2. MECHANICAL VENTILATION
Ist
Introduced in 1950’s during polio epidemic in the
west.
Normal gas exchange is dependent on two processes.
Oxygenation – deals with the process of gas exchange
with in the lung at alveolar level (external) or at the
tissue level (internal).
Ventilation – deals with the movement of air in and out
of the lungs.
3. GOALS OF MECHANICAL VENTILATION
1. Improve ventilation
2. Reduce the ventilation perfusion mismatch.
3. Reexpand the atelectatic or collapsed lung
segment.
4. Reduce the work of breathing.
4. COMMON INDICATIONS FOR MECHANICAL
VENTILATION
1. Respiratory failure
Inadequate oxygenation – PaO2 < 60 mmHg
CO2 Retention (ventilation abnormalities)
PaCO2 50 mmHg or more
2. Cardiovascular- Myocardial failure
3. Neurological disorder- decreased ventilatory
drive, increased ICP
4. Respiratory paralysis - Neuromuscular disorder,
LGB syndrome, snake bite,poisoning
5. BASIC TERMINOLOGY
Compliance – Stiffness of chest.
Change in volume per unit change in pressure.
Expressed in lit/cm of H2
O.
Resistance – Pressure difference between mouth and alveoli.
Most important factor – Radius of the airway.
Functional Residual capacity – Volume of gas that is present
in the lungs at the end of expiration. Normal FRC 30ml/kg.
Closing capacity – Refers to volume of gas present in the
lung at which small conducting airways begin to collapse.
Tidal volume – Volume of gas that flows in and out during
quite breathing. 6-8 ml/kg.
Cont……
6. Minute ventilation – Tidal volume X rate.
I.E. Ratio- Normal 1:2 to 1:3
PIP- Highest pressure during the Inspiratory time.
Positive end expiratory pressure – (PEEP)- Minimum positive pressure in
airways during expiration.
It keep alveoli open at the end of expiration.
Normal PEEP ( Physiological PEEP) is 2-3 cmH2
O
FIO2
(Fractional inspired oxygen) concentration - 0.21-1.00
Mean Airway pressure (MAP) – Average positive pressure generated in the
lungs throughout the respiratory cycle.
K(Ti x PIP)
MAP = + PEEP
Ti + Te
8. MODES OF VENTILATION
Spontaneous Mode – Patients is breathing on his own-
CPAP (continuous positive airway pressure)
PSU (pressure support ventilation).
Controlled mechanical ventilation (CMV)- ventilation controls all the
ventilation while patient has minimal or no respiratory efforts. It delivers
pre selected ventilatory rate, tidal volume and inspiratory flow rate.
Indication – Apnea, depression of CNS, neuromuscular paralysis
significant fatigue of the ventilatory muscles.
Continuous positive pressure ventilation (CPPV) -It delivers a positive
pressure breathing. Airway pressure never return to zero.
Cont….
9. Assisted mechanical ventilation
It is patients triggered positive pressure ventilation, used during weaning
of patients from CMV.
Assist control ventilation
Assisted Mechanical ventilation + CMV
The ventilator may be triggered by the patients, spontaneous inspiratory
effort or by a timing devise whichever comes first.
Intermittent Mandatory ventilation (IMV) - delivers a preset number of
controlled breaths at preset intervals. In between these breaths patients is
allowed to breath spontaneously.
Pressure controlled
Volume controlled
Synchronized Intermittent mandatory Ventilation (SIMU)
- Pressure support
- Volume support
- The ventilation delivered mandatory breath is synchronized to begin with patients
own breathing efforts.
10. INITIAL VENTILAOR SETTINGS
1. 1. Rate – Physiological norm for age
2. Select VT
~6-8ml/kg or PIP~15 CM H2
O (Normal lungs)
20-25 cmH2
O (Moderate disorder)
25-30 cm H2
O (Severe disease)
3. I:E ratio – Begin with 1:2. Initial T1
may be 0.4-0.5 sec in a young infant
&higher value is chosen for older children.
4. In obstructive disease use longer Te
and avoid prolonged Ti
.
5. Assess chest expansion and breath sounds to determine adequacy of
ventilation.
6. Measure PaCO2
– Adjust VT
/PIP or rate to maintain PaCO2
between 35-45
mmHg.
1
11. CARE OF PATIENT ON VENTILATOR
1. Repositioning of patient 2-4 hrly.
2. Change of ventilator tubing periodically.
3. Filling up of humidifier with sterile water daily.
4. Wash compressor filter daily.
5. Culture of respiratory endotracheal secretions daily to
monitor the microbial flora.
6. Majority of ventilated children may be fed enterally
via a nasogastric tube.
Cont….
12. 7. Sedation and muscle relaxant – Particular attention is needed in
following situations
-Requirement for high airway pressure
-Critically inadequate oxygenation (ARDS)
-Ventilator intolerance in anxious patient.
-Need for controlled hyperventilation .
Before switching to muscle relaxant (Pancuronium,vecuronium)
adequate sedation and analgesia should be achieved with help of diazepam
( 0.2 mg/kg i.v.) and morphine (0.1-0.2 mg/kg i.v.).
13. Monitoring
Physical examination:-Breathing rate,Signs
of resp.distress,B.P.,HR.Skin color,Chest
movement,
Invasive monitoring:-ABG analysis
Non invasive monitoring:-Chest
radiography,ECG.Pulse
oxymetry,Capnography.
