SEMINAR ON MECHANICAL VENTILATION Guide Dr. G.Singh (MS) Co-Guide Dr. A.M. Lakra (MD) -Rajan Kumar
Cornerstone for intensive care medicine
Ventilate is derived from Latin word “ventus” meaning wind.
Ventilation is movement of air into and outside the body
The ventilators must overcome the pressure generated by the elastic recoil of the lung at end inspiration plus the resistance to flow at the airway.
Ventilators provide infusion of a blend of air or oxygen into the circuit.
In 1543, Vesalius demonstrated the ability to maintain the beating heart in animals with open chest.
In 1780, such technique were first applied to humans
In 1887, fell-o-dwyer apparatus was used for translaryngeal ventilation via a bellows.
In 1928, the drinker–Shaw iron lung based on negative pressure ventilation
From 1930-1950 – such machines were the mainstay in ventilation of victims of polio epidemics
Inspiratory Reserve Volume
Expiratory Reserve Volume
Inspiratory Capacity (IRV + TV)
Functional Residual Capacity (ERV + RV)
Vital capacity (IRV + TV + ERV)
Total Lung Capacity (IRV + TV + ERV + RV)
Ventilators are specially designed pumps that can support the ventilatory function of the respiratory system and improve oxygenation through application of high oxygen content gas and positive pressure.
Pneumotachometer, valves & solenoids
Chamber for nebulising drug
Achieve and maintain adequate pulmonary gas exchange
Minimise the risk of lung injury
Reduce patient work of breathing
Optimise patient comfort
1. ICU Ventilators
The condition of lung is poor
2. Anaesthetic ventilators
The condition of lung is good
3. Transport ventilator
The ventilator is compact and used for transportation of victim/patients from one site to other
(a) High frequency ventilator
(i) High frequency positive pressure ventilator
(ii) High frequency jet ventilator
(iii) High frequency oscilitation ventilator
A. Positive pressure ventilation (PPV)
(a) Non invasive PPV
(i) Nasal mask
(ii) Facial mask
These has less complications and as effective as invasive ventilators
(b) Invasive PPV
(i) Nasotracheal tube
(ii) Oro tracheal tube
B.Negative pressure ventilation
Iron lung machine
The machine creates a negative pressure to expand the chest wall so that the lungs can expand inside it with the negative intrapleural pressure.
Gas flows only down the pressure gradient, i.e. from areas of high pressure to low pressure.
Exhalation is a passive process, ventilators expend energy only during inhalation
Mechanical ventilation is produced through the interaction of only 5 variables
inspiratory: expiratory (I:E) ratio
Improve O2 &CO2 gas exchange
Prevent progressive hypercapnia
Reverse acute respiratory acidosis
Improve ventilation distribution
Prevent and reverse lung collapse
Reduce venous admixture
Assist respiratory muscle
Decreased O2 cost of breathing
Relieve resp. distress
Improve lung compliance
Increase alveolar recruitment
- Return lung to resting lung volumes
On the basis of blood gas analysis
1. PO2 <50mmHg on room air
<60mmHg on oxygen support (FIO2 >50%)
2. PCO2 >50mmHg
3. pH <7.25
4. PO2/FIO2 <250mmHg
5. p (A-a ) O2 gradient >350 mmHg on 100% O2.
On the basis of pulmonary function
Resp. Rate >35/min
Vital capacity <15ml/kg
Dead space volume (VD/VT) >0.6 (60%)
Tidal volume <5ml/kg
Basic physics related to mechanical ventilation
Paw = flow× resistance + volume ∕ compliance + PEEP
Pressure at point B is equivalent to the alveolar pressure and is determined by the volume inflating the alveoli divided by the compliance of the alveoli plus the baseline pressure (PEEP).
Pressure at point A (equivalent to airway pressure measured by the ventilator) is the sum of the product of flow and resistance due to the tube and pressure at point B.
Flow, volume and pressure are variables while resistance and compliance are constants.
It follows from the relationship between pressure, flow and volume that by setting one of pressure, volume or flow and the pattern in which it is delivered which includes the time over which it is delivered the other two become constants.
It also follows that it is not possible to present more than one of these variables at a time.
Time cycled – these cycle to expiration once a predetermined time is elapsed since inspiration.
