Загрузил Юлія Ткаченко

Blood GAS analysis

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ABG CASE
STUDIES &
INTERPRETATION
It’s not magic understanding ABG’s,
it just takes a little practice!

Acid base balance- relative constancy of concentration
of hydrogen ions in internal environments of an
organism that provides high-grade completeness of the
metabolic processes proceeding in cells and fabrics.

Hydrogen index (pH) - negative decimal
logarithm of the activity, or concentration,
of hydrogen ions in solution (-lg[H]). Its the
main quantitative characteristic of the
acidity of aqueous solutions.
Hydrogen indicator was
introduced S. Serensen
(S.Sеrensen) in 1909 He
suggested abbreviation "PH"
instead - lg[H +].
 Indicator value pH depends on the ratio between positively
charged ions (forming an acidic environment) and negatively
charged ions (forming an alkaline environment).
 The human body constantly strives to balance this ratio,
maintaining a strictly defined level pH. When the balance is
disturbed, they can occurmany serious diseases.
 at pH equal to 7.0 talk about neutral environment.
 The lower the level pH - the more acidic the environment (from
6.9 to 0).
 The alkaline environment has a high level pH (from 7.1 to 14.0).
1. Functional systems support acid base balance in
the body
The acid-base state is maintained by powerful homeostatic
mechanisms.
They are based on the features of physicochemical properties
blood buffer systems and physiological processes, in which the
systems participate: external respiration, kidneys, liver,
gastrointestinal tract, etc.
Buffers systems
Role buffer systems is in support normal pH blood.
Buffer system represents by itself mixture weak acids and her
salt, formed strong basis.
Plasma exposure strong acid causes a reaction of buffer
systems, as a result of which a strong acid is converted into a weak
one.
The same exactly happens and when exposed to biological
liquid strong basis, which after interaction with buffer systems
turns into weak basis.
As a result of these processes pH changes either do not occur
or are minimal.
All these systems are in the blood, where they maintain a pH =
7.4, despite the entry into the blood from the intestines and tissues
of significant amounts of acids and small quantity basics.
Maintenance of stability of active reaction of blood is provided
buffer systems, Which include:
1. Bicarbonate buffer system [carbon acid - H2СО3, bicarbonate
sodium - NaHCO3)] - the main buffer of intercellular fluid and blood,
is formed in the kidneys and facilitates the excretion of H+.
2. Phosphate buffer system [monobasic (NаН2RO4) and dibasic
(Na2NRA4) phosphate sodium] - facilitates breeding H+ in tubules
kidney. The main role isregulation CLR inside the cells (especially the
kidneys), supports the "regeneration" of the bicarbonate system in the
blood.
3. Plasma protein buffer system - the main intracellular buffer.
In an acidic environment, it binds hydrogen ions, in an alkaline
environment - gives.
4. Hemoglobin buffer system [Hemoglobin - potassium salt of
hemoglobin] - plays a major role in the transport of CO2 from tissues
to the lungs, begins to act within minutes.
2. Involvement of bodies in
regulation of acid base balance
Respiratory system.The respiratory system is involved in
regulation acid base balance, changing voltage CO2 in the blood.
Closely bound to bicarbonate buffer.
-at reduction frequencies breath (hypoventilation) increases CO2
concentration in the blood, which leads to an increase in the
concentration of H2СО3 and developing acidosis.
-at increase frequencies breath (hyperventilation) decreases voltage
CO2, decreases number H2СО3 and developing alkalosis.
