1. MECHANICAL VENTILATION

2. Indications Relieve respiratory distress Rest respiratory muscles
Decrease work of breathing
Improve oxygenation
Prevent or reverse atelectasis
Improve ventilation
Decrease O2 consumption
Permit sedation
Stabilize chest wall
Prevent complications

3. Ventilator indications:
hypoxic respiratory failure
O2sat<90%
Pao2<60(with Fio2.60%)
Example ARDS
Always should be treated even contiouss
Hepercapnic respiratory failure
Acute:Pco2>50, PH<7.3
Chronic:Loss of contiousness
Respiratory depression
Upto date

4. CONTRAINDICATIONS Intracranial pressure (ICP) > 15 mm Hg
Hemodynamic instability
Recent facial, oral, or skull surgery
Tracheoesophageal fistula
Recent esophageal surgery
Active hemoptysis
Nausea
Air swallowing
Active untreated tuberculosis
Radiographic evidence of bleb
Singulation (hiccups)

5. Mechanical Ventilation
Abbreviations:
VT: Tidal volume (ml)
RR: Respiratory Rate (bpm)
MV: Minute Volume = VT x RR (l/m))
FiO2: Fraction of inspired Oxygen
PEEP: Positive end expiratory pressure (cmH20)
(I:E) Ratio : Ratio of inspiratory to expiratory time.
Ti: Inspiratory time
Flowrate: Speed of gas flow in liters per minute.

6. Ventilator settings Ventilator mode Respiratory rate
Tidal volume or pressure settings
Inspiratory flow
I:E ratio
PEEP
FiO2
Inspiratory trigger

7. Mode
FIO2
20% -100%
Rate
4-30
Tidal volume
4-9 cc/kg
Flow
Lit/min
PEEP/CPAP
0-22 mmH2O
Pressure
5-20 mmH2O
Just for PSV Mode
P ins
5-40mm H2o
Just for CMV Mode
Trigger
1cc/sec (flow trigger)
-1 Cm H2O(pressure trigger)
Always on minimum
I/E ratio
1/4 1/3 1/2 1/

8. Respiratory Rate

9. Tidal Volume or Pressure setting
Maximum volume/pressure to achieve good ventilation and oxygenation without producing alveolar overdistention
Max cc/kg = 10 cc/kg
Some clinical exceptions

10. Tidal Volume
Vt > TLC can result in over-distended lung and lung injury
TLC reduced in lung disease
TLC  plateau pressure = 30 – 35 cmH2O

11. Tidal Volume Airway Pressures

12. Tidal Volume What Vt should be used?
Traditionally ml/kg
“Kg” based on ideal body weight
PBW (male) = [(Ht in inches) – 60]
PBW (female) = [(Ht in inches) – 60]
Theoretically prevents atelectasis
Most appropriate if normal lungs
Anesthesia, drug overdose

13. Tidal Volume What Vt should be used?
Lung disease present
8 –10 ml/kg
Regardless of Vt
Pplateau < 30 – 35 cmH2O

14. Vt Obstructive Lung Disease
How do you avoid/correct autoPEEP?
Use smaller tidal volumes
Vt = 6 – 8 ml/kg
 Respiratory rate
 Flow rate
(typical default flow rate ~ 60 L/min)

15. Vt ARDS What is the recommended Vt in ARDS?
Vt = 6 ml/kg
Vt < 6 ml/kg if Pplateau > 30 – 35 cmH2O
What are the complications of low Vt?
Elevated PaCO2
Permissive hypercapnea
Alveolar de-recruitment
Hypoxemia

16. Sighs
Because a spontaneously breathing individual typically sighs 6-8 times per hour to avoid microatelectasis, giving periodic machine breaths of times the preset tidal volume 6-8 times per hour was once recommended. Often, the peak pressure needed to deliver such a volume would predispose the patient to barotrauma.
Today, sighs are usually not used if the patient is receiving tidal volumes of mL/kg or requires the use of positive end-expiratory pressure (PEEP).

