advanced assessment techniques in critical care

8/16/2019 Advanced Assessment techniques in Critical Care

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Advanced AssessmentTechniques in Critical Care

Learning Objectives:

ÙDescribe techniques for measuring and

optimizing ventilatory mechanics.

ÙInterpret common ventilator wave form

abnormalities.

ÙExplain the significance of end-tidal

CO2 measurements.

Lung Mechanics

Purposes For Monitoring Mechanics

ÙDetermine appropriate ventilator

settings

utidal volume

uPEEP

uinspiratory flow rate/time

upressure support


ÙAssess condition of lungs

uconsolidation

usurfactant deficiency

ubronchospasm


ÙEvaluate therapeutic effects

ubronchodilators

urecruitment maneuvers

usurfactant

uweaning modesÙDetermine when to wean or

discontinue support


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Parameters Monitored

ÙDynamic compliance (CDYN) -

includes elastic recoil andresistance to flow

ÙStatic compliance (CST) - elasticrecoil of lung and thorax

ÙInspiratory/expiratory resistance

to flow

ÙTotal PEEP


ÙTotal PEEP - imposed (set) PEEP

+ intrinsic PEEP (PEEPi)uPEEPi - end-expiratory

pressure in lung that may

exceed set PEEP, esp. with

ƒ high rates

ƒ obstructive disease

ƒ active exhalation


ÙPEEPi

ucontinuous monitoring

possible at tip of ETT

umeasurement requires end-

expiratory pause and absence

of active exhalation to measure

usignificance of PEEPi

ƒ impairs triggering

ƒ causes hyperinflation


ÙIntratracheal pressure - GEEngstrom CarestationSpirodynamics(TM)

Images courtesy GE Healthcare

2 mm OD sensor tube

ETT > 6.5 mm

Click to visit GE Engstrom Carestation web sitehttp://www.gehealthcare.com/euen/respiratory-care/products/engstrom-carestation/index.html


ÙIntratracheal pressure

umeasured at distal end of ETT

umore closely reflects alveolar

pressure

Image courtesy GE

Healthcare


ÙIntratracheal pressure - GE Engstrom

Carestation Spirodynamics(TM)

intratracheal sensor ventilator

wye


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ueasy detection of total PEEP

PEEPTOTAL




uCompliance values calculated at

three points along VP curve: 5 -15%,

45-55%, and 85-95% of the

inspiratory phase.

uInflection points readily discernable

FYI - click to download article: Practical assessment of

respiratory mechanics

http://bja.oxfordjournals.org/cgi/content/full/91/1/92

Measuring Compliance/Resistance

ÙStabilize patient- tachypnea,active expiration will confound

results by increasing intrinsicPEEP

ÙMeasure:

uexhaled TV

upeak inspiratory pressure (PIP)

uPEEP (total)

uplateau pressure (Ppt)- for

volume control modeuinspiratory flow


ÙIn pressure control mode,

including pressure control with

volume guarantee, the peakpressure is also the plateau

pressure.

ÙChanging to volume control

enables measuring plateau; but,mechanics will not be the same.

ÙUse dynamic compliance for

mechanics.


ÙSimple calculation

uPEEPtotal = (PEEP +

PEEPintrinsic)

udynamic compliance =

tidal volume/(PIP - PEEP)ustatic compliance =

tidal volume/(Ppt - PEEP)

uresistance = (PIP- Ppt)/flow

FYI - Click for article on monitoring mechanics during ventilation

http://www.medscape.com/viewarticle/417584_6


ÙUnits of measurement:

uCompliance- V/P -- Liters/cm H2O

ƒ normal - > .06 L/cm H2O

ƒ very low - .02 L/cm H2O

uResistance- P/flow -- cmH2O/L/sec

ƒ normal - 5 cm H2O/L/sec

ƒ high - > 10 cm H2O/L/sec


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ÙChanges in lung mechanics for anindividual patient are more

revealing than absolute numbers.

ÙEveryone must measure by sametechnique.

ÙSystem must be leak-free

ÙExamine trends and pre- post-therapy values.

Abnormal Cst

ÙDecreased Cst (CDYN if resistance

is constant)

uARDS, ALI

uExtrathoracic restriction

ƒ obesity

ƒ ascites, distension

uThoracic restriction

uVolume-occupying lesions

ƒ pneumothorax

ƒ pleural effusion

Implications- Decreased Cst

ÙIncreased work of breathing (WOB)

ÙIncreased ventilation pressure

requirement s==>

uExcessive shear forces on lung

tissue, causing inflammation

uHyperinflation of compliant lung

units, causing volutrauma

Implications- increased Cst

ÙAppropriate PEEP setting

ÙResolution of pathology

PEEP Therapy

Benefits of PEEP in ARDS

ÙPrevents alveolar collapse

(AKA de-recruitment)

ÙRe-recruits collapsed alveoli

ÙReduces shear forces required to

ventilate collapsed alveoli- prevents

atelectrauma

ÙIncreases ventilation-perfusion

matching- improves oxygenation


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Adverse Effects of PEEP

Ùincreased pulmonary vascular

resistance (PVR)

Ùincreased alveolar dead space (VDA)

