Acid base regulation Flashcards

1
Q

sO2

A

amount of Hb saturated with O2

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2
Q

FCOHb

A

CO bound to HB

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3
Q

FiO2

A

Fraction of inspired O2

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4
Q

pAtm

A

biometric pressure

normally lefty at sea level

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5
Q

Blood gases values in systemic arteries

A

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

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6
Q

blood gas values in systemic veins

A

PaO2 5.3Kpa
SaO2 75%
PaCO2 6.1Kpa

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7
Q

Compensation

A

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

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8
Q

what occurs to compensate for change in pH

A

acidosis to comp for alkalosis

alkalosis to comp for acidosis

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9
Q

type 1 resp failure

A
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
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10
Q

Type 2 resp failure

A
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
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11
Q

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

A

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

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12
Q

guidelines for PaO2

A

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

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13
Q

what causes acidosis

A

diahorrea

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14
Q

what causes alkalosis

A

vomiting

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15
Q

ABG interpretation procedure

A

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

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16
Q

order of reporting an ABG

A

compensation
aetiology
disturbance
oxygenation

17
Q

normal values for ABG

A
[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
18
Q

Base excess

A

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

19
Q

HCO3- range

A

if out by enough something is wrong

20
Q

standard BE

A

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

21
Q

hyperoxaemia

A

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

22
Q

interpreting AGM

A

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

23
Q

Alkalaemia

A

higher than normal pH in blood

proton conc in blood at a point in time

24
Q

acidaemia

A

lower than normal pH in the blood

proton conc in the blood at a point in time

25
alkalosis
circumstanbces that will decrease [H+] and increase pH | cause CO2 to be cleared and O2 to be used
26
acidosis
circumstances that will increase [H+] and decrease pH
27
what is an acid
any molecule with loosely bound H+ ions (protons) dissociation depends on strength of acid higher conc H+ = lower pH
28
what is a base
anionic | capable of reversibly binding to protons
29
acid and bases in the body
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
30
equilibrium between CO2 and bicarb
H2O + CO2 -- H2CO3 -- HCO3-
31
Pitts and Swann experiment
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
32
converting between [H+] and pH
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)
33
where do acids come from in body
respiratory acids - CO2 metabolic acid - pyruvate, lactic, HCL, septic ratio - resp:met = 100:1
34
Sorensen eqn
pH = -log10[H+]
35
Henderson eqn
to calculate the dissociation constant Ka | Ka = {H+][HCO3-]/[CO2][H2O]
36
Henderson-hasselbach eqn
combination of Henderson and Sorenson eqn | pH = pKa + log[HCO3-]/[CO2]
37
units for [H+] used in eqns
mol/L