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Acute Hypoxemic Respiratory Failure. Margaret J. Neff, MD MSc Assistant Professor of Medicine Pulmonary & Critical Care. “Your patient’s sat is 88%”. 55 y/o man with a history of mild COPD 3 days s/p elective surgery bilateral knee replacements

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Acute hypoxemic respiratory failure

Acute Hypoxemic Respiratory Failure

Margaret J. Neff, MD MSc

Assistant Professor of Medicine Pulmonary & Critical Care

Your patient s sat is 88
“Your patient’s sat is 88%”

  • 55 y/o man with a history of mild COPD

  • 3 days s/p elective surgery

    • bilateral knee replacements

  • Uneventful post-operative course except for an ileus and ongoing complaints of pain

  • Had been on room air during the day

    • You’re called with this sat at 3 a.m.

He says he can t catch his breath
“He says he can’t catch his breath”

  • Repeat sat confirmed: 88%

  • CXR done in the a.m. had shown mild bibasilar atelectasis

    • possible RLL infiltrate

  • ABG: 7.45/32/60 on room air

  • On high flow oxygen, his PaO2 is 100

Causes of hypoxemia
Causes of Hypoxemia

  • Decreased PiO2

  • Hypoventilation

  • Diffusion abnormality

  • Ventilation/Perfusion mismatch

    • Dead space (high V/Q)

    • Shunt (low V/Q)

Decreased pio 2
Decreased PiO2

  • High altitude

  • Iatrogenic

    • i.e. wrong gas mixture

  • Unlikely to be an issue in clinical hypoxemia

  • Aa gradient normal


  • Essentially alveolar hypoventilation

  • CNS drive depressed

  • Pain and splinting

  • Thoracic or abdominal restriction

  • Commonly seen clinically

    • May be manifest as bibasilar atelectasis

    • Hypoxemia reverses if take deep breath

  • Aa gradient normal

Diffusion abnormality
Diffusion Abnormality

  • Acute or chronic disease which affects the ability for oxygen to transport from alveolus to capillary

  • Common in moderate to severe lung disease, vascular disease, etc

  • Unlikely to cause acute hypoxemia

  • Aa gradient increased

Ventilation perfusion mismatch dead space
Ventilation/Perfusion MismatchDead Space

  • Areas with normal ventilation, reduced perfusion (high V/Q ratio)

  • Pulmonary embolus is a good example

  • Dead space and poor CO2 removal require increased minute ventilation

  • May or may not be hypoxemia

  • Aa gradient increased

Ventilation perfusion mismatch shunt
Ventilation/Perfusion MismatchShunt

  • Areas with decreased ventilation and normal perfusion (low V/Q)

  • Consolidation from pneumonia

  • Can increase if lose ability for hypoxic pulmonary vasoconstriction

    • non-selective vasodilators: nitrates, nipride

  • Poorly oxygen responsive

  • Aa gradient increased

Your patient is still sob
“Your patient is still SOB”

  • Unlikely a problem with PiO2 or diffusion

  • May be some degree of hypoventilation due to narcotic use

  • Sputum with lots of polys and GPC

  • Repeat CXR shows consolidated RLL

  • Other possibilities?

Your next admit is here
“Your next admit is here”

  • 45 y/o man with diabetes and urosepsis

    • progressively hypotensive, tachypneic

  • Intubated for respiratory distress and hypoxemia: oxygen sat on high flow oxygen of 90%

Effusion or edema
Effusion or Edema?

