Overview

ARDS and Lung Protection Kristina Sullivan, MD Associate Professor University of California, San Francisco Department of Anesthesia and Perioperative Care Division of Critical Care Medicine

Case 52 y.o. man admitted 7 days prior with severe pancreatitis s/f pancreatic debridement. The patient has ARDS and is currently being mechanically ventilated with a low tidal volume strategy. His blood pressure and heart rate are within normal range. He is not currently requiring pressors.

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Definition and causes of ARDS Low tidal volume strategy Fluid conservative therapy Interventions for refractory hypoxemia Evidence for low tidal volume strategy in the operating room

Case • How is the patient’s ARDS currently being managed in the ICU? • How can you extend that care in the operating room?

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Acute Respiratory Distress Syndrome

Conditions that Predispose to ARDS

• What is ARDS? – non-cardiogenic pulmonary capillary leak syndrome

• Criteria – PaO2/FiO2 ratio < 300 (Acute Lung Injury or ALI) – PaO2/FiO2 ratio < 200 (ARDS) – Bilateral infiltrates on CXR – no evidence of left atrial hypertension or wedge < 18

• Infection – pneumonia, sepsis • Aspiration – gastric contents, near drowning, toxic inhalation • Trauma – pulmonary contusion, fat emboli, burns, multiple fractures • Other - pancreatitis, massive transfusion, cardiopulmonary bypass, drug reaction, BMT

PIP versus Pplat Peak pressure = Dynamic + Static Resistance

Pathogenesis of ARDS

Plateau pressure = Static Resistance

• Pathogenesis

Paw (cm H2O)

– Loss of integrity of alveolar capillary membrane – Alveolar and interstitial edema – Flooding of alveoli with proteinaceous exudate and inflammatory cells – Development of pulmonary fibrosis

PIP

Normal

PIP

PPlat

PPlat

PIP

PPlat

High Raw

Low Compliance

Time (sec)

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NHLBI ARDS Network

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Fluid and Catheter Treatment Trial (FACTT)

N Engl J Med 2006;354:2564-75

Comparison of two fluid-management strategies in ALI

N Engl J Med 2006;354:2564-75

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Case Simplified Fluid Conservative Protocol • Patient must be out of shock for at least 12 hrs • Target CVP < 4 with urine output ≥ 0.5 ml/kg/hr • Net even fluid balance over first seven days

You go up to see the patient in preparation for surgery and you find that the patient has gone into severe respiratory failure requiring an FiO2 = 90% and a high level of PEEP. The patient is noted to have a respiratory acidosis with a pH = 7.15. What other therapies might this patient be receiving?

Calfee and Matthay, Chest 2007

Other Therapies for Severe Acute Lung Injury – High PEEP – Recruitment maneuvers – Alternative Ventilator Strategies: • High-frequency oscillatory ventilation

– Inhaled Nitric Oxide – Prone Positioning – ECMO – Paralytics

High versus standard PEEP: Is high PEEP safe? • ARDSnet ALVEOLI trial, NEJM 2004 • 2 trials on standard vs. high PEEP (JAMA 2008) – Multifaceted Lung Open Ventilation study (LOV) – Positive End-expiratory Pressure Setting in Adults with ALI (EXPRESS)

• No difference in mortality in any of these three trials Diaz et al, CCM 2010 Gropper et al, A & A 2010

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Recruitment Maneuvers • What is a recruitment maneuver? – Sustained inspiratory hold (~30-60 seconds) at higher than normal airway pressures – Sustained pressure = 40-45 cm H20

• What is the goal? – to recruit atelectatic/flooded alveoli – Increase lung capacity

• What are the potential adverse effects? – Hypotension – Barotrauma – Requirement for sedation +/- paralysis

• Not recommended or discouraged based on current evidence

Inhaled Nitric Oxide

High Frequency Oscillatory Ventilation (HFOV) • Oscillating piston (180-900 x/minute) – Very small tidal volumes (1-2.5 ml/kg)

• High mean airway pressure – Goal is to recruit atelectatic lung segments and improve oxygenation

• May require heavy sedation +/- paralysis • Can lead to hypotension from high intrathoracic pressures • No confirmed mortality benefit • Skilled health care team is necessary (MD’s, RT’s, nursing)

Effect of nitric oxide on mortality

• Selective pulmonary vasodilator • Delivered only to ventilated alveolar units • Improvement in V/Q matching and PaO2/FiO2 ratio

Adhikari, N. K J et al. BMJ 2007;334:779

Copyright ©2007 BMJ Publishing Group Ltd.

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Extracorporeal Membrane Oxygenation (ECMO)

Prone positioning • Better matching of ventilation and perfusion • Opening of dependent collapsed lung segments • Improves oxygenation in about 70% of patients • Now at least four large RCT’s showing no improvement in mortality • Technically challenging

• Veno-venous circuit that relieves lungs from role in gas exchange • Oxygenation and removal of CO2 • Requires large bore IV access and anticoagulation

When is ECMO Considered? • No firm criteria • CESAR trial criteria:

• Severe ARDS: – Lung injury score > 3, hypercapnic acidosis with pH 3 (consolidation, P/F ratio, PEEP, and compliance) or – Hypercapnic respiratory failure with pH48 hours in the ICU • Risk factors independently associated with the development of ARDS included the size of the tidal volume during the first day, receipt of transfused blood products, a history of restrictive lung disease, and acidemia • Short patients and women received statistically larger tidal volumes than men Gajic et al, Crit Care Med 2004

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Ventilator Settings as a risk factor for ARDS in mechanically ventilated patients • Retrospective study of 3,261 patients who required >48 hours of mechanical ventilation • 205 out of 3,261 patients developed ARDS • Development of ARDS was independently associated with a high initial VT setting, high peak airway pressures, and the use of high PEEP

Does tidal volume in the operating room matter?

Gajic et al, Intensive Care Med 2005

Interleukin levels and TNF • Mixed data on whether conventional tidal volume compared with low tidal volume ventilation in healthy patients undergoing elective surgery results in increased concentration of inflammatory cytokines • 4 RCT show no difference

-52 patients undergoing esophagectomy -conventional vs. protective ventilation strategy during OLV -protective strategy resulted in - lower interleukin and TNF levels - higher P/F ratio at 1 hour - decreased duration of mechanical ventilation Anesthesiology 2006; 105:911-19

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May 2011

-100 patients ASA I or II s/f elective lobectomy -conventional versus protective strategy during OLV

-Single center randomized controlled trial -149 patients undergoing elective cardiac surgery -Median ventilation time not significantly different -low VT group had a higher proportion free of ventilation at 6 hours -Fewer patients in low VT group required reintubation

Summary

-4420 consecutive patients without ALI undergoing high risk elective surgery -ALI most common cause of post-operative respiratory failure (83 total patients) -Intraoperative peak airway pressure but not tidal volume was associated with increased risk Fernandez-Perez et al, Thorax 2009; 64(2): 121-127

• Low tidal volume ventilation and fluid conservative treatment are the mainstays of ARDS treatment • For refractory hypoxemia, patients may receive alternative/rescue therapies such as higher PEEP, recruitment maneuvers, and/or nitric oxide • If available, ECMO is a reasonable option for refractory hypoxemia or severe respiratory acidosis • Consider lower tidal volumes at PBW in mechanically ventilated patients in the operating room (especially those undergoing single lung ventilation)

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