ARDS , Respiratory failure , respiratory distress ,

1. CUTE
ESPIRATORY
ISTRESS
YNDROME
Moderator : Dr. Mahesh
Presenter : Dr. Vinaykumar S Appannavar
A
R
D
S

2. Learning objectives
• Definitions
• Calculations – Carrico index – P/F ratio
• Signs and symptoms
• Aetiology and pathogenesis
• Non -pulmonary causes of ARDS
• Respiratory failure
• Basics
• Monitoring
• Management
• Mechanical ventilation – Concepts, Phases, Modes , Settings

3. Definitions
• It is often used to indicate signs and symptoms of abnormal
respiratory pattern
• New Berlin Definition of ARDS
• Simplified Consensus Definition of ALI

4. New Berlin Definition criteria
1. Within 1 week of a known clinical insult or new or worsening respiratory
symptoms
2. Bilateral opacities not fully explained by effusions
lobar/lung collapse or nodules
3. Need objective assessment ( 2D Echo ) to exclude
hydrostatic oedema , provided no risk factors
4. Carrico index – PaO2 / FiO2 ratio
• </= 300 mmHg with PEEP >/= 5 cm H2O - MILD
• </= 200 mmHg with PEEP >/= 5 cm H2O - MODERATE
• < 100 mmHg with PEEP >/= 5 cm H2O - SEVERE

5. Simplified Consensus Definition of ALI
• Acute onset – less than 7 days
• Severe hypoxemia ( PaO2 / FiO2 < 300
for ALI and < 200 for ARDS )
• Diffuse bilateral pulmonary infiltrates
on frontal radiograph consistent with
pulmonary edema

6. Calculations – Carrico index – P/F ratio
• To identify acute hypoxemic respiratory failure at any time while the patient is receiving supplemental O2
• Partial pressure of arterial oxygen – Pa02 - P
• Fraction of inspired oxygen – FiO2 – F
• A P/F Ratio less than 300 indicates acute respiratory failure , it also indicates what the pO2 would be on
room air.
1. P/F ratio < 300 is equivalent to pO2 < 60 mm Hg on room air
2. P/F ratio < 250 is equivalent to pO2 < 50 mm Hg on room air
3. P/F ratio < 200 is equivalent to pO2 < 40 mm Hg on room air
Ex – PaO2 is 90 mmHg on 40% Oxygen( FiO2 = 0.40). The P/F ratio is 90/0.40 = 225
The pO2 on room air = 45mmHg – less than the cut off.

7. • When the pO2 is unknown because an ABG is not
available, the SpO2 measured by pulse oximetry can be
used to approximate the pO2
Ex : Suppose a patient on 40% oxygen has a pulse oximetry
SpO2 of 95%. Referring to the Table above, SpO2 of 95% is
equal to a pO2 of 80mmHg. The P/F ratio = 80/0.40 = 200.
The patient may be stable receiving 40% oxygen, but
still has severe acute respiratory failure. If oxygen were
withdrawn leaving her on room air, the pO2 would only be
40 mmHg

8. Relation : FIO2 (%) and litres per minute (O2)
• Mask, Nasal Cannula (NC), Venturi mask (Venti-mask), NRB – mask
• Venturi mask – delivers (FiO2) @ 24%, 28%,31%,35%,40% and 50%
• NRB – mask delivers @ 100% oxygen
• Ex : pO2 of 85mmHg on ABG while receiving
5 L/min of oxygen(40% oxygen)
40% 0f O2 - an FIO2 of 0.40 ,
the P/F ratio = 85 / 0.40 = 212.5.

9. Signs and symptoms
• Restlessness
• Dyspnoea
• Tachypnoea
• Cough
• Chest wall retractions
• Nasal flaring
• Fever
• Stridor , wheeze, grunting
• Extreme tiredness
• Disorientation
• Shortness of breath
• Tachycardia
• Laboured/rapid breathing
• Cyanosis
• Thick frothy sputum
• Acidotic breathing
• Abnormal breath sounds ;
crackles
• Decreased PaO2
LateEarly

