‫بسم هللا الرحمن الرحیم‬
‫نگرشي گذرا بر اصول و مباني كار‬
‫ونتیالتورها‬
‫)دستگاههاي تهویه مكانیكي(‬
MECHANICAL
VENTILATION
Dr.Jarahzadeh
Intensivist
Mechanical Ventilation
This is Positive Pressure Ventilation
“Regular” breathing is negative pressure
ventilation
Airway Pressure
If we measure the pressure in the tubing at
the end of expiration, it will be barometric
pressure. (To make it easier, we call it “zero”)
Inhalation generates a negative pressure so
that air will flow from “zero” to “negative”
Machines generate a postitive pressure so
that air will flow from “positive” to “zero”
Pressures
PEAK INSPIRATORY
PRESSURE (PIP)
• PIP: Pressure at end of active inspiration
necessary to overcome airway resistance (flow
resistance) and lung compliance (tissue
resistance)
• Airway resistance can increase work of breathing
• PIP reflects both airway tone and lung stiffness increased by bronchospasm and/or atelectasis
Peak Pressure (Ppeak)
PPeak = PPlat + PRes
Where PRes reflects the resistive
element of the respiratory system (ET
tube and airway)
PLATEAU PRESSURE
• Pressure required to overcome tissue
resistance
and inflate alveoli
• Measured via 2 second pause at end
inspiration
• Gas flow ceases
• Static pressure measurement
• General measurement of lung stiffness
PPlat
Measured by occluding the ventilator 3-5 sec at the
end of inspiration
Should not exceed 30 cmH2O
PIP:
Pressure
compliance
resistance
volume
flow
PEEP
PEEP
time
No active breathing
Treats lung as single unit
PIP
resistance
flow
Pplat
end-inspiratory
alveolar pressure
Flow=0
compliance
tidal volume
PEEP
Respiratory System Compliance
Cs =
Correct for gas compression
Tidal volume
PPlat - PEEP
Total PEEP
Cd=TV/PIP-PEEP
Decreased with:
•
•
•
•
•
•
congestive heart failure
ARDS
atelectasis
consolidation
fibrosis
hyperinflation
• tension pneumothorax
• pleural effusion
• abdominal distension
• chest wall edema
• thoracic deformity
normal 80-100 mL/cm H2O
Compliance pressure (Pplat)
• Represent the static end inspiratory recoil
pressure of the respiratory system, lung
and chest wall respectively
• Measures the static compliance or
elastance
ΔPeso ≈ ΔPpl
Benditt, Respir Care 2005; 50:68
PIP
Crs =
Ppl
(Peso)
Ccw =
tidal volume
Pplat - PEEP
tidal volume
Peso
Palv
(Pplat)
CL =
tidal volume
(Pplat – PEEP) - Peso
In clinical practice Ccw ignore due to large size
Inspiratory Resistance
Ri =
Increased with:
PIP - Pplat
flow
measure with 60 L/min (1 L/s)
constant flow
• Secretions
• Bronchospasm
• Small endotracheal tube
Normal: 5 - 10 cm H2O/L/s for intubated ventilated adults
flow
Auto -PEEP
inhalation
Flow and RR and
Ti/Te
time
0
auto-PEEP
exhalation
History
780
1530 paracelsus
pulmator 1907 druger
denhart 1945(iron lung)
1981microprocesores
(pnumatice chang to electeric &
electeronic)
Paracelsus (1493-1541)
used ‘Fire Bellows’ connected
to a tube inserted into
patient’s mouth as a device
for assisted ventilation. This
was the first study (1550)
which credited him with
the first form of mechanical
ventilation.
Fire Bellows’
Draeger Pulmotor
Alfred f.jones
(1864)
PPV-NPV
‫گروه بندي کلی ماشینهاي مكانیكي‬
‫ فشار منفي‬‫‪ -‬فشار مثبت‬
An iron lung in use (1960)
‫معایب ونتیالتورهای با فشار منفی‬
‫‬‫‬‫‬‫‬‫‬‫‬‫‬‫‪-‬‬
‫حجم زیاد‬
‫توجه زیاد به قفسه سینه تا ریه ها‬
‫کاهش شدید مراقبت های پرستاری‬
‫القائ فشار منفی روی قلب و عروق‬
‫عدم رعایت بهداشت‬
‫کاهش تحرک بیمار‬
‫زخم بستر و فشاری‬
‫نا کارامدی در ریه های سخت و فیبروزه‬
Lung Functions
Oxygenation
Ventilation
Neurohormonal
DEFINITIONS
• Ventilation: Movement of Air Into and
Out of the Lung (Breathing)
• Respiration: Extraction of Oxygen from
Inspired Air and Release of Carbon
Dioxide (Gas Exchange)
1.Internal
2.external
CLINICAL OBJECTIVES OF
MECHANICAL VENTILATION
Provides Supplemental Oxygen and remove Waste
Product of metabolism ( CO2 )
Unloading ventilatory muscle (Keep WOB
reasonable)
Recruits Collapsed Alveoli to Support Respiration
• Increases Functional Residual Capacity (FRC) Keep lungs
adequately inflated
Ventilate safely and avoid complications
Achieve patient/ventilator synchrony with minimal
sedation and no paralysis
Mechanical Ventilation
... is a therapy.
What are the indications?
How do we administer it?
How do we assess it?
What is the end point?
In USA:
1-3 million need MV outside operating
room
50/000 ventilator
Indications for
Mechanical Ventilation
Acute Respiratory Failure (66%)






Acute Respiratory Distress Syndrome
Heart Failure (through pulmonary edema/hypertension)
Pneumonia
Sepsis
Complications of Surgery
Trauma
Coma (15%)
Acute Exacerbation of Chronic Obstructive
Pulmonary Dz (13%)
Neuromuscular Disease (5%)
Esteban A, Anzueto A, Alia I, et al. How is mechanical ventilation employed in the intensive care unit? An
international utilitzation review. American Journal of Respiratory Critical Care Medicine 2000; 161: 1450-1458
Discontinuing
Mechanical Ventilation
Death
Weaning

Up to 25% of patients have respiratory distress
severe enough to require reinstitution of ventilator.
Extubation