- hypercapnia, hypoxemia

Ùdecreased venous return

udecreased cardiac output (QT)

udecreased mixed venous saturation

(SvO2)

udecreased urine output

Adverse Effects of PEEP

Ùhyperinflation- volutrauma

Ùright-to-left shunt with patentforamen ovale (PFO)

uPFO present in 15-25% normal adults

uincreasing PEEP decreases PaO2

Optimal PEEP

ÙDefined- level of PEEP that imposes

favorable volume-pressure

relationship on the majority of lung

units ==>

ugreatest Cst

ugreatest SvO2

uimproved ventilation-perfusion (VQ)

matching

ureduced shear forces required for

ventilation

Optimal PEEP

ÙMethods for determination

ulower inflection point of PV curve

ustepwise incremental Cst

measurement

ustepwise decremental Cst

measurement

ualternative method (Mercat, et al)

uvolume-oriented - FRC

measurement

Optimal PEEP

ÙMethods for determination

ulocate lower inflection point (LIP)

of PV curve

uOptimal PEEP = LIP + 2-3 cm H2O

Pressure

Volume

LIP

Optimal PEEP

Ùlower inflection point (LIP) of PV

curve

udisagreement among observers

ucontroversy over significance ofLIP


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Stepwise Decremental Technique

ÙAdjust TV to desired level

(


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Ventilator Graphics

Analysis

Applications For Graphics

ÙAssess lung mechanics

uresistance

ucompliance

uWOB

ÙDetect ventilation problems

uPEEPi

ulung overdistension

upatient/ventilator asynchrony

Applications For Graphics

ÙEvaluate interventions

ubronchodilator therapy

uventilator settings

ƒ primary mode

ƒ tidal volume, drive pressure

ƒ PEEP

ƒ ventilation times

ƒ trigger level

ƒ rise time

ƒ expiratory flow limit (PSV)

Graphic Types

Ùwaves

upressure-time

uflow-time

uvolume-time

Graphic Types

Ùwaves

upressure-time

Courtesy Newport Medical

Graphic Types

Ùwaves

uflow-time



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Graphic Types

Ùwaves- comparing volume, vs. pressure

control (PRVC, etc. = pressure control)


Graphic Types

Ùwaves

uvolume-time


Graphic Types

Ùloops

upressure-volume


mandatory breath

Graphic Types

Ùloops

upressure-volume


spontaneous breath

Graphic Types

Ùloops

uflow-volume


mandatory breath

Graphic Types

Ùloops

uflow-volume


mandatory breath


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Clinical Applications

For Graphics

Compliance- pressure volume curve

ÙLower inflection point (LIP) - opening ofatelectatic units

ÙUpper inflection point (UIP) -hyperinflation

Compliance- pressure volume curve

Pressure cm H2O

Volume

mL

50

1000

LIP

UIP

greatest

compliance

Qualitative assessment of compliance

normal CL decreased CL

Volume

mL

Detecting intrinsic peep

Ùzero end-expiratory flow (EEF) ==>

zero PEEPi

0

flow

0

flow

non-zero EEF

zero EEF

Detecting intrinsic PEEP during

expiratory hold

Ùmeasured during absence of patient

effort

pressure

0

total

PEEP

57


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Lung overdistension

"beak"

volume

pressure

Patient/ventilator asynchrony

Courtesy Newport

Medical

Scooping on theupswing of the flowwaveform

Significant pressuredrop at the onset of

patient effort

Inspiratory flow/rise- pressure wave


Linear or bowed upwardrise in pressure after

trigger on the pressurewave

Slow rise in pressure,

concave shape of the

pressure wave

Expiratory flow-cycling (PSV)


Patient expiratory effort

Late termination

Inability to trigger

Spontaneous WOB

spontaneous breaths

Inspiration ExpirationPawcmH

2O/

mbar

LITERS

0.6

VT

LITERS

0.6

VT

WOB WOB

Increased WOB

Bronchodilator effectiveness



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Summary and Review

ÙVentilator graphics

utypesunormal waveforms

uabnormal waveforms

ÙETCO2 monitoring

uapplications

uinterpretation of P(a-et)CO2

END

References

ÙChiumello D, Cressoni M, Chierichetti M, Tallarini F,Botticelli M, Berto V, Mietto C, Gattinoni L. Nitrogen

washout/washin, helium dilution and computed

tomography in the assessment of end expiratory lung

volume. Crit Care. 2008 Dec 1;12(6):R150.

ÙMacnaughton PD. New ventilators for the ICU--

usefulness of lung performance reporting. Br J Anaesth2006 Jul;97(1):57-63.

ÙMercat A, et al. Positive End-Expiratory Pressure

Setting in Adults With Acute Lung Injury and Acute

Respiratory Distress Syndrome: RandomizedControlled Trial. JAMA. 2008;299(6):646-655.

ÙPepe PE, Hudson LD, Carrico CJ. . Early application ofpositive end-expiratory pressure in patients at risk for

the adult respiratory-distress syndrome. N Engl J Med.

1984 Aug 2;311(5):281-6.

References

ÙPinsky MR. Cardiovascular issues in respiratory care.Chest 2005;128:5925-75.

ÙCujec B, Polasek P, Mayers I, Johnson D.. Positive end-

expiratory pressure increases the right -to-left shunt in

mechanically ventilated patients with patent foramenovale. Annals Int Med 1993 Nov 1;119(9):887-94.

ÙRouby JJ, Lu Q, Goldstein I. .Selecting the right level ofpositive end-expiratory pressure in patients with acute

respiratory distress syndrome. Am J Respir Crit Care

Med. 2002 Apr 15;165(8):1182-6.

ÙMaggiore SM, Jonson B, Richard JC, Jaber S, Lemaire

F, Brochard L. .Alveolar derecruitment at decremental

positive end-expiratory pressure levels in acute lunginjury: comparison with the lower inflection point,

oxygenation, and compliance. Am J Respir Crit Care

Med. 2001 Sep 1;164(5):795-801

References

ÙGirgis K, Hamed H, Khater Y, Kacmarek RM. ADecremental PEEP Trial Identifies the PEEP Level That

Maintains Oxygenation After Lung Recruitment. Respir

Care 2006;51:1132-38.

ÙStenqvist, O. Practical assessment of respiratory

mechanics. Br. J. Anaesth 2003;91:92-105.

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