View
227
Download
3
Category
Tags:
Preview:
Citation preview
The Map Between Lung Mechanics and Tissue Oxygenation
The Map Between Lung Mechanics and Tissue Oxygenation
Alveolar UnitsAlveolar Units
Gas exchangeCommunication with capillary
network
Gas exchangeCommunication with capillary
network
vv
O2
O2 O
2O
2
O2
O2
O2
O2
O2
O aaO2
O2 O
2O
2 O2
O22
Lung Compliance and ElasticityLung Compliance and Elasticity
Compliance is ability of lungs to stretch Low compliance in fibrotic lungs (and other restrictive
lung diseases) and when not enough surfactantElasticity (= Elastance) is ability to return to original
shape Low Elasticity in case of emphysema due to destruction
of elastic fibers.Normal lung is both compliant AND elastic
Compliance is ability of lungs to stretch Low compliance in fibrotic lungs (and other restrictive
lung diseases) and when not enough surfactantElasticity (= Elastance) is ability to return to original
shape Low Elasticity in case of emphysema due to destruction
of elastic fibers.Normal lung is both compliant AND elastic
Pulmonary circulationPulmonary circulation
• Thin walled, greater internal diameters and less vascular smooth muscle than the systemic vessels.
• Rapidly divides into 280 billion capillaries.• More distensible and compressible than the systemic
system and there is less resistance to blood flow.• Lower intravascular pressures• Are subject to alveolar and pleural pressures.• Form a sheet of blood
• Thin walled, greater internal diameters and less vascular smooth muscle than the systemic vessels.
• Rapidly divides into 280 billion capillaries.• More distensible and compressible than the systemic
system and there is less resistance to blood flow.• Lower intravascular pressures• Are subject to alveolar and pleural pressures.• Form a sheet of blood
Gas meets bloodGas meets blood
A >a >vA >a >v
a >A >va >A >v
a >v >Aa >v >A
Best V/Q !!!
ARDS…ARDS…
Ware & MatthayNEJM,2000
Lung Fluid Balance = Formation and Resolution of Lung Edema in ALI/ARDS
Lung Fluid Balance = Formation and Resolution of Lung Edema in ALI/ARDS
Gas meets bloodGas meets blood
A >a >vA >a >v
a >A >va >A >v
a >v >Aa >v >A
Best V/Q !!!
Gas meets bloodGas meets blood
A >a >vA >a >v
a >A >va >A >v
a >v >Aa >v >A
Best V/Q !!!
V/Q inequalityV/Q inequality• Increases A-a PO2
(norm. 5-20 mmHg)• Reduces PaO2
V/Q more blood than gas venous admixture V/Q more gas than blood venous admixture
• Q flows only through unaffected regions, thus it relatively there
• Increases A-a PO2
(norm. 5-20 mmHg)• Reduces PaO2
V/Q more blood than gas venous admixture V/Q more gas than blood venous admixture
• Q flows only through unaffected regions, thus it relatively there
Pulmonary MeasuresPulmonary Measures
• P/F ratio = Pa02/ Fi02 • 100/ 0.21= 470
• P/F ratio = Pa02/ Fi02 • 100/ 0.21= 470
Which is BESTWhich is BEST
• P/F ratio –1. 90 on 1.0
–2. 60 on 0.50
–3. 70 on 0.21
• P/F ratio –1. 90 on 1.0
–2. 60 on 0.50
–3. 70 on 0.21
What can I do about it?What can I do about it?
Blood flow increase towards lung basesBlood flow increase towards lung bases
• Zone 3: – resistance decrease due to distension
related to volume weight and gravity (dependence: water glass)
–Pa and Pv are higher than PA• What does this have to do with my
patient?
• Zone 3: – resistance decrease due to distension
related to volume weight and gravity (dependence: water glass)
–Pa and Pv are higher than PA• What does this have to do with my
patient?
Lung Fluid Balance = Formation and Resolution of Lung Edema in ALI/ARDS
Lung Fluid Balance = Formation and Resolution of Lung Edema in ALI/ARDS
When you ventilate only with…..When you ventilate only with…..
