Aim of Work:

The aim of this randomized, double-blinded, study is to compare between three modes of ventilation during cardiopulmonary bypass in pediatric patients with pulmonary hypertension undergoing corrective cardiac surgeries.

Hypothesis:

The hypothesis of the present study is that high frequency low volume positive pressure ventilation is better than continous positive airway pressure (CPAP)and passive deflation on direct PAP (pulmonary artery pressure ) reading and immediate oxygenation after cardiopulmonary bypass CPB in pediatric patients undergoing cardiac surgeries for congenital heart defects.

The patients will be randomized in a double blinded fashion to get enrolled into 3 equal groups: Group HFPPV patients (n = 8) will receive high frequency positive pressure ventilation during cardiopulmonary bypass at tidal volume 2 ml/kg and respiratory rate 80, whereas Group CPPV patients (n = 8 ) will receive continuous positive airway pressure of 10 cmH2O during the bypass, while Control group patients (n = 8 ) will be disconnected from the ventilation (passive deflation) .The study will be conducted in the pediatric cardio-thoracic operation rooms in AbulReesh Hospital in Cairo University.

Advanced Monitoring where Naso-pharyngeal temperature probe will be placed, a Central venous catheter to monitor central venous pressure and an arterial cannula to monitor invasive blood pressure after that, standard cardiopulmonary bypass technique will be used in all patients. Before aortic cannulation, patients will receive IV heparin 400 U.kg-1 aiming to produce activated clotting time ACT value > 400 sec. A membrane oxygenator (minimax plus; Medtronics Inc.) will be used during cardiopulmonary bypass. Priming solution in the form of iso-tonic saline solution supplemented with heparin added to fresh whole blood in appropriate amounts to achieve a haematocrit 20-25% during CPB will be used. Furosemide in a dose of 1 mg/kg/min will be given to all patients. Venting of left heart will be performed with a left atrial vent inserted through a small incision at the inter-atrial septum. Anesthesia during CPB will be given by Sevoflurane administrated via a vaporizer inserted into the oxygenator gas supply with a constant gas flow 3 liter/min. A non-pulsatile roller pump (model10.10.00; Stocket instruments; Munich, Germany) will be used and the pump flow will be adjusted at 2.4 to 2.6 L/min /m2 during the normothermic period targeting mean arterial blood pressure between 40 and 60 mmHg. Moreover, all patients will receive milrinone loading dose of 50mcg/kg/min the maintanence 0.5-1 mcg/kg/min and or adrenaline 0.02-0.1 mcg/kg/min will be utilized to facilitate weaning from CPB.

After sternotomy and direct exposure of the pulmonary artery, the pulmonary artery systolic pressure (PASP) will be monitored by a direct arterial catheter 22 gauge inserted by the surgeon into the pulmonary artery, was calculated and recorded immediately after sternotomy, after aortic clamp removal, and 10 minutes after initiation of protamine infusion).

After application of aortic cross clamp and administration of cold blood cardioplegia solution (Saint Thomas cardioplegic solution) 40 ml/Kg to be followed by doses of 10ml/Kg every 30 minutes.), Group A patients will receive high frequency low volume positive pressure ventilation (HFPPV) during cardiopulmonary bypass at tidal volume Vt 2 ml/kg and respiratory rate RR 80, whereas Group B patients (n =8 ) will receive continous positive airway pressure CPAP of 10 cmH2O, and group C patients will be disconnected from the ventilator (passive deflation) .

Finally, Lung Ultrasound Score will be obtained after induction of anesthesia and at the end of surgery after chest closure, The duration of mechanical ventilation, length of stay in the intensive care unit and immediate post bypass oxygenation as well as the requirement for inotropic and vaso-tropic support during the first 24 hours study period will be recorded for all patients

Lung ultrasound protocol:

Lung ultrasound will be performed after induction of anesthesia and at the end of the operation with a 5-MHz curved array probe (MindrayDC-N6; Mindray; Shenzhen, China). Patients will be investigated in supine position by a well-trained physician recording five seconds videos that will be assessed by two different observers who will be blinded from the patient data. Lung ultrasound will be assessed for the presence of B lines.

Inclusion Criteria:

• Age: 4 months to 6 years.
• ASA I, II, III.
• Patients undergoing atrial septal defect or ventricular septal defect or common atrio-ventricular canal corrective cardiac surgeries on cardiopulmonary bypass
• Patients suffering moderate to severe pulmonary hypertension.

Exclusion Criteria:

• Any congenital anomalies of the lung as cystic fibrosis, congenial diaphragmatic hernia.
• ASA IV.
• Mild pulmonary hypertension or normal PAP.
• Patients who will require high doses of inotropes (adrenaline > 0.1 mcg/kg/min or milrinone > 1 mcg/kg/min) will be excluded from the study.