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Blood gas workshop How do we interpret the results ?

Josep Roca Hospital Clínic Universitat de Barcelona Spain

AGENDA  DIAGNOSTIC AND MONITORING TECHNIQUES  THE BASICS  PHYSIOLOGICAL BACKGROUND  CLINICAL SCENARIO

ERS 2006, Munich

 CONCLUSIONS

clinical diagnosis & assessment  RESPIRATORY BLOOD GAS MEASUREMENTS

monitoring techniques  PULSE OXIMETRY

ERS 2006, Munich

 END-TIDAL O2 & CO2  TRANSCUTANEOUS DE O2 & CO2 MEASUREMENTS

Future challenges

ERS 2006, Munich

Assessment of tissue hypoxia

mitochondrial respiration

ERS 2006, Munich

Near-Infrared Spectroscopy (NIRS)

ERS 2006, Munich

Nitroso-RedoxBalance

AGENDA  DIAGNOSTIC AND MONITORING TECHNIQUES  THE BASICS  PHYSIOLOGICAL BACKGROUND  CLINICAL SCENARIO

ERS 2006, Munich

 CONCLUSIONS

Arterial blood gas measurements  PULMONARY GAS EXCHANGE PaO2 PaCO2

 ACID – BASE STATUS

ERS 2006, Munich

pH PaCO2 Base excess

Arterial blood gas measurements FIO2 0.21 & BP 760 mmHg  PULMONARY GAS EXCHANGE PaO2 PaCO2

90-95 mmHg 35-45 mmHg

ERS 2006, Munich

 ACID – BASE STATUS pH

7.38 – 7.42

PaCO2 Base excess

respiratory component

- 2 to + 2

metabolic component

Arterial blood gas measurements FIO2 0.21 & BP 760 mmHg  HYPOXEMIA PaO2

< 80 mmHg

 RESPIRATORY FAILURE (hypoxemic)

ERS 2006, Munich

PaO2

< 60 mmHg

 RESPIRATORY FAILURE (hypercapnic) PaCO2

> 50 mmHg

Oxy-haemoglobin dissociation % SaO2 100 75

60 mmHg 50

ERS 2006, Munich

25

0

P50

PaO2 (mmHg)

Arterial blood gas measurements FIO2 0.21 & BP 760 mmHg  PULMONARY GAS EXCHANGE PaO2 PaCO2

 ACID – BASE STATUS ERS 2006, Munich

pH PaCO2

respiratory alcalosis (low PaCO2) or acidosis (high PaCO2)

Base excess

metabolic alcalosis (positive BE) or alcalosis (negative BE)

Arterial blood gas measurements  REDUNDANT VARIABLES CO2 content Actual bicarbonate

ERS 2006, Munich

Standard bicarbonate

Arterial blood gas measurements  ADDITIONAL INFORMATION REQUESTED Barometric pressure (BP) FIO2 or low flow oxygen therapy

ERS 2006, Munich

Patient temperature

inspiratory O2 partial pressure (PIO2) depends on BP and FIO2

AGENDA  DIAGNOSTIC AND MONITORING TECHNIQUES  THE BASICS  PHYSIOLOGICAL BACKGROUND  CLINICAL SCENARIO

ERS 2006, Munich

 CONCLUSIONS

ERS 2006, Munich

I

.

VA/Q

v .

PaO2 16

FACTORS GOVERNING PaO2 & PaCO2 INSPIRED OXYGEN ALVEOLAR VENTILATION

VENTILATION-PERFUSION IMBALANCE SHUNT

ERS 2006, Munich

CARDIAC OUTPUT

OXYGEN UPTAKE

DIFFUSION

Protective Ventilatory Strategy in ARDS Open lung minus baseline differences

ERS 2006, Munich

r 2 = 0.77

250

5

200

0

150 100 50

-5 -10 -15

0

-20

-50

-25

-100

-30 0

100

200

300

400

Recruited Volume (ml)

r 2 = 0.79

10

D Shunt %

∆ PaO2 (mmHg)

