Intubation and mechanical ventilation 22, Dr Virbhan Balai

1. INTUBATION AND
MECHANICAL VENTILATION
Dr Virbhan Balai

2. TRACHEAL INTUBATION IN
ADULTS
• INTRODUCTION — Laryngoscopy and
tracheal intubation are essential skills for the
emergency clinician.
• This topic will discuss the-
– Indications
– Contraindications
– Preparation, Equipment
– Techniques needed to perform tracheal intubation
in adults.

3. INDICATIONS
• The most common indications for tracheal
intubation are-
– Acute respiratory failure.
– Inadequate oxygenation or ventilation.
– Airway protection in a patient with altered mental
status.
– In the perioperative setting- General anesthesia.
– Short-term hyperventilation to manage ↑ed ICP.

4. CONTRAINDICATIONS
• There are few absolute contraindications to tracheal
intubation.
• Supraglottic or glottic pathology that precludes placement
of an ETT.
– Blunt trauma to the larynx may cause a laryngeal fracture or
disruption of the laryngotracheal junction
– Penetrating trauma of the upper airway may also result in
conditions exacerbated by ETT placement.
• Relative contraindications to tracheal intubation involve
– Potential difficulties performing the procedure- Anatomic
features, injuries, or illness.

5. ANATOMY
ORAL CAVITY

6. • Modified Mallampati Scoring:[3]
• Class I: Soft palate, uvula, fauces, pillars
visible.
• Class II: Soft palate, uvula, fauces visible.
• Class III: Soft palate, base of uvula visible.
• Class IV: Only hard palate visible

8. LARYNGEAL INLET

10. • PREPARATION — have a mental or written checklist for
the necessary tools and steps.
• Essential preparations include the following:
– Assess the patient's airway.
– Preoxygenate the patient whenever possible.
– Place a functioning suction device and bag-valve mask at the
bedside.
– Attach monitors, including BP, pulse oximetry, and cardiac .
– Establish intravenous access.
– Whenever possible, two peripheral intravenous catheters should
be placed.
– Prepare all necessary medications for RSI- induction agent and a
neuromuscular blocking agent.

11. • Array the tools needed to perform intubation beside the clinician. These
include:
– Laryngoscope handle and assorted blades.
– Check for adequate lighting and the integrity of all parts.
– Endotracheal tubes and a stylet.
– Include ETTs one size larger and one size smaller than the ETT to be used
initially.
– Adjunct airway management devices (eg, ETT introducer or "bougie").
– Oral and nasal airways.
– Rescue airway (eg, laryngeal mask airway (LMA), Combitube).
– End-tidal CO2 monitor (eg, capnography) and esophageal detector to confirm
proper ETT placement.
– Equipment to hold the tube in position (eg, tape, prefabricated ETT holder).
– Check the cuff of the ETT for leaks by inflating it and removing the syringe
(the cuff should remain inflated) and then deflating it.
– Avoid contaminating the ETT.

12. • Perform all emergent intubations with a stylet in the
ETT.
• It is essential to have a clear back-up approach prepared
in advance in case of an unsuccessful intubation
attempt.
• This may consist of a rescue airway (eg, LMA), or in
the case of a failed airway, cricothyroidotomy.
• Proper patient positioning is crucial to successful
laryngoscopy.
• An assistant strong enough to lift the patient's head
should stand at the bedside to help with positioning.

13. • The "STOP MAID" mnemonic is described here:
• S: Suction
• T: Tools for intubation (laryngoscope blades, handle)
• O: Oxygen
• P: Positioning
• M: Monitors, including ECG, pulse oximetry, blood pressure, end-
tidal CO2, and esophageal detectors
• A: Assistant; Ambu bag with face mask; Airway devices (different
sized ETTs, 10 mL syringe, stylets); Assessment of airway difficulty
• I: Intravenous access
• D: Drugs for pretreatment, induction, neuromuscular blockade (and
any adjuncts)

14. LARYNGOSCOPE DESIGN
• The Macintosh – curved.
• Miller – straight.
• The curved blade is designed to minimize stimulation of the
posterior epiglottis.
• The straight blade may offer advantages in particular
circumstances, such as
– When the glottis is deep.
– Prominent upper incisors complicate insertion of a curved blade,
or
– A long, floppy epiglottis obscures the glottis and must be lifted
out of the line of sight.

15. Macintosh laryngoscope blade

16. MILLER AND PHILLIPS
LARYNGOSCOPE BLADES

17. LARYNGOSCOPY TECHNIQUE
• Key points
• The critical step in DL is to locate the epiglottis.
• Limit the depth of insertion of the laryngoscope
blade so it does not bypass the epiglottis.
• The best ways to improve a limited laryngeal
view are to:
– Increase elevation of the patient's head and flexion of
their cervical spine AND
– Perform bimanual laryngoscopy by manipulating the
epiglottis with the laryngoscope and the glottis with
the right hand.