10 - 20 % of extubated patients who were
successfully weaned require reintubation.
Brochard L, Rauss A, Benito S, et al. Comparison of three methods of gradual withdrawing from ventilatory support during
weaning from mechanical ventilation. American Journal of Respiratory Critical Care Medicine. 1994; 150: 896-903.
Esteban A, Frutos F, Tobin MJ, et al. A comparison of four methods of weaning patients from mechanical ventilation. New
England Journal of Medicine. 1995; 332: 345-350.
Mechanical Ventilation
Mechanical Ventilation
Tidal breath controlled entirely by the
ventilator
Or
Interactive with patient effort.
MODES OF
VENTILATION
• Classified by the Amount of Work Assumed
by the Ventilator
• Control or Assist Control
• Classified by the Target Used to End
Inspiratory Phase of Each Delivered Breath
• Volume or flow target :set flow and volume as
cycling variable so pressure is dependent
• Pressure target :set time or flow as cycling variable
so volume or flow dependent
VOLUME TARGETED
VENTILATION
• Set Tidal Volume (TV)
• Inspiratory Cycle Ends When TV Delivered
• Ventilator Generates Sufficient Pressure to
deliver set volume
• Independent of Airway Resistance
• Independent of Lung Compliance
• High-Pressure Limit Alarm
• Alveolar Stretch Injury
WK505
Effort
Volume
-Controlled Ventilation
Nilsestuen, Respir Care 2005; 50:202-232
PRESSURE TARGETED
VENTILATION
• Constant Inspiratory Pressure
• Tidal Volume Becomes Variable
• Affected by Airway Resistance, Lung Compliance,
Patient Effort
• Causes of Decreased Tidal Volume
• Increased Resistance
• Decreased Compliance
• Decreased Patient Effort
• Low minute ventilation alarm
Why does the Volume variable
with similar pressure?
‫)‪Transpulmonary Pressure(PTp‬‬
‫( ‪PTp=(PA-PpL‬‬
‫گرادیان فشاری بین فشارداخل وخارج ریوی که مسئول باز نگه‬
‫داشتن راه هوایی میباشد‪.‬‬
‫)‪Transairway Pressure(PTA‬‬
‫‪PTA=Paw-Palv‬‬
‫مسئول حرکت گاز ازخالل راه هوایی می باشد‪.‬جزء مقاومت راه هوایی‬
‫)‪Transthorasic Pressure(PTT‬‬
‫‪PTT=Palv-Pbs‬‬
‫گرادیان فشاری بین فشارالوئولی وفشار سطح بدن‬
‫فشار الزم برای اتساع وجمع شدن همزمان ریه ها وقفسه سینه یا‬
‫جزء االستیک‬
‫)‪PRESSURE(spont Breathing‬‬
‫انتهای دم‬
‫داخل الوئول‬
‫داخل پلور‬
‫‪0 cmH2o‬‬
‫‪-10 cmH2o‬‬
‫فشار ترانس پولمونار ‪PL=0-(-10 )=10cmH2o‬‬
‫انتهای باز دم‬
‫‪0 cmH2o‬‬
‫‪-5 cmH2o‬‬
‫‪PL=0-(-5)=5cmH2o‬‬
Pressures around the
balloon
Palv = Ptp + Ppl
Palv = 0, the same as
the room if no air is
flowing into the lung.
Ppl is subatmspheric
due to the recoil of the
lung away from the
jar.
PPlat = PAlv
PPlat = Transpulmonary Pressure +
Ppl
transpulmonary
pressure = 15 cm H2O
Ppl =+15 cm H2O
Pplat 30 cm H2O
Stiff chest wall
PPlat = PAlv;
PPlat = Transpulmonary Pressure
+ Ppl
-15 cm H2O
transpulmonary
pressure = 45 cm H2O
Pplat 30 cm H2O
Active inspiratory effort
PPlat
Pplat 30 cm H2O,
VCV
PPlat = PAlv;
= Transpulmonary
Pressure?
Pplat 30 cm H2O,
VCV
Pplat 30 cm H2O,
PCV
Active inspiratory effort
Volume variable with similar pressure
Risk of VILI“ : Transpulmonary
Pressure or Pplat
Risk of VILI may be different with the
same PPlat
Ventilator mode
Mechanical Ventilation
Mode classify by these three variable :
Trigger (initiate breath): patient or set machine
timer
Limit, Factors are operator-specified values
(control gas delivery during the breath): flow or
inspiratory pressure
Cycle (terminates the inspiration) : flow or
inspiratory time or volume
Pressure is often a backup safety cycle variable
‫‪Trigger or sensitivity‬‬
‫‪: trigger variable‬در واقع عامل شروع كننده و به‬
‫عبارتي محرك انجام عمل دم توسط ونتیالتور است‬
‫تغییر مي تواند تغییر فشاري و یا فلو باشد و در پاسخ به آن ‪،‬‬
‫دم آغاز میشود‬
‫پس یك ‪ trigger‬مي تواند به دو فرم باشد‬
‫‪* Flow trigger‬‬
‫‪*pressure trigger‬‬
‫) ‪*NAVA (Neurally Adjusted Ventilatory Assist‬‬
‫‪Trigger or sensitivity‬‬
‫‪pressure trigger‬را معموال" روي ‪ -./5‬تا ‪- 2‬‬
‫سانتي متر آب‬
‫‪Flow trigger‬را معموال" روي‪ 1‬تا ‪ 2‬لیتردردقیقه‬
‫‪: lag time‬‬
‫زمان تاخیر از زمان حس كردن و نتیالتور تا شروع‬
‫دم را ‪ lag time‬میگویند‬
‫اهمیت این زمان در اعمال كار اضافي به سیستم تنفس‬
‫است ‪.‬‬
‫‪:Trigger‬‬
‫عملكرد اصلي آن هماهنگي بین بیمار و دستگاه است‬
‫محدوده آن بین ‪ -./5‬تا ‪ -10‬سانتي متر آب‬
‫آنرا بطور معمول ‪ -2‬سانتي متر آب كمتر از فشار انتهاي بازدمي‬
‫تنظیم مي كنیم‬
‫یعني اگر ‪ peep‬را ‪5‬گذاشتیم ‪ trigger‬را ‪ -3‬مي گذاریم تا وقتي‬
‫فشار در این مدار به این حد رسید‪ Trigger‬نماید‪.‬‬
‫در مدهایي نظیر ‪SIMV‬نباید ‪ trigger‬را بیش از ‪ -1‬تا ‪ -2‬سانتي‬
‫متر آب گذاشت و حساسیت را باال برد زیرا‬
‫این افزایش حساسیت سبب افزایش كوشش دمي و خستگي‬
‫عضالت و افزایش كار عضالني میشود ‪.‬‬
Trigger
The inspiratory effort necessary to trigger a
breath has been estimated to be about 17%
and about 12% of the total inspiratory effort
during pressure and flow triggering,
respectively
‫‪Limit‬‬
‫‪ :Limit‬متغیري است كه اجازه تخطي در جریان‬
‫دم را نمي دهد و اغلب همان ‪ control varible‬است‬
‫و سبب ختم دم مي شود ( ولي نه همیشه )‬
‫‪Cycle‬‬
‫متغییري است كه سبب ختم دم مي شود كه مي تواند‬
‫فشار ‪ ،‬حجم‪ ،‬زمان و یا ‪ ( Flow‬جریان دمي ) باشد ‪.‬‬
Patient ventilator
interaction
Initiation of inspiration :Trigger
Inspiration :limitation
Inspiration to expiration :cycling
Expiration
Expiration to inspiration :Trigger
‫‪BEST PEEP‬‬
‫عبارت است از ميزان پيپ اعمال شده اي كه سبب بهترين‬
‫اكسيژناسيون شود ‪ ،FRC‬پذيرش ريه و اكسيژناسيون را‬
‫افزايش داده و سبب كاهش شانت شود‪.‬وهمچنين حداقل اثر‬
‫برروی هموديناميک‪.‬‬
Auto-PEEP or Intrinsic
PEEP
What is Auto-PEEP?

