early detection and management of respiratory failure
TRANSCRIPT
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Early Detection and Interventions in Respiratory
Failure
Dr Nigam Prakash Narain
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Definition: Respiratory Failure
• Defined as inadequate gas exchange due to pulmonary or non-pulmonary causes leading to hypoxemia, hypercarbia or both.
• Documented by PaCO2 > 50 mm of Hg or PaO2 < 50-60 mm of Hg.
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Status of ABG
• Arterial Blood Gas analysis: single most important lab test for evaluation of respiratory failure.
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Respiratory Failure: Causes
1. Upper airways obstruction:
> Laryngomalacia
> Subglottic stenosis
> Laryngotracheobronchitis
> Tracheitis & Epiglottitis
> Retropharyngeal / Peritonsillar abscess
> Acute hypertrophic tonsillitis
> Diphtheria
> foreign body, trauma, vocal cord palsy
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2. Lower airway obstruction: > Bronchiolitis, Asthma, Foreign body3. Alveolar and pleural disease: > pneumonia, pulmonary edema, effusion empyma, pneumothorax, ARDS4. CNS causes: > Infections, injury, trauma, seizures > tetanus, SMA, Polio > AIDP, Phrenic nerve injury > Myasthenia gravis, botulism, > Muscle dystrophies, Polymyositis > Congenital myopathies, muscle fatigue
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Respiratory failure:clinical manifestations
• Tachypnea
• Exaggerated use of accessory muscles
• Intercostal, supraclavicular and subcostal retractions
• In neuromuscular disease, the signs of respiratory distress may not be obvious
• In CNS disease, an abnormally low respiratory rate, and shallow breathing are clues to impending respiratory failure
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Presentation
• Three distinctive clinical profiles have been suggested in children:
1. Mechanical dysfunction of airways
2. Neuromuscular dysfunction
3. Breathing control dysfunction
• A rapid assignment to one of these profiles facilitates early diagnosis and treatment
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Profile 1: Mechanical dysfunction of airways
• Most common type
• Results from alterations in the mechanical properties of the airways, lung parenchyma or chest wall.
• Present with typical signs of respiratory distress:
increased effort, Tachypnea, retractions, accessory muscle use, nasal flaring, adventitious breath sounds, grunting
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Profile 2: neuromuscular disease
• Results from myopathies involving resp muscles or polyneuropathies / phrenic nerve injuries
• Associated with an increased neural output, but is not effectively translated into effective contractions
• Tachypnea, shallow respiratory efforts and profound dyspnea are characteristic
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Profile 3: Alteration in control of breathing
• Usually results from CNS injury / developmental deficits
• Ondine’s curse, Apnea of prematurity, CNS injury / depression
• Associated with decreased neural output to resp muscles, thus signs of respiratory distress are unusual, even with significant respiratory compromise
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Evaluation of Respiratory failure
The following parameters are important in evaluation of respiratory failure:
1. PaO2
2. PaCO2
3. Alveolar-Arterial PO2 Gradient
P(A-a)O2 Gradient = PIO2 – PaCO2 / R
where PiO2 = partial pressure of inspired air, R = 0.84. Hyperoxia Test
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PaO2 / PaCO2
• Normal value depends on :
a. Position of patient during sampling
b. Age of patient
• PaO2 (Upright) = 104.2 -- 0.27 x age (Yrs)
• PaO2 (Supine) = 103.5 – 0.47 x age (Yrs)
• PaCO2 : normal value= 35-45 mm of Hg
unaffected by age/ positioning
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Alveolar-Arterial O2 gradient
• Normal P(A-a)O2 gradient: 5-10 mm of Hg
• A sensitive indicator of disturbance of gas exchange.
• Useful in differentiating extrapulmonary and pulmonary causes of resp. failure.
• For any age, an A-a gradient > 20 mm of Hg is always abnormal.
