ABG - Interpretation

3.To determine alveolar ventilation
2.To determine acid-base status
1.To determine oxygenation
Systematic Analysis of ABG Arterial Blood
Gases

--- XXX Diagnostics ----
Blood Gas Report
248 05:36 Jul 22 2009
Pt ID 2570/00
Measured 37.00 C
pH 7.463
pCO2 44.4 mm Hg
pO2 113.2 mm Hg
Corrected 38.60 C
pH 7.439
pCO2 47.6 mm Hg
pO2 123.5 mm Hg
Calculated Data
HCO3 act 31.1 mmol / L
HCO3 std 30.5 mmol / L
BE 6.6 mmol / L
O2 CT 14.7 mL / dl
O2 Sat 98.3 %
Ct CO2 32.4 mmol / L
pO2 (A-a) 32.2 mm Hg
pO2 (a/A) 0.79
Entered Data
Temp 38.6 0 C
Ct Hb 10.5 g/dl
FiO2 30.0 %
Measured Values
Temp Correction
? Any Value
Calculated Data
Which are the useful ones?
Entered Data
Derived from other sources

Traditional Measurements
Additional options include:
– Co-oximeter; measures O2 saturation
– Na+, K+, Ca2+, Cl -
– Haematocrit

Temperature Correction:
A spin-off of microprocessor capability?
“There is no scientific basis ... for applying temperature
corrections to blood gas measurements…”
- Shapiro BA, OTCC, 1999.
■ Uncorrected pH & pCO2 are reliable reflections of in-vivo acid
base status
■ Temperature correction of pH & pCO2 do not affect
calculated bicarbonate pCO2 reference points at 37o C are
well established as reliable reflectors of alveolar ventilation
■ Reliable data on DO2 and oxygen demand are unavailable at
temperatures other than 37o C
Blood Gas Report
248 05:36 Jul 22 2009
Pt ID 2570/00
Measured 37.00 C
pH 7.463
pCO2 44.4 mm Hg
pO2 113.2 mm Hg
Corrected 38.60 C
pH 7.439
pCO2 47.6 mm Hg
pO2 123.5 mm Hg
Calculated Data
BE 6.6 mmol / L
O2 CT 14.7 mL / dl
O2 Sat 98.3 %
Ct CO2 32.4 mmol / L
pO2 (a/A) 0.79
Entered Data
Temp 38.6 0 C
Ct Hb 10.5 g/dl
FiO2 30.0 %

( )
Acid Base Equation
Henderson - Hasselbach Equation
Blood Gas Report
248 05:36 Jul 22 2009
Pt ID 2570/00
Measured 37.00 C
pH 7.463
pCO2 44.4 mm Hg
pO2 113.2 mm Hg
Corrected 38.60 C
Calculated Data
BE 6.6 mmol / L
O2 CT 14.7 mL / dl
O2 Sat 98.3 %
t CO2 32.4 mmol / L
pO2 (a/A) 0.79
Entered Data
Temp 38.6 0 C
Ct Hb 10.5 g/dl
FiO2 30.0 %
pH = pKa + log
[Salt]
[Acid]

Standard Bicarbonate:
Plasma HCO3 after equilibration to a PCO2 of 40 mm Hg
: Reflects non-respiratory acid base change
: Does not quantify the extent of the buffer base
abnormality
: does not consider actual buffering capacity of blood
Base Excess:
 Base to normalise HCO3 (to 24) with PCO2 at 40 mm
Hg (Sigaard-Andersen)
: Reflects metabolic part of acid base 
: No info. over that derived from pH, pCO2 and HCO3
: Misinterpreted in chronic or mixed disorders
Blood Gas Report
248 05:36 Jul 22 2009
Pt ID 2570/00
Measured 37.00 C
pH 7.463
pCO2 44.4 mm Hg
pO2 113.2 mm Hg
Corrected 38.60 C
Calculated Data
BE 6.6 mmol / L
O2 CT 14.7 mL / dl
O2 Sat 98.3 %
t CO2 32.4 mmol / L
pO2 (a/A) 0.79
Entered Data
Temp 38.6 0 C
Ct Hb 10.5 g/dl
FiO2 30.0 %

