2. Learning objectives
• Indications of ventilator support
• Basic Ventilator Parameters
• Modes of ventilation
• Troubleshooting ventilator for simples issues
• Basics of NIV
3. Mechanical ventilation
Mechanical ventilation is a form of life support.
A mechanical ventilator is a machine that takes over
the work of breathing when a person is not able to
breathe enough on their own.
4.
5. Indications of mechanical ventilation
• Alveolar filling processes – Pulmonary edema, Tumour
• Pulmonary vascular disease – Pulmonary embolism, amniotic
fluid embolism
• Central airway obstruction – Tumour, tracheal stenosis, Laryngeal
angioedema
• Distal airway obstruction – AEBA/AECOPD
• Hypoventilation
a) Decreased Central Drive - GA, Drug overdose
b) Peripheral Nervous/Resp. Muscle dysfunction – Myasthenia
gravis, GBS, cervical quadriplegia
c) Chest wall & pleural disease – pneumothorax, flail chest
• Increased ventilatory demand – severe sepsis, septic shock,
severe metabolic acidosis
6.
7. Basic Ventilator Parameters
• Tidal Volume
• Frequency / Respiratory rate
• FiO2
• PEEP
• Flow rate
• I:E ratio
• Trigger
• Mode
8.
9. Tidal Volume
• the lung volume representing the
normal volume of air displaced between normal
inhalation and exhalation when extra effort is not
applied
• 6-8ml/kg
• ARDS, low tidal volume ventilation (4-8ml/kg)
10. Frequency
• Number of breaths per min
• 12-16/min
• > 20/min, associated with auto-PEEP
11. FiO2
• Initial, set at 100%
• Adjust after ABG, aim PaO2 80 to 100mmHg
• Best keep below 50% to avoid oxygen induced lung
injury
12. Positive end-expiratory pressure
(PEEP)
• Reinflates collapsed alveoli and maintain inflation
during exhalation
• Increases FRC, useful to treat refractory hypoxemia
• Initial PEEP : 5 cm H2O
13. Flow rate
• Peak flow rate: max flow delivered by ventilator
during inspiration
• Inspiratory flow needs to be sufficient to overcome
pulmonary and ventilatory impedance
• 60 L /min
14. I:E Ratio
• Usually, 1: 2 to 1:4
• Larger I:E ratio, possibility of air trapping, auto-
PEEP
• Inverse I:E ratio, to correct refractory hypoxemia in
ARDS patients
18. Volume-limited ventilation
• Aka volume-controlled/volume-cycled ventilation
• We set the Tidal Volumes, peak flow rate, RR, PEEP, Fi O2,
but
Airway pressures (peak, plateau, and mean) varies
Pressure-limited ventilation
• Aka pressure-cycled ventilation
• We set the inspiratory pressure, I:E ratio, RR, PEEP, Fi O2,
but
Tidal volume varies
• Peak airway pressure = IP + PEEP is a constant
19. Volume-limited ventilation
• Controlled mechanical ventilation (CMV): minute ventilation is
based on set RR & TV, patient does not initiate additional breath
• Assist control (AC): minute ventilation is based on set RR & TV,
plus patient’s initiated breaths. Each patient-initiated breath
receives the set tidal volume from the ventilator.
• Intermittent mandatory ventilation (IMV): same as AC except
patients increase the minute ventilation by spontaneous
breathing, rather than patient-initiated ventilator breaths.
• Synchronised intermittent mandatory ventilation(SIMV): variation
of IMV, in which the ventilator breaths are synchronized with
patient inspiratory effort
20. Pressure-limited ventilation
• Pressure controlled ventilation similar to CMV
• Pressure-limited assist control (triggering additional
ventilator-assisted, pressure-limited breaths.)
• pressure-limited intermittent mandatory
ventilation (IMV) or synchronized intermittent
mandatory ventilation (SIMV) (increase the minute
ventilation by initiating spontaneous breaths.)
21.
22. Pressure support ventilation (PSV)
• a flow-limited mode of ventilation that delivers
inspiratory pressure until the inspiratory flow
decreases to a predetermined percentage of its
peak value. This is usually 25 percent
• Set IP, PEEP, FiO2
• No RR, patient triggers each breath
23. CPAP
• delivery of a continuous level of positive airway pressure.