18. Overview
• The basic steps for performing DL and tracheal intubation include the following:
– Obtain assistance.
– Prepare equipment, monitors, and medications.
– Assess, preoxygenate, and position the patient.
– Open the patient's mouth and carefully position the laryngoscope.
– Deflect the tongue and soft tissue out of the line of sight.
– Locate the epiglottis.
– Identify and optimize the view of the glottis using bimanual laryngoscopy, head
elevation, and neck flexion (head elevation and neck flexion
are NOT performed when cervical spine precautions are necessary).
– Insert the tracheal tube.
– Confirm positioning of the tube within the trachea using CO2 detection,
physical examination, and a chest radiograph.
– Secure the tracheal tube.
– Set parameters for mechanical ventilation.
– Provide sedation and analgesia as needed

19. Positioning the patient
• Elevation of the patient's head by approximately 5 to 7 cm.
• Flexing their cervical spine, and performing external laryngeal
manipulation.
• Bag-mask ventilation can be performed between attempts as needed.
• A useful guide for determining adequate head elevation is to
ensure that the patient's ear (external auditory meatus) and
sternal notch are aligned when examined from the side.
• This alignment also allows for flexion of the cervical spine.
• In some patients, cervical flexion makes it difficult to insert the
laryngoscope blade.
• To offset this & provide easier access to the mouth, place towels or
blankets behind the thoracic spine.
• Tilting the head back by extending the cervical spine (primarily
the atlanto-occipital joint) can compromise the glottic view.

21. Opening the mouth and inserting the
blade
• The scissor technique is an effective and time-honored method for opening
the mouth.
• To perform the technique, hold the tips of the thumb and middle finger of
the right hand together, insert them between the upper and lower incisors,
and "scissor" them past one another by flexing each digit.
• An alternative method of opening the mouth involves pushing the occiput
with the right hand, thereby extending the neck and changing the angle of
insertion.
• Regardless of the method chosen, the blade is inserted in a controlled
fashion to avoid injuring teeth or soft tissue.
• Difficulty inserting the blade may occur when the mouth is small, the chest
wall is large, or the cervical spine is held in extreme flexion.
• If the patient has a small mouth, a smaller blade (eg, Macintosh or Miller
size 2) or having an assistant retract the lip may be helpful.

23. Optimizing the view
• General guidance — The following techniques can be used to
improve an inadequate view of the glottis:
• Be certain the tip of the laryngoscope blade is correctly seated in the
vallecula when performing curved blade laryngoscopy.
• Make certain the tongue is well controlled and completely contained
within the left side of the mouth.
• Increase the degree of cervical flexion by lifting the head and
flexing the neck.
• Have an assistant perform these maneuvers.
• Avoid the common tendency to extend the neck, which generally
does not improve the view.
• Should the techniques above fail, use a laryngoscope blade of a
different size or shape, a tracheal tube introducer, or try a different
approach (eg, paraglossal straight blade).

24. Glottic view scores
• Two scoring systems are used to describe the view of the glottis obtained
by DL.
• The Cormack-Lehane system provides a general description using four
categories:
– Grade I is a full view of the entire glottis;
– Grade II is a view of the posterior portion of the glottic opening;
– Grade III is a view of the epiglottis only; and with
– Grade IV neither the epiglottis nor the glottis can be seen.
• The POGO score attempts to quantify the percentage of glottic opening .
– POGO score of 50 percent means that approximately half of the glottis can be
seen.
– POGO score greater than 50 percent should allow placement of a tracheal tube
with relative ease.
– Extremely limited views (eg, POGO score of zero, Cormack-Lehane score of
III or IV) suggest that tube placement will be difficult

25. CORMACK-LEHANE GRADING SCHEME
FOR LARYNGOSCOPY

26. CURVED BLADE LARYNGOSCOPY
• Step 1: Open the mouth sufficiently to allow
blade insertion without traumatizing the teeth .
• Step 2: Insert the blade and control the tongue.
• Step 3: Carefully advance the blade toward the
epiglottis in a controlled manner, gently lifting
the blade tip every few centimeters.
• Step 4: Advance the tip of the blade into the
vallecula, the recess between the base of the
tongue and the epiglottis.
• Step 5: Identify the best spot for elevating the
epiglottis.

27. • Each spooning movement involves advancing the blade
a few millimeters and then lifting forward in the
direction of the handle.
• The lift should be sufficient to allow pulling the handle
back without levering on the teeth.
• Touching the teeth indicates excessive levering or
insufficient lift.
• Alternatively, external manipulation of the larynx can
be used to identify the best location for the blade tip.
• This is done by pressing on the thyroid cartilage with
the fingers of the right hand.

28. • Step 6: Lift the laryngoscope in the direction of the handle,
thereby exposing the glottis; do not lever back on the teeth with
the laryngoscope handle.
• Keep your elbow in (ie, arm adducted) for maximal lifting strength.
• When lifting a laryngoscope with a curved blade, the correct force
vector points approximately 45 degrees from the plane of the floor.
• Lift in the direction of the junction of the ceiling and the wall
beyond the patient's feet.
• This lifting motion elevates the epiglottis, keeps the tongue out of
the line of sight, and maximizes exposure of the glottis.
• The natural inclination for many novice intubators is to lever
backwards on the laryngoscope handle.
• This motion impairs the laryngoscopist's view and can damage
teeth.

