Airway Pressure Release Ventilation

APRV review and indications in paediatrics

APRV

        Terminology How it works Indications Advantages/disadvantages Review of paediatric studies Set-up (paed specific) Weaning Discussion

APRV

 Continuous positive airway pressure with regular, brief releases in airway pressure to facilitate alveolar ventilation and CO2 removal  Time triggered, pressure limited, time cycled mode  Allowing unrestricted spon. Breathing throughout the ventilatory cycle

Terminology

 P high = the baseline airway pressure level,  P low = airway pressure resulting from airway release (PEEP)  Time high = the length of time that P high is maintained  Time PEEP = time spent in airway release at P low

How does it work?

 The constant airway pressure at P high facilitates alveolar recruitment and therefore enhances gas diffusion  The long time at P high allows alveolar units with slow time constants to open  The timed releases in pressure T PEEP allows alveolar gas to be expelled via natural lung recoil not with repetitious opening of alveoli

APRV waveform

Indications

      Recruitable low compliance lung disorders Lung dysfunction secondary to thoracic restriction i.e.. obesity, acites Inadequate oxygenation with FiO2 > .60

PIP> 35 cmH2O and /or PEEP>10 cmH2O Lung protective strategies (high PEEP, low Vt) are failing Can be used with other interventions i.e.. INO therapy, prone positioning

Advantages

 Significantly lower peak Paw and improved oxygenation when compared to conventional ventilation  Requires lower min. vol. suggesting decreased dead space ventilation  Avoids low volume lung injury by avoiding repetitious opening of alveoli

Advantages

 Allows for spontaneous breathing at all points in the respiratory cycle  Spon. breathing tends to improve V/Q matching  Decreased need for sedation and near eliminating need for neuromuscular blockade

Disadvantages

 Volumes affected by changes in compliance and resistance and therefore close monitoring required  Integrating new technology  Limited research and clinical experience

Paediatric Studies

 Studies in the paediatric population are few and small  Several are ongoing  3 published  Most evidence is extrapolated from the adult studies

Airway pressure release ventilation in paediatrics Schultz T, et al. Pediatric Crit Care Med. 2001 jul;2(3):24 3-6

    a prospective, randomized, cross-over trial of 15 PICU pt. >8kg Randomized to either VCV (9) or APRV (6) APRV had lower PIP and Pplat than VCV in all patients No sig. differences in physiologic variables e.g.. EtCO2

Airway Pressure Release in a Paediatric Population Jones R, Roberts T, Christensen D. St.Luke’s Reginal Medical Center, Boise, ID AARC open Forum 2004

    A case series of 7 paediatric patients aged 3 to 13 with ALI All failing conventional PPV with severe hypoxemia 2 failed HFOV with severe hypoxemia 6/7 lower PIP, all had higher MAP, all had improved oxygenation, all had lower FiO2 requirements

Airway Pressure Release Ventilation: A Pediatric Case Series Krishnan,J. ,Morrison, M.: University of Maryland, Pediatric Pulmonology 42:83-88. 2007

    retrospective review of 7 pediatric cases Approved by the University of Maryland institutional review board All pt.s failed on conventional ventilation Implemented similar starting parameters as to be described later

Case 1

      9 y.o. leukemia with septic shock, ARDS and MSOF SIMV PC , FiO2 = 1.0, PIP/PEEP= 38/14 cmH2O, PaO2= 91 mmHg Failed HFOV secondary to hypotension APRV – Phigh 37 cmH20, Plow 0cmH2O with Pmean of 32 cmH2O PaO2 improved over 84 hrs and required no NMB Weaned and d/ced home

Case 2

 5 y.o. 60% body area burns with development of sepsis and ARDS  Failed convention ventilation (39/19) and was placed on HFOV with intractable hypercarbia (PaCO2= 121mmHg)  APRV of 40/0 PaCO2 improved to 78mmHg  MSOF worsened and pt. made limited resuscitation

Case 3

 8 y.o. CF with development of ARDS  Pt. required heavy sedation with CV with 30/13 and FiO2 = .50

 APRV settings 28/0 and sedation was decreased and pt. was extubated to NIV  No NMB was required

Case 4

      4 y.o. with fever, jaundice, hepatomegaly, pancytopenia and hypofibrinogenemia Requiring CRRT for MSOF and ARDS CV with 40/10 cmH20 and FiO2 = 1.0

APRV 34/0 and O2 weaned to .6 and NMB was lifted Weaned to CPAP and septic shock resolved but pt suffered an intracranial haemorrhage which led to his death Autopsy revealed hemophagocytic lymphohistiocytosis

Case 5

     1 y.o. leukemia post bone marrow transplant with sepsis and neutropenia and graft vs host disease and tracheotomy Difficult to ventilate with PaCO2 of 64mmHg and tachypnea and distress APRV 30/0 cmH20 and was rapidly weaned with noted increase in comfort Weaned to FiO2 to .45 and PaCO2 = 39mmHg Later exacerbation of leukemia resulted in renal failure

Hints for set-up

 P high = same as plateau or 125% of mean Paw  PEEP = 0 cmH2O  T PEEP = long enough to get returned Vt but not long enough to derecruit – titrate to end at 25 50% of the PEF  T high = manipulated to achieve RR  PS = set to avoid flow hunger with spon. resps.

 Be patient  The change to APRV may not provide instant improvement in oxygenation  The effects may take hours to be realized  Has been shown that the maximum benefit occurred at approx. 8 hours after implementation

Weaning

    Decrease FiO2 first and then P high is small increments As compliance improves the TCs lengthen and T PEEP may need adjustment to allow for adequate Vt When P high is weaned to a low level consider extubation Lengthen T high and therefore decreasing the # of pressure releases per minute

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