17. I:E Ratio
1:2
Prolonged at 1:3, 1:4, …
Inverse ratio

18. FIO2
The usual goal is to use the minimum Fio2 required to have a PaO2 > 60mmhg or a sat >90%
Start at 100%
Oxygen toxicity normally with Fio2 >60%

19. Inspiratory flow Varies with the Vt, I:E and RR
Normally about l/min
Can be majored to l/min

24. Positive end-expiratory pressure
PEEP is a mode of therapy used in conjunction with mechanical ventilation. At the end of exhalation (either mechanical or spontaneous), patient airway pressure is maintained above atmospheric pressure by exerting a pressure that opposes complete passive emptying of the lung. This pressure is typically achieved by maintaining a positive pressure flow at the end of exhalation.

25. Positive end-expiratory pressure
PEEP therapy can be effective when used in patients with a diffuse lung disease that results in an acute decrease in functional residual capacity (FRC). In many pulmonary diseases, FRC is reduced because of the collapse of the unstable alveoli. This reduction in lung volume decreases the surface area available for gas exchange and results in intrapulmonary shunting. If the FRC is not restored, a high concentration of inspired oxygen may be required to maintain the arterial oxygen content of the blood at an acceptable range.

26. Positive end-expiratory pressure
Applying continuous positive pressure at the end of exhalation (eg, PEEP, continuous positive airway pressure [CPAP]) causes an increase in alveolar pressure and an increase in alveolar volume. This increase in lung volume increases the surface area by reopening or stabilizing collapsed or unstable alveoli. This “splinting” or “propping open” of the alveoli with positive pressure may provide a better matching of ventilation to perfusion, thereby reducing the shunt effect.

27. Positive end-expiratory pressure
Once a true shunt is changed to a ventilation/perfusion mismatch, lower concentrations of oxygen can be used to maintain an adequate PaO2. PEEP therapy has also been effective for improving lung compliance. When the FRC and lung compliance are decreased, more energy and volume are needed to inflate the lung. By applying PEEP, the lung volume at the end of exhalation is increased, which decreases the work of breathing because the lung is already partially inflated; therefore, less volume and energy are needed to inflate the lung.

28. Positive end-expiratory pressure
In summary, when used to treat patients with a diffuse lung disease, PEEP should improve compliance, decrease dead space, and decrease the intrapulmonary shunt effect. The most significant benefit of PEEP is that the patient can maintain an adequate PaO2 at a lower and safer concentration of oxygen (<60%), thereby reducing the risk of oxygen toxicity.

29. Positive End-Expiratory Pressure
PEEP maintains positive airway and alveolar pressure throughout expiration.

30. PEEP/CPAP Indications
Refractory hypoxemia
PaO2/FIO2 < 150
Prototypic disease = ARDS
COPD with air-trapping
“Physiologic” PEEP

31. PEEP/CPAP Where do you start? Where do you stop? PEEP = 5 –7 cmH2O
Increase in increments of 2-3 cmH2O
Where do you stop?
Goals:
Adequate oxygenation
FIO2 reduced to acceptable level
No upper limit exists

32. Positive End-Expiratory Pressure
Physiologic Effects
Increases end-expiratory volume
Prevents alveolar collapse
Reduces shunt fraction
Improves PaO2
May over-distend alveoli
Ventilator-induced lung injury

33. Positive End-Expiratory Pressure
Physiologic Effects
Increases pleural (intra-thoracic) pressure
Reduces venous return
Reduces cardiac output and DO2

34. PEEP What are the secondary effects of PEEP? Barotrauma
Diminish cardiac output
Regional hypoperfusion
NaCl retention
Augmentation of ICP?
Paradoxal hypoxemia

35. PEEP Relative Contraindications: Barotrauma Airway trauma
Unilateral lung disease
Hemodynamic instability
Hypovolemia
ICP?
Bronchopleural fistula

36. PEEP/CPAP Why might PEEP worsen hypoxemia in unilateral lung disease?
Effects of PEEP go to normal alveoli and not diseased alveoli

