Mechanical ventilation provides positive pressure ventilation to support patients who are unable to breathe adequately on their own. The document discusses various modes of mechanical ventilation including controlled mandatory ventilation, volume control ventilation, pressure control ventilation, assisted-control ventilation, synchronized intermittent mandatory ventilation, and pressure support ventilation. It explains the basic parameters used in mechanical ventilation like tidal volume, respiratory rate, PEEP, and I:E ratio. It also discusses principles of weaning a patient from mechanical ventilation and assessing readiness for weaning.

1. Mechanical Ventilation:
Basic Modes
Dr. Shahnawaz Alam
Guided by:-Dr. Vikas Chandra Jha
HOD Neurosurgery
Moderated by:-Dr.Saraj kumar Singh
Asst.Prof.(Dept. of Neurosurgery)

2. Objectives
 To understand the basic modes of ventilator.
 The basics of Invasive positive pressure ventilation (IPPV) &
Noninvasive positive pressure ventilation (NIPPV).
 How ventilator helps in reducing the work of breathing &
restore adequate gas exchange.
 The principles of bedside monitoring: Pressure and volume
alarms/Flow and pressure time curves.

3. “OUTCOME IN ICU DEPENDS
ON VENTILATOR SETTINGS”
“AS A NEUROSURGERY
RESIDENT/NEUROGURGEON,
WOULD BE PRIMARILY
RESPONSIBLE FOR PATIENT
CARE IN NEURO-ICU”

4. What are ventilator ?
• A machine that generates a controlled flow of gas into a patient’s
airways by assisting or replacing spontaneous breathing.
• Supportive role to buy time.
Negative pressure ventilation
Positive pressure ventilation: Simple
pneumatic system/New generation
microprocessor controlled systems.

5. Who needs a ventilator?
• Can’t oxygenate (low PaO2/SpO2).
• Can’t ventilate (high PaCO2).
• Can’t generate enough tidal volume due to muscle or nerve
weakness→ high PaCO2 /low SpO2.
• Can’t participate or protect airway (low GCS).
• If you’re not sure whether or not the patient needs a ventilator
→ the patient needs a ventilator!

6. Goals of Mechanical Ventilation
• Correct hypoxemia – PO2 > 60mmHg or SpO2 > 90%.
• Correct hypercapnia – PCO2 ~ 40mmHg.
• Reduce work of breathing
• Provide rest to respiratory muscles and reduce oxygen cost of
breathing.

7. Basic Ventilator Parameters
• Tidal volume(Vt)
• Frequency (f)
• FiO2 SPO2
• Airway pressure
• Positive End Expiratory Pressure(PEEP)
• I:E Ratio
Ve=Vt x f Ve = PaCO2

8. Tidal Volume
• Volume of air needed to adequately remove CO2 from the
blood.
• Usually 6-10 ml/kg of body weight.
• Current literature lower tidal volume practice.

9. Frequency
• The frequency that the tidal volume must be delivered to
adequately remove CO2.
• Usually 12-14/min may be increased or decreased as
indicated by arterial CO2 levels.
• Actual rate may be higher than the set rate if the patent is
initiating spontaneous breaths.

10. FiO2
• FiO2 is the amount of oxygen delivered to the patient.
• Oxygen concentrations of greater than 0.50 (50%) increase
the risk of oxygen toxicity if delivered for more than 24 hours.

11. POSITIVE END EXPIRATORY PRESSURE(PEEP)
• Elevation of baseline Paw above Patm.
• Not a standard mode of ventilation but used as adjunct to other
modes.
Hazards of PEEP:
•Lowers venous return, CO
•Barotrauma (PEEP>10 cm H2O)
•Increased CVP, ICP

12. I:E Ratio
• The normal ratio of inspiration to expiration is 1: 1.5 - 1: 2.
• Longer Ti → opening of stiff alveoli units → improves
oxygenation.
• Shorter Ti → encourages lung emptying.
• Te → prevent alveoli from collapse →intrinsic PEEP
→reduction of shunting.
• Thus, adjustments in I:E ratios are goal oriented.
• Ratios >1 inverse ratio ventilation.

13. Pressure Waveforms
Depicts changes in airway pressure over time
 Baseline is normally zero. If PEEP is applied, the baseline
pressure will equal the PEEP.

14. Starting a ventilator-Mode
• Mode denotes interplay b/w patient and the ventilator.
• Describes the style of breath support based on relationship
between the various possible types of breath and inspiratory
phase variables.

