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

Spontaneous Breathing Pressure (cm H2O) Flow (L/m) Volume (mL) Time (sec)

Continuous Positive Airway Pressure (CPAP) (cm H2O) CPAP Level Flow (L/m) Volume (mL) Time (sec)

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 Ventilation Phase 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 Ventilation The Mode

Triggered Modes of Ventilation Pressure Support Ventilation Control Trigger Limit Target Cycle Pressure Patient Flow Patient Triggered, Pressure Limited, Flow Cycled Ventilation

PSV

PSV

Pressure Support Ventilation (PSV) Longer Inspiration Set PS Level Pressure (cm H2O) Better Efforts Flow Cycling Flow (L/m) Volume (mL) Time (sec) Patient Triggered, Flow Cycled, Pressure limited Mode

CPAP+PSV Pressure (cm H2O) Flow (L/m) Volume (mL) Time (sec) Set PS Level Pressure (cm H2O) CPAP Level Flow Cycling Flow (L/m) Volume (mL) Time (sec) Patient Triggered, Flow Cycled, Pressure limited Mode

Pressure Support Ventilation Settings 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 Ventilation Indications, 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 Disadvantages 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 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 Modes SIMV

VC-SIMV: +Efforts

VC-SIMV/PSupp

PCV+ PSupp

Thank You