man and machines: insights into ventilation strategies may 2006 dr geoff shaw dept of intensive care...

Man and machines: Insights into

ventilation strategies May 2006

Dr Geoff ShawDept of Intensive Care Christchurch Hospital

Clin Sen Lecturer Dept of Medicine CSM&HS University of Otago, NZ

Senior fellow Dept of Mechanical Engineering, University of Canterbury, NZ

The ventilator is our identity


Mechanical ventilation has been used clinically for about 80 years…..

First there was

Polio in California

Negative pressure ventilation…


Then there was

Dr H Lassen at Copenhagen’s Blegdams Hospital

Positive Pressure Ventilation:Positive Pressure Ventilation:90% death rate 90% death rate 90% survival 90% survival

PEEP

1967 First report of ARDS:Ashbaugh DG, Bigelow DB, Petty TL, Levine BE. Acute respiratory

distress syndrome in adults. Lancet; 1967,(II) 319-323

1972 First formal investigation of the effect of PEEPImproved PaO2 by applying 0-15cm PEEP in 10 patients

with ARDS. Putative mechanism prevention of airway closure

Falke KJ, Pontoppidan H, Kumar A et al Ventilation with end-expiratory pressure in acute lung disease; J Clin Invest 1972, 51:2315–2323

1975 “Optimum PEEP”Defined as best O2 transport (CO X O2 content)highest compliance of respiratory system.Suter PM, Fairley B, Isenberg MD. Optimum end-expiratory airway

pressure in patients with acute pulmonary failure. N Engl J Med 1975; 292:284–289

“Super PEEP”that which produces minimal shuntKirby RR, Downs JB, Civetta JM et al. High level positive end expiratory pressure (PEEP) in acute respiratory insufficiency. Chest 1975; 67:156–

163

1981 “Minimal PEEP”2cm higher than lower inflection point of inflation limb of the

pressure volume curveLemaire F, Harf A, Simonneau G et al [Gas exchange, static pressure volume curve and positive-pressure ventilation at the end of

expiration. Study of 16 cases of acute respiratory insufficiency in adults]. Ann Anesthesiol Fr 1981;22:435–441

PEEP

PV Curve

Radford EP (1957) Recent studies of the mechanical properties of mammalian lungs. In: Remington JW (ed) Tissue elasticity American Physiological Society Washington, pp 177–190

Lower inflection point

Upper inflection point

VILI

Webb & Tierney ARRD 1974;110;556

PIP=14, PEEP=0 PIP= 45, PEEP=10 PIP= 45, PEEP = 0

Other therapies

1979 “ECMO”:NIH trial 90% mortality in both groups. High volumes and pressuresZapol WM, Snider MT, Hill JD et al. Extracorporeal membrane

oxygenation in severe acute respiratory failure. A randomized prospective study. JAMA 1979;242:2193–2196

1980’s “ECO2R” (Extracorporeal CO2 removal)Concept of “lung rest” Normal gas exchange targetsUnacceptable complications especially bleedingGattinoni L, Agostoni A, Pesenti A et al. Treatment of acute respiratory

failure with low-frequency positive pressure ventilation and extracorporeal removal of CO2. Lancet 1980;II:292–294

Gattinoni L, Pesenti A, Mascheroni D et al. Low-frequency positive-pressure ventilation with extracorporeal CO2 removal in severe acute respiratory

failure. JAMA 1986; 256:881–886

Concepts of ARDS in 1980’s

Lungs homogeneous, heavy and stiff

Normalise pCO2 by use of high pressures and volumes

Use of PEEP to normalise pO2

Barotrauma = “complication”

Major concerns were haemodynamic impairments caused by PEEP

“Baby Lung”

Quantitative assessment of CT images in ARDS. amount of normally aerated tissue = 5-6 yr old child

Gattinoni L, Pesenti A, The concept of the “baby lung”. Intensive Care Med; 2005:31:776-784

“Baby Lung”

Gattinoni L, Pesenti A, Baglioni S et al. Inflammatory pulmonary edema and positive end-expiratory pressure: correlations between imaging and physiologic studies. 1988; J Thorac Imaging 3:59–64

Respiratory compliance correlates with amount of normally aerated tissue

Bone RC The ARDS lung. New insights from computed tomography. JAMA 1993; 269:2134–2135


“Sponge Lung”

Assumes lung oedema in ARDS is evenly distributed throughout the lung from sternum to vertebrae. (not gravitationally dependent).

