assessment of CRS function

Question 1

Where is the ideal location to monitor the function of the CRS

Answer 1

closer to where the blood exits the heart
- the later in the chain, the more it reflects things that have happened along the way

however there are advantages to monitoring lower in the chain
- tells us whether the whole system is working
- but if something has gone wrong does not tell us where

Question 2

what 2 factors can we measure to tell us more about tissue oxygen delivery

Answer 2

• venous oxygen
• tissue perfusion (oxygen consumption)

Question 3

discuss

Question 4

what drives tissue perfusion

Answer 4

mean arterial blood pressure (pushes blood from arteries to arterioles to capillaries)

Question 5

discuss invasive measurement of arterial blood pressure

Answer 5

• direct/invasive blood pressure measurement
• gives real time beat by beat measure
• gives more information from trace
• more accurate
• painful (need to dig through lots of tissue to find deep artery) usually inserted under anaestheisa
• done almost always in equine surgery (submandibular artery)

works by
- inserting a cannula into a peripheral artery
- connect cannula to transducer
- reported as systolic/diastolic (mean)

Question 6

discuss the different methods of non-invasive arterial blood pressure measurements

Answer 6

sphygmomanometry
- cuff inflated and uses stethoscope to listen for when noise is gone, when noise returns (systolic) when noise is at max (diastolic) and sound that you can just barely hear before letting cuff off (diastolic)
oscillometric
- cuff attahced to machine which listens for sys/diastolic/mean
doppler
- only generates one parameter
- U/s waves bounce off moving structures (pulsing blood vessels or moving blood within vessels)
- change in frequency audible (higher frequency = blood closer)

Question 7

what is a central venous pressure, how is it set up and what does it tell you

Answer 7

• CVP measures pressure of blood returning to the right side of the heart
• usually reflects the volume of blood returning (is circulating blood ok)
• works by inserting jugular catheter until almost in cranial vena cava
• length in cm in manometer indicates pressure

Question 8

what does blood oxygen content tell us and how is it assessed

Answer 8

• shows effective lung function
• shows effective ventilation

assessed by mucous membrane colour, pulse oximetry and blood gas analysis

Question 9

discuss how ocygen is transported in the body

Answer 9

• O2 bound to haemoglobin

Question 10

explain how pulse oximetry works and what a pulse ox machine tells you

Answer 10

• uses 2 wavelengths of light to measure oxygenated hemoglobin
• measures pulse rate and strength (audible beep)
• shines infrared light across capillary bed and measures O2 saturation in pulsetile blood

Question 11

what are the pitfalls of pulse oximetry

Answer 11

doesnt tell us about:
- oxygen carrying capacity (how many red cells are there? how much Hb? doesnt pick up anemia)
- assisted oxygenation
- smoke inhalation (carbon monoxide poisioning)

Question 12

what can mucous membrane colour tell us and what is cyanosis

Answer 12

• mm colour gives estimation og oxygen content

cyanosis = blue/cyan colour of mucous membranes (bad!)
- indicates deoxygenated hemoglobin (need 5mg/dl unoxygenated Hb for cyanosis to occur, nomrla animal is 15g/dl)
- HOWEVER if animal is anemic, cyanosis is not a reliable sign of hypoxamia

Question 13

explain why O2 and CO2 transport are integrated

Answer 13

• acidity of the tissues encourages O2 unloading
• release of CO2 in the lungs facilitates O2 uptake
• release of O2 favours CO2 uptake in carbamino machanisms (Hb becomes weaker acid and better buffer)
• Hb acid forms flip flop from one form to another

Question 14

what is the bohr affect

Answer 14

release of CO2 in the lungs facilitates O2 uptake

Question 15

what does a blood gas analysis tell you

Answer 15

• pH
• HCO3
• PaCO2
• PaO2

Question 16

explain the reasons for primary distrubances of pH

Answer 16

• buffers are the immediate first line defence against pH changes
• lungs and kidney also help to maintain pH balance in the long term: resp compensation acts wihtin minutes, renal over hours/days
• for respiratory disturbace the compensatory response will be renal, seen as a change in HCO3
• for metabolic disturbance the responce will be respiratory and renal and you will see a change in PaCO2

Question 17

what is capnogrpahy and why is it important

Answer 17

• in normal circumstances, metabolic rate doesnt alter much so ventilation determines arterial CO2
• arterial CO2 therefore tells us about ventilation
• CO2 is very soluble so the CO2 in the alveolar space is a god approximation of arterial CO2
• CO2 in the exhaled breath can be measured by capnography
• is often the very first thing the change in cardiac arrest/animal stops breathing

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