basics mechanical ventilation

7/23/2019 Basics Mechanical Ventilation

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BASICS OF MECHANICALVENTILATION

Muthiah P. Muthiah, MD, FCCP

Associate Professor of Medicine

Pulmonary & Critical Care & Sleep MedicineUniversity of Tennessee, Memphis



MECHANISM OF BENEFIT

Improves gas exchange (positivepressure improves V/Q matching,decrease intrapulmonary shunting)

Decreases work of breathing



Some Conditions Requiring MV

Pneumonia / ALI /ARDS

Acute Pulmonary Edema

Severe Sepsis / Shock Severe Exacerbations of Asthma / COPD

Neuro: Guillain–Barre/ Myasthenia /

Drug OD etc.



MAIN INDICATION

Acute Respiratory Failure:

inability to oxygenate arterial blood

adequately and/or loss of capacity to sustain adequate

alveolar ventilation

Clinically manifested by presence of rapid,shallow breathing



Suggested Criteria fro MV

RR > 35

VC < 10 ml/Kg

NIF < -25 CmH2O INC in PaCO2 (> 10)

PaO2 < 55 mmHg despite supplemental

O2 > 45%



Some Modes of Ventilation

AC

SIMV

SIMV + PS PSV

PC

BiLevel / APRV VC Plus



INDICATION

Ultimately,decision to initiate mechanicalventilation must take clinicalcircumstances into account as well as

physiologic derangements



VENTILATOR CYCLINGMECHANISMS

Volume-cycled: inspiration terminated after delivery of a

preset tidal volume

Pressure-cycled: inspiration terminated when a preset maximum

pressure reached.



VENTILATOR CYCLINGMECHANISMS

Flow-cycled: inspiration terminated when particular flow

rate reached. (e.g. Pressure supportventilation)

Time-cycled: inspiration terminated following a preset

inspiratory time. (e.g.Home ventilators)



Basic Ventilator Modes “Control” modes

Volume control (Assist control): AC. Pressure control: PC.

Mixed Synchronized Intermittent Mandatory

Ventilation (SIMV) with support (controlled &s pontaneous)

“Spontaneous” Modes Pressure Support (PS) CPAP (NOT A MODE!!)



Mode characteristics

What parameters do I have to set/order?

What initiates a breath?

What terminates a breath (i.e. how theventilator cycle )?

What are the flow characteristics?

What are the pressure characteristics?

What are the determinants of VT ?



General Measures in Patientson Mechanical Ventilation

Use as low FiO2 as possible

Head of bed at 30o to decrease risk ofaspiration

GI bleed prophylaxis:H2 blockers, PPIs or Sucralfate

DVT prophylaxis on all patients:

TED hose plus pneumatic compression stocking orSQ heparin



FAST HUG

Feeding

Analgesia

Sedation T hromboembolism Prophylaxis

Head of Bed Elevation

Ulcer Prophylaxis Glucose Control

FA

STH

UG



Assist Control

Ventilator senses an inspiratory effort bythe patient and responds by delivering apreset TV.

Patient work required to trigger theventilator

A control mode back-up rate is set toprevent hypoventilation



Assist control (AC)

Flow: constant

Pressure:

Increases as lungs distend untilinspiration terminates; pressurepotentially varies breath to breath

VT : Fixed



Assist control (AC)

Orders: RR, VT , FIO2 +/- PEEP

Initiate: patient or controlled

Breaths beyond set rate get the set VT Termination: VT – “volume-cycled”

Example initial orders: AC / RR 14 / Vt 400 ml / PEEP 5 / FiO2 100



AC/CMV

Airway

pressure

Time

Inspiration Expiration

Ventilator triggered

breath

Patient triggered breath



Assist Control (AC) Advantages:

Reduced work of breathing Allows patient to increase minute ventilation;

can’t decrease below set VE

Minimal VE is ensured

Disadvantages potential adverse hemodynamic effects or

inappropriate hyperventilation airway pressures vary with changes in lung

compliance



SIMV with PS

Degree of ventilatory support determined by theselected IMV rate.