Gas in dependent regions is squeezed out by superimposed pressure including the weight of the heart

Superimposed pressureOpeningPressure

Alveolar Collapse(Reabsorption) 40-60cmH2O

Small AirwayCollapse 10-20cmH2O

Inflated 0

(modified from Gattinoni))

Consolidation

“Permissive hypercapnia”

1990 Low tidal volumes to rest lung; CO2 levels allowed to permissively rise

Changed the goals of ventilation

Hickling KG, Henderson SJ, Jackson R. Low mortality associated with low volume pressure limited ventilation with permissive hypercapnia in severe adult respiratory distress syndrome. Intensive Care Med 1990; 16:372–377

Permissive hypercapniaLate ’90’s: clinical trials of low tidal volume ventilation

Amato MB, Barbas CS, Medeiros DM, Magaldi RB, Schettino GP, Lo-Physirenzi-Filho G, Kairalla RA, Deheinzelin D, Munoz C, Oliveira R, et al. Effect of a protective-ventilation strategy on mortality in the acute respiratory distress syndrome. N Engl J Med

1998;338:347–354. 63 patients

Acute Respiratory Distress Syndrome Network. Ventilation with lower tidal volumes compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med 2000;342:1301–1308.

861 patients

Stewart TE, Meade MO, Cook DJ, Granton JT, Hodder RV, Lapinsky SE,Mazer CD, McLean RF, Rogovein TS, Schouten BD, et al. Evaluation of a ventilation strategy to prevent barotrauma in patients at high risk for acute respiratory distress syndrome. N

Engl J Med 1998;338:355–361. 120 patients

Brochard L, Roudot-Thoraval F, Roupie E, Delclaux C, Chastre J, Fernandez-Mondejar E, Clementi E, Mancebo J, Factor P, Matamis D, et al. Tidal volume reduction for prevention of ventilator-induced lung injury in acute respiratory distress syndrome. Multicenter Trial Group on Tidal Volume Reduction in ARDS. Am J Respir Crit Care Med 1998;158:1831–1838

116 patients

Brower RG, Shanholtz CB, Fessler HE, Shade DM, White P Jr, Wiener CM, Teeter JG, Doddo JM, Almog Y, Piantadosi S. Prospective, randomized, controlled clinical trial comparing traditional versus reduced tidal volume ventilation in acute respiratory distress syndrome patients. Crit Care Med 1999;27:1492–1498.

52 patients

Confusion and controversy!

Eichacker PQ,. Gerstenberger EP, Banks SM, Cui X, Natanson C. Meta-analysis of acute lung injury and acute respiratory distress syndrome trials testing low tidal volumes. Am J Respir Crit Care Med Vol 166. pp 1510–1514, 2002

Lung recruitment in ARDS

68 patients with ARDS:

Highly variable % potentially recruitable lung 13% ±11%

% potentially recruitable correlated with % lung maintained afterapplication of PEEP

Higher % potentially recruitable lung correlated with:Lung weightPaO2/FIO2 ratioComplianceDead spaceMortality

Gattinoni L, Caironi P, Cressoni M, et al. Lung recruitment in patients with the acute respiratory distress syndrome. N Engl J Med 2006;354:1775-86.

Mortality relates to recruitable lung


Lung recruitment in ARDS

Gattinoni L Am J Respir Crit Care Med 2001; 164:1701–1711

Lower inflection point?

Upper inflection point

Over-stretch = “Volutrauma”

Ventilation induced lung injury (VILI)

Epithelial and endothelial cells are anchored to the lung “skeleton”


Bunched up collagen fibres

Elastin fibres

Stress and strain

Stress = K (Youngs module of material) x StrainStress = PL (transpulmonary pressure)

Strain = Vt (Δ Lung Vol) / “baby lung” (volume at ZEEP)

K = E spec (Specific lung elastance)

Hence:

E spec = PL x Baby Lung / Vt

E spec = Transpulmonary Pressure at which the EELV doubles (~12-13cm normally)

Gattanoni’s hypothesis...

If…

E spec is constant within narrow limits in ARDS

Then…

An estimate of stress and strain can be made by knowing either size of “baby lung”, or PL

(Neither are measured routinely in ICU)

“Volutrauma”: Volume–dependent elastance E2

Bersten AD. Measurement of overinflation by multiple linear regression analysis in patients with acute lung injury. Eur Respir J 1998; 12: 526–532.

Linear portion; constant compliance; independent of volume (E1)

Non-linear portion; volume dependent compliance (E2)

Pressure

Vo

lum

e Paw = Airway pressure

E1 = volume-independent respiratory elastance

E2 = Volume-dependent component of elastance

VT = tidal volume

Po = static recoil pressure at end-expiration PEEP (tot)

VEI = End expiratory volume above resting volume

= safe zone

= dangerous overstretched zone


“Volutrauma”:

= safe zone

= dangerous overstretched zone

%E2 was >30% in 50% of data where Pel <30 cm!