Oxygenation
Parameters:O2 Content of blood:
Hb x O2 Sat x Const. + Dissolved O2
Blood Gas Report
248 05:36 Jul 22 2009
Pt ID 2570/00
Measured 37.00 C
pH 7.463
pCO2 44.4 mm Hg
pO2 113.2 mm Hg
Corrected 38.60 C
Calculated Data
BE 6.6 mmol / L
O2 CT 14.7 mL / dl
O2 Sat 98.3 %
t CO2 32.4 mmol / L
pO2 (a/A) 0.79
Entered Data
Temp 38.6 0 C
Ct Hb 10.5 g/dl
FiO2 30.0 %
Oxygen Saturation
Hb x O2 Sat x Const. + Dissolved O2
Alveolar / arterial gradient
Arterial / alveolar ratio
At sea level :-
Normal PaO2 = 75 to 100 mm Hg
Normal PvO2 = 30 – 40 mm Hg

Oxygen Saturation
Most blood gas machines estimate
saturation from an idealized
dissociation curve
Gold standard is co-oximetry
Errors may occur with abnormal
haemoglobins.
Oxygen content is calculated from
this.

Alveolar-arterial Difference
(Age and FiO2 dependent derivative)
■ It predicts the degree of shunt by comparing the partial pressure of O2 in the
(A) alveoli to that in the (a) artery.
■ The difference between them gives us an idea how well the oxygen is moving
from the alveoli to the arterial blood.
– The PaO2 is obtained from the ABG
(PAO2 - PaO2)
• Calculation of the A-a Gradient helps distinguish basic pathogenic causes of
hypoxemia. In general, diffusion defects, ventilation-perfusion defects, and right-
left shunts result in a widened A-a Gradient whereas hypoventilation and
residence at high altitudes do not.

Inspired O2 = 21%= piO2 = (760 - 45) x 0.21=150 mm Hg
palvO2 = piO2 - pCO2 / RQ
= 150 - 40/0.8
= 150 – 50 = 100 mm Hg
Palv O2 - part O2 = 10 mm Hg
part O2 = 90 mm Hg
O2
CO2
Normal = < [(age in yrs/4)+4]
RQ = CO2 produced/O2 consumed

Computation of Alveolar-arterial Difference
■ A-a (O2) = (FiO2%/100) * (Patm - 47 mmHg) - (PaCO2/0.8) - PaO2
Where:
FiO2 Room Air = 21 %
Atmospheric Pressure= 760 mm Hg at sea level
Water vapor pressure pH2O (mmHg) = 47 mm Hg at 37 degrees Celsius
Respiratory quotient RQ (VCO2/VO2) = 0.8 (usual)
■ Normal range increases with age. 5 to 20 is normal up to middle age
Hypoxemia with a normal gradient suggests: Hypoventilation (decreased respiratory drive or neuromuscular
disease) Low FiO2
Hypoxemia with an increased gradient suggests: Ventilation-perfusion imbalance -also known as V/Q
mismatch (asthma, COPD) Shunt : Cardiac right to left shunt such as patent foramen ovale, alveolar collapse,
(atelectasis), intraalveolar filling (pneumonia, pulmonary edema), or intrapulmonary shunt.
Supplemental O2 will help to correct the hypoxemia in hypoventilation and V/Q mismatch but not hypoxemia
resulting from a shunt.
• Normal oxygenation for age can be estimated pao2 = 104.2 - (0.27 x age) or
• More crudely, normal oxygenation for age is roughly 1/3 of the patient's age subtracted from 100.
Estimated normal gradient= (Age/4) + 4

Oxygenation Failure
piO2 = 150
piCO2 = 40
Palv O2 = 150 – 40/0.8
= 150 – 50
= 100
pO2 = 45
O2
CO2
Ventilation Failure
piO2 = 150
piCO2 = 80
Palv O2 = 150 – 80/0.8
= 150 – 100
= 50
pO2 = 45
 = 100-45 = 55  = 50-45 = 5
760 – 45 = 715
(atm) -- (Wat vapour pressure)
21% of 715 =150

PaO2 / FiO2 Ratio or "P/F" Ratio
(Carrico index)
■ Another much friendlier method ( because it doesn't use the
alveolar gas equation) used to predict shunt.
■ Just like the name says, PaO2 is divided by FiO2
■ Normal PaO2/FiO2 is >400 mmHg
■ Recent Berlin criteria defines mild ARDS at a ratio of <300

