Ultrasonography Versus Capnography in Detecting Endotracheal Tube Placement During Intubation in a Tertiary Hospital.

This was a prospective, observational study conducted at the Tribhuvan University Teaching Hospital (TUTH) and Manmohan Cardiothoracic Vascular and Transplant Center (MCVTC) operating rooms from January 2017 to July 2017. Ethical approval from the Institutional Review Board (IRB) of Institute of Medicine (IOM) and the Department of Anaesthesiology, Maharajgunj Medical College (MMC) was taken. Written informed consent was taken.

ASA I and II patients over 16 years of age were included in this study. Patients with difficult airway and anticipated difficult intubation, respiratory diseases, poor functional status, emergency case, and patients at risk of aspiration were excluded.

The diagnostic characteristics of real-time, suprasternal, transtracheal ultrasonography and capnography were tested by calculating their respective sensitivities, specificities, positive predictive values (PPV), negative predictive values (NPV), accuracies and likelihood ratios. Comparison of time taken for confirmation of endotracheal tube position from the beginning of laryngoscopy, by ultrasonography versus capnography was done using t-statistics.

The degree of agreement of result between ultrasonography and capnography was tested with kappa statistics.

Out of the 95 patients studied, 11 had oesophageal intubation (Incidence of 11.57%). The overall accuracy of both ultrasonography and capnography was 96.84%. The sensitivity, specificity, PPV, NPV with their corresponding 95% confidence intervals (CI) for ultrasonography were 97.62% (91.66% - 99.71%), 90.91% (58.72% - 99.77%), 98.80% (92.67% - 99.81%), 83.33% (55.66% - 95.22%) respectively; and that for capnography were 96.43% (89.92% - 99.26%), 100% (71.51% - 100%), 100% (100% - 100%) and 78.57% (54.69% - 91.76%) respectively.

The likelihood ratio of a positive and a negative result for ultrasonography were 10.74 and 0.03 respectively, and that for capnography were infinity and 0.04 respectively.

The kappa value was 0.749 (95% CI: 0.567 - 0.931) which meant a good degree of agreement of result between these two methods.

The average time taken for confirmation of endotracheal tube by ultrasonography and capnography were 26.79 ± 7.64 seconds and 43.03 ± 8.71 seconds (mean ± standard deviation) respectively. The median time for confirmation was 26 seconds with interquartile range [15 - 37] seconds for ultrasonography and 42 seconds with interquartile range [29 - 55] seconds for capnography. Ultrasonography was found to be faster than capnography by 16.36 ± 3.23 seconds (mean ± standard deviation) and the difference in time was significant (p = 0.011).

During the study, one patient had unanticipated difficult intubation, and four had hypotension after induction of anaesthesia. These patients were excluded from the study and no sequalae of hypotension was seen in the patients, or no hypoxemia occured in the patient with unanticipated difficult intubation.

Inclusion criteria

• ASA I and II patients of both sexes above 16 years of age undergoing general anaesthesia with endotracheal tube placement.

Exclusion criteria

• - Patient refusal
• ASA physical status III and above
• History of prior difficult bag and mask ventilation or difficult intubation
• History of prior oro-nasal or neck injuries, burns or scars
• Active oral, pharyngeal or tracheal infection or inflammatory changes
• Anticipated difficult airway or difficult intubation during preanaesthetic examination, with Mallampati grades II and above
• Lung parenchymal and pleural diseases. Examples: asthma, COPD, bronchiectasis, reactive lung diseases, pneumonia, tuberculosis, pleural effusion, pneumothorax, lung or pleural malignancy etc.
• Emergency surgery