ABG 2022

‫الرحيم‬ ‫الرحمن‬ ‫هللا‬ ‫بسم‬
“
‫م‬ ‫اال‬ ‫لنا‬ ‫علم‬ ‫ال‬ ‫سبحانك‬ ‫قالوا‬
‫ا‬
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‫م‬
”
‫العظيم‬ ‫هللا‬ ‫صدق‬
Monira Taha

Arterial Blood Gases
Made Easy
Dr.Monira Taha
Emergency Medicine
Monira Taha

Learning outcomes
• Disorders of gas exchange
• Disorders of acid–base balance
• When and why is an ABG required?
• Making ABG interpretation easy
• The ABG in practice
Monira Taha

Pulmonary Gas Exchange
The efficiency of gas exchange is evaluated by
 Pao2,
 PaCO2 ,
 PO2(A-a)
 Response to 100% O2.
Monira Taha

Alveolar – arterial (A-a) Po2 gradient
• A-a gradient=150-PaO2-1.25(paCO2)
Calculate your PO2(A-a) gradient
• PO2(A-a)= 5-10 mmHg
• If normal with RF indicate hypoventilation
• if more than 20 indicate intrinsic lung disease
• IF 20 – 30 Mixed.
Monira Taha

Hypercapnic Respiratory Failure type||
(PAO2 - PaO2)
Alveolar
Hypoventilation
V/Q abnormality
increased
normal
PaCO2 >46mmHg
Not compensation for metabolic alkalosis
Central
Hypoventilation
Neuromuscular
Problem

You follow up 3 patient in ER all with disturbed
conscious level Two patient came to you due to
drug over dose, third one came after blunt chest
trauma.
• Patient 1 PaO2 55 mmHg, Paco2 70mmHg
• Patient 2 PaO2 40 mmHg, Paco2 70mmHg
history of vomiting
• Patient 3 PaO2 40mmHg, Paco2 40mmHg
What is suspected clinical difference ?????
A-a gradient=150-PaO2-1.25(paCO2)
Monira Taha

• Hypoxemia
• decrease in the arterial oxygen content in the
blood
• Hypoxia
• decreased oxygen supply to the tissues.
Hypoxemic Hypoxia
Normoxaemic Hypoxia
Monira Taha

Types of hypoxia
Types Definintion Typical cases
Hypoxic oxygen tension High altitude – hypoventilation – V/Q
mismatch.
Anemic carrying capacity Anemia – blood loss – CO poisoning
Stagnant perfusion Heart failure – Shock – ischemia
Histotoxic Cellular hypoxia Cyanide – other metabolic poisons –
shifting of O2-HB curve.
Monira Taha

Grading of hypoemiaxia
Respiratory
failure
Monira Taha

O2Hgb dissociation curve
0 20 40 60 80 100 120 140 160
0
20
40
60
80
100
%
Sat
PO2 mmHg

PaO2-FiO2 ratio
 Normal PaO2/FiO2 is 300-500
 <200 indicates a clinically significant gas
exchange derangement
 Ratio often used clinically in ICU setting
Monira Taha

Definition of acid-base
term
-Acidemia serum pH < 7.36
-Alkalemia serum pH > 7.44
-Acidosis a primary pathophsiological
processes that increase H and
decrease the serum pH
-Alkalosis a primary pathophsiological
processes that decrease H and
increase the serum pH
Monira Taha

-Metabolic acidosis a primary process that cause HCO3 to fall.
-Metabolic alkalosis a primary process that cause HCO3 to rise.
-Respiratory acidosis a primary process that cause CO2 to rise.
-Respiratory alkalosis a primary process that cause CO2 to fall.
-Mixed disorder a condation in which more than one primary
acid-base process is occurring.
-compensation a physiologic process to an acidosis or
alkalosis which partially turn the pH towards
normal.
Monira Taha
Monira Taha

Organ Compensation
• Respiratory which is rapid and immediate through
stimulation of respiratory center in the brainstem
• Renal is slow and takes several days occurs by
excretion of H+ and the relation to the filtered
HCO-
3
Monira Taha

Henderson Hasselbalch equation
pH = 6.1 +
Respiratory Alkalosis
HCO-3
PaCO2 X 0.03
Monira Taha

Common Laboratory tests in acid – base evaluation
1- The Arterial Blood Gas ( ABG)
2- The Serum Anion Gap
3- Urine pH
Monira Taha
Monira Taha