37. PEEP/CPAP

38. PEEP/CPAP Complications
What is the most feared complication?
Barotrauma
What is the most common?
Reductions in cardiac output
Loss of venous return to right atrium
Paradoxical movement of intraventricular septum
Pulmonary vessel compression

39. Ventilator Settings Changing Initial Settings
Base changes in FIO2 on:
ABG’s
Pulse oximetry
Base changes in Vt and/or RR on:
Normalizing pH, NOT PaCO2 or HCO3-
Avoid “routine” ABG’s

40. Oxygenation decisions
With the target PaO2 identified, the FIO2 can be adjusted using the following formula:
New FIO2 = (old FIO2 X desired PaO2)/measured PaO2

41. Ventilation Decisions
New rate = (old rate X measured PCO2)/desired PCO2

42. Assist-control, volume
Ref: Ingento EP and Drazen J: Mechanical ventilators, in Hall JB, Scmidt GA, and Wood LDH(eds.): Principles of Critical Care. New York, McGraw-Hill, Inc., 1992, p.144.
In assist control modes (pressure control, volume control), the machine will deliver a full breath whether it is triggered by patient effort (note the negative deflection in the uppermost graph indicating patient effort) or triggered by the machine (the machine will act if a set amount of time (T) elapses without discernible patient effort).
Ingento EP & Drazen J: Mechanical Ventilators, in Hall JB, Scmidt GA, & Wood LDH(eds.): Principles of Critical Care

43. IMV, volume-limited
Ref: Ingento EP and Drazen J: Mechanical ventilators, in Hall JB, Scmidt GA, and Wood LDH(eds.): Principles of Critical Care. New York, McGraw-Hill, Inc., 1992, p.145.
“Positive pressure, volume-cycled breaths are delivered at a preset rate similar to control mode ventilation, except that between breaths, the inspiratory valve to the patient is open, allowing for spontaneous breathing.”
Ingento EP & Drazen J: Mechanical Ventilators, in Hall JB, Scmidt GA, & Wood LDH(eds.): Principles of Critical Care

44. SIMV, volume-limited
Ref: Ingento EP and Drazen J: Mechanical ventilators, in Hall JB, Scmidt GA, and Wood LDH(eds.): Principles of Critical Care. New York, McGraw-Hill, Inc., 1992, p.146.
(Would we also want to put slides with pressure mode graphs as well to show the different flow characteristics ??)
During SIMV, the ventilator divides time by the set rate to determine cycle-length. During the early part of this cycle, the patient may breath spontaneously without support. During the terminal phase of this cycle (% varies by manufacturer) the ventilator will synchronize a full breath with detected effort by the patient.
Ingento EP & Drazen J: Mechanical Ventilators, in Hall JB, Scmidt GA, & Wood LDH(eds.): Principles of Critical Care

45. MODE
TRIGGER
CYCLING
Clinical situation
PCV
TIME
PRESSURE
PNEUMOTHPRAX,THORAX SURGERY,FLAIL CHEST
CMV
VOLUME
COMPLETE APNEA,FULL SUPPORT
ACMV
TIME/PATIENT
CHF,EDEMA ,ARDS
SIMV
APNEA,ARDS,ASTHMA,COPD,ILD,…
PSV(spont)
PATIENT
FLOW
WEANING

46. PCV: pressure controled Ventilation
CMV: controled mode ventilation
ACMV: Assist controled mode ventilation
SIMV: spontanous intermittent mandatory ventilation
PSV:pressure support ventilation
ASV:asssist spontanous ventilation

47. همیشه دم اکتیواست و باز دم پسیو PCV
مثلا هر 5 ثانیه دستگاه یک دم میدهد.
بیمار اپنه کامل باشد
حجم متغیر خواهد بود.
CMV
ACMV
همه تنفس های بیمار را ساپورت می کند حتی اگر 30تنفس در دقیقه
خطر بارو تروما
SIMV
تنفس های بیمار را بیشتر از ریت دستگاه ساپورت نمی کند
PSV
فشار اعمال شده هنگام دم باعث افزایش حجم جاری می شود.

48. Trigger:
به ونتیلاتور می فهماند که تنفس بیمار شروع شده است.