• functionally similar to PEEP.
• no additional pressure above the level of CPAP is provided
• patients must initiate all breaths.
• Indications: OSA, cardiogenic pulmonary edema, obesity
hypoventilation syndrome
24. Bilevel Positive Airway Pressure
(BPAP)
• used during noninvasive positive pressure ventilation
(NPPV)
• delivers a preset inspiratory positive airway pressure (IPAP)
and expiratory positive airway pressure (EPAP)
• The tidal volume correlates with the difference between the
IPAP and the EPAP.
• Bigger difference between IPAP & EPAP, bigger is the TV
25. Airway Pressure Release
Ventilation (APRV)
a high continuous positive airway pressure (P high) is
delivered for a long duration (T high) and then falls to a lower
pressure (P low) for a shorter duration (T low)
26. Airway Pressure Release
Ventilation (APRV)
• transition from P high to P low deflates the lungs and
eliminates carbon dioxide.
• Alveolar recruitment is maximized by the high
continuous positive airway pressure
• difference between P high and P low is the driving
pressure
• T high and T low determine the frequency
• Spontaneous breathing is possible at both P high and P
low
27. APRV
When do we use it?
- No universally accepted indications
- APRV, to recruit alveoli and improve oxygenation
- Contraindications: severe obstructive airway
disease or high ventilatory requirement
28. Initial setting
• Mode : SIMV / VC / PC
• Fi O2 0.5
• VT 6-8ml/kg
• RR 15
• PEEP 5cm H2O
• IP 5cmH20
34. Indications of NIV
• Conditions known to respond to NIV:
1. AECOPD with hypercapnia acidosis
2. Cardiogenic pulmonary edema
3. Acute hypoxemic respiratory failure
4. Prevent post-extubation respiratory failure
35. Contraindications of NIV
●Cardiac or respiratory arrest
●Inability to cooperate, protect the airway, or clear secretions
●Severely impaired consciousness
●Nonrespiratory organ failure that is acutely life threatening
●Facial surgery, trauma, or deformity
●High aspiration risk
●Prolonged duration of mechanical ventilation anticipated
●Recent esophageal anastomosis
36. Mode of ventilation
• Assist control: get a guaranteed minimal minute
ventilation
• PSV: maximize patient comfort and synchrony
• CPAP: use for patients with acute respiratory failure
due to cardiogenic pulmonary edema
37. What’s next?
• Monitoring for success or failure?
- Any improvement of pH & PaCO2 after 1-2hours
- Inability to tolerate the interfaces, worsening
oxygenation, inability to clear secretions, agitation,
worsening encephalopathy
• Complications: Local skin damage, eye irritation,
sinus pain, mild gastric distension
Obsolete, used in 1920 for polio, muscular failure, muscular dystrophy
SIMV and AC are the most frequently used forms of volume-limited mechanical ventilation [5]. Possible advantages of SIMV compared to AC include better patient-ventilator synchrony, better preservation of respiratory muscle function, lower mean airway pressures, and greater control over the level of support [6]. In addition, auto-PEEP may be less likely with SIMV. In contrast, AC may be better suited for critically ill patients who require a constant tidal volume or full or near-maximal ventilatory support.
SIMV and AC are the most frequently used forms of volume-limited mechanical ventilation [5]. Possible advantages of SIMV compared to AC include better patient-ventilator synchrony, better preservation of respiratory muscle function, lower mean airway pressures, and greater control over the level of support [6]. In addition, auto-PEEP may be less likely with SIMV. In contrast, AC may be better suited for critically ill patients who require a constant tidal volume or full or near-maximal ventilatory support.
The work of breathing is inversely proportional to the pressure support level, provided that inspiratory flow is sufficient to meet patient demand [13,14]. In other words, increasing the level of pressure support decreases the work of breathing. The work of breathing is also inversely proportional to the inspiratory flow rate. Increasing the inspiratory flow rate shortens the time until the maximal airway pressures are achieved, which decreases the work of breathing
Potential uses — PSV seems particularly well suited for weaning from mechanical ventilation because it tends to be a comfortable mode, giving the patient greater control over the inspiratory flow rate and respiratory rate. However, clinical studies have failed to show that PSV improves weaning. (See "Methods of weaning from mechanical ventilation", section on 'Choosing a weaning method'.)