Oxygenation:
Limitations of Parameters
O2 Content of blood:
Useful in oxygen transport calculations
Blood Gas Report
248 05:36 Jul 22 2009
Pt ID 2570/00
Measured 37.00 C
pH 7.463
pCO2 44.4 mm Hg
pO2 113.2 mm Hg
Corrected 38.60 C
Calculated Data
BE 6.6 mmol / L
O2 CT 14.7 mL / dl
O2 Sat 98.3 %
t CO2 32.4 mmol / L
pO2 (a/A) 0.79
Entered Data
Temp 38.6 0 C
Ct Hb 10.5 g/dl
FiO2 30.0 %
Alveolar / arterial gradient
Reflects O2 exchange with fixed FiO2
Impractical
Differentiates hypoventilation as cause
O2 saturation
Ideally measured by co-oximetry
Calculated values my be error prone
Alveolar / arterial ratio
Proposed to be less variable
Same limitation as A-a gradient
Never comment on the oxygenation status without
knowing the corresponding FiO2.
Calculate the expected paO2 (generally five times the FiO2)

The Blood Gas Report:
The Essentials
pH 7.40 + 0.05
PCO2 40 + 5 mm Hg
PO2 80 - 100 mm Hg
HCO3 24 + 4 mmol/L
O2 Sat > 95
A-a  2.5 + (0.21 x Age) mm Hg
Blood Gas Report
Measured 37.00 C
pH 7.463
pCO2 44.4 mm Hg
pO2 113.2 mm Hg
Calculated Data
O2 Sat 98.3 %
pO2 (A - a) 32.2 mm Hg
Entered Data
FiO2 30.0 %

Technical Errors
Avoid
– Insufficient sample
– Hemolysis of the specimen
■ General Recommendations
– Do not cool
– Analyze within 30 min.
– For samples with high paO2 e.g. shunt or with high
leucocyte or platelet count – analyse within 5 mon
– When analysis is delayed for more than 30 min, use
glass syringes and ice slurry
– Inspect sample for clots
– Mix blood thoroughly by inverting syringe 10 times
– Only 0.05 ml of heparin required to anticoagulated 1
ml of blood

Technical Errors
Correct method of mixing of the arterial sample with the anticoagulant in two dimensions to
prevent stacking of red blood cells.

Before you Begin Reading an ABG
First: Initial Clinical Assessment
• From history, clinical examination and initial investigations, - most likely A-B disorder ?
Second: Acid-Base Diagnosis
• Perform a systematic evaluation of the blood gas and other results and make A-B
diagnosis
Finally: Clinical Diagnosis
• Synthesize the information to make an overall clinical diagnosis
Structured Approach to Assessment

Before you Begin Reading an ABG
■ Never comment on the ABG without obtaining a relevant clinical history of
the patient because History gives a clue to the etiology of the given acid–
base disorder.
Importance of Clinical History / Examination
Hypotension, renal failure, uncontrolled diabetic status, of treatment with
drugs such as metformin is likely to have
Metabolic acidosis
History of diuretic use, bicarbonate administration, high-nasogastric aspirate,
and vomiting
Metabolic alkalosis
COPD, muscular weakness, postoperative cases, and opioid overdose Respiratory acidosis
Sepsis, hepatic coma, and pregnancy Respiratory alkalosis

Acid Base Evaluation
■ 'Acid-base physiology' by Kerry Brandis –from http://www.anaesthesiaMCQ.com

■ The Boston Approach: Present method – uses
– Six bicarbonate based bedside rules to assess compensation
■ Copenhagen Approach - uses
– Four SBE-based bedside rules to assess compensation
■ Standard bicarbonate
■ Buffer Base
■ Base Excess
■ Stewart Method : Physicochemical approach
– superior to the physiologic approach, but it requires multiple calculations and
additional laboratory values and is thus more challenging to use in the clinical
setting.
The Great Atlantic Acid Base Debate

"The traditional measurements of pH, pCO2 and plasma bicarbonate
concentration continue to be the most reliable biochemical guides
in the analysis of acid-base disturbances. These measurements,
when considered in the light of the appropriate clinical information
and a knowledge of the expected response of the intact patient to
primary respiratory or metabolic disturbance, allow rational
evaluation of even the most complicated acid-base disorders.”
- Schwartz and Relman in 1963 (Boston)

