8/13/2018

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Hypoxemia in the ED Joseph Shiber, MD, FACP, FACEP, FCCM

Director Advanced Lung/ECMO Service

Professor of Emergency Medicine, Neurology, and Surgery

19 y/o woman SOB s/p bicyclist struck

• Helmeted, no LOC and GCS 15

• Open Femur Fx and closed Humerus Fx

• Hr 100, BP 120/75, RR 22, Sat 89% on RA; 93% on NRB

• Initial CXR Normal

• FAST (-) but repeat Lung increased B – Lines

• More dyspneic unable to talk, appears distressed

• Plan for Intubation: Pre-oxygenation? RSI vs DSI? Sux vs Roc?

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Now what?

• Sat 85% on 100% FiO2

• Increase PEEP?

• Bilateral Chest Tubes?

• Ask for Bronch?

• Disconnect and Bag Pt?

• Turn MV up to 11?

Outline

• O2 and Lung Physiology

• ARDS

• Lung Protective Ventilation: ARDSNet

• Prone Positioning

• Oscillator (HFOV)

• Airway Pressure Release Ventilation (APRV)

• Adjuncts: iNO, Flolan, Paralytics, Steroids

• Extracorporeal Therapies (ECMO, ECLA, ECCO2R)

• Permissive Hypoxemia

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O2 Delivery

• DO2 = CO x Hgb x Sat + 0.003 x PO2

• Tissue extraction only 25% at rest but can increase to 60%

• O2 delivery increases by 2-4 fold by increased CO (HR, SV) and Min Ventilation

• Re-Distribute blood/O2 To brain, heart, muscle while Away skin, gonads, GI

• Brain least tolerant of hypoxia but better tolerates IF good cerebral perfusion

• Usual Targets: CI 2L, Hgb 7g, Sat 88%, PO2 55 = adequate tissue metabolism

Causes of Hypoxemia

• V/Q Mismatch: pneumonia, CHF, ARDS, pulm contusion, PE

• Shunt: intra-cardiac R to L (PFO) or intra-pulmonary

• Hypoventilation: drugs, weakness, airway [A-a Gradient will be NORMAL]

• Diffusion ABNL: interstitial fibrosis

• Low PO2: high altitude, scuba, enclosed fire, simple asphyxiants

• Low Venous Sat: profound shock or critical anemia [adds to other causes]

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Lung Physiology

• Work of Breathing: Resistance to Airflow + Compliance of Lung/Chest Wall

• WOB increased: metabolic rate (fever, sepsis, SZ), bronchial DO, over-resuscitation

• Lung Injury: Stress (transpulmonary pressure) and Strain (change in volume)

• O2 toxicity: >80% avoid if possible while <40% considered “Safe”

• Restrictive Volume ~ Dry Sick Lungs>Wet Sick Lungs (but keep out of shock)

ARDS

1st described in 1967 by Ashbaugh series12 patientsAffects 200,000 patients annuallyLife threatening condition characterized by

HypoxemiaReduced lung compliance

Alveolar capillary damage leading to InflammationPermeabilityEdemaNecrosisFibrosis

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ARDS Definition

Etiologies

• Treatment of underlying condition #1 priority

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Lung Protective Ventilation: ARDSnet

• Mortality reduction 8% using 6 vs 12 cc/kg IBW, PLP<30 vs 50

• Protects non-ventilated lung

• Why is it a problem to breath at Normal volumes 8-10 cc/kg?

