Acid Base balance & arterial blood gas

Question 1

pH< 7.35
pH > 7.45
pH between 7.35 nd 7.45?

Answer 1

1) acidosis
2) alkalosis
3) this is either normal or has a mixed acid base balance.

Question 2

what are the buffer for acid base balance?

Answer 2

• proteins
• haemoglobin
• carbonic acid/bicarbonate

Question 3

where will acid/ alkali be excreted from?

Answer 3

lungs
kidneys

Question 4

what are the normal values of ABG?
pH
pO2
pCO2
bicarbonate

Answer 4

pH= 7.35-7.45

pO2= 12-13 kPa

pCO2 = 4.5- 5.6 kPa

bicarbonate = 22-26 mol/l

Question 5

when will acid base disturbances occur?

Answer 5

when…

• there is a problem with ventilation
• there is a problem with renal function
• overwhelming acid or base load the body can’t handle.

Question 6

step 1 interpretation of ABG results

Answer 6

assess the oxygenation (look at pO2)

Question 7

if someone is hypoxic and has a very low RR, what is most likely going on?

Answer 7

this would suggest that they have chronic cyanosis which means the body has become used to this increased firing.

Question 8

what are the different ways to measure oxygenation?

Answer 8

pulse oximetry

Question 9

what if there if a low pO2, what may there be a problem with?

Answer 9

There may be a problem with:
- getting oxygen into the lungs
- oxygen getting into the blood
- oxygenation of tissues.

Question 10

high pO2, what can this cause?

Answer 10

• retinal damage
• mucus membrane damage
• alveoli collapse

Question 11

what are the adverse effects of high oxygen levels?

Answer 11

• increased risk of hypercapnic respiratory failure in acute exacerbations of COPD
• increased mortality survivors of cardiac arrest
• increased mortality in intensive care patients
• increased mortality in acute severe asthma.

Question 12

why are high oxygen levels bad?

Answer 12

• generate free radicles
• collapse of alveoli due to atelectasis
• irritation to mucus membranes
  …. leads to ocular toxicity, myocardial damage, neuro damage etc …

Question 13

what is the British thoracic society guidelines?

Answer 13

• oxygen is a treatment for hypoxia not dyspnoea alone.
• in an unstable medical emergency give high conc of oxygen then titrate to target once stable.
• target 94-96% normally
• 88-92% for type 2 respiratory failure.

Question 14

step 2 interpretation of ABG results?

Answer 14

assess the PH

pH< 7.35 is acidosis
ph> 7.45 is alkalosis

pH between 7.35 and 7.45 = normal or mixed acid base abnormality

Question 15

acidosis ?

alkalosis?

Answer 15

acidosis= too much pco2 and you cannot get rid of it.

alkalosis= too little pCO2.

Question 16

step 3 interoperation of ABG?

Answer 16

what appears to be the cause for the acidosis/ alkalosis?

Question 17

if the ph is low:

what would a respiratory cause for the acidosis look like in the ABG?

what might a metabolic cause for this acidosis look like in the ABG?

Question 18

step 4 in interoperation of ABG?

Answer 18

is there compensation seeming to occur?

remember we said that the body will always try to maintain pH between 7.35-7.45. Compensation is altering of function of the respiratory or renal system in an attempt to correct an acid - base imbalance

Question 19

if the pH is low because of a respiratory cause, how might the body compensate?

if the pH is high because of a respiratory cause, how might the body compensate?

if the pH is low because of a metabolic cause, how might the body compensate?

Question 20

how do you know if compensation is occurring?

Answer 20

if pCO2 and HCO3- is moving in the same direction, compensation is possibly occurring.

• if both values move in opposite directions, more than 1 pathology must be present.

Question 21

in a patient with COPD, why would you expect them to have a high pCO2?

Answer 21

because they have an obstructive disease, they can’t actually respire enough to release the CO2.

Question 22

what drug is given to reverse opioid overdose?

Answer 22

naloxone

Question 23

what happens in chronic respiratory alkalosis?

Answer 23

in chronic respiratory acidosis, the kidneys compensate by retaining bicarbonate. this takes a few days to reach its maximal value.

Question 24

what would the values for acute and chronic respiratory acidosis?

Answer 24

acute:

pH= 7.20
pO2= 28.7kPa
pCO2= 11 kPa
HCO3- = 25 mmol/l

chronic:
pH = 7.32
pO2= 6.0 kPa
pCO2= 10.6 kPa
HCO3- = 37 mmol/l

Question 25

what are causes of hyperventilation?

Answer 25

• acute severe asthma
• pulmonary embolism
• pulmonary oedema
• anxiety attack

Question 26

what things cause an abnormal level of central respiratory drive?

Answer 26

• hypoxia
• direct stimulation of respiratory centre
• psychogenic

Question 26

chronic respiratory alkalosis- high altitude?

what happens?
is there compensation?

Answer 26

• hyperaemia Is induced, hyperventilation is prominent.
• compensation occurs by renal excretion of bicarbonate.

Question 27

kussmal breathing?

Answer 27

rapid deep breathing at a consistent pace.

Question 28

diabetic ketoacidosis?

Answer 28

hyperventilation to blow out increased CO2.

Question 29

WHAT DOES IT SHOW IF THERES A LOW BICARBONATE?

Answer 29

compensation for the increased CO2.