Blood Gases / Acid-Base - Welcome to NHS Networks ... Gases / Acid-Base Neonatal Ventilation Workshop June 2010 Dr. Julian Eason Consultant Neonatologist Why are blood gases performed?

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?