Pel,dyn =Dynamic elastic airway pressure

“Volutrauma”:

Airway Pressure-time curves

a =the slope of the P-t relation at t = 1 sc = the pressure at t = 0. b = dimensionless number shape of the P-t curve

During inspiration, if:b <1, P-t curve is convex; ↑ complianceb >1 P-t curve is convex; ↓ compliance b =1 P-t curve is straight; ↔compliance

Ranieri VM, Zhang H, Mascia L, et al. Pressure–time curve predicts minimally injurious ventilatory strategy in an isolated rat lung model. Anesthesiology 2000; 93:1320–8

Airway Pressure-time curves

Ranieri VM, Zhang H, Mascia L, et al. Pressure–time curve predicts minimally injurious ventilatory strategy in an isolated rat lung model. Anesthesiology 2000; 93:1320–8

Hypothetical model of Pplateau vs Vt ~based

on meta analysis of 5 trials of low volume ventilation

Eichacker PQ,. Gerstenberger EP, Banks SM, Cui X, Natanson C. Meta-analysis of acute lung injury and acute respiratory distress syndrome trials testing low tidal volumes. Am J Respir Crit Care Med Vol 166. pp 1510–1514, 2002

Condom model demonstrating intrapulmonary stresses

Mead J, Takishima T, Leith D. Stress distribution in lungs: a model of pulmonary elasticity. J Appl Physiol 1970; 28:596-608

“Atelectasis” as modelled by applying negative pressure to a condom surrounded by an “alveolar pressure” of 20 cmH2O

Under-stretch = “Atelectrauma”

Shear forces in the zone of lung opening, caused by stretching of densely distributed alveolar membranes, obliquely attached to bronchiolar basal membranes

Jonson B. Elastic pressure-volume curves in acute lung injury and acute respiratory distress syndrome Intensive Care Med 31:205–212, 2005, with permission from: Jonson B (1982) In: Prakash O (ed) Applied physiology in clinical respiratory care. Nijhoff, The Hague, pp 123– 139

“Atelectrauma”

Atelectasis = Stress

Mead J, Takishima T, Leith D. Stress distribution in lungs: a model of pulmonary elasticity. J Appl Physiol 1970; 28:596-608

Mead and colleagues have postulated that:

Peff =-PL (V/V0)2/3

Where PL = Palv - Ppl

PL = transpulmonary pressure, Palv = alveolar pressure,

Ppl = pleural pressure

V = Inflated volume,

V0 = collapsed volume

Consider inflating a partially collapsed lung to PL=30cmH2O.

Let the volume of the degassed region be 1/10 of its final inflated volume.

PL is therefore amplified by 102/3

Thus the initial pressure tending to expand the atelectatic region is:

30 x 102/3 = 140 cm H2O !!

Surfactant depletion in pig model

Courtesy of Gary Nieman, Syracuse NY

Recruitment occurs throughout static inflation

Alveolar wall stress in 2-D condom model

Wall areas stressed next to regions of hyperiflation and collapse

Hickling KG: Reinterpreting the pressure-volume curve in patients with acute respiratory distress syndrome. Curr Opin Crit Care 2002, 8:32–38 Published with permission from:Rimensberger PC, Cox PN, Frndova H, et al.: The open lung during small tidal volume ventilation: Concepts of recruitment and “optimal” positive end expiratory pressure. Crit Care Med 1999, 27:1946–1952.

Saline-lavaged rabbits

Solid lines show re-inflation plots after deflation from 30 cm H2O airway pressure to different end-expiratory pressures.

Little hysteresis with deflation to 15 cm H2O, little derecruitment above that pressure.

Deflation /re-inflation PV curves

P/-V Tool 2P/-V Tool 2

Start/StopStart/Stop

Cursor 2Cursor 2

Cursor 1Cursor 1

Actual Settings P-start cmH2O P-top cmH2O end PEEP cmH2O Ramp speed cmH2O/s T-pause s T-total s

SettingsSettings

CloseClose

3.78

30

15

492

Xxxxxxxxx erttrert

Xxxxxxxxx erttrert

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P

V2000-/12-1215:33:34

PlotPlot

535

10

3

231

History

1 / 5

Cursor 1 Cursor 2 C cursor

Insp. limb 100 / 5 900 / 22 37.5

Exp. limb 155 / 5 1120 / 22 36.5

Current settings

Total time

To open setting window

Start/Stop button

Cursor buttons

To open Plot window

To select and view stored

curves

Date & time

Stored curves

Expiratory limb (yellow)

Assist lines

Inspiratory limb (green)

Data of insp. limbData of Exp. limb

Compliances for both red lines

Cursor 2 for both limbs

Cursor 1 for both limbs

Hickling KG. Using the expiratory pressure volume curve- VILI at the bedside. 25 th Symposium of Intensive Care and Emergency Medicine, March 21-25, 2005

Galileo datalogger: Inflation deflation method

Flow

Pre

ssu

re


Galileo datalogger: Inflation deflation method

Pressure

Vo

lum

e

Models of threshold opening and closing pressures

Inspiratory tidal PV plots

Incremental = black symbols Decremental = open symbols

TOP = 0–40, TCP = 0–4.

