and quality
Blood pressure
SpO2, mucous membrane colour and CRT
What are ventricular arrhythmias commonly associated with?
Splenic or liver masses
Which drug is used to treat ventricular arrhythmias? Dosage?
Lidocaine IV
Dog and Horse: 2-4mg/kg slow bolus
Cat: 0.25-0.75mg/kg bolus
Followed by CRI at 10-100microg/kg/min
What type of fluids are commonly given during anaesthesia? Why?
Crystalloid
Relative hypovoleamia
What is the most common crystalloid fluid given during anaesthesia? Why? How is it given and what is the dosage?
CSL (Compound Sodium Lactate)
Because it is ‘balanced’
~5ml/kg/hr
In an emergency - rapid bolus of 5-10ml/kg
When are colloids given?
Total Protein (TP) <35g/l If better intravascular filling is required
What are the 6 types of fluid potentially given during anaesthesia?
CSL Colloids Plasma Fresh Whole Blood Packed Red Blood Cells (PRBC) Human Serum Albumin (HSA)
When would plasma be given?
Same reasons as colloids
If clotting factors are required
What is the average blood volume of a dog? Cat?
Dog: 80-90ml/kg
Cat:60-70ml/kg
What fluids should be given if >10% total blood volume has been lost?
Crystalloid
What fluids should be given if 10-25% total blood volume has been lost?
Colloid
What fluids should be given if >25% total blood volume has been lost?
Blood
When would blood or PRBCs be necessary?
PCV<10g/dl
What are the two most common inotropic drugs used in a) SA and b) Equine anaesthesia?
SA: Dopamine
Eq: Dobutamine
Why is dopamine not used in horses?
Causes tachycardia
What receptors does dopamine act on?
DA receptors at LOW concentration
b1 receptors at MEDIUM concentration
a1 receptors at HIGH concentration
What receptors does dobutamine act on?
Mainly b1
a1 and b1 in peripheral vasculature tend to cancel out -> + inotropic effect, with little effect on vascular resistance
Why may dobutamine be better than dopamine?
Mild chronotropic effects
Less arrythmogenic than dopamine
What dose is dobutamine given at?
0.5-10 microg/kg/min
What are the secondary effects of hypothermia?
Reduced requirement for anaesthetics* Pharmacokinetics and pharmacodynamics of drugs altered -> prolonged recovery ^Clotting time -> ^blood loss Shivering -> ^O2 demand in recovery Risk of surgical wound infections Unpleasant!
*How much is MAC reduced for every degree C reduction in body temperature?
5%
How may hypothermia be prevented during anaesthesia?
Rebreathing circuits Heat and moisture exchangers (HMEs) Warm IV fluids Bubble wrap/foil blankets/leg wraps/heated water blankets/warm air blowers Warm room Warm lavage of body cavities
What is the Cushing reflex?
Hypertensive
Bradycardic
Breathing changes if not ventilated
Indicative of impending DEATH - attempt to maintain perfusion.
Due to medullary compression with increased intracranial pressure (due to mass in head etc.)
What can increased ICP (Intracranial Pressure) cause?
Cushing reflex - Bradycardia with hypertension, and respiratory changes if not ventilated.
How can increased ICP be treated?
Hyperventilate as an emergency measure
Mannitol - osmotic effects reduce blood viscosity, improving flow and O2 delivery, and also remove fluid from brain tissue
Hypertonic saline
Furosemide (~synergistic with mannitol)