Steps in Acid-Base Analysis
■ Step 1. Consider the clinical settings! Anticipate the disorder!
■ Step 2. Look at the pH?
■ Step 3. Who is the culprit for changing pH?...Metabolic / Respiratory process
■ Step 4. If respiratory…… acute and /or chronic?
■ Step 5. If compensations appropriate?
■ Step 6. If metabolic, Anion gap increased and/or normal or both?
■ Step 7. Is more than one disorder present? Mixed one?
• Arterial Blood Gases: A Simplified Bedside Approach; Vishram Buche, J Neonatal Biol. 2014, 3:4
• Boston method

First : Check the Consistency of Report
■ Assess the internal consistency of the values using the Henderseon-Hasselbach equation:
[H+] = 24 (PaCO2)
[HCO3-]
■ If the pH and the [H+] are inconsistent, the ABG is probably not valid.
pH Approx H+
(mmol/l)
7.0 100
7.05 89
7.10 79
7.15 71
7.20 63
7.25 56
7.3 50
pH Approx H+
(mmol/l)
7.35 45
7.40 40
7.45 35
7.50 32
7.55 28
7.60 25
7.65 22
• The hydrogen ion is calculated by subtracting the two digits after the decimal point of pH from 80,
e.g., if the pH is 7.23 then [H+] = 80 - 23 = 57

Step 2: pH
Look at the pH
Is the patient acidemic pH < 7.35 (acidosis +)
or
alkalemic pH > 7.45 (alkalosis +)
A normal pH does not rule out acid base disorder
• Interpretation of arterial blood gas; Pramod Sood, Gunchan Paul, and Sandeep Puri Indian J Crit Care
Med. 2010 Apr-Jun; 14(2): 57–64.

Step 3: Who is the Culprit - Pattern
■ In a normal ABG
 pH and paCO2 move in opposite directions.
 HCO3
-and paCO2 move in same direction.
? Primary Disturbance
Acidemia: With HCO3 < 20 mmol/L = metabolic
With PCO2 > 45 mm hg = respiratory
Alkalemia: With HCO3 > 28 mmol/L = metabolic
With PCO2 < 35 mm Hg = respiratory
1. When the pH and paCO2 change in the same direction (which normally should
not), the primary problem is metabolic;
2. When pH and paCO2 move in opposite directions and paCO2 is normal, then the
primary problem is respiratory.
If [HCO3] and PCO2 move in opposite directions THEN a mixed disorder must be present

Step 3 contd…
The exception :
When the metabolic component is also acid [ both are contributing to the acid
pH.
Mixed Disorder–if HCO3
- and paCO2 change in opposite direction (which they normally
should not), then it is a mixed disorder: pH may be normal with abnormal paCO2 or
abnormal pH and normal paCO2)
Here, we should look at the % difference and decide which is the dominant disturbance?
If the pH is below normal and the pCO2 is elevated, the
primary disorder is respiratory acidosis

Step 4 : Acute or Chronic?
■ Ratio of rate of change in H+ to change in paCO2 -- - --helps in
guiding us to conclude whether the respiratory disorder is acute, chronic,
or acute on chronic
If Respiratory, is it Acute or Chronic?
Respiratory Acidosis  H+ /  PaCO2
(per 10 mmHg
increase in PaCO2
(up to a PaCO2 of 70)
Fall in pH
ACUTE < 0.08 = 0.08 X (PaCO2 - 40)
CHRONIC > 0.03 = 0.03 X (PaCO2 - 40)
ACUTE on CHRONIC 0.03 to 0.08

Step 5: – Compensations
Rules of Compensations:
1. Depends upon the proper functioning of the organ system involved in the
response (lungs or kidneys) and on the severity of acid–base disturbance.
2. Acute compensation occurs within 6–24 h and chronic within 1–4 days.
Respiratory compensation occurs faster than metabolic compensation.
3. In clinical practice, it is rare to see complete compensation.
■ The maximum compensatory response in most cases is associated with
only 50–75% return of pH to normal. However, in chronic respiratory
alkalosis, the pH may actually completely return to normalcy in some cases

Appropriate Compensation During Simple Acid-Base
Disorders
DISORDER EXPECTED COMPENSATION
Metabolic
METABOLIC ACIDOSIS PCO2 = 1.5 × [HCO3
− ] + (8 ± 2)
METABOLIC ALKALOSIS PCO2 increases by 7 mm Hg for each 10 mEq/L increase in serum
[HCO3
− ]
Respiratory Acidosis
ACUTE [HCO3−] increases by 1 for each 10 mm Hg increase in PCO2
CHRONIC [HCO3
− ] increases by 3.5 for each 10 mm Hg increase in PCO2
Respiratory Alkalosis
ACUTE [HCO3−] falls by 2 for each 10 mm Hg decrease in PCO2
CHRONIC [HCO3−] falls by 4 for each 10 mm Hg decrease in PCO2
• Nelson, Textbook of Pediatrics, 21 e
Step 5: – Compensation
adequate?