• “Baby-Lung” concept of ARDS by Gattinoni

• Not stiff simply small BUT may have recruitable volume

• Chest CT to evaluate and then PEEP/MAP trial. POCUS easy, repeatable

Posterior-Basilar: CXR underestimates

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Using ARDSnet

• PCO2 clearance with low TV requires high RR

• May need deep sedation or NMBA to tolerate ARDSnet

• Spontaneous breathing decreases lung inflammation

• VAP, diaphragm paralysis, atelectasis = smaller lung

• Available lung not able to meet gas exchange needs

Oscillator: HFOV

• Constant high MAP, insignificant TV, 300-600 RR

• Improves recruitment and lung inflammation

• Reduces volutrauma & atelectrauma but not barotrauma

• Requires deep sedation and paralysis: no breathing

• Reduced pulm toilet and humidification = VAP, severe plugging

• Two trials (-) for early use so only consider rescue Tx

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Prone Positioning

• Improves V/Q matching, secretion clearance and lymphatic drainage

• Assists recruitment of posterior-basilar segments

• Decreased mortality but requires >12-16 hrs daily

• Very work intensive if not specialty bed

• Requires expertise to avoid complications

• Consider other positions or avoid need to prone

Airway Pressure Release Ventilation

• Three decades considered rescue mode for ARDS

• Improves V/Q, P/F, Peak Pressure, CO, gut/renal perfusion

• Spontaneous breathing: comfort, diaphragm strength

• Animal models: prevented pathological lung changes

• Reduced endothelial injury, IL1,6,8 levels, surfactant loss

• Reduced micro-strain: blocks process leading to VILI

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APRV: How it Works

• CPAP with Brief Releases

• Recruits but Stabilizes Lung

• Requires Spontaneous Breathing

• Prolonged Time Hold

• “Open-Lung” Model of Protective Ventilation

• Dynamic settings adjusted to current lung status

APRV: Benefits

• Very low rate ARDS (1.3%) in high-risk trauma cohort

• Used as Primary mode of MV to prevent ARDS/VILI

• Low mortality (3.9%) vs. similar groups (14.1%)

• Decreased Opiate and Sedative requirement in TBI

• Actually had lower pain scores and less need for BAL

• Decreased time on MV, ICU LOS, and mort trend w/ARDS

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Adjuncts: selective pulmonary vasodilators

• iNO: improves oxygenation but not survival

• May increase renal dysfunction, methemoglobin

• Epoprostenol (PGI2) inhaled: improves oxygenation

• Unclear if improves outcomes

• Temporizing measures while implementing other Tx

Paralytics

• Early trial but only briefly (<48 hrs)

• Gain benefits but avoid complications: severe weakness, PTSD

• Reduce MV dysynchrony: tolerate ARDSnet regimen

• Reduce O2 consumption: take over work of breathing

• Improve compliance of chest wall/abdomen: temporary while address IACS

• Cisatracurium (Nimbex) preferred: no renal or hepatic clearance

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Steroids for ARDS

• Solumedrol 1mg/kg/Day (initial dose can be split Q12 or Q8)

• Slow taper over 1 month: Meduri Protocol

• Reduced mortality

• Decreased time on MV and in ICU w/o increase risk infection

• Prevent progression of exudative phase to proliferative/fibrotic phase

• Needs to be started <14 d

Extracorporeal Therapies: ECMO

• 1st used in adults 1972

• VA for pulmonary & cardiac support

• VV pulmonary: true “lung rest” to allow recovery

• Ultraprotective MV: not relying on lung for gas exchange

• CO2 removal low blood flow (<1L/min) = smaller access

• Oxygenation needs >60% CO (5-6L/min) = larger access

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Overview

• ECMO does NOT fix anything but allows for Tx of disease

• Sometimes Time is the Tx

• “Time at a Cost” needed to make Dx and then Tx

• Allows for interventions that could not be done: Bronch, Whole-Lung Lavage

• Improvements in technology has made easier & safer

• 75% of Adult ECMO Pts have been in last 5 yrs: H1N1

ECMO

• Dual Heart-Lung bypass or only Lung

• Oxygenation and CO2 removal

• VV: True Lung Rest ARDS, air leak, Asthma/COPD, DAH

• VA: PE, Blunt Cardiac Injury, pneumonectomy, myocarditis, MI, Cardiac Arrest

• Different configurations for VV or VA

• Two Catheters vs Single dual-lumen catheter (VV only)

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VV: Pulmonary

47 y/o Flu: 25F Fem Outflow; 23F IJ Inflow

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VA: Cardiac and Pulmonary

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Indications

• VV: ARDS: PaO2/FiO2 <80 mmHg despite optimization

• Murray Score: P/F, PEEP, compliance, CXR quadrants

• Hypercapnic respiratory failure: pH <7.20

• VA: Refractory cardiogenic shock

• Cardiac arrest with chance of recovery

• Failure to wean from cardiopulmonary bypass

• As a bridge to cardiac transplantation or VAD

V-V ECMO

If Risk Death>Risk of ECMO it should be Considered

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Contraindications

• If the cause is irreversible

• For respiratory failure, if on MV>10 D outcomes may be poor in this population

• May exclude: >70, morbid obesity, neurologic dysfunction, poor preexisting status

