blood gas analysis in neonates. 6 simple steps will help to read blood gas

1. Interpretation of Blood gases
-Dr.Lingaraj Mulage

2. Introduction
 Interpretation of the blood gas by health-care personnel is a critical step in the
management of sick infants and newborns.
 Blood gas aids the clinician in treatment plan and prognostication.
 It reflects the sickness of the infant and provides essential information of an ongoing
change in the clinical status of the sick infant.

3. Indication for blood gas analysis
(1) Infants with respiratory distress on oxygen therapy, non-invasive/ invasive
ventilation to know oxygenation and ventilation status
(2) Sick infants with sepsis, shock, decreased cardiac output, PDA to assess organ
perfusion status
(3) Metabolic disorders (perinatal asphyxia, renal failure, suspected or proven inborn
error of metabolism)
(4) Monitoring neonates on therapeutic hypothermia, circulatory support, renal
replacement therapy
(5) Post-surgery monitoring

4. Terminologies Used in Blood Gas Analysis
Temperature:
 All tests are measured at 370C
 If the patients temperature is not entered then the blood gas values can be estimated
as follows:
1) Subtract 5 mm Hg pO2 per 1ºC below 37ºC
2) Subtract 2 mm Hg PCO2 per 1ºC below 37ºC
3) Add 0.012 pH units per 1ºC below 37ºC

5. Terminologies Used in Blood Gas Analysis
pH:
pH is defined as decimal logarithm of the reciprocal of the hydrogen
ion. Blood pH is acidity or alkalinity of blood.
Normal pH is maintained between 7.35 to 7.45.
PaO2:
The partial pressure of oxygen in arterial blood (paO2) refers to
pressure exerted by oxygen in the blood.
The normal values for PaO2 is 60-80 mmHg.

6. Terminologies Used in Blood Gas Analysis
PaCO2 :
 The partial pressure of Carbon dioxide in arterial blood (PaCO2) refers to pressure
exerted by carbon dioxide in the blood.
 The normal values for PaCO2 is 35-45 mmHg.
Base Excess (BE) Buffer base (BB): is a mixture of weak acid and conjugate base
which prevents changes in pH. 25% of BB is constituted by hemoglobin buffer, 50% by
bicarbonate and 25% by other buffers (proteins, phosphate, sulphate).
 Normal BB is 48-49 mmol/L.
 Base excess (BE) refers to actual base excess in variance from (above or below) total
buffer base (BB). If BB is 38, it means BE is –10 (also called base deficit). If BB is 56, it
means BE is +8.

7. Terminologies Used in Blood Gas Analysis
Standard HCO3 (SBC) It is used to denote value of HCO-3, at standard pCO2 of
40mmHg and temperature of 37oC. This is used to separate respiratory effect of pCO2
on actual HCO-3 (ABC) and evaluate metabolic status (Copenhagen approach).
Standard pH (St. pH) is the pH purely due to metabolic status, adjusted for pCO2 of 40
mmHg and temperature of 37oC.
Standard Base Excess (SBE): is the amount of alkali available to return the ECF pH to
normal pH (7.40) under standard conditions (at 37oC at a PCO2 of 40 mm Hg),
assuming that hemoglobin is 5gm/dl. Hemoglobin which buffers entire ECF is taken as
1/3rd of the standard hemoglobin (15 g/dl).

8. Terminologies Used in Blood Gas Analysis
CH+:
Concentration of hydrogen ion in nmol/L at 37 C and patients temperature.
O2 sat:
Proportion/percentage of hemoglobin which is saturated with oxygen.
Aa DO2 :
Alveolar to arterial oxygen gradient. Normal value is 5 to 15 mm Hg
RQ:
Amount of CO2 liberated per minute divided by amount of O2 utilised per minute.
Normal values are 200 ml/250 ml =0.8.
FiO2:
Inspired oxygen fraction concentration

9. Details of pH
 pH=pK + log (HCO3/H2 CO3) (Henderson-Hasselbach euqation)
 Normal 7.35-7.45
Ideal 7.4± 2 S.D.
Alkalosis>7.5
Acidosis <7.3
Severe acidosis <7.2