Ren regulate the acid-base state, eliminating or reducing
violations by removal protons (H+) and increasing or decreasing
[NaCO3ˉ] in liquid media.
Secretion H+ is regulated by CO2 content in extracellular fluid:
the higher the concentration of CO2 - the more excretion H +, which
leads to increased acidity of urine.
When increases level H+ in blood, the kidneys produce HCO3ˉ,
which helps maintain it in the body correlation acids/basis at the
level of 1:20. If the extracellular fluid increases HCO3ˉ or decreases
[H+], the kidneys are delayed H+ and remove HCO3-, in this case the
urine becomes alkaline.
Acidosis increases the synthesis and excretion of ammonia in the
kidneys, alkalosis has the return action.
Liver. Its cells synthesize proteins of the buffer system; oxidized organic acids to CO2
and water; lactate is converted to glucose and c glycogen, together acidic and alkaline
metabolic products are excreted from the body with bile.
Gastrointestinal highway. At tinning liquid environments organism selection
salt acids in cavity stomach is inhibited, at acidified - intensifies.
selection HCO3- in strait pancreatic bets intensifies at tinning liquid
environments, at acidified - decreases.
Bone cloth. On+, K +, Ca2 +, Mg2 +, what contained in bone fabric,, can exchange
on ions hydrogen,, compensatingacidosis. INheavy cases this process maybe cause to
decalcification skeleton.
3. Violation acid-base state of the
body
In terms pathology acid-base balance can change both in the acidic
(acidosis) and in the alkaline (alkalosis) side.
acidosis - acid-base imbalance, characterized by the appearance in
the blood of an absolute or relative excess of acids and an increase in
the concentration of hydrogen ions.
alkalosis - acid-base imbalance, in which there is an absolute or
relative increase quantity basics and reducing the concentration of
hydrogen ions.
Classification of acid-base disorders
1. For mechanism of development of acidosis and alkalosis are
divided into:
1. Respiratory (gas, respiratory)
2. Metabolic (non-gas, exchange)
2. According to the degree of severity distinguish:
1. Compensated acidosis and alkalosis. With compensated
acidosis and alkalosis buffer and physiological systems of the body
involved in the neutralization and excretion of acidic and alkaline
products provide support pH within normal limits.
2. Decompensated acidosis and alkalosis. With decompensated
acidosis and alkalosis there is depletion and insufficiency protective
mechanisms,, pH shifts beyond the norm.
Acid base imbalances
•
Metabolic acidosis
 • Metabolic alkalosis
 • Respiratory acidosis
 • Respiratory alkalosis
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3
LUNGS
REN
Metabolic
•
METABOLIC ACIDOSIS: Decrease the
HCO3 - --> the pH goes down.
•
Compensation: Respiratory Alkalosis
(hyperventilation) will bring the pH back near
normal.
•
Causes: Diarrhea, DKA, LA, renal failure.
•
METABOLIC ALKALOSIS: Increase the
HCO3 - --> the pH goes up.
•
Compensation: Respiratory Acidosis
(hypoventilation) can help to bring the pH+
Respiratory
•
RESPIRATORY ACIDOSIS: Increase the
PCO2---> the pH goes down. Hypoventilation.
Compensation: Metabolic Alkalosis can help
bring the pH back near normal.
• Causes: pneumonia, Bronchitis,Asthma
•
RESPIRATORY ALKALOSIS:Decrease the
PCO2-> the pH goes up.Hyperventilation.
• Compensation: Metabolic Acidosis can
help bring the pH back near normal.
METABOLIC ALKALOSIS
CAUSES:
•
Vomiting: Lose enough stomach acid to produce
alkalosis.
•
Diuretics: Loop diuretics and thiazides can lead to
hypokalemia ------> secondary metabolic alkalosis.
•
Transfusion of large quantities of alkaline solutions
•
Antacids
overuse
RESPIRATORY ACIDOSIS:
causes:
CNS DEPRESSION