• VA: Anticoagulation is contraindicated: bleeding, TBI, ICH

• For cardiac failure, if VAD or transplant is contraindicated

Outcomes

The Conventional MV vs ECMO for Severe Acute Respiratory failure (CESAR) trial randomly assigned 180 patients with severe ARDS to a single ECMO center in the UK or continued conventional management

ECMO had significantly increased survival without disability at six months: 63 vs 47%

85% percent of the patients referred to an ECMO center were managed with ECMO, while the others improved with advanced conventional ventilation and management

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Newest ARDS Study NEJM 2018

• Randomized Study 125 in each group: Control vs ECMO (earlier use than rescue)

• 11% mortality decrease in ECMO group

• BUT allowed “Crossover” of RESCUE ECMO for 35 pts in Control Group

• IF account for these pts then mortality decrease is 24%

• Still use conservative Tx unless Pt in extremis or clearly will reach that point soon

21 y/o man MVC: L SQ air

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Thoracotomy x2: 6.88/97/49

23F Drain and 21F Return

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Hospital Course

• 7.44/45/67 Ventilation easier to achieve than Oxygenation

• No heparin for >48 hrs as L Chest STILL OPEN

• Closed at bedside s/p packs removed

• PO2 steadily improved and APRV weaned “Drop & Stretch”

• REST SETTINGS 35% FiO2

• Coughing and suctioning old blood from lung injury

• CXR improving daily

Day 5: decannulated day 6

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Permissive Hypoxemia

• Sat <88%

• DO2 = CO x 1.34 Hgb x Sat + 0.003 x PO2

• Delivery is 4x HIGHER than tissue consumption at rest

• Can tolerate low Sat ~80% IF CO/CI and Hgb are OPTIMAL

• May need to lower O2 consumption: hypothermia, sedation, paralytics(?)

• Verify adequate tissue oxygenation: Lactate, Venous Sat, UO, CNS exam

Case #2: 26 yo man s/p OD

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Time Course

• 7.22/58/49 on 100% (5am on arrival) Bronchoscopy – vomitus in airways

• 7.29/50/45 (7am 2 hr later) Sedation/paralytics OFF. PRVC changed to APRV

• 7.30/48/66 (10am 3 hr later) Pressors OFF and Pt awake writing notes

• 7.39/45/89 on 70% (8 hr later) so P/F 127 No Longer SEVERE ARDS

• 7.46/47/122 on 40% (2 d later) so P/F >300 No Longer Qualifies for ARDS

Accept Less than Optimal numbers to prevent VILI and allow lung recovery

5 days s/p Adm

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ED Management Guide

• Volume or Pressure Control mode: 6cc/kg Ideal wt. Plateau P <30

• PEEP titrate for goal: Oxygenation (Sat, P/F) and Recruitment (CT, US, Vol/Pres)

• Optimize Position: upright, decub, prone

• Consider Inhaled Flolan

• Consider IV Steroids

• Trial APRV (if comfort level) vs Paralytic

• Consult or Transfer for ECMO

Questions and Comments

Thank You for Your Attention

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References

• Thiagarajan RR, Brogan TV, Scheurer MA, et al. Extracorporeal membrane oxygenation to support cardiopulmonary resuscitation in adults. Ann Thorac Surg. 2009; 87(3):778-785.

• ECMO registry of Extracorporeal Life Support Organization. Available at http://www/elso.med.umich.edu. Accessed March 9th, 2011.

• Brogan TV, Thiagarajan RR, Rycus PT, et al. Extracorporeal membrane oxygenation in adults with severe respiratory failure: a multi-center database. Intensive Care Med. 2009; 35(12):2105-2114.

• Peek GJ, Mugford M, Tiruvoipati R, et al. Efficacy and economic assessment of conventional ventilatory support versus extracorporeal membrane oxygenation for severe adult respiratory failure (CESAR): a multicentre randomised controlled trial. Lancet. 2009; 374(9698):1351-1363.

• Davies A, Jones D, Bailey M, et al. Extracorporeal membrane oxygenation for 2009 influenza A(H1N1) acute respiratory distress syndrome. JAMA. 2009; 302(17):1888-1895.