29. Laryngoscope lifting

30. INCORRECT LARYNGOSCOPE MOTION

31. • Step 7: Optimize the glottic view as needed with external
laryngeal manipulation, head elevation, and neck flexion.
• Step 8: Place the tracheal tube.
• Once the tip of the ETT has passed the vocal cords, the
laryngoscopist should pause and ask an assistant to remove the
stylet.
• Inserting the ETT further with the stylet in place may cause injury or
obstruct tube passage.
• Advance the ETT until it rests at 21 cm at the front incisors for
a woman or 23 cm for a man.
• Adjustment may be needed based upon the position noted on chest
x-ray.

32. • Stop laryngoscopy and perform bag-mask
ventilation with high flow oxygen if the
patient's SpO2 falls below 90 percent.
• Individual attempts at intubation should not
exceed 30 seconds

33. STRAIGHT BLADE LARYNGOSCOPY
Uses and advantages —
• It frequently allows a more complete view of the laryngeal
inlet since the epiglottis is lifted out of the way.
• Also provides a superior view
– When the larynx is situated anterior to the line of sight or
– In pt`s with a receding chin or pathology at the BOT .
• It is often easier to insert a straight blade if
– The pt's mouth is small
– Mouth-opening is limited, or
– The front incisors are prominent.
• May be more effective during difficult intubations,
particularly if a paraglossal approach is used.

34. Straight blade techniques
• A straight blade may be inserted to the right of the
tongue (paraglossal technique) or in the midline.
• The paraglossal approach involves inserting the
straight blade into the natural gutter between the
tongue and the lower molars.
• When using a midline approach, the technique is
much like that for a curved blade, with the
exception of lifting the epiglottis.
• The "retromolar" or "molar" approach uses a
more extreme insertion site lateral to the molars.

35. • Paraglossal technique — The paraglossal technique using
a straight laryngoscope blade is performed as follows:
• Step 1: Introduce the blade into the mouth to the right of
the tongue, between the tongue and the patient's right
lower molars.
• Step 2: Advance the tip of the blade along the tongue
into the groove between the tongue and tonsillar pillar.
• Step 3: In a controlled and deliberate manner, continue
to advance the blade tip while looking for the epiglottis.
• Step 4: Use lateral and anterior pressure to keep the
tongue displaced to the left.

36. • Step 5: Once the epiglottis is identified, advance the tip of the blade
posterior to the epiglottis and into the laryngeal inlet. Use the blade tip
to lift the epiglottis anteriorly (upwards in the supine patient), exposing
the glottis.
• Avoid levering back with the laryngoscope.
• Step 6: Optimize the glottic view as needed with external laryngeal
manipulation, head elevation, and neck flexion.
• If the view remains poor, turning the head slightly to the right may be
helpful.
• Step 7: Insert the tracheal tube.
• Insert the endotracheal tube (ETT) from the right side of the mouth.
• insert it directly into the trachea while watching the tube pass between the
vocal cords.

37. ANATOMIC
LANDMARKS
DURING DIRECT
LARYNGOSCPY

38. CONFIRMING PROPER
TRACHEAL TUBE PLACEMENT
• End-tidal carbon dioxide — EtCO2 determination (either colorimetric or
quantitative capnography) is the most accurate means of confirming proper ETT
placement.
– Esophagus may yield small but detectable amounts of CO2 during the first few
positive pressure ventilations.
– Thus, at least five exhalations with a consistent CO2 level must be evident
before one can confidently assume that the ETT is in the trachea.
– In pt`s without detectable pulses, gas exchange in the lungs is markedly
reduced and CO2 may not be detectable, despite proper positioning of the ETT.
– Pt`s in cardiac arrest may not generate CO2, making the absence of CO2
detection meaningless.
– However, when CO2 is detected in the cardiac arrest patient and persists for six
breaths, the ETT is in the airway.
• Physical examination and plain chest radiography may provide useful information
but cannot be used as proof of proper placement.

39. CO2 detector for
endotrachel tube
confirmation.

40. • Clinical findings —
• visualization of the ETT through the cords.
• Listen for equal breath sounds in both axillae.
• No breath sounds should be appreciable over
the epigastrium.
• Rise of the chest wall with positive pressure
ventilation.
• Mist in the ETT with each exhalation.

41. • Alternative methods — Alternative methods for
determining proper ETT placement have been used
successfully in pulseless patients.
• One example is the suction method.
• This approach uses syringe or bulb suction devices to
distinguish between the trachea and the esophagus.
• The likelihood of tracheal placement is high if over 30
mL of gas can be withdrawn from the ETT into the bulb
without resistance.
• Fiberoptic visualization of the tracheal rings and carina
may also be used to confirm tracheal placement.

42. • Chest x-ray (usually AP) –
– Helpful for determining the depth of the ETT in
the trachea.
– But cannot reliably exclude esophageal intubation
• Ultrasound is the subject of ongoing study in
both adult and pediatric populations as a
method for confirming ETT placement.

