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Pulmonary Critical Care ------------- The Approach to Acute Respiratory Failure

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Title: Pulmonary Critical Care ------------- The Approach to Acute Respiratory Failure


1
Pulmonary Critical Care-------------The
Approach to Acute Respiratory Failure
  • By John J. Beneck MSPA, PA-C

2
Objectives
  • Understand lung function as it applies to
    pathological processes including
  • Air movement
  • Diffusion
  • Circulation
  • Gas transport
  • Understand Acute Respiratory Failure with regard
    to
  • Clinical manifestations
  • Etiology
  • Presentation
  • Diagnosis
  • Treatment

3
Objectives (Cont)
  • Understand the role of PPV in the care of
    respiratory failure
  • Introduce various mechanical ventilation
    modalities and weaning strategies
  • Understand ARDS with regard to
  • Definition
  • Presentation
  • Diagnosis / Differential Diagnosis
  • Etiology
  • Complications
  • Treatment
  • Prognosis

4
Abbreviations
  • ARDS-Acute respiratory distress syndrome
  • BNP-B type naturetic peptide
  • CBC-Complete blood count
  • CK-MB-MB fraction of creatinine kinase
  • CMP-Complete metabolic panel
  • CMV-Continuous mechanical ventilation
  • DVT-Deep vein thrombosis
  • ED-Emergency department
  • F/U-Follow up
  • FiO2-Fraction of inspired oxygen
  • GI-Gastrointestinal
  • Hb-Hemoglobin
  • Mg-Magnesium
  • MI-Myocardial infarction
  • mmHg-Millimeters of mercury
  • NIF-Negative inspiratory force
  • NPPV-Noninvasive positive pressure ventilation
  • PAO2-Partial pressure of oxygen in the alveoli
  • PaO2/CO2-Partial pressure of oxygen and CO2 in
    the arteries
  • Patm-Atmospheric pressure
  • PH2O-Partial pressure of water vapor
  • PCWP-Pulmonary capillary wedge pressure
  • PE-Pulmonary embolus
  • PNA-Pneumonia
  • PPV-Positive pressure ventilation
  • R-diffusion coefficient of CO2
  • SOB-Short of breath
  • VTE-Venous thromboembolism

5
Case 1
  • 18 year old male in ED with history of anxiety
    and acute onset of dyspnea and SOB. P 94, R 28,
    BP 132/78, T 37.0, SaO2 99 on room air.

6
Case 2
  • You are called for a 58 year old female admitted
    2 days prior with sepsis. Now with severe SOB. P
    110, R36, BP 105/66, T37.6, SaO2 90 on 4
    liter nasal cannula.

7
Case 3
  • You are called for a 78 year old male admitted 10
    hours prior for exacerbation of COPD. He is
    obtunded and barely rousable. P 88, R 6, BP
    146/88, T 36.8, SaO2 95 on 4 liter nasal
    cannula.
  • ABG 7.13 / 103 / 86 / 33 / 93

8
Lung Function
  • Oxygenation
  • Ventilation
  • Dependent on circulation

9
Air Movement - Breathing
  • Negative intra-thoracic force
  • The role of the pleura
  • Compliance
  • Airway resistance
  • Radial traction dec resistance pulls on tubes
    to make a larger lumen

10
Factors Affecting Intra-thoracic Force
  • Trauma
  • Neuromuscular disease
  • Pleural effusion
  • Pneumothorax
  • Sedation

11
Factors Affecting Compliance
  • Chest wall compliance
  • Trauma
  • Hyper-expansion gets bigger b/c lungs push it
    out. Ribs lever against diaphragm. Dec chest
    wall compliance
  • Pleural changes
  • Lung compliance
  • Interstitial edema
  • Fibrosis
  • Air trapping

12
Factors Affecting Resistance
  • COPD
  • Asthma
  • Pulmonary edema
  • Airway edema

13
Après Air Movement(What Comes Next)
  • Diffusion in the lungs
  • Circulation
  • Diffusion in the tissues

14
Circulatory Gas Transport
  • Pulmonary circulation
  • Gas transportability
  • Systemic circulation

15
Gas Diffusion
  • Layers
  • Surfactant
  • Alveolar membrane
  • Interstitial fluid
  • Capillary membrane
  • Plasma
  • Healthy barrier is 0.5 microns
  • Different gases behave differently

