Diagnosis and Management of Acute Respiratory Failure

1
Diagnosis and Management of Acute Respiratory
Failure
Steven B. Leven, M.D., F.C.C.P. Clinical
Professor, Pulmonary/Critical Care Medicine
UCI Director MICU and Respiratory Therapy, UCI
Medical Center


2
Objectives

• Understand the causes of hypoxia and hypercapnea
• Know the clinical manifestations of respiratory
  failure
• Be familiar with various oxygen delivery systems
• Know indications and contraindications to
  noninvasive positive pressure ventilation
• Know indications for endotracheal intubation
• Be familiar with basic modes of mechanical
  ventilation

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CASE 1

• J.T. is a 68-kg, 42-yr old female admitted
  after a drug overdose complicated by emesis and
  aspiration. Intubation and mechanical
  ventilation are initiated in the emergency
  department.

4
CASE 1

• Mechanical ventilation
• AC (volume) mode
• Tidal volume 750 mL
• 16 breaths/min
• FIO2 1.0
• PEEP 5 cm H2O

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CASE 1

• Peak airway pressure 52 cm H2O
• Inspiratory plateau pressure (IPP) 48 cm H2O
• pH 7.38, PaCO2 36 PaO2 57
• Sinus tach at 166, BP 75/50, no urine output
• Patient very agitated and fighting vent
• What would you do?

6
CASE 2

• L.W. is a 62-yr-old, 52-kg female with severe
  emphysema. For 2 days she has had progressive
  dyspnea and was found unresponsive. ABG on
  5liters NC pH 7.07 pCO2 87 pO2 62.
• She required intubation and initiation of
  mechanical ventilation.

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CASE 2

• ICU ventilator settings
• AC, rate 12 breaths/min
• Tidal volume 500 mL
• FIO2 100
• PEEP 5 cm H2O

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CASE 2

• RR 24
• IE ratio 11.5
• Peak pressure 50 cm H2O, IPP 35 cm H2O
• End expiratory pressure is 20 cm
• pH 7.20, PaCO2 60, PaO2 215
• Sinus tach 157
• BP 78/45
• No urine output
• Patient very agitated
• What would you do?

9
CASE 3

• 37 year old healthy malpractice plaintiff
  attorney presents to ER with 24 hour history of
  generalized weakness. Last week he had a mild
  bout of gastroenteritis after eating under cooked
  chicken. He could walk with difficulty when he
  arrived at ER 8 hours ago. Now he needs help to
  reposition himself in bed and he coughs when he
  attempts to drink.

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CASE 3

• Exam normal except weakness
• Chemistries and CBC normal
• RA ABG pH 7.41 pCO2 41 pO2 84
• Vital Capacity 840cc (12cc/Kg)
• CXR at left

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CASE 3

• Where should this patient be cared for? ICU?
  Tele? Ward? Home?
• Should this patient be fed?
• Should he be advised to call a lawyer?
• Would you put him on BiPAP?
• Anything else you would do?

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Case 4

• A 25-year-old lady, Miss. Poor Compliance, is
  rushed into your Emergency Department. She is an
  asthmatic who on arrival is sitting forward in
  the tripod position, using her accessory muscles
  to breath. She is tachypneic, diaphoretic,
  agitated and unable to talk. During a nebulizer
  tx with albuterol she becomes dusky and poorly
  responsive.

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Case 4
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Plan of care?

• Get ABG?
• Start BiPAP?
• Discuss patients feelings about being ill?
• Get advice from resident (oops, he is running a
  code)
• Other?

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Acute Respiratory Failure

• Hypoxemic
• Room air PaO2 ? 50 torr
• Hypercapnic
• PaCO2 ? 50 torr
• Acute vs chronic
• Often Multifactorial

ARF 15
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Pathophysiology of Hypoxemia

• Ventilation/perfusion mismatch
• Shunt effect (intracardiac or intrapulmonary)
• Decreased diffusion of O2
• Alveolar hypoventilation
• FIO2 lt 21 (eg. High altitude)

ARF 16
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Pathophysiology of Hypercapnia

• Alveolar ventilation is the prime determinant of
  CO2 exchange during mechanical ventilation
• VA 1/pCO2
• VA(VT-VD)f
• Change in any variable affects pCO2

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Causes of Hypercapnia

• Inability to sense elevated PaCO2
• Inability to signal respiratory muscles
• Inability to effect a response from respiratory
  muscles
• Increased dead space

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Inability to effect adequate response from
respiratory muscles

• Imbalance between demand for respiratory muscle
  work and the ability to supply that work
• Examples of increased demand bronchospasm,
  fever, low lung compliance, pleural effusion
• Decreased supply poor cardiac output,
  malnutrition, deconditioning

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Increased Dead Space (wasted ventilation)

• Hypovolemia
• Low cardiac output
• Pulmonary embolus
• High airway pressures
• Short-term compensation by increasing tidal
  volume and/or respiratory rate

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Manifestations of Respiratory Distress

