MECHANICAL VENTILATION FROM BASICS TO APPLIEDS

1. Approach to Mechanical Ventilation
Presentator : Dr. Sanjay JR3
Moderator : Dr. Lubna Zafar
Department of Medicine, JNMC,
AMU, Aligarh

2. Introduction
• Mechanical Ventilation ( MV ) is used to assist
or replace spontaneous breathing.
• Special devices to support :
1. Ventilatory function
2. Improve Oxygenation through high-Oxygen
content gas & Positive Pressure

3. • Objectives :
1. decrease work of breathing thus avoiding
respiratory muscle fatigue
2. to reverse life-threatening hypoxemia &
progressive respiratory acidosis
• Primary indication for initiation : Respiratory
Failure , when chronic not obligatorily treated
with MV but may be lifesaving in Acute

6. Respiratory Failure
• 2 basic types
1. Hypoxemic : Arterial O2 saturation (SaO2) <90%
despite increased Inspired O2 fraction, results
from Ventilation-Perfusion mismatch or Shunt
2. Hypercarbic : Elevated Arterial CO2 partial
pressure (PCO2) usually >50mmHg
• results from conditions that decrease Minute V.
or increase Physiologic Dead Space such that
Alveolar V. inadequate to meet metabolic
demands

7. Respiratory Failure
All 3 may coexist

8. Indications of MV
1. Acute Respiratory Failure with Hypoxemia :
65% of all ventilated cases
• Acute Respiratory Distress Syndrome(ARDS)
• Heart Failure with Pulmonary Edema
• Pneumonia
• Sepsis
• Complications of Surgery & Trauma
2. Hypercarbic Ventilatory Failure :
• Coma (15%)
• Exacerbations of Chr. Obstr. Pul. dis.(COPD ; 13%)
• Neuromuscular diseases (5%)

9. 3. Adjunct to other forms of therapy :
• To reduce cerebral blood flow in pts with
increased intracranial pressure
• With endotracheal intubation for airway
protection
• In Critically ill pts may be indicated before
diagnostic or therapeutic procedures

10. Indications for mechanical ventilation
Indications Parameters
Acute Ventilatory Failure PaCO2 >50mmHg
pH< 7.30
Apnea
Impending Ventilatory Failure TV< 3 to 5ml/kg
Frequency >25 to 30
Minute ventilation >10/ L
Vital Capacity< 15ml / kg
Rising PaCO2> 50mm Hg
Severe Hypoxemia PaO2< 60 mmhg at FiO2 >50%
PaO2 <40 mm hg at any FiO2
PaO2 / FiO2 <300
Prophylactic ventilatory support prolonged shock , CAD
head injury, thoracic/ abd surg
smoke inhalation

11. Types of MV
• 2 basic types :
1. NIV provided with tight-fitting face mask ,
nasal mask or hood , implemented as bilevel
positive airway pressure ventilation (BiPAP)
or pressure-support ventilation (PSV)
2. Conventional MV is implemented by cuffed
tube insertion into trachea to allow
conditioned gas delivered to airways & lungs
at pressures above atmospheric pressure .

13. Noninvasive Ventilation
• Effective in : Acute or chronic respiratory failure
• Ass. with fewer complications- pneumonia &
tracheolaryngeal trauma
• NIV effective in : RF arising from exacerbations of
COPD
• Both modes BiPAP/PSV, apply preset positive
pressure during insp. & lower pressure during
exp. , well tolerated by conscious pt & optimize
pt-ventilator synchrony

14. Limitations of NIV
1. Pt intolerance : interface required for cause
physical & psychological discomfort
2. Acute hypoxemic respiratory failure

15. • Most important group for NIV trial : pt with
COPD exacerbations & resp.acidosis(pH<7.35)
• In pts with ventilatory failure having blood pH
levels between 7.25 and 7.35, low failure
rates(15-20%) & good outcomes
• Severely ill pts with blood pH <7.25, higher
failure rates as pH decreases

16. • In pts with milder acidosis(pH>7.35) NIV not
better than conventional treatments :
1.Controlled Oxygen delivery 2.Pharmacotherapy
for exacerbations of COPD (systemic
glucocorticoids, bronchodilators , if needed
antibiotics)
• NIV is not useful in majority of cases of resp.
failure & can delay lifesaving ventilatory support,
can result in aspiration or hypoventilation

17. Contraindications for NIV
1. Cardiac or Respiratory Arrest
2. Severe Encephalopathy
3. Severe Gastrointestinal Bleed
4. Hemodynamic Instability
5. Unstable Angina & Myocardial Infarction
6. Facial Surgery or Trauma
7. Upper Airway Obstruction
8. High-risk Aspiration and/or Instability to protect
airways
9. Inability to clear Secretions