At each PEEP level the volume at equivalent pressures and the mean tidal PV slope are greater during decremental PEEP.

Hickling KG: Reinterpreting the pressure-volume curve in patients with acute respiratory distress syndrome. Curr Opin Crit Care 2002, 8:32–38 Redrawn from:Hickling KG: Best compliance during a decremental, but not incremental, positive end-expiratory pressure trial is related to open-lung positive end expiratory pressure: a mathematical model of acute respiratory distress syndrome lungs. Am J Respir Crit Care Med 2001, 163:69–78


Hickling KG: Best compliance during a decremental, but not incremental, positive end-expiratory pressure trial is related to open-lung positive end expiratory pressure: a mathematical model of acute respiratory distress syndrome lungs. Am J Respir Crit Care Med 2001, 163:69–78

The mean tidal PV slope plotted against PEEP

Incremental PEEP = black symbols Decremental PEEP = open symbols

Max PV slope with:Incremental PEEP is at 20 cm H2ODecremental PEEP is at 16 cm H2O


Hickling KG. Using the expiratory pressure volume curve- VILI at the bedside. 25th Symposium of Intensive Care and Emergency Medicine, Brussels, Belgium, March 21-25, 2005

Simulated data

Max change in slope corresponds to beginning of de-recruitment

But very difficult to judge slope changes by eye especially when very steep

Hence a flow pressure curve can indicate the max rate of de-recruitment

Flow pressure curves


Galileo datalogger: Flow-Pressure

Flow

Pre

ssu

re

Derecruitment

Hickling KG: Reinterpreting the pressure-volume curve in patients with acute respiratory distress syndrome. Curr Opin Crit Care 2002, 8:32–38 Redrawn from:Crotti S, Mascheroni D, Caironi P, et al.: Recruitment and de-recruitment during acute respiratory failure: A clinical study. Am J Respir Crit Care Med 2001, 164:131–140.


(A)Airway pressure vs volume /recruited volume determined from CT(open circles and dotted line; expressed as percent of maximum volume) and recruitment (black circles and solid line; expressed as percent maximum recruitment)

(B) Frequency distribution of estimated opening pressures.Note that recruited volume continues throughout inflation, up to 50 cm H2O pressure.

TOP

TCP

Pressure

Num

ber

of U

nits Skewed normal distribution

Unique to a patient and condition

Recruitment is described by Threshold Opening Pressure (TOP)

Derecruitment is described by Threshold Closing Pressure (TCP)

Real-time acquisition of threshold opening and closing pressures

Chase J, Yuta T, Shaw G, Horn B, Hann C A minimal model of mechanically ventilated lung mechanics to optimise ventilation therapy in the treatment of ARDS in critical care. Proceedings of the 12th International Conference on Bioengineering, Singapore 2005

Unique distributions for different levels of PEEP are found

PEEP

TOP

TCP



Optimisation of ventilationParameter identification = patient specific model

Simulation to determine effect of settings on PV curve

Optimise ventilator settings as desired

‘Strengths’ in using this approach…..Real time assessment of recruitment status which is dependent on PEEP, ventilation strategy, and disease

Readily identifies TCP distributions

optimization of PEEP

Provides opportunity to simulate a ventilation strategy before application.

TOP distribution characteristics

Prediction of “overstretch”. E.g. Δ recruitment < % max rate

? Correlated with E2% or CT scan

Although flow resistive forces through the endotracheal tube are accounted for, the model assumes the pressure at the carina will reflect what is happening to alveolar units.

Unforeseen resistive changes (eg major bronchial airway obstruction) could therefore lead to incorrect inferences about recruitment status

Limitations…

Needs to be clinically validated

A model for teaching and researchMechanical lung model with 6 units of variable compliance (weighted) bellows and variable insp /exp resistances (taps)

Mimicking nature

5cm PEEP 15cm PEEPSponsored by NZ$8000 grant from Hamilton Medical, Switzerland

Mimicking nature

Normal PV loop PV loop of “Asthma” PV loops at different levels of PEEP

(Note tidal volume is referenced to zero volume)

Chase JG, Yuta T, Shaw GM, Mulligan K, Hann CE. A novel mechanical lung model of pulmonary diseases to assist with teaching and research (in review )

Mind what you have learned.

Save you it can.

Acknowledgements

Dr Chris HannDr Chris HannAssoc. Prof. Assoc. Prof. Geoff ChaseGeoff Chase

Toshi YutaToshi Yuta

Kerry MulliganKerry Mulligan

Beverley HornBeverley Horn

man and machines: insights into ventilation strategies may 2006 dr geoff shaw dept of intensive care...

Documents

peep slide

minimal peep

optimum peep

nz slide

identity slide

super peep

survival slide

endexpiratory pressure