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OXYGENATION &
VENTILATION
MONITORING
Point of Discussion
1. Indices of oxygenation
2. Indices of ventilation
3. Pulse oximetry
4. Capnography
5. Arterial and v...
Indices of Oxygenation
Alveolar Arterial O2 Gradient
Alveolar Gas Capillary Blood
initial Initial
Thickness
A-a Gradient
Pulse Oximetry
O2-Hg Dissociation Curve
PaO2 (mm Hg)
90
60
Sources of error
 Poor peripheral perfusion
 Dark skin
 False nails or nail varnish
 Lipaemia
 Bright ambient light
...
The Ventilation Vital Sign
Capnography
Capnograhy vs Capnometry?
 Capnography- Continuous analysis and
recording of Carbon Dioxide concentrations in
respiratory...
Semi-Quantitative Capnometry
 Relies on pH change
 Paper changes color
 Purple to Brown to Yellow
Quantitative Capnometry
 Absorption of infra-
red
light
 Gas source
 Side Stream
 In-Line
Factors in choosing
device:
...
Waveform Capnometry
 Adds continuous
waveform display to
the ETCO2 value.
 Additional
information in
waveform shape
can ...
Why ETCO2 I Have my Pulse
Ox?
Oxygen Saturation
Reflects
Oxygenation
SpO2 changes lag
when patient is
hypoventilating o...
What does it really do for me?
Bronchospasms:
Asthma, COPD,
Anaphlyaxis
Hypoventilation:
Drugs, Stroke, CHF,
Post-Ictal
...
NORMAL CAPNOGRAM
Phase I Phase IIIPhase II
Inspiratory PhaseExpiratory Phase
70
60
50
40
30
20
10
0
PetCO2
Time
mm Hg
Phas...
ABNORMALITIES
Abnormality Indication
Increased Phase III slope Obstructive lung disease
Phase III dip Spontaneous respirat...
ABNORMALITIES
Abnormality Indication
Sudden increase in ETCO2 Sodium bicarb administration
Release of limb tourniquet
Grad...
USES
 Metabolic
 Assess energy expenditure
 Cardiovascular
 Monitor trend in cardiac output
 Can use as an indirect F...
PaCO2-PetCO2 gradient
 Usually <6mm Hg
 PetCO2 is usually less
 Difference depends on the number of
underperfused alveo...
LIMITATIONS
 Critically ill patients often have rapidly
changing dead space and V/Q mismatch
 Higher rates and smaller T...
PULMONARY USES
 Effectiveness of therapy in bronchospasm
 Monitor PaCO2-PetCO2 gradient
 Worsening indicated by rising ...
NORMAL Waveform
70
60
50
40
30
20
10
0 Time
mm Hg
• Square box waveform
• ETCO2 35-45 mm Hg
• Management: Monitor Patient
Sudden  in ETCO2 to 0
70
60
50
40
30
20
10
0 Time
mm Hg
• Loss of waveform
• Loss of ETCO2 reading
• Dislodged tube
• ET ...
Esophageal Intubation
70
60
50
40
30
20
10
0 Time
mm Hg
• Absence of waveform
• Absence of ETCO2
• Management: Re-Intubate
CPR
70
60
50
40
30
20
10
0 Time
mm Hg
• Square box waveform
• ETCO2 15-20 mm Hg with adequate CPR
• ETCO2 falls bellow 10 ...
Return of Spontaneous
Circulation
70
60
50
40
30
20
10
0 Time
mm Hg
• During CPR sudden increase of ETCO2 above
10-15 mm H...
Gradual Decrease in ETCO2
70
60
50
40
30
20
10
0 Time
mm Hg
• Hyperventilation
• Decreasing temp
• Gradual  in volume
Hyperventilation
70
60
50
40
30
20
10
0 Time
mm Hg
• Shortened waveform
• ETCO2 < 35 mm Hg
• Management: If conscious give...
Gradual Increase in ETCO2
70
60
50
40
30
20
10
0 Time
mm Hg
• Fever
• Hypoventilation
Hypoventilation
70
60
50
40
30
20
10
0 Time
mm Hg
• Prolonged waveform
• ETCO2 >45 mm Hg
• Management: Assist ventilations
Rising Baseline
70
60
50
40
30
20
10
0 Time
mm Hg
• Patient is re-breathing CO2
• Management: Check equipment for adequate...
Curare Cleft
70
60
50
40
30
20
10
0 Time
mm Hg
• Curare Cleft is when a neuromuscular blockade
wears off
• The patient tak...