Step 5: If Respiratory – Compensation adequate?
Respiratory Acidosis:
Acute (< 24 hrs):
“The 1- for 10 rule of Acute Respiratory Acidosis”
[HCO3
-] h by 1 mEq/L for every 10 mm Hg h in paCO2 > 40
 [HCO3] = 1/10  PCO2
Chronic (> 24 hrs):
“The 4 for 10 rule of Chronic Respiratory Acidosis”
[HCO3
-] h by 4 mEq/L for every 10 mmHg h in paCO2 > 40
 [HCO3] = 4/10  PCO2
Expected HCO3
= 24 + [(Actual pCO2-40)/10]
Expected HCO3
= 24 +[4*(Actual pCO2-40)/10]
Rule
1
Rule
2

Respiratory Alkalosis:
Acute (1 – 2 hrs):
“The 2 for 10 rule of Acute Respiratory Alkalosis”
[HCO3
-] i by 2 mEq/L for every 10 mmHg i in paCO2 < 40.
 [HCO3] = 2/10  PCO2
Chronic (> 2 days):
“The 5 for 10 rule of Chronic Respiratory Alkalosis”
[HCO3
-] i by 5 mEq/L for every 10 mmHg i in paCO2 < 40.
 [HCO3] = 5/10  PCO2
Step 5: If Respiratory – Compensation adequate?
• A Critique of the Parameters Used in the Evaluation of Acid Base Disorders -- Whole blood Buffer Base and Standard Bicarbonate
Compared with Blood pH and Plasma Bicarbonate William B. Schwartz and Arnold S. Relman, NEJM 1963,;268:1382-1388
Rule
3
Expected HCO3
= 24 – [2 (40 - Actual pCO2)/10]
Expected HCO3
= 24 - [5*(40 - Actual pCO2)/10]
(range: +/- 2)
Rule
4

Step 5: If Metabolic – Compensation adequate?
Metabolic Acidosis: – Winter’s Equation:
“The One & a Half plus 8 Rule - for a Metabolic Acidosis”
Expected paCO2 = (1.5 x HCO3+ 8) + 2 )
Metabolic Alkalosis:
“The Point Seven plus Twenty Rule - for a Metabolic Alkalosis”
Expected pCO2 = (0.7 x[ HCO3 + 20] + 5) OR 40 + [0.7 ΔHCO3]
If not:
• actual PCO2 > expected : hidden respiratory acidosis
• actual PCO2 < expected : hidden respiratory alkalosis
• If HCO3 10, PaCO2 should be 21 – 25
• If PaCO2 is < 21, additional respiratory acidosis
• If PaCO2 is > 25, additional respiratory alkalosis
Rule
5
Rule
6

Step 6: If Metabolic – Anion gap?
Anion gap = Na – (Cl + HCO3
--) Usually < 12
# Exception : Severe hypoalbuminemia
If AG > 12
Anion gap Met. Acidosis (AGMA)
[CAT MUDPILES]
If AG < 12
Non Anion gap Met. Acidosis (NAGMA)
[USED CAR]
Cyanide, CO
Arsenic
Tolune
Methanol
Uremia
Diabetic
Ketoacidosis
Paraldehyde
Infection
Lactic acid
Ethylene Glycol
Salicylate poisoning
Uretero-Sigmoid diversions
Saline administration
Endocrinopathies (Addisons, Prim hyperparathyroid)
Diarrhea
Carbonic Anhydrase inhibitors
Alimentation, hyper
Renal Tubular Acidosis

Step 6: If Metabolic – Anion gap?
Anion gap = Na – (Cl + HCO3
--) Usually < 12
NEW Mnemonics
If AG > 12
Anion gap Met. Acidosis (AGMA)
DULSI
If AG < 12
Non Anion gap Met. Acidosis (NAGMA)
RAGE
• Diabetic Ketoacidosis
• Uremia
• Lactic acidosis
• Salicylate poisoning
• Intoxicants
• Methanol,
• Ethanol,
• Ethylene glycol
• Renal Tubular Acidosis
• Acetazolamide, ammonium chloride
• GI
• Diarrhea,
• Enterienteric Fistula,
• Ureterosigmoidostomy
• Endocrinopathies
• Addisons,
• Primary Hyperparathyroidism
• Spiranolactone
• Triamterene
• Amiloride

