Acute respiratory distress syndrome resident survival guide

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ayokunle Olubaniyi, M.B,B.S [2]

Overview

Below is a table showing The Berlin definition of Acute Respiratory Distress Syndrome:

	Acute Respiratory Distress Syndrome
Timing	❑ Within 1 week of a known clinical insult or new or worsening respiratory symptoms
Chest imaging i.e., CXR or CT	❑ Bilateral opacities—not fully explained by effusions, lobar/lung collapse, or nodules
Origin of edema	❑ Respiratory failure not fully explained by cardiac failure or fluid overload ❑ Need objective assessment (e.g., echocardiography) to exclude hydrostatic edema if no risk factor present
Oxygenation (Corrected for altitude)
Mild	❑ 200 mm Hg < PaO2/FiO2 ≤ 300 mmHg with PEEP or CPAP > 5 cm H2O
Moderate	❑ 100 mm Hg < PaO2/FIO2 ≤ 200 mm Hg with PEEP ≥ 5 cm H2O
Severe	❑ PaO2/FiO2 ≤ 100 mm Hg with PEEP ≥ 5 cm H2O

Causes

Life Threatening Causes

Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated. This is a life-threatening condition with majority of patients requiring mechanical ventilation.

Common Causes

• Aspiration of gastric contents
• Drug overdoses e.g., Acetylsalicylic acid, narcotics
• Fat embolism
• Massive blood transfusion
• Near-drowning (fresh or salt water)
• Pancreatitis
• Pneumonia
• Sepsis (gram-positive/gram-negative bacteria, viruses, fungi, and parasites)
• Severe trauma

Management

Characterize the symptoms: ❑ Chest pain ❑ Cough ❑ Cyanosis ❑ Diaphoresis ❑ Dyspnea ❑ Fever ❑ Hypotension ❑ Tachycardia ❑ Tachypnea

Patient evaluation: ❑ Obtain a detailed history: ♦ Age ♦ History of heart disease ♦ History of chest infection ❑ Examine the patient: ♦ Head/Neck - Neck veins (flat, no ↑JVP) ♦ Chest - No S3/S4, no murmurs ♦ Limbs - Hyperdynamic pulses, no edema

Urgent Labs: ❑ ABG ❑ Calculate A-a gradient ❑ CBC ❑ Electrolytes ❑ BUN ❑ Creatinine ❑ CXR - normal-sized heart, peripheral distribution of infiltrates, air-bronchogram (80%) Consider additional tests, if necessary: ❑ Bronchoalveolar lavage - gram stain, culture & cytology ❑ Bronchoscopy ❑ BNP - <100 pg/mL ❑ CT ❑ Echocardiography ❑ EKG - sinus tachycardia, non-specific ST-T wave changes ❑ Lung biopsy ❑ PAWP - <15 mmHg

Diagnostic Criteria - The Berlin Definition

Emergent therapy ❑ Pulse oximetry ❑ Administer 100% oxygen - non-rebreather face masks, nasal prongs ❑ Initiate management of the underlying precipitating factor ❑ Consider right heart catheterization if hypotension persists

❑ Check vital signs ❑ Assess hemodynamic status: ♦ RR<35 bpm ♦ PaC02 <35 mmHg ♦ Sp02 >88%

Stable

Unstable

❑ Maintain Sp02 between 88-95% by adjusting Fi02 ❑ Treat underlying disease

❑ Transfer ICU ❑ Intubate (indications) ❑ Mechanical ventilation protocol

Supportive treatment ❑ Analgesia - morphine ❑ Conservative fluid management ❑ Conscious sedation - lorazepam ❑ DVT prophylaxis ❑ Glucose control ❑ Nurse 30-45 degrees head-up position ❑ Nutritional support (enteral feeds) ❑ NPO (in severely ill) ❑ Prevent pressure ulcers ❑ Stress ulcer prophylaxis - PPI

Mechanical Ventilation Protocol

❑ Calculate the predicted body weight (PBW) Males - 50 + 2.3 [height (inches) - 60] Females - 45.5 + 2.3 [height (inches) - 60] ❑ Ventilator mode - volume assist-control ❑ Set tidal volume (VT) to 8 ml/kg PBW ❑ ↓VT to 6 ml/kg PBW over the next 4 hours ❑ Flow rate - 60-80 lpm ❑ Ventilation rate - start at 18, adjust based on CO2 and ventilatory needs (max = 35 bpm) ❑ I:E ratio = 1:10 to 1:30 ❑ Adjust VT and RR to achieve pH and plateau pressure goals below

