The changes in the cuff pressure in the absence of nitrous oxide are less clear.In the current study, we aim to determine the changes in cuff pressure over time in infants undergoing myelomeningocele repair in prone position under general anesthesia in the absence of N2O.

Introduction:

During perioperative period some factors may change the endotracheal tube (ETT) cuff pressure. They include time (1), changes in core temperature (2), neuromuscular blockade (3), sedation (4), altitude (5), use of nitrous oxide (6,7), changes in tracheal muscle tone and respiratory system impedance (8), different body, head and neck positions (9), mechanical ventilation and transoesophageal echocardiography probe insertion (10).

Some have chosen to avoid the use of nitrous oxide (N2O) during surgery because of the theoretical risk of multiple deleterious effects on the neurologic, cardiovascular, hematologic and immune systems. In addition, N2O diffuses into all gas-filled cavities increasing their sizes and pressures including ETT cuffs (11). ETT cuff pressure increases after exposure to nitrous oxide (12).

However, the changes in the cuff pressure in the absence of nitrous oxide are less clear. Kako et al. (13) investigated the relationship between head and neck position and ETT cuff pressure in children in the absence of N2O in the supine position. In this study, 1000 intracuff readings were evaluated in 200 children based on position of the head and neck. They found that cuff pressure increased in two-thirds of the measurements 545 out of 1000 when compared with the neutral position. Most frequently change was noted with neck flexion. The mean increase in cuff pressure was 7.2±8.3 cmH2O from the neutral position (p<0.05).

In the current study, we aim to determine the changes in cuff pressure over time in infants undergoing myelomeningocele repair in prone position under general anesthesia in the absence of N2O.

Methods:

This prospective observational study was approved by the Institutional Review Board of Istanbul Science University. After parents are given a detailed explanation about of the procedure of ETT placement for general anesthesia, consent for their children's participation will be sought. The study will be registered at ClinicalTrials.gov.

Twenty infants undergoing repair of myelomeningocele will be recruited. Their airways will be secured with a cuffed ETT. All infants will undergo surgery in the prone position.

Anesthesia will be induced with a combination of oxygen, air, sevoflurane, intravenous remifentanil and rocuronium. After tracheal intubation with a high volume low pressure cuffed ETT (Nextech®, Istanbul, Turkey), the cuff will be inflated until there is no audible gas leak. The observer will check the gas leak using a stethoscope guided inflation over the trachea while holding continuous positive airway pressure of 20-25 cm H2O (14).

The ETT cuff pressures will be monitored simultaneously with a cuff manometer and pressure transducer (15). The measurements will be observed continuously. When the cuff pressure is noted to exceed 15 cmH2O, the cuff will be deflated immediately to less than 15 cmH2O. The time when the correction occurred, the time interval between corrections and the number of corrections during surgery will be recorded.

The baseline cuff pressure will be assessed in the supine position after which time a second measurement will be made in the prone position. A blind investigator will check and record the cuff pressure. If the pressure is between 10-15 cmH2O, no intervention will be performed. If the pressure exceeds 15 cmH2O, the cuff pressure will be managed as described above. The cuff pressures will be compared over time within patients. In addition, heart rate, end-tidal CO2, temperature and peak airway pressure will be recorded every 15 min.

Statistics:

All data that are normally distributed will be summarized as means ± standard deviation. Data that are not normally distributed will be summarized as medians and 25-75th percentile. Cuff pressure and all other interval data that will be measured over time will be analyzed using repeated-measures ANOVA with the Tukey (or Dunnett) post-hoc test. Comparing supine and prone positions, cuff pressures will be analyzed using two-way repeated measures ANOVA. Baseline demographic data will be compared using unpaired t-test for normally distributed data and Mann Whitney U test for data that are not normally distributed. P<0.05 will be accepted.

Inclusion Criteria:

• male and female infants undergoing meningomyelocele repair

Exclusion Criteria:

• tracheal intubation with uncuffed tube, the use of N2O during anesthesia, accompanying disease like hydrocephalus

1-30 days old infants undergoing meningomyelocele repair