18. NIV Monitoring
• Reduction in respiratory frequency & decrease
in use of accessory muscles : good indicators
of therapeutic benefit
• Arterial Blood Gases should be determined
within hours of initiation
• Lack of benefit within time frame: alerts for
need of conventional MV

19. Conventional MV
• During intubation to avoid brain-damaging
hypoxia
• Mild sedation may facilitate procedure
• Opiates & benzodiazepines good choices but
can have deleterious effect on hemodynamics
if depressed cardiac function or low systemic
vascular resistance

20. • Morphine can promote histamine release from
tissue mast cells & worsen bronchospasm in pts
with asthma; fentanyl, sufentanil, & alfentanil are
acceptable alternatives
• Ketamine may increase systemic arterial pressure
& ass. with hallucinatory responses
• Shorter acting agents – Etomidate & Propofol
used for induction & maintenance of anesthesia
fewer adverse hemodynamic effects

21. Avoid Neuromuscular Paralysis
1. Renal failure
2. Tumor lysis syndrome
3. Crush injuries
4. Medical conditions associated with
hyperkalemia
5. Muscular dystrophy syndrome
• Deploarizing Neuromuscular blockers such as
succinylcholine chloride, must be avoided

22. Principles of MV
• Basic Goals:
1. Optimize Oxygenation
2. Avoiding ventilator-induced lung injury due
to overstrech and collapse/re-recruitment
known as protective ventilatory strategy

23. • High airway pressures & volumes and
overstreching of lung as well as collapse/re-
recruitment leads to poor clinical outcomes
(barotrauma&volume trauma)
• Normalisation of pH by CO2 elimination rqd
but risk of lung damage ass. with large volume
& high pressures to achieve it given concept of
permissive hypercapnia, as excess acidosis
prevented by pH buffering

25. Modes of Ventilation
• Mode : manner in which ventilator breaths are
triggered, cycled, & limited
1. Trigger : either inspiratory effort or time-
based signal, defines what ventilator senses
to initiate assisted breath
2. Cycle : factors that determine end of
inspiration. eg. In volume cycled vent., insp.
ends specific TV is delivered , other types :
pressure cycling & time cycling

26. 3. Limiting factors : operator-specified values ,
e.g airway pressure, monitored by transducers
internal to ventilator circuit throughout
resp.cycle
• If specified values exceeded, inspiratory flow
terminated & ventilator circuit vented to
atmospheric pressure or specified pressure at
end of expiration(positive end-expiratory
pressure or PEEP)

28. Volume Controlled Ventilation

29. Pressure Controlled Ventilation

30. Basic modes of ventilation
CMV PCV PS
Breath Mandatory/Assisted Mandatory/Assisted Spontaneous
Control Volume Pressure Pressure
Trigger Time / Flow or pressure Time / Flow or pressure Flow or
pressure
Limit Volume or flow Pressure Pressure
Cycling Time / Volume or flow Time Flow
Expiratory PEEP PEEP PEEP

31. Assist-Control Ventilation
• Most widely used mode
• Inspiratory cycle initiated by pt’s inspiratory
effort or if none detected within specified
time window, by timer signal within ventilator
• Every breath delivered, pt- or time triggered,
consists of operator-specified tidal volume
• Ventilatory rate determined by pt or operator-
specified backup rate, whichever of higher
frequency

32. ACMV used for initiation of MV because
• Ensures backup minute ventilation in absence
of intact respiratory drive
• Allows for synchronization of ventilator cycle
with pt’s inspiratory effort
Problems can arise when ACMV used in pts
with tachypnea due to nonrespiratory or
nonmetabolic factors, such as anxiety, pain, &
airway irritation :

33. 1. Respiratory alkalosis may develop & trigger
myoclonus or seizures
2. Dynamic hyperinflation leading to increased
intrathoracic pressures ( auto-PEEP) if
inadequate time available for complete
exhalation between inspiratory cycles
• auto-PEEP limit venous return, decrease
cardiac output, & increase airway pressures
predisposing to barotrauma

34. Intermittent Mandatory Ventilation
• 0perator sets no. of mandatory breaths of fixed
volume to be delivered by ventilator, between
those breaths, pt can breathe spontaneously
• In most frequently used synchronized
mode(SIMV), mandatory breaths are delivered in
synchrony with pt’s inspiratory efforts at
frequency determined by operator
• If pt fails to initiate breath, ventilator delivers
fixed tidal-volume breath & resets internal timer
for next inspiratory cycle

35. • SIMV differs from ACMV in that only preset
number of breaths are ventilator-assisted
• SIMV allows pts with intact respiratory drive
to exercise inspiratory muscles between
assisted breaths, useful for both supporting &
weaning intubated pts
• SIMV difficult to use in pts with tachpnea bcz
may attempt to exhale during vent-
programmed inspiratory cycle

36. • If tachypnea represents response to
respiratory or metabolic acidosis, change in
ACMV will increase minute vent., normalize
pH while underlying process is further
evaluated & treated

