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Blood Gases / Acid-Base
Neonatal Ventilation Workshop
June 2010
Dr. Julian EasonConsultant Neonatologist
Why are blood gases performed?
• Diagnostic assessment of oxygenation capacity of lungs
• Therapeutic assessment of oxygen pressure in blood
• Assess respiratory adequacy• Assess acid-base status
How are blood gases performed?
• Aseptic technique• Arterial, Capillary, Venous• Machine measures pH, PaCO2, PaO2• Serum bicarbonate calculated
• Air bubbles, fluid dilution and pain can alter results
Normal Values
pHPaCO2PaO2
BicarbonateBase Excess
Normal Values
pH 7.32 – 7.44PaCO2 4.7 – 6.0 kPaPaO2 8.0 – 9.3 kPa
Bicarbonate 22 - 28Base Excess -4.0 – 4.0 mEq/L
Clinical condition must be incorporated into any blood gas analysis
Acid-base and buffers
• pH is a method of measuring small concentrations of acid in solution
• A buffer resists changes in pH by undergoing a reversible reaction
• pH stability maintains enzyme function, muscle and metabolic activity
• Buffering systems– Carbonic acid – bicarbonate system– Haemoglobin– Phosphate
Base Excess
• Buffer base is total of all anionic buffer components in the blood
• Base excess is the amount of deviation of patient’s buffer base from normal– “How much extra basic chemicals the patient has in the
blood.”• Base excess can be a negative value
– BE of -8 means 8mEq/L of base needs to be added to normalise the pH.
• More than just bicarbonate
Approach to the abnormal blood gas
• What is wrong?
• What caused it?
• What is being done about it?
Approach to the abnormal blood gas
• What is wrong?
• What caused it?
• What is being done about it?
• Look at pH• Look at PaCO2• Look at bicarbonate
value
• Acidosis v Alkalosis• Respiratory v Metabolic• Compensated v not
Clinical Scenarios
Clinical Scenario 1
32/40, Received steroids. PROM 3/7. NVD. Apgars 61,95. 10 mins of age on CDS. Grunting resps. Gas taken
Sample cap
pH 7.18
PaCO2 7.8
PaO2 5.8
Bicarb 18
BE -9.6
Clinical Scenario 1
32/40, Received steroids. PROM 3/7. NVD. Apgars 61,95. 10 mins of age on CDS. Grunting resps. Gas taken
• PEEP applied 4cmH2O during transfer
• T 36.6°C. Sats 92% in 35% FiO2• Rpt gas on admission
Sample cap cap
pH 7.18 7.2
PaCO2 7.8 8.2
PaO2 5.8 4.5
Bicarb 18 20
BE -9.6 -5.9
Clinical Scenario 1
32/40, Received steroids. PROM 3/7. NVD. Apgars 61,95. 10 mins of age on CDS. Grunting resps. Gas taken
• PEEP applied 4cmH2O during transfer
• T 36.6°C. Sats 92% in 35% FiO2• Rpt gas on admission
• CPAP driver 5-6cmH2O. Day 1 fluids. Sats 92% in air
Sample cap cap cap
pH 7.18 7.2 7.29
PaCO2 7.8 8.2 5.5
PaO2 5.8 4.5 5.1
Bicarb 18 20 19.6
BE -9.6 -5.9 -3.6
Clinical Scenario 2
25/40, Day 3. Ventilated SIMV 22/4, Rate 40, I time 0.34, Sats 90% in FiO2 35%. Gas taken
Sample art
pH 7.16
PaCO2 7.2
PaO2 5.6
Bicarb 22
BE -3.9
Clinical Scenario 2
25/40, Day 3. Ventilated SIMV 22/4, Rate 40, I time 0.34, Sats 90% in FiO2 35%. Gas taken
• Pressure 24/4, Rate 45. Sats87% in FiO2 50%
• Repeat gas taken after 30mins
Sample art art
7.16
7.2
5.6
22
-3.9
pH 7.03
PaCO2 11.5
PaO2 3.4
Bicarb 17.4
BE -8.4
Clinical Scenario 2
25/40, Day 3. Ventilated SIMV 22/4, Rate 40, I time 0.34, Sats 90% in FiO2 35%. Gas taken
• Pressure 24/4, Rate 45. Sats87% in FiO2 50%
• Repeat gas taken after 30mins
• Cold light test positive• Chest drain inserted. Improves
clinically. Remains ventilated
• 7 days later, shown gas by nurse
Sample art art
7.16
7.2
5.6
22
-3.9
7.03
11.5
3.4
17.4
-8.4
pH
PaCO2
PaO2
Bicarb
BE
Clinical Scenario 2
25/40, Day 3. Ventilated SIMV 22/4, Rate 40, I time 0.34, Sats 90% in FiO2 35%. Gas taken
• Pressure 24/4, Rate 45. Sats87% in FiO2 50%
• Repeat gas taken after 30mins
• Cold light test positive• Chest drain inserted. Improves
clinically. Remains ventilated
• 7 days later, shown gas by nurse
Sample art art art
7.16
7.2
5.6
22
-3.9
7.03
11.5
3.4
17.4
-8.4
pH 7.30
PaCO2 8.6
PaO2 5.5
Bicarb 27.8
BE 1.2
Clinical Scenario 3
34/40, PROM 24hrs. NVD. Postnatal ward. Feeds. Grunting resps at 5hrs of age. Moved to SCBU. Gas taken
Sample cap
pH 7.01
PaCO2 14.0
PaO2 14.4
Bicarb 24.4
BE -10.9
Clinical Scenario 3
34/40, PROM 24hrs. NVD. Postnatal ward. Feeds. Grunting resps at 5hrs of age. Moved to SCBU. Gas taken
• Given 30% oxygen. 10ml/kg fluid bolus. Partial septic screen. IV antibiotics
• 4hrs later, gas is taken
Sample cap cap
pH 7.01 6.91
PaCO2 14.0 12.5
PaO2 14.4 5.6
Bicarb 24.4 17.3
BE -10.9 -15.1
Clinical Scenario 3
34/40, PROM 24hrs. NVD. Postnatal ward. Feeds. Grunting resps at 5hrs of age. Moved to SCBU. Gas taken
• Given 30% oxygen. 10ml/kg fluid bolus. Partial septic screen. IV antibiotics
• 4hrs later, gas is taken
• Intubated 2.5mm ETT. Surfactant. SIMV 18/4, Rate 50, I 0.32, FiO250%. 10ml/kg fluid bolus.
• Gas taken. Retrieval team called.
Sample cap cap cap
7.06
11.8
4.1
15.6
-16.0
pH 7.01 6.91
PaCO2 14.0 12.5
PaO2 14.4 5.6
Bicarb 24.4 17.3
BE -10.9 -15.1
Clinical Scenario 3
34/40, PROM 24hrs. NVD. Postnatal ward. Feeds. Grunting resps at 5hrs of age. Moved to SCBU. Gas taken
• Given 30% oxygen. 10ml/kg fluid bolus. Partial septic screen. IV antibiotics
• 4hrs later, gas is taken
• Intubated 2.5mm ETT. Surfactant. SIMV 18/4, Rate 50, I 0.32, FiO250%. 10ml/kg fluid bolus.
• Gas taken. Retrieval team called.
• Reintubated 3.5mm ETT. Ventilation Central lines. Inotropes.
Sample cap cap cap art
7.06
11.8
4.1
15.6
-16.0
pH 7.01 6.91 7.28
PaCO2 14.0 12.5 3.9
PaO2 14.4 5.6 8.9
Bicarb 24.4 17.3 13.2
BE -10.9 -15.1 -12.0
Any Questions?