When and why is an ABG required?
• To Establish A Diagnosis
• To Assess Illness Severity
• To Guide And Monitor Treatment
• Why not ?????
• Venous Blood Gas Analysis
• SaO2
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COMMON ABG VALUES
• PaO2 > 10.6 kPa or > 80 mmHg
• serum pCO2 40 mm Hg
• serum pH 7.36 - 7.44
• serum H 40 nEq/L
• serum HCO3 24 mEq/L
• Na 135−145 mmol/L
• K 3.5−5 mmol/L
• Cl 95−105 mmol/L
Monira Taha
Monira Taha

To answer these question 9 steps must be followed:
1. How is the patient?
2. Assess oxygenation
3. Evaluate PH and narrow down to two possible
process.
4. Evaluate the PCO2 and narrow down to one possible
process.
5. Use appropriate compensation formula.
6. Determine if any other process present.
7. Evaluate the serum anion gap and Delta Gap.
8. check the urine pH .
9. Differential diagnosis for each process present.
Monira Taha
Monira Taha

1- How is the patient?
• Will provide useful clues to help with
interpretation of the results.
Monira Taha

2- Assess oxygenation
– Is the patient hypoxemic?
– The PaO2 should be > 10 kPa (75 mmHg)
the % inspired concentration X 5.
Monira Taha

pH<7.35 there is metabolic acidosis or
respiratory acidosis or both.
pH>7,45 there is metabolic alkalosis or
respiratory alkalosis or both.
3-Evaluate PH and narrow down to
two possible process:
Monira Taha
Monira Taha

4- Evaluate the PCO2 and narrow down to one
possible process:
pH<7.35 PCO2<40
there is metabolic acidosis
pH<7.35 PCO2>40
there is respiratory acidosis
pH>7.45 PCO2<40
there is respiratory alkalosis.
pH>7.45 PCO2>40
there is metabolic alkalosis.
Monira Taha
Monira Taha

What disorder is
present?
pH pCO2 or HCO3
Respiratory Acidosis pH low pCO2 high
Metabolic Acidosis pH low HCO3 low
Respiratory Alkalosis pH high pCO2 low
Metabolic Alkalosis pH high HCO3 high
Monira Taha

5-Use appropriate compensation formula.
• Metabolic acidosis:
PCO2=1.5(HCO3)+8 2
• Metabolic Alkalosis:
PCO2=0.9(HCO3)+16
• Respiratory acidosis: increase CO2 (10 mm Hg) =1 unite
Acute(<8h): decrease PH 0.08 and increase in HCO3 1 mEq/l
Chronic(>12): decrease PH0.03 and increase in HCO3 4 mEq/l
• Respiratory alkalosis: decrease CO2 (10 mm Hg) = 1 unite
Acute: increase PH 0.08 and decrease in HCO3 2 mEq/l
Chronic: increase PH 0.03 and decrease in HCO3 5 mEq/lMonira Taha
Monira Taha

6-Determine if any other process present.
• in case of metabolic acidosis
If measured pCO2 less than calculated mixed respiratory alkalosis.
more than calculated mixed respiratory acidosis.
equals calculated a pure metabolic acidosis with
expected degree of compensation .
• In case of metabolic alkalosis
If measured pCO2 less than calculated (5mm Hg) or pCO2 is less than 40 mm
Hg mixed respiratory alkalosis.
more than calculated (5mm Hg) or pCO2 is more than 50-55
mm Hg mixed respiratory acidosis.
equals calculated a pure metabolic alkalosis with
expected degree of compensation .
Monira Taha
Monira Taha

• In case of respiratory acidosis
If measured pH or HCO3 less than calculated mixed metabolic
acidosis.
more than calculated mixed metabolic
alkalosis
equals calculated a pure respiratory
acidosis with expected degree of compensation.
• In case of respiratory alkalosis
If measured pH or HCO3 less than calculated mixed metabolic
acidosis.
more than calculated mixed metabolic
alkalosis
equals calculated a pure respiratory alkalosis
with expected degree of compensation.
Monira Taha
Monira Taha

7-Evaluate the anion gap Delta Ratio.
Serum anion = Serum cation
Unmeasured anion +measured anion = measured cation +unmeasured cation
Anion Gap (unmeasured anion – unmeasured cation) =
Measured cation (Na) – Measured anion
(HCO3,CL)
Anion Gap = 140 – ( 104 + 24) = 140 – 128 = 12 _+ 3
Monira Taha
Monira Taha

