basic principles of gas exchange under mechanical ventilation · 2020. 4. 18. · mechanical...
TRANSCRIPT
Basic principles of gas exchange under Mechanical Ventilation
Lorenzo Del Sorbo, MD
Mechanical Ventilation:From physiology to clinical practice
Toronto, April 14th 2020
• gas exchange abnormalities
• physiologic principles
• clinical cases
Outline
Hypoxemia and impaired CO2 clearance are characteristics of ARDS
90 --
Radermacher et al. AJRCCM 2017
ARDS
• hypoventilation
• ↓ PIO2
• ↓ diffusion
• V/Q mismatch
• shunt
+ ↓ PvO2
mechanisms of
hypoxemia
V/Q ratio
Radermacher et al. AJRCCM 2017
V/Q ratio
Shunt
Radermacher et al. AJRCCM 2017
Higher VA/Q
Lower VA/Q
Shunt
Alveolar inhomogeneity
Lower pleural pressure
Higher pleural pressure
Shunt
Radermacher et al. AJRCCM 2017
Dead spacePaCO2=
V’CO2
V’A
= V’CO2
RR (Vt-Vd)
= V’CO2
RR (1-Vd/Vt)
Higher VA/Q
Lower VA/Q
Shunt
Alveolar inhomogeneity
Lower pleural pressure
Higher pleural pressure
Dead space
Nuckton T.J., et al. NEJM 2002
Ventilatory ratio
Pratik et al. AJRCCM 2013 & 2019
Radermacher et al. AJRCCM 2017
Clinical examples
1° case: ARDSVCV 430 ml X 25 RR, PEEP 15, Pplat 27, FiO2 40%, pH 7.31, paCO2 38, paO2 53
Brun-Buisson C, et al. ICM 2004
ARDS: hypoxemia
ARDS: means to decrease hypoxemia•Increase FiO2: not effective if hypoxemia is only from shunt
increased risk of O2 toxicity
Martin and Grocott. CCM 2013
ARDS: means to decrease hypoxemia - é FiO2
Increased risk of reabsorption atelectasis
Santos C, et al. AJRCCM 2000
Courtesy of L. Gattinoni and R. Fumagalli
Low trans-pulmonary
pressure
2° case: ARDS VCV 300 ml X 27 RR, PEEP 15
Pplat 30, FiO2 100%,pH 7.31, paCO2 38, paO2 40
Courtesy of L. Gattinoni and R. Fumagalli
intermediate trans-pulmonary
pressure
ARDS VCV 280 ml X 24 RR, PEEP 20, Pplat 30, FiO2 70%, pH 7.35, paCO2 38, paO2 74
Recruitment
Excessive trans-pulmonary
pressure
Courtesy of L. Gattinoni and R. Fumagalli
ARDS VCV 320 ml X 35 RR, PEEP 20, Pplat 32, FiO2 90%, pH 7.21, paCO2 54, paO2 74
Recruitment
and
overdistension
Courtesy of L. Gattinoni and R. Fumagalli
Excessive Trans-pulmonary
PressureVILI
non-recruiters
VCV 320 ml X 35 RR, PEEP 20, Pplat 32, FiO2 100%, pH 7.21, paCO2 54, paO2 64
CO2 clearance
ARDS: recruitment
Gattinoni L et al., NEJM 2006
Grasso S, et al. AJRCCM 2005
ARDS: recruitment
Goligher E, et al. AJRCCM 2014
ARDS: recruitment
3° case: ARDS
VCV 320 ml X 27 RR, PEEP 15Pplat 30, FiO2 100%,
pH 7.31, paCO2 51, paO2 70
Gattinoni L, et al. AJRCCM 2013
VCV 320 ml X 27 RR, PEEP 15Pplat 27, FiO2 60%,
pH 7.33, paCO2 48, paO2 70
Sud S, et al. ICM 2010
Guerin C, et al. AJRCCM 2014
Prone Position– induced Improvement in Gas Exchange Does Not Predict Improved Survival in ARDS
