Anaesthetic respiratory physiology.

Question 1

Overall what is the respiratory control in Shippeys drawing?

Answer 1

peripheral chemorecetors in the carotid body (CNIX)
and aortic arch (thoraco) respond to O2, CO2 and H+ (mostly CO2).
central chemo receptors on the medulla respond to H+.

Phrenic nerve works the diaphragm, intercostal nerves do the intercostals.

J receptors sense over stretching in the lung.(hearing Breuer).

Question 2

When thinking about Shippeys picture of the O2 dissociation curve, what way is an easier way of thinking about the two axis?

Answer 2

The bottom - Kpa axis is like the force driving O2.

The vertical, saturation axis is O2 loading.

Question 3

Why is Shippeys picture of the O2 dissociation curve sigmoidal?

Answer 3

due to allosteric binding. The first O2 is the hardest to add to Hb, the second is easier, the third easier and the fourth a bit harder.

This can be seen if we start from the 0 point of the axis and work our way up.

Question 4

What does the Bohr effect shift Shippeys picture of the O2 dissociation curve to the right?

Answer 4

It means that O2 will be offloaded more easily to tissues at the same Kpa. This is useful when tissues are working, which is what shift the curve i.e. increased temp, CO2 etc.

Question 5

Why is 75 important Shippeys picture of the O2 dissociation curve?

Answer 5

This is generally how saturated blood is by the time it returns to the heart i.e. venous saturation.

Question 6

Why does the foetal line on Shippeys picture of the O2 dissociation curve shift to the left?

Answer 6

It means that for the same O2 pressure, more O2 will be offloaded to foetal Hb from mums.

Question 7

What is a physiologicall shunt?

Answer 7

results when the alveoli of the lungs are perfused with blood as normal, but ventilation (the supply of air) fails to supply the perfused region

Question 8

In Shippeys drawing, where is there more ventilation in the lungs?

Answer 8

zone 1 at the top.

Question 9

In Shippeys drawing where is there more perfusion in the lungs?

Answer 9

Zone 3 at the bases.

Question 10

What is the VQ in lung zone 1 in Shippeys drawing?

Answer 10

V:q

Question 11

What is the VQ in lung zone 2 in Shippeys drawing?

Answer 11

V:Q

Question 12

What is the VQ in lung zone 3 in Shippeys drawing?

Answer 12

v:Q

Question 13

What is the state of the blood at lung zone 1 due to V:q in Shippeys drawing?

Answer 13

hypercapnia

Question 14

What is the state of the blood at lung zone 3 due to v:Q in Shippeys drawing?

What do we call this?

Answer 14

hypoxaemia

Shunt

Question 15

On Shippeys drawing, what is the normal saturation when blood leaves the heart, compared to when it returns?

Answer 15

falls from 97 to 75%.

Question 16

In Shippeys drawing, what are the factors that effect how much O2 is delivered to the tissues?

Answer 16

CO x Hb x Sp02 (plus a little dissolved O2 - but we can ignore that).

Question 17

In Shippeys drawing, what can we do as junior doctors to increase the O2 being delivered to tissues by the equation - CO x Hb x Sp02?

Answer 17

CO - give fluids etc.
Hb - transfusion
SPO2 - give O2

Question 18

What are the different types of tissue hypoxia in Shippeys drawing?

Answer 18

hypoxic - not enough O2)
Anaemic - not enough Hb.
Stagnant - no blood moving - less CO
Cytotoxic - cyanide poisoning - Hb can’t pick up O2.