• Altered mental status especially anxiety!!!
• Anxiety is a result of respiratory distress,
  almost NEVER the cause.
• Increased work of breathing
• Tachypnea, nasal flaring
• Accessory muscle use, retractions, paradoxical
  breathing pattern, respiratory alternans
• Catecholamine release
• Tachycardia, diaphoresis, hypertension
• Abnormal ABG not always!!!
• Neuromuscular failure is different from above
  monitor vital capacity intubate near 15cc/kg

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Oxygen Supplementationlow flow systems 1-10 LPM

• 100 O2 mixes with room air to determine FIO2 -
  definition
• FIO2 varies with patients breathing pattern
• Rapid inspiration entrains more room air
• Deep breaths entrain more room air
• Rapid respiratory rate entrains more room air
• Patients in more distress get lower FIO2
• FIO2 is unknown since amount of entrainment is
  unknown
• Any humidity in gas comes from entrained air-
  wall O2 has 0 relative humidity
• Low flow devices
• Simple Nasal Cannulas
• Simple masks

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High Flow O2 Devices gt 20 - 60 lpm

• Device provides 100 of gas to patient -
  definition
• No entrainment of room air if mask fits
• FIO2 is known and exact
• Relative humidity depends on the device
• High flow devices
• High flow nasal cannula
• Venturi mask
• Aerosol mask heated or cool
• Nonrebreather mask some characteristics of both
  high and low

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O2 Devices
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Aerosol O2 devices
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BiPAP or NPPV

• Contraindications
• Cardiac or respiratory arrest
• Inability to cooperate, protect the airway, or
  clear secretions
• Nonrespiratory organ failure, esp shock
• Facial surgery, trauma, or deformity
• Prolonged duration of mechanical ventilation
  anticipated
• Recent esophageal anastomosis
• A need for emergent intubation is an absolute
  contraindication to NPPV
• Set inspiratory pressure (IP) and exp pressure
  (PEEP)
• Mean pressure determines oxygenation
• IP PEEP determines ventilatory assist

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Endotracheal Intubation

• .An opening must be attempted in the trunk of
  the trachea, into which a tube or cane should be
  put You will then blow into this so that lung
  may rise again.And the heart becomes strong.
• -Andreas
  Vesalius (1555)

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Indications for Endotracheal Intubation

• Airway protection (outside ICU?)
• Relief of airway obstruction
• Respiratory failure or impending respiratory
  failure
• Hypoxic or
• Hypercapneic or both
• Need for hyperventilation - ?ICP
• Unsustainable work of breathing
• Facilitate suctioning/pulmonary toilet
• Shock !!!!!!!!!!!

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Decision to intubate

• Clinical decision-not based on ABG
• Error on the side of patient safety
• What is the safest way to navigate illness?
• Intubation is not an act of weakness
• Think ahead- if need to intubation is expected in
  next 24hr, intubate now
• Endotracheal tubes are not a disease and
  ventilators are not an addiction i.e. Intubation
  does not cause ventilator dependence

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Modes of Mechanical VentilationPoint of
Reference Spontaneous Ventilation
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Continuous Positive Airway Pressure (CPAP)

• No machine breaths delivered
• Allows spontaneous breathing at elevated baseline
  pressure
• Patient controls rate and tidal volume

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Assist-Control Ventilation

• You set tidal volume and minimum rate
• Additional breaths delivered with minimal
  inspiratory effort - pt sets actual rate
• Advantages reduced work of breathing allows
  patient to modify minute ventilation
• Most patients should start with this mode
• Rate 12, TV 8-10 cc/kg, FiO2 100 PEEP 5

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Synchronized Intermittent Mandatory Ventilation
(SIMV)

• Volume cycled breaths at a preset rate
• Additional spontaneous breaths at tidal volume
  and rate determined by patient
• Invented as weaning mode
• Best weaning mode is sink or swim
• Best use is to mitigate AutoPEEP

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Pressure-Support Ventilation

• Pressure assist during spontaneous inspiration
  with flow-cycled breath
• Pressure assist at constant pressure continues
  until inspiratory effort decreases
• Delivered tidal volume dependent on set pressure,
  inspiratory effort and resistance/compliance of
  lung/thorax

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Inspiratory Plateau Pressure

• Airway pressure measured at end of inspiration
  with no gas flow present
• Estimates alveolar pressure at end-inspiration
• IPP is best indicator of alveolar distension
• PIP IPP airway resistance

Peak pressure
Plateau pressure
Inspiration Expiration
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Inspiratory Plateau Pressure

• High inspiratory plateau pressure stiff lungs
• Barotrauma - no
• Volutrauma yes pneumothorax, etc
• Decreased cardiac output
• Methods to decrease IPP
• Decrease tidal volume
• ??? Decrease PEEP
• Goal IPP usually ? 30 cm H2O
• ARDS protocol tidal volume 6 cc/kg IBW

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Auto-PEEP - common

• Occurs in setting of severe COPD or asthma
• Very uncomfortable for patient - agitation
• Can be measured on most ventilators
• Increases peak, plateau, and mean airway
  pressures
• Hypotension impaired venous return
• Suspect in setting of COPD or asthma pt who is
  agitated or hypotensive this is common!!!