Breathing around ETT
70
60
50
40
30
20
10
0 Time
mm Hg
• Angled, sloping down stroke on the waveform
• In adults may mean ...
Obstructive Airway
70
60
50
40
30
20
10
0 Time
mm Hg
• Shark fin waveform
• With or without prolonged expiratory phase
• C...
Oscillation in Inspiratory Phase
70
60
50
40
30
20
10
0 Time
mm Hg
J Int Care Med, 12(1): 18-32, 1997J Int Care Med, 12(1)...
Oscillation in Inspiratory Phase
70
60
50
40
30
20
10
0 Time
mm Hg
J Int Care Med, 12(1): 18-32, 1997J Int Care Med, 12(1)...
Oscillation and slow Inspiration
70
60
50
40
30
20
10
0 Time
mm Hg
J Int Care Med, 12(1): 18-32, 1997J Int Care Med, 12(1)...
6 Step ABG’s Analysis
Blood Gases
1. Acidemic/Alkalemic?
 This refers to the pH
 Normal pH= 7.40 ± 0.05
 Acidemia pH < 7.40
 Alkalemia pH > 7.40
 Norma...
2. Primary -osis
pH emia PaCO2 HCO3 1 ° osis
<7.40 acidemia <40 <24 1°Metabol
ic
acidosis
<7.40 acidemia >40 >24 Respirato...
2. Respiratory process acute or
chronic ?
 Respiratory Acidosis Acute :
∆ pH= 0.08x(PaCO2-40)/10
 Respiratory Acidosis C...
4. Metabolic acidosis
 Anion gap vs. Nongap acidosis
 Anion gap (AG) = Na-Cl-HCO3
3. Adequate degree of
compensation for Metabolic
Acidosis ?
 Calculated (expected) PaCO2 for Gap
acidosis (Winte r’s fo r...
4. Calculated (expected) HCO3
 Calculated (expected) HCO3 =
(Pt.’s AG-nl gap) + measured HCO3
 Calculated HCO3>30 associ...
4. Metabolic acidosis
 Check for Osmolar gap (OG)
OG:Measured osmol – Calculated > 10
Calculated Osmol=
(2xNa) + glucose/...
5. Calculate Urinary AG
 Determines renal vs. extrarenal causes
 UAG=UNa+UK-UCl (nl -10 to 10).
 UAG <-10 = extrarenal ...
6. Adequate degree of compensation for Metabolic
Alkalosis ?
For every ∆ 1 in HCO3 the paCO2 ∆ 0.6
Adequate degree of compensation ?
PrimaryPrimary
problemproblem
CompensationCompensation For everyFor every
∆∆ inin
Expect...
ABG Problems:
145145 100100 1616
4.04.0 1212 1.01.0
 7.2/26/85/95% on
RA
Answer
 Metabolic acidosis
 145-100-12=AG 33
 Expected PaCO2 1.5x12 +8 ±2=26±2
appropriate
 Expected HCO3= (33-12) + 1...
ABG Problems
 7.1/35/60/90% on
RA
135135 106106 1616
4.24.2 1010 1.01.0
Answer
 Metabolic acidosis
 135-106-10 = AG 19
 Expected PaCO2 1.5 x 10 +8 ±2=23±2
Measured >calculated
 Concomitant r...
ABG Problems
 HIV, HBV associated ESLD, ARF with pleural
effusions, tachypneic RR 34
 7.48/28/55/90% on 4L NC
155|97|41/...
Answer
Respiratory alkalosis
∆ H:748-740=8
∆ paCO2: 40-28=12
8/12=0.67 Acute on chronic respiratory alkalosis.
Acute from ...
