DID YOU KNOW? - Draeger1. Kackmarek R, Wilkins R, Stoller JK. Egan's Fundamentals of Respiratory...
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TIME CONSTANT DID YOU KNOW? What is it? How is it calculated? Why is it relevant? The time constant (TC) is the time used by the lung to be filled during inhalation (inspiratory TC) or to be emptied during exhalation (expiratory TC) at a stable pressure 1,2 . The Expiratory Time Constant (TCe ) provides information on respiratory mechanics. It can be used whenever expiration is assumed to be passive. An accurate setting of the ventilator parameters can prevent VILI (Ventilator Induced Lung Injury) and VALI (Ventilator Associated Lung Injury), decreasing the different types of trauma (barotrauma, volutrauma, atelectrauma). TC is measured in seconds and is the product of compliance and resistance. TC = C L x R aw 1. Kackmarek R, Wilkins R, Stoller JK. Egan's Fundamentals of Respiratory Care. 9th ed. Philadelphia: Mosby/Elsevier; 2009 2. Beachey W. Respiratory Care Anatomy and Physiology. 2nd ed. Philadelphia: Mosby/Elsevier; 2007 3. Hess DR. Respiratory mechanics in mechanically ventilated patients. Respir Care 2014;59:1773-94 Why is it helpful to improve outcome? • TCe can be used to assess respiratory mechanics and to optimize settings to protect the lungs. • TCe directly helps to individually adjust optimal expiratory time. Short TCe can lead to VILI Monitor Tidal Volume, driving and plateau pressure Long TCe can lead to hyperinflation Monitor Intrinsic PEEP This is valid when the lung is free from any diseases. • 1 TC • 2 TC • 2 TC 63 % 86 % 95 % TCi TCe Time Constant 0% 1 2 3 4 5 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 100,0% 86,5% 13,5% 5,0% 1,8% 0,7% 99,3% 98,2% 95,0% 36,8% 63,2% 0,0% Percent of Steady State Value
Transcript of DID YOU KNOW? - Draeger1. Kackmarek R, Wilkins R, Stoller JK. Egan's Fundamentals of Respiratory...
TIME CONSTANT
DID YOU KNOW?
What is it?
How is it calculated?
Why is it relevant?
The time constant (TC) is the time used by the lung to be filled during inhalation (inspiratory TC) or to be emptied during exhalation (expiratory TC) at a stable pressure 1,2.
The Expiratory Time Constant (TCe) provides information on respiratory mechanics. It can be used whenever expiration is assumed to be passive.
An accurate setting of the ventilator parameters can prevent VILI (Ventilator Induced Lung Injury) and VALI (Ventilator Associated Lung Injury), decreasing the different types of trauma (barotrauma, volutrauma, atelectrauma).
TC is measured in seconds and is the product of compliance and resistance.
TC = CL x Raw
1. Kackmarek R, Wilkins R, Stoller JK. Egan's Fundamentals of Respiratory Care. 9th ed. Philadelphia: Mosby/Elsevier; 20092. Beachey W. Respiratory Care Anatomy and Physiology. 2nd ed. Philadelphia: Mosby/Elsevier; 20073. Hess DR. Respiratory mechanics in mechanically ventilated patients. Respir Care 2014;59:1773-94
Why is it helpful to improve outcome?
• TCe can be used to assess respiratory mechanics and to optimize settings to protect the lungs.
• TCe directly helps to individually adjust optimal expiratory time.
Short TCecan lead to VILI Monitor Tidal Volume,
driving and plateau pressure
Long TCecan lead to hyperinflation Monitor Intrinsic PEEP
This is valid when the lung is free from any diseases.
• 1 TC • 2 TC • 2 TC63% 86% 95%
TCi
TCe
Time Constant
0%1 2 3 4 5
10%
20%
30%
40%
50%
60%
70%
80%
90%
100% 100,0%
86,5%
13,5%5,0%
1,8% 0,7%
99,3%98,2%
95,0%
36,8%
63,2%
0,0%
Perc
ent o
f Ste
ady
Stat
e Va
lue