Normally, at end expiration, the lung
volume is equal to the FRC

When PEEPi occurs, the lung volume at
end expiration is greater then the FRC
Auto-PEEP or Intrinsic
PEEP
Why does hyperinflation occur?

Airflow limitation because of dynamic collapse or
lesions that increase expiratory resistance

No time to expire all the lung volume (high RR or
Vt)

Expiratory muscle activity
Auto-PEEP or Intrinsic
PEEP
Auto-PEEP is measured in a relaxed pt with
an end-expiratory hold maneuver
Exiratory flow pattern
flow
Flow Waveform
inhalation
time
0
auto-PEEP
exhalation
No active exhalation or inspiratory effort
Treats lungs as single compartment
PIP
pressure
PIP
auto PEEP
set PEEP
time
Auto-PEEP or Intrinsic
PEEP
Adverse effects:





Predisposes to barotrauma
Predisposes hemodynamic compromises
Diminishes the efficiency of the force
generated by respiratory muscles
Augments the work of breathing
Augments the effort to trigger the ventilator
sensitivity
-1 cm H2O
auto-PEEP
10 cm H2O
trigger effort = 11 cm H2O
sensitivity
-1 cm H2O
auto-PEEP
3 cm H2O
trigger effort = 4 cm H2O
Auto-PEEP should be measured with set PEEP = 0
‫(‪Inspiratory plateau(Pause‬‬
‫پالتوي دمي (‪ )Inspiratory plato‬با مسدود كردن دریچه‬
‫بازدمي در پایان دم ‪ ,‬فشار دمي در حد ثابتي باقي مانده و حفظ‬
‫مي شود چون این فشار ثابت است به آن فشار مسطح دمي مي‬
‫گویند ‪.‬‬
‫بااعمال این فشار جریان هوا بیشتر به قسمت هاي محیطي‬
‫انتشار یافته و بنابراین ‪ VD‬یا حجم فضاي مرده كاهش مي یابد‬
‫بدین وسیله مي توان به وجود نشت در سیستم تنفسي پي برده و‬
‫كمپلیانس ریه و مقاومت آنرا مانیتوركرد ‪.‬‬
‫‪ )Flow‬یا ‪)Flow Peak‬‬
‫اگر حجم جاري یك بیماري ‪1000‬سی سی تنظیم شده وزمان دم‬
‫یك ثانیه باشد فلوي دمي ‪ 60‬لیتردر دقیقه مي شود‬
‫اكثر ونتیالتورها مي توانند فلوي بیش از ‪ 120‬تا ‪ 180‬لیتر در‬
‫دقیقه بدهند‬
‫هر چه میزان ‪ Flow Peak‬بیشتر ‪ ،‬زمان دم كوتاه تر و زمان‬
‫بازدم طوالني ترو ‪ I/E Ratio‬كمتر مي شود وبنابراین‬
‫دربیماران‪ COPD‬مناسب است‪.‬‬
‫باید دانست كه این سرعت باال ایجاد جریان گردابي یا توربوالنت‬
‫مي كند‪.‬‬
‫سوال ‪ Flow‬به چه صورت به بيمار تحويل ميشود؟‬
‫‪ -1‬مربعي يا ‪Square‬‬
‫در این حالت سرعت جریان دمي بالفاصله به حداكثر رسیده ودر‬
‫تمامي مدت زمان دم حفظ مي شود و ناگهان قطع مي شود‪.‬‬
‫این روش بیشتر در بیماران بیهوش بكار مي رود زیرا عضالت‬
‫تنفسي فلج بوده و ریه ها سالم هستند‬
‫‪ -2‬سينوسي يا سينوزوئيدال ‪:Sinusoidal‬‬
‫در این حال جریان دمي بتدریج به حداكثر رسیده و بتدریج هم كاهش‬
‫مي یابد كه در تنفس ‪ Spont‬بیشتر دیده مي شود‪.‬‬
‫‪ -3‬صعودي ‪ Accelerating‬يا ‪Ascending‬‬
‫‪:Ramp‬‬
‫در اين حال جريان دمي بتدزيج به حداكثر خود ميرسد و ناگهان‬
‫قطع مي شود‪.‬‬
‫‪ -4‬نزولي ‪ Desending ramp‬يا‬
‫‪Decelerating‬‬
‫در این حال جریان دمي به سرعت به پیك رسیده وسپس بتدریج‬
‫كاهش مي یابد‪.‬‬
‫در بیماران مبتال به ‪ ARDS‬كاربرد دارد‪.‬‬
Flow pattern
‫‪Fio2‬‬
‫بر اساس ‪Pao2‬در‪ ABG‬است‪.‬‬
‫‪ Pao2‬باید به گونه اي انتخاب شود كه اشباع هموگلوبین )‪(Spo2‬‬
‫بیش از ‪ %90‬باشد تا ‪ Pao2‬هم باالتر از ‪ 60‬میلي جیوه شود‪.‬‬
‫اگر در درصد اكسیژن دمي ‪ Fio2‬بیش از ‪60‬درصد تنظیم شده‬
‫و ‪ pao2‬ما همچنان كمتر از ‪ 60‬میلي متر جیوه بود ‪ .‬اولین اقدام‬
‫‪:‬‬
‫افزایش ‪ peep‬است و نه درصد اكسیژن دمي‬