Simple Ventilation termsSimple Ventilation terms• Fraction of Inspired Oxygen (FIO2)
– Amount or percent of oxygen mixed into the atmospheric pressurized gas
• Optimal < 40%• Any patient on > 50% for more than two days is very sick and at
risk for long vent stays
• Pressure– A means of measuring and/or controlling the effects of
the volume delivery to the lung• Peak pressures > 50 cm H20 indicate stiff sick lungs and risk
for long vent stays• Mean pressures or Plateau pressures > 35 cm H20 may
indicate respiratory distress syndrome and very long vent stays• Pressure control ventilation may also indicate respiratory
distress syndrome and very long vent stays
• Fraction of Inspired Oxygen (FIO2)– Amount or percent of oxygen mixed into the
atmospheric pressurized gas• Optimal < 40%• Any patient on > 50% for more than two days is very sick and at
risk for long vent stays
• Pressure– A means of measuring and/or controlling the effects of
the volume delivery to the lung• Peak pressures > 50 cm H20 indicate stiff sick lungs and risk
for long vent stays• Mean pressures or Plateau pressures > 35 cm H20 may
indicate respiratory distress syndrome and very long vent stays• Pressure control ventilation may also indicate respiratory
distress syndrome and very long vent stays
Simple Ventilation TermsSimple Ventilation Terms
• Minute ventilation (VE or MV): – the amount of volume exhaled per minute (VE) or
measured as RR × VT (MV) – Normal 8-10 liters/minute
• Peak Inspiratory Pressure (PIP)– peak pressure measured when the
tidal volume is pushed into the airways– value used to set high and low
pressure alarm limits
• Minute ventilation (VE or MV): – the amount of volume exhaled per minute (VE) or
measured as RR × VT (MV) – Normal 8-10 liters/minute
• Peak Inspiratory Pressure (PIP)– peak pressure measured when the
tidal volume is pushed into the airways– value used to set high and low
pressure alarm limits
Simple Ventilation TermsSimple Ventilation Terms
• Flow rate: The rate of speed of volume delivery– impacts I:E ratio–slow flow: ↑ I time, ↓ E time– fast flow: ↓ I time, ↑ E time
• Flow rate: The rate of speed of volume delivery– impacts I:E ratio–slow flow: ↑ I time, ↓ E time– fast flow: ↓ I time, ↑ E time
SIMPLE METHODSSIMPLE METHODS
• Ventilatory Modes–CMV, IMV, SIMV, A/C, PCV
• Adjuncts to Mechanical Ventilation–PEEP, CPAP, PSV
• Ventilatory Modes–CMV, IMV, SIMV, A/C, PCV
• Adjuncts to Mechanical Ventilation–PEEP, CPAP, PSV
Simple Ventilation Modes and AdjunctsSimple Ventilation Modes and AdjunctsWhen anticipation is that the patient will not require lengthy
support > 3-5 days, simple modes are generally applied:
• Modes– Controlled Mandatory or assist control ventilation:
CMV or ACMV– Intermittent Mandatory Ventilation: IMV– Synchronized Intermittent Mandatory Ventilation:
SIMV
When anticipation is that the patient will not require lengthy support > 3-5 days, simple modes are generally applied:
• Modes– Controlled Mandatory or assist control ventilation:
CMV or ACMV– Intermittent Mandatory Ventilation: IMV– Synchronized Intermittent Mandatory Ventilation:
SIMV
Volume vs… Pressure Control VentilationVolume vs… Pressure Control Ventilation
Volume Ventilation
• Volume delivery constant• Inspiratory pressure varies• Inspiratory flow constant• Inspiratory time determined by
set flow and VT
Volume Ventilation
• Volume delivery constant• Inspiratory pressure varies• Inspiratory flow constant• Inspiratory time determined by
set flow and VT
Pressure Ventilation
• Volume delivery varies • Inspiratory pressure constant• Inspiratory flow varies• Inspiratory time set by
clinician
Pressure Ventilation
• Volume delivery varies • Inspiratory pressure constant• Inspiratory flow varies• Inspiratory time set by
clinician
Lung Compliance and ElasticityLung Compliance and Elasticity
Compliance is ability of lungs to stretch Low compliance in fibrotic lungs (and other restrictive
lung diseases) and when not enough surfactantElasticity (= Elastance) is ability to return to original
shape Low Elasticity in case of emphysema due to destruction
of elastic fibers.Normal lung is both compliant AND elastic
Compliance is ability of lungs to stretch Low compliance in fibrotic lungs (and other restrictive
lung diseases) and when not enough surfactantElasticity (= Elastance) is ability to return to original
shape Low Elasticity in case of emphysema due to destruction
of elastic fibers.Normal lung is both compliant AND elastic
Pre
ssur
e
time
PIP:complianceresistancevolumeflowPEEP
PEEP
PEEP
PIP
Pplat
resistanceflow
compliancetidal volume
No active breathingTreats lung as single unit
end-inspiratoryalveolar pressure
What else can I look at??What else can I look at??