MA - causes
• ketoacidosis
• diabetic, alcoholic, starvation
• lactic acidosis
• acute renal failure
• toxins
• renal tubular acidosis
• GIT loss of HCO3
• diarrhoea
• drainage of pancreatic
or bile juice
Na+
Cl-
AG
HCO3
-
normal
anion gap
Na+
Cl-
AG
HCO3
-
physiologic
situation
Na+
Cl-
AG
HCO3
-
high
anion gap
Monira Taha

Monira Taha
AG corrected (cAG) = AG + 2.5 [4 - albumin]

 Delta gap = (actual AG – 12) + HCO3
 If delta gap > 30 additional metabolic alkalosis
 If delta gap < 18 additional non-gap metabolic acidosis
 If delta gap 18 - 30 no additional metabolic disorders
Monira Taha

Delta gap = (actual AG – 12) + HCO3

8-The urine pH
• Normally urine is acidic why? <5
• Academia urine become maximally
acidotic
• Alkalemia urine pH > 6
• -in case of renal tubular acidosis(RTA)
there is inappropriate secretion of HCO3
lead to acidemia but alkalotic urine
Monira Taha
Monira Taha

9-Generate the diffferential
diagnosis.
Monira Taha
Monira Taha

ABG Made Easy
ARE YOU READY
Monira Taha

A 20-years-old patient with diabetes is admitted with lethargy,
polydipsia, and polyuria.
pH: 7.24 pCO2: 24 PaO2: 90 mm Hg HCO3:10
Na:130 K: 4.5 CL: 94 RBS:600
Urine pH: 5
STEP 1: How is the patient?
STEP 2: Assess oxygenation
STEP 3: Evaluate PH and narrow down to two possible process.
pH< 7.36
Conclude: Either a metabolic or Respiratory acidosis is present.
STEP 4: Evaluate the PCO2 and narrow down to one possible process.
pCO2<40 mmHg
Conclude: At least a metabolic acidosis is present.
STEP 5: Use a formula for a metabolic acidosis and compare the
predicted pCO2 with the actual pCO2.
Expected pCO2= 1.5(HCO3)+8 2 =23 mmHg.
Actual pCO2=24 mm Hg. Monira Taha
Monira Taha

STEP 6: Determine if any other process present.
The expected Value Closely matches the actual value of pCO2.
Conclude: -A pure metabolic acidosis is present.
-The metabolic acidosis is fully Compensated.
-No other processes are present.
STEP 7: Evaluate the anion gap.
Anion Gap = (Na) – (HCO3 + CL)
Corrected (Na)=0.016(glucose – 100) + serum Na = 138
Anion Gap = 138 –(94+10) = 34
Conclude: An elevated gap metabolic acidosis is present.
STEP 8: Check The urine pH.
Urine pH = 5.0 ( appropriate in the setting of acidemia).
STEP 9: Generate the differential diagnosis.
pH: 7.24 pCO2: 24 HCO3:10
Na:130 K: 4.5 CL: 94 RBS:600
Urine pH: 5
Monira Taha
Monira Taha

Type of metabolic acidosis:
1- Elevated gab metabolic acidosis
2-Normal Gab metabolic acidosis
Monira Taha
Monira Taha

Elevated gab metabolic acidosis
MUD PILERS
1-Methenol / Ethanol
2-Uremia
3-DKA
4-paraldehyde ingestion
5- INH, Iron toxicity
6-Lactic acidosis: Ischemia, sepsis……
7-Ethylene glycol
8- Rhabdomyolysis
9-Salicylate poisoning
Monira Taha
Monira Taha

• A 25-year-old man, with no significant medical history,
presents to the emergency department with a 2-day
history of fever, productive cough and worsening
breathlessness.
• Examination He is hot and flushed with a temperature
of 39.3°C. He does not appear distressed but is using
accessory muscles of respiration. There is diminished
chest expansion on the left with dullness to
percussion, bronchial breathing and coarse crackles in
the left lower zone posteriorly. Pulse 104 beats/min
Respiratory rate 28 breaths/min Blood pressure
118/70 mmHg SaO2 (room air) 89%
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On room air pH 7.50 PCO2 28.1 mmHg
PO2 57.8 mmHg Bicarb 23.9 mmol/L
BE −0.5 mmol/L SO2 88.7% K 3.7 mmol/L Na
138 mmol/L Cl 99 mmol/L urine pH: 6
1. Describe his gas exchange.
2. Describe his acid–base status.
3. Should the patient receive supplemental O2?
4. Is pulse oximetry a suitable alternative to
repeated ABG monitoring in this case?
Monira Taha