‫در بیمارن مبتال به ‪ COPD‬باید ‪ Pao2‬بین ‪ 50‬تا ‪ 55‬درصد حفظ‬
‫شود در این بیماران ابتدا ‪Fio2‬را حدود‪ 30‬درصد تنظیم میكنیم‬
‫‪ Fio2‬بدنبال ‪ CPR‬و پیپ باال در شروع ‪%100‬باید باشد‪.‬‬
‫‪Fio2=100 for 12hr‬‬
‫‪Fio2=100 for 24hr‬‬
‫‪Fio2=60 for 36hr‬‬
‫‪:Sigh‬‬
‫‪ - sigh‬به معناي دم عمیق است‬
‫در حالت نرمال انسان بطور متوسط هر ‪ 5‬تا‪ 10‬دقیقه یك دم‬
‫عمیق انجام میدهد ‪.‬‬
‫هدف از ‪ sigh‬در انسان جلوگیري از انسداد راههاي هوایي‬
‫كوچك و بازكردن آلوئولها است‪.‬‬
‫در برخي از ونتیالتورها هم براي مشابه سازي این حالت تنظیم و‬
‫تعداد ‪ sigh‬تعبیه شده است ‪.‬‬
‫هر ‪ sigh‬بطور متوسط ‪ 2.5‬برابر حجم جاري بوده و بطور‬
‫متوسط ‪ 10‬بار در ساعت اتفاق مي افتد‬
I:E RATIO
Defined: Inspiratory time: expiratory
time
Normal physiologic I:E Ratio is close to
1:2. (take a regular breath, then
exhale…notice it takes longer to
passively exhale that same breath than
to inhale.)
I:E Ratio
This ratio is usually changed as follows:
With obstructive type disease→ I:E from 
1:2 up to 1:2.5 or 1:3. This creates more
time for those patients to exhale what is
being obstructed by their disease process.
Modes of Ventilation
Spontaneous Modes
Three basic means of providing support for continuous
spontaneous breathing during mechanical
ventilation
Spontaneous breathing
CPAP
PSV – Pressure Support Ventilation
Modes of Ventilation
Spontaneous Modes
Spontaneous breathing
Patients can breathe spontaneously through a ventilator
circuit; sometimes called T-Piece Method because it
mimics having the patient ET tube connected to a
Briggs adapter (T-piece)
Advantage
Ventilator can monitor the patient’s breathing and activate an
alarm if something undesirable occurs
Disadvantage
May increase patient’s WOB with older ventilators
CPAP
This is not a true support-mode of ventilation,
Each inspiration and charges the circuit to a constant,
operator-specified pressure that can range from 0 to
20 cmH2O
CPAP is used to assess extubation potential in
patients who have been effectively weaned
in patients with intact respiratory system function who
require an endotracheal tube for airway protection
CPAP
Independent
Variables(Set by User)
FIO2
Level of CPAP
Dependent
Variables(Monitored by User)
Tidal volume
Rate, flow pattern
Airway pressure
PaO2, PaCO2, I/E ratio
Trigger/Cycle Limit
No trigger
Pressure limit
Advantages
Allows assessment of spontaneous
function
Helps prevent atelectasis
Disadvantages
No backup
Initial Settings
FIO2 = 0.5–1.0
CPAP = 5–15 cmH2O
CMV – Continuous Manditory
Ventilation
The Original Mechanical Vent
Has since been replaced in most
locations in the hospital by fancier
settings
Still used in the Operating Room
CMV
Three Variables
1) Respiratory Rate
2) Tidal Volume
3) FIO2
CMV
CMV
The Tidal Volume with the set FIO2 gets
blown into the patient at the set
respiratory rate.
CMV
CMV – RR / Vt / FIO2
CMV 12 / 600 / 30%
Minute Ventilation = Respiratory Rate *
Tidal Volume
12 / min * 600 cc = 7.2 L/min
PAo2 = FIO2 (760 – 47)-Paco2/0.8
30% * 713 = 213.9 mmHg O2
CMV
Advantages
Easy to set up: need a bellows, a motor,
and a timer.
 Easy to adjust the settings