10. Aetiology and Pathogenesis

11. Non-pulmonary causes of RD
EXAMPLES MECHANISMS
CARDIOVASCULAR • Left to right shunt
• CCF
• Cardiogenic shock
• Pulmonary blood/water content
• Metabolic acidosis
• Baroceptor stimulation
CENTRAL NERVOUS
SYSTEM
• Raised ICP
• Encephalitis
• Toxic encephalopathy
• Stimulation of brainstem respiratory
centres
METOBOLIC • DKA
• Organic acidaemia
• Hyperammonaemia
• Stimulation of central and peripheral
chemoreceptors
RENAL • RTA
• HTN
• Stimulation of central and peripheral
chemoreceptors
• Left ventricular dysfunction
SEPSIS • Toxic shock syndrome
• Meningococcaemia
• Cytokine stimulation of RS centres
• Baroceptors stimulation
• Metabolic acidosis

13. Respiratory failure
• It occurs when oxygenation and ventilation are insufficient to meet the
metabolic demands of the body
• Abnormality in A. lung and airways
B. Chest wall and muscles of respiration
C. Central and peripheral chemoreceptors
• It is traditionally defined as respiratory dysfunction resulting in PaO2 < 60
torr with breathing of room air and PaCO2 >50 torr resulting in acidosis
• General condition of the patient to be considered
• ALI ARDS

14. Clinical manifestation of Respiratory failure
Site of pathology Symptoms
Lung and airways Nasal flaring , retractions, tachypnoea, wheezing
stridor , grunting
Chest wall and muscles of
respiration
Nasal flaring , tachypnoea , paradoxical breathing
Respiratory control Shallow or slow respirations , abnormal respiratory
pattern , apnoea

15. Pathophysiology of RF
1. Hypoxic respiratory failure- failure of oxygenation
2. Hyper carbic respiratory failure- failure of
ventilation
• Hypoxic respiratory failure results from intra
pulmonary shunting, venous admixture and
inadequate diffusion of oxygen
RF
Alveolar
ventilation
Pulmonary
capillary
perfusion
Diffusion
capacity
Composition
of inspired
gas
Arterial gas
Small airway obstruction Collapsed/fluid in alveoli
• Interstitial oedema
• fibrosis
• ARDS, Pneumonia
• Atelectasis, pulmonary oedema

16. • Ventilation – perfusion Mismatch (V/Q)
- For exchange of O2 and CO2 to occur
alveolar gas must be exposed to blood in pul.
Capillaries
• Intrapulmonary shunting
• Dead space ventilation
• VD/VT = 0.33

17. • Diffusion
- Gas exchange requires diffusion across the interstitial space b/w alveoli and
pulmonary capillaries
-Presence of hyper carbia in disease that impair diffusion is indicative of
alveolar hypoventilation.
Ex – Interstitial pneumonia, ARDS and airway obstruction

19. Basics – Hb-O2 dissociation curve

20. Monitoring
• Clinical examination
- Pulse oximetry
- Respiratory rate
- Progression with time
- abnormal clinical findings, CXR , CT scan
• Blood gas abnormalities(ABG)
- Metabolic acidosis with respiratory compensation
- Respiratory acidosis with Metabolic compensation
• Assessment of oxygenation and ventilation deficits
- A-aO2 gradient, P/F Ratio, PaO2/PAO2 ratio

21. Management
The goal is to ensure a patent airway and provide necessary support .
1. Oxygen administration
- FiO2 % O2 delivered = 21% + [(nasal cannula flow (L/Min) * 3)]
- simple mask, Venturi mask, Partial Rebreather and NRB’s with
reservoir bags

22. 2. Airway Adjuncts
- Maintaining of a patent airway
is a critical step
[A] – Oropharyngeal airway
[B] – Nasopharyngeal airway
[A] [B]
3. Inhaled gases
- It helps > airway obstruction and improving
ventilation
[A] – Heliox(60%) - viscous, less dense, laminar flow
- laryngotracheobronchitis, subglottic stenosis
[B] – Nitric oxide (5-20ppm) – pulmonary vasodilator,
- improves pul. Blood flow and V/Q mismatch

23. 4. Positive pressure respiratory Support
• Non-invasive , is useful in treating both hypoxemic and hypo
ventilatory RF.
• Helps to aerate partially atelectatic, prevent alveolar collapse
and increases FRC
• It improves pulmonary compliance and reduces intra
pulmonary shunting
• CPAP – FiO2 can be adjusted through an Oxygen blender. The
delivery of O2 through high flow nasal cannula helps to wash
out CO2 from naso-pharynx & prevents rebreathing
• Benefits –extrathoracic airway obstruction, < lung compliance
• Potential risk – nasal irritation, hyperinflation &abdominal
distention