0 20 40 60-20-40-60
0.2
0.4
0.6
LITERS
Paw
cmH2O
VT
Pressure-Volume Loop ChangesPressure-Volume Loop Changes
Indicates a drop in compliance (higher pressure for the same volume)
0 20 40 602040-60
0.2
0.4
0.6
LITERS
Paw
cmH2O
VT
Changes in CompliancesChanges in Compliances
B
A
0 20 40 60-20-40-60
0.2
0.4
0.6
LITERS
Paw
cmH2O
C
A = inspiratory pressure
B = upper inflection point
C = lower inflection point
VT
OverdistensionOverdistension
• Respiratory rate
• Max RR at 35 breaths/min
• Efficiency of ventilation decreases with increasing RR
• Decreased time for alveolar emptying
• TV
• Goal of 10 ml/kg
• Risk of volutrauma
• Other means to decrease PaCO2
• Reduce muscular activity/seizures
• Minimizing exogenous carb load
• Controlling hypermetabolic states
• Permissive hypercapnea
• Preferable to dangerously high RR and TV, as long as pH > 7.15
RR and TV are adjusted to maintain VE and PaCO2
• I:E ratio (IRV)
• Increasing inspiration time will increase TV, but may lead to auto-PEEP
• PIP
• Elevated PIP suggests need for switch from volume-cycled to pressure-cycled mode
• Maintained at <45cm H2O to minimize barotrauma
• Plateau pressures
• Pressure measured at the end of inspiratory phase
• Maintained at <30-35cm H2O to minimize barotrauma
Vent settings to improve ventilationVent settings to improve ventilation
•PEEP • Increases FRC
• Prevents progressive atelectasis and intrapulmonary shunting
• Prevents repetitive opening/closing (injury)
•Recruits collapsed alveoli and improves V/Q matching• Resolves intrapulmonary shunting• Improves compliance
•Enables maintenance of adequate PaO2 at a safe FiO2 level
•Disadvantages• Increases intrathoracic pressure (may
require pulmonary a. catheter)• May lead to ARDS• Rupture: PTX, pulmonary edema
PEEP and FiO2 are adjusted in tandem
Oxygen delivery (DO2), not PaO2, should be used to assess optimal PEEP.
Vent settings to improve oxygenationVent settings to improve oxygenation
• Pressure Limited– FiO2
– Rate– I-time– PEEP– PIP
• Pressure Limited– FiO2
– Rate– I-time– PEEP– PIP
• Volume Limited– FiO2– Rate– Tidal Volume– PEEP– I time
• Volume Limited– FiO2– Rate– Tidal Volume– PEEP– I time
MV
MAP
Dealers ChoiceDealers Choice
ARDSnetARDSnet
NIH NHLBI ARDS Clinical Trials Network NIH NHLBI ARDS Clinical Trials Network
Downloaded from www.ardsnet.org
APRVAPRV
HFOVHFOV
Effects of PPV on AfterloadEffects of PPV on Afterload
• RV afterload (overall: increased)– increased: Starling resistor phenomenon– decreased: RV compression, pulmonary
vasodilation due to increased lung volume• LV afterload: decreased due to LV and
thoracic aorta compression
• RV afterload (overall: increased)– increased: Starling resistor phenomenon– decreased: RV compression, pulmonary
vasodilation due to increased lung volume• LV afterload: decreased due to LV and
thoracic aorta compression
Pulsus ParadoxusPulsus Paradoxus
SummarySummary
• What we can do?–hold to a standard of care–define and report appropriately–communicate scientifically–evaluate in the presence and the
absence of invasive monitoring
• What we can do?–hold to a standard of care–define and report appropriately–communicate scientifically–evaluate in the presence and the
absence of invasive monitoring
SummarySummary
• Discuss, defend, discuss• turn turn turn• oygenate?• ventilate?• flow that blood
• Discuss, defend, discuss• turn turn turn• oygenate?• ventilate?• flow that blood
Recommended