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OXYGENATION & VENTILATION MONITORING
Point of Discussion
1. Indices of oxygenation 2. Indices of ventilation3. Pulse oximetry4. Capnography5. Arterial and venous blood gases
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 Poorly adherent probe Excessive motion Carboxyhaemoglobin or methaemoglobin
The Ventilation Vital Sign
Capnography
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
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:
Warm up time Cost Portability
Waveform Capnometry
Adds continuous waveform display to the ETCO2 value. Additional information in waveform shape can provide clues about causes of poor oxygenation.
Why ETCO2 I Have my Pulse Ox?
Oxygen SaturationReflects OxygenationSpO2 changes lag when patient is hypoventilating or apneicShould be used with Capnography
Carbon Dioxide
Reflects Ventilation
Hypoventilation/Apnea detected immediately
Should be used with pulse Oximetry
Pulse Oximetry Capnography
What does it really do for me?
Bronchospasms: Asthma, COPD, AnaphlyaxisHypoventilation: Drugs, Stroke, CHF, Post-IctalShock & Circulatory compromiseHyperventilation Syndrome: Biofeedback
Verification of ETT placementETT surveillance during transportControl ventilations during CHI and increased ICPCPR: compression efficacy, early signs of ROSC, survival predictor
Non-Intubated Applications Intubated Applications
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 spacePhase II : alveolar gas begins to mix with the
dead space gas
Phase III: elimination of CO2
from the alveoli
Phase IV
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 outputHypovolemia
Sudden in ETCO2 to 0 Dislodged tubeVent malfunctionET obstruction
Sudden in ETCO2 Partial obstructionAir leak
Exponential Severe hyperventilationCardiopulmonary event
ABNORMALITIES
Abnormality IndicationSudden increase in ETCO2 Sodium bicarb administration
Release of limb tourniquetGradual Hyperventilation
Decreasing tempGradual in volume
Increased baseline RebreathingExhausted CO2 absorber
Gradual increase FeverHypoventilation
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
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
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
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
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 obstruction• Management: Replace ETT
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 mm Hg • Management: Change Rescuers
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
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 gives biofeedback. If ventilating slow ventilations
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 oxygen flow• If patient is intubated allow more time to exhale
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
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
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)
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
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
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
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 Normal PaCO2 = 40 ± 5 (35-45) Normal HCO3 = 24 ± 2 (22-26)
2. Primary -osis
pH emia PaCO2 HCO3 1 ° osis
<7.40 acidemia <40 <24 1°Metabolic acidosis
<7.40 acidemia >40 >24 Respiratory acidosis
>7.40 alkalemia
>40 >24 Metabolic alkalosis
>7.40 alkalemia
<40 <24 Respiratory alkalosis
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
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 (Winter’s formula) Calculated PaCO2=(1.5 x HCO3) +8±2 Measured PaCO2>Calculated PaCO2
then concomitant respiratory acidosis Measured PaCO2<Calculated PaCO2
then concomitant respiratory alkalosis
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
4. Metabolic acidosis
Check for Osmolar gap (OG)OG:Measured osmol – Calculated > 10Calculated Osmol=(2xNa) + glucose/18 + BUN/2.8 +ethanol/4.6
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 unresponsive
UAG> 10 = renal b/c kidneys unable to make NH3Cl to excrete acid. UCl low (<25) saline responsive
6. Adequate degree of compensation for
Metabolic Alkalosis ?
For every 1 in HCO3 the paCO2 0.6
Adequate degree of compensation ?
Primary Primary problemproblem
CompensatioCompensationn
For For every every inin
ExpecteExpected d
Metabolic Metabolic AcidosisAcidosis
Respiratory alkalosisRespiratory alkalosis1 1 ↓↓ HCO3 HCO3 PaCO2 PaCO2 ↓↓ 1.2 1.2
Metabolic Metabolic AlkalosisAlkalosis
Respiratory acidosisRespiratory acidosis1 1 ↑↑ HCO3 HCO3 PaCO2 PaCO2 ↑↑ 0.6 0.6
Respiratory Respiratory Acidosis AcuteAcidosis Acute
Metabolic AlkalosisMetabolic Alkalosis1 1 ↑↑ PaCO2 PaCO2 HCO3 HCO3 ↑↑ 0.1 0.1
Respiratory Respiratory Acidosis ChronicAcidosis Chronic
Metabolic AlkalosisMetabolic Alkalosis1 1 ↑↑ PaCO2 PaCO2 HCO3 HCO3 ↑↑ 0.4 0.4
Respiratory Respiratory Alkalosis AcuteAlkalosis Acute
Metabolic AcidosisMetabolic Acidosis1 1 ↓↓ PaCO2 PaCO2 HCO3 HCO3 ↓↓ 0.2 0.2
Respiratory Respiratory Alkalosis ChronicAlkalosis Chronic
Metabolic AcidosisMetabolic Acidosis1 1 ↓↓ PaCO2 PaCO2 HCO3 HCO3 ↓↓ 0.4 0.4
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) + 12 =33 Concomitant metabolic alkalosis
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 respiratory acidosis Expected HCO3 = 19-12 +10 = 17 Concomitant nongap metabolic acidosis Next calculate UAG
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\
Answer
Respiratory alkalosis H:748-740=8 paCO2: 40-28=128/12=0.67 Acute on chronic respiratory
alkalosis. Acute from tachypnea chronic from ESLD
7.47/18/98 on 50% face mask