Early Detection and Interventions in Respiratory

Failure

Dr Nigam Prakash Narain

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.

Status of ABG

• Arterial Blood Gas analysis: single most important lab test for evaluation of respiratory failure.

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

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

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

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

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

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

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

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

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

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.

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

Hypoventilation-Diagnosis

• PaO2

• PaCO2 is always increased

• A-a gradient is normal (≤ 10 mm of Hg)

• Hyperoxia Test : dramatic rise in PO2

V/Q mismatch- Diagnosis

• PaO2

• A-a gradient is

• PaCO2 may or may not be elevated

• Hyperoxia test : Dramatic rise in PaO2

R-L shunt: diagnosis

• PaO2 is

• PaCO2 is usually normal

• A-a gradient is

• Hyperoxia Test : Poor / No response

Hypercapnia :Causes

• Hypoventilation

• Severe low V/Q mismatch: major mechanism of hypercapnia in intrinsic lung disease.

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.

Respiratory failure:Interventions

• Supportive therapy

• Specific therapy

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

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.

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.

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

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

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

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.

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.

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.