Prince Sattam Bin AbdulAziz
University
College Of Pharmacy
Acid Base balance
A 62-year-old woman has been hospitalized in the ICU for several weeks. Her hospital
stay has been complicated by aspiration pneumonia and sepsis, requiring
prolonged courses of antibiotics.
For the past few days, she has been having high temperatures again, and her stool
output has increased dramatically
. Her most recent stool samples have tested positive for Clostridium difficile toxin,
laboratory tests
serum Na 138 mEq/L, K 3.5 mEq/L, Cl 115 mEq/L, albumin 4.4 g/dL, pH 7.32, Paco2 30
mm Hg, and HCO3 − 15 mEq/L.
Which one of the following acid-base disturbances is consistent with this patient’s
ABG?
A. AG metabolic acidosis.
B. Normal AG metabolic acidosis.
C. Saline-responsive metabolic alkalosis.
D. Acute respiratory acidosis.
Complete
• The compensation for a respiratory acidosis is metabolic (alkalosis /acidosis )……
• The compensation for a respiratory alkalosis is metabolic ………..(acidosis/Alkalosis)
• The compensation for metabolic acidosis is a respiratory ………….
………..(acidosis/Alkalosis)
• RR in respiratory alkalosis is …… ( increased /decreased )
• Metabolic acidosis Hco3- (increased/decreased)
• Respiratory acidosis Pco2 (increased/decreased)
Anion gab facts
• Anion gap is reflective of unmeasured acids. ( T/F)
True
• An increase in anion gap suggests an increase in the number of negatively
charged weak base in the plasma. ( T/F)
False /weak base
• Serum anion gap (SAG) can be used to elucidate cause of metabolic acidosis ( T/F)
true
• Anion gap may be elevated in conditions such as renal failure, lactic acidosis,
ketoacidosis, and salicylate, methanol, or ethylene glycol toxicity
True
How to calculate Anion gab
• Calculate the anion gap (AG) = [Na+] − [Cl− + HCO3−].
• Calculate anion gab for in the previous case
Normal AG = 140 − [105 + 24] = 6–12 mEq/L.
If AG is more than 12, there is a primary metabolic acidosis
regardless of pH or HCO3
−.
• Back to the first question
laboratory tests
serum Na 138 mEq/L, K 3.5 mEq/L, Cl 115 mEq/L, albumin 4.4 g/dL, pH 7.32, Paco2 30
mm Hg, and HCO3 − 15 mEq/L.
Which one of the following acid-base disturbances is consistent with this patient’s ABG?
A. AG metabolic acidosis.
B. Normal AG metabolic acidosis. (non anion gab
C. Saline-responsive metabolic alkalosis.
D. Acute respiratory acidosis.
• The cause of her normal anion gab metabolic acidosis ?
A . Clostridium difficile toxin causing diarrhea
B. Aspiration pneumonia
C. Use of antibiotics
Interpreting ABGs
• Step 1 - check the pH?
• Step 2 - What is the CO2?
• Step 3 - Watch the bicarbonate?
• Step 4 - Look for compensation?
• Step 5 - What is the PaO2 and SaO2?
Respiratory Acidosis
• Carbonic acid excess
• Exhaling of CO2
inhibited
H2CO3
• Carbonic acid builds up
• pH falls below 7.35
• Cause = Hypoventilation (see chart)
Acid-Base Imbalances
• Normal
1.2 mEq/L
24 mEq/L
H2CO3 ……………… HCO3
1
20
7.4
Respiratory Acidosis
1
13
7.21
•
•
•
•
•
Signs and Symptoms of Respiratory
Acidosis
Breathlessness
Restlessness
Lethargy and disorientation
Tremors, convulsions, coma
Respiratory rate rapid, then gradually
depressed
• Skin warm and flushed due to vasodilation
caused by excess CO2
18
Treatment of Respiratory Acidosis
• Restore & improve alveolar ventilation
• IV lactate solution (converted to bicarbonate ions
in the liver).