A 42-year-old obese woman with DM diagnosed 2 month ago presents to
your clinic for a routine physical. She is asymptomatic and take only
glyburide. She has no history of hypertension, although her family
history is positive. On physical examination, she is found to have a blood
pressure of 180/110 mm Hg. You order an electrolyte panel and notice
that her (HCO3) is elevated.
• pH: 7.49 pCO2: 45 PaO2: 90 mm Hg HCO3: 33
• Na: 142 K: 4.1 Cl: 98 BUN: 14
• Urine pH: 6.5
Monira Taha
Monira Taha

pH>7.44
Conclude: Either a metabolic or Respiratory alkalosis is present.
pCO2>40 mmHg
Conclude: At least a metabolic alkalosis is present.
STEP 5: Use a formula for a metabolic alkalosis and compare the
Expected pCO2= .9(HCO3)+ 16 =46 mmHg.
Actual pCO2=45 mm Hg.
pH: 7.49 pCO2: 45 HCO3: 33
Na: 142 K: 4.1 Cl: 98 BUN: 14
Urine pH: 6.5
Monira Taha
Monira Taha

The expected Value Closely matches the actual value of pCO2.
Conclude: -A pure metabolic alkalosis is present.
-The metabolic alkalosis is fully Compensated.
= 142 – (98 + 34)= 10
Conclude: normal as expected
Urine pH = 6.5 (a propriate in the setting of alkalosis).
pH: 7.49 pCO2: 45 HCO3: 33
Na: 142 K: 4.1 Cl: 98 BUN: 14
Urine pH: 6.5
Monira Taha
Monira Taha

In case of normal renal function the patient
must be either :
- ECF volume depleted and NaCl depleted
- Mineralocorticoid excess
♠ Saline-Responsive “chloride-responsive”
metabolic alkalosis.
♠ Saline-non Responsive
Monira Taha
Monira Taha

Volume Depletion metabolic alkalosis.
• At level of glomeruli :
- decrease glomerular filtration rate so decrease filtered HCO3
• At level of proximal tubule :
-Increase Angiotensin II lead to increase Na reabsorption.
-No CL to accompany Na Thus HCO3 become the anion of
choice.
• At level of distal tubule :
-Increase Aldosterone lead to Na absorption (K – H) secretion.
- Absorbed Na accompanies HCO3 into blood stream
Monira Taha
Monira Taha

Bicarbonate as a Buffer
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Saline-Responsive “chloride-responsive”
DAMPEN
• Diuretics.
• Adenoma”secreting villous adenoma of the colon”.
• Miscellaneous”Bartter’s syndrome,K
deficiency,Bulimia”.
• Posthypercapnia
• Emesis.
• Nasogastric Tube.
Monira Taha
Monira Taha

Bartter’s syndrome.
• Tubular defect in Na reabsorption in the
loop of Henle lead to mild volume depletion
so increase Aldosterone which lead to
hypokalemic metabolic alkalosis.
Monira Taha
Monira Taha

Saline-non Responsive metabolic
alkalosis.
• Alkali ingestion with decrease GFR.
• Syndrome of mineralo-corticoid excess.
• Exogenous steroid administration.
• Licorice ingestion (contain a potent analogue of
aldosterone)
• Cushing syndrome.
• Primary hyperaldosteronism.
Monira Taha
Monira Taha

Metabolic
alkalosis
Normal kidney
function
Saline
responsive
Saline
nonresponsive
Abnormal
kidney function
Alkali ingestion
Monira Taha
Monira Taha

