Mechanical Ventilation 1

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Objectives

Discuss indications and techniques for noninvasive positive pressure ventilation (NPPV)Describe types of breaths and modes of mechanical ventilationOutline settings and monitoring for initiation of mechanical ventilation

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Case Study65-year-old with an exacerbation of COPD

Using accessory muscles and wheezing after 2 bronchodilator treatments

HR 110 beats/min, BP 160/110 mm Hg, RR 30 breaths/min, T 99F(37.2C)ABG on 3 L/min O2: pH 7.24, PCO2 60 mm Hg (8 kPa), PO2 65 mm Hg (8.7 kPa)

What type of respiratory support should What type of respiratory support should be initiated? be initiated?

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Candidates for NPPV

Respiratory condition expected to improve in 48-72 hoursAlert, cooperativeHemodynamically stableAble to control airway secretionsAble to coordinate with ventilatorNo contraindications

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Case Study

Avoids complications of intubationPreserves airway reflexesImproved patient comfortLess need for sedationShorter hospital/ICU stayImproved survival

What are advantages of using non-What are advantages of using non-invasive positive pressure ventilation invasive positive pressure ventilation in this patient?in this patient?

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Case StudyABG on 3L/min O2: pH 7.24, PaCO2 60 mm Hg (8 kPa), PaO2 65 mm Hg (8.7 kPa)

HR 110 beats/min, BP 160/110 mm Hg,RR 30 breaths/min

What are the goals for respiratory What are the goals for respiratory support?support?

What settings should be selected for What settings should be selected for NPPV?NPPV?

How should the patient be monitored?How should the patient be monitored?

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Case Study

After 1 hr of NPPV, the patient has not improvedArterial blood gas on 40% O2: pH 7.20, PaCO2 65 mm Hg (8.7 kPa), PaO2 58 mm Hg (7.8 kPa)

HR 115 beats/min, BP 142/98 mm Hg, RR 32 breaths/min

What is the next step? What is the next step?

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Case StudyOrotracheal intubation is performed

What ventilator mode should be What ventilator mode should be selected?selected?

What tidal volume is optimum?What tidal volume is optimum?

What rate of ventilation should be What rate of ventilation should be set?set?

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Respiratory Cycle

Types of breaths: volume-cycled, time-cycled, flow-cycled

Triggering

Cycling

Respiratory Cycle

ExpirationInspiration

Time (sec)

Air

wa

y P

res

su

re (

cm

H2O

)

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Modes of Mechanical Ventilation

Interface of breath types with patientAssist-control (AC)Pressure support (PSV)Synchronized intermittent mandatory (SIMV)

Continuous positive pressure airway pressure (CPAP)—not a mode of ventilation

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Airway Pressure/Flow Tracings

Expiration

Inspiration

Pre

ssu

reP

ress

ure

Time

Time

Spontaneous ventilation

CPAP

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Assist-control ventilation Volume or time-cycled breaths

Pressure support ventilation Flow-cycled breaths

Modes of Mechanical Ventilation

ExpirationInspiration

Volume assist-control

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Synchronized intermittent mandatory ventilation Volume or time-cycled breaths

SIMV + PSV

Modes of Mechanical Ventilation

Volume-cycled breathSpontaneous

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Patient with COPD exacerbation who failed NPPV

Case Study

What ventilator mode should be What ventilator mode should be selected?selected?

What tidal volume is optimum?What tidal volume is optimum?

What rate of ventilation should be set?What rate of ventilation should be set?

What FIOWhat FIO22 should be delivered? should be delivered?

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Initiation of Mechanical Ventilation

Familiar ventilation modeInitial FIO2 = 1.0; decrease to maintain SpO2 >92% to 94%

Initial tidal volume = 8-10 mL/kgRate and minute ventilation appropriate for clinical needsPEEP to support oxygenationCall critical care consultant for help

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Case Study

Chest radiographVital signsSpO2

Patient-ventilator synchronyArterial blood gas

InspiratorypressuresInspiratory:expiratory ratioAuto-PEEPVentilator alarms

What monitoring and assessment is What monitoring and assessment is needed after initiation of mechanical needed after initiation of mechanical ventilation?ventilation?

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Peak inspiratory pressure (Ppeak)Inspiratory plateau pressure (Pplat) Indicator of alveolar distension

Inspiration Expiration

PpeakPplat

Inspiratory Pressures

Ppeak

Pplat

Pplat 30 cm H2O

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Determinants of inspiratory time with volume ventilation

Tidal volumeInspiratory flow rateInspiratory waveform

Inadequate expiratory timeIncomplete exhalationBreath stacking

Inspiratory: Expiratory Ratio

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Diagnosis Measurement Waveform analysis

Auto-PEEP

Auto-PEEP

Gasflow

Auto-PEEP

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Auto-PEEP

Consequences Inspiratory pressures Hypotension Worsened oxygenation Interventions to decrease auto-PEEP Respiratory rate Tidal volume Gas flow rate

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Questions Questions

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Key PointsGoals of NPPV and mechanical ventilation are support of oxygenation and ventilation and reduction in work of breathingNPPV is best used in the alert, cooperative patient whose condition will improve in48-72 hoursConsider the advantages/disadvantages of different modes when selecting ventilatory supportUse guidelines when initiating mechanical ventilation and adjust based on monitoring