DRUGS:Opiates,sedatives,anaes 
thetics
OBESITY

HYPOVENTILATION SYNDROME
STROKE
NEUROMUSCULAR
DISORDERS:


NEUROLOGIC:
POLIO,GBS,TETANUS,BOTULISM
MUSCULAR DYSTROPHY
AIRWAY OBSTRUCTION

CHEST WALL RESTRICTION
ACUTE ASPIRATION,
LARYNGOSPASM
PLEURAL: Effusions, empyema,
pneumothorax,fibrothorax
CHEST WALL: Kyphoscoliosis,
scleroderma,ankylosing
spondylitis,obesity
SEVERE PULMONARY
RESTRICTIVE DISORDERS


PULMONARY FIBROSIS
PARENCHYMAL INFILTRATION:
Pneumonia, edema
RESPIRATORY ALKALOSIS
Causes:
• High altitude
• Psychogenic hyperventilation
• Neuromuscular disease
• Respiratory center depression
• Inadequate mechanical ventilation
• Sepsis
• Burns
Metabolic
acidosis
Causes:
•
Metabolic
acidosis: Is caused by a
decreaseinHCO3-concentration inblood.
• Causes:
1.Increased production of acids:
Lactate acidosis, ketoacidosis,
Salicylate poisoning.
2.Loss of HCO3-: Diarrhea and kidneys
renal tubular acidosis
3.Blood profile: pH
decreased
 [HCO3-] decreased, PCO2 decreased
Compensation of Metabolic
acidosis:
•
•
•
Respiratory
compensation:
decrease in pH stimulates respiratory
center causing hyperventilation which
produces decrease in PCO2.
Renal Compensation: excess H+
is excreted as titratable acid and
NH4+.
Treatment: lactate
containing
solution which converts HCO3- ion
the liver.
Assessment of acid base status
• Direct arterial blood measurements: ABG
pH
NB: use heparinised blood,
pCO2
measured within 10 minutes
pO2
• Derived measures:
Bicarbonate (HCO3-)
Normal Values:
pH =7.35-7.45
(7.4)
HCO3-=22 - 26mEq / L
pCO2 = 35 - 45mm Hg
(24mEq / L)
(40mm Hg )
Metabolic alkalosis
Metabolic acidosis
Respiratory acidosis
Respiratory Alkalosis
Metabolic Acidosis
pH 7.30
 PaCO2 40
 HCO3 15

Metabolic Alkalosis
pH 7.50
 PCO2 40
 HCO3 30

Respiratory Acidosis
pH 7.30
 PaCO2 60
 HCO3 26

Respiratory Alkalosis
pH 7.50
 PaCO2 25
 HCO3 23

What are the compensations?

Respiratory acidosis --metabolic
alkalosis

Respiratory alkalosis --metabolic
acidosis

In respiratory conditions, therefore,
the kidneys will attempt to compensate
and visa versa.

•
Buffers kick in within minutes.
 Respiratory compensation is rapid and
starts within minutes and complete
within 24 hours. Kidney compensation
takes hours and up to 5 days
Acid base disorder-worksheet
Practice ABG’s
1. Respiratory
alkalosis
 2. Respiratory
acidosis
 3. Metabolic acidosis
4.Compensated
 Respiratory
 acidosis
 5. Metabolic alkalosis
 6. Compensated
Respiratory acidosis
 7. Compensated





Metabolic
alkalosis
8. Metabolic acidosis
9. Respiratory
acidosis
10. Metabolic alkalosis
STEPS OF ASSESSING ABG
•
STEP 1: Diagnose whether it is
acidosisor alkalosis- (pH will help)
•
STEP2:Diagnose whether
compensatedor non compensated
•
STEP3:Diagnosewhetheritis
metabolic or respiratory(Look at the
value of bicarbonate and pCO2)
Work sheet
Diarrhea may lead to----------?
 Acid loss due to vomiting and gastric
suction maylead to ______
alkalosis?
 Overuse of _________may lead to
metabolic alkalosis?


Problem#1



•
•
67 year female known diabetic for past
20years presented with sudden onset
of severe chest pain and Shortness of
breath.
ABG analysis showed:
pH 7.36
PCO2 33 mmHg
HCO3 18 mmol/L
•
Discuss the probable diagnosis.
•
•
•
Problem #2
A 30-year
old man with DM presents
with polyuria, polydipsia, fever, cough, and
purulent sputum.
 His ABG shows the following Na+140 /
Cl- 104
K+7.0
 pH:
6.95
 pCO2 : 33
 Hco3 : 7.0
 Discuss the probable diagnosis.

Problem#3
• 45 year old male was admitted to the
emergency room with complaints of
mild vomiting, associated with
disorientation and muscular
weakness. His blood investigations
showed the following
 pH =7.20
Na -137meq/l
HCO3-=16mEq /L
 pCO2 = 34mm Hg
 Glucose=685mg/dl
 urea49mg/dl

Cl-108meq/l
K -5.8
Problem #4
•
60 year male presents to the ED
from a nursing home. You have no
history other than he has been
breathing rapidly and is less
responsive than usual.




•
•
•
Na+ 123 Cl- 99 HCO3 - 5
pH 7.31pCO2 10
Discuss the probablediagnosis.
Problem # 5





60year old
man was admitted with severe
abdominal pain, which started some 2 hours
back.
Clinically he was in a state of shock with
distended abdomen. Femoral pulses could not
be palpable
His ABG shows the follows pH :
7.05
pCO2: 26.3 mmHg
HCO3: 7 mmol/L Discuss the probable
diagnosis.
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