Laparoscopy is the preferred surgical approach in certain abdominal procedures as it provides several advantages compared to open surgery, including minimal surgical incision, shorter hospital stays, less pain after the operation, and earlier mobilisation. However, gas insufflation into the abdomen increases abdominal pressure with consequent changes in respiratory mechanics and derecruitment of lung volume. Patients undergoing laparoscopic surgery are normally anaesthetised, muscle relaxed, intubated and mechanically ventilated. Intraoperative lung-protective ventilation has been recommended to reduce postoperative pulmonary complications. One of the guiding principles of lung-protective ventilation is to recruit the lung and to use the lowest level of positive-end expiratory pressure (PEEP) that keeps the lung open. However, adequate tools are lacking in the operating theatre for monitoring lung volume recruitment and guiding the anaesthetist in the selection and adjustment of the optimal PEEP level for each individual patient. The forced oscillation technique (FOT) is a non-invasive method for the assessment of lung mechanics, which has been successfully applied in ventilated patients.
This study will evaluate whether this novel approach of continuous monitoring of respiratory mechanics is feasible in children undergoing laparoscopic appendectomy. The results will help paediatric anaesthetists to formulate new evidence-based ventilation guidelines and policies to optimise and personalize the ventilation strategy in children undergoing laparoscopic surgery. This novel, custom-made device for the anaesthesia setting has the potential to be highly valuable in clinical practice in the future, particularly when caring for children with complex co-morbidities and/or surgery affecting the cardio-respiratory system, for example, neonates with diaphragmatic hernias or gastroschisis.
Professor Britta Regli-von Ungern Sternberg, Dr Michael Collin and Dr Mon Ohn
Perth Children’s Hospital, Western Australia.
The project was awarded $A70,000 funding through the ANZCA research grants program for 2023.
Laparoscopy, using “keyhole” surgery performed in the stomach area, is a common surgical technique. The gas blown into the abdomen to create the space required to operate increases abdominal pressure, and changes lung function through airway collapse and altered blood flow.
Patients undergoing laparoscopic surgery are normally anaesthetised, muscle paralysed, receive a breathing tube and will need to be on a ventilator for the duration of surgery. The ventilator must generate pressure to blow oxygen into the lung and inflate them. Prolonged positive pressure ventilation, particularly at higher pressures, is damaging to the delicate lining of the lung. The continual opening and closing and/or over-distention of the air sacs caused by the ventilator seems to be the most important trigger for lung damage. The younger and smaller the child is, the more susceptible the airway is to damage; similarly, the lower the safety margin is with pressures that are safe to use.
During the operation the use of ventilator techniques or strategies that are lung-protective is recommended to reduce postoperative lung complications. Unfortunately, adequate tools for monitoring and guiding lung volume recruitment for the anaesthetist are lacking in the operation theatre.
The forced oscillation technique (FOT) is a non-invasive method for the assessment of lung mechanics and has been previously used in ventilated patients. It applies small pressure waves down into the airway and detects the reflected/returning waves allowing assessment of the airway. While intermittent assessments have been performed in the past, our study proposes a novel continuous technique not previously used in the anaesthetic setting.
The aim of the COMET study was to assess the feasibility of this novel continuous assessment of respiratory mechanics in theatre and to track their changes as measured by FOT, in children undergoing laparoscopic appendectomy, a commonly performed surgical procedure in children.
The equipment used in COMET was developed by biomedical engineers at the Politecnico di Milano, Milan, Italy. Once the equipment was designed, built and bench tested in Milan, it was flown to Western Australia, accompanied by a biomedical engineer who worked with our research team to integrate this novel FOT equipment into the theatres in Perth Children’s Hospital. The system is connected between the patients breathing tube and the ventilator tubing. Ideally this equipment should have the least amount of dead space possible to be compatible for children with small tidal volumes. A limitation of equipment is that it introduces approximately 40ml of dead space. We are unable to use the equipment in very small children. In order to extend the use of the novel continuous FOT equipment to neonates and infants with tidal volumes of 3-4 ml/kg, in the Constellation part of the grant, we aimed to develop new dead space connectors.
The COMET study demonstrated the feasibility of this new technique of tracking lung function during laparoscopic surgery. This equipment would allow paediatric anaesthetists to use real time data to continually optimise the ventilator settings required for a child. It could then allow formulation of new evidence-based ventilation guidelines and policies to optimise and personalize the ventilation strategy in children undergoing laparoscopic surgery.
Working with engineers at Politecnico di Milano as well as anaesthetists, our Senior Coordinator of Clinical Science who is developed a high- level design brief was developed. We then were able to identify and connect with partners with the appropriate skills and experience to produce a prototype which could meet the technical and clinical parameters. We then worked with ADARSH Engineering, a WA owned and operated manufacturer and fabricator of component part to completed several rounds of Computer Assisted Designing (CAD) and 3D printing to custom make a T-connector that eliminates the need for several connector pieces. The size and therefore the dead-space is significantly reduced. This will allow the equipment to be used with much smaller children.
The COMET feasibility study has demonstrated that continuous measurement and determinant of respiratory mechanics in paediatric patients, under general anaesthesia for a laparoscopic appendicectomy, using respiratory oscillometry is achievable as demonstrated by the successful attainment of measurements of both Xrs and Rrs in 99/ 100 of patients. Data was excluded for one patient due to the fact they were recruited outside of normal work hours. Furthermore, the setup and usage of the respiratory oscillometry equipment, within the theatre and specifically within the anaesthetic circuit, although not explicitly recorded, did not appear to contribute to time delays or prolonged stays in theatre as demonstrated by the collection of data being complete by 90 minutes in the longest surgical procedure. It is also unlikely that the equipment contributed to an increase in PRAE events as the number of PRAE events reported are within expected published rates.
A continual measurement of respiratory mechanics in theatre could allow for a more tailored approach to pulmonary recruitment and the more accurate application of PEEP. Together with strategies aimed at managing increased pulmonary resistance, this may translate to a reduction in PRAE in paediatric patients undergoing general anaesthesia and warrants further investigation.
A limitation of equipment used in the COMET study is that it introduces approximately 40ml of dead space. This means that it is not suitable for use in very small children. Through the work undertaken in the Constellation part of this project which included CAD and 3D printing we were able to design and custom-make a T-connector that eliminates the need for several connector pieces. The size and therefore the dead-space is significantly reduced and would allow use of the continuous FOT equipment in much smaller children.
- Poster 2024 Child Health Symposium, Perth Children's Hospital
- Forced Oscillation Technique (FOT) to Investigate Lung Mechanics in Paediatric Laparoscopic Appendectomy.
- Cormac O’Brien, David Sommerfield, R Nazim Khan, Michael Collin, Raffaele Dellacà, Emanuela Zannin, Graham Hall and Britta S von Ungern-Sternberg
Manuscript in preparation
- Changes in respiratory mechanics and lung recruitment in children undergoing laparoscopic appendectomies – the COMET study
- Neil Hauser, Emanuela Zannin, Julie Nguyen, Anwen Taplin, Sara Vigevani, David Sommerfield, Raffaele Dellaca` , R. Nazim Khan, Aine Sommerfield and Britta S. von Ungern-Sternberg