2. Identify Normal ABG values
Define pH
List main acids and base in the body
Define Acidaemia and Alkalaemia
Discuss acid base regulation
Explore the causes of disturbance
Outline treatments
Objectives
3. Blood Gas Values
pH
Pa02
PC02
BE
ST Bicarb
7.35 – 7.45
10 – 13.5
4.5 – 6.0
-2 - +2
22 - 26
4. p stands for “potenz”, a German word for power or
potency
H stands for Hydrogen
Discovered by a Danish Chemist named Soren Peder
Lauritz Sorensen in 1909 who was studying the
effects of ion concentrations on proteins
pH is a simple way of expressing this concentration
What is pH
6. We are measuring the concentration of H+
A high concentration of H+ will result in a lower pH
A low concentration of H+ will result in a higher pH
pH
7. Acids
Acids are substances that
contain and can
therefore release
hydrogen ions
Hydrochloric acid (HCI)
Carbonic Acid (H2C03)
Lactic Acid (C6H603)
H+ H+
H+
8. Bases
Substances that are able
to combine with H+ ions
(essentially antacids)
The chemical opposite of
an acid
Bicarbonate (HC03-)
HC03-
HC03-
HC03-
9. Proteins within the body rely on a narrow pH range
7.35 - 7.45
Outside of this range proteins begin to lose their structure
and function
In the Body
1 10
14. Standard bicarbonate is the calculated
bicarbonate concentration of the sample corrected to
a pC02 of 5.3kpa
Base Excess is the amount of acid or base/alkali
in mmols required to restore 1 litre of blood to a
normal pH at a pC02 of 5.3kpa
Standard Bicarbonate & Base Excess
15. Carbonic acid-bicarbonate buffer
system can compensate for an excess
or shortage of H+
H20 + C02 H2C03H+ + HC03-
Buffering
16.
17. H2C03 Carbonic Acid is a weak acid and can
donate H+ if there is a shortage
HC03- Bicarbonate is a weak base and can accept
H+ if there is an excess
Remember acid+base = neutral
Buffering
19. Respiration is controlled by the Medulla in the brain
Central Chemo-receptors pick up changes in the concentration
of CO2 and H+ in the blood
High CO2 or H+ will produce deeper more rapid breathing
Low CO2 or H+ will produce slower more shallow breathing
WHY?
Respiratory Regulation
20. Cells in the distal tubules sense pH change
The kidneys secrete H+
Reabsorb Bicarbonate ions
Make new Bicarbonate
Metabolic Regulation
21. 5-step approach
(Resuscitation Council)
1. How is the patient
2. What is the Ph
3. Is the patient hypoxaemic
4. What is the respiratory component
5. What is the metabolic component
22. Maintaining pH
Respiratory
C02 is an acid when
dissolved in blood
C02 is made
throughout the body
C02 is exhausted out of
the lungs
Metabolic
New bicarbonate
(HC03-)can be produced
by the kidney
Bicarbonate (HC03-) can
be reabsorbed by the
kidney
Excretion of H+
23. Respiratory v Metabolic Imbalance
Respiratory pC02
Lungs can only breath
fast or slow
Changes in pC02 are
instant
Metabolic HC03-/H+
HC03- can be used up
slowly or quickly
H+ can be produced
slowly or quickly
Reabsorbing or
replacing HC03- takes
days
25. Treat Cause
Hyperglycaemia give insulin
Dehydration give fluids
Renal Impairment give renal replacement therapy
Shock support blood pressure
Surgery for ischaemic bowel
Treatment for Metabolic Acidosis
30. Respiratory Acidosis
Hypoventilation due to
Respiratory Disease
CNS depression
Circulatory Failure
Neuromuscular disorders
Reduced lung
capacity/thoracic injuries
Respiratory Alkalosis
Hyperventilation due to
Anxiety
Pyrexia
Pain
Over ventilation
Hypoxia
Aspirin overdose
31. Check airway and ensure patent
Ventilate to increase rate and tidal volume
Non-invasive ventilation
Avoid Opiates
Bronchodilators
Drain effusions
Treat infections
Treatment of Respiratory Acidosis
32. Reduce ventilation
Paper bag re-breath CO2
Treat pain and fever
Check for overdose and consider active
charcoal/RRT/IV fluids
Coach patient to reduce anxiety
Treatment of Respiratory Alkalosis