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Causes of Hypoxemia
1. Low PiO2 ~ at high altitude
2. Hypoventilation ~ Normal A-a gradient
3. Low V/Q mismatch ~ A-a gradient
4. R/L shunt ~ A-a gradient
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Hypoventilation-Diagnosis
• PaO2
• PaCO2 is always increased
• A-a gradient is normal (≤ 10 mm of Hg)
• Hyperoxia Test : dramatic rise in PO2
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V/Q mismatch- Diagnosis
• PaO2
• A-a gradient is
• PaCO2 may or may not be elevated
• Hyperoxia test : Dramatic rise in PaO2
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R-L shunt: diagnosis
• PaO2 is
• PaCO2 is usually normal
• A-a gradient is
• Hyperoxia Test : Poor / No response
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Hypercapnia :Causes
• Hypoventilation
• Severe low V/Q mismatch: major mechanism of hypercapnia in intrinsic lung disease.
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Status of ABG
• It is not possible to predict PaO2 and PaCO2 accurately using clinical criteria.
• Thus, the diagnosis of Respiratory failure depends on results of ABG studies.
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Respiratory failure:Interventions
• Supportive therapy
• Specific therapy
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Supportive therapy
• Secure the airway• Pulse oximetry• Oxygen: by mask, nasal cannula, head box• Proper positioning• Nebulization if indicated• Blood sampling: Routine, electrolytes, ABG• Secure IV line• CXR: upright AP & lateral views
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Hypoxemic / Non - Hypercapnic respiratory failure
• The major problem is PaO2.
• If due to low V/Q mismatch; oxygen therapy.
• If due to pulmonary intra-parenchymal shunts (ARDS), assisted ventilation with PEEP may be needed.
• If due to intracardiac R-L shunt: O2 therapy is of limited benefit. Surgical t/t is needed.
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Hypercapnic Respiratory failure
• Key decision is whether mechanical ventilation is required or not.
• In Acute respiratory acidosis: Mechanical ventilation must be strongly considered.
• Chronic Resp acidosis: patient should be followed closely, mech ventilation is rarely required.
• In acute-on-chronic respiratory failure, the trend of acidosis over time is a crucial factor.
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Mechanical Ventilation: Indications
1. PaO2< 55 mm Hg or PaCO2 > 60 mm Hg despite 100% oxygen therapy.
2. Deteriorating respiratory status despite oxygen and Nebulization therapy
3. Anxious, sweaty lethargic child with deteriorating mental status.
4. Respiratory fatigue: for relief of metabolic stress of the work of breathing
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Mechanical Ventilation: Strategies
• Non-Invasive Ventilation: CPAP / BIPAP
• Invasive Ventilation: SIMV, A/C, PAV
• Other approaches to mechanical ventilation:
a. High frequency ventilation (HFV)
b. Permissive Hypercapnia
c. Prone positioning
d. ECMO
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HFV
• 3 types: Oscillatory, Jet & Flow interruption• Very small tidal volumes are used
(<1ml/kg), very rapid rates (150-1000 bpm) and lower mean airway pressures are used.
• This approach is used to minimize the possibility of barotrauma to airways.
• Used if conventional ventilation fails to improve gas exchange
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Permissive Hypercapnia
• Allows the PaCO2 to rise into the 60-70 mm of Hg range, as long as the patient is adequately oxygenated (SaO2> 92%), and able to tolerate the acidosis.
• This strategy is used to limit the amount of barotrauma and volutrauma to the patient.
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Prone positioning
• Positioning the patient in the prone position has been shown to improve oxygenation and reduce ventilator induced lung injury.
• However, the outcome may not be improved.
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ECMO
• Used in the treatment of newborns and small infants with life threatening, refractory respiratory failure, unresponsive to mechanical ventilation.
• Inhales nitric oxide may improve oxygenation by reducing increased pulmonary vascular resistance.
• Inhaled NO is now being used in place of ECMO in NICU in some centers.