Step 7: Does the anion gap explain the change in bicarbonate?
Corrected HCO3
-- = HCO3
-- + (AG - 12)
 anion gap (Anion gap -12) ~  [HCO3]
If  anion gap is greater; consider additional metabolic alkalosis
If  anion gap is less ; consider a non-anion gap metabolic acidosis

Step 7: contd…
Corrected HCO3
- = HCO3
- + (AG - 12)
Does the anion gap explain the change in bicarbonate ?
Example 1
• HCO3 10, AG 26
Corrected HCO3 = 10 + (26 -12) = 24
No additional disturbance
Example 2
• HCO3 15, AG 26
Corrected HCO3 = 15 + (26 -12) = 29
Additional metabolic alkalosis

Summary
■ Remember by heart: (CO2 is a respiratory acid)
■ pH and HCO3: Moves in same direction
■ pH and PCO2: Moves in opposite direction
■ When the pH and paCO2 change in the same direction (which
normally should not), the primary problem is metabolic;
■ HCO3 and PCO2: Moves in same direction (simple disorder)
■ HCO3 and PCO2: Moves in opposite directions (Mixed disorder)

Aids to Interpretation of Acid-Base Disorders
Clue Significance
High Anion Gap Always strongly suggest metabolic acidosis
Hyperglycemia If ketone bodies are present in urine – diabetic ketoacidosis
Hypokalemia and/or
hypochloremia
Suggest metabolic alkalosis
Hyperchloremia Common with normal anion gap metabolic acidosis
Elevated creatinine and
urea
Suggest uremic acidosis or hypovolemia (prerenal renal failure)
Elevated creatinine Consider ketoacidosis: ketones interfere in the laboratory method
(Jeffe reaction) used for creatinine measurement & give falsely
elevated result; typically urea will be normal
Elevated glucose Consider ketoacidosis or hyperosmolar non-ketotic syndrome
Urine dipstick tests for
glucose and ketone
Glucose detected if hyperglycemia, ketone detected if
ketoacidosis

Case 1
Blood Gas Report
Measured 37.00 C
pH 7.30
pCO2 76.2 mm Hg
pO2 45.5 mm Hg
Calculated Data
O2 Sat 78 %
pO2 (A - a) 9.5 mm Hg
pO2 (a / A ) 0.83
Entered Data
FiO2 21 %
pH < 7.35; acidemic
pCO2 > 45; respiratory acidemia
 CO2 = 76- 40=36;
Expected pH = 36/10 x 0.08 = 0.29
Expected pH = 7.40 – 0.29 = 7.11
Chronic resp. acidosis
Limits:
HCO3 = 4/10 of pCO2
= 4/10 x 36 = 10.8
Limits of HCO3=24+11=35
Pure Resp Acidosis
Hypoxia:
Normal A-a gradient
Due to hypoventilation

Case 2
Blood Gas Report
Measured 37.00 C
pH 7. 24
pCO2 49.1 mm Hg
pO2 66.3 mm Hg
Calculated Data
O2 Sat 92 %
pO2 (A - a) 9.5 mm Hg
pO2 (a / A ) 0.83
Entered Data
FiO2 30 %
pH < 7.35; acidemic
pCO2 > 45; respiratory acidemia
 CO2 = 49 - 40= 9;
Expected  pH = 9/10 x 0.08 = 0.072
Expected pH = 7.40 – 0.072 = 7.328
Acute resp. acidosis
Limits:
HCO3 = 1/10 of pCO2
= 1/10 x 9 = 0.9
Limits of HCO3=24+1=25
Resp Acidosis + Metabolic Acidosis
Hypoxia:
piO2=715x0.3=214.5 / PalvO2=214 - 49/0.8=153
153-66=87

