Sarah M. McMullen, R5 CCM

Tuesday November 3, 2009

This presentation has been adapted to enhance online viewing

to review the benefits of allowing preserved spontaneous breathing in acute respiratory failure, emphasizing ALI/ARDS

to review partial ventilatory support modalities used in acute respiratory failure

to present the results of a systematic review

Acute inflammatory lung injury › resulting from direct or indirect pulmonary insult

American-European Consensus Conference (1994) definitions:› ALI

Acute pulmonary failure with PaO2/FiO2 <300mmHg Bilateral infiltrates on chest film PCWP <18 mmHg, or no clinical evidence of elevated LAP

› ARDS as above, with PaO2/FiO2 <200mmHg, regardless of

PEEP

The Lancet 2007

EARLY› Exudative: infiltration, activation of inflammatory

cells endothelial injury, capillary disruption, pulmonary oedema› Proliferative: fibroblastic infiltration and

remodelling LATE› Fibrotic: consolidation, fibrosis stiff lungs

Alveolar collapse› Superimposed pressure on the lung› Cephalad shift of diaphragm

Diffuse lung consolidation, multifocal patchy involvement and lobar or segmental disease

Primarily in DEPENDANT lung regions› Ventilation and perfusion are no longer matched› Severe arterial hypoxaemia

Gattinoni et al JAMA 1994

Open Lung Approach: PEEP, low tidal volume, static peak pressures, permissive hypercapnia

Adjuncts: prone position, inverse ratio, iNO, tracheal insufflation, HFO, liquid ventilation, ECMO, pharmacologics

Haemodynamics Monitoring Gastrointestinal Renal CNS Weakness Immune system Sleep

Barotrauma Heterogeneous ventilation Physiologic dead space and shunt Diaphragm and respiratory muscles disuse,

atrophy Mucociliary dysmotility Ventilator-associated pneumonia (VAP) Ventilator-associated lung injury (VALI)

VENTILATOR ASSOCIATED LUNG INJURY: COMPONENTS

VOLUTRAUMA

overdistension (High EIV) damage

ATELECTRAUMA

shear injury BIOTRAUMA

inflammatory mediator-related injury

BAROTRAUMA

high pressure damageOXYGEN TOXICITY

VILI/VALIThe Lancet 2003

Early institution of modes allowing spontaneous breathing (SB) helps mitigate complications associated with controlled mechanical ventilation (MV)

Physiologic and haemodynamic benefits are associated with preserved SB

Improved VA/Q matching, gas exchange› By allowing contraction of the diaphragm

› Improved ventilation of dependant areas better V/Q matching, less atalectasis and shunt

Improved cardiac indices: CO, CI, and less use of vasopressors/inotropes

No increase to oxygen cost of breathing Less analgo-sedative drugs

Pressure Support SIMV APRV – airway pressure release ventilation PAV – proportional assist ventilation NAVA – neurally adjusted ventilatory assist

Gold standard of partial ventilatory support Can be used in early ARF and during weaning The patient’s inspiratory effort triggers the ventilator, which

delivers a flow up to a preset pressure limit depending on the desired minute volume› Note: the pressure delivered is independent of the amount of

patient effort Flow cycles off when a percentage of peak inspiratory flow

is reached. Tidal volumes vary as in spontaneous breathing

Developed as a method of partial ventilatory support to facilitate weaning

A demand valve was placed so the spontaneous breath could occur without having to breathe through the various valves and apparatus of the ventilator.

The patient could breathe spontaneously while also

receiving mandatory breaths. As the patient’s respiratory function improved, the

number of mandatory breaths was decreased

emedicine

Continuous positive airway pressure with an intermittent release phase

Phigh for a prolonged time (Thigh): adequate lung volume, alveolar recruitment

Time-cycled release phase to Plow for a short time (Tlow): CO2 removal (ventilation)

Unrestricted spontaneous breathing allowed at any time

emedicine

Mode of ventilation during which the pressure delivered by the ventilator was positively related to the inspired flow and volume› i.e., pressure in proportion to patient effort

Preset PROPORTION between applied pressure and inspiratory muscle effort› Proportionality constants in the equation of motion

dictate how much the applied pressure will increase for a given increase in inspiratory muscle effort

emedicine

NAVA uses the electrical activity of the diaphragm (EAdi) to control the ventilator

Eadi represents the central respiratory drive and reflects the length and intensity of the patient's neural effort.

Mechanical inspiratory assist starts when the respiratory center initiates the breath and is therefore independent of any pneumatic component.

