ARDSRuchi KapoorApril 2015

A 34 year old paraplegic man with history of neurogenic bladder is admitted to the ICU for septic shock due to UTI. He is given IVF, Zosyn and intubated for decreased level of consciousness. CXR is normal with the ETT in the appropriate position.

2 days later he is evaluated for persistent hypoxemia on mechanical ventilation.

Vital Signs are: T 37.1 °C (98.8 °F), BP 90/50 mm Hg, HR 96/min, RR 26/min.

Oxygen saturation on an FIO2 of 0.8 is 89%.

Pulmonary examination reveals bilateral inspiratory crackles.

Cardiac examination reveals distant, regular heart sounds.

Lab results:Hgb 13.2 g/dLWBC 10,000/uL.ABG on FiO2 80%: pH 7.48, pCO2 30 mm Hg, pO2 60 mmHg

Urine and blood cultures grow E. Coli that is sensitive to Zosyn.

Follow-up CXR shows diffuse bilateral infiltrates without cardiomegaly. CVP is 8 mm Hg.

Which of the following is the most likely cause of this patient's hypoxemia?

A. Acute respiratory distress syndromeB. E. coli pneumoniaC. Heart failureD. Idiopathic acute eosinophilic pneumonia

Lab results:Hgb 13.2 g/dLWBC 10,000/uL.ABG on FiO2 80%: pH 7.48, pCO2 30 mm Hg, pO2 60 mmHg

Urine and blood cultures grow E. Coli that is sensitive to Zosyn.

Follow-up CXR shows diffuse bilateral infiltrates without cardiomegaly. CVP is 8 mm Hg.

Which of the following is the most likely cause of this patient's hypoxemia?

A. Acute respiratory distress syndromeB. E. coli pneumoniaC. Heart failureD. Idiopathic acute eosinophilic pneumonia

Objectives

What is ARDS? – The Definition

Why does it happen? – The Pathophysiology

How to manage it? – The Basic Ventilation Strategy

What is ARDS?

ARDS is lung injury that leads to:

Impaired gas exchange

Decreased lung compliance

Increased pulmonary arterial pressure

Definition of ARDS

Acute onset (within 1 week of clinical insult)

Bilateral pulmonary edema

PaO2/FiO2 <200 (or <300 if PEEP >5 cmH2O)

Exclude cardiogenic pulmonary edema

Risk Factors (i.e. “clinical insult”)

Sepsis

Aspiration

Pneumonia

Pancreatitis

Trauma

Massive transfusion

TRALI

Burns

Drugs and alcohol

Lung transplant

Hematopoietic stem cell transplant

Pathophysiology of ARDS

Capillary endothelium is activated.

Endothelium releases pro-inflammatory cytokines (e.g. TNF, IL-8) that recruit neutrophils to the lungs.

Neutrophils are activated and release toxic mediators (e.g. reactive oxygen species, proteases)

Causes further damage of capillary endothelium, and now of alveolar epithelium, leading to pulmonary edema.

Starts with capillary endothelium. Ends with alveolar epithelium.

Pulmonary Edema

Breakdown of barriers

Lymphatic movement

ALVEOLAR EDEMA

Alveolar lumen FULL of fluid

Interstitial fluid

Pulmonary capillary

NORMAL ALVEOLI

Alveolar lumen EMPTY of fluid

Pulmonary capillary

Protein

A 50-year-old previously health man is evaluated in the ICU for ARDS due to severe community-acquired pneumonia. He is intubated and placed on mechanical ventilation.

Vital Signs: 38.3 °C (100.9 °F), 120/60 mm Hg, 110 beats/min.Oxygen saturation by pulse oximetry is 96%. Physical exam is unremarkable except for bilateral inspiratory crackles.

Ideal Body weight is 60 kg. Initial ventilator settings are volume control withRate 18 / TV 420 / PEEP 10 / FiO2 0.8

Peak pressure is 34 cm H2O. Plateau pressure is 32 cm H2O.

Which of the following is the most appropriate next step in management?

A. Decrease respiration rateB. Decrease tidal volumeC. Increase FIO2

D. Increase PEEP

Ideal Body weight is 60 kg. Initial ventilator settings are volume control withRate 18 / TV 420 / PEEP 10 / FiO2 0.8

Peak pressure is 34 cm H2O. Plateau pressure is 32 cm H2O.

Which of the following is the most appropriate next step in management?

A. Decrease respiration rateB. Decrease tidal volumeC. Increase FIO2

D. Increase PEEP

Lung protective ventilation

Avoid further damage to an already edematous and injured lung by preventing overdistention of alveoli

Use Low Tidal Volume Ventilation (LTVV)

Based on predicted/ideal body weight, not actual body weight

Allow for permissive hypercapnia and respiratory acidosis.

Step-by-Step approach toLow Tidal Volume Ventilation1. Set mode to volume assist-control

2. Set initial Tidal Volume (TV) to 8 mL/kg

3. Reduce TV to 7 then 6 mL/kg over 1-3 hrs

4. Keep plateau pressure (Pplat) 25 – 30 cm H20

5. Adjust FiO2 and PEEP to keep PaO2 55 – 80

FiO2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

PEEP 5 5 - 8 8 - 10 10 10 - 14 14 14 - 18 18 -24

A 63-year-old man with ARDS due to aspiration pneumonia is evaluated in the ICU. He has just been intubated and placed on mechanical ventilation

Vital signs: 37.0 °C (98.6 °F), 150/90 mm Hg, 108 beats/min. Height: 150 cm (59 in) Weight: 70.0 kg (154.3 lb). Ideal body weight: 52.0 kg (114.6 lb).

Physical exam is only notable for crackles in the lower left lung field. Patient is sedated.

Mechanical ventilation is on the assist/control mode at a rate of 18/min. Positive end-expiratory pressure is 8 cm H2O, and FIO2 is 1.0.

Which of the following is the most appropriate tidal volume?

A. 300 mLB. 450 mLC. 700 mLD. 840 mL

Mechanical ventilation is on the assist/control mode at a rate of 18/min. Positive end-expiratory pressure is 8 cm H2O, and FIO2 is 1.0.

Which of the following is the most appropriate tidal volume?

A. 300 mLB. 450 mLC. 700 mLD. 840 mL

Summary

ARDS is acute lung injury with bilateral pulmonary edema and hypoxia that is NOT cardiogenic in origin

ARDS occurs when capillary endothelium and alveolar epithelial barriers break down.

The cornerstone of management in ARDS is low-tidal volume ventilation to prevent overdistention of alveoli.

References

The ARDS Definition Task Force*. Acute Respiratory Distress Syndrome: The Berlin Definition. JAMA. 2012;307(23):2526-2533. doi:10.1001/jama.2012.5669.

Ferguson et al. The Berlin Definition of ARDS: An Expanded Rationale, Justification, and Supplementary Material. Intensive Care Med. 2012;38(10):1573-1582. doi:10.1007/s00134-012-2682-1

Piantadosi CA, Schwartz DA. The Acute Respiratory Distress Syndrome. Ann Intern Med. 2004;141:460-470. doi:10.7326/0003-4819-141-6-200409210-00012

The Acute Respiratory Distress Syndrome Network. Ventilation with Lower Tidal Volumes as Compared with Traditional Tidal Volumes for Acute Lung Injury and the Acute Respiratory Distress Syndrome. N Engl J Med. 2000;342(18):1301-1308. DOI: 10.1056/NEJM200005043421801

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