2. Objectives
At the end of this presentation the learner will be able
to:
Define ABGs
Introduction of ABGs and buffer system
Difference between respiratory and metabolic acidosis
and alkalosis
Describe interpretation briefly
Enumerate the techniques of laboratory sample and
trial error
3. Acid base disturbance
Plasma pH
Acidosis / Alkalosis
Introduction to ABGs
Indications of ABGs
ABGs sampling
ABGs intrepretation
4. Arterial Blood Gases
Definition:
Arterial blood gases (ABG’s)
is a collective term applied to three separate
measurements PH, PCO2 and PO2 generally made
together to evaluate acid-base status, ventilation and
arterial oxygenation
5. Introduction of ABG
An arterial blood gas (ABG) is a blood test that
measures oxygen and carbon dioxide levels in
your blood. It also measures your body’s acid-base
(pH) level, which is normally balanced when you are
healthy.
is a common investigation in emergency
departments and intensive care units for monitoring
patients with acute respiratory failure
6. Significance of ABGs
To document respiratory failure and assess its
severity
To monitor patients on ventilators and assist in
weaning
To assess acid base imbalance in critical illness
To assess response to therapeutic interventions and
mechanical ventilation
To assess pre-op patients
7. Indications for arterial blood
sampling/analysis
•Collapse of unknown cause
•Respiratory distress — hypoxia
•Titration of artificial ventilation
•Altered level of consciousness
•Poisons/toxin ingestion
•Metabolic disorders — diabetic ketoacidosis
•Trauma — management of raised intracranial
Pressure
•Shocked patient — sepsis, cardiogenic
•Evaluation of intervention – fluid resuscitation
•Inotropic therapy
8. Arterial blood gas test
results may show whether:
Your lungs are getting enough oxygen
Your lungs are removing enough carbon dioxide
Your kidneys are working properly
The results show if the patient is acidaemic or
alkalemic and whether the cause is likely to have a
respiratory or metabolic component.
9. Normal values of ABGs
PH(power of
hydrogen ions)
7.35 - 7.45
PCO2(partial pressure
of carbon dioxide)
35 – 45 mm Hg
PO2(partial pressure of
oxygen)
80 – 100 mm Hg
HCO3(bicarbonates) 22 – 28 mEq/L
O2 saturtion 95-100%
12. PH
To quantify the H+ concentration in blood, a
simplified mathematical expression, called pH, is
used. In health, the normal range for pH is 7.35–7.45
(Box 2). PH is a negative logarithm, which means that
the higher the H+ concentration, the lower the pH
and vice versa
When the lungs and kidneys are working together,
they are able to maintain the pH of the blood within
its narrow range of 7.35–7.45
13.
14. What is Plasma pH?
Plasma pH is an indicator of hydrogen H(ion)
concentration and measures the acidity and
alkalinity of blood.
Homeostatic mechanisms keep pH within normal
range.(7.35-7.45)
These mechanism consist of Buffer system the
KIDNEY the LUNGS.
↑ H(ion) ↓pH and the solution becomes Acidic.
↓H(ion) ↑pH and the solution become alkaline.
15. Relationship between pH and H+
Equivalent values of pH and H+
pH [H+]
(nanomoles/l) pH [H+]
(nanomoles/l)
6.8 158 7.4 40
6.9 125 7.5 31
7.0 100 7.6 25
7.1 79 7.7 20
7.2 63 7.8 15
7.3 50
16. Buffer system
Buffer system prevent major changes in the pH of the
body fluid by removing or releasing hydrogen ion.
Hydrogen ions are buffered by both intracellular and
extracellular buffers.
Major extracellular buffer system is BICARBONATE
CARBONIC ACID buffer system which is assessed
when arterial blood gas are measured.
Normally there are 20 parts of bicarbonate (HCO3) to 1
part of carbonic acid(H2CO3).
If ratio is altered pH will be change.
17. Cont…..
Less important buffer in ECF include the inorganic
phosphates and plasma proteins.
INTERACELLULAR BUFFERS include organic and
inorganic phosphates RBCs and Hb.
Kidney regulates bicarbonate level in the ECF and can
regenerate bicarbonate ions as well as reabsorbs them
from the renal tubular cells.
In respiratory acidosis and most cases of metabolic
acidosis the kidney excrete hydrogen ion and conserve
bicarbonate ions to help restore balance.
The kidney is unable to compensate metabolic acidosis
created by renal failure.
18. Cont…..
The LUNGS under the control of Medulla control
the carbon dioxide and thus the carbonic acid
content of the ECF.
They do so by adjusting ventilation in response to
the amount of CO2 in the blood.
A rise in partial pressure of CO2 in arterial blood is
a powerful stimulant to respiration.
