Monitoring of mechanical ventilation involves assessing pressure, flow, volume, and calculated and measured parameters. Calculated parameters include compliance, resistance, and time constants. Waveform analysis uses pressure, flow, and volume waveforms. Loops such as pressure-volume and flow-volume can be used to evaluate lung mechanics. Monitoring compliance, resistance, and loops can help determine the condition of the lungs.

1. Monitoring of Mechanical
Ventilation
Olu Albert, MPH,RRT
Clinical Manager
Respiratory Care, ASIA PACIFIC
Philips Health

2. Monitoring of Mechanical Ventilation
• Pressure, Flow, and Volume in ventilator circuit
• Calculated “Monitored” Parameters
– Compliance
– Resistance
– MAP
– Time Constants
• Waveform Analysis (Measured Parameters)
– Pressure
– Flow
– Volume
• Loops
– Pressure volume
– Flow volume

3. Calculated Parameters

4. Pressure
Time
PIP:
compliance
resistance
volume
flow
PEEP
PEEP

5. PEEP
PIP
Pplat
Raw= Pta /V
compliance
tidal volume
end-inspiratory
alveolar pressure
Pta = PIP - Pplat

6. PIP
Pressure(cmH2O)Volume(mL)Flow(L/min)
Lucangelo, Respir Care 2005; 50:55

7. Monitoring Compliance and Airway
Resistance

8. normal 100 mL/cm H2O
Cst =
Pplat - PEEP
Tidal Volume
Compliance
• Mainstem Intubation
• Congestive Heart Failure
• ARDS
• Atelectasis
• Consolidation
• Fibrosis
• Hyperinflation
• Tension Pneumothorax
• Pleural Effusion
• Abdominal Distension
• Chest Wall Edema
• Thoracic Deformity
Decreased with:
Correct for gas compression
Total PEEP

9. Increased with:
Raw =
PIP - Pplat
flow
Airway Resistance (Raw)
• Secretions
• Bronchospasm
• Small endotracheal tube
• Mucosal edema
Normal: 5 - 10 cm H2O/L/s for intubated ventilated adults
measure with 60 L/min (1 L/s)
constant flow

10. Calculation of Cs & Raw
A patient is volume ventilated at the
following settings: PIP = 24 cmH20, Pplt
= 17 cmH20, and VT = 400 ml, PEEP = 5
cmH20. What is Pta? What is the Cst?
Flow was 35 L/min. What is the Raw? Is
the Raw normal?

11. • Pta = PIP – Pplt = 24-17 = 7 cmH20
• Cst = VT /Pplt-PEEP =400 ml/(17-
5cmH20)= 33.3mL/cmH20
• Raw = Pta/Flow
Flow = 35 L/min, 35 L/60 sec = 0.58 L/s
Raw = 7 cmH20/0.58 L/s = 12 cmH20/L/sec

12. Pplat 30 cm H2O
Transpulmonary
Pressure = 15 cm H2O
Pplat = Palv;
Pplat = Transpulmonary Pressure?
+15 cm H2O
Stiff chest wall

13. PCV 20 cm H2O,
PEEP 10 cm
H2O =Pplat 30
cm H2O
-15 cm H2O
Transpulmonary
Pressure = 45 cm H2O
Active inspiratory effort
Pplat = Palv;
Pplat = Transpulmonary Pressure?

14. Pplat 30 cm H2O,
VCV
Pplat 30 cm H2O,
PCV
Active inspiratory effort
Pplat 30 cm H2O,
VCV
Pplat = Palv;
Pplat = Transpulmonary Pressure?
Risk of VILI may be different with the same Pplat

16. Mean Airway Pressure (MAP)
• MAP is affected by PIP, PEEP, Total Cycle Time
(TCT) and RR
• MAP = ½ (PIP-PEEP) x (Ti/TCT) + PEEP
• MAP is useful to monitor to assess the
benefits and side effects of Positive Pressure
Ventilation (= Mean Alveolar Pressure)

17. Time Constants

18. Time Constants
• Is the length of time lung units require to fill &
empty
• T = Raw X Cst where: T = Time Constants
Raw = Airway Resistance
Cst = Static Compliance

19. Clinical Applications: Time Constant
• “Fast” alveoli = short time constant (fast filling)
--Pulmonary fibrosis (low Cst & low Raw)
• “Slow” alveoli = long time constant (slow filling)
--Asthma (high Cst & high Raw)

20. Waveform Analysis

22. Pressure-Controlled Ventilation
Lucangelo, Respir Care 2005; 50:55

23. Pressure-Controlled Ventilation
Increasing airways resistance
Decreasing lung compliance
Lucangelo, Respir Care 2005; 50:55

24. WK505 Effort
Nilsestuen, Respir Care 2005; 50:202-232
Volume-Controlled Ventilation

25. Recognizing Auto-PEEP

26. set PEEP
auto PEEP
pressure
time
PIP PIP
No active exhalation or inspiratory effort
Treats lungs as single compartment

27. Dhand, Respir Care 2005; 50:251

28. Problems with Auto-PEEP
• Increased Pplat and over-distention
– Increase work-of-breathing
– Hemodynamic effects
– Pneumothorax
• Difficulty triggering ventilator

29. 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
PEEP
7 cm H2O
PEEP
10 cm H2O
PEEP
10 cm H2O
Auto-PEEP should be measured with set PEEP = 0

30. Ways to reduce Auto-PEEP:
• Increasing inspiratory flow
• Reduce minute ventilation (Ve)
• Suctioning the patient
• Changing the modes to allow for more
spontaneous breaths

31. In VCV, use the following to evaluate
the graphics:
• What is the flow pattern?
• What is the PEFR
• Is auto-PEEP present?
• Is a leak present?
• What is PIP?
• Is flow to the patient adequate?
• Has the sensitivity been set appropriately?

32. Pressure-Volume Loops

33. 0 10 20 30 40
00.40.81.21.6
normal
ARDS
airway pressure (cm H2O)
volumeaboveFRC(liters)
lower inflection
point
upper inflection
point

35. Flow-Volume Loop

36. Dhand, Respir Care 2005; 50:256

37. Dhand, Respir Care 2005; 50:246

38. Key Points:
• Monitoring of mechanically ventilated patients
is dependent on the assessment of lung
mechanics
• Evaluation of Compliance, Resistance and PV
curves/loops can help us determine the
baseline condition of lung mechanics