A surgeon refers a 22-year-old man with a
hernia to you because of some laboratory
tests she found on preoperative testing. The
patient has a medical history of kidney stones.
• pH: 7.29 pCO2: 32 PaO2: 90 mm Hg
HCO3: 15
• Na: 138 K: 3 Cl: 110
• Urine tests: pH: 6 Na: 35 K: 45 Cl: 75
Monira Taha
Monira Taha

pH: 7.29 pCO2: 32 HCO3: 15
Na: 138 K: 3 Cl: 110
Urine tests:pH: 6 Na: 35 K: 45 Cl: 75
pH<36
STEP 4: Evaluate the PCO2 and narrow down to one possible
process.
pCO2<40 mmHg
STEP 5: Use a formula for a metabolic acidosis and compare the
Expected pCO2= 1.5(HCO3)+8 2 =30 mmHg.
Actual pCO2=32 mm Hg. Monira Taha
Monira Taha

pH: 7.29 pCO2: 32 HCO3: 15
Na: 138 K: 3 Cl: 110
Urine tests:pH: 6 Na: 35 K: 45 Cl: 75
The expected Value Colsely matches the actual value of pCO2.
Conclude: -A pure metabolic acidosis is present.
-The metabolic acidosis is fully Compansated.
Anion Gap = 138 –(110+15) = 13
Conclude: Anormal gap metabolic acidosis is present.
Urine pH = 6.0 ( inappropriate high in the setting of acidemia).
STEP 9: Generate the diffferential diagnosis.
Monira Taha
Monira Taha

Normal Gab metabolic acidosis
DUR HAM
1-Diarrhea
2-Uretreral diversion
3-RTA
4-Hyperalimination
5-Acetazolamide
6-Miscellaneous (post-Hypocapnia)
Monira Taha
Monira Taha

RTA
-Type I distal
II proximal
III both
IV hyperkalaemic type
Now only I II IV
-How to differentiate from GIT loss.
Monira Taha
Monira Taha

-Type I Distal RTA:
• Defect in H secreation and HCO3
generation.
• Instead of H kidney secrete Ca,K,Na
• Urine is alkaline
Monira Taha
Monira Taha

Type II Proximal RTA:
• No reabsorption of filtered HCO3.
• Decrease HCO3 in blood.
• Decrease filtered HCO3.
• Decrease loss of HCO3.
• So no electrolyte abnormality as type I.
• Urine is acidic.
Monira Taha
Monira Taha

Type IV Hyperkalaemic RTA
(Hypoaldosteronism)
 Hypercholeramic ( Cl is retained when HCO3 is
lost )
 Hyperkalemic
Monira Taha
Monira Taha

Acid ingestion or infution
 Amonium chlorid and the amino-acid of
parental nutrition are metabolized in the
liver to HCL produce transient normal
gab metabolic acidosis.
Monira Taha
Monira Taha

Acetazolamide and ingestion of
carbonic anhydrase inhibitors
 Acetazolmide is used in TTT of glucoma
inhibits carbonic anhydrase in the eye also
in the kidney so interfere with HCO3
reabsorption and generation lead to loss of
HCO3 in urine.(RTA)
Monira Taha
Monira Taha

Posthypocapnia
♠ Renal tubular cell compansate for
respiratory alkalosis by decrease HCO3
generation and absorption.
♠ If hypocapnia treated rapidly renal function
take 1-2 days to resolve so during this
period normal gab metabolic acidosis will be
present.
Monira Taha
Monira Taha

• A 21-year-old woman is thrown from her
horse at a local event. On the way to
hospital she has become increasingly
drowsy and the paramedics have inserted
an oropharyngeal airway and given high-
flow oxygen via a face-mask with
reservoir. An arterial blood gas sample
has been taken.
Monira Taha

• Arterial blood gas analysis reveals:
Inspired oxygen 40% (FiO2 0.4)
normal values
PaO2 140 mmHg > (75 mmHg) on air
pH 7.16 7.35 – 7.45
PaCO2 70 mmHg 35- 45 mmHg
Bicarbonate 23.6 mmol l-1 22 – 26 mmol l-1
Base excess -2.4 mmol l-1 +/- 2 mmol l-1
Monira Taha

Initial Information
A 65-year-old man with severe COPD has been found
collapsed in the respiratory unit. On initial assessment by the
ward nurse he is apnoeic but has an easily palpable carotid
pulse. The nurse is attempting to ventilate his lungs with a bag-
mask and supplemental oxygen (with reservoir) and has called
the cardiac arrest team.
On arrival:
• Oropharyngeal airway, ventilated with bag-mask, oxygen
at 15 l min-1
• Carotid pulse palpable, 90 min-1, SpO2 99%
• Comatose (GCS 3)
Monira Taha

Monira Taha
estimated
normal values
PaO2 (147 mmHg) > (75 mmHg) on air
pH 7.10 7.35 – 7.45
PaCO2 (140 mmHg) (35 – 45 mmHg)
HCO3
- 36 mmol l-1 22 – 26 mmol l-1
BE + 12 mmol l-1 +/- 2 mmol l-1