At regular intervals, ventilator delivers a breathbased upon a preset TV and rate.

Pt allowed to breathe spontaneously at TV and

rate determined according to need and capacity



SIMV

Airway

pressure

Time

Inspiration Expiration


breath



SIMV

Airway

pressure

Time

Inspiration

Expiration


breathPatient triggered breath

Inspiration

Expiration


breath



SIMV with PS

Potential advantages More comfortable for some patients

Less hemodynamic effects

Potential disadvantages Increased work of breathing, especially when

weaning



PS ventilation

Flow-cycled: preset pressure sustained until inspiratory

flow tapers to 25 % of max

Comfortable ventilatory modality Patient with greater control over ventilator

cycling and flow rates

Close monitoring because neither TV nor MVguaranteed



Pressure Support (PS)

Orders: Pinsp above PEEP, FIO2 +/- PEEP Initiate: Patient only Termination:

Flow 25% of max (flow cycled) Flow:

decelerating rate; patient can increase Pressure: constant

Volume: varies with pressure, effort, and compliance of

lung and chest wall



Pressure Support (PS)

Potential advantages Patient comfort Decreased work of breathing

May enhance patient-ventilator synchrony

Potential disadvantages

Variable VT if pulmonaryresistance/compliance changes rapidly



CPAP



T-piece (T-tube)

Orders: FIO2

Initiate: Patient Termination: Patient Flow: Patient Pressure: negative with inspiration Volume: varies with effort and compliance

Spontaneous breathing through an ETT



T-piece



Managing the ventilatedpatient

Initial orders

Normal lungs Obstructive lung disease

Acute Lung Injury/ARDS



Suggested guidelines formechanical ventilation

Maintain Plateau Pressure < 30 cm H2O

PS during spontaneous breaths

Use lowest FIO2 to maintain acceptablearterial PaO2

Keep patient comfortable

Anxiety, pain, WOB (RR < 20-30)



Short-Term: Normal Lungs

Post-op, procedures, drug overdose:

AC or SIMV/PS

VT : 6 - 8 cc/kg (IBW) RR: 10 - 14 I:E – 1:2 (default) PEEP: 5 cm H2O FIO2 to keep SpO2 > 92% HOB up >30 (ALL pts)



Elevated ICP: Normal lungs

Closed head injury

Same guidelines as normal lungs Avoid PEEP unless need for hypoxemia

Hyperventilate? PaCO2 30-35 (controversial)

Sedation



Obstructive Lung Disease

COPD, Asthma

AC, SIMV/PS

VT : 8 cc/kg

RR:8 - 12

I:E – shorter I time

Good sedation for first 24h (rest) Bronchodilators



Acute Lung Injury/ARDS

AC, PC , BiLevel / APRV

VT : 6 cc/kg

I:E- 1:2

RR: 15-25

PEEP: > 8-10

Sedation



MV –Adjustment phase

Target Spo2 : > 94%, paO2 > 60 mmHg

Target pco2: based on pH

To adjust ventilation (co2): change eitherRR (and /or TV)

To adjust oxygenation: change either FIO2or PEEP




Monitor Peak and Plateau pressures

Peak Pressure-Plateau Pressure= Airwayresistance

Peak airway pressure should be < 45-50 cm

H2O (decrease barotrauma)




Provide appropriate I:E ratio Normal ratio of 1:2 COPD/asthma require much longer expiratory

time to avoid air trapping

Attempt to shorten inspiratory time, leaving restof cycle for exhalation : Decrease tidal volume Decrease respiratory rate Increase peak flow