15. The ventilator circuit

16. ventilatory phases
• Each ventilatory breath has
four phases:
1. Initiation phase
2. Inspiratory phase
3. Plateau phase
4. Expiratory phase

17. Variables
• Respiration is a dynamic process in which pressure, volume and flow
are function of time . They are called as variables.
• There are two kinds of variables- Control variables & Phase
variables.
Control Variables
• Control the delivery of a breath.
• The clinician can choose to keep either volume or pressure constant
from breath to breath.
• The control variables are used to describe modes of ventilation -
 Volume-controlled (VC) ventilation
 Pressure-controlled (PC) ventilation

18. Phase Variables
• How the ventilator
controls the phases of the
respiratory cycle depends
upon the phase variables.
• Four phase variables are -
– Trigger variable
– Limit variable
– Cycle variable
– Baseline variable

20. Trigger Variables
• Determine how a breath is started.
• A breath can be initiated (triggered) either by:
– The ventilator
– The patient
 Ventilator-triggered breaths: initiated in response to a timer
inside the ventilator. The exact time interval is determined by
the set rate.

21.  Patient-triggered breaths are termed as:
– Spontaneous breath: completely regulated by the patient
with no contribution by the ventilator.
– Assisted breath: initiated by the patient, but all other
aspects of the breath are controlled by the ventilator.
– Supported breath: initiated and ended by the patient, but
the breath is delivered under positive pressure by the
ventilator.
 Trigger variables: pressure/flow/volume/time.

22. Cycle Variables
• Determine how a breath ends.
• The change over from inspiration to expiration and from
expiration to inspiration is called cycling.
• It can be determined by :
• Volume cycle (desired volume met)
• Flow cycle (desired flow met)
• Pressure cycle (desired pressure met)
• Time cycle (elapsed time met)

23. Limit Variable

24. Baseline Variable

25. CONTROLLED Vs ASSISTED VENTILATION
Controlled breaths are time triggered breaths.
• Patient cannot initiate breath sequence irrespective of effort.
• May be volume or pressure targeted.
• Patient cannot control RR, VT or Paw.
Assisted breaths are triggered by patients’ effort (Flow/ Pressure)
• Once breath is initiated, pre-set VT or Paw attained by the
ventilator.
• Patient can control RR but not VT or Paw.

26. BREATH TYPE:
Spontaneous vs Mechanical vs Assisted

27. INVASIVE
IPPV
FULL
SUPPORT
CMV
VOLUME
CONTROL
PRESSURE
CONTROL
PARTIAL
SUPPORT
SIMV PSV

28. Basic Modes of Ventilation
• Controlled Mandatory Ventilation (CMV): Pressure control(PC) or
Volume control(VC)
• Asst-Control Mandatory Ventilation (ACV)
• Intermittent Mandatory Ventilation(IMV)
• Synchronized Intermittent Mandatory Ventilation(SIMV)
• Pressure Support Ventilation (PSV)
• Combinations: SIMV(PC)+PS / SIMV(VC)+PS

29. PATIENT COMFORT SCALE
+ -
Spontaneous
Breathing
Controlled
Mechanical
Ventilation
Assist
Control
Ventilation
Synchronized
Intermittent
Mechanical
Ventilation
Pressure
Support
Ventilation
Pressure
Control
Ventilation

30. Controlled mandatory ventilation(CMV)
• Delivers Preset Vt(or pressure) at a time triggered (preset) RR(f).
• As it controls both Vt (pressure) and f Ve
• Patient cann’t breath spontaneously/change the ventilator ‘f’
• Suitable when no breathing efforts/disease or Under heavy sedation
and muscle relaxants.
• Asynchrony and increased work of breathing.
• Not suitable in awake or has respiratory efforts.
• Cann’t be used during weaning.

31. Volume Control Ventilation
• Ventilator delivers a pre-set TV.
• Pressures may vary with changes in R and CL but volume remains constant.
• Inspiration ends when the pre-set TV is reached/certain time elapses
(inspiratory hold).
• Time triggered, Flow limited, Time/Volume cycled ventilation.

32. Settings:
• Vt , f, Flow/ Time and FiO2
• VT: 6 – 12 ml/kg
• f: 10 – 15 bpm
• FiO2: lowest possible to achieve
oxygenation.
• I:E : 1:2 – 1:4
Monitoring and alarms:
• PIP and Pplat relates to CL.
• High/Low pressure alarm: 5 – 10 cmH2O
above/below ventilating pres.
• Low pressure and volume alarms signify
leak in system.

33. Pressure Control Ventilation
• Provides pre-set pressure to the airways, not exceeding the set level
irrespective of changes in CL and R.
• Vt is variable depending on compliance, Raw , set pressure and patient effort.
• Expiration occurs once a pre-set Ti has elapsed.
• Time triggered, Pressure limited, Time cycled ventilation.