Case 3
Blood Gas Report
Measured 37.00 C
pH 7. 23
pCO2 23 mm Hg
pO2 110.5 mm Hg
Calculated Data
O2 Sat %
pO2 (A - a) mm Hg
pO2 (a / A )
Entered Data
FiO2 21.0 %
pH < 7.35; acidemic
Limits:
Expected pCO2 = (1.5 x HCO3) +8 +2
= (1.5 x 14)+8+2
= 29+2 = 27 to 31
Met. acidosis + Resp. alkalosis
HCO3 < 22;
Metabolic acidemia
If Na = 130, Cl = 100
Anion Gap = 130 – (100+14)
= 130 – 114 = 16
Normal AG = 12;  Gap = 16-12 = 4
 HCO3 = 24 -14 = 10, 2.5 accounted for by resp. alkalosis
 / 3.5 indicates additional non-gap acidosis

Case 4
Blood Gas Report
Measured 37.00 C
pH 7. 48
pCO2 33 mm Hg
pO2 100.5 mm Hg
Calculated Data
O2 Sat %
pO2 (A - a) mm Hg
pO2 (a / A )
Entered Data
FiO2 21.0 %
pH > 7.35; alkalemia
pCO2 = 33 ,
Resp. alkalosis
HCO3 – normal
No compensation, yet

Case 5
Blood Gas Report
Measured 37.00 C
pH 7. 18
pCO2 41 mm Hg
pO2 100 mm Hg
Calculated Data
O2 Sat %
pO2 (A - a) mm Hg
pO2 (a / A )
Entered Data
FiO2 21.0 %
pH < 7.35; acidemic
pCO2 = Normal,
No compensation, yet
HCO3 < 24
Metabolic acidosis

Problem
Studies
• Gleson, C., & Devaskar, S. (2011). Avery’s Diseases of the Newborn (9th Ed.). Philadelphia: W.B.
• Saunders. ISBN: 978-1437701340.
• Gomella, T.L. (2009). Neonatology: Management, Procedures, On-Call Problems, Diseases and
Drugs (6th Edition). Norwalk, Conn.: Appleton & Lang. ISBN: 9780071544313
• Karlsen, K.A. (2012). The S.T.A.B.L.E. Program. Park City: The S.T.A. B.L.E. Program.

Practice Problem #1
■ A 31 week old infant is one hour old. CXR shows
■ diffuse atelectasis with air bronchograms.
■ CBG – 7.29/59/42/26

Practice Problem #1
■ Acidosis
■ pCO2 is high indicating a respiratory problem
■ leading to the acidosis
■ Capillary specimen
■ No compensation
■ Uncompensated respiratory acidosis
■ Treatment: NCPAP or MV

Practice Problem #2
■ A 33 week infant is receiving mechanical
■ ventilation for severe TTN. Settings: IMV 25, PIP 18,
■ PEEP 4, .30.
■ ABG: 7.49/26/95/22

Practice Problem #2
■ Alkalemia
■ The PaCO2 is low indicating a respiratory alkalosis
■ Pa02 is high
■ No compensation
■ Uncompensated Respiratory Alkalosis
■ Treatment: wean the PIP or rate along with Fi02

Practice Problem #3
■ 26 week infant has been on the ventilator for 2
■ weeks for RDS. PIE is present.
■ CBG: 7.37/55/65/29

Practice Problem #3
■ pH normal
■ pCO2 is high indicating a respiratory problem, which could lead to
acidosis
■ Capillary specimen
■ Compensation present – pH normal with abnormal HCO3 and pC02.
pH closer to acidosis
■ Compensated respiratory acidosis
■ Treatment: no action needed. Further increases in the pCO2 could
result in decompensation.

Practice Problem #4
■ 26 week old infant on the ventilator for RDS.
■ Settings: IMV 30, 19/5, and .40.
■ Infant has lost 30 gms in the past 12 hours with a Na of 148.
■ ABG: 7.29/53/55/17

Practice Problem #4
■ Acidemia
■ The PaCO2 is high indicating a respiratory acidosis and the
HCO3 is low indicating a metabolic acidosis.
■ Oxygen level adequate.
■ No compensation – pH not normal
■ Uncompensated mixed acidosis.
■ Treatment: increase alveolar ventilation and consider giving
volume to correct the hypovolemia

Practice Problem #5
■ Term infant with tight nuchal cord. Infant pale,
grunting, with cap refill of 8 seconds.
■ ABG: 7.15/40/75/15/-15

Practice Problem #5
■ Acidosis
■ Metabolic in origin – decreased HCO3 with normal pCO2
■ Oxygen level adequate
■ No compensation – pCO2 normal
■ Uncompensated Metabolic Acidosis
■ Treatment: consider volume or HCO3 depending on
respiratory assessment.

ABG - Interpretation

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ABG - Interpretation