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IE Ratio during Mechanical Ventilation

• If expiratory time too short for full exhalation
• Breath stacking
• Auto-PEEP
• Reduce auto-PEEP by reducing inspiratory
  time/increasing expiratory time
• Increase peak inspiratory flow rate 100 lpm
• Decrease respiratory rate (use IMV without PSV)
  rate of 12 usually is good
• Decrease tidal volume to 8 cc per kg IBW

39
CASE 1

• J.T. is a 68-kg, 42-yr old female admitted
  after a drug overdose complicated by emesis and
  aspiration. Intubation and mechanical
  ventilation are initiated in the emergency
  department.

40
CASE 1

• Mechanical ventilation
• AC (volume) mode
• Tidal volume 700 mL
• 10 breaths/min
• FIO2 1.0 always start at 100
• PEEP 5 cm H2O

41
CASE 1

• Peak airway pressure 52 cm H2O
• Inspiratory plateau pressure (IPP) 48 cm H2O
• pH 7.38, PaCO2 36 torr PaO2 57 torr
• Sinus tach at 166, BP 75/50
• Patient very agitated and fighting vent
• What are the issues here?

42
CASE 1

• What is diagnosis?
• What are the consequences of
• FIO2 100?
• TV 10cc/Kg?
• High inspiratory plateau pressure?
• Hypotension and tachycardia?
• agitation and fighting vent
• What variables should be changed to improve
  PaO2? BP? Protect lungs?

43
ARDS

• Decreased lung compliance results in high airway
  pressures
• Tidal volume goal 6cc/Kg
• Maintain IPP ? 30 cm H2O
• PEEP to improve oxygenation
• Aim for FIO2 50 - O2 toxic at gt 50
• Patients often need volume loading
• Sedation usually needed and sometimes also
  paralytic

44
CASE 2

• L.W. is a 62-yr-old, 52-kg female with severe
  emphysema. For 2 days she has had progressive
  dyspnea and was found unresponsive. ABG on
  5 liters NC pH 7.07 pCO2 87 pO2 42.
• She required intubation and initiation of
  mechanical ventilation.

45
CASE 2

• ICU ventilator settings
• AC, rate 12 breaths/min
• FIO2 1.0
• Tidal volume 600 mL
• Peak flow 50 l/sec
• PEEP 5 cm H2O

46
CASE 2

• RR 24
• IE ratio 11.5
• Peak pressure 50 cm H2O, IPP 35 cm H2O
• End Expiratory Alveolar Pressure 20 cm H2O
• pH 7.28, PaCO2 60 torr, PaO2 215 torr
• Sinus tach 157
• BP 78/45
• No urine output
• Patient very agitated

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CASE 2

• What complication of therapy is at work?
• What variable(s) should be changed to improve the
  ABG ? BP? UO? Agitation?
• change in peak flow rate ?
• change in respiratory rate ?
• change in ventilator mode?
• bronchodilators ?

48
Analysis - Patient L.W.

• Hypercapnia acceptable if pH OK
• High peak airway pressure can be OK
• Wide peak-plateau pressure difference indicates
  obstructive disease
• Be alert for auto-PEEP
• Hypotension and tachycardia suggest auto-PEEP and
  or inadequate preload

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Obstructive Airway Disease

• Obstructive diseases require adequate expiratory
  time
• PaCO2 should be kept at patients baseline level

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CASE 3

• 37 year old healthy lawyer admitted from ER with
  24 hour history of generalized weakness. Last
  week he had a mild bout of gastroenteritis. He
  could walk with difficulty when he arrived at ER
  12 hours ago. Now he needs help to reposition
  himself in bed and he coughs when he attempts to
  drink.

51
CASE 3

• Exam normal except weakness
• Chemistries and CBC normal
• RA ABG pH 7.41 pCO2 41 pO2 84
• Vital Capacity 840cc (12cc/Kg)

52
CASE 3

• What is this patients diagnosis?
• Is this patient in respiratory failure?
• What is this patients most urgent need?

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CASE 3Neuromuscular Respiratory Failure

• Patients do not appear to struggle
• ABG does not tell you when to intubate
• Delay may result in aspiration and arrest
• Follow vital capacity closely in ICU
• Intubate when VC approaches 15cc/Kg

54
Case 4

• A 25-year-old lady, Miss. Poor Compliance, is
  rushed into your Emergency Department. She is an
  asthmatic who on arrival is sitting forward in
  the tripod position, using her accessory muscles
  to breath. She is tachypneic, diaphoretic,
  agitated and unable to talk. During a nebulizer
  tx with albuterol she becomes dusky and poorly
  responsive.

55
Case 4
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Plan of care?

• Get ABG?
• Start BiPAP?
• Discuss patients feelings about being ill?
• Check her health insurance
• Get advice from resident (oops, he is running a
  code)
• Other?