300

500

0

100

200

300

400

500

Recruited Volume (ml)

FACTORS GOVERNING PaO2 & PaCO2 INSPIRED OXYGEN ALVEOLAR VENTILATION

VENTILATION-PERFUSION IMBALANCE SHUNT

ERS 2006, Munich

CARDIAC OUTPUT

OXYGEN UPTAKE

DIFFUSION

FACTORS GOVERNING PaO2 & PaCO2 INSPIRED OXYGEN ALVEOLAR VENTILATION

VENTILATION-PERFUSION IMBALANCE SHUNT

ERS 2006, Munich

CARDIAC OUTPUT

OXYGEN UPTAKE

DIFFUSION

INTERACTION MIXED VENOUS AND ARTERIAL PO2 Healthy subjects

0.3 0.6

100

Arterial PO2 (mm Hg)

90

0.9

COPD

80

1.2 patients 1.5 1.8

70

60 50

ERS 2006, Munich

40 30 15

20

25

30

35

40

Mixed venous PO2 (mm Hg)

45 32

ERS 2006, Munich

DETERMINANTS OF HYPOXEMIA IN COPD EXACERBATION Low Mixed Venous PO2

Ventilation-Perfusion Worsening

26%

46%

28% Increased Oxygen Consumption Barberà JA et al. ERJ 1997; 10: 1285 19

AGENDA  DIAGNOSTIC AND MONITORING TECHNIQUES  THE BASICS  PHYSIOLOGICAL BACKGROUND  CLINICAL SCENARIO

ERS 2006, Munich

 CONCLUSIONS

 PULMONARY GAS EXCHANGE & ACID – BASE STATUS

PaCO2

90 37

Base excess

0

pH

7.40

ERS 2006, Munich

PaO2

normoxemia normocapnia normal BE normal pH

 PULMONARY GAS EXCHANGE & ACID – BASE STATUS

PaO2 PaCO2 Base excess ERS 2006, Munich

pH

90 37

normoxemia normocapnia

0

normal BE

7.40

normal pH

 PULMONARY GAS EXCHANGE & ACID – BASE STATUS FIO2 0.21 & BP 760 mmHg

PaO2 PaCO2 Base excess ERS 2006, Munich

pH

90 37

normoxemia normocapnia

0

normal BE

7.40

normal pH

 PULMONARY GAS EXCHANGE & ACID – BASE STATUS FIO2 0.21 & BP 760 mmHg

PaCO2

55 50

Base excess

+6

pH

7.38

ERS 2006, Munich

PaO2

respiratory failure hypercapnia metabolic alcalosis normal pH

 PULMONARY GAS EXCHANGE & ACID – BASE STATUS FIO2 0.21 & BP 760 mmHg

PaCO2

55 54

Base excess

0

pH

7.34

ERS 2006, Munich

PaO2

respiratory failure hypercapnia normal BE low pH

 PULMONARY GAS EXCHANGE & ACID – BASE STATUS FIO2 0.21 & BP 760 mmHg

PaCO2

70 25

Base excess

-10

0

pH

7.31

7.39

ERS 2006, Munich

PaO2

55 40

Alveolar Gas Equation

ERS 2006, Munich

PAO2 = (BP - PH2O) x FIO2 -

PACO2 RER

AaPO2 = PAO2 - PaO2

 PULMONARY GAS EXCHANGE & ACID – BASE STATUS FIO2 0.21 & BP 760 mmHg

PaCO2

70 25

Base excess

-10

0

pH

7.31

7.39

48

44

ERS 2006, Munich

PaO2

AaPO2

55 40

ERS 2006, Munich

 PULMONARY GAS EXCHANGE & ACID – BASE STATUS FIO2

0.21

1.0

PaO2 PaCO2

50 35

55 36

Base excess

-3

-3

pH

7.43

7.42

ERS 2006, Munich