A pilot feasibility study of Permissive Hypercapnia, Alveolar Recruitment, Low Airway Pressure (PHARLAP) in patients with ARDS

The PHARLAP strategy incorporates a step-wise recruitment manoeuvre to PEEP 40cmH2O in pressure control ventilation, decremental PEEP titration and tolerance of hypercapnia. The staircase recruitment manoeuvre and PEEP titration are performed once per day for 5 days with small re-recruits throughout the day if the patient is disconnected or desaturates. The combination of these individual therapies represents a treatment approach considered by some to be the best available care. In fact these therapies have been shown to improve blood oxygenation, reduce lung injury and attenuate cytokine response. The PHARLAP strategy has been compared to the current best practice in a pilot randomized, controlled study (ACTRN12607000465459). As compare to the current best practice, the PHARLAP strategy allowed an oxygenation and compliance improvement and an attenuation of some inflammatory cytokines over a 7 day period. The PHARLAP strategy includes pressure control ventilation (PCV, 15 cm H2O above PEEP) with patients in supine, 30 degrees head up. The fraction of inspired oxygen (FIO2) is reduced until oxygen saturation was 90-92%. For the SRM, the PEEP is increased in a stepwise manner to 20, then 30 and then 40 cm H2O every two minutes, and then reduced to 25, then 22.5, then 20, then 17.5 or then 15 cm H2O every three minutes until a decrease in SaO2 of 1% from maximum SaO2 is observed. This is defined as the derecruitment point. PEEP is then increased to 40 cm H2O for one minute and returned to a PEEP level 2.5 cm H2O above the de-recruitment point (defined as optimal PEEP). Following this SRM step the tidal volume is decreased to achieve a plateau pressure less than 30 cm H2O. Hypercapnia is tolerated and acidosis will only be treated if the pH is less than 7.15 by increasing respiratory rate to a maximum of 38 breaths per minute, or administration of sodium bicarbonate. The participants will receive one SRM daily (with decremental PEEP titration). In addition, PEEP will be transiently elevated to 40 cm H2O (with PCV at 15 cm H2O) for one minute if oxygen desaturation less than 90% occurred or after disconnection from the ventilator. Patients are assessed daily for weaning. Weaning will be commenced when all of the following occurred: respiratory rate < 35 breaths per minute, PaO2 > 60 mm Hg, SpO2 > 90% with fraction of inspired oxygen < 0.4 and PEEP < 10 cm H2O, mean arterial pressure > 60 mm Hg without inotrope infusions or sedatives.