In paediatric anaesthesia, use of cuffed endotracheal (ET) tubes is subject to much debate. The concern is the possibility of damage to tracheal mucosa by excessive pressure from the cuff. The cuff pressure can increase during anaesthesia, especially if nitrous oxide is used.

Using saline to inflate the cuff has been shown to reduce intra-operative cuff pressure variation in adult studies, although it is not standard practice. Although the literature contains reports of cuff pressure increases during paediatric anaesthesia, there are no reports of attempts to address this. Use of pressure monitoring is recommended by AAGBI, but may not be consistently done. A safe method of limiting pressure, that is effective, imposes minimal extra workload and has minimal cost, would reduce risk to patients.

This study aims to investigate the effect on intra-operative cuff pressure of using saline to inflate the ET tube cuff, compared to standard practice of air inflation. Continuous pressure monitoring will be used to determine the proportion of cases where interventions are required to keep the pressure below a safe maximum level.

During surgery under anaesthesia, use of cuffed endotracheal (ET) tubes is standard practice in adults. The cuff prevents air leak and protects the airway from soiling. Traditionally, in paediatric practice an uncuffed ET tube is used, sized according to the child's age. This prevents damage to the lining of the trachea by excessive pressure from the cuff.

The debate regarding the use of cuffed ET tubes in children is long-standing. New insight into the understanding of paediatric airway anatomy and newer designs of cuffed ET tubes (such as the MicroCuff Endotracheal tube, Halyard Health UK) have resulted in a shift towards their more frequent use. Studies suggest cuff pressures should be maintained below 20 - 25cm H2O, to minimise airway complications related to high pressures on the tracheal lining leading to inadequate blood flow, potentially causing swelling and, rarely, tracheal stenosis. This is of particular importance in small children, where even slight swelling can significantly reduce the airway diameter, with potentially serious consequences. Use of pressure monitoring is recommended by AAGBI, but may not be consistently done. A safe method of limiting pressure, that is effective, imposes minimal extra workload and has minimal cost, would reduce risk to patients.

The widespread use of nitrous oxide (N2O) in paediatric anaesthesia raises another issue. Nitrous oxide diffuses easily into the ET tube cuffs, raising the pressure within them. Various interventions have been trialled in adult studies to address this. Inflating ET tube cuffs with a mixture of air and N2O may be beneficial, but varying concentrations of N2O during anaesthesia limit the benefits. Filling the cuff with saline instead of air has been shown to prevent increases in cuff pressures in the adult population without any adverse safety issues, but it is still not standard practice.

Despite reports of similar variation in cuff pressures in paediatric patients, there have been no reported studies to date comparing the intra-operative changes in cuff pressures in children when the cuff is inflated with saline instead of air.

Therefore, the investigators propose to determine whether filling the ET tube cuff with saline prevents the changes in intra-cuff pressures, in children undergoing balanced anaesthesia with N2O, that are seen with air filled cuffs.

CLINICAL RELEVANCE The use of cuffed tubes in paediatric anaesthesia has become more and more common over the last decade. Newer, more anatomically based designs have helped to overcome many of the potential problems, but the issue of safe cuff pressures remains paramount.

Work in the adult literature has demonstrated the pressure at which there is a reduction in capillary perfusion. In paediatrics, the huge variation in capillary perfusion pressure makes finding an exact 'safe' level for every patient very difficult, but attempts have been made to characterise what an 'unsafe' level is.

The widespread use of nitrous oxide in paediatric anaesthesia also complicates the situation. The cuffs on modern paediatric cuffed tubes are very thin, allowing gasses to diffuse into them more easily. This means the volume (and thus the pressure) at the beginning of anaesthesia is not the same as at the end. Studies have also shown that the incidence of post-operative airway complications increases as the cuff pressure increases.

The AABGI has recently recommended cuff pressure monitoring as a minimum standard of care. However, achieving this through a lengthy case, where access to the airway may be limited, can prove challenging.

This studies hypothesis is that the use of saline, instead of air, in the cuff will lead to reduced pressure variation during anaesthesia, meaning that the pressure in the cuff at the end would be the same as at the beginning. This would minimise risk of complications for the patient and give a high level of patient safety and satisfaction, with minimal extra workload for the anaesthetist or expense for the NHS.

Inclusion Criteria:

• Parent/guardian's written informed consent / age-appropriate participant assent
• Age: Birth to 16 years
• Elective surgery
• Endotracheal intubation with a cuffed tube required as part of general anaesthesia lasting longer than 45 minutes
• Planned use of N2O as part of balanced anaesthesia
• For questionnaire follow up; aged over 8 years without significant neurological impairment

Exclusion Criteria:

• Weight less than 3kg
• Laryngeal or tracheal pathology, including respiratory tract infections
• Difficulty in intubation (>2 attempts)
• NG tube placement during anaesthesia
• Nose, throat or airway surgery

Individual participant data will not be shared outside the immediate research team

• Participants will be split into two age groups, 'under 8 years' and '8 years and over', and a stratified randomisation method will be used to randomise each group, using a previously verified, sealed envelope, method and using blocks of unequal size.
• Envelopes will be prepared using a random number table by an individual with no further role in the study
• Each participant will be given a unique randomisation code matching the randomisation list
• A record of each randomisation will be recorded on the Enrolment Log (TAFR01502)