A 75-year-old woman is admitted to the ED following a VF cardiac
arrest, witnessed by paramedics. This had been preceded by
30 min of severe central chest pain. Spontaneous circulation
restored after 2 shocks, but the patient remained apnoeic and
unresponsive. The paramedics intubated her trachea and
ventilated her with an automatic ventilator.
On arrival:
• Tube confirmed in trachea, tidal volume of 900 ml, rate of
18 breaths min-1, 100% oxygen
• Pulse 100 min-1, BP 90/54 mmHg
• Comatose (GCS 3)
Monira Taha

normal values
PaO2 (192 mmHg) > (75 mmHg) on air
pH 7.56 7.35 – 7.45
PaCO2 (20 mmHg) (35 – 45 mmHg)
HCO3
- 20 mmol l-1 22 – 26 mmol l-1
BE - 4 mmol l-1 +/- 2 mmol l-1
Monira Taha

• A 34-year-old morbidly obese woman with a body
mass index of 49
• has an ABG sample taken as part of her
preoperative assessment for
• weight reduction surgery.
• Apart from morbid obesity and type 2 diabetes, she
is otherwise
• well and has no respiratory symptoms.
Monira Taha

• pH 7.35 PCO2 54.8 mmHg
• PO2 72.2 mmHg
• Bicarb 29 mmol/L
• BE +3.8 mmol/L
• SO2 96% K 4.7 mmol/L Na 134 mmol/L
• Cl 102 mmol/L urine pH:
• a) Describe her gas exchange.
• b) Describe her acid–base status.
• 2. What is the most likely diagnosis?
Monira Taha

• A72-year-old woman with a brain tumor
diagnosed 3 month ago presents with an acute
change in mental status that began aboute 1
hour ago. She is currently comatose and
exhibits Kussmaul’s respiration. A CT scan of
the head reveals an intracerebral hemorrhage
with midline shift.
• pH: 7.57 pCO2: 20 PaO2: 90 mm Hg
HCO3: 18
• Na:136 Cl: 103
• Urine pH: 7
Monira Taha
Monira Taha

pH: 7.57 pCO2: 20 HCO3: 18
Na:136 Cl: 103
Urine pH: 7
pH>7.44
pCO2<40 mmHg
Conclude: At least a respiratory alkalosis is present.
STEP 5: Based on the history use a formula for acute respiratory
alkalosis and compare the predicted pH 0r (HCO3) with the actual pH 0r
(HCO3)
If we use the pH: for every decrease of 10 mm Hg in the pCO2, expect the
pH to increase (from 7.40) by 0.08
Because the pCO2 decrease by 20 ,the pH should increase by 0.16 to a
value of 7.56 (expected pH).
Actual pH = 7.57 Monira Taha
Monira Taha

The expected Value Closely matches the actual value of pH
Conclude: -An acute respiratory alkalosis is present.
-The kidney have not had time to Compensated.
Anion Gap = 136 –(103+21) = 12
Conclude: unlikely that an elevated gap metabolic acidosis is present.
Urine pH = 7.0 ( appropriate in the setting of alkalemia).
pH: 7.57 pCO2: 20 HCO3: 18
Na:136 Cl: 103
Urine pH: 7
Monira Taha
Monira Taha

Respiratory Alkalosis
• Hpoxia : Pneumonia, Pulmonary embolism,
pulmonary edema.
• Hyperdynamic states: Pain, Fever, Sepsis,
Pregnancy, Hyperthyrodism.
• CNS disorders: CVA, Infection, Subarachnoid
Hemorrhage.
• Drugs: Salicylates, catecholamines.
Monira Taha
Monira Taha

• The patient from previous case survives 2
more days with the same breathing pattern.
• pH: 7.47 pCO2: 21 HCO3: 15
• Na:136 Cl: 110
• Urine pH: 6.5
Monira Taha
Monira Taha

pH: 7.47 pCO2: 21 HCO3: 15
Na:136 Cl: 110
Urine pH: 6.5
pH>7.44
pCO2<40 mmHg
STEP 5: Based on the history use a formula for chronic respiratory
alkalosis and compare the predicted pH 0r (HCO3) with the actual pH 0r
(HCO3)
If we use the pH: for every decrease of 10 mm Hg in the pCO2, expect the
pH to increase (from 7.40) by 0.03
Because the pCO2 decrease by 20 ,the pH should increase by 0.06 to a
Actual pH = 7.47
Monira Taha
Monira Taha