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Oxygenation and ventilation monitoring

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Capnography, Pulse oximetry and blood gas monitoring

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Oxygenation and ventilation monitoring

  1. 1. OXYGENATION & VENTILATION MONITORING
  2. 2. Point of Discussion 1. Indices of oxygenation 2. Indices of ventilation 3. Pulse oximetry 4. Capnography 5. Arterial and venous blood gases
  3. 3. Indices of Oxygenation
  4. 4. Alveolar Arterial O2 Gradient Alveolar Gas Capillary Blood initial Initial Thickness A-a Gradient
  5. 5. Pulse Oximetry
  6. 6. O2-Hg Dissociation Curve PaO2 (mm Hg) 90 60
  7. 7. Sources of error  Poor peripheral perfusion  Dark skin  False nails or nail varnish  Lipaemia  Bright ambient light  Poorly adherent probe  Excessive motion  Carboxyhaemoglobin or methaemoglobin
  8. 8. The Ventilation Vital Sign Capnography
  9. 9. Capnograhy vs Capnometry?  Capnography- Continuous analysis and recording of Carbon Dioxide concentrations in respiratory gases ( I.E. waveforms and numbers)  Capnometry- Analysis only of the gases no waveforms
  10. 10. Semi-Quantitative Capnometry  Relies on pH change  Paper changes color  Purple to Brown to Yellow
  11. 11. Quantitative Capnometry  Absorption of infra- red light  Gas source  Side Stream  In-Line Factors in choosing device:  Warm up time  Cost  Portability
  12. 12. Waveform Capnometry  Adds continuous waveform display to the ETCO2 value.  Additional information in waveform shape can provide clues about causes of poor oxygenation.
  13. 13. Why ETCO2 I Have my Pulse Ox? Oxygen Saturation Reflects Oxygenation SpO2 changes lag when patient is hypoventilating or apneic Should be used with Capnography Carbon Dioxide Reflects Ventilation Hypoventilation/Apn ea detected immediately Should be used with pulse Oximetry Pulse Oximetry Capnography
  14. 14. What does it really do for me? Bronchospasms: Asthma, COPD, Anaphlyaxis Hypoventilation: Drugs, Stroke, CHF, Post-Ictal Shock & Circulatory compromise Hyperventilation Syndrome: Biofeedback Verification of ETT placement ETT surveillance during transport Control ventilations during CHI and increased ICP CPR: compression efficacy, early signs of ROSC, survival predictor Non-Intubated Applications Intubated Applications
  15. 15. NORMAL CAPNOGRAM Phase I Phase IIIPhase II Inspiratory PhaseExpiratory Phase 70 60 50 40 30 20 10 0 PetCO2 Time mm Hg Phase I: anatomical dead space Phase II : alveolar gas begins to mix with the dead space gas Phase III: elimination of CO2 from the alveoli Phase IV
  16. 16. ABNORMALITIES Abnormality Indication Increased Phase III slope Obstructive lung disease Phase III dip Spontaneous respiratio Horizontal Phase III with large ET-art CO2 change Pulmonary embolism  cardiac output Hypovolemia Sudden  in ETCO2 to 0 Dislodged tube Vent malfunction ET obstruction Sudden  in ETCO2 Partial obstruction Air leak Exponential  Severe hyperventilation Cardiopulmonary event
  17. 17. ABNORMALITIES Abnormality Indication Sudden increase in ETCO2 Sodium bicarb administration Release of limb tourniquet Gradual  Hyperventilation Decreasing temp Gradual  in volume Increased baseline Rebreathing Exhausted CO2 absorber Gradual increase Fever Hypoventilation
  18. 18. USES  Metabolic  Assess energy expenditure  Cardiovascular  Monitor trend in cardiac output  Can use as an indirect Fick method, but actual numbers are hard to quantify  Measure of effectiveness in CPR  Diagnosis of pulmonary embolism: measure gradient