43. • Mainstem bronchus intubation —
• Endobronchial intubation can produce major complications
over time, such as hypoxia, hypercapnia, and
pneumothorax.
• Endobronchial placement occurs more often in women and
during emergency intubations.
• EtCO2 detection does not distinguish between endotracheal,
endobronchial (too deep), and supraglottic (too shallow)
ETT placement.
• Breath sounds that are significantly louder on one side
suggest endobronchial intubation.
• Ultrasound can be used to confirm ventilation by observing
the “lung sliding sign .

44. • Depth of tracheal tube insertion — In women
the ETT should be inserted to a depth of 20 to 21
cm.
• In men the appropriate depth is 22 to 23 cm.
• Use the teeth or gums as the benchmark for
insertion depth (rather than the lips) because they
are fixed landmarks.
• The tip of a properly placed ETT should lie
approximately 2 cm above the carina(CXR-AP).

45. • POSTINTUBATION MANAGEMENT
• The ETT should be secured with tape or a
commercially available tube holder.
• Tube holders are often easier to manage if the
position of the ETT must be changed and may
be more comfortable for patients.
• Sedation and analgesia are provided using
validated treatment algorithms.

46. COMPLICATIONS
• Direct blunt or penetrating trauma to the oropharynx,
larynx, and trachea can occur from the laryngoscope or
the stylet and tracheal tube.
• Lacerations of the lips, teeth, tongue, pharyngeal wall,
laryngeal structures, including the glottis and the
esophagus.
• Glottic trauma may involve vocal cord injury or
dislocation of the arytenoid cartilages.
• Cervical spinal cord injury in susceptible individuals.
• Dislocation of the temporomandibular joint-: may
occur if great force is used to open the mouth.

47. • Nontraumatic complications-
– Aspiration of gastric contents.
– Bronchospasm.
– Hypoxic injury from prolonged attempts at intubation.
– Unrecognized esophageal intubation.
– Tachycardia, arrhythmias, hypertension, and
myocardial ischemia or infarction may result.
– Long-term consequences of tracheal tube placement
include damage to the airway, including
laryngomalacia, tracheomalacia, or laryngeal stenosis.

48. OVERVIEW OF MECHANICAL
VENTILATION

49. INTRODUCTION
• Mechanical ventilation is also called positive pressure
ventilation.
• Following an inspiratory trigger, a predetermined mixture of
air is forced into the central airways and then flows into the
alveoli.
• As the lungs inflate, the intraalveolar pressure increases.
• A termination signal eventually causes the ventilator to stop
forcing air into the central airways and the central airway
pressure decreases.
• Expiration follows passively, with air flowing from the
higher pressure alveoli to the lower pressure central
airways.

50. INDICATIONS
• It is indicated for acute or chronic respiratory
failure, which is defined as
– Insufficient oxygenation
– Insufficient alveolar ventilation, or both.
• Mechanical ventilation should be considered early
in the course of illness and should not be delayed
until the need becomes emergent.
• Physiologic derangements and clinical findings
can be helpful in assessing the severity of illness.

51. PHYSIOLOGIC OBJECTIVES
Support pulmonary gas exchange based on alveolar ventilation and arterial oxygenation
Reduce the metabolic cost of breathing by unloading the ventilatory muscles
Minimize ventilator-induced lung injury
CLINICAL OBJECTIVES
Reverse hypoxemia
Reverse acute respiratory acidosis
Relieve respiratory distress
Prevent or reverse atelectasis
Reverse ventilatory muscle fatigue
Permit sedation and/or neuromuscular blockade
Decrease systemic or myocardial oxygen consumption
Stabilize the chest wall

52. PARAMETER VALUE
CLINICAL ASSESSMENT
Apnea
Stridor
Severely depressed mental status
Flail chest
Inability to clear respiratory secretions (eg, excessive
secretions, loss of protective reflexes, neuromuscular
failure)
Trauma to mandible, larynx, trachea
LOSS OF VENTILATORY RESERVE
Respiratory rate >35 breaths/min
Tidal volume <5 mL/kg
Vital capacity <10 mL/kg
Negative inspiratory force Weaker than –25 cm H2O (2.44 kPa)
Minute ventilation <10 L/min
Rise in PaCO2 >10 mmHg (1.33 kPa)
Refractory hypoxemia
Alveolar-arterial gradient (FiO2 = 1) >450
PaO2/PAO2 <0.15
PaO2 with supplemental O2 <55 mmHg (7.32 kPa)
RESPIRATORY ABNORMALITIES SUGGESTIVE OF THE NEED FOR MECHANICAL VENTILATION

53. BENEFITS — The principal benefits of
mechanical ventilation during respiratory
failure are-
1. Improved gas exchange- by improving ventilation-
perfusion (V/Q) matching.
2. Decreased work of breathing.

54. • TYPES OF BREATHS — Mechanical
ventilation can deliver different types of
breaths-
– Volume control.
– Volume assist.
– Pressure control.
– Pressure assist, and
– Pressure support.

