Monitoring of Mechanical Ventilation by OluAlbert

Monitoring of Mechanical Ventilation

Olu Albert, MPH,RRTClinical ManagerRespiratory Care, ASIA PACIFICPhilips Health

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

Calculated Parameters

Pre

ssu

re

Time

PIP:complianceresistancevolumeflowPEEP

PEEP

PEEP

PIP

PplatRaw= Pta /V

compliancetidal volume

end-inspiratory

alveolar pressure

Pta = PIP - Pplat

PIP

Pre

ssure

(cm

H2O

) V

olu

me (

mL)

F

low

(L/m

in)

Lucangelo, Respir Care 2005; 50:55

Monitoring Compliance and Airway Resistance

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

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

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?

• 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

Pplat 30 cm H2O

TranspulmonaryPressure = 15 cm H2O

Pplat = Palv; Pplat = Transpulmonary Pressure?

+15 cm H2O

Stiff chest wall

PCV 20 cm H2O,

PEEP 10 cm

H2O =Pplat 30

cm H2O

-15 cm H2OTranspulmonaryPressure = 45 cm H2O

Active inspiratory effort


Pplat 30 cm H2O,

VCV

Pplat 30 cm H2O,

PCV

Active inspiratory effort

Pplat 30 cm H2O,

VCV


Risk of VILI may be different with the same Pplat

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)

Time Constants

Time Constants

• Is the length of time lung units require to fill & empty

• T = Raw X Cst where: T = Time ConstantsRaw = Airway ResistanceCst = Static Compliance

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)

Waveform Analysis

Pressure-Controlled Ventilation


Pressure-Controlled Ventilation

Increasing airways resistance

Decreasing lung compliance


WK505 Effort

Nilsestuen, Respir Care 2005; 50:202-232

Volume-Controlled Ventilation

Recognizing Auto-PEEP

set PEEP

auto PEEP

pre

ssu

re

time

PIP PIP

No active exhalation or inspiratory effort

Treats lungs as single compartment

Dhand, Respir Care 2005; 50:251

Problems with Auto-PEEP

• Increased Pplat and over-distention

– Increase work-of-breathing

– Hemodynamic effects

– Pneumothorax

• Difficulty triggering ventilator

sensitivity

-1 cm H2Oauto-PEEP

10 cm H2O

trigger effort = 11 cm H2O

sensitivity

-1 cm H2Oauto-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

Ways to reduce Auto-PEEP:

• Increasing inspiratory flow

• Reduce minute ventilation (Ve)

• Suctioning the patient

• Changing the modes to allow for more spontaneous breaths

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?

Pressure-Volume Loops

0 10 20 30 40

0 0

.4

0.8

1

.2 1

.6

normal

ARDS

airway pressure (cm H2O)

vo

lum

e a

bo

ve F

RC

(li

ters

)

lower inflection

point

upper inflection

point

Flow-Volume Loop

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

Monitoring of Mechanical Ventilation by OluAlbert

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