34. Settings
• Pressure: < 30 cm H2O
• f : 10-15 bpm
• I:E ratio: 1:2 - 1:4
• Ti and flow rate depend on I:E ratio and f
Monitoring and alarms:
• Low Volume alarm: increased resistance
or decreased compliance (in VCV
signifies leak).
• Low pressure alarm: ≈10 cm H2O below
patients ventilation pressure leak in
the system.

35. ASSIST /CONTROL MODE
• A set Vt (VC) or a set pressure and time (PC) is delivered at a minimum rate.
• Additional ventilator breaths are given if triggered by the patient.
• Mandatory breaths: Ventilator delivers preset volume and preset flow rate
at a set back-up rate.
• Spontaneous breaths: Additional cycles can be triggered by the patient but
otherwise are identical to the mandatory breath.

36. • Vt of each delivered breath is the same, whether it is assisted or
controlled breath.
• Minim. breath rate is guaranteed (controlled breaths with set Vt).

37. Pros:
• Asynchrony taken care of to some extent.
• Low WOB as every breath is supported and Vt is guaranteed.
Cons:
• Hyperventilation
• Natural breaths are not allowed
• Breath stacking
• High volumes and pressures
 C/I: Irregular RR/Hiccoughs/Brainstem injury
 Hyperventilation and breath stacking can be overcome by
choosing optimal ventilator settings and appropriate sedation

38. Intermittent Mandatory Ventilation(IMV)
• Machine breaths are delivered at a set rate (volume or pressure limit).
• Patient is allowed to breath spontaneously from either a demand valve or a
continuous flow of gases but not offering any inspiratory assistance.
• Patient’s capability determines Vt of spontaneously breaths.
• Some freedom to breath naturally even on mechanical ventilator.

39. Pros:
• Freedom for natural spontaneous breaths even on machine.
• Lesser chances of hyperventilation.
Cons:
• Asynchrony/Random chance of breath stacking.
• Increase WOB.
• Random high airway pressure (barotrauma) and lung volume
(volutrauma).
 The con’s have been addressed in newer modes like SIMV and PSV
and IMV is not an option in most modern ventilators.

40. Synchronized Intermittent Mandatory Ventilation
(SIMV)
• Ventilator delivers either patient triggered assisted breaths or time triggered
mandatory breath in a synchronized fashion so as to avoid breath stacking.
• If the patient breathes between mandatory breaths, the ventilator will allow
the patient to breathe a normal breath by opening the demand (inspiratory)
valve but not offering any inspiratory assistance.
• If patient does not make an inspiratory effort then ventilator will deliver a
time triggered mandatory breath.

41. Synchronisation window
• Time interval just prior to time trigger when the ventilator is
sensitive to patient effort and assisted breath is delivered.
• Varies in different manufacturers but 0.2-0.5 sec bfr time trigger
is standard.
• If the patient makes a spontaneous inspiratory effort that falls in
sync window, the ventilator is patient triggered to deliver an
assisted breath and will count it as mandatory breath.
• If the pt triggers outside this window, vent will allow this
spontaneous breath to occur by opening the demand
(inspiratory) valve but does not offer any inspiratory assistance.

42. SIMV contin…
• Mandatory breaths are ‘sychronised’ with patient effort.
• Mandatory breaths may be time triggered (poor RR) or patient
triggered (good RR).Thus, mandatory breaths my be assisted or
controlled.
• Mandatory breaths can be set as volume controlled or pressure
controlled.
• The problem of ‘breath stacking’ and dysynchrony addressed
But the problems of WOB and Raw during spontaneous breath
persisted.
• This is tackled with use of Pressure Support as adjunct.

43. In SIMV -3 types of breathing:
1. Patient initiated assisted ventilation
2. Ventilator generated controlled ventilation
3. Unassisted spontaneous breath

44. DUAL CONTROL MODES
Advantages of Pressure control ventilation
(Rapid decelerating flow)
+
Advantages of volume-control ventilation
(constant MV)

45. PRESSURE REGULATED VOLUME CONTROL(PRVC)/
ADAPTIVE PRESSURE CONTROL (APC)/AUTOFLOW
• Achieve volume support while
keeping PIP lowest possible.
• Ventilator gives a trial breath and
calculates Pplat & compliance.
• Pressure gradually increased till it
reaches set Vt.
• PIP is kept at lowest by altering the
flow rate and inspiratory time in
response to changing compliance or
Raw.