24. BiPAP – Bilevel positive airway pressure
• This device allows to set an expiratory PAP and inspiratory PAP
• The additional iPAP during inspiration helps augment tidal volume and
improve alveolar ventilation in low compliance & obstructive lung disease
• Benefits – Children with neuromuscular weakness, diseases of intrathoracic
airway obstructions

25. 5. Endotracheal intubation and mechanical ventilation
• ID = [Age(in years)/4] + 4
• Indications
A. Primary respiratory disorder
1.Severe Hypoxemia (PaO2 <60 mmHg on 60% FiO2)
2.Severe Hypoventilation ( PaCO2 > 50 mmHg )
B. Primary Neuromuscular disorder
- Myopathy, lack of airway protection, Need for sedation
C. Tight control of PaCO2 and pH
- Raised ICP , Severe pulmonary hypertension

26. • Administration of sedative and analgesic
followed by a paralytic agent – facilitates
intubation
• Midazolam, Lorazepam, ketamine,
propofol are commonly used sedatives
• Vecuronium, Rocuronium are paralytic
agents
• CXR should also be obtained to confirm
proper placement of tracheal tube.
Which should lie roughly halfway b/w the
glottis and carina.

27. Mechanical ventilation
• The need to assist lung function , supporting left ventricular performance
and treating intra cranial hypertension
• Mechanical ventilation is also used in patients whose respirations are
unreliable – unconscious patients, neuromuscular dysfunction, and when
deliberate hyperventilation is desired
• The goals are to maintain sufficient oxygenation and ventilation to ensure
tissue viability
• Aim is to protect lungs from damage due to O2 toxicity, Barotrauma,
atelectrauma , volutrauma , and biotrauma

28. Basic concepts of Ventilator management
• Equation of motion
• Baby lung concept
• Open lung concept / Critical opening pressure
• Functional Residual Capacity

29. 1. Equation of Motion
• A pressure gradient is required for air to
move from one place to another
• Normal and Ventilation
• Pressure necessary to move air requires 2
factors
1. Lung elastance
2. Chest wall elastance
• Elastance = P/ V
• Compliance = 1/Elastance [Static process]
• Resistance = P/ Flow [Dynamic process]
• Pressure gradient = V/C + (Flow * R)

30. 2. Baby lung concept
• This concept originated when multiple CT
scan examinations that the aerated tissue
has the dimensions of the lung of a 5-6 yr
old child (300-500gm of aerated tissue)
• ARDS lung is not only stiff but also small
• Functional – Gentle lung ventilation is
needed
• The smaller the baby lung <the potential
for damage and VILI

31. 3. Open lung concept
• Collapsed or atelectatic alveoli require a
considerable amount of pressure to open
• Recruitment
• In disease condition alveoli tend to collapse
• The minimum pressure required to keep
open the lung may cause
1.Barotrauma
2. Volutrauma
• Tidal recruitment – injurious to the lung

32. • Safe zone of ventilation
• Keeping tidal ventilation b/w the upper and
lower Inflection points [PFLEX]
• PEEP – 6ml/kg of tidal volume

34. 4. Functional Residual Volume
• During inspiration – O2 enters alveoli
• During expiration - O2 is being removed by
pulmonary capillary circulation
• FRC – Volume of gas left at the end of the
expiration
• In diseases that decreases FRC – Hypoxia
• Application of PEEP
• Increasing the inspiratory time [Ti]

35. Ways to increase MAP

36. Phases of Mechanical ventilation
• The planning of a ventilatory strategy must consider the 4 phases of
respiratory cycle
1. Initiation of respiration and a variable that is controlled – MODE
2. Inspiratory phase characteristics – pressure and volume delivered
3. Termination of inspiration – CYCLE
4. Expiratory phase characteristics

37. 1. Mode
• The initiation of inspiration may be set to occur at a predetermined
rate and interval regardless of patient effort
• Control mode – breath control is entirely by ventilator
• Support mode – supports the patient inspiratory effort based on set t
. trigger values
• Triggers – flow triggered and pressure triggered

