APRV Ventilation Mode

APRV Ventilation Mode

Airway Pressure Release Ventilation A Type of CPAP Continuous Positive Airway Pressure (CPAP) with an intermittent release phase. Patient cycles between two levels of CPAP higher (P High) and the lower (P Low) The patient can breath spontaneously at either level Maintains an optimal FRC Maintain adequate lung volume and alveolar recruitment. Occasional pressure releases augments CO 2 removal

The Values P High - the upper CPAP level. Analogous to mean airway pressure and thus affects oxygenation P Low - is the lower pressure setting (PEEP). T High - is the time spent at P High T Low - is the release time allowing CO 2 elimination

Definition Use of high-flow (demand valve) CPAP circuit allows: Integrated, unrestricted spontaneous breathing: Can happen any time regardless of the ventilator cycle. If no spontaneous effort APRV becomes inverse ratio pressure-limited, time cycled Minute Volume Ventilation i.e. Pressure Control Ventilation (PCV)

Mechanism of Action 1 In ARDS: Functional Residual Capacity and lung compliance are reduced, Work of Breathing elevated. CPAP application restores FRC Inspiration starts from an improved PV relationship Facilitates spontaneous ventilation, Improves oxygenation Minute Ventilation/CO 2 removal depends upon: Lung compliance and Airway resistance, Magnitude and duration of pressure release. Patient s spontaneous breathing efforts Helps drive inspired gas to the non-dependent lung: Patient s own respiratory muscles/pl p changes without changes in applied airway pressures augment VR/inc CO 2 More physiologic gas distribution IMPROVE V/Q matching

Mechanism of Action 2 Spontaneous Breathing: Improves pulmonary mechanics; PaO 2 /dead space Improves comfort, patient-vent synchrony Reduction in amount of sedation necessary Decrease in intra-thoracic and R atrial pressures Increase venous return/improve pre-load/inc CO 2 Application of P high and T high : (80-95%) of the cycle time - open lung, Mean airway pressure is increased Insures almost constant lung recruitment, Decreases repetitive inflation/deflation Decreases risk of Ventilator Induced Lung Injury Decreases need for recruitment manoeuvres

Indications ALI/ARDS and atelectasis post major surgery FiO 2 > 50%/Elevated PCO 2 Asynchronous with vent RR >30 High airway pressures Poor/decreasing lung compliance Labile BP Difficult to sedate

Contraindications Patients who require deep sedation for more management of underlying disease Cerebral Oedema with increased ICP Status Epilepticus NeuroMuscular disease not investigated but not supported Obstructive lung disease; asthma/copd Due to restrictive lung pressures.

Initial Settings - P High Set at plateau/static pressure (Pplat) Typically about 20-25 cmh 2 O Patients with Pplat >/= 30 cmh 2 O, set at 30 cmh 2 O Avoid over distension; max P High 35 cmh 2 O. Exceptions for higher settings- Morbid obesity Decreased thoracic/abdominal compliance (ascites)

Initial Settings P Low Set PEEP at 0 cmh 2 0 Provides a rapid drop in pressure and maximum delta P for unimpeded expiratory gas flow Delta P is a mathematical term used to illustrate a change (Δ) in pressure (P) - (ΔP) Avoid lung collapse during T low.

Initial Settings T High Inspiratory time is set at a minimum of ~ 4.0 seconds (4-6) Progressively increased Progress slowly, Older patients may be fragile The Target is oxygenation.

Initial Settings - T Low Release Time of 0.2 1sec In ARDS attempt to NOT have exhalation progress to complete emptying Do not let expiratory flow return to zero Regional auto-peep is desirable with APRV It is important that the lungs are not allowed to return to residual volume during T low as this would result in atelectasis, derecruitment, reduced alveolar stability, increased inflammatory cytokine release, reduced surfactant and therefore ventilator induced lung injury and worsening hypoxaemia.

Settings Overview Pressure Settings P High desired mean airway pressure + 3 cmh 2 O (20 to 30 cm) P Low usually set at 0 cmh 2 O (0 to 5 cm) Time Settings T High usually set at 5.0 seconds (4.5-6.0 sec) T Low usually set at 0.7 seconds (0.5-0.8 sec) FiO 2 Target to >50% Setting Maximum Minimum P high 30 cmh 2 O (pressures above this may be required in certain circumstances) P low 0 cmh 2 O 0 cmh 2 O T high 12 15 seconds 4 seconds T low 1 second 0.2 second At pressures<20 cmh 2 O discontinuation of APRV may be possible

On The Ventilator

APRV Monitoring Release tidal volume at least 5 ml/kg Arterial oxygen saturation Haemodynamicly Stable ABGs 20 minutes after initial setup When on APRV record theses settings and observations: P high (in place of P insp) P low (in place of PEEP) T high (in place of ventilator rate) T low (in place of I:E ratio)

Adjusting for Hypercapnia Goal PaCO2 < 8kpa ph >7.2 Decrease sedation to allow spontaneous breathing Increase P-High by 2cmH 2 O Increase T-Low by 0.05 seconds Repeat until P-High 40cmH 2 O and T-Low 0.9 seconds Decrease T-High to 4sec CALL Doctor if still not at goal. Titrate FiO 2 by 10-20% every 30 mins. Goal FiO 2 is 21%. CHECK ABG 30-60 mins after each change

Adjusting for Hypocapnea Goal PaCO2 >4kpa ph <7.5 If PaO2 > 13kpa, decrease P-High by 2cmH 2 O Decrease T-Low by 0.05sec Repeat until P-High 20cmH 2 O and T-Low 4sec CALL Doctor if still not at goal. Titrate FiO 2 by 10-20% every 30 mins. Goal FiO 2 is 21%. CHECK ABG 30-60 mins after each change

Adjusting for Hypoxemia Goal PaO2 >8 SpO2 > 92% Increase P-High by 2cmH 2 O If PCO2 < 6.6, then decrease T-Low by 0.05 Repeat until P-High 40cmH 2 O, T-Low 0.4 Increase P-High by 2cmH 2 O (Until P-High 50cmH 2 O) CALL Doctor if still not at goal. Titrate FiO 2 by 10-20% every 30 mins. Goal FiO 2 is 21%. CHECK ABG 30-60 mins after each change

Weaning Increase T High to eliminate release ventilations until at the minimum allowed by the ventilator - Now on CPAP Once FiO 2 is weaned to < 50% and illness resolving: Drop P High by 2cmH 2 O increments until below 20cmH 2 O Avoid abrupt changes as increased O 2 demand results in increased CO 2 production Once near comfortable CPAP setting - transition to CPAP and wean to extubate Add pressure support (PS) judiciously Add PS to P High in order to decrease WOB but avoid over distension. P High + PS </= 30 cmh 2 O