Dr Mohamad Abdelsalam

ICU Department

KFHJ

Why Is RV Failure

Particularly Important In

ARDS?

Acute right ventricular failure

can adversely affect the outcome

of acute respiratory distress

syndrome.

How Does RV Failure

Affect LV Function?

Acute RV failure can compromise

LV function by decreasing LV

diastolic filling.

In acute pressure or volume

overload, RV dilatation shifts the

interventricular septum to the left,

thereby decreasing LV volume,

diastolic filling and cardiac output.

Also, low right-sided cardiac output

can result in left-sided underfilling

and decreased LV stroke volume.

By reducing cardiac output, acute

decompensation of the right

ventricle can compromise oxygen

delivery and initiate or potentiate

tissue hypoxia.

Role Of Mechanical Ventilation In

Acute RV Failure.

Mechanical ventilation plays a

key role in the development of

acute RV failure in patients with

ARDS.

How Does High PEEP

Alter RV Function?

By increasing intrathoracic

pressure, PEEP may reduce venous

return and decrease RV preload.

By increasing airway pressure,

PEEP may overdistend alveoli and

compress alveolar capillaries,

resulting in an increase in

pulmonary vascular resistance and

hence RV afterload.

PEEP may reduce cardiac

output either by decreasing RV

preload or increasing RV

afterload.

Plateau Pressure As An

Important Predictor Of Acute

Cor Pulmonale In ARDS.

Low Tidal Volume Ventilation Has

Become The Standard Of Care For

Patients With ARDS

The progressive reduction in tidal volume

and plateau pressure has been associated

with a dramatic decrease in the incidence of

acute cor pulmonale.

A recent study of more than 350

patients with ARDS has found a strong

relationship between plateau pressure

and the incidence of acute cor

pulmonale.

Jardin and Vieillard-Baron. Intensive Care Med, 2007.

For a plateau pressure < 27 cm H2O,

the incidence of acute cor pulmonale

was very low (~ 10%).

When the plateau pressure ranged

from 27 to 35 cm H2O, the incidence

of acute cor pulmonale reached 30%.

At a plateau pressure >35 cm H2O,

60% of the patients developed acute

cor pulmonale.

The right ventricle rapidly

fails as the plateau pressure is

progressively increased.

Serial echocardiography in a patient with severe ARDS illustrating the impact of

plateau pressure on RV function and hemodynamics.

PEEP As A Predictor Of

Acute Cor Pulmonale In

ARDS.

Does Increasing PEEP While

Limiting Plateau Pressure Alter

RV Function?

In a small series of patients with severe

ARDS, a group of investigators compared a

low level with a high level of PEEP titrated

for a plateau pressure of 30 cm H2O.

Mekontso et al. Intensive Care Med, 2009.

In the high PEEP group,

echocardiography showed marked

RV dilatation with paradoxical

septal movement.

Panel A, ARDS patient ventilated with a PEEP of 7 cm H2O and plateau pressure

of 27 cm H2O. Panel B, 15 minutes after increasing PEEP to 14 cm H2O, with the

same plateau pressure (by decreasing tidal volume).

Increasing PEEP while limiting

plateau pressure may alter RV

function and depress cardiac output.

Another group of investigators studied the

effect of increasing PEEP on RV function in

patients with severe ARDS ventilated with

low tidal volume and limited plateau

pressure.

Fougeres et al. Crit Care Med, 2010.

They found that increasing PEEP

while limiting plateau pressure to 30

cm H2O did not increase the incidence

of acute cor pulmonale.

Open lung strategy with high PEEP,

low tidal volume and limited plateau

pressure may be hemodynamically

well tolerated.

Why Does The Impact Of PEEP On

RV Function Vary Greatly Among

Patients With ARDS?

Data are conflicting regarding the

hemodynamic impact of high PEEP

on RV function during lung

protective ventilation.

Is It The Effect Of PEEP On The Lung

(Recruitment vs. Overdistension) That

Determines Its Impact On The Right

Ventricle?

The effect of PEEP on RV function

may be determined by its ability to

recruit the lung.

Lung recruitment improves lung

compliance, decreases plateau pressure

and improves oxygenation, all of which

are beneficial to the right ventricle.

PEEP-induced lung recruitment may unload the right

ventricle by decreasing plateau pressure and increasing

PaO2.