37. Pressure-Support Ventilation
• Ventilation is patient-triggered, flow cycled, &
pressure-limited
• Graded assistance & operator sets pressure
level (rather than volume) to augment every
spontaneous respiratory effort
• Pressure adjusted by observing pt’s
respiratory frequency
• Inspiration is terminated when inspiratory
airflow falls below certain level

38. • Pt receive ventilator assistance only when
ventilator detects inspiratory effort
• PSV used with SIMV to ensure volume-cycled
backup for pts whose resp. drive is depressed
• PSV well tolerated by most pts who are being
weaned
• PSV parameters can be set to provide full
vent.support & withdrawn to load
resp.muscles gradually

39. Other Modes of Ventilation
• Each with its own acronym
• Each with specific modifications:
1. Manner & Duration in which pressure is
applied to airway & lungs
2. Interaction between mechanical assistance
provided by ventilator & pt’s respiratory
effort

40. Pressure-Control Ventilation(PCV)
• PCV : time-triggered, time-cycled, and
pressure-limited
• Specified pressure : imposed at airway
opening throughout inspiration
• Since inspiratory pressure specified by
operator, tidal volume & inspiratory flow rate
dependent

41. • PCV : preferred mode for pts in whom it is
desirable to regulate peak airway pressures :
1. Pts with preexisting barotrauma
2. Post-thoracic surgery pts in whom shear
forces across fresh suture line should be
limited
• When PCV used minute vent. altered through
changes in rate or pressure-control value, with
consequent changes in TV

42. Inverse-Ratio Ventilation
• Variant of PCV with prolonged inspiratory time
with appropriate shortening of expiratory time
• Used in severe hypoxemic resp. failure but no
clinical-trial shown it improves outcome
• Increases mean distending pressures without
increasing peak airway pressures
• Work in conjunction with PEEP to open
collapsed alveoli & improve oxygenation

43. Continuous Positive Airway Pressure
(CPAP)
• Not true support mode of vent. bcz all vent.
occurs through pt’s spontaneous efforts
• Vent. gives fresh gas to breathing circuit with
each insp. & sets it to constant, operator-
specified pressure
• Uses
1. to assess extubation potential in weaned pts
requiring little vent.support
2. in pts with intact resp.system function but for
airway protection

44. Nonconventional Ventilatory Strategies
• Several strategies for improving gas exchange
& survival rates in severe hypoxemic
respiratory failure
1. High-frequency oscillatory ventilation(HFOV)
2. Airway pressure release ventilation (APRV)
3. Partial liquid ventilation (PLV) using
perfluorocarbons & administration of nitric
oxide gas delivered through airways

45. Salvage techniques
• 1. Extracorporeal membrane oxygenation
(ECMO) documented positive outcomes , with
popularity of venous-venous access
• Guidelines for ECMO centres are there, if
considered pts with severe resp.failure refractory
to conventional therapy can be referred
• 2. Prone positioning : several multi-centric
randomized trials in acute lung injury & refractory
hypoxemia shown it improves ventilation-
perfusion matching & provides short and long
term survival advantage

46. New Ventilator Modes
• To improve pt-ventilator synchrony by
allowing pts to trigger ventilator with their
own effort,
• Incorporating flow algorithms that terminate
cycle once preset criteria are reached
• Improved pt comfort
• Modes that synchronize not only timing but
levels of assistance to match pt’s effort

47. • 2 modes are designed to deliver assisted
breaths through algorithms incorporating not
only pressure, volume, and time but also
1. Overall respiratory resistance as well as
compliance in case of PAV (Proportional
Assist Ventilation)
2. Neutral activation of diaphragm in case of
NAV (Neurally adjusted Ventilatory-assist
Ventilation)

49. Protective Ventilatory Strategy
• In Acute Resp.failure, several RCTs indicate
protective ventilation approach guided by
following principles safe & offers good
outcome :
1. Set target tidal volume close to 6mL/kg of
ideal body weight
2. Prevent plateau pressure (static pressure in
airway at end of inspiration) >30cm H20

50. 3. Use lowest possible fraction of inspired
oxygen (FiO2) to keep SaO2 at >_ 90%
4. Adjust PEEP to maintain alveolar patency
while preventing overdistention and
closure/reopening

51. Troubleshooting : identification and resolution of technical
malfunctions in patient- ventilator system

53. Patient Management
• Once pt’s gas exchange stabilised, definitive
therapy for underlying process responsible for RF
continued
• Modifications in ventilator therapy parallel with
changes in pt’s clinical status
• With improvement in resp. function, first priority
: reduce level of mechanical ventilatory support
• Pts whose condition continues to deteriorate
after ventilatory support initiated may require
increased O2, PEEP, or alternative modes of vent.