55. • They are defined by the combination of three
features:
1. Trigger – Breaths can be triggered by a timer
(ventilator-initiated breaths) or patient effort (patient-
initiated breaths).
2. Target – The flow of air into the lung can target a
predetermined flow rate (ie, the peak inspiratory flow
rate) or pressure limit.
3. Termination – The signal for a ventilator to end
inspiration may be volume-, time-, or flow-related.

56. • Volume control — VC breaths are ventilator-
initiated breaths with a set inspiratory flow rate.
• Inspiration is terminated once the set tidal volume
has been delivered.
• Airway pressure is determined by the airways
resistance, lung compliance, and chest wall
compliance.
• Modes of mechanical ventilation that can deliver
VC breaths include volume-limited assist control
and volume-limited synchronized intermittent
mandatory ventilation.

57. • Volume assist — VA breaths are patient- initiated
breaths with a set inspiratory flow rate.
• Inspiration is terminated once the set tidal volume
has been delivered.
• Airway pressure is determined by the airways
resistance, lung compliance, and chest wall
compliance.
• Modes of mechanical ventilation that can deliver
VA breaths include volume-limited assist control
and volume-limited synchronized intermittent
mandatory ventilation.

58. • Pressure control — PC breaths are ventilator-initiated
breaths with a pressure limit.
• Inspiration is terminated once the set inspiratory time
has elapsed.
• The tidal volume is variable and related to compliance,
airway resistance, and tubing resistance.
• A consequence of the variable tidal volume is that a
specific minute ventilation cannot be guaranteed.
• Modes of mechanical ventilation that deliver PC
breaths include pressure-limited assist control and
pressure-limited synchronized intermittent mandatory
ventilation.

59. • Pressure assist — Pressure assist (PA) breaths are
patient-initiated breaths with a pressure limit.
• Inspiration is terminated once the set inspiratory time
has elapsed.
• The tidal volume is variable and related to compliance,
airway resistance, and tubing resistance.
• A consequence of the variable tidal volume is that a
specific minute ventilation cannot be guaranteed.
• Modes of mechanical ventilation that deliver PA breaths
include pressure-limited assist control and pressure-
limited synchronized intermittent mandatory
ventilation.

60. • Pressure support — PS breaths are patient-
initiated breaths with a pressure limit.
• The ventilator provides the driving pressure for
each breath, which determines the maximal
airflow rate.
• Inspiration is terminated once the inspiratory flow
has decreased to a predetermined percentage of its
maximal value.
• Pressure support is a mode of mechanical
ventilation.

61. MODES
• The modes of mechanical ventilation are
distinguished from another by the types of
breaths that they deliver.
• Common modes include-
– Assist control.
– Synchronized intermittent mandatory ventilation.
– Pressure support, numerous other modes also
exist (table 4).

62. Mode
Breath
strategy
(target)
Trigger Cycle
(breath
termination)
Types of breaths
Ventilator Patient Mandatory Assisted Spontaneous
CMV
Volume-
limited
Yes No Volume Yes No No
Pressure-
limited
Yes No Time Yes No No
AC
Volume-
limited
Yes Yes Volume Yes Yes No
Pressure-
limited
Yes Yes Time Yes Yes No
IMV
Volume-
limited
Yes Yes Volume Yes Yes* Yes*
Pressure-
limited (also
called APRV)
Yes Yes Time Yes Yes* Yes*
PSV
Pressure-
limited
No Yes
Flow,
pressure, or
time
No Yes No
CPAP No Yes Flow No Yes No
Tube
compensatio
n
No Yes Flow No No Yes
Modes of mechanical ventilation

63. INITIATION
• Invasive versus noninvasive — Mechanical
ventilation can be delivered invasively or
noninvasively.
• The decision about whether to initiate invasive or
noninvasive mechanical ventilation requires that
the entire clinical situation be considered.
• A trial of NPPV is worthwhile in pt`s with acute
cardiogenic pulmonary edema or hypercapnic
respiratory failure due to COPD.
• Invasive mechanical ventilation is appropriate for
most other patients.

64. • Choosing a mode — The selection of the mode is
generally based on clinician familiarity and institutional
preferences.
• Level of support — The level of ventilatory support
refers to the proportion of the patient's ventilatory needs
that are met by the ventilator.
• The level of ventilatory support is determined by the
mode and other settings.
1. Assist control provides the most support.
2. Synchronized intermittent mandatory ventilation provides
the widest range of support, and
3. Pressure support tends to provide less support.

65. • Settings — There are numerous settings that need to be
considered when mechanical ventilation is initiated.
• These include the trigger mode and sensitivity, respiratory
rate, tidal volume, positive end-expiratory pressure, flow
rate, flow pattern, and fraction of inspired oxygen.
• Trigger — There are two ways to initiate a ventilator-
delivered breath-:
1. Pressure triggering or
2. Flow-by triggering.
• When pressure triggering is used, a ventilator-delivered
breath is initiated
• A trigger sensitivity of -1 to -3 cm H2O is typically set.

66. • Auto-PEEP (intrinsic positive end-expiratory
pressure) interferes with pressure triggering.
• Auto-PEEP refers to end-expiratory pressure that
is created when inspiration begins before
expiration is complete.
• When flow-by triggering is used, a continuous
flow of gas through the ventilator circuit is
monitored.
• A ventilator-delivered breath is initiated when the
return flow is less than the delivered flow, a
consequence of the pt's effort to initiate a breath.

