CPAP/PSV

Objectives

Understand the difference between CPAP, PEEP and PSV

Know the breath types with PSV: supported breaths Know the phase variables of the PSV: trigger, limit

and cycle Understand the ETS cycling mechanisms: flow and

time Setting the Level of Pressure Support Adjustment of pressure support Using PSV with different modes: SIMV Using PSV for weaning Advantages and disadvantages of PSV

CPAP

Continuous Positive Airway Pressure: CPAP

Ventilators can provide CPAP for spontaneously breathing patients Helpful for improving oxygenation in

patients with refractory hypoxemia and a low FRC

CPAP setting is adjusted to provide the best oxygenation with the lowest positive pressure and the lowest FiO2

Spontaneous Breath

Time (sec)

Flow(L/m)

Pressure(cm H2O)

Volume(mL)

Spontaneous Breathing

Time (sec)

Flow(L/m)

Pressure(cm H2O)

Volume(mL)

CPAP Level

Continuous Positive Airway Pressure (CPAP)

CPAP

CPAP

CPAP

CPAP

PEEP

PEEP: Positive End Expiratory Pressure

The term PEEP is defined as positive pressure at the end of exhalation during either spontaneous breathing or mechanical ventilation. However, use of the term commonly implies that the patient is also receiving mandatory breaths from a ventilator.

PEEP becomes the baseline variable during mechanical ventilation

PEEP

Helps prevent early airway closure and alveolar collapse and the end of expiration by increasing (and normalizing) the functional residual capacity (FRC) of the lungs

Facilitates better oxygenation

NOTE: PEEP is intended to improve oxygenation, not to provide ventilation, which is the movement of air into the lungs followed by exhalation

Pressure Support VentilationPhase Variables, Breath Type and Sequence

Pressure Support Ventilation: PSV

Patient triggered, pressure targeted, flow cycled mode of ventilation

Requires a patient with a consistent spontaneous respiratory pattern

The ventilator provides a constant pressure during inspiration once it senses that the patient has made an inspiratory effort

Patient Trigger

Pressure Limit

Flow Cycled

Flow Cycling During PSV

Flow cycling occurs when the ventilator detects a decreasing flow, which represents the end of inspiration

This point is a percentage of peak flow measured during inspiration PB 7200 – 5 L/min Bear 1000 – 25% of peak flow Servo 300 – 5% of peak flow

No single flow-cycle percent is right for all patients

Flow Cycling During PSV Effect of changes in

termination flow

A: Low percentage (17%)

B: High percentage (57%)

Newer ventilators have an adjustable flow cycle criterion, which can range from 1% - 80%, depending on the ventilator

PSV: Time Cycling

NOTE: During pressure support ventilation (PSV), inspiration ends if the inspiratory time (TI) exceeds a certain value. This most often occurs with a leak in the circuit. For example, a deflated cuff causes a large leak. The flow through the circuit might never drop to the flow cycle criterion required by the ventilator. Therefore, inspiratory flow, if not stopped would continue indefinitely. For this reason, all ventilators that provide pressure support also have a maximum inspiratory time.

Supported Breaths

Pressure Support VentilationThe Mode

Triggered Modes of VentilationPressure Support Ventilation

Control Trigger Limit Target Cycle

Pressure Patient Pressure Flow

Patient Triggered, Pressure Limited, Flow

Cycled Ventilation

PSV

PSV

Time (sec)

Flow(L/m)

Pressure(cm H2O)

Volume(mL)

Set PS Level

Flow Cycling

Better Efforts

Longer Inspiration

Patient Triggered, Flow Cycled, Pressure limited Mode

Pressure Support Ventilation(PSV)

CPAP+PSVCPAP+PSV

Time (sec)

Flow(L/m)

Pressure(cm H2O)

Volume(mL)

Set PS Level

Flow Cycling

Patient Triggered, Flow Cycled, Pressure limited Mode

CPAP Level

Pressure Support VentilationSettings and Adjustment

Setting the Level of Pressure Support

Goal: To provide ventilatory support Spontaneous tidal volume is 10 – 12 mL/Kg of

ideal body weight Maintain spontaneous respiratory rate

<25/min

Goal: To overcome system resistance (ET Tube, circuit, etc.) in the spontaneous or IMV/SIMV mode Set pressure at (PIP – Pplateau) achieved in a

volume breath or at 5 – 10 cm H2O

Setting the Level of Pressure Support

Exercise: Using the PIP and the PPlateau from the pressure waveform below, recommend a pressure support setting for this patient (patient is in VC-SIMV mode) 35

25

Answer: 10 cm H2O

The Results of Your Work

35 cm H2O

10 cm H2O

PS=6, VT= 350

PS=10, VT= 600

Pressure Support VentilationIndications, Advantages and Disadvantages

Pressure Support Ventilation: Indications

Spontaneously breathing patients who require additional ventilatory support to help overcome WOB, CL, Raw Respiratory muscle weakness

Weaning (either by itself or in combination with SIMV)

Pressure Support Ventilation: Advantages

Full to partial ventilatory support Augments the patients spontaneous

VT Decreases the patient’s spontaneous

respiratory rate Decreases patient WOB by

overcoming the resistance of the artificial airway, vent circuit and demand valves

Allows patient control of TI, I, f and VT

Pressure Or Volume-Targeted Ventilation

ADVANTAGES

Full to partial ventilatory support Augments the patients spontaneous

VT Decreases the patient’s spontaneous

respiratory rate Decreases patient WOB by

overcoming the resistance of the artificial airway, vent circuit and demand valves

Allows patient control of TI, Vm , f and VT

Set peak pressure Prevents respiratory muscle atrophy Facilitates weaning Improves patient comfort and

reduces need for sedation May be applied in any mode that

allows spontaneous breathing, e.g., VC-SIMV, PC-SIMV

DISADVANTAGES

Requires consistent spontaneous ventilation

Patients in stand-alone mode should have back-up ventilation

VT variable and dependant on lung characteristics and synchrony

Low exhaled VE Fatigue and tachypnea if PS

level is set too low

PS with Other ModesSIMV

VC-SIMV: +Efforts

VC-SIMV/PSupp

PCV+ PSupp

Thank You