46. OTHER MODES
Inverse Ratio Ventilation (IRV)
• Longer inspiratory time; I:E = 2:1 – 4:1.
• Beneficial in ARDS by – reducing
intrapulmonary shunt, reduced dead
space ventilation, Better V/Q matching.
• Higher MAP - more chances of
barotrauma.
• May worsen pulmonary edema.
• Requires sedation and paralysis.

47. Spontaneous Modes
 Three basic means of providing support for continuous
spontaneous breathing during mechanical ventilation:
• Pressure Support Ventilation-PSV
• Continuous positive airway pressure- CPAP
INDICATIONS
• Spontaneously breathing patients who require
additional ventilatory support to help overcome -
 WOB, CL, Raw
 Respiratory muscle weakness
• Weaning

48. Pressure Support Ventilation
• Applicable on Spontaneous breaths/No mandatory breaths.
• Pressure (or Pressure above PEEP) is the setting variable.
• The ventilator provides a constant pressure during inspiration
once it senses that the patient has made an inspiratory effort.
• Patient effort determines size of breath and flow rate.
• Patient triggered, pressure targeted, flow cycled mode of
ventilation.

49. ADVANTAGES
• Full to partial venti. support/
Facilitates weaning
• Augments the patients spont Vt.
• Decreases patient WOB by
overcoming the resistance of
the artificial airway, vent circuit
and demand valves.
• May be applied in any mode
that allows spontaneous
breathing, e.g., VC-SIMV, PC-
SIMV.
DISADVANTAGES
• Requires consistent spont
ventilation.
• Patients in stand-alone mode
should hv back-up ventilation.
• Vt variable and dependant on
lung characteristics and
synchrony.
• Fatigue and tachypnea if PS
level is set too low.

50. ASSESMENT OF READYNESS TO WEAN
General preconditions:
• Reversal of primary problem
• Patient is awake and responsive
• ability to cough
• No or minimal inotropic support
• Normalising metabolic status
• Adequate Hb concentration
Objective values:
• Vital Capacity > 10 ml/kg
• RR <35
• Tidal volume > 5ml/kg
• Max inspiratory pressure <-25 cm
H2O
• RR /Vt <100 b/min/L
{Rapid Shallow Breathing Index (RSBI)}
• PaCO2 < 50 mmHg
• PaO2 > 90 mm Hg at FiO2 0.4
• PaO2/ FiO2 > 200

51. Causes of failure to wean:
1. Hypoxemia: Diffuse pulmonary/Focal pulmonary disease (Pneumonia)
/Pulmonary edema
2. Insufficient Ventilatory Drive: d/t to metabolic alkalosis/Inadequate CNS drive
(Ex: sedatives, malnutrition)
3. Excessive Ventilatory Drive:Excessive CO2 production (sepsis, agitation, fever,
high carbohydrate intake)
4. Respiratory Muscle Weakness: Neuromuscular disease/Malnutrition/Drugs
(Neuromuscular blocking agents, Corticosteroids,aminoglycosides)
5. Excessive WOB: Airway obstruction/Bronchospasm/Secretions/Increased Raw
(ETT)/ETT too small/Chest motion restriction (pain, bandages)
6. Phrenic nerve Injury: especially with contralateral pulmonary disease

52. Bedside Monitoring
VARIABLE FLOW EXAHALATION
AIRWAY OBSTRUCTION

53. Bedside Monitoring
AUTOCYCLING
LEAK

54. Important Pitfalls and Problems Associated with PPV
• Heart and circulation
- Reduced venous return and afterload
- Hypotension and reduced cardiac output
• Lungs: Barotrauma/VILI/Air trapping
• Gas exchange
- May increase dead space (compression of capillaries)
- Shunt (e.g., unilateral lung disease - the increase in
vascular resistance in the normal lung associated with
PPV tends to redirect blood flow in the abnormal lung)

55. Barotrauma
• Microscopic rupture of the alveolus with subsequent entry of
air into the pleural space (pneumothorax) and/or the tracking of
air along the vascular bundle to the mediastinum
(pneumomediastinum), 6-25%.
• Large TV and elevated PIP and Pplat are risk factors.
• PIP <45 mm Hg and Pplat <30-35 mm Hg are recommended.

56. Volutrauma
• local over distention of normal alveoli.
• over distention-an inflammatory cascade causing additional
damage to previously unaffected alveoli.
• ARDS like clinical scenario.
• PEEP may be beneficial in preventing this type of injury.
• Protective lung ventilation strategy is recommended in all
patients with ARDS or acute lung injury.

58. Oxygen toxicity
• Complication has been reported in patients given a
maintenance FIO2 of 50% or above for longer duration.
• Cause a variety of complications-mild tracheobronchitis,
absorptive atelectasis, hypercarbia, and diffuse alveolar
damage that is indistinguishable from ARDS.
• Encouraged to use the lowest FIO2 that accomplishes the
needed oxygenation.
• If necessary, PEEP should be considered a means to improve
oxygenation while a safe FIO2 is maintained.