67. FLOW-BY TRIGGERING IN MECHANICAL
VENTILATION

68. • The trigger sensitivity should allow the patient to
trigger the ventilator easily.
• A trigger sensitivity that is too sensitive may cause a
breath to be delivered in response to patient movement
or subtle pressure deflections caused by water moving
within the ventilator tubing.
• In contrast, a trigger sensitivity that is not sensitive
enough increases patient effort.
• Pressure triggering can be used with the assist control
or synchronized intermittent mandatory ventilation
modes of mechanical ventilation.

69. • Tidal volume — The tidal volume is the amount of air
delivered with each breath.
• During volume-limited ventilation, the tidal volume is
set by the clinician and remains constant.
• During pressure-limited ventilation, the tidal volume is
variable.;
• The appropriate initial tidal volume depends on
numerous factors, most notably the disease.
• ARDS –tidal volumes of ≤6 mL per kg of predicted
body weight improved mortality in patients with ARDS

70. • Respiratory rate — An optimal method for
setting the respiratory rate has not been
established.
• For most patients, an initial respiratory rate b/w
12 and 16 breaths/minute is reasonable.
– For pt`s receiving assist control, the RR is typically
set four breaths per minute below the pt's native
rate.
– For pt`s receiving synchronized intermittent
mandatory ventilation, the rate is set to ensure that
at least 80 percent of the patient's total minute
ventilation is delivered by the ventilator.

71. • Return to the previous respiratory rate is
indicated if the patient develops auto-PEEP >5
cm H2O.
• For pt`s with ARDS, the required RR is higher
(up to 35 breaths /minute), in order to facilitate
low tidal volume ventilation.

72. • PEEP — Applied PEEP (extrinsic positive end-expiratory
pressure) is generally added to mitigate end-expiratory
alveolar collapse.
• A typical initial applied PEEP is 5 cm H2O.
• However, up to 20 cm H2O may be used in patients
undergoing low tidal volume ventilation for ARDS.
• Elevated levels of applied PEEP can have adverse
consequences, such as-:
– Reduced preload (decreases cardiac output).
– Elevated plateau airway pressure (increases risk of barotrauma),
and
– Impaired cerebral venous outflow (increases intracranial
pressure).

73. • Flow rate — The peak flow rate is the maximum
flow delivered by the ventilator during
inspiration.
• Peak flow rates of 60 L per minute may be
sufficient, although higher rates are frequently
necessary.
• An insufficient peak flow rate is characterized by
– Dyspnea
– Spuriously low peak inspiratory pressures, and
– Scalloping of the inspiratory pressure tracing

74. • The need for a high peak flow rate is particularly
common among patients who have
– Obstructive airways disease with
– Acute respiratory acidosis.
• In such patients, a higher peak flow rate shortens
inspiratory time and increases expiratory time (ie,
decreases the inspiratory to expiratory [I:E] ratio).
• These alterations increase carbon dioxide
elimination and improve respiratory acidosis,
while also decreasing the likelihood of dynamic
hyperinflation (auto-PEEP).

75. • Flow pattern — Microprocessor-controlled
mechanical ventilators can deliver several
inspiratory flow patterns, including a square
wave (constant flow), a ramp wave
(decelerating flow), and a sinusoidal wave.
• The ramp wave may distribute ventilation
more evenly than other patterns of flow,
particularly when airway obstruction is
present.

76. VENTILATOR FLOW AND PRESSURE
WAVEFORMS

77. • Fraction of inspired oxygen — The lowest
possibleFiO2 necessary to meet oxygenation goals
should be used.
• As an example, a patient with IHD requires
greater oxygenation than a patient with chronic
hypoxemia due to lung disease.
• Typical oxygenation goals include an PaO2 ≥ 60
mmHg and SpO2 ≥ 90 percent.
• In patients with ARDS, targeting a PaO2 of 55 to
80 mmHg and a SpO2 of 88 to 95 percent is
acceptable.

78. • ASYNCHRONY — Patient-ventilatory asynchrony
exists if the phases of breath delivered by the ventilator
do not match that of the patient.
• It is common during mechanical ventilation: more than
10 percent of breaths are asynchronous in
approximately 24 percent of mechanically ventilated
pt`s.
• Patient-ventilator asynchrony can cause dyspnea,
increase the work of breathing, and prolong the
duration of mechanical ventilation .
• It can be detected by careful observation of the patient
and examination of the ventilator waveforms.

79. There are several common causes of patient-
ventilator asynchrony:
1. Ineffective triggering of a ventilator-delivered
breath – Ineffective triggering may occur in as
many as one-third of inspiratory effort.
2. Double triggering ventilator-delivered breaths –
When this occurs, the ventilator delivers two
breaths in rapid sequence.
3. This can be lessened or eliminated by decreasing
the trigger sensitivity (eg, from -1 to -3 cm H2O).

