Establishing the Need for Mechanical Ventilation

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Establishing the Need for Mechanical Ventilation

• Chapter 5

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Ventilation to help maintain normal respiratory
balance, homeostasis

• Is the patient awake or asleep?
• If asleep/unconscious are they able to be
  aroused? To what extent?
• What is the color, appearance and texture of the
  patients skin?
• Cyanosis is evident where? - nailbeds and lips
• Pale and diaphoretic
• Take the vital signs.
• RR, HR, BP, body temperature, and SpO2

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Dyspnea

• Patients appear alarmed
• Eyes wide open
• Forehead furrowed
• Nostrils are flared
• May be sweating and flushed or ashen, pale and
  cyanotic
• May try to sit up, lean forward
• Use accessory muscle of respiration
• May complain about not getting enough air
• Paradoxical or abnormal movement of the thorax
  and abdomen
• Abnormal breath sounds
• Tachycardia arrhythmias and hypotension

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Acute Respiratory Failure

• Respiratory activity is absent or is insufficient
  to maintain adequate oxygen uptake or carbon
  dioxide clearance
• Inability to maintain arterial oxygen carbon
  dioxide and pH at acceptable levels
• Two forms
• Lung failure accompanied by hypoxemia
• Pump failure accompanied by hypercapnia

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• Acute hypoxic respiratory failure
• Acute life threatening or vital organ threatening
  tissue hypoxia
• Result of
• severe V/Q mismatching
• diffusion defects
• right to left shunting
• alveolar hypoventilation

• Acute hypercapnic respiratory failure
• Inability of the body to maintain normal PCO2
• Three disorders that lead to pump failure
• Central nervous system disorders
• Neuromuscular disorders
• Disorders that increase the work of breathing

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Clinical Rounds 5-1 p.67Stroke Victim

• A 58 year old male patient is admitted to the
  emergency department from his home after a
  suspected stroke (CVA). Vital signs reveal a HR
  94, RR 16, normal temp, BP 165/95. The patients
  pupils respond slowly and unequally to light.
  Breath sounds are diminished in the bases. A
  sound similar to snoring is heard on inspiration.
  The patient is unconscious and unresponsive to
  painful stimuli. What is the most appropriate
  course of action at this time?

• Intubate to protect the airway
• Admit the patient to ICU
• Further evaluate VS, SpO2 monitoring, ABG values.
  Electrolytes, and neurological status
• Establishing mechanical ventilation may be
  necessary as the patient is unconscious and
  unresponsive

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Clinical Rounds 5-2 p.68Unexplained acute
respiratory failure

• A stat ABG performed on a patient admitted
  through the ED reveals the following
  7.15/83/34/28 on RA. The patient was found
  unconscious in a nearby park, no other history is
  available. What is the most appropriate course
  of action at this time?

• The problem may be drug related, try naloxone
  (Narcan)
• Intubate and begin ventilation
• Assess further with
• VS
• SpO2 monitoring
• ECG
• breath sounds
• ABG values
• Electrolytes
• blood alcohol levels
• toxicology screening
• Neurological status evaluation

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Clinical Rounds 5-3 p.68Ventilation in
Neuromuscular Disorders

• CASE ONE
• A 68 year old female patient with a history of
  myasthenia gravis has been in the hospital for 12
  days. She was admitted because her primary
  disease had worsened. The patient is unable to
  properly perform MIP and SVC maneuvers because
  she cannot seal her lips around the mouthpiece.
  Her attempts produced these values MIP -34cmH2O
  SVC 1.2L. What should the clinician recommend?

• In spite of the leak, parameters are still
  acceptable.
• Adapt of mouth seal to the system for
  measurements
• Continue to monitor MIP and VC q8
• Request an evaluation of anticholinesterase
  therapy
• Keep the patient NPO and provide suctioning at
  the bedside until swallowing ability can be
  evaluated
• Monitor SpO2 and/or ABG values if symptoms become
  worse

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Clinical Rounds 5-3 p.68Ventilation in
Neuromuscular Disorders

• CASE TWO
• A 26 year old male patient who is recovering
  from mycoplasmal pneumonia complains of tingling
  sensations and weakness in his hands and feet.
  He is admitted to the general floor for
  observation. Over several hours the patient
  becomes unable to move his legs. A respiratory
  therapist is called to assess him. What should
  the RT recommend at this time?

• The history and symptoms suggest Guillain-Barré
  syndrome
• The MIP and VC indicate muscle weakness and the
  ABG results show acute respiratory failure
• Provide ventilation if ARF is confirmed
  consider possibilities of using NPPV, IPPV (oral,
  nasal, or tracheostomy)

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Clinical Rounds 5-4 p.69Asthma

• A 13 year old girl is seen in the ED for acute
  exacerbation of asthma. Continuous nebulizer
  therapy with a beta 2 adrenergic bronchodilator
  is administered. The patient has been given a
  high dose of corticosteroids and is receiving
  oxygen. Four hours after admission, she is alert
  and responsive. Her RR is 20. Course crackles
  and end-inspiratory wheezes are heard clearly
  throughout both lung fields. What recommendation
  for continuous respiratory care should be made
  for this patient?

• The patient appears to be improving
• Continue drug therapy reducing dosage and
  frequency
• Continue to monitor the patient

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Physiological Measurements in Acute Respiratory
Failure

• Ventilatory Mechanics
• MIP/NIF maximum inspiratory pressure or negative
  inspiratory force ability to generate enough
  volume to produce an effective cough
• Normal -50 to -100 cm H2O
• 0-20cmH2O is inadequate
• VC vital capacity ability to take in a large
  volume of air to generate a strong cough
• Normal 65-75ml/kg IBW (as high as 100ml/kg)
• lt15ml/kg IBW is inadequate
• PEFR peak expiratory flow rate indicator of
  airway patency
• Normal 350-600 L/min
• 75-100L/min is inadequate
• FEV1 forced expiratory volume in one second
• Normal 80 VC 50-60 ml/kg IBW
• lt10ml/kg IBW is inadequate
• RR respiratory rate elevated RR increases WOB
• Normal 12-20
• gt35 inadequate for alveolar ventilation
• Ve minute ventilation
• Normal 5-6l/min
• gt10 l/min concerning

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Failure of Ventilation

• Single best indicator of ventilation is PaCO2
• Elevated PaCO2 suggested the Vds is increased in
  relation to Vt
• Normal Vd/Vt 0.3-0.4 gt0.6 is a critical increase
  in dead space
• Alveolar Ventilation VA Vt-Vd

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Failure of Oxygenation

• Indicator of oxygenation status is PaO2
• Normal PaO2 is 80-100 mmHg on room air
• Total oxygen carrying capacity
• CaO2(Hb x 1.34) x SaO2 (PaO2 X 0.003)
• Normal 16-20 vol
• Alveolar to arterial oxygen gradient
• PAO2 (PB PH2O) x FiO2 PaCO2 x 1.25)
• P(A-a)O2
• 2-30 mmHg on RA 350-450 mmHg on 100 O2
• Arterial to alveolar PO2 ratio PaO2/PAO2
• Normal 0-75-0.95
• PaO2/FiO2
• Normal 350-450

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Standard Criteria for Initiating Mechanical
Ventilation

• Apnea or absence of breathing
• Acute respiratory failure
• Impending respiratory failure
• Refractory hypoxic respiratory failure
• Ventilatory insufficiency and the need to protect
  the airway or manage secretions

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Consider alternatives to invasive PPV

• High flow oxygen
• NPPV
• Intubation without ventilation
• Ethical considerations

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Case Studies1-5p.75