59. VENTILATOR ASSOCIATED PNEUMONIA
(VAP)
• Defined as pneumonia occuring > 48 hrs after intubation and
mechanical ventilation.
• Estimated incidence is 10-25%, mortality of 33-76%.
• Early onset (2-5 days) – S.Pneumoniae, H. Influenzae,MSSA, E.Coli,
Klebsiella.
• Late onset (> 7 days) – P. Aeruginosa, Acinetobacter, MRSA, other
MDR pathogens.

60. VAP Contn…
DIAGNOSIS
 Presence of a new or progressive infiltrate in CXR plus two of
the following:
• Fever > 38 0C.
• Leukocytosis/ Leukopenia.
• Purulent tracheobronchial secretions.
• Respiratory tract sampling using BAL, mini BAL, tracheo-
bronchial aspiration for microscopy and quantitative culture.

61.  PREVENTION
‘bundled approach’ has shown to reduce the incidence of
VAP by 95%.
Components :
• Appropriate cuff/Change of circuit every 7 days.
• HME filter and suction devices changed daily.
• ETT with dorsal lumen for sub-glottic secretions.
• Elevation of head 30-45o.
• Strict hand hygiene/Oropharyngeal decontamination.
• Sedative vacation; early extubation.
• Non invasive ventilation.
• Prophylactic antibiotics are not recommended.

62. TREATMENT:
• Emperical antibiotic therapy after sampling.
• Choice of antibiotic depends on local prevalance of organisms
and the patient’s risk for MDR infection.
• Low risk – Ceftriaxone/ Levo, ciprofloxacin/ Ampicillin
sulbactam/ Ertapenem.
• High risk –Antipseudomonal (Cefipime/Ceftazidime/
carbapenems/ Piperacillin TZ) + Fluroquinolone/ Aminoglycoside
+ Linezolid/ Vancomycin.

64. NON- INVASIVE PPV
• NIPPV is ventilator support
provided without invasive
airway control-No
tracheostomy /No ETT.
• Mostly used to provide
pressure support during
spontaneous ventilation,
BiPAP, CPAP.
• Also used as an option for
weaning.

65. ADVTG:
 Allows the patients to
maintain normal functions-
Speech/Eating.
 Helps avoid the risks and
complications related to:
Intubation/Sedation.
 Less ventilator-associated
Pneumonia.
DISADVTG:
 Less airway pressure is
tolerated.
 Does not protect against
aspiration.
 No access to airway for
suctioning.

66. Continuous positive
airway pressure (CPAP)
• PEEP applied to spontaneous
breathing patient.
• Can be applied via ETT/face
mask/nasal mask.
• Less adverse effects than PEEP
because of spontaneous rather
than PPV.
Bilevel positive airway pressure
(BiPAP)
• Inspiration positive pressures to
inspiration (IPAP) and expiration (EPAP).
• IPAP provides pressure support during
inspiration and EPAP helps in
recruitment and FRC.
• Initially IPAP – 8 cm H2O, EPAP – 4 cm
H2O; maybe increased or decreased in
2cm.

67. Clinical Use of NIPPV in ICU
• Decompensated COPD (Hypercapnic Respiratory Failure).
• Cardiogenic pulmonary edema.
• Hypoxic respiratory failure.
• Other possible indications: Weaning (post-extubation)/Obesity
hypoventilation syndrome.

68. Contraindications to NIPPV
• Cardiac or respiratory arrest/Non-respiratory organ failure.
• Severe encephalopathy (e.g., GCS < 10).
• Severe upper gastrointestinal bleeding.
• Hemodynamic instability or unstable cardiac arrhythmia.
• Facial surgery, trauma, or deformity Upper airway obstruction.
• Inability to cooperate/protect the airway.
• Inability to clear respiratory secretions/High risk for aspiration.

69. SUMMARY
• Ventilator is a support measure, not a treatment modality.
• So pay more attention at the disease that created ventilator dependency rather
than at the knob of ventilator.
• Proper understanding of ventilator function and modes are vital to provide
individualized therapy to a wide range of patients.
• Ventilator graphics can provide valuable information regarding settings and
pulmonary characteristics.
• Early weaning is the norm.
• VILI and VAP are dreaded complications - prevention is better than cure.

70. REFERENCES
• 1. Clinical Application of Mechanical Ventilation – David W Chang, 4th Edition
• 2. The ICU book – Paul L. Marino, 4th edition