• Treat underlying dysfunction or disease
e.g. pul odema, Res depression
19
19
Respiratory Alkalosis
• Carbonic acid deficit
• Increased exhaling
of CO2
• Carbonic acid decreases
H2CO3
• pH rises above 7.45
• Cause = hyperventilation (see chart)
Acid-Base Imbalances
• Normal
1.2 mEq/L
24 mEq/L
H2CO3 ……………… HCO3
1
20
7.4
Respiratory Alkalosis
1
40
7.70
Respiratory Alkalosis
• Conditions that stimulate respiratory center:
– Oxygen deficiency at high altitudes
– Pulmonary disease and Congestive heart failure –
caused by hypoxia
– Acute anxiety
– Fever, anemia
– Early salicylate intoxication
– Cirrhosis
– Gram-negative sepsis
23
Treatment of Respiratory Alkalosis
• Treat underlying cause
• Breathe into a paper bag
• IV Chloride containing solution (hydrochloric
acid, arginine chloride & ammonium
chloride), – Cl- ions replace lost bicarbonate
ions
24
Metabolic Acidosis
•
•
•
•
Base-bicarbonate deficit
Low pH (< 7.35)
Low plasma bicarbonate (base)
Cause = relative gain in H+
(lactic acidosis, ketoacidosis)
or actual loss of HCO3
(renal failure, diarrhea)
Acid-Base Imbalances
• Normal
1.2 mEq/L
24 mEq/L
H2CO3 ……………… HCO3
1
20
7.4
Metabolic Acidosis
• Kidney failure (decrease in bicarbonate)
1
10
7.10
Symptoms of Metabolic Acidosis
•
•
•
•
Headache, lethargy
Nausea, vomiting, diarrhea
Coma
Death
28
Treatment of Metabolic Acidosis
•
•
•
•
Treat the causes
Improve renal perfusion & acid excretion
NaHCO3, Dose = (weight Kg x base deficit x 0.3)
Ensure adequate ventilation
29
29
Metabolic Alkalosis
•
•
•
•
Bicarbonate excess
High pH (> 7.45)
Loss of H+ ion or gain of HCO3
Most common causes vomiting, gastric
suctioning (NG tube)
• Other: Abuse of antacids,
K+ wasting diuretics
Acid-Base Imbalances
• Normal
1.2 mEq/L
24 mEq/L
H2CO3 ……………… HCO3
1
20
7.4
Metabolic Alkalosis
1
30
7.58
Symptoms of Metabolic Alkalosis
•
•
•
•
•
Respiration slow and shallow
Hyperactive reflexes ; tetany
Often related to depletion of electrolytes
Atrial tachycardia
Dysrhythmias
33
Treatment of Metabolic Alkalosis
• Electrolytes to replace those lost
• Treat underlying disorder
• IV chloride containing solution e.g saline (Chloride
Responsive)
• Aldosterone antagonist (Chloride resistant)
34
34
Assessing ABGs
•
•
•
•
•
•
pH
7.35 - 7.45
PaCO2
35 - 45 mmHg
HCO3
22 - 26 mEq/L
Base Excess
-2 - +2 mEq/L
PaO2
80 - 100 mm Hg
O2 saturation
95 - 100 %
Interpreting ABGs
Uncompensated
• pH abnormal (high or low)
• One component abnormal (high or low
CO2 or HCO3)
• The other component is normal
(The component not causing the acid-base
imbalance is still normal)
Partly compensated
• pH not normal (but moving toward
normal)
• Both CO2 and HCO3 are outside normal
range
• The component that was normal is
changing in order to compensate
Interpreting ABGs
Compensated
• pH normal
• Other values abnormal in
opposite directions
• One is acidotic the other alkaline
Interpreting ABGs
• Determine amount of hypoxemia
present
• Normal PaO2 (adults - room air)
• < 70 years = 80-100 mm Hg
70-79 = 70-100 mm Hg
• Drops 10 mm Hg for each decade
Interpreting ABGs
• Hypoxemia = < 70 mm Hg
(for adult < 70 years old)
• Mild
= 60-80 mm Hg
• Moderate = 40-60 mm Hg
• Severe = < 40 mm Hg
Interpreting ABGs
• Oxygen saturation (pulse
oximetry)
• 95-100%
• < 91% confusion
• < 70% life threatening
Case 1
• 80 year old female with severe
pneumonia, fever
• pH = 7.25
• PaCO2 = 55 mm Hg
• HCO3 = 24 mEq/L
• PaO2 = 65 mm Hg
• O2 sat = 80%
Acidosis or alkalosis?
