Fluid Management in Acute Respiratory Distress Syndrome by Dr. Stacey Valentine.
Hi.
My name is Stacey Valentine, and I'm a physician here at Children's Hospital, Boston, in the
Division of Critical Care.
And I'm going to talk to you about fluid management in Acute Respiratory Distress Syndrome, or
ARDS.
And just as a disclosure, I'm going to talk about some of the principles that we use here
at Children's Hospital, Boston.
But you may need to adapt these principles to your own management and your patients at
your own hospital based on the protocols and guidelines that you have.
Introduction.
So let's just start off by talking about acute lung injury and ARDS.
Both acute lung injury and its more severe form, ARDS, are the result of a large-scale
pulmonary inflammatory response, leading to hypoxemia and respiratory failure.
The common pathway of this inflammatory response is diffuse alveolar damage.
And this results in pulmonary edema, secondary to the pulmonary endothelium and the epithelium
damage, so it is more permeable to water and proteins.
Mechanically ventilated patients are at risk for developing acute lung injury and ARDS.
The challenge of fluid management in critically ill pediatric patients with respiratory failure
is to maintain intravascular volume to ensure adequate end-organ perfusion, while also trying
to minimize extravascular lung water and subsequent pulmonary edema.
Pathophysiology.
So what goes wrong in terms of ALI and ARDS?
Well, in acute lung injury, you have injury to the lung parenchyma and/or endothelium.
And this disrupts the alveolar epithelial barrier and disrupts that function, and the
normal safety mechanisms of a lung are disrupted, see a loss of the osmotic pressure gradient
that leads to leaky barriers.
You have increased sensitivity to hydrostatic forces, and you have impaired alveolar fluid
clearance.
Fluid then accumulates in the alveolar space when this protective mechanism fails, either
by overwhelming the active reabsorption mechanism or actually injuring the capillary alveolar
membrane.
This increased fluid accumulation becomes secondary to this failed reabsorption mechanism
and leads to pulmonary edema.
Principles of Management.
High pulmonary vascular pressures inflow can cause increasing stress to the failure of
these capillaries.
By reducing pulmonary pressures, we can actually decrease pulmonary edema.
In different studies when they target extravascular lung water in targeted therapies, with less
fluid administration these patients had improved outcomes.
Over the past 30 years, clinical evidence has been mounted that positive fluid balance
is associated with worsened clinical outcomes in patients with acute lung injury and acute
respiratory distress syndrome.
However, the challenge is trying to figure out how to manage patients with ALI and ARDS
when they are in shock.
The first challenge is that patients who are in shock have increased pulmonary and systemic
vascular permeability.
You need to give IV fluids to maintain adequate venous return while minimizing lung edema.
In the early phase of ARDS, when patients are in shock, you need to give IV fluids to
prioritize venous return and perfusion.
And this may be at the expense of creating pulmonary edema.
You need to constantly assess perfusion, urine output, lactate, and fluid responsiveness
and the priority is to maintain perfusion while at the expense of possibly increasing
lung water.
We know that in sepsis this early volume resuscitation improves outcomes in severe sepsis.
We also know that once patients are out of shock, volume overload and dilutional hypoproteinemia
can worsen outcomes in patients with ARDS.
However, in the post-shock phase of ARDS, we try to use what is called "conservative
fluid management," trying to restrict fluids, giving diuretics, and now prioritizing decreasing
lung water.
So in summary, it's to try to maintain a systemic vascular perfusion while trying to deal with
increasing pulmonary and systemic vascular permeability.
With this third space loss and impaired venous return and shock, this becomes difficult.
Evidence for Fluid-Restrictive Strategies.
So what's the background in these studies?
Well, back in 1987, Simmons et al looked at ARDS survivors, and those who had less positive
fluid balance had increasing survival.
Multiple studies since then have looked at fluid balance in patients with ALI and ARDS
out of shock, and what they've shown is that increasing fluid balance is associated with
decreased survival.
Decreasing this fluid balance is associated with improved survival and improved pulmonary
outcomes.
All of these studies paved the way to the FACTT trial looking at fluid and catheter
management in patients with ALI and ARDS.
What this trial did was randomize patients to a conservative fluid management to a liberal
fluid management in patients with ALI and ARDS.
Looking at their primary end point of mortality, and their secondary end points of duration
of mechanical ventilation, and ventilator free days, ICU length of stay, and oxygenation
index, as well as non-pulmonary organ dysfunction.
What they showed in the conservative arm, the main cumulative fluid balance was far
lower than that in the liberal arm, almost 7 liters difference over seven days.
The patients in the conservative arm had improved pulmonary outcomes and did not have any significant
increase in non-pulmonary organ dysfunction.
There was no change in mortality between the two groups.
It's important to note, when interpreting this study, is that the patients who are enrolled
in this protocol were all out of shock.
So as we talked about before in those challenges, these patients were in the ALI/ARDS category,
non-shock, so they were already fluid resuscitated.
And if the patients developed shock, they were taken off the protocol and not entered
back until 12 hours after shock had been reversed.
More recently, Rosenberg et al in 2009, looked at conservative fluid strategy versus a liberal
fluid strategy, and again they showed that decreasing fluid balance improved pulmonary
outcomes.
So in summary, patients with acute respiratory failure are at risk for developing acute lung
injury.
And positive fluid balance has been implicated in decreased and worsened pulmonary outcomes.
This overwhelming inflammatory response in acute injury and ARDS leads to extravascular
pulmonary water accumulation making careful fluid management necessary.
The key features in acute lung injury in ARDS is to make sure that you maintain adequate
perfusion to your organs.
So using fluid when patients are in shock, but then, once patients are out of shock,
to start to minimize this fluid to preserve pulmonary function.
The fluid restrictive strategy has been shown, in a randomized multi-center trials, to improve
the duration of mechanical ventilation, oxygenation index, and ICU length of stay in adult patients
with ALI and ARDS.
Further research is needed to understand this impact in critically ill children with ALI
and ARDS.
This concludes the talk on fluid management and acute lung injury and ARDS.
Thank you very much for listening.
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