Conclude: -An chronic respiratory alkalosis is present.
-The kidney have Compensated for this degree of alkalosis.
Anion Gap = 136 –(110+15) = 11
Urine pH = 6.5 ( appropriate in the setting of alkalemia).
pH: 7.47 pCO2: 21 HCO3: 15
Na:136 Cl: 110
Urine pH: 6.5
Monira Taha
Monira Taha

• A 20-year-old man is brought to the emergency
room by his sister, who tells you he took a
bottle of pills.
• pH: 7.35 pCO2: 15 PaO2: 85mmHg
HCO3: 8
• Na:140 Cl: 104 K:3.5
• Urine pH: 5.0
Monira Taha
Monira Taha

pH: 7.35 pCO2: 15 HCO3: 8
Na:140 Cl: 104 K:3.5
Urine pH: 5.0
STEP 3: Evaluate PH and narrow down to two possible
process. pH<36
Conclude: Either a metabolic or Respiratory acidosis is
present.
STEP 4: Evaluate the PCO2 and narrow down to one possible
process.
pCO2<40 mmHg
STEP 5: Use a formula for a metabolic acidosis and compare
the predicted pCO2 with the actual pCO2.
Expected pCO2= 1.5(HCO3)+8 2 = 20 mmHg.
Actual pCO2= 15 mm Hg. Monira Taha
Monira Taha

The actual value of pCO2 is less than expected . The only
process that can decrease pCO2 beyond that predicted is a
respiratory alkalosis.
Conclude: -A mixed metabolic acidosis and respiratory alkalosis
are present.
Anion Gap = (Na) – (HCO3 + CL)= 28
Conclude: An elevated gap metabolic acidosis is present.
Urine pH = 5.0 (appropriate in the setting of academia).
pH: 7.35 pCO2: 15 HCO3: 8
Na:140 Cl: 104 K:3.5
Urine pH: 5.0
Monira Taha
Monira Taha

A57-year-old patient with a long history of
smoking presents to you in the clinic. He is not
in distress, but he tells you he develops
dyspnea on exertion. You send him four
pulmonary function test and ABG.
• pH: 7.35 pCO2: 50 PaO2: 55mmHg HCO3:
27
• Na:143 Cl: 105
• Urine pH: 5.0
Monira Taha
Monira Taha

pH: 7.35 pCO2: 50 HCO3: 27
Na:143 Cl: 105
Urine pH: 5.0
pH<36
pCO2 > 40 mmHg
Conclude: At least a respiratory acidosis is present.
STEP 5: Because the patient clinacally does not have an acute process use a
formula for chronic respiratory acidosis and compare the predicted pH 0r
(HCO3) with the actual pH 0r (HCO3)
If we use the pH: for every increase of 10 mm Hg in the pCO2, expect the pH to
decrease (from 7.40) by 0.03
Because the pCO2 increase by 10 ,the pH should decrease by 0.03 to a value
of 7.37 (expected pH).
Monira Taha

Conclude: -An chronic respiratory acidosis is present.
Anion Gap = (Na) – (HCO3 + CL) = 10
Conclude: unlikely that an elevated gap metabolic acidosis is
present.
Urine pH = 5 ( appropriate in the setting of acidosis).
pH: 7.35 pCO2: 50 HCO3: 27
Na:143 Cl: 105
Urine pH: 5.0
Monira Taha
Monira Taha

Respiratory Acidosis
• Brain :Stroke, Hemorrhage, Mass, Hypoglycemia, Truma,
Toxin.
• Spinal cord :Transection at C3-C5, Trauma, Tumor,
Transverse myellitis.
• Phrenic nerve :Pancost tumor, Mediastinal tumor .
• Diaphragm :Hypophosphatemia, fatigue, Myasthenia
gravis, Tetanus.
• Chest wall :Kyphoscoliosis, Morbid obesity.
• Pleural space: Pneumothorax, Flail chest.
• Alveoli :Severe Plmonary edema, Emphysema.
• Bronchioles,Bronchi :COPD, Asthma, Sarcoidosis.
• Trachia, Upper air way :Foreign body aspiration.
Monira Taha
Monira Taha

