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Definitions. The 1994 North American-European Consensus Conference (NAECC) criteria: Onset - Acute and persistent Radiographic criteria - Bilateral pulmonary infiltrates consistent with the presence of oedema

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Definitions
Definitions

  • The 1994 North American-European Consensus Conference (NAECC) criteria:

    • Onset - Acute and persistent

    • Radiographic criteria - Bilateral pulmonary infiltrates consistent with the presence of oedema

    • Oxygenation criteria - Impaired oxygenation regardless of the PEEP concentration, with a Pao2/Fio2 ratio  300 mmHg (40 kPa) for ALI and  200 mmHg (27 kPa) for ARDS

    • Exclusion criteria - Clinical evidence of left atrial hypertension or a pulmonary-artery catheter occlusion pressure of  18 mm Hg.

Bernard GR et al., Am J Respir Crit Care Med 1994


Mortality from ards
Mortality from ARDS

  • ARDS mortality rates - 31% to 74%

  • The variability in the rates quoted is related to differences in the populations studied and in the precise definitions used.

  • The main causes of death are nonrespiratory causes (i.e., die with, rather than of, ARDS).

  • Respiratory failure has been reported as the cause of death in 9% to 16% of patients with ARDS.

  • Early deaths (within 72 hours) are caused by the underlying illness or injury, whereas late deaths are caused by sepsis or multiorgan dysfunction.

  • There is a controversy about the role of hypoxemia as a prognostic factor in adults. Nevertheless, in some studies, both Pao2/Fio2 ratio and Fio2 were variables independently associated to mortality.

Frutos-Vivar F, et al. Curr Opin Crit Care. 2004.

Vincent JL, et al. Crit Care Med. 2003.

Ware LB. Crit Care Med. 2005.


Clinical disorders associated with the development of ali ards
Clinical Disorders Associated with the Development of ALI/ARDS

  • Direct insult

  • Common

    • Aspiration pneumonia

    • Pneumonia

  • Less common

    • Inhalation injury

    • Pulmonary contusions

    • Fat emboli

    • Near drowning

    • Reperfusion injury

  • Indirect insult

  • Common

    • Sepsis

    • Severe trauma

    • Shock

  • Less common

    • Acute pancreatitis

    • Cardiopulmonary bypass

    • Transfusion-related TRALI

    • Disseminated intravascular

  • coagulation

    • Burns

    • Head injury

    • Drug overdose

Atabai K, Matthay MA. Thorax. 2000.

Frutos-Vivar F, et al. Curr Opin Crit Care. 2004.


Epidemiology
Epidemiology ALI/ARDS

  • NIH, 1972 - Incidence of ARDS in the United States: 75 cases per 105 person.years population (approximately 150,000 cases per year)

  • International multi-center ALI/ARDS cohort studies, 1989 - 2002

    • Incidence estimates of ALI/ARDS = 1.3 to 22 cases per 105 person.years

  • ARDS Network Study (NAECC definitions), 2003 - Incidence of ALI/ARDS in the United States: 32 cases per 105 person.years (range 16 - 64)

  • ARDS Network Study (NAECC definitions), 2003 - The average number of cases of ALI per ICU bed per year (2.2) varied significantly from site to site (range 0.7 - 5.8)


Definitions

The ARDS Lungs ALI/ARDS

Vt

  • External forces applied on the lower lobes at end inspiration and end expiration in a patient in the supine position and mechanically ventilated with positive end-expiratory pressure.

    • Large blue arrows: Forces resulting from

    • tidal ventilation

    • Small blue arrows: Forces resulting from

    • positive end-expiratory pressure (PEEP)

    • Green arrows: forces exerted by the

    • abdominal content and the heart on the

    • lung

aerated lung

Vt

consolidated lung

PEEP

Rouby JJ, et al. Anesthesiology. 2004.


Definitions

Ventilator induced lung injury ALI/ARDS

Positive pressure ventilation may injure the lung

via several different mechanisms

Alveolar distension

“VOLUTRAUMA”

Repeated closing and opening

of collapsed alveolar units

“ATELECTRAUMA”

Oxygen toxicity

Lung inflammation

“BIOTRAUMA”

VILI

Multiple organ dysfunction syndrome


Ventilator induced lung injury conceptual framework
Ventilator-induced Lung Injury ALI/ARDSConceptual Framework

  • Lung injury from:

    • Overdistension/shear - > physical injury

    • Mechanotransduction - > “biotrauma”

    • Repetitive opening/closing

    • Shear at open/collapsed lung interface

  • Systemic inflammation and death from:

    • Systemic release of cytokines, endotoxin, bacteria, proteases

“volutrauma”

“atelectrauma”


How much collapse depends on the plateau

Less Extensive ALI/ARDS

Collapse But

Greater PPLAT

100

R = 100%

R = 93%

Total Lung Capacity [%]