Tidal volume is determined by set inspiratory flow and inspiratory time
These cycled to expiration once a predetermined pressure is reached, so if there is leak in circuit the predetermined pressure will not reached and pt. will remain in inspiration conversely, if airway pressure is high, bronchospasm or tube kinking there will be premature end of inspiration and patient can be hypoventilated.
Volume cycled – Inspiration is terminated when a preset tidal volume is delivered.
So theoretically, the patient cannot be hypoventilated even if the lung compliance (airway pressure) changes but actually this is not the case, a portion of tidal volume is lost (120-150ml) in the ventilator breathing circuit and if patient’s pulmonary compliance is decreased (peak inhalation pressure will increase) the delivered tidal volume can further be decreased.
The accurate, tidal volume reaching to patients can only be calculated by putting a spirometer at the endotracheal tube.
e.g. most commonly used in ICUs
Disadvantage – they deliver fixed tidal volume so if airway pressure becomes high and still same tidal volume is be delivered the chances of barotrauma are increased.
Dual control – can work in both volume control and pressure control mode and can switch over from one mode to other depending on requirements.
Modes of mechanical ventilations
Characterized by three variables
The parameter used to initiate or ‘ trigger ’ a breath
The parameter used to ‘ limit ’ the size of breath, and
the parameter used to terminate inspiration or ‘ cycle ’ the breath.
In controlled ventilation modes – time triggered Inspiratory phase is concluded once a desired volume, pressure or flow is attained but the expiratory time (Et) will form the difference between the inspiratory time (It) and the preset respiratory cycle time.
In Assist mode – the ventilator is pressure or flow triggered
The magnitude of the breath is controlled or limited by one of three variables
in this mode patient’s own effort is nil. Only ventilator is delivering the preset tidal volume at preset frequency
Assist controlled ventilation(AC): in this mode assist means the ventilator supplementation of patient initiated breath (which itself doesnot have adequate tidal volume) and control means back up rate which is set up by clinician.
Synchronized intermittent mandatory ventilation (SIMV ): in this mode ventilator will deliver only between patient’s efforts or to coincide with the beginning of spontaneous effort.
Advantages of SIMV over CMV
Less haemodynamic depression
Patient on CMV/IPPV need heavy sedation or muscle relaxant.
Less V/Q mismatch
No sense of breathlessness between ventilatory cycles
More rapid weaning
1.increased work of breathing can cause muscular fatigue.
2.increased chances of hypocapnia (due to hyperventilation)
Positive end expiratory pressure (PEEP)
In thoracic surgery to minimize postoperative bleeding.
Physiological PEEP (in normal intubated patient to prevent atelectasis)
Mechanism of PEEP
Positive pressure given at end expiration prevents alveoli to collapse and small airways to close. So more time is available for gaseous exchange
Side effects of PEEP
Hypotension and decrease in cardiac output: PEEP compresses venules in alveolar septa leading to decreased venous return. So optimal PEEP is the value which maintain oxygen saturation >90% without decreasing the cardiac output significantly.
Increased pulmonary artery pressure and right ventricular strain: it is due to compression of capillaries in alveolar septa.
Increased dead space because of overdistension of normal alveoli.
Increased pleural and mediastinal pressure.
These increased pressures can cause pulmonary barotrauma
Inverse ratio ventilation (IRV): ratio of inspiration to expiration is reversed(2:1, while normal ratio is 1:2). Prolonged inspiration will maintain positive pressure. So more or less it acts like PEEP. It is better than PEEP and there is even distribution of ventilation.
Pressure support ventilation (PSV ): if a patient is on spontaneous respiration with adequate frequency but not adequate tidal volume,this mode is helpful in increasing the tidal volume.
Pressure controlled ventilation (PCV): in this mode pressure is preset and ventilator terminates inspiration once preset pressure is achieved. So if airway pressure varies patient is prone for ventilation but advantage is that chances of barotrauma is less and there is choice of extending inspiratory time, facilitating better oxygen.
BIPAP : bipap means positive pressure both during inspiration and expiration. Typical setting is 8-20 cm H2O positive pressure during inspiration and 5 cm H2O during expiration.it is combination of PSV and PEEP.
Airway pressure release ventilation (APRV) applied to patient on CPAP where there is periodic release of CPAP to decrease the incidence of barotrauma and hypotension.