Prone positioning in ARDS: less VILI
Gattinoni L, et al. ICM 2013
Mutoh T, et al. Am Rev Respir Dis 1992
Guerin C, et al. ICM 2014
ARDS4° case:ARDS (post-trauma)
HR 135, BP 90/60, Hb 71, Lactate 5.1SvO2 50%VCV 480 ml X 27 RR, PEEP 16Pplat 30, FiO2 100%,pH 7.31, paCO2 38, paO2 40
• Improve hemodynamics(DO2/V’O2)
Courtesy of R. Fumagalli
ARDS (post-trauma)
HR 100, BP 110/60, Hb 95, Lactate 2SvO2 80%VCV 460 ml X 23 RR, PEEP 18Pplat 28, FiO2 80%,pH 7.37, paCO2 46, paO2 60
Post fluid resuscitation and PRBC transfusion
Courtesy of R. Fumagalli
Better DO2/V’O2
ARDS (post-trauma)
HR 100, BP 110/60, Hb 95, Lactate 2SvO2 80%VCV 460 ml X 23 RR, PEEP 18Pplat 28, FiO2 80%,pH 7.37, paCO2 46, paO2 60
Post fluid resuscitation and PRBC transfusion
Better DO2/V’O2
Improving perfusion in ventilated alveoli
Better V/Q
5° case: ARDS
Failed prone positionVCV 320 ml X 27 RR, PEEP 15
Pplat 30, FiO2 100%,pH 7.31, paCO2 38, paO2 40
Improving perfusion in ventilated alveoli
NEJM 1993
6° case: COPD exacerbation
Vt 450 mlRR 27iPEEP 18Ppeak 61FiO2 30%pH 7.25paCO2 80paO2 50
Main issue: hypoxemia/hypercapnia?Vt 450 mlRR 27iPEEP 18Ppeak 61FiO2 30%pH 7.25paCO2 80paO2 50
Effects of ñFiO2ñ PAO2ñ PaO2Change in Hypoxic pulmonary vasoconstrictionHaldane effectChange in V/QDecrease respiratory driveñ PaCO2
High V/Q
Low V/Q
Vt 450 mlRR 27iPEEP 18Ppeak 61FiO2 30%pH 7.25paCO2 80paO2 50
Expiratory flow limitation:
Main issues:
Dynamic hyperinflation:
V’exp(t) = V(t)
R*C (t)
V(trapped) = VT x t
TE
7° case: pulmonary embolism
Lower V/QñA-a difference
Dead spaceñPaCO2
V/Q=1V
V/Q=1V/Q=1V
V/Q=1
Acute pulmonary hypertension (also from high intra-thoracic pressure during MV) may aggravate hypoxemiaby low MvO2or by intra-cardiac right-to-left shunting
Petersson J, et al. Eur Respir J 2014
PaCO2 may increase or decrease according to the response of the respiratory drive to increase dead space and hypoxemia
Vt 450 ml, RR 35, FiO2 50%, pH 7.48, paCO2 30, paO2 70
Courtesy of L. Gattinoni and R. Fumagalli
Excessive Trans-pulmonary
PressureVILI
Pplat 35, FiO2 100%, pH 7.11, paCO2 64, paO2 40
8° case: refractory respiratory failure
ARDS
Courtesy of R. Fumagalli
HbO2 75%
HbO2 75%
HbO2 (75% + 75%)/2=75%
ARDS
Courtesy of R. Fumagalli
HbO2 90%
HbO2 90%
HbO2 (90% + 90%)/2=90%
VV-ECMOPre-pulmonary
-Increased SvO2-CO2 clearance
90%
60
Conclusions
Conclusions
Hemodynamics (DO2/V’O2)
Physiologic interpretation of the effects of the bedside maneuvers
ARDS is an hypoxemic syndrome, but
Carbon Dioxide elimination is the true target of ventilation (BAD CO2 ELIMINATION = risk of VILI)
Conclusions
In refractory cases…..
……think out of the BOX
Extra-Corporeal (gas exchange) Life Support
