Effect of Placing the Endotracheal Tube Beyond Cervical C7 Level in Anterior Cervical Decompression and Fusion Surgery: An Observational Study On Endotracheal Cuff Pressure Changes

Endotracheal intubation is performed in operation theatre to secure the patient's airway during general anaesthesia undergoing surgery. The procedure involves placing a specialised tube known as endotracheal tube (ETT) from either nose or mouth into the trachea. The ETT used usually has a cuff at the distal part of the tube which functions as a seal to the trachea for proper delivery and monitoring of artificial ventilation. The cuff also serves as protection against the ingress of pathogens and fluids from the pharyngeal space into the lower airways and lungs. During intubation, the cuff usually positioned just beyond the vocal cord which is anatomically situated at cervical vertebrae C5 to C6 in adult.

After intubation, the endotracheal cuff pressure (ETCP) is usually checked once or intermittently and kept within appropriate range as cuff overinflation can cause complications that range from mild sore throat to tracheal ischemia, tracheal rupture and fistula formation. The recommended range for ETCP is between 20 to 30 cmH2O, although variability is reflected in the literature, where there is no clear consensus of target cuff pressures. For surgeries performed on head and neck region, the monitoring of ETCP is difficult as this might intrude into the sterile surgical field.

Anterior decompression and fusion (ACDF) surgery is commonly performed to treat cervical spine issues such as herniated discs, spinal stenosis, or degenerative disc disease. During ACDF, the surgeon accesses the cervical spine from the anterior of the neck, and part of the procedure involves moving aside the soft tissues to gain access to the spine. While doing this, a surgical retractor is often used to hold the tissues aside carotid sheath laterally, and the trachea and the oesophagus medially. This will provide the surgeon with a clear view of the surgical site. Placement of a retractor during ACDF may inadvertently lead to compression or pressure on the endotracheal cuff. Jain et al reported the mean retraction time was 171 minutes and the ETCP rise as high as 50 mmHg after retractor placement. This causes airway complications such as dysphagia, sore throat and dysphonia. Similarly, overinflation of the ETCP will cause surgeons to have difficulties in accessing their intended surgical sites. It is not uncommon for the spine surgeons to request for a lower ETCP intraoperatively to enable a better visualisation of surgical field. Garg et al in his study has shown that during application of retractor, there was a significant increase of ETCP up to 168%.

Many authors have tried to minimise the airway complication of ACDF surgeries by using different methods. Malhotra S et al examined inflation of cuff with air, saline and lignocaine towards the incidence and severity of hoarseness and dysphagia. Other authors tried reducing the ETCP after retractor placement and meta-analysis by Miller et al showed that this may be a protective measure to decrease the severity of dysphagia. Meta-analysis by Tsalimas et al reported postoperative dysphagia range from 1 to 79%. Despite its high incidence, it is poorly understood; its pathogenesis remains relatively unknown, and its risk factors are still widely debated. One of possible cause is elevated ETCP due to indirect compression by the retractor on the soft tissues.13 Thus, maintaining ETCP between 15 and 20 mmHg could lower the complication rate after intubation. Kim et al and Sedef et al suggested ETCP of 20 cmH2O (15 mmHg) may decrease the incidence of dysphagia, sore throat and dysphonia. Sejkorova ́ et al reported postoperative hoarseness, dysphagia, and recurrent laryngeal nerve palsy had a higher incidence in the unregulated ETCP, however only hoarseness was statistically predominant complication. Ratnaraj et al found less sore throat 24 h after surgery (74% in the unregulated ETCP vs. 51% in the ETCP adjusted to 20 mmHg, p < 0.05). However, two RCTs done by Ratnaraj et al and Kowalczyk et al found no difference in the incidence of dysphagia. Only one RCT done in 177 patients by In 't Veld BA et al found ETCP regulated at 20 mmHg did not decrease the risk of dysphagia, dysphonia and sore throat, hence did not recommend routine ETCP adjustment after retractor placement in patients undergoing ACDF.

In literature review exploring the correlation between retractor placement and ETCP studies, all studies that were done with normal intubation and ETT placement. None mentioned the depth of the ETT placement and these it is postulated that normal practise of placing the ETT cuff beyond larynx would inadvertently leave the ETT cuff in the cervical region and hence be directly retracted during surgery. The investigators hypothesise that positioning the endotracheal cuff deeper beyond the cervical vertebrae C7 into the thoracic region would not cause significant rise in cuff pressure during retractor placement based on the assumption that the surgical retractor would not be directly compressing on the cuff.