High frequency ventilation : this mode is applicable in conditions in which adequate tidal volume cannot be delivered. So minute volume is maintained by high frequency.
TYPES OF WAVES FORMS
Setting of ventilator
Trigger sensitivity (for assist mode)
-1 to -2 cmH2O
Normal ABG Values
7.35 - 7.45
35 – 45 mmHg
70 – 100 mmHg
93 - 98%
22 – 26 mEq/L
-2.0 to 2.0 mEq/L
Ventilator parameters adjustment according to blood gases _____ PO2 _____ PO2 ____ ____ PCO2 ____ ____ PCO2 Ti FiO2 RATE PEEP PIP Goals
Level of activity
Response to stimulus
Movement of chest
Adequacy of mechanical breath
Capillary gas determination
Monitoring of O2 & CO2 status
Ti & I:E Ratio
Trends of Ventilator Parameters
Adequacy of Circulation
When to do Chest X-ray ?
At the start of ventilation
Before surfactant administration
After ET tube change
Prior to extubation
ET tube culture
Humidification & warming of ventilator circuit gases
Position of patient
Fluid & electrolytes
Sedation in Mechanically Ventilated Patients
Maintenance of Sedation
Titrate dose to ordered scale
Motor Activity Assessment Scale MAAS
Sedation-Agitation Scale SAS
Modified Ramsay Sedation Scale
Rebolus prior to all increases in the maintenance infusion
Daily interruption of sedation
NEUROMUSCULAR BLOCKING AGENTS
Difficult to asses adequacy of sedation
Polyneuropathy of the critically ill
Use if unable to ventilate patient after patient adequately sedated
Have no sedative or analgesic properties
Is it working ?
Look at the patient !!
Listen to the patient !!
Pulse Ox, ABG, EtCO 2
Chest X ray
Look at the vent (PIP; expired TV; alarms)
When in doubt, DISCONNECT THE PATIENT FROM THE VENT, and begin bag ventilation.
Ensure you are bagging with 100% O2.
This eliminates the vent circuit as the source of the problem.
Bagging by hand can also help you gauge patient’s compliance
Airway first: is the tube still in? (may need DL/EtCO2 to confirm) Is it patent? Is it in the right position?
Breathing next: is the chest rising? Breath sounds present and equal? Changes in exam? Atelectasis, bronchospasm, pneumothorax, pneumonia? (Consider needle thoracentesis)
Circulation: shock? Sepsis?
Well, it isn’t working…..
Right settings ? Right Mode ?
Does the vent need to do more work ?
Patient unable to do so
Underlying process worsening (or new problem?)
Does the patient need to be more sedated ?
Does the patient need to be extubated ?
Patient - Ventilator Interaction
Vent must recognize patient’s respiratory efforts (trigger)
Vent must be able to meet patient’s demands (response)
Vent must not interfere with patient’s efforts (synchrony)
Improving Ventilation and/or Oxygenation
can increase respiratory rate (or decrease rate if air trapping is an issue)
can increase tidal volume/PAP to increase tidal volume
can increase PEEP to help recruit collapsed areas
can increase pressure support and/or decrease sedation to improve patient’s spontaneous effort
Weaning from ventilator
It means discontinuing the ventilatory support.
1. pO2 >60 mm Hg (or oxygen saturation > 90%) on FIO2 <50% and PEEP <5mmHg.
2. pCo2 <50 mmHg
3. Respiratory rate <20/min
4. Vital capacity >15ml/kg
5. VD/VT <0.6
6. Tidal volume > 5ml/kg
7. Minute ventilation <10 litres/min
8. Inspiratory pressure <-30 cm H2O
9. rapid shallow breathing index (RSBI) should be <100
= respiratory rate (breaths/min)/tidal volume (in litres)
10. Arterial pH is normal
11. Normal cardiac status
12. Normal electrolytes
13. Adequate nutritional status
Method of weaning
Although weaning process vary from patient to patient and is possible to wean patient in any mode of ventilation except control mode ventilation
Pulmonary (ventilator assoc. pneumonia)
iv cannula related
complications due to prolonged intubation
Laryngeal ulcer and granuloma
cardiovascular: right ventricular strain or even rt ventricular failure
liver and kidney dysfunction due to decreased cardiac output