PSV is frequently combined with synchronized intermittent mandatory ventilation (SIMV). The ventilator delivers the set respiratory rate using SIMV, but patient-initiated breaths beyond the set respiratory rate are delivered using PSV. The purpose of adding PSV for patient-initiated breaths is to overcome the resistance of the endotracheal tube and ventilator circuit. The necessary level of pressure support is unknown and generally estimated. Resistance of the endotracheal tube is related to the tube diameter and inspiratory flow rate [16]. With small endotracheal tubes (eg, <7 mm), a pressure support level ≥10 cm H2O may be needed to overcome the resistance [17,18]. Levels of pressure support higher than that required to overcome resistance will augment tidal volume.
Disadvantages — PSV is poorly suited to provide full or near-full ventilatory support. The following characteristics of PSV are disadvantages in that setting:
●Each breath must be initiated by the patient. Central apnea may occur if the respiratory drive is depressed due to sedatives, critical illness, or hypocapnia due to excessive ventilation [19].
●An adequate minute ventilation cannot be guaranteed because tidal volume and respiratory rate are variable.
●Ventilator asynchrony can occur when PSV is employed for full ventilatory support, potentially prolonging the duration of mechanical ventilation [20,21].
●PSV is associated with poorer sleep than AC. Specifically, there is greater sleep fragmentation, less stage 1 and 2 non-rapid eye movement (NREM) sleep, more wakefulness during the first part of the night, and less stage 3 and 4 NREM sleep during the second part of the night [22].
●Relatively high levels of pressure support (eg, >20 cm H2O) are required during full ventilatory support to prevent alveolar collapse (which can lead to cyclic atelectasis and ventilator-associated lung injury) and to attain a stable breathing pattern [23,24]. Such high levels of pressure support are not as comfortable as moderate levels (eg, 10 to 15 cm H2O) [25]. (See "Ventilator-induced lung injury".)
While PSV is poorly suited to provide full or nearly full ventilatory support in general, it is a particularly poor choice for patients who also have increased airway resistance (eg, COPD or asthma exacerbation). Minute ventilation is more likely to be insufficient when airway resistance is high, which may be related to decreased airflow causing inspiration to be terminated after a smaller than optimal tidal volume has been delivered [26,27]. In addition, PSV does little to decrease auto-positive end-expiratory pressure (auto-PEEP, also known as intrinsic PEEP), which can increase patient work and worsen respiratory muscle fatigue [28]. Choosing a higher percentage of the peak inspiratory flow as the trigger to end inspiration may improve auto-PEEP slightly [29].
BiPAP is the name of a portable ventilator manufactured by Respironics Corporation; it is just one of many ventilators that can deliver BPAP.
The exact size of the tidal volume is related to both the driving pressure and the compliance.
T high is set to 5.4 seconds and whose T low is set to 0.6 seconds has an inflation-deflation cycle lasting 6 seconds. This allows 10 inflations and deflations to be completed each minute.
Spontaneous breathing is possible at both P high and P low, although most spontaneous breathing occurs at P high because the time spent at P low is brief. This is a novel feature that distinguishes APRV from other types of inverse ratio ventilation (IRV).
The exact size of the tidal volume is related to both the driving pressure and the compliance.
T high is set to 5.4 seconds and whose T low is set to 0.6 seconds has an inflation-deflation cycle lasting 6 seconds. This allows 10 inflations and deflations to be completed each minute.
Spontaneous breathing is possible at both P high and P low, although most spontaneous breathing occurs at P high because the time spent at P low is brief. This is a novel feature that distinguishes APRV from other types of inverse ratio ventilation (IRV).
Contraindications — APRV and its related modes are infrequently used in patients with severe obstructive airways disease or a high ventilatory requirement because hyperinflation, high alveolar pressure, and pulmonary barotrauma may result.
Special attention should be paid to the possible adverse effects of raising PEEP which can cause barotrauma and hypotension. Raising FiO2 does not come without its concerns as high FiO2 can cause oxidative damage in the alveoli. Another important aspect of managing oxygen content is to define a goal for oxygenation. In general, there is little benefit from keeping oxygen saturation above 92-94% except for cases of carbon monoxide poisoning for example. A sudden drop in oxygen saturation should raise suspicion for tube misplacement, pulmonary embolism, pneumothorax, pulmonary edema, atelectasis, or development of mucus plugs.
