Aim

• To optimize gas exchange
• Help patient work of breathing
• Minimize ventilator-induced lung injury

Objectives of Mechanical Ventilation 

• Improved pulmonary gas exchange

• Relief of respiratory distress 

• Management of pulmonary mechanisms 

• Provide airway protection

• Provide general cardiopulmonary support

Indications of Mechanical Ventilation

1 Respiratory failure

• Apnea
• Respiratory arrest
• Inadequate ventilation
• Inadequate oxygenation.

2 Cardiac insufficiency

3 Neurologic dysfunction 

• Central hypoventilation
• Apnea
• GCS< 8
• Inability to protect airway

Changes that can be made in a ventilator

• RR- Respiratory rate
• PIP- Peak inspiratory pressure

• PEEP- Peak end expiratory pressure
  • It is used to prevent alveolar collapse at the end of inspiration, to
  • recruit collapsed lung spaces or to stent open floppy airways
• Tidal volume

Choosing the Mode

1. Aim to Control every breath in heavy sedation 
2. Consider complete muscle relaxation in difficult ventilation
3. Use SIMV when patient likely to breathe spontaneously.
4. The common modes are volume limited and pressure limited. They are determined as below
   1. • Volume limited: -preset tidal volume
   2. • Pressure limited:- preset PIP
5. Start Fi02- at 100% (Or 60% as applicable)  and quickly wean down to minimum to maintain saturations
6. Set I:E ratio – at 1:2-1:3.
7. Use Higher inspiratory times to improve oxygenation.
8. Lower rate and higher expiratory time-1:3-1:4 may be needed in asthma
9. Tigger Sensitivity- set it at 0 to -2. (Setting above zero is too sensitive, and negative setting means the patient does more breathing)
10. Volume Limited- Tidal Volume 8-10ml/kg .If leak present around ET tube, set initial tidal volume to 10-12ml/kg.

Maintenance of Ventilation

• Based on blood gases and oxygen saturations.
• Do not make more than 1 alteration at any one time.

For oxygenation

Adjust 

• FiO2
• PEEP
• Inspiratory time
• PIP
• Increase MAP.

Treatment in Special circumstances

Hypoxemia-

1. Increase FiO2 and MAP. 
2. In volume limited mode- Increase tidal volume or/ and PEEP or/ and inspiratory time.
3. In pressure limited mode- Increase PIP or/ andPEEP or/ and Inspiratory time.

Other measures

• Normalize cardiac output(fluids and inotropes)
• Maintain normal Hb and hematocrit
• Maintain normothermia
• Deepen sedation or paralysis in difficult cases 

In worsening cases

Get Chest XRay 

• Look for air leak ( especially if increasing PEEP decreased saturation)
• Suspect low cardiac output due to tamponade effect of high PEEP
• Look for pneumothorax.

Common causes of hypoxia 

Hypoventilation

• Dead space ventilation
• Increased CO2 production
• Hyperthermia,
• ET Tube issues like –  block, malposition, kink, circuit leak, ventilator malfunction

Hypercarbia

General measures

• Increase sedation
• Change endotracheal tube if blocked, kinked, malplaced or out, check placement with X ray chest.
• Fix leaks in the circuit
• Maintained by keeping Hct >30%.

Permissive Hypercapnia-higher paCO2 are acceptable in exchange for

limited peak airway pressures, as long as ph>7.25

Permissive Hypoxemia PaO2 of 55-65; SaO2 88-90% is acceptable in exchange for limiting FiO2 <60% , as long as there is no metabolic acidosis.

In  volume limited Mode

• Increase tidal volume
• In rate

Increase expiratory time to >1:3 (In asthma)

In pressure limited Mode

• Increase PIP
• Decrease Positive End Expiratory Pressure (PEEP)
• Increase rate
• Decrease dead space (increase Cardiac Output, decrease PEEP, vasodilator, shorten ET tube)

TROUBLESHOOTING

Patient fighting ventilator with desaturation : Consider DOPE

D-Displacement

• Check tube placement 

O-Obstruction

• Is the chest rising?
• Breath sounds present and equal? 
• Changes in examination?
• Examine circulation:?Shock, ?Sepsis.

