Anaesthetics Flashcards
What is the oxygen cascade?
flow of oxygen from air to mitochondria
as move down from air there is a physiological decrease in PaO2
O2 moves from areas of _____
high partial pressure to low partial pressure - hence pulmonary capillaries have low PaO2 compared to alveoli so it moves across
What is V/Q mismatch?
idea that perfusion and ventilation does not completely match
Define deadspace? What conditions can increase it
areas that are ventilated but not adequately perfused
PE and hypotension
anatomically the mouth, pharynx and large areas are deadspcare
Why do you not give too much oxygen in COPD?
those with COPD have developed over time to only perfuse the areas of lungs that are not diseased, adding O2 can result in increased perfusion to areas that are not well ventilated and result in hypercapnia as the haemoglobin picks up the CO2 there instead as has higher affinity
What is shunt? Causes?
areas that are perfused but not adequately ventilated
alveolar collapse, pneumonia, pulmonary oedema, COPD
What is the oxygen dissociation curve?
sigmoidal curve
binding to O2 to one HB subunit causes a conformational change making other subunits more likely to bind
means O2 collection is maximised in areas of high concentration and easy to offload in areas of low O2
acidosis and temp increase can shift curve to right making O2 more likely to be released (exercising tissues produce heat and lactic acid so need more O2)
Cardiac output =
HR x SV
MAP =
CO x SVR
Conditions that too much O2 can be bad?
COPD / type 2 resp failure
post MI ( new research)
List 4 types of oxygen masks and use?
Nasal cannula - on ward with low O2
Hudson face mask - when in recovery and cannot nose breathe
Venturi - gives targeted fio2 if risk of type 2 respiratory failure
15l/min non rebreather mask - acutely unwell patient
What do you need to do with non-rebreather mask?
occlude valve before putting on and ensure bag filled
What is important to consider with oxygen therapy?
it is very drying, makes it difficult to cough up secretions and damages alveoli and surfactant, need to consider humidification
Define sepsis?
Dysregulated host response to infection
can be considered as patient with signs of infection and NEWS > 5
Fluid requirements for maintenance in adults?
25-30ml/ kg/ day of water
1mmol/kg/day of Na, K, Cl
50-100 g glucose
Paediatric fluid reuquirements?
100mls/kg/day for first 10kg
50mls/kg/day for next 10kg
20mls/kg/ day for remaining weight
Fluid resuscitation?
500mls bolus of crystalloid given over less than 15 minutes
if no response continue giving bolus of 250mls-500mls until given 2000mls, if still no response, need expert help
How many mmol/l of Na and Cl in 0.9% saline?
154
In acid base derangement compensation by the lungs is ____ but by kidneys is ______
compensation by lungs is fast but by kidneys is slow
so if there is HCO3 compensation then this is a chronic condition
What is base excess?
indicates how much acid required to return the blood to a normal ph
so negative = too much acid
positive = too much alkali
normal base excess is -2 to +2
When assessing a patient with COPD - what do you want to know about co2 retention?
is it acute or chronic
check if bicarb is raised - if it is this suggest chronic retention
Why is temperature control in anaesthesia important?
patients autonomic reflexes are blocked by anaesthetic so they cannot shiver etc. and cannot adjust their own temperature. When patients become colder their coagulation is affected making surgery more risky, at even colder temperatures the heart rate will be slowed.
How can you check you are ventilating someone appropriately/ correct placement of airway adjunct?
misting of mask
chest rising and falling
capnography trace
3 common presentations in SHDU? (explain)
nausea and vomiting - need to rule out it is not being caused by a bowel obstruction
post op ileus - could be due to abdominal surgery or opioids or a combination
basal atelectasis - partial collapse of base of lung, usually due to inadequate respiratory effort as do not have enough analgesia
When under anaesthetic what BP is okay? Why?
Anaesthetic drops the BP but generally not too worried about this.
Usually aiming for a systolic around 80. Aim for 90 in older people or those who are normally hypertensive.
You do not need as high a BP with anaesthetic because your kidneys and brain which usually need the higher BP are resting. Having a lower BP also makes surgery easier because there is less bleeding in the surgical field.
Where do you have to be to receive inotropes or vasopressors?
HDU or ICU
What do vasopressors do and what is indication?
They cause vasoconstriction by stimulating vascular smooth muscle contraction. Given to increase MAP.
Often given in cases of shock where patients have not responded to fluids.
MOA of Metaraminol?
alpha agonist
MOA of Noradrenaline?
Alpha agonist
MOA of adrenaline?
Alpha agonist
MOA of vasopressin?
hormone that causes vasoconstriction
MOA of ephedrine?
alpha and beta agonist
MOA of phenylephrine?
alpha agonist
List 6 vasopressors?
metaraminol
noradrenaline
adrenaline
vasopressin
ephedrine
phenylephrine
Adrenaline and noradrenaline need given through?
central venous line as very irritant
What is a central venous line/ catheter?
essentially a large cannula put into a large central vein e.g. internal jugular, subclavian, or femoral
How do you give TPN?
Ideally through a central venous line as very irritant
What is an art line? Indications?
arterial line, catheter/ cannula inserted into an artery - often the radial artery
Continuous blood pressure monitoring.
Continuous mean arterial pressure monitoring.
Frequent arterial blood gas specimens.
Frequent blood sampling for diagnostic testing
What are inotropes?
drugs that increase the contractility of the heart to increase cardiac output and therefore MAP
Inotrope use vs vasopressors?
inotropes and vasopressors will both increase MAP but use depends on why MAP is low, if you have low MAP cause of cardiogenic shock then you want inotropes so heart pumps better, but if you have low MAP cause of vasodilation e.g. septic shock you want vasopressors so that systemic vascular resistance increases
Examples when inotropes are given?
given when cardiac output is low, for example in heart failure, post MI or following heart surgery
Examples of inotropes?
mainly catecholamines
adrenaline
dobutamine
isoprenaline