80. 3. Prolonged inspiratory time – Inspiratory time is
the tidal volume divided by the inspiratory flow
rate.
4. Attempts to increase the minute ventilation by
raising only the tidal volume result in an
increased inspiratory time, causing patient
discomfort and asynchrony .
• Breath stacking is a manifestation of asynchrony
that occurs when a patient triggers a new breath
before the completion of the prior ventilator-
delivered breath.

81. Modes of mechanical ventilation
• The mode refers to the method of inspiratory
support.
• Common modes of mechanical ventilation are
described in this topic.

82. • VOLUME-LIMITED VENTILATION — Volume-limited
ventilation (also called volume-controlled or volume-cycled
ventilation) requires the clinician to set the peak flow rate, flow
pattern, tidal volume, RR, applied PEEP, and FiO2.
• Inspiration ends after delivery of the set tidal volume.
• The I:E ratio are determined by the peak inspiratory flow rate.
• Airway pressures (peak, plateau, and mean) depend on both the
ventilator settings and patient-related variables (eg, compliance,
airway resistance).
• High airway pressures may be a consequence of
– Large tidal volumes,
– A high peak flow,
– Poor compliance (eg, acute respiratory distress syndrome, minimal
sedation), or
– Increased airway resistance.

83. Waveforms for volume-cycle ventilator

84. Airway pressures during various modes of
ventilation

85. • Modes — Volume-limited ventilation can be
delivered via several modes, including CMV, assist
control AC, IMV, and SIMV.
• CMV — During CMV, the minute ventilation is
determined entirely by the set respiratory rate
and tidal volume.
• The patient does not initiate additional minute
ventilation above that set on the ventilator.
• CMV does not require any patient work.

86. • AC — During AC, the clinician determines the minimal
minute ventilation by setting the respiratory rate and tidal
volume.
• The patient can increase the minute ventilation by triggering
additional breaths.
• Each patient-initiated breath receives the set tidal volume
from the ventilator.
• Pressure regulated volume control (PRVC) is similar to AC.
• The main difference is that the ventilator is able to auto
regulate the inspiratory time and flow so that the tidal
volume generates a smaller rise in the plateau airway
pressure.

87. • IMV — IMV is similar to AC in two ways:
– The clinician determines the minimal minute ventilation
(by setting the RR and tidal volume) and
– The patient is able to ↑the minute ventilation.
• IMV differs from AC in the way that the minute
ventilation is increased.
• Pt`s increase the minute ventilation by spontaneous
breathing, rather than patient-initiated ventilator
breaths.
• The precise minute ventilation depends on the size of
the tidal volume for each spontaneous breath.

88. • SIMV — SIMV is a variation of IMV, in which the
ventilator breaths are synchronized with patient inspiratory
effort.
• SIMV (or IMV) can be used to titrate the level of
ventilatory support over a wide range.
• This is an advantage unique to these modes.
• Ventilatory support can range from full support (set
respiratory rate is high enough that the patient does not
overbreathe) to no ventilatory support (set respiratory rate is
zero).
• The level of support may need to be modified if
hemodynamic consequences of positive pressure ventilation
develop.

89. • Comparisons — SIMV and AC are the most frequently
used forms of volume-limited mechanical ventilation.
• 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.
– Auto-peep may be less likely with simv.
• In contrast, AC may be better suited for critically ill
pt`s who require a constant tidal volume or full or near-
maximal ventilatory support

90. Methods of weaning from
mechanical ventilation
• Weaning is the process of decreasing the amount
of support that the patient receives from the
mechanical ventilator.
• The purpose is to assess the probability that
mechanical ventilation can be successfully
discontinued.
• Traditional methods of weaning include
spontaneous breathing trials (SBTs), progressive
decreases in the level of pressure support during
PSV, and progressive decreases in the number of
ventilator-assisted breaths during IMV.

91. • An SBT refers to a patient breathing through the endotracheal tube
either without any ventilator support (eg, through a T-piece) or
with minimal ventilator support (eg, a low level of pressure support,
automatic tube compensation (ATC), or continuous positive airway
pressure (CPAP)).
• Once it has been determined that a patient is ready to be weaned,
we suggest weaning via once-daily SBTs, rather than PSV or IMV
(Grade 2B).
• For most p`ts, the SBT may be performed using a T-piece, low level
of pressure support (eg, ≤8 cm H2O), ATC, or CPAP (eg, ≤5 cm H2O).
• However, for pt`s with a small, high resistance endotracheal tube
(size ≤7.0 mm), we suggest using low level pressure support or ATC,
rather than a T-piece or CPAP (Grade 2C).

92. • An initial SBT of 30 minutes duration is generally sufficient
to determine whether mechanical ventilation can be
discontinued.
• For pt`s who fail their initial SBT, or required prolonged
mechanical ventilation prior to the initial SBT (eg, more
than ten days), we suggest that subsequent trials be 120
minutes, rather than 30 minutes (Grade 2C).
• Weaning by progressive decreases in the level of pressure
support (2 to 4 cm H2O per day) during PSV is a reasonable
alternative for pt`s who do not tolerate SBTs. We suggest
that IMV alone NOT be used for weaning (Grade 1B).