P-Pneumothorax

• Check ABG
• Check Saturation
• Chest XRay for pneumothorax and other lung conditions

E-Equipment failure 

• Examine ventilator
• Check ventilator circuit/humidifier

Consider increasing sedation/muscle relaxation

Consider nosocomial infection

WEANING FROM MECHANICAL VENTILATION

Consider weaning when 

• FiO2 requirement is down to 40%
• Improvement in secretions
• Improvement in Chest X rays
• Improvement in clinical condition
• Muscle relaxant and Sedative is stopped 

Method of weaning

• Decrease FiO2 to keep SpO2>94,
• Decrease SIMV rate to 10 (reduce by 3-4breaths/min).
• Decrease the PIP to 20cm of water by reducing 2cm H2O each time
• Decrease tidal volume to no less than 5ml/kg to prevent atelectasis 

Ventilator rate and PIP can be exchanged alternately 

If at any time patients oxygen requirement increases greater than 60% or spontaneous ventilation is fast or distressed with accessory muscle use, patient gets agitated or lethargic, hypercarbia on ABGs, pause weaning and increase support level.

EXTUBATION CRITERIA

Clinical assessment 

• Adequate cough 
• Absence of excessive tracheobronchial secretion 
• Resolution of disease acute phase for which the patient was intubated
• SIMV rate of < 10 breaths per minute ( occasionally done at  20)
• Some will need pressure support 5-10 mm Hg PEEP. Can switch to CPAP if PEEP required provided child is breathing by itself
• Presence of airway reflexes
• Minimal secretions
• Patent upper airway
• Minimal O2 requirement <30% with SpO2 >94 

Objective measurements 

• Clinical stability 
• Stable cardiovascular status 
• (systolic BP 90–160 mmHg, no or minimal vasopressors) 

Stable metabolic status 

• Adequate oxygenation Sa,O2 .90% on FiO2 of < 0.4
• PEEP < 8 cmH2O 
• Adequate pulmonary function 
• No significant respiratory acidosis 
• Adequate mentation (No sedation or adequate mentation on sedation 
• Awake patient
• Adequate muscle tone(squeeze examiners fingers/vigorous cough), Minimal/no inotropic support, normal electrolytes and no fluid overload 

Extubation procedure

Prior Extubation

• In Prolonged intubation give dexamethasone 24hrs prior to planned extubation at 0.15mg/kg and to be continued
• Keep NPO 4hrs before planned extubation

Just before extubation

• Suction endotracheal tube and deflate cuff if using a cuffed tube.
• Suction the oral cavity and nostrils.
• Suction the NGT before removing to empty the stomach
• Nasal cannula to be taped to the face before extubation
• Keep oxygen by face mask ready. Correct size mask and bag 
• Keep laryngoscope and correct size ETTube ready.
• Nebulisation with beta stimulant/adrenaline post extubation
• Intravenous steroids dexamethasone 0.6mg/kg iv(maximum dose of 12mg) stat
• Intravenous frusemide may be needed
• Keep CPAP ready with settings
• Blood gas 20mins after extubation
• Post extubation CXR if clinically indicated by desaturation or increased work of breathing
• Keep ventilator to be on standby at least 24hrs post extubation.
• Anticipate extubation failure in all patients and parents should be made aware earlier on so that there is no disappointment.

COMPLICATIONS OF VENTILATION

1. Barotrauma/ volutrauma: 
   1. PIE
   2. Pneumothorax
   3. Pneumopericardium
   4. Pneumoperitoneum
   5. Subcutaneous
   6. Emphysema.
2. Decreased cardiac filling and poor perfusion.
3. Organ dysfunction , renal, hepatic, and CNS.
4. Pulmonary parenchymal damage.
5. Tracheal mucosal swelling, ulceration..
6. Laryngeal edema, subglottic stenosis.