Oxygenation Goal - Pa02 = 55 - 60 mmHg or Sp02 = 88 - 95% ❑ Start at FiO2 of 1.0 (100% O2); PEEP of 5 cmH2O ❑ Check ABG/pulse oximeter

Sp02 < 88%

Sp02 > 95%

Adjust FiO2/PEEP based on ARDSnet PEEP/FiO2 ladder Monitor ABG Note - Maintain FiO2 < 0.6

↓FiO2 until Sp02 is > 95%

Assess perfusion ( BP, urine output)

Adequate

Inadequate

Strict input/output monitoring

Administer volume (fluid management)

Check plateau pressure Goal - Pplat ≤ 30 cmH20 ❑ Hold 'inspiratory hold' button for 0.5 seconds ❑ Check after each setting change or at least q 4hourly

> 30 cmH20 ↓VT by 1 ml/kg steps Min = 4 ml/kg

< 25 cmH20 & VT < 6 ml/kg ↑VT by 1 ml/kg until Pplat > 25 or VT = 6 ml/kg

< 30 + breath stacking or dys-synchrony May ↑ VT in 1 ml/kg to 7 or 8 ml/kg, if Pplat remains ≤ 30 cmH20

Achieve pH goal Goal = 7.30 - 7.45 pH 7.15 - 7.30 - ↑RR until pH > 7.30 or PaC02 < 25; max set RR = 35 pH <7.15 ❑↑RR to 35; if pH is still < 7.15, ↑VT by 1 ml/kg until pH > 7.15 - you may exceed Pplat target of 30 ❑ Give NaHC03 pH > 7.45 - ↓RR

Weaning

ARDSNet PEEP/FiO2 Ladder

FiO2	0.3	0.4	0.4	0.5	0.5	0.6	0.7	0.7	0.7	0.8	0.9	0.9	0.9	1.0
PEEP	5	5	8	8	10	10	10	12	14	14	14	16	18	20

Weaning

Conduct DAILY CPAP trial: ❑ Criteria: ♦ Fi02 ≤ 0.40 & PEEP ≤ 8 ♦ PEEP and FiO2 ≤ values of previous day ♦ Patient has spontaneous breathing efforts (may decrease vent set rate by 50% for 5 minutes to detect effort) ♦ Systolic BP ≥ 90 mm Hg without vasopressor support ♦ No neuromuscular blocking agents or blockade ❑ Process: ♦ Set CPAP to ≤5 cmH20; FiO2 to ≤0.50

RR ≤ 35 bpm for 5 mins

Yes

No

Pressure support (PS) trial ♦ Set PEEP ≤ 5; FiO2 ≤ 0.50 Note - Set pressure support based on RR during the CPAP trial

Discontinue trial Return to previous A/C settings Reassess next day or as directed by physician Find out reasons for trial failure

CPAP RR < 25

CPAP RR = 25 - 35

Set PS at 5 cm H20; PEEP at 5

Set PS at 20 cm H20; PEEP at 5

Assess for tolerance (for up to 2 hours): ❑ Sp02 ≥ 90 &/or PaO2 ≥ 60% ❑ Spontaneous VT ≥ 4 ml/kg PBW ❑ RR ≤ 35 bpm ❑ pH ≥ 7.30 ❑ No respiratory distress (any 2 or more) ♦ HR > 120% of baseline ♦ Marked accessory muscle use ♦ Abdominal paradox ♦ Diaphoresis ♦ Marked dyspnea

♦ ↓ PS by 5 q 1-3 hours (for RR ≤ 35) or every 5 mins (for RR < 25) ♦ ↑ PS by 5 if RR > 35 Note - If PS is ≥ 10 cmH20 in the evening or RR > 35 @ PS of 20, resume A/C and attempt weaning the next day

No

Yes

❑ ↑ PS by 5 when RR > 35 ❑ Attempt weaning as ordered by physician Note - PS of 5 or 10 cmH20 may be maintained overnight

Trial of unassisted breathing Extubated with face masks, nasal prongs oxygen, or room air or T-tube breathing or Trach mask breathing or CPAP ≤ 5 cmH20 with no PS or IMV assistance

Reassess for tolerance (same as above)

Tolerated (for at least 30 mins)

Not tolerated

Extubate

Resume pre-weaning A/C settings

Dos

• Nurse patient in semi-recumbent position (30-45 degrees) to reduce the risk of hospital-acquired pneumonia, especially those on enteral feeds.
• Conscious sedation and analgesia to reduce oxygen consumption.
• FiO2 is usually kept below 0.5 to reduce oxygen toxicity.
• Daily spontaneous breathing trials.