Respiratory Acidosis
• CO2 + H2O → H2CO3 → HCO3 + H
The amount of H produced equal amount of HCO3
why pH fall?????
Monira Taha
Monira Taha

• The patient in previous case presents to
the emergency room 1 month later in
respiratory distress. He is wheezing and his
respiratory rate is 33 breath/minute.
• pH: 7.29 pCO2: 61 PaO2: 45mmHg
HCO3: 29
• Na:142 Cl: 100
• Urine pH: 5.0
Monira Taha
Monira Taha

pH: 7.29 pCO2: 61 HCO3: 29
Na:142 Cl: 100
Urine pH: 5.0
pH<36
pCO2 > 40 mmHg
STEP 5 :Because the patient clinacally have an acute process on top of
chronic use a formula for both chronic and acute respiratory acidosis and
delineate all the possible combination.
Evaute using the formula for chronic respiratory acidosis
Monira Taha

The actual pH is lower than expected value
Conclude: A mixed chronic respiratory acidosis and metabolic acidosis
- an acute on chronic
Evaute using the formula for acute respiratory acidosis
If we use the pH: for every increase of 10 mm Hg in the pCO2, expect the
pH to decrease (from 7.40) by 0.08
Because the pCO2 increase by 20 ,the pH should decrease by 0.16 to a
Actual pH = 7.29
The actual pH is higher than expected value
Conclude: A mixed acute respiratory acidosis and metabolic alkalosis
pH: 7.29 pCO2: 61 HCO3: 29
Na:142 Cl: 100
Urine pH: 5.0
Monira Taha
Monira Taha

Conclude: -A mixed chronic respiratory acidosis and metabolic acidosis
- A mixed acute respiratory acidosis and metabolic alkalosis
pH: 7.29 pCO2: 61 HCO3: 29
Na:142 Cl: 100
Urine pH: 5.0
Monira Taha
Monira Taha

• A 45-year-old diabetics patient presents with
acute obtundation.
• pH: 7.01 pCO2: 80 PaO2: 50mm Hg
HCO3: 20
• Na:140 Cl: 97 K: 5.5
• Urine pH: 5.0
Monira Taha
Monira Taha

pH: 7.01 pCO2: 80 HCO3: 20
Na:140 Cl: 97 K: 5.5
Urine pH: 5.0
pH<36
pCO2 > 40 mmHg
STEP 5: Evaute using the formula for acute respiratory acidosis
Monira Taha

The actual pH is lower than expected value
Conclude: A mixed acute respiratory acidosis and metabolic acidosis.
Conclude: an elevated gap metabolic acidosis is present.
pH: 7.01 pCO2: 80 HCO3: 20
Na:140 Cl: 97 K: 5.5
Urine pH: 5.0
Monira Taha
Monira Taha

A 78-year-old nursing home patient has been
vomiting for several days, and has rapiddly
developed a fever and increasing shortness of
breathing over the past several hours. Her
respiratory rate is 35 breaths/minute and she
has consolidative signs in the right base of the
lung.
• pH: 7.69 pCO2: 20 PaO2: 60 mm Hg
HCO3: 25
• Na:138 Cl: 97
• Urine pH: 8.0
Monira Taha
Monira Taha

pH: 7.69 pCO2: 20 HCO3: 25
Na:138 Cl: 97
Urine pH: 8.0
pH>7.44
pCO2<40 mmHg
STEP 5: Based on the history use a formula for acute respiratory alkalosis and
compare the predicted pH 0r (HCO3) with the actual pH 0r (HCO3)
If we use the pH: for every decrease of 10 mm Hg in the pCO2, expect the pH
to increase (from 7.40) by 0.08
Because the pCO2 decrease by 20 ,the pH should increase by 0.16 to a value
Actual pH = 7.69
Monira Taha
Monira Taha

The actual pH is higher than expected value
Conclude: A mixed acute respiratory alkalosis and metabolic
alkalosis.
Conclude: no elevated gap metabolic acidosis .
Urine pH = 8 ( appropriate in the setting of alkalosis).
pH: 7.69 pCO2: 20 HCO3: 25
Na:138 Cl: 97
Urine pH: 8.0
Monira Taha
Monira Taha

A 65-year-old man with COPD and congestive
heart failure presents with increasing
shortness of breathing and wheezing for the
past 4 hours. He is currently on furosemide.
• pH: 7.40 pCO2: 60 HCO3: 37
• Na:140 Cl: 90
• Urine pH: 5.0
Monira Taha

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