Forti et al. Journal of Medical Case Reports 2010, 4:339 http://www.jmedicalcasereports.com/content/4/1/339 be related to the disruption of the normal activity of the respiratory muscles. The disruption begins with the induc- tion of anaesthesia and may continue into the post-opera- tive period. Anaesthetics and drugs used in the peri- operative period affect the central regulation of breathing and change the neural drive to the respiratory muscles and, in particular, to the diaphragm [3]. On the first post- operative day after a sternotomy, the observed decrease in forced vital capacity (FVC) is reported to be around 70% of the preoperative value. Ten days after surgery, when most patients can be discharged from the hospital, the FVC has increased but still remains at 30% lower than the preoperative value [4]. It has been reported that high fre- quency percussive ventilation (HFPV) improves gas exchange where normal ventilation and lung recruitment therapy have failed. HFPV VDR4 (Percussionaire Bird Technologies, ID, USA) is a ventilatory technique that delivers small bursts of high flow respiratory gas into the lung at high rates. It is classified as a pneumatically-powered, pres- sure-regulated, time-cycled, high-frequency flow inter- rupter modality of ventilation. The core of this system is the phasitron, which acts as a piston mechanism. The piston switches a high-pressure gas supply at a fre- quency rate of 200-1200 bpm to a low pressure rate, with high gas flow velocity. During inspiration, lung volumes are progressively increased in a controlled, stepwise fashion by repeatedly fading subtidal volume deliveries until an oscillatory pla- teau is reached and maintained [5]. At the end of inspiration, the lung is allowed to empty passively until a preset expiratory base-line is reached. It has been noted that gas exchange is as good as, if not better than, conventional ventilation (CV) at lower airway pressures. As described by Krishnan and Brower [6], there are six mechanisms that may contribute to gas exchange during all forms of high frequency ventilation: (1) direct bulk flow - the flow of inspired air in proximal alveoli leading to gas exchange by traditional methods (as with CV); (2) longitudinal dispersion is secondary to mixing from turbulent and swirling flow patterns; (3) variable flow is directed between adjacent lung regions with differences in compliance and resistance; (4) asym- metric velocity profiles - the laminar flow pattern in which gas in the centre of the airway advances inward and gas outside the centre flows in a retrograde way; (5) cardiogenic mixing - mechanical agitation from the nor- mal heart beat, especially in peripheral lung units; and (6) molecular diffusion - the mixing of air in the smal- lest lung units near the alveolo-capillary membrane. HFPV is designed to be used in conjunction with mechanical ventilation or as a stand-alone treatment. This is the first case report of this ventilation modality Page 2 of 5 in a patient with severe hypoxaemia after cardiac surgery. Case presentation A 75-year-old Caucasian man developed a lung infection with severe hypoxaemia [arterial partial pressure of oxy- gen (PaO2)/fractional inspiratory oxygen (FiO2) of 90] ten days after aortic valve replacement due to a severe aortic stenosis. He weighed 80 Kg and had a body surface area of 1.98 m2, an ejection fraction (EF) of 27 percent and a history of post ischaemic dilated cardiomiopathy, severe aortic stenosis with a mean gradient of 63 mmHg, hypertension and insulin dependent diabetes mellitus - there had been no alcohol or tobacco use in the last ten years. We do not have the data for the preoperative gas exchange data or the haemodynamic data; we only have the preoperatory lung function test, which shows a mod- erate obstructive disease. The patient was operated via a median sternotomy. The aortic valve was replaced with a biological Hancock 21 mm valve. The weaning from the extracorporeal cir- culation (ECC) was performed with an intraortic balloon pump with a high dose of inotropic drugs (norephinefr- ine 0.25 μg/kg/min and levosimendan 0.2 μg/kg/min). The time taken for the intervention was 260 min glob- ally, including 55 min of aortic clamp and 125 min of ECC. The total fluid balance at the end of the operation was +1000 mL. On the second post-operative day PaO2/FiO2 slowly decreased to 90 on the tenth day. We performed CV in increased pulmonary residual volume modality (Dräger Evita XL) with recruitment manoeuvre, high positive end expiratory pressure (PEEP) level (14 cmH2O), low tidal volume (6-8 mL/Kg), peak inspiratory pressure (PIP) of 38 cmH2O, mean airway pressure (MArP) of 24 cm H2O without any significative increase of respiratory parameter. Cardiac output, systemic and pulmonary pressures, were monitored. The patient was ventilated for four days in a pressure regulated volume controlled modality. On days 3 and 4 we started a recruitment manoeuvre in the pressure-controlled mode at an inspiratory pla- teau pressure of 45 cm of water, a PEEP of five cm of water, a respiratory rate of ten breaths per minute and a 1:1 ratio of inspiration to expiration for two minutes. After the recruitment manoeuvre, PEEP at a level of 14 cm of water was applied. The PEEP level of 14 cm of water reflects the upper inflection point on the deflation limb of the pressure/volume curve and it can be used to prevent alveolar re-collapse and instability; after that we switch into pressure support ventilation but with an unsatisfactory gas exchange. On day six we restarted with pressure regulated volume-controlled modality for two days. On days eight