Main Disadvantage

If the Patient is breathing spontaneously,
the patient will be fighting the ventilator.
PCV
Time triggered, time cycled, and pressure limited
During the inspiratory phase, a given pressure is
imposed at the airway opening, and the pressure
remains at this user-specified level throughout
inspiration
tidal volume and inspiratory flow rate are dependent
rather than independent variables
PCV is the preferred for barotrauma and for
postoperative thoracic
When PCV is used, minute ventilation and tidal
volume must be monitored;
PCV
Independent Variables(Set by
User)
FIO2
Inspiratory pressure level
Ventilator rate
Level of PEEP
Pressure limit
I/E ratio
Dependent
Variables(Monitored by User)
Tidal volume
Flow rate, pattern
Minute ventilation
PaO2, PaCO2
Trigger/Cycle Limit
Timer/patient
Timer/pressure limit
Advantages
System pressures regulated
Useful for barotrauma treatment
Timer backup
Disadvantages
Requires heavy sedation
Not useful for weaning
Initial Settings
FIO2 = 1.0
PC = 20–40 cmH2O
PEEP = 5–10 cmH2O
f = 12–15/min
I/E = 0.7/1–4/1
Assist Control Mode
Ventilation (ACMV)
The patient is spontaneously breathing
so we are assisting his VENTILATION.
ACMV
In inspiratory cycle is initiated either by the patient's
inspiratory effort or, if no patient effort is detected
within a specified time window, by a timer signal
within the ventilator.
Every breath delivered, whether patient or timer
triggered, consists of the operator-specified tidal
volume.
Ventilatory rate is determined either by the patient or
by the operator-specified backup rate, whichever is of
higher frequency(
ACMV
ACMV is commonly used for initiation of
mechanical ventilation because it
ensures a backup minute ventilation
Allows for synchronization of the
ventilator cycle with the patient's
inspiratory effort
Problems of ACMV
When is used in patients with tachypnea due to nonrespiratory
or nonmetabolic factors such as anxiety, pain, or airway
irritation.
Respiratory alkalemia may develop and trigger myoclonus or
seizures.
Dynamic hyperinflation (so-called auto-PEEP) may occur if the
patient's respiratory mechanics are such that inadequate time is
available for complete exhalation between inspiratory cycles.
ACMV is not effective for weaning patients from mechanical
ventilation because it provides full ventilator assistance on each
patient-initiated breath
ACMV
ACMV
Independent
Variables(Set by User)
FIO2
Tidal volume
Ventilator rate
Level of PEEP
Inspiratory flow pattern
Peak inspiratory flow
Pressure limit
Dependent
Variables(Monitored by User)
Peak airway pressure, PaO2, PaCO2
Mean airway pressure
I/E ratio
Trigger/Cycle Limit
Patient/timer
Pressure limit
Advantages
Timer backup
Patient-vent synchrony
Patient controls minute ventilation
Disadvantages
Not useful for weaning
Potential for dangerous respiratory
alkalosis
Initial Settings
FIO2 = 1.0
Vt = 10–15 mL/kg
f = 12–15/min
PEEP = 0–5 cmH2O
Inspiratory flow = 60 L/min
Modes of Ventilation
Intermittent Mandatory Ventilation – IMV
Periodic volume or pressure targeted breaths occur at set
interval (time triggering)
Between mandatory breaths, the patient breathes
spontaneously at any desired baseline pressure
without receiving a mandatory breath
Patient can breathe either from a continuous flow or gas or from a
demand valve
Modes of Ventilation
Intermittent Mandatory Ventilation – IMV
Indications
Facilitate transition from full ventilatory support to
partial support
Advantages
Maintains respiratory muscle strength by avoiding
muscle atrophy
Decreases mean airway pressure
Facilitates ventilator discontinuation – “weaning”
Modes of Ventilation
IMV-Intermittent Mandatory Ventilation
Complications
When used for weaning, may be done too quickly and
cause muscle fatigue
Mechanical rate and spontaneous rate may
asynchronous causing “stacking”
May cause barotrauma or volutrauma
SIMV
The major difference between SIMV and ACMV is
that in the former the patient is allowed to breathe
spontaneously, i.e., without ventilator assist, between
delivered ventilator breaths.
However, mandatory breaths are delivered in
synchrony with the patient's inspiratory efforts at a
frequency determined by the operator.
If the patient fails to initiate a breath, the ventilator
delivers a fixed-tidal-volume breath and resets the
internal timer for the next inspiratory cycle
SIMV
SIMV allows patients with an intact
respiratory drive to exercise inspiratory
muscles between assisted breaths,
making it useful for both supporting and
weaning intubated patients.
SIMV
SIMV may be difficult to use in patients with tachypnea because
they may attempt to exhale during the ventilator-programmed
inspiratory cycle.
When this occurs, the airway pressure may exceed the
inspiratory pressure limit, the ventilator-assisted breath will be
aborted, and minute volume may drop below that programmed
by the operator.
In this setting, if the tachypnea is in response to respiratory or
metabolic acidosis, a change to ACMV will increase minute
ventilation and help normalize the pH while the underlying
process is further evaluated
SIMV
SIMV
Independent
Variables(Set by User)
FIO2
Tidal volume
Ventilator rate
Level of PEEP
Inspiratory flow pattern
Peak inspiratory flow
Pressure limit
Same as for ACMV
Dependent
Variables(Monitored by User)
Peak airway pressure, PaO2, PaCO2
Mean airway pressure
I/E ratio
Same as for ACMV
Trigger/Cycle Limit
Patient/timer
Pressure limit