16
Factors Affecting Diffusion
  • Type of gas
  • Membrane thickness
  • Pressure gradient
  • Blood flow

17
Normal Oxygenation
  • Its all about DIFFUSION
  • Confounders
  • Other gases N2, H2O, CO2, trace gases
  • Speed of the blood
  • Erythrocyte exposure time 0.75 - 0.25 seconds
  • Diffusion membrane
  • Hemoglobin status

(Rest)
(Exercise)
18
Oxygen Cascade
  • Inspired oxygen 160 mmHg
  • Alveolar oxygen 100 mmHg
  • Oxygen in blood 90 mmHg
  • Dissolved in plasma
  • Oxygen at tissue (mitochondrial) level
  • 4 - 20 mmHg

19
Pulmonary Math
  • Alveolar gas equation (short)
  • PAO2 (P atm - P H2O) x FiO2 - PaCO2 / R
  • (760-47) x FiO2() PaCO2 / 0.8
  • 713 x 0.21 40 / 0.8
  • 150-50
  • Approx 100 mmHg

20
A(Alveolar)-a(Arterial) GradientA-a Gradient
  • PAO2 PaO2
  • (P atm P H2O) x FiO2 - PaCO2 / R - PaO2
    (obtained from ABG)
  • (760-47) x FiO2() PaCO2 / 0.8 PaO2
  • 713 x 0.21 40 / 0.8 PaO2
  • 150 50 PaO2
  • 100 PaO2
  • Normal gradient Age/44
  • In a healthy young adult, this is about 10 mmHg
    but can change dramatically with diseases
    affecting diffusion membrane

21
Oxygen in the Blood
  • Total O2
  • Total O2 (Hb(g/dl) x 1.34 x SaO2) (PaO2 x
    0.003)
  • (14 x 1.34 x 0.98) .
    (90 x 0.003)
  • 18.4 ml/100ml blood .
    0.27 ml/100ml blood

22
Point for Possible Confusion
  • PaO2 and SaO2 are completely different, though
    interdependent measurements

23
Oxyhemoglobin Dissociation Curve
  • What moves it to the right?
  • Lower pH
  • Higher PaCO2
  • Higher temp
  • Higher level of 2,3 BPG
  • Usually induced by chronic hypoxemia

24
CO2 Transport
  • CO2 transport
  • 23 bound to Hb Carbaminohemoglobin
  • 70 as HCO3 Bicarbonate
  • 7 dissolved in plasma
  • Volatile as H2CO3
  • H20 CO2 H2CO3 H HCO3-
  • Amount present is unmeasureable due to volatility
    but proportional to PaCO2

25
Normal VentilationAir Movement Diffusion
  • Inspiration
  • Negative intrathoracic pressure via diaphragm and
    intercostal muscles
  • Simple diffusion of O2 and CO2
  • Expiration
  • Positive intrathoracic pressure via relaxation of
    diaphragm and intercostals
  • Lung recoil

26
Working Together
  • V/Q Ventilation / Perfusion
  • Matching/mismatching
  • Shunting
  • PNA, pulmonary edema, atelectasis
  • Dead space ventilation
  • Pulmonary embolism
  • Compensatory mechanisms
  • Pulmonary arteriole constriction

27
Acute Respiratory FailureWhere To Start
  • Where does the problem lie?
  • Air movement
  • Apnea/Hypopnea
  • Airway resistance
  • Asthma
  • Edema
  • Lung or chest wall compliance
  • Restriction/Trauma
  • Interstitial fibrosis
  • Air trapping

28
Acute Respiratory FailureWhere Else
  • Diffusion abnormalities
  • Interstitial edema/fibrosis
  • Gradient abnormalities
  • Relation to diffusion membrane
  • (A-a gradient)
  • Ambient hypoxemia
  • V/Q mismatch
  • Shunting
  • Dead space ventilation