  • “Bilateral infiltrates consistent with pulmonary edema”

  • meets radiographic criteria for acute lung injury

CT reveals normal parenchyma but bilateral effusions

Courtesy of G. Rubenfeld

Pleural effusion
Pleural Effusion

1 day later

After CT insertion

Acute lung injury ali
Acute Lung Injury (ALI)

  • Clinical diagnosis (AECC definition)

  • CXR: bilateral infiltrates consistent with pulmonary edema

  • PaO2/FiO2 ratio < 300 (< 200 for ARDS)

  • No evidence of left atrial hypertension

    • PAWP < 18 if available


Ali risk factors
ALI Risk Factors

  • Trauma

  • Sepsis

  • Aspiration

  • Multiple transfusions

  • Pancreatitis, overdose, near drowning

  • Still up to 20% of patients without a defined risk factor

    • in other words, don’t have to have a risk to have ALI/ARDS

Ali pathophysiology
ALI Pathophysiology

  • Inflammatory process and increased vascular permeability

  • Bronchoalveolar lavage fluid: neutrophil predominant

    • those with persistent neutrophils in BAL tend to have a worse clinical course

Ali clinical manifestations
ALI: clinical manifestations

  • Early in the course of ARDS, hypoxemia often dominant

  • Due primarily to intrapulmonary shunting

    • atelectasis and alveolar flooding

    • disruption of normally protective hypoxic pulmonary vasoconstriction

Ali clinical manifestations1
ALI: clinical manifestations

  • After 3-7 days, poor compliance can become the major problem

    • fibroproliferative stage

  • Increasing dead space (can exceed 70%)

    • fibrosis, microthrombi in vessels

    • can lead to pulmonary hypertension and right heart dysfunction

Ali management
ALI: Management

  • Lung protective ventilation

    • 22% reduction in mortality

    • Tidal volume 6 ml/kg (PBW)

    • Pst < 30 cmH2O

    • allowing pH down to 7.15 if necessary

    • confirms previous animal studies showing increased systemic inflammation with higher tidal volumes, precipitated by lung stretch

NEJM 2000

Other potential therapies
Other Potential Therapies

  • Prone positioning?

  • Steroids?

  • Anti-inflammatory agents?

  • Surfactant?

  • Anti-oxidants?

  • Inhaled nitric oxide?



  • Hypothesized to be effective due to intense inflammatory response seen in ARDS patients

    • Bronchoalveolar lavage with >70% neutrophils (normally < 2%)

    • Plasma IL6 levels elevated

  • Previous studies using steroids early in ARDS have not proven beneficial1

1 Crit Care Med 23:1294-1303

Steroids late in ards
Steroids Late in ARDS

  • After first 3-7 days, ARDS progresses in many patients to a fibrotic stage

    • Proliferation of alveolar type II cells

  • Several small studies of steroids at this phase1

    • Inconclusive, in part due to study design

    • Possibly due to the need for a balance of pro- and anti-inflammatory mediators

1 JAMA 280:159-165

Recent steroid trial
Recent Steroid Trial

  • NIH sponsored ARDS network (“LaSRS”)

    • 10 sites nationally conducting ARDS studies

  • Enrolled patients at day 7-28 of ARDS

    • Receive steroids 2mg/kg/d (tapered over 2 weeks)

  • 180 patients enrolled

    • No difference in mortality (increased with steroids if given >14 days after ALI)

    • Steroids: more vent-free days, shock-free days; also more neuromuscular complications

NEJM 2006; 354(16):1671

Factt study

  • Liberal vs conservative fluid mgmt

    • No difference in mortality

    • Conservative strategy resulted in better lung fxn and shorter time on vent & in ICU

      • Fluid strategy initiated after shock resuscitation

  • PAC vs CVC

    • No difference in mortality

    • More complications in PAC

NEJM 2006; 354(21):2213-24 & NEJM 2006;354(24):2564-75

What else can we do for ards patients
What else can we do for ARDS patients?