  19. 19. PaCO2-PetCO2 gradient  Usually <6mm Hg  PetCO2 is usually less  Difference depends on the number of underperfused alveoli  Tend to mirror each other if the slope of Phase III is horizontal or has a minimal slope  Decreased cardiac output will increase the gradient  The gradient can be negative when healthy lungs are ventilated with high TV and low rate  Decreased FRC also gives a negative gradient by increasing the number of slow alveoli
  20. 20. LIMITATIONS  Critically ill patients often have rapidly changing dead space and V/Q mismatch  Higher rates and smaller TV can increase the amount of dead space ventilation  High mean airway pressures and PEEP restrict alveolar perfusion, leading to falsely decreased readings  Low cardiac output will decrease the reading
  21. 21. PULMONARY USES  Effectiveness of therapy in bronchospasm  Monitor PaCO2-PetCO2 gradient  Worsening indicated by rising Phase III without plateau  Find optimal PEEP by following the gradient. Should be lowest at optimal PEEP.  Can predict successful extubation.  Dead space ratio to tidal volume ratio of >0.6 predicts failure. Normal is 0.33-0.45  Limited usefulness in weaning the vent when patient is unstable from cardiovascular or pulmonary standpoint  Confirm ET tube placement
  22. 22. NORMAL Waveform 70 60 50 40 30 20 10 0 Time mm Hg • Square box waveform • ETCO2 35-45 mm Hg • Management: Monitor Patient
  23. 23. Sudden  in ETCO2 to 0 70 60 50 40 30 20 10 0 Time mm Hg • Loss of waveform • Loss of ETCO2 reading • Dislodged tube • ET obstruction • Management: Replace ETT
  24. 24. Esophageal Intubation 70 60 50 40 30 20 10 0 Time mm Hg • Absence of waveform • Absence of ETCO2 • Management: Re-Intubate
  25. 25. CPR 70 60 50 40 30 20 10 0 Time mm Hg • Square box waveform • ETCO2 15-20 mm Hg with adequate CPR • ETCO2 falls bellow 10 mm Hg • Management: Change Rescuers
  26. 26. Return of Spontaneous Circulation 70 60 50 40 30 20 10 0 Time mm Hg • During CPR sudden increase of ETCO2 above 10-15 mm Hg • Management: Check for pulse
  27. 27. Gradual Decrease in ETCO2 70 60 50 40 30 20 10 0 Time mm Hg • Hyperventilation • Decreasing temp • Gradual  in volume
  28. 28. Hyperventilation 70 60 50 40 30 20 10 0 Time mm Hg • Shortened waveform • ETCO2 < 35 mm Hg • Management: If conscious gives biofeedback. If ventilating slow ventilations
  29. 29. Gradual Increase in ETCO2 70 60 50 40 30 20 10 0 Time mm Hg • Fever • Hypoventilation
  30. 30. Hypoventilation 70 60 50 40 30 20 10 0 Time mm Hg • Prolonged waveform • ETCO2 >45 mm Hg • Management: Assist ventilations
  31. 31. Rising Baseline 70 60 50 40 30 20 10 0 Time mm Hg • Patient is re-breathing CO2 • Management: Check equipment for adequate oxygen flow • If patient is intubated allow more time to exhale
  32. 32. Curare Cleft 70 60 50 40 30 20 10 0 Time mm Hg • Curare Cleft is when a neuromuscular blockade wears off • The patient takes small breaths that causes the cleft • Management: Consider neuromuscular blockade re- administration
  33. 33. Breathing around ETT 70 60 50 40 30 20 10 0 Time mm Hg • Angled, sloping down stroke on the waveform • In adults may mean ruptured cuff or tube too small • Management: Assess patient, Oxygenate, ventilate and possible re-intubation
  34. 34. Obstructive Airway 70 60 50 40 30 20 10 0 Time mm Hg • Shark fin waveform • With or without prolonged expiratory phase • Can be seen before actual attack • Indicative of Bronchospasm( asthma, COPD, allergic reaction)
  35. 35. Oscillation in Inspiratory Phase 70 60 50 40 30 20 10 0 Time mm Hg J Int Care Med, 12(1): 18-32, 1997J Int Care Med, 12(1): 18-32, 1997
  36. 36. Oscillation in Inspiratory Phase 70 60 50 40 30 20 10 0 Time mm Hg J Int Care Med, 12(1): 18-32, 1997J Int Care Med, 12(1): 18-32, 1997
  37. 37. Oscillation and slow Inspiration 70 60 50 40 30 20 10 0 Time mm Hg J Int Care Med, 12(1): 18-32, 1997J Int Care Med, 12(1): 18-32, 1997
  38. 38. 6 Step ABG’s Analysis Blood Gases