Some potentially recruitable units open only at high pressure

R = 81%

More Extensive

Collapse But

Lower PPLAT

60

R = 59%

From Pelosi et al

AJRCCM 2001

20

R = 22%

0

0

60

20

40

Pressure [cmH2O]

R = 0%

How Much Collapse Depends on the Plateau


Pv relationships ards supine

Denver Health ALI/ARDS

·

·

·

·

·

TLC

Ventral Alveoli

·

·

·

·

·

·

·

·

·

·

·

·

·

FRC

·

·

·

·

·

Dorsal Alveoli

·

·

·

·

PV Relationships(ARDS, Supine)

VL

(% TLC)

-20

-15

-10

-5

0

5

10

15

20

25

30

Ptp (cm H2O)


Ards network low v t trial
ARDS Network Low V ALI/ARDST Trial

  • Patients with ALI/ARDS (NAECC definitions)of < 36 hours

  • Ventilator procedures

    • Volume-assist-control mode

    • RCT of 6 vs. 12 ml/kg of predicted body weight PBW Tidal Volume

      (PBW/Measured body weight = 0.83)

    • Plateau pressure  30 vs.  50 cmH2O

    • Ventilator rate setting 6-35 (breaths/min) to achieve a pH goal

      of 7.3 to 7.45

    • I/E ratio:1.1 to 1.3

    • Oxygenation goal: PaO2 55 - 80 mmHg/SpO2 88 - 95%

    • Allowable combination of FiO2 and PEEP:

      FiO2 0.3 0.4 0.4 0.5 0.5 0.6 0.7 0.7 0.7 0.8 0.9 0.9 0.9 1.0 1.0 1.0 1.0

      PEEP 5 5 8 8 10 10 10 12 14 14 14 16 18 18 20 22 24

  • The trial was stopped early after the fourth interim analysis (n = 861

    for efficacy; p = 0.005 for the difference in mortality between groups)

ARDS Network. N Engl J Med. 2000.


Ards network improved survival with low v t

1.0 ALI/ARDS

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

0

20

40

60

80

100

120

140

160

180

ARDS Network: Improved Survival with Low VT

Proportion of Patients

Lower tidal volumes

Survival

Discharge

Traditional tidal values

Survival

Discharge

Days after Randomization

ARDS Network. N Engl J Med. 2000.


Ards network additional findings
ARDS Network: Additional Findings ALI/ARDS

In ALI and ARDS patients, 6 ml/kg PBW tidal volume ventilation strategy was associated with:

  • PaO2/FiO2 lower in 6 ml/kg low VT group

  • High RR prevented hypercapnia with minimal auto-PEEP (difference of median intrinsic PEEP between the groups was < 1 cm H2O)

  • No difference in their supportive care requirements (vasopressors-IV fluids-fluid balance-diuretics-sedation)

  • ~10% mortality reduction

  • Less organ failures

  • Lower blood IL-6 and IL-8 levels

ARDS Network. N Engl J Med. 2000. Parsons PE, et al. Crit Care Med. 2005.

Hough CL, et al. Crit Care Med. 2005. Cheng IW, et al. Crit Care Med. 2005.


Definitions

Open lung concept ALI/ARDS

exp

insp


Definitions

40 ALI/ARDS

Opening

pressure

30

Closing

pressure

20

From Crotti et al

AJRCCM 2001.

10

0

0

5

10

15

20

25

30

35

40

45

50

Paw [cmH2O]

Opening and Closing Pressures in ARDS

High pressures may be needed to open some lung units, but once open, many units stay open at lower pressure.

50

%


Recruitment maneuvers rms
Recruitment Maneuvers (RMs) ALI/ARDS

  • Proposed for improving arterial oxygenation and enhancing alveolar recruitment

  • All consisting of short-lasting increases in intrathoracic pressures

    • Vital capacity maneuver (inflation of the lungs up to 40 cm H2O, maintained for 15 - 26 seconds) (Rothen HU. BJA. 1999; BJA 1993.)

    • Intermittent sighs (Pelosi P. Am J Respir Crit Care Med. 2003.)

    • Extended sighs(Lim CM. Crit Care Med. 2001.)

    • Intermittent increase of PEEP (Foti G. Intensive Care Med. 2000.)

    • Continuous positive airway pressure (CPAP) (Lapinsky SE. Intensive Care Med. 1999. Amato MB. N Engl J Med. 1998.)

    • Increasing the ventilatory pressures to a plateau pressure of 50 cm H2O for 1-2 minutes (Marini JJ. Crit Care Med. 2004. Maggiore SM. Am J Respir Crit Care Med. 2003.)