The greater the lung is recruited, the less the right

ventricle is overloaded.

Slutsky et al. NEJM 2006.

Conversely, when PEEP fails to recruit

the lung, it may induce overdistension,

thereby compressing pulmonary

capillaries and increasing RV afterload.

What is good for the lung (recruitment)

may be good for the heart (unloading)

and what is bad for the lung

(overdistension) may be bad for the

heart (overloading).

Improved Oxygenation Does Not

Necessarily Mean Improved

Outcome.

Three large randomized controlled

trials did not show a survival benefit

of high PEEP over low PEEP during

lung protective strategy.

High PEEP improved arterial

oxygenation but failed to

improve survival of patients

with ARDS.

RV failure may explain why

high PEEP failed to improve

outcome of ARDS.

Despite its beneficial effect on lung

recruitment, high PEEP could have

been detrimental to RV function,

cardiac output and oxygen delivery.

SaO2 vs. SvO2 ─ What Should Be Our Goal?

Cardiac Output Is The Major

Determinant Of Oxygen

Delivery.

Decreased cardiac output associated

with high PEEP counterbalances the

increase in oxygen saturation, and

oxygen delivery is ultimately

reduced.

PEEP May Paradoxically

Reduce Oxygen Delivery.

The primary goal of mechanical

ventilation is to maintain adequate

tissue oxygenation, while avoiding

ventilator-induced lung injury.

The adequacy of tissue oxygenation is

better assessed by measuring mixed or

central venous oxygen saturation rather

than arterial oxygen saturation.

SaO2 represents arterial

oxygenation, while SvO2 reflects

the balance between oxygen

delivery and oxygen consumption.

SvO2 is a more reliable index of

oxygen delivery and tissue

oxygenation than SaO2.

SaO2 vs. SvO2 ─ What

Determines Optimal

PEEP?

The Ultimate Goal Of PEEP

Is To Increase Oxygen

Delivery.

Optimal PEEP may be the level of

PEEP at which oxygen delivery

(rather than oxygen saturation) is

maximal.

Accordingly, PEEP can be adjusted

to achieve the highest SvO2 (or

ScvO2) rather than SaO2.

Cardioprotective Ventilatory

Strategy.

Echocardiography is considered

the best method for noninvasive

assessment of RV function.

Abnormal echocardiographic findings

in ARDS include RV dilatation,

paradoxical septal motion and biphasic

pattern of pulmonary blood flow, which

indicates severe acute cor pulmonale.

TEE of mechanically ventilated patient with severe ARDS

showing RV dilatation and paradoxical septal motion.

Caille and Viellard-Baron. Open nuclear Med J, 2010.

Echocardiography allows the

adjustment of ventilator settings (tidal

volume, PEEP and plateau pressure)

according to RV function.

In the presence of echocardiographic

evidence of RV failure, ventilatory

management should aim to limit the

plateau pressure to < 27 cm H2O.

At a plateau pressure below 27

cm H2O, the incidence of acute

cor pulmonale is very low.

Plateau pressure limitation, on the

other hand, requires progressive

reduction of tidal volume which often

leads to hypercapnia, a potent

pulmonary vasoconstrictor.

Correcting hypercapnia by increasing

respiratory rate may induce intrinsic

PEEP, which can adversely affect the

function of the right ventricle.

Balancing the cardioprotective effect of

pressure-limited ventilation with the

adverse hemodynamic consequence of

permissive hypercapnia is particularly

challenging in ARDS.

Low PEEP As An Important

Component Of The

Cardioprotective Ventilatory

Strategy

PEEP should be high enough to protect

against lung injury caused by

recruitment/derecruitment and to keep

the lung open at end expiration.

At the same time, PEEP should be low

enough to avoid alveolar

overdistension which is both

detrimental to the lung and to the right

ventricle.

PEEP should be titrated to open

the lung and keep it open without

overloading the right ventricle.

Protect The Lung And

The Heart As Well.

Remember that limiting plateau

pressure to below 27 cm H2O (by

decreasing tidal volume and PEEP) is

the most important component of

cardioprotective ventilatory strategy.

Do No Harm Rather

Than Do Good.

Remember that the only strategy that

improved outcome of ARDS did so

because of doing no harm (avoiding

ventilator-induced lung injury) NOT

doing good (improving oxygenation).

Thank You