  39. 39. 1. Acidemic/Alkalemic?  This refers to the pH  Normal pH= 7.40 ± 0.05  Acidemia pH < 7.40  Alkalemia pH > 7.40  Normal PaCO2 = 40 ± 5 (35-45)  Normal HCO3 = 24 ± 2 (22-26)
  40. 40. 2. Primary -osis pH emia PaCO2 HCO3 1 ° osis <7.40 acidemia <40 <24 1°Metabol ic acidosis <7.40 acidemia >40 >24 Respirato ry acidosis >7.40 alkalemia >40 >24 Metabolic alkalosis >7.40 alkalemia <40 <24 Respirato ry alkalosis
  41. 41. 2. Respiratory process acute or chronic ?  Respiratory Acidosis Acute : ∆ pH= 0.08x(PaCO2-40)/10  Respiratory Acidosis Chronic : ∆ pH= 0.03x(PaCO2-40)/10  Respiratory Alkalosis Acute : ∆ pH= 0.08 x (40-PaCO2)/10  Respiratory Alkalosis Chronic : ∆ pH= 0.03 x (40-PaCO2)/10
  42. 42. 4. Metabolic acidosis  Anion gap vs. Nongap acidosis  Anion gap (AG) = Na-Cl-HCO3
  43. 43. 3. Adequate degree of compensation for Metabolic Acidosis ?  Calculated (expected) PaCO2 for Gap acidosis (Winte r’s fo rm ula )  Calculated PaCO2=(1.5 x HCO3) +8±2  Measured PaCO2>Calculated PaCO2 then concomitant re spirato ry acido sis  Measured PaCO2<Calculated PaCO2 then concomitant re spirato ry alkalo sis
  44. 44. 4. Calculated (expected) HCO3  Calculated (expected) HCO3 = (Pt.’s AG-nl gap) + measured HCO3  Calculated HCO3>30 associated metabolic alkalosis  Calculated HCO3<23 associated nongap metabolic acidosis  AKA Delta Delta ∆ ∆
  45. 45. 4. Metabolic acidosis  Check for Osmolar gap (OG) OG:Measured osmol – Calculated > 10 Calculated Osmol= (2xNa) + glucose/18 + BUN/2.8 +ethanol/4.6
  46. 46. 5. Calculate Urinary AG  Determines renal vs. extrarenal causes  UAG=UNa+UK-UCl (nl -10 to 10).  UAG <-10 = extrarenal b/c kidneys making a lot of NH3Cl to buffer acidosis  UCl nl/high (>40) AKA saline unre spo nsive  UAG> 10 = renal b/c kidneys unable to make NH3Cl to excrete acid.  UCl low (<25) saline re spo nsive
  47. 47. 6. Adequate degree of compensation for Metabolic Alkalosis ? For every ∆ 1 in HCO3 the paCO2 ∆ 0.6
  48. 48. Adequate degree of compensation ? PrimaryPrimary problemproblem CompensationCompensation For everyFor every ∆∆ inin ExpectedExpected ∆∆ Metabolic AcidosisMetabolic Acidosis Respiratory alkalosisRespiratory alkalosis 11 ↓↓ HCO3HCO3 PaCO2PaCO2 ↓↓ 1.21.2 Metabolic AlkalosisMetabolic Alkalosis Respiratory acidosisRespiratory acidosis 11 ↑↑ HCO3HCO3 PaCO2PaCO2 ↑↑ 0.60.6 RespiratoryRespiratory Acidosis AcuteAcidosis Acute Metabolic AlkalosisMetabolic Alkalosis 11 ↑↑ PaCO2PaCO2 HCO3HCO3 ↑↑ 0.10.1 RespiratoryRespiratory Acidosis ChronicAcidosis Chronic Metabolic AlkalosisMetabolic Alkalosis 11 ↑↑ PaCO2PaCO2 HCO3HCO3 ↑↑ 0.40.4 RespiratoryRespiratory Alkalosis AcuteAlkalosis Acute Metabolic AcidosisMetabolic Acidosis 11 ↓↓ PaCO2PaCO2 HCO3HCO3 ↓↓ 0.20.2 RespiratoryRespiratory Alkalosis ChronicAlkalosis Chronic Metabolic AcidosisMetabolic Acidosis 11 ↓↓ PaCO2PaCO2 HCO3HCO3 ↓↓ 0.40.4
  49. 49. ABG Problems: 145145 100100 1616 4.04.0 1212 1.01.0  7.2/26/85/95% on RA
  50. 50. Answer  Metabolic acidosis  145-100-12=AG 33  Expected PaCO2 1.5x12 +8 ±2=26±2 appropriate  Expected HCO3= (33-12) + 12 =33  Concomitant metabolic alkalosis
  51. 51. ABG Problems  7.1/35/60/90% on RA 135135 106106 1616 4.24.2 1010 1.01.0
  52. 52. Answer  Metabolic acidosis  135-106-10 = AG 19  Expected PaCO2 1.5 x 10 +8 ±2=23±2 Measured >calculated  Concomitant respiratory acidosis  Expected HCO3 = 19-12 +10 = 17  Concomitant nongap metabolic acidosis  Next calculate UAG
  53. 53. ABG Problems  HIV, HBV associated ESLD, ARF with pleural effusions, tachypneic RR 34  7.48/28/55/90% on 4L NC 155|97|41/117 4.7| 18|1.7
  54. 54. Answer Respiratory alkalosis ∆ H:748-740=8 ∆ paCO2: 40-28=12 8/12=0.67 Acute on chronic respiratory alkalosis. Acute from tachypnea chronic from ESLD  7.47/18/98 on 50% face mask

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