WEANING / Liberation from MV

Process used safely remove patient fromMechanical Ventilation

First condition before starting the

liberation process: Satisfactory control of the condition

that initially caused the need forassisted breathing

Weaning actually starts soon afterPlacing on MV: Eg. : Decreasing Oxygen



TRIALS OF SPONTANEOUSBREATHING

Decision to extubate based upon clinicalassessment during course of the trial,

usually (not always) supplemented by ABG

Trial of spontaneous breathing once a day

shown to be as effective as multiple trials

R id Sh ll B thi I d



Rapid Shallow Breathing IndexRSBI, or Tobin Index

Measured as respiratory frequency (f)divided by tidal volume (TV) in liters

Eg.: RR 18, Vt 500 ml: 18 ÷ 0.5 = 36 <105:

80 % chance of weaning success >105:

95% chance of weaning failure

Q i k V t Ti A f



Quick Vent Tips: A few caseScenarios

Initial Settings

Appropriate Vt in ARDS

Low pressure High pressure

High pr with Pk – Pl diff >10

High pr with Pk – Pl diff <10 Difficult to Oxygenate patient

Which mode of ventilation is usually selected wheniniti tin m ch nic l ntil ti n in p ti nt h just



initiating mechanical ventilation in a patient who justgot intubated for respiratory failure followingCommunity Acquired Pneumonia?

A. Assist Control

B. SIMV

C. Pressure SupportD. CPAP

E. APRV

What is optimal tidal volume for a patient who



p pweighs 70 Kgs, and is now getting intubated forrespiratory failure after he developed ARDS?

A. 420 ml

B. 700 ml

C. 840 mlD. 1 L

E. 1230 ml

Which are usual appropriate initial settings



Which are usual appropriate initial settingsfor a patient who weighs 70 Kgs, and is nowgetting intubated for respiratory failure

after he developed ARDS?

A. SIMV/ RR 28/ VT 840 ml/ PEEP 5/ O2 50%

B. AC / RR 14 / 420 ml / PEEP 5 / O2 100%

C. PSV / PS 10/ PEEP 5

D. CPAP 10 / O2 100%

A patient is on the ventilator, and thel l i i ff Wh t



low pressure alarm is going off. Whatare the possible reasons for this to

happen?A. Tube disconnect

B. Thick secretions

C. Excess fluid in the tubing

D. Pneumothorax

E. Right main stem intubation

A patient is on the ventilator, and thehigh pressure alarm is going off What



high pressure alarm is going off. Whatare the possible reasons for this to

happen?A. Tube disconnect

B. Auto PEEP

C. Bronchopleural fistula

D. Hypoxemia

E. Hypoventilation

A patient is on the vent, and the High pralarm is going off Peak pr: 55 Plateau Pr



alarm is going off. Peak pr: 55, Plateau Pr32. What should be considered in the diff

diagnosis in this patient?A. Worsening ARDS

B. Worsening bronchospasm

C. Right main stem intubationD. Pneumothorax

E. Tube disconnect

A patient is on the vent, and the Highl i i ff P k 55



pressure alarm is going off. Peak pr: 55,Plateau Pr 50. What should be considered in

the diff diagnosis in this patient? A. Worsening ARDS

B. Worsening bronchospasm

C. Thick secretions

D. Patient is biting the tube

E. ET Tube is blocked

A patient who weighs 70 Kgs is on the



p g gventilator, and you are called to evaluate thepatient for low SPO2 of 78%. Patient is on

A/C mode, RR 14, PEEP 5, Vt 450, O2 100%.Peak pr 35, Plateau Pr 28, minute ventilaton14 LPM.

He has bilateral breath sounds, and a statCXR shows bilateral diffuse infiltrates.ABG: pH 7.37 / paCO2 46 / paO2 51 / SaO2 81%.

What should be the initial intervention toimprove the patient’s oxygenation status?

What should be the initial interventiont impr ve the patient’s x enati n



to improve the patient s oxygenationstatus?

A. Increase the tidal volume to 600 ml and callthe fellow

B. Increase the RR 22 and call the fellow

C. Change the mode to PSV and call the fellowD. Increase the PEEP to 10 and call the fellow

E. Administer Neuromuscular blockade with

Norcuron and call the fellow



Q?

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