Lapinsky SE and Mehta S, Critical Care 2005


Other manoeuvres
Other manoeuvres ALI/ARDS

  • Prone positioning ventilation

  • Prolonged inspiration

  • Inverse ratio ventilation


Limit of open lung strategy
Limit of open lung strategy ALI/ARDS

  • To minimise VILI to the less damaged alveoli

    • need to minimise individual alveolar volume – cannot measure this hence use pressure as surrogate

    • i.e max insp pressure (plateau pressure 30-32cm H20)

    • as PEEP increases and max pressure remains unchanged ,TV will decrease

      • Alveolar ventilation will decrease

      • alv V: dead space vent ratio will decrease

PaCO2 increases - Resp acidosis


Increasing paco2
Increasing PaCO2 ALI/ARDS

  • Management options

Increase resp rate

Anatomical dead space 150ml


Increasing paco21
Increasing PaCO2 ALI/ARDS

  • Permissive hypercapnia

  • Tracheal gas insufflation – attempting to reduce dead space

Accompanying as alveolar ventilation decreases will require increasing FIO2 and eventually will result in alveloar hypoxia and arterial hypoxaemia


High frequency ventilation
High frequency ventilation ALI/ARDS

  • High frequency Jet ventilation

    • Delivers very short high pressure jets of air and relies on passive exhalation

  • High frequency flow interrupter:

    • eg infant star – relies on high frequency interruption of flow , passive exhalation – normal circuit

  • High frequency oscillatory ventilation

    • pressurised circuit , uses a diaphragm piston unit to actively move gas in and out of the lungs – requires special non-compliant circuit , active expiration



Definitions

High-frequency Oscillatory Ventilation ALI/ARDS

Characterized by rapid oscillations of a reciprocating diaphragm, leading to high-respiratory cycle frequencies, usually between 3 and 9 Hz in adults(180 -600breaths per min), and very low VT (0.1-3ml/kg). Ventilation in HFOV is primarily achieved by oscillations of the air around the set mean airway pressure mPaw (35cm -45cm H2O).


Definitions

High-frequency Oscillatory Ventilation ALI/ARDS

  • Active expiration

Pressurised circuit


Definitions

High-frequency Oscillatory Ventilation ALI/ARDS

0.1-3ml/kg

3-9 hz

35cm H20

90 cm



Definitions

Pressure attenuation during HFOV ALI/ARDS

Distal airways

Increase the frequency:

What happens to TV:

decreases

What happens to VILI:

Decreases and hence wish to maximise this

What happens to PaCO2:

Increases – alveolar MV decreases


Further questions
Further questions ALI/ARDS

If PaCO2 is rising and pH is < 7.25: What adjustments may be required?

  • Increase alveolar ventilation – how?

  • Increase amplitude

  • Decrease frequency

  • Remove ETT suction elbow

2. Decrease dead space

  • Introduce cuff leak

  • Tracheal gas insufflation


Definitions

Further Questions ALI/ARDS:

What effect does this ventilation have on RV function:

Increase after load

Decrease preload

In which conditions would HFOV be contraindicated:

  • Severe obstructive airways disease

  • Intractable shock - must not be hypovolaemic (CVP at least 8mmHg)

  • Intracranial hypertension


Recruitment manoeuvre prior to connection to hfov
Recruitment Manoeuvre prior to connection to HFOV ALI/ARDS

  • May cause barotrauma , volutrauma and haemodynamic compromise

    • Hence these manoeuvres should not be attempted without a senior member of the intensive care medical team being present

  • recommended manoeuvre:

    • Perform endotracheal toilet bfore manoeuvre

    • Patient requires to be heavily sedated +/- paralysed

    • should not be hypovolaemic or intractable shock

    • Ventilator mode PCV

    • High pressure alarm increased

    • PEEP gradually increased to 25 cm H2O whilst observing haemodynamics

    • Measure lung compliance and gradually reduce peep to level just above point that results in a loss in lung compliance


Final questions
Final Questions ALI/ARDS

Diagnosis of pneumothorax:

  • high index of suscpician

  • Desaturation

  • haemodynamic change

  • Chest sounds difficult

  • mPaw and ∆P may not change

  • Decrease chest wiggle on side of pneumothorax

Abrupt rise in paCo2 and increase in ∆P -

. Airway obstruction

Change in resistance


High frequency oscillatory ventilation
High-frequency Oscillatory Ventilation ALI/ARDS

  • Characterized by rapid oscillations of a reciprocating diaphragm, leading to high-respiratory cycle frequencies, usually between 3 and 9 Hz in adults, and very low VT. Ventilation in HFOV is primarily achieved by oscillations of the air around the set mean airway pressure mPaw.

  • HFOV is conceptually very attractive, as it achieves many of the goal of lung-protective ventilation.

    • Constant mPaws: Maintains an “open lung” and optimizes lung recruitment

    • Lower VT than those achieved with controlled ventilation (CV), thus theoretically avoiding alveolar distension.

    • Expiration is active during HFOV: Prevents gas trapping

    • Higher mPaws (compared to CV): Leads to higher end-expiratory lung volumes and recruitment, then theoretically to improvements in oxygenation and, in turn, a reduction of FiO2.

Chan KPW and Stewart TE, Crit Care Med 2005