Same as for ACMV
Advantages
Timer backup useful for weaning
Disadvantages
Potential dysynchrony
Initial Settings
FIO2 = 1.0
Vt = 10–15 mL/kg
f = 12–15/min
PEEP = 0–5 cmH2O
Inspiratory flow = 60 L/min
Same as for ACMV
Modes of Ventilation
Pressure Support Ventilation – PSV
Patient triggered, pressure targeted, flow cycled mode of
ventilation
Requires a patient with a consistent spontaneous respiratory
pattern
The ventilator provides a constant pressure during inspiration once
it senses that the patient has made an inspiratory effort
Modes of Ventilation
PSV
Modes of Ventilation
PSV
Indications
Spontaneously breathing patients who
require additional ventilatory support to
help overcome
WOB, CL, Raw
Respiratory muscle weakness
Weaning (either by itself or in combination
with SIMV)
Modes of Ventilation
PSV
Advantages
Full to partial ventilatory support
Augments the patients spontaneous VT
Decreases the patient’s spontaneous respiratory rate
Decreases patient WOB by overcoming the
resistance of the artificial airway, vent circuit and
demand valves
Allows patient control of TI, I, f and VT
Modes of Ventilation
PSV
Advantages
Set peak pressure
Prevents respiratory muscle atrophy
Facilitates weaning
Improves patient comfort and reduces need
for sedation
May be applied in any mode that allows
spontaneous breathing,
VC-SIMV, PC-SIMV
Modes of Ventilation
PSV
Disadvantages
Requires consistent spontaneous ventilation
Patients in stand-alone mode should have
back-up ventilation
VT variable and dependant on lung
characteristics and synchrony
Low exhaled
Fatigue and tachypnea if PS level is set too
low
Modes of Ventilation
Flow Cycling During PSV
Flow cycling occurs when the ventilator
detects a decreasing flow, which
represents the end of inspiration
This point is a percentage of peak flow
measured during inspiration
PB 7200 – 5 L/min
Bear 1000 – 25% of peak flow
Servo 300 – 5% of peak flow
No single flow-cycle percent is right for all
patients
Modes of Ventilation
PSV during SIMV
Spontaneous breaths during SIMV can be supported with
PSV (reduces the WOB)
PCV – SIMV with PSV
Modes of Ventilation
PSV during SIMV
Spontaneous breaths during SIMV can be supported with PSV
VC – SIMV with PSV
Modes of Ventilation
PSV
NOTE: During pressure support ventilation (PSV),
inspiration ends if the inspiratory time (TI) exceeds a
certain value. This most often occurs with a leak in
the circuit. For example, a deflated cuff causes a
large leak. The flow through the circuit might never
drop to the flow cycle criterion required by the
ventilator. Therefore, inspiratory flow, if not stopped
would continue indefinitely. For this reason, all
ventilators that provide pressure support also have a
maximum inspiratory time.
Modes of Ventilation
PSV
Setting the Level of Pressure Support
Goal: To provide ventilatory support
Spontaneous tidal volume is 10 – 12 mL/Kg of
ideal body weight
Maintain spontaneous respiratory rate <25/min
Goal: To overcome system resistance (ET Tube,
circuit, etc.)
in the spontaneous or IMV/SIMV mode Set pressure
at (PIP – Pplateau) achieved in a volume breath or
at 5 – 10 cm H2O
Modes of Ventilation
PSV
Exercise: Using the PIP and the PPlateau from the
pressure waveform below, recommend a pressure
support setting for this patient (patient is in VC-SIMV
mode)
35
25
Answer: 10 cm H2O
Modes of Ventilation
PSV - The results of your work
35 cm H2O
10 cm H2O
Independent
Variables(Set by User)
FIO2
Inspiratory pressure level
PEEP
Pressure limit
Dependent
Variables(Monitored by User)
Tidal volume
Flow rate, pattern
Minute ventilation
PaO2, PaCO2
I/E ratio
Trigger/Cycle Limit
Inspiratory flow
Pressure limit
Advantages
Assures synchrony
Good for weaning
Disadvantages
No timer backup
Initial Settings
FIO2 = 0.5–1.0
PS = 10–30 cmH2O
5 cmH2O usually the level used
PEEP = 3–5 cmH2O
Spontaneous Modes
VS (Volume support)
Modes of Ventilation
Spontaneous Modes
Bilevel Positive Airway Pressure (BiPAP)
Commonly patient triggered but can be time triggered, pressure
targeted, flow or time cycled
The operator sets two pressure levels
IPAP (Inspiratory Positive Airway Pressure)
IPAP is always set higher than EPAP
Augments VT and improves ventilation
EPAP (Expiratory Positive Airway Pressure)
Prevents early airway closure and alveolar collapse at the end of
expiration by increasing (and normalizing) the functional residual
capacity (FRC) of the lungs
Facilitates better oxygenation
Modes of Ventilation
Spontaneous Modes
Bilevel Positive Airway Pressure (BiPAP)
The operator sets two pressure levels
-IPAP
-EPAP
NOTE: The pressure difference between IPAP and EPAP is pressure support
Modes of Ventilation
(Mandatory Minute Ventilation)
MMV
also called minimum minute ventilation
Provides a predetermined minute ventilation when the
patient’s spontaneous breathing effort becomes
inadequate
Useful for preventing hypoventilation and respiratory
acidosis in the final stages of weaning with SIMV
Need to keep watch spontaneous minute volume
(distressed pt. may increase RR with lower tidal
volume)
SVCC Respiratory Care Programs
ASV (adaptive support ventilation)
Clinician enters pt. data & % support
Vent. calculates needed min. vol. & best
rate/TV to produces least work.
Targeted TV’s given as press. control or
press. support breaths
Breath is: PC if time triggered, PS if pt.
triggered
ASV (adapt. sup. vent.)
Vent. measures & analyzes data & mechanics
each breath for:
compliance
resistance
