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Mechanical Ventilation

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on 16 October 2013

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Transcript of Mechanical Ventilation

Mechanical Ventilation
Ryan Laschober

Positve Presure Ventilation
Ventilator Breath
Initiation: negative pressure deflection-spontaneous inspiratory effort (pt)
If the negative pressure exceeds the pressure activation level, a breath is initiated.
Inflation: constant inflation rate, usually 60L/min (1L/sec) so 500mL is <sec
Peak airway pressure: determined by volume, resistance, compliance
Plateau pressure: pressure while breath is held in lungs
Exhalation: passive, driven by elastic recoil. Faster in lungs who are less compliant (ARDS). Time should be twice inflation time. I:E 1:2
End-Exiparatory Pressure: pressure at end of exipiration

Low Volume Ventilation
Low volume ventilation is designed to reduce ventilator-induced lung injury
Initiation volume is 6-8mL/kg (half of traditional volumes)
Tidal volume based on predicted body weight because it most accurately approximates lung volumes
low volume PEEP prevents alveolar collapse
End-inspiratory pressure should be kept below 30cm H2O, improves overall outcomes


Pressure Cycled
Volume Cycled
mechanical breath delivered at a specific volume
Inflation volume is constant, but inflation pressure can increase or decrease based on lung mechanics (i.e. increased resistance)
What's best?
Mechanical breath delivered at specific pressure
Volume changes with mechanical properties of lungs
Pressure Cycled- inflation volume varies with mechanical properties of lungs. Theoretical decreased risk of ventilator-induced lung injury, however this is unproven
Volume Cycle Ventilation is preferred because a constant volume can be assured despite lung mechanic changes
One must be careful though because intrathoracic pressures can reach high levels if lung compliance decreases
Cardiac Performance
PPV can reduce ventricular filling: impedes venous return and reduces cardiac distensibility
PPV can increase ventricular emptying due to less pressure required to eject the stroke volume
if Intrathoracic pressure > central venous pressure (hypovolemia)- then mechanical ventilation will decrease cardiac stroke output
when ventricular filling is adequate, then mechanical ventilation will act to increase cardiac stroke output

Ventilator Dependent Patient
Peak Pressure
highest pressure during inhalation
directly correlates with airway resistance
inverse relationship with lung compliance
Plateau Pressure
expiratory limb occluded and inflation volume held in lungs
inverse relationship with lung compliance
not correlated with airway resistance
Monitoring Pressures
Peak Pressure increased, Plateau pressure is unchanged
Obstruction (tube/secretions), bronchospasm
RX= suctioning or aerosolized bronchodilator
Peak and plateau pressures both increased
Pneumothorax, atelectacis, acute pulmonary edema, worsening pneumonia, ARDS
RX=exam, stat CXR
Pressure Changes
Airway Resistance
Thoracic Compliance Changes
Peak pressure decreased = possible cuff leak
Modes of Ventilation
Assist Control
Assist= ventilator breath can assist patients breath
Control= if patient does not initiate breath, breath will be provided at specific rate
Allows patient to initiate ventilator breaths
Ventilator breath provided every time patient initiates breath
can be problematic in rapid breather
leads to over distension and possible alveolar rupture, PTX, and pneuomomediastinum
Reducing air trapping:
low volume ventilation
6ml/kg vs tradiational 12ml/kg
increase inspiratory flow rate (increases time between breaths), allows for time to exhale tidal volume
change mode
Allows patient to breath spontaneously between ventilator breaths, breath not supported by ventilator
Better for rapid ventilation
Work of breathing increased due to increased resistance from tube (no assistance in breathing)
Use for pt who is breathing rapidly and is at risk for air trapping, not for weaning
Low Volume Ventilation settings
Step 1: Initial settings
Tidal volume at 8mL/kg based on predicted body weight
RR at 12-14 breaths/min
PEEP of 5-7 cm H2O
FiO2 100%
Step 2: Volume Reduction
Reduce tidal volume by 1 mL/kg ever 2 hours until Vt is 6 mL/kg
When 6mL/kg, measure end-inspiratory plateua pressure (Ppl)
If Ppl >30cm H20, decrease Vt in 1ml/kg increments until Ppl <30cm H20 or Vt=4ml/kg
Step 3: Adjust for Respiratory Acidosis
7.15-7.30, increase RR until >7.3 or RR of 35 bpm
<7.15, RR to 35BPM. If pH still <7.15, increase Vt in 1mL/kg increments until pH 7.15 (Permissive Hypercapnia)
Step 4: Achieving a Non-Toxic FiO2% (<60%)
Decrease FiO2 in 10-20% increments until <60% or SaO2 =88%
FiO2 >60% add PEEP in increments of 2-3cm H2O until FiO2 <60% and SaO2>88%

Keeps distal airspaces open
reduces venous return
Used in
ARDS who require FiO2>60% to maintain sats >88%
low volume ventilation to prevent collapse of distal airways
Migration of tube
Paranasal Sinusitis
Ventilator associated PNA
Laryngeal Damage
Tube to Trach not exact science
After 5-7 days assess likelihood of extubation. If unlikely in next week, then trach
"The Acute Respiratory Distress Syndrome Network. Ventilation with Lower Tidal Volumes as Compared with Traditional Tidal Volumes for
Acute Lung Injury and the Acute Respiratory Distress Syndrome." N Engl J Med 2000; 342:1301-1308 (n.d.): n. pag. Web.

Katz, J. A., S. E. Zinn, G. M. Ozanne, and B. B. Fairley. "Pulmonary, Chest Wall, and Lung-thorax Elastances in Acute Respiratory Failure." Chest 80 (1981): 304-11. Web.

Marini JJ. "Lung Mechanics Determinations at Bedside: Instrumentation and Clinical Application." Respir Care 35 (1990): 635-62. Print.

Marino, Paul L., Kenneth M. Sutin, and Paul L. Marino. The Little ICU Book. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2009. Print.

Tobin MJ. "Respiratory Monitoring." JAMA 264 (1990): 244-51. Web.

Works Cited
little data on best tidal volume
IMPROVE study compared 10-12ml/kg of PBW vs 6-8ml/kg PBW in major abdominal surgery intraoperatively and postop
at 7 days lower volume (6-8ml/kg) patients:
decreased adverse pulmonary and extrapulmonary events (11% vs 28%)
decreased need for ventilation (5% vs 17%)
Shorter hospital stay (2.5days)
Not assoc with decreased ARDS risk
No mortality benefit
What we will Discuss:
Basics of ventilation
Modes of ventilation
Initial Ventilator settings
Initial adjustments to settings to reach ideal levels
Basics of dealing with changes in ventilator pressures
to trach or not to trach?
methods of weaning from vent
What we will not discuss:
Indications for ventilation
Intubation steps
Goal: Vt = 6ml/kg, Ppl<30cm H20, pH = 7.30-7.45
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