19. Acid Base Disturbances
Acid base disturbances are commonly encountered in
clinical practice especially in critical care units
identification of specific acid base imbalance is
important in as certaining the underlying cause of the
disorder and determining appropriate treatment.
20. Types Of Acid Base Disturbance
There are two main types of acid base disturbance.
Acidosis:
A distinctly abnormal condition resulting from the
accumulation of acid or from the depletion of alkaline
reserves. In acidosis, the pH of the blood is abnormally
low.
Alkalosis:
An abnormal condition resulting from the
accumulation of base or the depletion of acid.The pH of
an alkalotic body measures above normal.
21. Acute and Chronic Metabolic Acidosis
Metabolic acidosis is a common clinical
disturbance characterized by a low pH(↑ H ion)
and low plasma bicarbonate concentration. It is
due to gain of hydrogen ion and loss of
bicarbonate.
22. Pathophysiology
Anion gap acidosis results from direct loss of
bicarbonate, (Diarrhea, lower intestinal fistulas,
ureters ostomies, renal insufficiency, excessive
administration of chloride and the administration of
TPNs without bicarbonate.
It results from the excessive accumulation of fixed
acid. If increased 30mEq/L or more, then a high anion
gap metabolic acidosis is present regardless of the
values of pH and bicarbonate ions.
24. Medical management
Administration of sodium bicarbonate I.V. for severe
cases
Evaluation and correction of electrolyte imbalances
and ultimately correction and management of the
underlying cause.
25. Nursing management
Keep sodium bicarbonate ampules handy for emergency
administration.
Monitor vital signs, laboratory results and level of consciousness
frequently.
Watch out for signs of decreasing level of consciousness.
Record intake and output accurately to monitor renal function.
For management of vomiting (common to metabolic acidosis),
position the patient to prevent aspiration.
Prepare for possible seizures and administer appropriate
precautions.
Provide good oral hygiene after incidences of vomiting. Use
sodium bicarbonate washes to neutralize acid in the patient’s
mouth.
26. Acute and chronic Metabolic Alkalosis
Metabolic alkalosis is clinical disturbance
characterized by a high pH and high plasma
bicarbonate concentration. It can be produced by gain
of bicarbonate or a loss of hydrogen ion.
27. Pathophysiology
The common cause of metabolic alkalosis is vomiting
or gastric suction with loss of hydrogen and chloride
ions.
Other situation predisposing to metabolic alkalosis
include those associated with the loss of potassium
such as diuretic therapy that promote excretion of
potassium and the ACTH secretion.
28. Medical Management
Electrolyte replacement
Treat underlying cause
A chloride containing solution e.g saline(chloride
Responsive)
Aldosterone antagonist ( Chloride resistant)
30. Nursing management
Dilute potassium when giving via I.V. containing
potassium salts. Monitor the infusion rate to prevent
damage and watch out for signs of phlebitis.
Watch for signs of muscle weakness, tetany or
decreased activity.
Monitor vital signs frequently and record intake and
output to evaluate respiratory, fluid and electrolyte
status.
Observe seizure precautions
31. Acute and chronic respiratory Acidosis
Respiratory acidosis is clinical disturbance in which
the pH is less than 7.35 and the PaCO2 is greater than
42 mmHg and a compensatory increase in the plasma
HCO3 occurs.
32. Pathophysiology
Respiratory acidosis is always owing to inadequate
excretion of CO2 with inadequate ventilation resulting
in elevated plasma CO2 concentration and
consequently increased levels of carbonic acid. In
addition to an elevated PaCO2 hypoventilation usually
cause a decrease in PaO2. It occur in emergency
situation such as acute pulmonary edema , aspiration
of a foreign object, atelectasis, pneumothorax,
overdose of sedatives, sleep apnea, morbid obesity.
34. Medical Management
Treatment is aimed at the underlying disease, and may
include:
Bronchodilator drugs to reverse some types of airway
obstruction
Noninvasive positive-pressure ventilation (sometimes
called CPAP or BiPAP) or a breathing machine, if
needed
Oxygen if the blood oxygen level is low
35. Nursing Management
Remain alert for critical changes in patient’s respiratory,
CNS and cardiovascular functions. Report such changes as
well as any variations in ABG values or electrolyte status
immediately.
Maintain adequate hydration.
Maintain patent airway and provide humidification if
acidosis requires mechanical ventilation. Perform tracheal
suctioning frequently and vigorous chest physiotherapy, if
ordered.
Institute safety measures and assist patient with
positioning.
Continuously monitor arterial blood gases.
36. Acute and chronic respiratory Alkalosis
Respiratory alkalosis is a clinical condition in which
the arterial pH is greater than 7.45and PaCO2 is less
than 35mmHg.
37. Pathophysiology
It is always caused by hyperventilation, which causes
excessive “blowing off” of CO2 and, hence, a decrease
in plasma carbonic concentration. Causes include
extreme anxiety, hypoxemia, early phase of salicylate
intoxication, gram negative bacteremia, and
inappropriate ventilator settings.