Consideration has to be made while increasing the rate, as this will also increase the amount of dead space and might not be as effective as tidal volume. While increasing volume or rate special attention should be paid to the flow-volume loop to prevent the development of auto-PEEP.
Special attention should be paid to the possible adverse effects of raising PEEP which can cause barotrauma and hypotension. Raising FiO2 does not come without its concerns as high FiO2 can cause oxidative damage in the alveoli. Another important aspect of managing oxygen content is to define a goal for oxygenation. In general, there is little benefit from keeping oxygen saturation above 92-94% except for cases of carbon monoxide poisoning for example. A sudden drop in oxygen saturation should raise suspicion for tube misplacement, pulmonary embolism, pneumothorax, pulmonary edema, atelectasis, or development of mucus plugs.
Consideration has to be made while increasing the rate, as this will also increase the amount of dead space and might not be as effective as tidal volume. While increasing volume or rate special attention should be paid to the flow-volume loop to prevent the development of auto-PEEP.
Special attention should be paid to the possible adverse effects of raising PEEP which can cause barotrauma and hypotension. Raising FiO2 does not come without its concerns as high FiO2 can cause oxidative damage in the alveoli. Another important aspect of managing oxygen content is to define a goal for oxygenation. In general, there is little benefit from keeping oxygen saturation above 92-94% except for cases of carbon monoxide poisoning for example. A sudden drop in oxygen saturation should raise suspicion for tube misplacement, pulmonary embolism, pneumothorax, pulmonary edema, atelectasis, or development of mucus plugs.
Consideration has to be made while increasing the rate, as this will also increase the amount of dead space and might not be as effective as tidal volume. While increasing volume or rate special attention should be paid to the flow-volume loop to prevent the development of auto-PEEP.
nasal mask, facemask, or nasal plugs
Generally, the straps should be loose enough to allow one or two fingers to pass between the face and the strap. When a nasal mask or prongs are used, a chin strap is usually necessary to maintain closure of the mouth.
trial that randomly assigned 26 patients, (COPD) exacerbation complicated by hypercapnia to receive NIV via face mask, nasal mask, or nasal prongs (pillows) [23]. The face mask conferred the greatest physiologic improvement, but the nasal mask was best tolerated.
Based on these studies, the oronasal mask is generally preferred over a nasal mask or nasal prongs during the initiation of NIV
Most patients with acute respiratory failure are mouth breathers; therefore, NIV delivered by a nasal mask or prongs (pillows) may result in a large air leak through the mouth and a worse outcome [26].
●The nasal air passages offer significant resistance to airflow, which can reduce the beneficial effects of NIV if a low level of positive airway pressure is used [20,27].
●The primary disadvantage of the full face and oronasal masks is that monitoring for aspiration is more difficult [28].
●Regardless of the interface chosen, heated humidification brings the relative humidity back toward the ambient range. This enhances patient comfort [29].
Refer table 3 comparison
Hypercapnic encephalopathy may be an exception to the rule that severely impaired consciousness is a contraindication to NIV [12,13]. Clinicians who choose to try NIV in this setting should monitor such patients closely. Improved consciousness should be apparent within one to two hours after the initiation of NIV. Patients who deteriorate or fail to improve should be promptly intubated. The likelihood that hypercapnic encephalopathy will respond to NIV is inversely related to the severity of the hypercapnia. Respiratory acidosis is NOT a contraindication to NIV
Initiate setting similar to intubated ventilation
Complications are due to local and related to the tightly fitting mask
Most complications due to NIV are local and related to the tightly fitting mask:
●Local skin damage may occur due to the pressure effects of the mask and straps [130]. Cushioning the forehead and the bridge of the nose prior to attaching the mask can decrease the likelihood of these problems.
●Modest mask leaks are common and do not preclude NIV. A mask leak can often be remedied by using a different mask or different ventilator settings.
●Eye irritation, sinus pain, or sinus congestion may occur and require either a lower inspiratory pressure or a facial mask rather than a nasal mask.
●Mild gastric distention occurs frequently but is rarely clinically significant at usual levels of inspiratory pressure. Routine use of a nasogastric tube is not warranted.