38. Control Modes
1. Intermittent mandatory ventilation [IMV]
- The inspiration is initiated at the set
frequency with timing independent of patient
effort
• In b/w machine delivered breaths, the patient can
breathe spontaneously
• Support – patient’s needs
• To prevent asynchrony - SIMV

39. Assist-control Mode
• In AC mode , each and every breath is triggered by pressure or flow
generated by patient efforts and assisted with either preselected inspiratory
pressure or volume
• On AC mode with backup rate @ 20 breaths /min
• Patient with 15 breaths /min will get 15 assisted + 5 additional breaths
• Patient with 25 breaths / min will get all breaths assisted

40. Control Variable

41. Support Modes
• Pressure- support ventilation(PSV) and
volume support ventilation(VSV) are
designed to support patients spontaneous
respiration
• With PSV initiation is by patient efforts ,
which is then “supported” by a rapid rise in
ventilator pressure up to preselected level
• SIMV+PSV will allow the patient to control
the rate, Vt, and inspiratory time
• Gentle mode of ventilation
• VSV – inspiratory pressure to support
spontaneous breath – preset Vt

43. 2. Inspiratory phase characteristics
• Ti – Inspiratory flow waveform and pressure rise time
can be adjusted
• In PCV – Ti is set in seconds
• IN VCV – TI is set in inspiratory flow ( Volume/ time)
• With increase in Ti – Improves MAP, Higher level of
PaO2
• In VCV – Inspiratory wave form [ ] is adjusted

44. 3. Cycle
• The 2 most commonly used inspiratory
terminating mechanisms in control modes
are 1. Time cycled and 2. Volume cycled
• Time cycled is always pressure limited
• Volume cycled is made pressure limited to
prevent barotrauma
• In PSV – 25% of PIP – flow cycled

45. 4. Expiratory phase manures
• The most useful – PEEP application
• Benefits – 1. Recruit atelectatic lung
2. increase FRC
• Auto PEEP/Air trapping
• Salutary effects include redistribution of
extravascular lung water away from gas
exchanging areas, improved V/Q
relationship and stabilisation of the chest
wall

47. Conventional ventilator settings
• Ti – Time given for inspiration
• Te – Time given for expiration
• I:E ratio – total of 1 sec
• R – No. of breaths/ min
• Tv- Tidal volume
• FiO2 – Fraction of inspired O2
• PIP – Max. pressure used to inflate lungs at
peak of inspiration
• Trig – Amount of air pushed by baby to
machine

48. Patient ventilator asynchrony
1. Triggering the ventilator
2. Selection of appropriate inspiratory time
3. Selection of inspiratory flow pattern
4. Use of support modes
5. Use of sedation and pharmacological paralysis

49. Complications
1. VILI
• In attempting to recruit and maintain FRC, the clinician must be careful
not to over distend alveoli
• Excessive PIP and Vt has to be avoided
• Decreased production and inactivation of surfactant results in
atelectasis and impairment of gas exchange
• Evidence – avoid Vt >/= 10ml/kg and Pplat >/= 30 cm H20 in severe acute
hypoxemic respiratory failure
• Insufficient PEEP

50. 2. Ventilator associated pneumonia [VAP]
• Multifactorial
• Aspiration
• New onset of fever and leukocytosis
• Demonstration of infiltrates by chest radiographs
• How to reduce - Elevation of bed for 30degress and use
of protocol for oral decontamination during mechanical
ventilation
• The regular assessment of extubation readiness and
liberation from mechanical ventilation as soon as
clinically possible

53. Conclusion and key messages
• Pediatric ALI/ARDS is an illness with high mortality and requires excellent
supportive care in PICU
• Severe sepsis and pneumonia – Leading predisposing conditions
• MV should be initiated early
• Lung protective strategies – Low Vt and optimal PEEP
• Recruitment maneuvers
• The impact of prone positioning on mortality is uncertain , it does not
improve oxygenation
• Supportive care including invasive monitoring , restricted fluid management
, attention to MODS and prevention of nosocomial infection are crutial to
improve the outcome

55. References
• Nelson textbook of Pediatrics – 01st South Asia edition
• Nelson textbook of Pediatrics – 21St International edition
• Medical emergencies in children- Meharban Singh – 05th edition
• PALS guidelines
• NCBI