39. Medical Management
Correcting the underlying disorder
Therefore emergent treatment is usually not indicated
unless the Ph level is greater than 7.45. Because
respiratory alkalosis usually occurs in response to
some stimulus, treatment is usually unsuccessful
unless the stimulus is controlled.
If the PaCO2 is corrected rapidly in patient with
chronic alkalosis, metabolic acidosis may develop due
to the renal compensatory drop in serum bicarbonate
40. Nursing management
Be alert for signs of changes in neurologic, neuromuscular
or cardiovascular functions.
Institute safety measures for the patient with vertigo or the
unconscious patient.
Encourage the anxious patient to verbalize fears
Administer sedation as ordered to relax the patient
Keep the patient warm and dry
Encourage the patient to take deep, slow breaths or breathe
into a brown paper bag (inspire CO2).
Monitor vital signs
Monitor ABGs, primarily PaCO2; a value less than 35
mmHg indicates too little CO2 (carbonic acid)
43. Blood Gas Interpretation
PH PCO2 HCO3 STATUS
7.11↓ 60↑ 22(N) Respiratory
Acidosis
7.55↑ 20↓ 22(N) Respiratory
Alkalosis
7.77↑ 35(N) 75↑ Metabolic
Alkalosis
7.10↓ 45(N) 11↓ Metabolic Acidosis
ABG results should be interpreted in light of the patient’s medical
history, present health status, and medical therapies.
44. How to interpret ABGs value
PH 7.26 ↓ Acid
PCO2 26↓ Metabolic
HCO3 16 ↓ Acid
Interpretation;
Partially compensated metabolic
acidosis
45. How to interpret ABGs value
PH: 7.82↑ Alkalosis
PCO2: 60 ↑ Acid
HCO3: 32 ↑ Alkalosis
Interpretation;
Partially compensated metabolic Alkalosis
46. How to interpret ABGs value
• PH: 7.11↓ Acid
• PCO2: 82 ↑ Acid
HCO3: 30 ↑ Alkalosis
Interpretation;
Partially compensated respiratory Acidosis
47. How to interpret ABGs value
PH: 7.55 alkalosis
PCO2: 21 alklosis
HCO3: 10 acid
Interpretation;
Partially compensated respiratory alkolsis
55. How sample is obtained/Arterial
puncture
Blood is usually withdrawn from the radial artery as it is
easy to palpate and has a good collateral supply. The
patient’s arm is placed palm-up on a flat surface, with the
wrist dorsiflexed at 45°. A towel may be placed under the
wrist for support. The puncture site should be cleaned with
alcohol or iodine, and a local anesthetic (such as 2%
lignocaine) should be infiltrated. Local anesthetic makes
arterial puncture less painful for the patient and does not
increase the difficulty of the procedure. The radial artery
should be palpated for a pulse, and a pre-heparinised
syringe with a 23 or 25 gauge needle should be inserted at
an angle just distal to the palpated pulse
56. Cont..
A small quantity of blood is sufficient. After the
puncture, sterile gauze should be placed firmly over
the site and direct pressure applied for several minutes
to obtain hemostasis. If repeated arterial blood gas
analysis is required, it is advisable to use a different site
(such as the other radial artery) or insert an arterial
line
58. Delivery/taking of sample to LAB
To ensure accuracy, it is important to deliver the
sample for analysis promptly If there is any delay in
processing the sample, the blood can be stored on ice
for approximately 30 min with little effect on the
accuracy of the results. Complications of arterial
puncture are infrequent. They include prolonged
bleeding, infection, thrombosis or arteriospasm
59. Technical Error
Excessive Heparin
Ideally : Pre-heparinised ABG syringes
Syringe FLUSHED with 0.5ml 1:1000 Heparin & emptied
DO NOT LEAVE EXCESSIVE HEPARIN IN THE
SYRINGE.It may lead to:
DILUTIONAL Effect ↑
HCO3 ↓
pCO2 ↓
60. Technical Errors
Risk of alteration of results↑ with
1)↓vol of sample
Syringes must have > 50% blood
Use only 3ml or less syringe
61. Technical Errors
Air Bubble
Contact with AIR BUBBLES
↑ pO2 &
↓ pCO2
Seal syringe immediately after sampling
Body Temperature
Affects values of pCO2 and HCO3- only
ABG Analyzer controlled for Normal Body
temperatures
62. Reference
Brunner and suddarth’s Text book of medical and
surgical .nursing 13 th edition .volume 1.
(jniee L.hinkle kerry H.cheever)
Hand book of blood gas/Acid base interpertation.
(2nd edition)
Winters RW. Terminology of acid base disorder.
Ann intern med