29
Acute Respiratory FailureWhere Else
  • Blood flow
  • Fast flow
  • Rest vs. exercise
  • Slow flow
  • HF
  • Pulmonary vascular resistance

30
Acute Respiratory FailureWhere Else
  • Gas transport
  • Hemoglobin level
  • Anemia
  • Oxyhemoglobin dissociation

31
Acute Respiratory FailureManifestations
  • Hypoxemia
  • Hypercapnia (ventilatory failure)
  • ABG representation
  • Rapid onset, severe V/Q mismatch

32
Acute Respiratory Failure Etiology
Complication of another condition
  • Pneumonia
  • COPD
  • Sepsis
  • MI
  • PE
  • Pulmonary edema
  • Pneumothorax
  • Lung Path.
  • Drugs
  • Shock
  • Trauma
  • ARDS

33
Acute Respiratory Failure Typical Presentation
  • Respiratory distress
  • ? Respiratory rate
  • Use of accessory muscles of respiration
  • Scalene m.
  • Sternocleidomastoid m.
  • Pectoralis Major m.
  • Abdominals

34
Acute Respiratory Failure Presentation (Cont)
  • Coma
  • Cyanosis
  • Diaphoresis sweating
  • Delirium
  • Lethargy (esp. with COPD)
  • CO2 narcosis / hypoxic drive

35
Acute Respiratory Failure Mimics
  • Anxiety
  • Pain
  • Agitation
  • Panic attack
  • Kussmauls breathing
  • Cheyne-Stokes breathing between
    hypo/hyperventilation

36
Acute Respiratory Failure Rapid Diagnostics
  • ABG the way to know
  • CXR
  • PA/Lat vs. portable
  • EKG
  • CBC, CMP, Mg, CK-MB, Troponin I

37
Acute Respiratory Failure Interventions
  • Hypoxemia
  • O2 delivery systems
  • Nasal cannula/Oxymizer
  • Simple mask - not used
  • Partial rebreather mask - not used
  • Venturi mask
  • Non-rebreather mask
  • To maintain PaO2 ? 60 or SaO2 ? 90

38
Acute Respiratory Failure Interventions
  • Ventilatory support
  • BIPAP (NPPV) non invasive pos pressure when we
    think it will only be for a short time.
  • Endotracheal intubation
  • Mechanical ventilation (PPV)

39
Reasons to Intubate
  • Airway obstruction
  • Airway protection
  • Secretion management
  • Unresponsive hypoxemia
  • Ventilation management
  • Acidosis
  • Apnea
  • Injury/toxicity
  • Anesthesia

40
Mechanical Ventilation Modes
  • CMV controlled mechanical ventilation
  • A/CMV assist/control mechanical ventilation
  • IMV/SIMV synchronized intermittent mandatory
    ventilation
  • PSV pressure support ventilation
  • PCV pressure control ventilation
  • PEEP positive end expiratory pressure

41
Consequences of PPV
  • Barotrauma
  • Vent. assoc. lung injury
  • Hemodynamic effects
  • Hemodynamic monitoring changes
  • Muscle atrophy
  • Impaired mucociliary clearance
  • O2 toxicity
  • GI
  • Splanchnic / Renal
  • Cerebral
  • Auto PEEP

42
Consequences of PPV (Cont)
  • Auto PEEP

43
CMV - Weaning Modalities
  • Treat underlying illness or cause of respiratory
    failure to maximum effect.
  • Treat complications.
  • Then...
  • Wean O2 / PEEP
  • ? Assist Breaths
  • Use of PSV
  • NIF
  • At least -20 cmH2O
  • F/U ABG

44
Acute Lung Injury (ALI)
  • Acute and persistent lung inflammation with
    increased vascular permeability
  • 3 clinical features
  • Bilateral infiltrates
  • PaO2 / FiO2 ratio 201-300 (room air PaO2 ? 60)
  • Lower value worse disease
  • No evidence of ? left atrial pressure
  • PCWP 18 mmHg or less

