Principles of mechanical ventilation 2

1. PRINCIPLES OF MECHANICAL
VENTILATION
and
BLOOD GAS INTERPRETATION
SAMIR EL ANSARY
ICU PROFESSOR
AIN SHAMS
CAIRO
elansarysamir@yahoo.com

2. Global Critical Care
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3. Definitions
• Tidal Volume (TV): volume of
each breath.
• Rate: breaths per minute.
• Minute Ventilation (MV): total
ventilation per minute. MV =
TV x Rate.
• Flow: volume of gas per time.

4. Definitions
• Compliance:
The distensibility of a system. The
higher the compliance, the easier
it is to inflate the lungs.
• Resistance:
Impediment to airflow.

5. Definitions
SIMV
Patient breathes spontaneously
between ventilator breaths.
• Allows patient-ventilator synchrony
• Making for a more comfortable
experience.

6. Definitions
• PIP: maximum pressure measured by
the ventilator during inspiration.
• PEEP: pressure present in the airways
at the end of expiration.
• CPAP: amount of pressure applied to
the airway during all phases of the
respiratory cycle.

7. Definitions
• PS: amount of pressure applied
to the airway during
spontaneous inspiration by the
patient.
• I-time: amount of time
delegated to inspiration.

8. Types of Ventilation
• Volume Control
• Pressure Control
• Pressure Support-CPAP
• Pressure-Regulated Volume
Control

9. Volume Control
• The patient is given a specific volume
of air during inspiration.
• The ventilator uses a set flow for a set
period of time to deliver the volume:
• TV (cc) = Flow (cc/sec) x i-time (sec)

10. Volume Control
• The PIP observed is a product of :
• lung compliance, airway
resistance and flow rate.
• The ventilator does not react to the
PIP unless the alarm limits are
violated.

11. Volume Control
• The PIP tends to be higher
than during pressure control
ventilation to deliver the same
volume of air.

12. Volume Control
• With SIMV, the patient can
breath spontaneously between
vent breaths.
• This mode is often combined with
PS.

13. Triggering the Ventilator

14. Pressure Control
• Patient receives a breath at a fixed
airway pressure.
• The ventilator adjusts the flow to
maintain the pressure.
• Flow decreases throughout the
inspiratory cycle.

15. Pressure Control
• The pressure is constant
throughout inspiration.
• Volume delivered depends upon the
inspiratory pressure, I-time,
pulmonary compliance and
airway resistance.

16. Pressure Control
• The delivered volume can vary from
breath-to-breath depending upon the
above factors. MV not assured.
• Good mode to use if patient has large
air leak, because the ventilator will
increase the flow to compensate it.

17. Volume vs. Pressure

18. Changes in ARDS
Volume Control Pressure Control
ARDS ARDS

19. CPAP-Pressure Support
•No mandatory breaths
• Patient sets the rate, I-time, and
respiratory effort.
• CPAP performs the same function as
PEEP, except that it is constant
throughout the inspiratory and
expiratory cycle.

20. CPAP-Pressure Support
• Pressure Support (PS) helps to
overcome airway resistance and
inadequate pulmonary effort and is
added on top of the CPAP
during inspiration.

21. CPAP-Pressure Support
• The ventilator increases the
flowduring inspiration to reach
the target pressure and make it easier
for the patient to take a breath.

22. SIMV + PS

23. Pressure-Regulated Volume
Control
• In this mode, a target minute
ventilation is set.
• The ventilator will adjust the flow to
deliver the volume without exceeding a
target inspiratory pressure.
•Decelerating flow pattern.

24. Pressure-Regulated Volume
Control
• No change in minute
ventilation if pulmonary
conditions change.
• Can ventilate at a lower PIP than in
regular volume control.

25. Pressure-Regulated Volume
Control
•Hard to use on a
spontaneously breathing
patient or one with a large
air leak.
•Not a “weaning” mode.

26. Initial Ventilator Settings
•Rate:
•20-24 for infants and
preschoolers
•16-20 for grade school kids
•12-16 for adolescents

27. Initial Ventilator Settings
• TV: 10-15ml/kg
• PEEP: 3-5cm H2O
• FiO2: 100%
• I-time: 0.7 sec for higher rates,
1sec for lower rates

28. Initial Ventilator Settings
•PIP (for pressure control)
about 24cm H2O
•Pressure Support
5-10cm H2O

29. Adjusting The Ventilator
• pCO2 too high
• pCO2 too low
• pO2 too high
pO2 too low
PIP too high

30. pCO2 Too High
• Patient’s minute ventilation is too
low.
• Increase rate or TV or both.
• If using PC ventilation, increase PIP.
• If PIP too high, increase the rate
instead.

31. pCO2 Too High
• If air-trapping is occurring, decrease
the rate and the I-time and increase
the TV to allow complete exhalation.
• Sometimes, you have to live with the
high pCO2, so use THAM or
bicarbonate to increase the pH to
>7.20.

32. pCO2 Too Low
• Minute ventilation is too high.
• Lower either the rate or TV.
• Don’t need to lower the TV if the
PIP is <20.
• PIP <24 is fine unless delivered TV
is still >15ml/kg.

