Intraoperative Support and Care Flashcards by Jamie Byrne

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

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In which species is cardiovascular and respiratory depression most marked?

Horses

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What factors influence the extent to which homeostatic mechanisms are Obtunded during anaesthesia?

Depth, drugs used, underlying health status

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What is the hypoxic pulmonary vasoconstriction reflex?

Blood diverted to oxygenated areas of the lungs (cf. all other organs in the body.)

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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

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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) *

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why is urine output an unreliable variable to measure during surgery?

^ADH leads to vUrine output (something to do with drugs?)

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*In which type of surgeries are blood has analyses particularly useful?

Chest surgeries

Equine surgery

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In blood transfusions, why may electrolyte imbalances occur?

Citrate anticoagulant is also transfused - this binds with Ca2+ -> v[Ca2+]

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What is the main aim of anaesthesia? How is this calculated?

Maintain tissue oxygen delivery.

Oxygen delivery = arterial oxygen content x cardiac output

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What basic parameters should you check if experiencing difficulties?

A airway
B breathing
C circulation

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When may respiratory support be required?

Maintain blood oxygen content by avoiding

hypoventilation
hypoxeamia
hypercapnia

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Define hypoxeamia.

Arterial PO2 < 60mmHg

SpO2 < 90%

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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

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Define hypercapnia.

Blood CO2 should be 35-45mmHg

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What may cause hypercapnia?

Hypoventilation
Rebreathing exhaled gas
^BMR
V/Q mismatch(?)

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What does hypercapnia lead to?

Tachycardia
Hypertension
Cardiac arrythmias
Increased intracranial pressure 
CV depression at very high levels 
Respiratory acidosis

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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)

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What is IPPV?

Intermittent positive pressure ventilation

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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

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why is negative thoracic pressure necessary?

Thoracic pump and cardiac output normal function

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What are the negative effects of IPPV?

Intrapleural pressure remains > 0 throughout cycle

Decreased venous return through thoracic pump -> vCO *

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In which scenarios are the negative effects of IPPV worst?

High pressures/long inspiratory times
Hypovoleamia
Heart failure

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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*

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* 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?

1. Attend problems with HR/rhythm 2. 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

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

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?

1. AV block - usually secondary, especially seen with a2 ags (^BP->vHR, baroreceptor response) define cause if possible, give atropine or glycopyrrolate. 2. 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?

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)

Intraoperative Support and Care Flashcards

17.2.14 (67 cards)