  • Minimize ICU-related complications

    • HOB elevation

    • DVT prophylaxis

    • Stress gastritis prophylaxis

    • Optimizing nutrition

      • Early enteral feeding +/- TPN

  • Invasive diagnostic strategies for ventilator-associated pneumonia

  • Tight glucose control

  • Sedation management

Rct of hob elevation
RCT of HOB Elevation

  • 1 year enrollment in MICU (Spain)

  • Randomized to HOB > 45° or supine

  • Excluded if recent abd or neurosurgery, refractory shock, re-intubation

  • Endpoint: clinically or microbiologically confirmed pneumonia

    • (not rigorously defined, though)

  • 86 patients enrolled

    • Mean age 65yr; 34% with COPD

Lancet 1999;354:1851-8


  • Nosocomial pneumonia lower in semi-recumbent group

    • 8% vs 34% for clinically suspected

    • 5% vs 23% for micro proven

  • Supine position and enteral feeding were independent risk factors for VAP

    • Highest risk when both occurred together

Ventilator associated pneumonia
Ventilator Associated Pneumonia

  • Often difficult diagnosis to make clinically

    • CXR in ALI patient is already abnormal

    • ET aspirates may just reflect colonization

    • May be on antibiotics for surgical procedures or other infections

Vap diagnosis
VAP Diagnosis

  • RCT of 413 patients intubated for at least 48 hours1

    • Clinical suspicion of VAP

    • No antibiotic change for prior 72 hours

  • Bronchoscopy vs ET aspirate

  • Bronch: Reduced mortality at day 14, decreased antibiotic use, more antibiotic free days, more appropriate abx choices

1 Ann Intern Med 2000;132:621-30

Tight glucose control in icu
Tight Glucose Control In ICU

  • Recognized hyperglycemia/insulin resistance in ICU patients

  • RCT of glucose control in SICU patients

    • 2/3 cardiac surgery patients

    • 13% with h/o diabetes

  • Glucose goals: 80-110 vs 180-200

  • Decreased mortality

    • (ICU) 4.6% vs 8%; (hospital) 10.9% vs 7.2%

  • Subsequent studies show benefit > 4yrs for CV surg patients; questions results in MICU

N Engl J Med 2001;3451359-67; Eur Heart J 2006 Apr 11 Epub; NEJM 2006 354(5):449-61

Interruption of sedative infusions in the icu
Interruption of Sedative Infusions in the ICU

  • Prospective, randomized trial

    • 150 patients receiving continuous infusions

      • Targeted Ramsay 3-4

    • Randomized to daily interruption of infusion or standard care

    • The intervention was disruption of infusion, not controlling dosing or sedation targets

    • Once patient awake, investigator notified primary team and decision made regarding resuming infusion (not based on protocol)

Kress, et al. NEJM 2000; 342:1471-7

Better outcomes with interruption of sedative analgesic infusion
Better Outcomes with Interruption of Sedative (& Analgesic) Infusion

  • 2 fewer days on ventilator (5 days vs 7)

  • 3.5 fewer days in the ICU (6.5 vs 10)

  • Fewer diagnostic tests to work up altered mental status (9% vs 27%)

  • No difference in complications

    • e.g. self-extubations (4% vs 7%)

Does deep sedation predispose to ptsd
Does Deep Sedation Predispose to PTSD? Infusion

  • Factual memory protected against post-traumatic stress disorder symptoms

  • Delusional memory was a risk for PTSD

  • Implications:

    • Deep sedation and complete amnesia may not be beneficial to patients

    • Side effects of drugs (hallucinations, nightmares) may be harmful

Jones, et al. Crit Care Med 2001;29:573-80

Ali outcomes
ALI: Outcomes Infusion

  • Improved mortality over the past 30 years

    • 60% mortality reduced to 30-40%

  • Most continue to improve lung function over the first year

    • often left with abnormal diffusion capacity

  • Evidence to suggest some loss in neuropsychiatric function/testing and neuromuscular function

Respiratory failure
Respiratory Failure Infusion

  • Your 2 patients did well

    • Patient with pneumonia continued to improve and transferred to rehab

    • Patient with urosepsis was in the ICU for 7 days with ALI but was extubated and doing well.

Acute respiratory failure
Acute Respiratory Failure Infusion

  • When faced with acute SOB, run through the list of possibilities while initiating diagnostic testing and applying oxygen

    • Think of the clinical scenario to help you trim the possibilities

    • See if interventions help

    • Diagnose and treat for the most life-threatening while you’re fine-tuning the diagnosis