Respiratory or metabolic?
Compensated or Uncompensated?
Level of hypoxemia?
Case 2:
A patient is in intensive care because he suffered a severe myocardial
infarction 3 days ago. The lab reports the following values from an
arterial blood sample:
– pH 7.3
– HCO3- = 20 mEq / L ( 22 - 26)
– pCO2 = 32 mm Hg (35 - 45)
Diagnosis
Metabolic acidosis
With partial compensation
• Case 3:
• A 44 year old moderately dehydrated man was
admitted with a two day history of acute
severe diarrhea. Electrolyte results: Na+ 134,
K+ 2.9, Cl- 108, HCO3- 16,
• Urea 31, Cr 1.5.
• ABG
pH - 7.31 pCO2 - 33 mmHg
HCO3 - 16 pO2 - 93 mmHg
• ????????? Diagnosis and Anion Gap
CASE 4:
• A 20 year old female with type I DM, presents to the emergency department with a 1
day history of nausea, vomiting, polyuria, polydypsia and vague abdominal pain. P.E.
noted for deep sighing breathing, orthostatic hypotension, and dry mucous
membranes.
• Lab. Findings are: Na 134 , K 6.0, Cl- 93, HCO3- 11 glucose 720, Urea 38, Cr 2.6.
UA: pH 5, ketones negative, glucose positive . Plasma ketones trace.
ABG: pH 7.27 HCO3- 10 PCO2 23
• What is the acid base disorder?
47
CASE 5
• A 70 year old man with history of CHF presents with
increased shortness of breath and leg swelling.
ABG:
• pH 7.24,
• PCO2 60 mmHg,
• PO2 52
• HCO3- 27
• What is the acid base disorder?
48
– Interprete ABG
– pH < 7.35
– PaCO2 >45
– HCO3 Normal
• Uncompensated
– pH < 7.35
– PaCO2 >45
– HCO3 Normal
– Respiratory Acidosis
• Question: Interprete ABG???
– pH Normal
– PaCO2 >45
– HCO3 > 26
• Compensated
– pH Normal
– PaCO2 >45
– HCO3 > 26
– Respiratory Acidosis
ABG interprete????
– pH > 7.45
– pH Normal
– PaCO2 < 35
– PaCO2 < 35
– HCO3 Normal
– HCO3 < 22
ABG Results
• Uncompensated
• Compensated
– pH > 7.45
– pH Normal
– PaCO2 < 35
– PaCO2 < 35
– HCO3 Normal
– HCO3 < 22
– Respiratory Alkalosis
– Respiratory Alkalosis
ABG interprete??
– pH < 7.35
– pH Normal
– PaCO2 Normal
– PaCO2 < 35
– HCO3 < 22
– HCO3 < 22
ABG Results
• Uncompensated
• Compensated
– pH < 7.35
– pH Normal
– PaCO2 Normal
– PaCO2 < 35
– HCO3 < 22
– HCO3 < 22
– Metabolic Acidosis
– Metabolic Acidosis
ABG interprete???
– pH > 7.45
– pH Normal
– PaCO2 Normal
– PaCO2 > 45
– HCO3 >26
– HCO3 > 26
ABG Results
• Uncompensated
• Compensated
– pH > 7.45
– pH Normal
– PaCO2 Normal
– PaCO2 > 45
– HCO3 >26
– HCO3 > 26
– Metabolic Alkalosis
– Metabolic Alkalosis