54. General Support during Ventilation
1. Sedation & Analgesia required to maintain
acceptable level of comfort
• Combination of benzodiazepine & opiod
administered i.v
• Oversedation must be avoided
• Daily interruption of sedation in pts with
improved ventilatory status results in shorter
time on ventilator and shorter ICU stay

55. 2. Immobilized pts : risk of DVT & Decubitus ulcers
• venous thrombosis prevention use :
subcutaneous heparin and/or pneumatic
compression boots, fractionated LMWH equally
effective
• decubitus ulcer prevention : frequent changes in
body position & use of soft mattress overlays and
air mattresses
• Early Mobilization recommended

56. 3. Prophylaxis against diffuse gastrointestinal
mucosal injury indicated
• Histamine-receptor (H2 receptor) antagonists,
antacids, & cytoprotective agents such as
sucralfate appear to be effective
4. Nutritional support by Enteral feeding through
nasogastric or orogastric tube should be initiated &
maintained whenever possible
• Parenteral nutrition alternative to Enteral in pts
with severe gastrointestinal pathology

58. Complications of MV
• Endotracheal intubation & MV have direct &
indirect effects on lung and upper airways ,
cardiovascular and gastrointestinal system
1. Pulmonary complications : barotrauma,
nosocomial pneumonia, oxygen toxicity,
tracheal stenosis, and deconditioning of
respiratory muscles

59. • Clinically significant pneumothorax requires tube
thoracostomy
• High risk of ventilator associated pneumonia
due to aspiration from upper airways through
small leaks around ET cuff, mc organisms
responsible are Pseudomonas aeruginosa, enteric
gram-negative rods, & Staphylococcus aureus
• High mortality rate of VAP, so early initiation of
empirical antibiotics against likely pathogens
recommended

60. 2. Hypotension resulting from elevated
intrathoracic pressures with decreased venous
return : responsive to intravascular volume
repletion
3. Hemodynamic monitoring with pulmonary
arterial catheter may be of value in identifying
cardiac or pulmonary origin of alveolar edema that
caused resp.failure
4. GIT effects of positive-pressure vent. : stress
ulceration & mild to moderate cholestasis

61. Weaning from MV
• Ventilatory Weaning Task Force cites following
conditions for weaning :
1. Lung is stable or resolving
2. Gas exchange is adequate, with low
PEEP(<8cmH2O) and FiO2(<0.5)
3. Hemodynamic variables are stable, and pt.
no longer receiving vasopressers
4. Pt is capable of initiating spontaneous
breaths

62. • Wean Screen based on variables should be done
atleast daily, if pt deemed capable of beginning to
wean, perform spontaneous breathing trial(SBT)
• SBT : integrated pt assessment during
spontaneous breathing with little or no
ventilatory support
• SBT implemented with T-piece using 1-5cm H2O
CPAP or 5-7cmH2O PSV from ventilator to offset
ET resistance

63. • If determined pt can breathe spontaneously,
decision to remove artificial airway should be
undertaken only when concluded pt :
1. has ability to protect airways
2. is able to cough & clear secretions
3. is alert enough to follow commands

64. • If upper airway difficulty is suspected do :
cuff-leak test(assessing presence of air
movement around deflated ET cuff)
• if it suggests risk of post-extubation stridor;
consider administration of systemic
corticosteroids prior to extubation

65. • Despite all precautions ~10-15% of extubated
pts require reintubation
• NIV can obviate reint. esp. in pts with
ventilatory failure secondary to COPD
exacerbation or Congestive Heart Failure
• Earlier extubation with prophylactic NIV
yielded good results

67. Prolonged MV and Tracheostomy
• From 5 to 13% pts undergoing MV require
prolonged MV(>21days)
• Individualized decision of tracheostomy : risk
& benefits of tracheostomy and prolonged
intubation as well as pt’s preferences &
expected outcomes
• Tracheostomy is thought more comfortable, to
require less sedation, & to provide more
secure airway and may reduce weaning time

68. • Trachestomy carries risk during 5-40% of
procedures : bleeding, cardiopulmonary
arrest, hypoxia, structural damage,
pneumothorax, pneumomediastinum, &
wound infection
• Long term risks : tracheal stenosis,
granulation, erosion of innominate artery
• If pt needs MV for >10-14days, tracheostomy
under optimal conditions is indicated

69. • 5-10% pts are deemed unable to wean in ICU,
these may benefit from transfer to special
units
• Units involve multidisciplinary approach
including nutrition optimization, physical
therapy with rehabilition, slower weaning
methods( including SIMV with PSV)
• Units have successful weaning rates of up to
30%

70. • Close to 2% of ventilated pts may become
dependent on ventilatory support to maintain
life.
• Taken care in chronic care institutions and
some with strong social, econoic, & family
support may live relatively fulfilling life with
at-home ventilation

71. Thank you