10.  H2O + CO2 = H2CO3- (Carbonic acid) = HCO3- (bicarbonate) + H+ (hydrogen ion).
 Acidosis due to hydrogen ion accumulation will result in left-shift of equation and increased
carbon dioxide which is cleared by lungs.
 Similarly, increased CO2 levels due to respiratory disease are compensated by the kidneys by
increased excretion of H+ ions.
 The respiratory compensation is faster than the renal compensation
The effect of buffers on pH

11. Blood Sampling and Normal Blood Gas Values

12. Normal Blood Gas

13. Normal blood gas values

14. Interpretation of ABG
The 6 Easy Steps to Basic ABG Analysis:
1. ls the pH normal?
2. ls the CO2 normal?
3. ls the HCO3 normal?
4. Match the CO2 or the HCO3 with the pH
5. Does the CO2 or the HCO3 go the opposite direction of the pH?
6. Are the p02 and the O2 saturation normal?

15. 1. An infant born at 31 weeks gestation is two hours old with the following
physical findings: respiratory rate 74 breaths per minute, heart rate 162
beats per minute, temperature 36.5°C (97.7°F), and grunting with moderate
retractions.
Capillary blood gas results are as follows:
 pH 7.30
 PCO2 56 mmHg
 HCO3– 26 mEq/liter
 PO2 40 mmHg.

16. After 4hrs
 pH = 7.22 mmHg,
 PaCO2 = 68 mmHg,
 PaO2 = 40 mmHg,
 HCO3- = 24 mEq/L

17. At 36hrs of life: on mechanical ventilation for respiratory
distress (Rate 30, PIP 19, PEEP +5, and FiO2 40%). Systolic
Murmur +
 pH = 7.28
 PaCO2 49 mmHg
 PaO2 = 56 mmHg
 HCO3- = 15 mEq/l.

18. On D5 of life: Mechanical ventilation rate 25, PIP 18, PEEP
+4, FiO2 30%.
 pH = 7.49 mmHg
 PaCO2 = 26 mmHg
 PaO2 = 95 mmHg
 HCO3- = 22 mEq/l

19. D6: On CPAP , Fio2: 21%, PEEP : 4 cm of H2O, SpO2 :96%.
Capillary blood gas
 pH = 7.52 mmHg
 PCO2 = 38 mmHg
 PO2 = 56 mm Hg
 HCO3- = 35 mEq.

20. Thank You !

21. Interpretation of ABG
Parameter Normal Work 1 Work 2 Work 3 Work 4
pH 7.35-7.45 7.27 7.52 7.18 7.60
PCO2 35-45 53 29 44 37
PO2 50-80 50 100 92 92
O2 sat % 90-95 79 98 95 98
HCO3 22-24 24 23 16 35
Interpretation Normal UcRAk+
Hyperoxia
Uc MAc Uc MAlk

22. Formulas for compensation of acid base imbalance

23. Interpretation of ABG
Parameter Normal Work 1 Work 2 Work 3 Work 4
pH 7.35-7.45 7.27 7.52 7.18 7.60
PCO2 35-45 53 29 44 37
PO2 50-80 50 100 92 92
O2 sat % 90-95 79 98 95 98
HCO3 22-24 24 23 16 35
Interpretation Normal Uc RAc+
Hypoxia
Uc MAc Uc MAlk

24. Interpretation of ABG
Parameter Normal Work 1 Work 2 Work 3 Work 4
pH 7.35-7.45 7.27 7.52 7.18 7.60
PCO2 35-45 53 29 44 37
PO2 50-80 50 100 92 92
O2 sat % 90-95 79 98 95 98
HCO3 22-24 24 23 16 35
Interpretation Normal Uc RAc+
Hypoxia
Uc Ralk Uc MAlk

25. Interpretation of ABG
Parameter Normal Work 1 Work 2 Work 3 Work 4
pH 7.35-7.45 7.27 7.52 7.18 7.60
PCO2 35-45 53 29 44 37
PO2 50-80 50 100 92 92
O2 sat % 90-95 79 98 95 98
HCO3 22-24 24 23 16 35
Interpretation Normal Uc RAc+
Hypoxia
Uc Ralk Uc MAc

26. Thank You !