14. MONITORING
1. ABGs & DO2
calculation within 20-30 min of
initiation
and after a change in setting and every 6 hourly.
2. Chest x-ray – Once daily or in 2 days.
3. I/O measurements – 8 hourly.
4. Electrolytes, urea, coagulation parameters
5. Nutritional support – Enteral and parenteral
6. Nutritional status and wt.
15. CLINICAL AND LABORATORY INDICES OF
ADEQUATE VENTILATION
Clinical Parameters
- Pink color
- Adequate chest expansion
- Absence of retractions
- CFT < 2 sec
- Normal blood pressure
Pulse Oxymetry
- O2 saturation 90-95%
Blood gases
- PaO2 - 50-80 mmHg
- PaCO2 - 40-50 mmHg
- pH - 7.35-7.45
16. Blood gas abnormalities and changes in the ventilator settings to
correct them
S.no Blood gas
abnormality
Corrective measures
FiO2
Rate PIP PEEP Ti
1. Hypercapnea
(PaCO2
> 50mm Hg)
- Increased Increased - -
2 Hypocapnea
(PaCO2
< 35mm Hg)
- Decreased Decreased - -
3 Hyperoxia (PaO2
> 100mm Hg)
Decreased - Decreased Decreased Decreased
4 Hypoxia (PaO2
<50mmHg)
Increased - Increased Increased Increased
17. WEANING FROM VENTILATOR
Criteria for weaning
Clinical –
1. Stable pulmonary status without evidence of pneumonia, severe
infection or bronchospasm.
2. Satisfactory muscle power.
3. Cardiovascular stability – No need for vasoactive drugs.
4. Afebrile.
18. Ventilation and oxygenation parameters
1. Tidal volume > 5 ml/kg
2. Vital capacity > 10 ml/kg
3. PaO2
> 60 mmHg at FiO2
< 0.4
4. Maximum voluntary ventilation > 2 x minute volume
5. PaO2
/ FiO > 200
6. Shunt fraction < 15%
7. VD
/VT
ratio < 0.6
8. FRC > 50% predicted
9. Minute ventilation > 180 ml/kg/min for PaCO2
of 40 mmHg
19. VENTILATOR EMERGENCY
D – Displacement of the tube
O – Obstruction of the tube
P – Pneumothorax
E – Equipment failure
Sudden fall of SPO2,Cyanosis,Pallor, Fall in BP. CFT,Bradycardia.
20. COMPLICATIONS OF VENTILATOR
Related to airway pressure and lung volume –
A.Barotrauma/Volutrauma – Pneumonia, Pneumothorax,
pneumopericardium, subcutaneous emphysema.
B.Decreased cardiac filling
C.Pulmonary parenchymal damage
D.Acid base disturbances
2. Related to Endotracheal Tube –
A.Tracheal, laryngeal & pharyngeal mucosal damage especially with
intubation > 3 weeks
B.Sinusitis
C.Laryngeal edema, subglottic stenosis
Cont….
22. DISEASE SPECIFIC INITIAL VENTILATOR
SETTINGS
PNEUMONIA
VT
- 6-8 ml/kg
PIP - 20-25 cm H2
O
PEEP - 4-5 cm H2
O
Rate - 40-50/min (Infant)
- 30-40 / min (older children)
I:E ratio - 1:2
ASTHMA/BRONCHIOLITIS
Permissive hypercapnea
PEEP is kept low to prevent air trapping
VT
- 6-8 ml/kg
PIP - 20-25 cm H2
O
PEEP - 3-4 cm H2
O
Rate 30/min (Infant)
20 / min (older children)
I:E ratio - 1:2 to 1:3
Cont….
23. ARDS
Oxygenation is maintained using high PEEP
VT
- 4-6 ml/kg
PEEP - 5-10cm H2
O
Rate 40/min (Infant)
20-30 / min (older children)
I:E ratio - 1:2 to inverse ratio
NORMAL LUNG AS IN SHOCK,.FLACCID PARALYSIS
IMV mode
In septic shock use of higher FiO2
upto 1 initially
VT
- 6-8 ml/kg
PEEP - 3-4 cm H2
O
Rate 40/min (Infant)
20-30 / min (older children)
I:E ratio - 1:2 to 1:3
24. NEWER MODALITIES
HIGH FREQUENCY VENTILATION (HFV)
This is mode of assisted ventilation, which employs
small tidal volume (1-3ml/kg body weight) and much higher
frequencies. It has adequate minute ventilation with relatively
low mean airway pressure.
Uses –
1. RDS with PPHN
2. RDS, HIE where conventional ventilation failed.
3. Pulmonary air leaks.
Complications of HFV –
1. Inadvertent PEEP
2. ICH
3. Necrotising tracheobronchitis
25. ISOLATED LUNG VENTILATION
Single lung ventilation has been increasingly used in
video assisted ,thoracoscopic intervention as well as open
thoracic surgical procedure.
HELIOX VENTILATION- HELIUM+OXYGEN
Has reduced density and hence lower resistance
in turbulent flow and more favorable diffusion.
PARTIAL LIQUID VENTILATION
Perflubron a highly oxygen soluble emulsion
It is heavy distribution to dependent lung regions after instillation.
This open and stabilizes collapsed alveolar units.
It also functions as a surfactant.
Permissive hypercapnia :-mantaining a
high level of PaCO2(45-55 mmHg),safe in
RDS,Status asthmaticus & Neonatal
resp.failure
