Does Operative Ventilator Management Impact the Incidence of ARDS?
Jacob Gutsche, MD
Assistant Professor
University of Pennsylvania
Philadelphia, Pennsylvania
Objectives
At the conclusion of this educational activity, the participants should be able to:
1. Understand the normal pulmonary anatomy and physiology
2. Discuss the incidence of acute lung injury and ARDS in cardiac surgery patients
3. Summarize the potential contribution of operative mechanical ventilation to acute lung injury in
cardiac surgery patients
4. Describe the optimal mode and settings of operative mechanical ventilation in cardiac surgery
patients.
Prior to 2000, standard postoperative and intraoperative ventilation used tidal volumes in the 10-15
mL/kg range. Large tidal volume ventilation strategies were considered safe and were thought to
prevent atelectasis. In addition, high level peep strategies necessary to prevent atelectasis were thought
to be potentially harmful. The publication of the ARDSnet trial revolutionized the care of patients with
acute respiratory distress syndrome (ARDS).(1) In this landmark trial, mechanically ventilated patients
with a combination of an acute decrease in the ratio of partial pressure of arterial oxygen to fraction of
inspired oxygen (PaO2/FiO2) to 300 or less, bilateral pulmonary infiltrates on a chest radiograph
consistent with the presence of edema, and a pulmonary-capillary wedge pressure of 18 mm Hg or less
were randomized to a low stretch versus standard ventilation strategy. The low stretch strategy
ventilated patients with tidal volumes ranging from 4-6 mL/kg based on ideal body weight while
maintaining a plateau pressure less than 30 mL of water. High levels of peep were maintained based on
an algorithm based on the FIO2. The standard ventilation group started with tidal volumes of 12 mL/kg
based on ideal body weight, and the ventilator settings were titrated to maintain a plateau pressure of
at least 45 cm of water or a tidal volume of 12 mL/kg. The trial was terminated after enrollment of 861
patients when interim analysis found that patients randomized to the low stretch group had a
significantly lower mortality (31.0 per- cent vs. 39.8 percent, P=0.007).
ARDS is a acute disease that is noted for diffuse inflammatory lung injury and loss of aerated tissue. The
lung is profoundly edematous and the chest radiograph is classically found to have diffuse infiltrates.
Management of patients with ARDS is supportive with a focus on source control.
Low stretch tidal volume ventilation has become the standard that all other modes of open lung
ventilation should be compared to in patients with lung injury. The goal of low stretch ventilation is to
minimize damage to more compliant areas of the lung while the source of ARDS is treated.(2)
Other modes that have been proposed to improve outcomes in ARDS include airway pressure release
ventilation, hi frequency oscillation, and alternative pressure control modes. At the current time none of
these has been shown to be superior to low-stretch ventilation.
ARDS is known to be a complication following cardiac surgery occurring in up to 0.4-1% of patients.
ARDS following cardiac surgery is associated with a high rate of mortality.(3) The mechanism of ARDS is
this patient group is likely multi-factorial and may be related to a combination of inflammation due to
the surgery and exposure to the cardiopulmonary bypass circuit, blood product administration. Patients
undergoing aortic surgery or having circulatory arrest are at even higher risk of developing ARDS after
surgery. Several small studies have analyzed the use of low stretch ventilation strategies in cardiac
surgery patients. These trials have attempted to demonstrate that low stretch ventilation may reduce
the risk of lung injury by measuring inflammatory markers as a surrogate for lung injury.(4) But none
have been powered to demonstrate differences in morbidity or mortality.
Recently, Futier and colleagues performed a multicenter, double-blind, parallel group trial randomizing
400 abdominal surgery patients to non-protective (10-12 mL/kg) versus a lung protective ventilation
strategy (6-8 mL/kg).(5) These patients were deemed to be at intermediate to high risk for pulmonary
complications. The patients randomized to the lung protective strategy had a lower incidence of major
pulmonary and extrapulmonary complications (10.5% vs 27.5%, relative risk, 0.40; 95% CI [0.24-0.68];
p=0.001).
More study is required to evaluate the overall benefit of lung protective strategies and the potential
benefit in the cardiac surgery patient cohort. At this time, lung protective strategy with a tidal volume of
6-8 mL/kg should be utilized with low to moderate levels of peep to prevent atelectasis.
References and Suggested Reading
1.
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5.
Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung
injury and the acute respiratory distress syndrome. The Acute Respiratory Distress Syndrome
Network. The New England journal of medicine 2000;342:1301-8.
Slutsky AS, Ranieri VM. Ventilator-induced lung injury. The New England journal of medicine
2013;369:2126-36.
Stephens RS, Shah AS, Whitman GJ. Lung injury and acute respiratory distress syndrome after
cardiac surgery. The Annals of thoracic surgery 2013;95:1122-9.
Reis Miranda D, Gommers D, Struijs A, Dekker R, Mekel J, Feelders R, Lachmann B, Bogers AJ.
Ventilation according to the open lung concept attenuates pulmonary inflammatory response in
cardiac surgery. European journal of cardio-thoracic surgery : official journal of the European
Association for Cardio-thoracic Surgery 2005;28:889-95.
Futier E, Constantin JM, Paugam-Burtz C, Pascal J, Eurin M, Neuschwander A, Marret E,
Beaussier M, Gutton C, Lefrant JY, Allaouchiche B, Verzilli D, Leone M, De Jong A, Bazin JE,
Pereira B, Jaber S, Group IS. A trial of intraoperative low-tidal-volume ventilation in abdominal
surgery. The New England journal of medicine 2013;369:428-37.