inspiratory & expiratory time constants
actual Ins-time, Exp-time, total F& min. vol.
pressures
Press. adjusts in +/- 2 cm H2O to achieve TV
ASV: Principle mode of
ventilation
Flow E
+
+
Flow I
*
*
no patient activity:
* machine triggered
patient is active:
* patient triggered
+ flow cycled
Pinsp
PEEP
+ time cycled
From Hamilton Medical
ASV - Considerations
Mandatory breaths = PC, pt. triggered = PS
both at same targeted TV and calculated press.
vent., mode is PC-SIMV/PS
If pt.’s f > “set” by vent., mode is PS
If pt.’s f < “set” by is apneic, all breaths are PC
Exp minute ventilation(100%-350%)support
VAPS: Volume Assured Pressure
Support
Combines volume ventilation & pressure support
(for mech., vol. limited breaths only)
Uses TV, peak flow, and pressure sup./control
settings
Targets PS level with at least set peak flow first
Continues until flow decreases to set peak flow, then:
If TV not delivered, peak flow maintained until vol.
limit
If TV or more delivered, breath ends
VAPS:
(and Pressure Augmentation) Considerations
The set TV is the minimum TV the patient
will receive
The set pressure support is the minimum
the patient will receive
The set peak flow is the minimum the
patient will receive
No ventilatory mechanics measured
VAPS: Volume Assured Pressure
Support
Pressure Regulated Volume
Control
Combines volume ventilation & pressure
control
(for mech., time-cycl. breaths only)
Set TV is “targeted”
Ventilator estimates vol./press.
relationship each breath
Ventilator adjusts level of pressure control
breath by breath
Pressure Regulated Volume Control
First breath = 5-10 cm H2O above PEEP
V/P relationship measured
Next 3 breaths, pressure increased to 75%
needed for set TV
Then up to +/- 3 cm H2O changes per
breath
Time ends inspiration
Pressure Regulated Volume
Control
BiLevel Ventilation:
APRV
Uses 2 pressure levels for 2 time periods
Plow & Phigh, Thigh and Tlow
Patient triggering & cycling can change
phases
PHIGH
P
PEEPLOW
TLOW
THIGH
Synchronized Transitions
T
From PB product lit.
Synchronized Transitions
BiLevel Ventilation:
APRV
Uses two levels of pressure for two time periods
Mandatory breaths at the higher pressure are time
cycled
Spontaneous breaths can be pressure supported
Spontaneous Breaths
P
Spontaneous Breaths
T
From PB product lit.
BiLevel Ventilation:
APRV
Pressure support may be applied at both
pressures during a spont. breath
If PS is set higher than PH, the PS pressure is applied to a
spontaneous effort at upper pressure
PHi
PHi + PS
Pressure Support
P
PEEPL
From PB product lit.
APRV
Airway Pressure Release Ventilation
Like BiPAP/BiLevel but time at the lower
pressure (“release time”) is usually
short,
1-1.5 seconds
Spontaneous breathing still allowed
throughout low & high pressures
APRV
Airway Pressure Release
Ventilation
From Mosby’s R. C. Equip. 6th ed. 1999.
APRV(Airway pressure release ventilation)
APRV(Airway pressure release ventilation)
Proportional Assisted
Ventilation(PAV)
Pmus=Pres +pel
Pmus=(flow /resistance)+(volume/elastance)
Pmus+Pappl=(flow/resistance)+(volume/elastance)
Proportional Assisted Ventilation
PSV
Main setting
parameter is
percent of assist
Proportional Assist Ventilation
Allows free flow based on patient effort
“Targets” portion of patient’s work during
“spontaneous” breaths
Automatically adjusts flow, volume and
pressure needed each breath
PAV continued
“Vol. assist %” reduces work of elastance
“Flow assist%” reduces work of
resistance's
Pressure adjusts during each breath to
control work level
Increased patient effort causes increased
applied pressure (and flow & volume)
PAV continued
Other controls useful for PAV
High pressure limit
High volume limit
Back-up ventilation mode
Typical alarms etc.
PAV - Considerations
Consistent level of support per breath
Patient controls breathing pattern
Patient triggered mode
(Unless back-up mode present)
Reduced support with Auto-PEEP
Cannot compensate for leaks (prototypes)
PAV continued
From Younes, M: Ch.15, in Tobin, MJ Prin. & Pract. Of
Mech. Vent. 1994 McGaw-Hill, Inc.
IRV
PCV with the use of a prolonged inspiratory time
Applied to patients with severe hypoxemic respiratory
failure
It is thought to work in conjunction with PEEP to open
collapsed alveoli and improve oxygenation
there are no convincing data to show that IRV
improves outcomes.
Open lung ventilation
(OLV)
Any of these specific modes with TV to
achieve 5–6 mL/kg, and PEEP achieve
maximal alveolar recruitment
PEEP > CCP (Critical closing pressure)
PC (above peep) <COP (Critical opening pressure)
Open lung ventilation
(OLV)
primary objectives of ventilator support are
maintenance of adequate oxygenation and
avoidance of cyclic opening and closing of
alveolar units by selecting a level of PEEP
that allows the majority of units to remain
inflated during tidal ventilation.
Achievement of eucapnia and normal blood
pH through adjustments in ventilator tidal
volume and breathing frequency are of lower
priority.
1.6
volume above FRC (liters)
1.2
0.8
0.4
normal
ARDS
upper inflection
point
0
lower inflection
point
0
10
20
30
airway pressure (cm H2O)
40
Respiratory asidosis+alkalosis
Vt(fav) = Paco2(pat) . Vt(pat) / Paco2(fav)
Vt=10-12cc/kg
F(fav) =Paco2(pat) . F(pat) / paco2(fav)
RR=12-16
Different types of
patient
COPD and Asthma
Goals:
 Diminish
dynamic hyperinflation
 Diminish work of breathing
 Controlled hypoventilation
(permissive hypercapnia)
Diminish DHI
Why?
Diminish DHI
How?