45
Acute Respiratory Distress Syndrome (ARDS)
  • Definition
  • Severe end of the spectrum of acute lung
    injury

46
Acute Respiratory Distress Syndrome
  • ALI - worse
  • PaO2 / FiO2 ratio 200 or less
  • Room air PaO2 ? 40
  • Diffuse alveolar damage
  • Low lung compliance
  • ? vascular permeability
  • ?? diffusion gradient

47
ARDS Presentation
  • Initial
  • Severe Hypoxemia
  • Tachypnea / Dyspnea
  • Diffuse rales
  • Rapid decline and need for mechanical ventilation
  • ABG
  • Acute respiratory alkalosis so hypoxic that
    they are hyperventilationg
  • Severe hypoxemia

48
ARDS Dx
  • Initially resembles CHF or Pulmonary Edema
  • Importance of clinical course
  • Swan Ganz catheter
  • BNP or NT-Pro BNP

49
ARDS Etiology
50
ARDS Occurrence
  • Approx. 190,600 cases / yr
  • 15 ICU pts
  • 20 mech vent pts

51
(No Transcript)
52
ARDS DDx
  • Diffuse alveolar hemorrhage
  • Acute interstitial pneumonia
  • Idiopathic acute eosinophilic pneumonia
  • Carcinoma

53
ARDS Complications
  • Mostly related to CMV
  • Barotrauma
  • Nosocomial Pneumonia
  • Multisystem failure
  • DVT pt not mobile
  • GI bleed
  • Malnutrition
  • Catheter related infections
  • Drug effects

54
ARDS Tx
  • O2
  • Prudent sedation / paralysis
  • Analgesia
  • Diuresis
  • PPV
  • Nutritional support
  • Glucose control
  • VTE prophylaxis
  • GI prophylaxis
  • Prudent transfusions
  • Monitor for nosocomial pneumonia

55
ARDS Prognosis
  • 25-30 mortality
  • Multisystem failure
  • Variable outcomes in survivors
  • Long term neurocognitive impairment
  • Ventilatory impairment resolves

56
Remember the Cases?
  • 18 year old male in ED with history of anxiety
    and acute onset of dyspnea and SOB. P 94, R 28,
    BP 132/78, T 37.0, SaO2 99 on room air. Panic
    attack
  • You are called for a 58 year old female admitted
    2 days prior with sepsis. Now with severe SOB. P
    110, R36, BP 105/66, T37.6, SaO2 90 on 4
    liter nasal cannula. Give more o2, investigate,
    ddx ARDS
  • You are called for a 78 year old male admitted 10
    hours prior for exacerbation of COPD. He is
    obtunded and barely rousable. P 88, R 6, BP
    146/88, T 36.8, SaO2 95 on 4 liter nasal
    cannula. Partially comp resp acidosis. Went into
    acute resp failure on acute resp acidosis.
    Decreased resp drive.
  • ABG 7.13 / 103 / 86 / 33 / 93
  • R.O.M.E. ?

57
References
  • 1. Prchal, J.T. Diagnosis and Treatment of
    Methemoglobinemia. In UpToDate, Rose, BD (Ed),
    UpToDate, Waltham, MA, 2006.
  • 2. Lyn-Kew, K., Hyzy, R.C. Physiologic and
    Pathophysiologic Consequences of Positive
    Pressure Ventilation. In UpToDate, Rose, BD (Ed),
    UpToDate, Waltham, MA, 2006.
  • 3. Hansen-Flaschen, J., Siegel, M.D. Acute
    Respiratory Distress syndrome Definition
    Epidemiology Diagnosis and Etiology. In
    UpToDate, Rose, BD (Ed), UpToDate, Waltham, MA,
    2006.
  • 4. Siegel, M.D. Acute Respiratory Distress
    Syndrome Pathophysiology Clinical
    Manifestations and Prognosis. In UpToDate, Rose,
    BD (Ed), UpToDate, Waltham, MA, 2006.
  • 5. Siegel, M.D. Supportive Care and Oxygenation
    in Acute Respiratory Distress Syndrome. In
    UpToDate, Rose, BD (Ed), UpToDate, Waltham, MA,
    2006.
  • 6. Lung Function Fundamentals. At
    www.anaesthetist.com/icu/organs/lung/lungvol.gif
    accessed 9/09.
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