Acid base regulation

Question 1

sO2

Answer 1

amount of Hb saturated with O2

Question 2

FCOHb

Answer 2

CO bound to HB

Question 3

FiO2

Answer 3

Fraction of inspired O2

Question 4

pAtm

Answer 4

biometric pressure

normally lefty at sea level

Question 5

Blood gases values in systemic arteries

Answer 5

PaO2 >10
SaO2 >95%
PaCO2 4.7-6.4Kpa

Question 6

blood gas values in systemic veins

Answer 6

PaO2 5.3Kpa
SaO2 75%
PaCO2 6.1Kpa

Question 7

Compensation

Answer 7

ventilation - rapid compensatory response to change in CO2 elimination and therefore pH
vent can comp for metabolic problem
changes in HCO3- and H+ retention/secretion in kidneys - slow comp response to change in pH
kidney can correct lung problem

Question 8

what occurs to compensate for change in pH

Answer 8

acidosis to comp for alkalosis

alkalosis to comp for acidosis

Question 9

type 1 resp failure

Answer 9

failure of pul gas exchange 
V/Q inequality
hypoxic 
O2 into blood impaired
CO2 out - fine because it is more diffusible 
PaO2<8KPa 
PaCO2 - low/normal 
hypoventilation 
diffusion abnormality 
pul oedema 
pneumonia 
atelectasis - collapse or closure of the lung - worse GE

Question 10

Type 2 resp failure

Answer 10

hypercapnic resp failure 
getting gas there problem
V/Q problem 
PaO2<8KPa - low but not really the problem - O2 down greater conc grad so fine 
PaCO2 >6.7KPa 
increased CO2 production 
decreased VCO2 elimination 
decreased CNS drive 
increased work of breathing 
pul fibrosis 
neuromuscular disease 
increased physiological dead space
obesity

Question 11

what can you tell from an arterial blood gas (ABG)

Answer 11

low or high pH
PaCO2
BE excess - assess metabolic component
is the patient hypoxemic

Question 12

guidelines for PaO2

Answer 12

> 10pKa normal
8-10 mild hypoxaemia
6-8 moderate hypoxaemia
<6 severe hypoxaemia

Question 13

what causes acidosis

Answer 13

diahorrea

Question 14

what causes alkalosis

Answer 14

vomiting

Question 15

ABG interpretation procedure

Answer 15

type of disturbance: acidosis/alkalosis/normal
aetiology of imbalance: resp/metabolic/normal
haemostatic comp: uncomp/partially/fully
oxygenation: hypoxaemia/normoxaemia/hyperoxaemia

Question 16

order of reporting an ABG

Answer 16

compensation
aetiology
disturbance
oxygenation

Question 17

normal values for ABG

Answer 17

[Hb] 130-170g/l 
pH 7.35 - 7.45 
pCO2 4.7-6.4Kpa 35-48mmHg 
PO2 >10Kpa/>10mmHg 
HCO3- 22-26mEq/L 
BE -2-+2mmol/L

Question 18

Base excess

Answer 18

bicarbonate measured compared to excreted because of CO2
bicarb and co2 in dynamic eq - should be able to calculate one form the other - how ever much the true value is out from the calculated value is the BE

Question 19

HCO3- range

Answer 19

if out by enough something is wrong

Question 20

standard BE

Answer 20

normal BE for 5g/dL [Hb]
corrective BE assuming specific HB conc
Hb conc and CO2 bound to Hb affect ratio of expected bicarb to actual
only useful in critical care

Question 21

hyperoxaemia

Answer 21

on oxygen
ifd hyperventilate for long time increase conc grad of O2 and CO2 between air in lung and blood
get rid of CO2 = high pH
base actively mops it up so this doesn’t happen

Question 22

interpreting AGM

Answer 22

if co2 match ph - resp problem - if BE normal uncomp - if BE opp to pH - comp
if co2 opp to ph - met problem being comp for by resp
if pH normal - fully comp
if both CO2 and BE match pH it is mixed

Question 23

Alkalaemia

Answer 23

higher than normal pH in blood

proton conc in blood at a point in time

Question 24

acidaemia

Answer 24

lower than normal pH in the blood

proton conc in the blood at a point in time

Question 25

alkalosis

Answer 25

circumstanbces that will decrease [H+] and increase pH | cause CO2 to be cleared and O2 to be used

Question 26

acidosis

Answer 26

circumstances that will increase [H+] and decrease pH

Question 27

what is an acid

Answer 27

any molecule with loosely bound H+ ions (protons) dissociation depends on strength of acid higher conc H+ = lower pH

Question 28

what is a base

Answer 28

anionic | capable of reversibly binding to protons

Question 29

acid and bases in the body

Answer 29

acidity of blood has to be closely monitored - otherwise changes 3D structure of channels, enzymes and hormones bases and conjugate acids are in equilibrium le chatelier's principle - change 1 thing and it causes a change in the other direction to keep the ratio - amount of unbinding and binding changes

Question 30

equilibrium between CO2 and bicarb

Answer 30

H2O + CO2 -- H2CO3 -- HCO3-

Question 31

Pitts and Swann experiment

Answer 31

identified the huge buffering capacity of blood that reacts almost immediately to imbalances dog anethesised - baseline bloods drawn dog injected with 14M acid thought dog would die actually pH only decreased a really small amount proton acceptor mop up extra protons - prevent change in pH

Question 32

converting between [H+] and pH

Answer 32

small value of [H+] inconvenient to use Sorensen scaled data using log10 conversion, add - in front to make value +ve pH = -log10[H+] [H+] = 10(to power -pH)

Question 33

where do acids come from in body

Answer 33

respiratory acids - CO2 metabolic acid - pyruvate, lactic, HCL, septic ratio - resp:met = 100:1

Question 34

Sorensen eqn

Answer 34

pH = -log10[H+]

Question 35

Henderson eqn

Answer 35

to calculate the dissociation constant Ka | Ka = {H+][HCO3-]/[CO2][H2O]

Question 36

Henderson-hasselbach eqn

Answer 36

combination of Henderson and Sorenson eqn | pH = pKa + log[HCO3-]/[CO2]

Question 37

units for [H+] used in eqns

Answer 37

mol/L