Diminish minute ventilation
Low Vt (6-8 cc/kg)
 Low RR (8-10 b/min)
 Maximize expiratory time

Diminish work of
breathing
How:

Add PEEP (about 85% of PEEPi)

Applicable in COPD and Asthma.
Controlled hypercapnia
Why?

Limit high airway pressures and thus
diminish the risk of complications
Controlled hypercapnia
How?
Control the ventilation to keep adequate
pressures up to a PH > 7.20 and/or a
PaCO2 of 80 mmHg
Controlled hypercapnia
Contrindication:
Head pathologies
 Severe HTN
 Severe metabolic acidosis
 Hypovolemia
 Severe refractory hypoxia
 Severe pulmonary HTN
 Coronary disease

ARDS
Ventilation with lower tidal volume as
compared with traditional volumes for
acute lung injury and the ARDS
The Acute Respiratory Distress Syndrome
Network
N Engl J Med 2000;342:1301-08
Methods
March 96 – March 99
10 university centers
Inclusion:
Diminish PaO2
 Bilateral infiltrate
 Wedge < 18

Exclusion
Randomized
Methods
A/C 28d or weaning
2 groups:


1. Traditional Vt (12cc/kg)
2. Low Vt (6cc/kg)
End point:



1. Death
2. Days of spontaneous breathing
3. Days without organ failure or barotrauma
Results
The trails were stopped after 861 pt
because of lower mortality in low Vt group
Conclusion
Type of patient
Tidal Volume
RR
PEEP
FIO2
Ins. Flow
I:E
Normal
10 cc/kg
10 to 12
0 to 5
100%.
60 l/min
1:2.
ARDS
6 cc/kg
10 to 12
5 to 15
100%.
60 l/min
1:2.
COPD
6 cc/kg
10 to 12
5 100%.
Trauma
10 cc/kg
10 to 12
100%.
60 l/min
1:2.
Pediatric
8-10 cc/kg Varies age 3 to 5
100%.
60 l/min
1:2.
100 to 120 1:3 to 1:4
Note
Note
PH>7.2
PCO2 <80 mmhg
Trigger to consider
Trigger to consider
The Wean
Step 1
1. Lung injury is stable or resolving
2. Gas exchange is adequate with low
PEEP and FIo2
3. Hemodynamics are stable without a
need for vasopressors
4. Patient can initiate spontaneous
breaths
If meeting all four criteria
The Wean
Step 2
Perform spontaneous breathing trial
(SBT) using a T-piece ,CPAP , or 5 cm
H2O PS for 30-120 minutes
Assessments include:
Gas exchange
Ventilatory pattern
Hemodynamics
comfort
The Wean
Patients passing this trial should
immediate ventilator removal
Patients failing this trial should return to
ventilator for the next 24 hours and then
be reassessed
The Wean
Gradual reduction may be worse than
every 24 hour SBT approach
RESPIRATORY RATE
• Number of Breaths Per Minute (BPM)
• Trigger: Factor that begins inspiratory phase
• Controlled Breaths
• Triggered by Ventilator
• Determined by Set Rate
• Ten BPM Setting: Breath is Triggered
Every 6 Seconds
• Assisted Breaths: Triggered by Patient Effort
• Ventilator Sensitivity Adjusted
• Avoid Insignificant Patient Effort Triggering a
Delivered Breath
1.6
volume above FRC (liters)
1.2
0.8
0.4
normal
ARDS
upper inflection
point
0
lower inflection
point
0
10
20
30
airway pressure (cm H2O)
40
Monitoring of the
patient
HYPOXIA: DIFFERENTIAL
DIAGNOSIS
• Hypoventilation
• V/Q Mismatch:
• Bronchospasm
• Increased Secretions
• Alveolar Edema (Hyaline Membranes on Histology
• Right to Left Cardiac Shunt
• Blood flows past non-ventilated alveoli
• Not amenable to increasing inspired oxygen fraction
• Atelectasis
• Lung Consolidation
• Pulmonary Edema
SYSTEMATIC
RESPONSE TO HYPOXIA
• Arterial Blood Gas
• Portable CXR
• With No Other Proximate Cause, Adjust
Ventilator Settings
• Maintain 100% FiO2
• Increase Mean Airway Pressure
• Increase Inspiratory Time
• Chemically paralyze patient
Oxygenation
What is the number one cause of
decreased oxygenation?
V-Q Mismatch
Oxygenation
What is the number one cause of V-Q
Mismatch?
Atelectasis
Oxygenation
How do we fix V-Q mismatch caused by
atelectasis?
Recruit the unused alveoli
increase “V”
to
Oxygenation
How do we recruit alveoli?
PEEP




Positive end expiratory pressure
Decreases the expiratory gradient
Causes air trapping
Trapped air tries to distribute evenly and leads to
opening of all airways.
Oxygenation
What about decreasing the expiratory
time relative to the inspiratory time?
This leads to air trapping. Since it
behaves like peep, we call it:
AUTO-PEEP
Oxygenation
All patients on a ventilator have some amount
of atelectasis
When a patient is oxygenating poorly, we can
try to improve VQ matching by fixing that
atelectasis with PEEP or AUTO-PEEP
Oxygenation
CMV 12 / 700 / 30% / +5
A-C 12 / 700 / 30% / +5
A-C 12 / 700 / 30% / I:E 2:1
SIMV 12 / 700 / 30% / PS12 / +5
PS 12 / +5
Oxygenation
Disadvantages to PEEP


PEEP increases mean intrathoracic pressure and
can seriously drop the Cardiac Output
PEEP can hyperinflate alveoli and cause
VOLUTRAUMA
Disadvantages to autoPEEP


Doesn’t work well with rapid RR
Doesn’t work well in COPDers
Driving Oxygenation
Increase and Decrease FIO2 as
needed.
When FIO2 gets over 50%, start thinking
about PEEP / auto-PEEP
When FIO2 requirements are falling,
think about losing PEEP
INCREASE PO2
• Increase Fio2
• Increase Mean Airway Pressure (Paw)
• Paw: Average Pressure Created Within
the Lung Over One Minute
• Paw Increased By
• Increases in PEEP
• Increases Inspiratory time
SYSTEMATIC
RESPONSE TO HYPOXIA
•
•
•
•
•
•
•
Turn FiO2 to 100%
Take Patient OFF Ventilator
Bag the Patient on FiO2 100%
Rapid Assessment ABC From “Patient to Wall”
Endotracheal Tube: Position, Patency
Auscultate: Rule Out Tension Pneumothorax
Ventilator: Circuit, Functional State, Oxygen
CHANGE PCO2
Alter Minute Ventilation
• Respiratory rate
• Tidal volume
Permissive Hypercapnia
• Used In Non-Compliant Lungs (ARDS)
• Non-Heterogeneous Process
• Avoidance of Barotrauma and Volutrauma to Unaffected
Regions
• Maintain pH > 7.25
• Proper Physiologic Milieu
• HCO3 if necessary
Different types of
patient
COPD and Asthma
Goals:
 Diminish
dynamic hyperinflation
 Diminish work of breathing
 Controlled hypoventilation
(permissive hypercapnia)
Diminish DHI
Why?
Diminish DHI
How?

Diminish minute ventilation
Low Vt (6-8 cc/kg)
 Low RR (8-10 b/min)
 Maximize expiratory time

Diminish work of
breathing
How:

Add PEEP (about 85% of PEEPi)

Applicable in COPD and Asthma.
Controlled hypercapnia
Why?

Limit high airway pressures and thus
diminish the risk of complications
Controlled hypercapnia
How?
Control the ventilation to keep adequate
pressures up to a PH > 7.20 and/or a
PaCO2 of 80 mmHg
Controlled hypercapnia
Contrindication:
Head pathologies
 Severe HTN
 Severe metabolic acidosis
 Hypovolemia
 Severe refractory hypoxia
 Severe pulmonary HTN
 Coronary disease

Trouble Shooting
Trouble Shooting
Doctor, doctor, his pressures are going
up!!!
What is your next step?
Trouble Shooting
Ask which pressure is going up
Trouble Shooting
Ppeak is up

Look at your Pplat
Trouble Shooting
If your Pplat is high, you are faced with
a COMPLIANCE problem
If your Pplat is N, you are faced with a
RESISTIVE problem
DD?
Trouble Shooting
Trouble Shooting
Doctor, doctor, my patient is very
agitated!

What is your next step?
Trouble Shooting
Look at your pt!
Trouble Shooting
At the time of intubation, fighting is
largely due to anxiety
But what do you do if pt is stable and
then becomes agitated?
Trouble Shooting
1.
2.
3.
4.
5.
6.
Remove pt from ventilator
Initiate manual ventilation
Perform P/E and assess monitoring indices
Check patency of airway
If death is imminent, consider and treat
most likely causes
Once pt is stabilized, undertake more
detailed assessement and management
Trouble Shooting
THE
END