Development of new evidence-based ventilation guidelines for children undergoing surgery with general anaesthesia

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Paediatric patients undergoing elective or emergency surgery, or who have been admitted to the Neonatal/Paediatric Intensive Care Unit (NICU/PICU), often require mechanical ventilation. During the perioperative period, these patients are at risk of several types of lung injury, including atelectasis (collapse of lung tissue), pneumonia (disease marked by inflammation of the lungs), pneumothorax (presence of air within the pleural cavity leading to lung collapse), Acute Lung Injury (ALI) and Acute Respiratory Distress Syndrome (ARDS). Anaesthetic management can contribute to these injuries, exacerbate any underlying lung conditions or even improve outcomes, depending on the specific situation. Moreover, several studies have shown that pulmonary complications, more specifically respiratory failure requiring ventilation, are associated with high morbidity and mortality along with increased health-related costs and greater length of hospital stay. Ventilation mode (volume, pressure or dual), modality (controlled, assisted, support ventilation) and respiratory parameters (e.g. tidal volume and respiratory rate) are the most important factors of mechanical ventilation. An important aspect of ventilation strategies is to optimise respiratory mechanics. A critical part of this process is knowing the normal range of respiratory mechanics during ventilation. This allows clinicians to define ventilation such that the respiratory mechanics can be maintained at a level expected for that particular patient and therefore protect against over- or under ventilation and thus minimise potential harm. While the normal ranges of a variety of respiratory outcomes during mechanical ventilation have been assessed in adults, there are no normal reference ranges of values available for the paediatric population. This precludes the formulation of clear evidence-based ventilation guidelines in children. Measurable mechanical and physiological parameters such as pulmonary compliance (ease of expansion of the lungs and thorax), respiratory resistance (resistance to flow of gases during ventilation), tidal volume (volume of air moved in and out during quiet/normal breathing) can be used to effectively monitor the effect of changes in mechanical ventilation and limit the risk of Ventilator-Induced Lung Injury VILI. Furthermore, the lack of precise data on these essential parameters as well as the implications relating to the lack of this important data, have been highlighted by experts from the recent American Thoracic Society workshop on the evaluation of respiratory mechanics and function in patients being cared for in paediatric and neonatal ICU settings (personal communication from Dr Carmichael-Peterson, Chair of the American Thoracic Society Task Force for the measurement of respiratory function in the ICU). Better ventilation strategies are also of particular importance in children with cardiac and/or respiratory co-morbidities undergoing anaesthesia as well as children with prolonged surgeries impacting on respiratory function, e.g. pneumoperitoneum, extensive abdominal surgery. This study aims at measuring lung function outcomes in children aged between 1 and 15 years old who are undergoing surgery under general anaesthesia and require mechanical ventilation. We hypothesise that by measuring the respiratory resistance and pulmonary compliance of children undergoing surgery before and after anaesthesia induction, we will be able to develop robust prediction equations and nomograms that define the values of physiological parameters to be programmed in mechanical ventilators for optimal lung function in anaesthetised children having surgery.

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