93. • Clinical impression determines whether a patient fails
or tolerates weaning.
• Patients who tolerate the SBT should be considered for
extubation.
• In contrast, patients who fail the SBT should be
returned to mechanical ventilation.
• When a patient fails weaning, the reason for failure
should be sought and corrected.
• Meanwhile, the patient should be assessed daily for
readiness to wean. We suggest weaning such patients
via once-daily SBTs, rather than SBTs multiple times
daily, PSV, or IMV (Grade 2B).

94. • A SBT refers to a patient spontaneously breathing through the
endotracheal tube (ETT) for a set period of time (usually 30 minutes
to two hours) either without any ventilator support (eg, through a T-
piece) or with minimal ventilator support.
• Methods of minimal ventilator support for a SBT include a low level
of PSV (eg, 5 to 7 cm H2O), automatic tube compensation (ATC), or
CPAP.
• A successful SBT is one where a patient passes a number of pre-set
physiologic criteria (eg, heart rate, respiratory rate, blood pressure,
gas exchange) at completion of the SBT that potentially indicate
candidacy for extubation.
• When a patient successfully passes a SBT and no contraindication to
extubation is present, the ETT is typically removed.
• When a patient fails a SBT, then the patient is typically not
extubated and a work up for weaning failure is performed.

95. • Our preference for SBTs as the initial weaning
strategy for most patients with acute respiratory
failure, is based upon clinical experience and
empirical studies, which indicate that compared to
other weaning methods, SBTs are simple,
efficient, safe, and effective.
• Patients undergoing daily SBTs were more likely
to wean successfully than those who were weaned
by IMV or PSV.

96. DISEASE-SPECIFIC
VENTILATORY MANAGEMENT
• Asthma and COPD —
• The major reason for instituting mechanical ventilation in these
patients is clinical manifestation of respiratory distress, related to
deteriorating gas exchange.
• For patients with severe asthma or COPD requiring mechanical
ventilation, following approach is recommend :
1. Use larger-sized endotracheal tube (eg, ≥8 mm).
2. Keep minute ventilation (MV) below 115 mL/kg.
3. Keep tidal volume (VT) below 8 mL/kg.
4. Maintain respiratory rate at 10 to 14 breaths per minute.
5. Maintain inspiratory flow rate at 80 to 100 liters/minute.
6. Allow increased expiratory time with decreased I:E ratio (1:3 or 1:4
up to 1:5).
7. Maintain plateau pressures below 30 cmH2O if possible.
8. Allow hypercapnea for patients with high peak pressures.

97. Acute cardiogenic pulmonary
edema
• Extrinsic positive end-expiratory pressure (PEEPe) can
be increased as tolerated to improve oxygenation and
further reduce preload.
• Excessive PEEPe can result in hypotension in patients
dependent upon preload to maintain cardiac output (eg,
patients with right ventricular dysfunction).
• Many patients with acute CPE benefit from NPPV
treatment. NPPV improves cardiac performance and
decreases pulmonary edema.
• However, some patients are not amenable to treatment
with NPPV .

98. • Acute respiratory distress syndrome — Acute respiratory distress
syndrome (ARDS) is defined as a syndrome of acute and persistent
lung inflammation with increased vascular permeability.
• ARDS is characterized by four features:
– Timing – Develops within one week of a known clinical insult or new
or worsening respiratory symptoms.
– Radiographic appearance – Bilateral opacities not fully explained by
effusions, lobar/lung collapse, or nodules.
– Pulmonary edema – Respiratory failure not fully explained by cardiac
failure or fluid overload; Need objective assessment (eg,
echocardiography) to exclude hydrostatic edema if no risk factor
present.
– Compromised oxygenation – Mild: 200 mmHg <PaO2/FiO2 ≤300
mmHg with PEEP or CPAP ≥5 cmH2O; Moderate: 100
mmHg <PaO2/FiO2 ≤300 mmHg with PEEP ≥5 cmH2O;
Severe: PaO2/FiO2≤100 mmHg with PEEP ≥5 cmH2O.

99. Rapid sequence intubation in adults
• DEFINITION — Rapid sequence intubation (RSI) is the
virtually simultaneous administration of a sedative and a
neuromuscular blocking (paralytic) agent to render a patient
rapidly unconscious and flaccid in order to facilitate
emergent endotracheal intubation and to minimize the risk
of aspiration.
• Preoxygenation is required to permit a longer period of
apnea without clinically significant oxygen desaturation.
• Bag-mask ventilation is avoided during the interval between
drug administration and endotracheal tube placement,
thereby minimizing gastric insufflation and reducing the
risk of aspiration

100. • Indications — RSI is the standard of care in
emergency airway management for intubations not
anticipated to be difficult.
• Contraindications — Contraindications to RSI are
relative.
• Circumstances exist where neuromuscular blockade is
undesirable due to the high likelihood of intubation or
mechanical ventilation failure.
• Depending on clinical circumstances, particular
sedative or neuromuscular blocking agents may be
relatively contraindicated, due to the risk of potential
side effects.

101. THANKYOU