33. pCO2 Too Low
• TV needs to be 8ml/kg or higher to
prevent progressive atelectasis
• If patient is spontaneously breathing,
consider lowering the pressure
support if spontaneous TV >7ml/kg.

34. pO2 Too High
• Decrease the FiO2.
• When FiO2 is less than 40%,
decrease the PEEP to 3-5 cm
H2O.
• Wean the PEEP no faster than
about 1 every 8-12 hours.

35. pO2 Too High
• While patient is on ventilator,
don’t wean FiO2 to
<25%
to give the patient a margin of
safety in case the ventilator quits.

36. pO2 Too Low
• Increase either the FiO2 or the mean
airway pressure (MAP).
• Try to avoid FiO2 >70%.
• Increasing the PEEP is the most efficient
way of increasing the MAP in the PICU.
• Can also increase the I-time to
increase the MAP (PC).

37. pO2 Too Low
• Can increase the PIP in Pressure
Control to increase the MAP,
but this generally doesn’t add
much at rates <30 bpm.

38. pO2 Too Low
• May need to increase the PEEP to
over 10, but try to stay <15
if possible.

39. PIP Too High
• Decrease the PIP (PC) or the TV
(VC).
• Increase the I-time (VC).
• Change to another mode of
ventilation.
Generally, pressure control achieves
the same TV at a lower PIP than
volume control.

40. PIP Too High
• If the high PIP is due to high
airway resistance, generally
the lung is protected from
barotrauma unless air-
trapping occurs.

41. Weaning Priorities
• Wean PIP to <35cm H2O
• Wean FiO2 to <60%
• Wean I-time to <50%
• Wean PEEP to <8cm H2O
• Wean FiO2 to <40%

42. Weaning Priorities
• Wean PEEP, PIP, I-time, and rate
towards extubation settings.
•Can consider changing to
volume control ventilation
when PIP <35cm H2O.

43. Complications
•Pulmonary
–Barotrauma
–Ventilator-
induced lung
injury
–Nosocomial
pneumonia
Tracheal stenosis
Tracheomalacia
Pneumothorax

44. Complications
• Cardiac
–Myocardial
ischemia
– Reduced cardiac
output
• Gastrointestinal
–Ileus
–Hemorrhage
–Pneumoperiteneum

45. Complications
•Renal
–Fluid
retention
 Nutritional
Malnutrition
Overfeeding

46. Acute Deterioration
• DIFFERENTIAL DIAGNOSES
 Pneumothorax
Right mainstem
intubation
Pneumonia Pulmonary
edema

47. Acute Deterioration
• DIFFERENTIAL DIAGNOSES
Loss of airway
Airway occlusion
Ventilator malfunction
Mucus plugging
Air leak

48. Physical Exam
• Tracheal shift
–Pneumothorax
• Wheezing
–Bronchospasm
–Mucus plugging
–Pulmonary edema
–Pulmonary thromboembolism

49. Physical Exam
• Asymmetric breath sounds
–Pneumothorax
–Mainstem intubation
–Mucus plugging with atelectasis

50. Physical Exam
• Decreased breath sounds
bilaterally
–Tube occlusion
–Ventilator malfunction
–Loss of airway

51. Pressure Patterns
• Elevated peak and plateau
pressures
–Pneumonia
–Pulmonary edema
–Pneumothorax
–Atelectasis
–Right mainstem intubation

52. Pressure Patterns
• Elevated peak pressure, normal
plateau pressure:
–Airflow obstruction
–Mucus plugging
–Partial tube occlusion

53. Pressure Patterns
• Reduced peak and plateau
pressure :
–Cuff leak
–Ventilator malfunction
–Large bronchopleural fistula

54. Extubation Criteria
•Neurologic
•Cardiovascular
•Pulmonary

55. Neurologic
• Protect his airway, e.g, have
cough, gag, and swallow
reflexes.
• low Level of sedation
• No apnea on the ventilator.

56. Neurologic
• Must be strong enough to generate a
spontaneous TV of 5-7ml/kg on 5-10
cm H2O PS
• or have a negative inspiratory force
(NIF) of 25cm H2O or higher.
• Being able to follow commands
is preferred.

57. Cardiovascular
• Patient must be able to increase
cardiac output to meet demands
of work of breathing.
• Adequate cardiac output without
being on significant inotropic support.
• Hemodynamically stable.

58. Pulmonary
• Patient should have a patent airway.
• If no air leak, consider decadron and
racemic epinephrine.
• Pulmonary compliance and
resistance should be near normal.

59. Pulmonary
• Patient should have normal blood gas and
work-of-breathing on the following settings:
–FiO2 <40%
–PEEP 3-5cm H2O
–PS 5-8cm H2O
–Spontaneous TV of 5-7ml/kg
–Adequate RR

60. Global Critical Care
https://www.facebook.com/groups/1451610115129555/#!/groups/145161011512
9555/
Wellcome in our new group ..... Dr.SAMIR EL ANSARY

61. GOOD LUCK
SAMIR EL ANSARY
ICU PROFESSOR
AIN SHAMS
CAIRO
elansarysamir@yahoo.com