During inspiration, the pressure delivered is proportional to the EAdi and the inspiratory pressure assist ceases when the neural activation of the diaphragm starts to decline after reaching the inspiratory maximum value.

Respiratory failure requiring mechanical ventilation remains one of the most common reasons for admission to an Intensive Care Unit (ICU).

Mechanical ventilation aims to restore gas exchange and to unload the work of breathing.

The adverse effects associated with controlled ventilation are being increasingly recognized, including haemodynamic compromise, the need for deep sedation and/or muscle paralysis and VALI.

Hypothesis› In contrast to controlled ventilation, partial

vent i latory support modes al low the preservation of spontaneous breathing efforts by the intubated patient, and contractions of the diaphragm, which may mitigate the adverse effects of controlled mechanical ventilation.

Objectives: To investigate:› which modes of ventilation allow preserved

spontaneous breathing during mechanical ventilation, and which of these modes have been investigated?

› what are the beneficial effects of preserved spontaneous breathing during mechanical ventilation in acute lung injury, and what are the effects on outcomes?

› what evidence exists (and of what level is it) that the use of partial ventilatory support in acute lung injury improves outcomes?

search strategy keywords:› common known modalities of assisted breathing › ALI/ARDS

MEDLINE, Cochrane, and EmBase electronic databases searched for articles in English, French and German.

Reference l ists from comprehensive reviews, observational studies and identified clinical trials were hand-searched. EXCLUDED: Studies pertaining to weaning, chronic ventilation,

non-invasive, ECMO.

Modified Oxford Centre for Evidence-Based Medicine Levels of Evidence System

1a Multicentre RCT/Meta-Analysis/SR of RCTs1b Good individual RCT

2a SR of cohort studies or missing criteria for SR in RCTs2b Prospective cohort/lower quality RCT3a SR of case control studies or missing criteria for SR in cohort studies

3b Retrospective cohort/case control study4a Case series/low quality 3b study

4b Clinical/observational study5 Experimental animal study6a Comprehensive review of the

literature without documented methodology6b Expert opinion/case report/technical note

Airway pressure release, pressure support, proportional assist, and synchronized intermittent mandatory ventilatory modes were most commonly investigated.

Only nine studies involving 664 patients

reported predefined outcomes: 2 RCTs (Grade 1b), 6 Grade 2b studies, 1 3b study

28 animal and 41 observational clinical studies consistently demonstrated findings of improved haemodynamics and gas exchange, without increased oxygen cost of breathing.

Six grade 2b studies demonstrated the same positive physiologic effects;

No study compared two different partial ventilatory modes, and none were powered to assess mortality.

30 Trauma patients at risk of ARDS; APRV vs PCV Mortality: not reported ICU LOS: 23+/-2d vs 30+/-2d (p<0.05) APRV vs PCV VFDs: 15 +/-2d vs 21 +/-2d, APRV vs PCV (p<0.05)

APRV associated with increased CRS, PaO2, CI, DO2 (p<0.05); decreased QVA/QT, O2 extraction (p<0.05)

pts with PCV needed higher doses of sufentanil,

midazolam, norepinephrine, dobutamine (all p<0.05).

APRV vs SIMV+PS in 58 adult pts with early ARDS Mortality: 17% APRV vs 18% SIMV (p=0.91)› BUT: underpowered, stopped early for futility

ICU-Free days: 11.9+/-1.7 vs 10.7+/-1.4 (APRV vs SIMV) VFDs: 13.4+/-1.7 vs 12.2+/-1.5 for APRV vs SIMV-PS Inspiratory pressure 25.9+/-0.6 vs 28.6+/-0.7 cmH20 for APRV vs

SIMV-PS (p=0.007) improved organ function: SOFA-score decreased by 2.8 +/-0.8 vs

1.7+/-0.2 (APRV vs SIMV) LIS decreased 0.8+/-0.1 vs 0.6+/-0.2 (APRV vs SIMV)

While unorthodox to include an expansive range of study designs and publication types within a systematic review, the scope was kept broad due to lack of volume of high quality studies, and there was no intention to undertake any statistical analysis.

Despite benefits of preserved spontaneous breathing consistently shown in clinical and experimental data,› the anticipated effects on outcomes in acute

respiratory failure and ALI/ARDS are not supported by high levels of evidence› but it is unknown whether this disparity mirrors

clinical practice.

Survey of Intensivists’ practices for ventilatory management in ALI/ARDS

Pilot study, RCT…?