LETTERS TO THE EDITOR: Letters & Announcements
To the Editor:
The narrowest portion of a child’s airway is at the cricoid ring (1). Uncuffed endotracheal tubes (ETT) are commonly used in children in an attempt to decrease the potential for pressure-induced tracheal injury. However, uncuffed ETT may increase the risk of aspiration of gastric contents and lead to erratic delivery of preset tidal volume during mechanical ventilation (2). Therefore, it is desirable to intubate the trachea with an appropriate, but not oversized, ETT. Tracheal intubation with an oversized ETT in a pediatric patient can lead to serious complications following extubation, including stridor, hoarseness, difficulty in breathing, increased work of breathing, respiratory failure, cardiac failure, and reintubation. A variety of formulas and techniques have been used in an attempt to find the ETT size that minimizes both pressure-induced tracheal injury and aspiration potential or variable ventilation (3).
It is recommended that ETT should allow small air leak at peak inflation pressure (PIP) of 20–30 cm H2O (4). Air leak following tracheal intubation can be recognized by the presence of audible leak, by auscultation over the trachea, and by palpation over the trachea. However, the methods described are subjective and cannot differentiate between an appropriately sized and an oversized ETT. Objective method to find whether the ETT is an oversized one for the trachea is not known. We describe a simple objective method to recognize an oversized ETT.
A ventilator having facilities for application of positive end expiratory pressure (PEEP) and measurement of PIP and inspiratory and expiratory tidal volume (ITV and ETV) is essential. If the ventilator has a leak compensation facility, it should be disabled. We use Datex-Ohmeda Aestiva/5 with smart vent (Datex-Ohmeda, Inc, Madison, WI) for ventilating a child. Method: 1) Intubate the child with an uncuffed ETT; the size is chosen on the basis of age of the patient (5). 2) Connect to the ventilator and ventilate with 10–15 mL/kg tidal volume and an appropriate respiratory rate. 3) Note PIP, ITV, and ETV. 3) Apply PEEP of 4–5 cm and increase it gradually (1–2 cm H2O at a time) until the PIP reaches to 25 cm H2O; keep observing the ITV and ETV. Usually PEEP required for achieving the target PIP is less than 10 cm H2O. While PEEP is adjusted to achieve target PIP of 25 cm H2O, the hemodynamics of the patient are carefully monitored. We believe, a difference of ∼10% tidal volume but not less than 5 mL between the ITV and ETV indicates suitability of the ETT, if the difference in the ITV and ETV is less than 5 mL, an increasing difference in the ITV and ETV with further increase in PEEP (2–5 cm H2O) also indicates suitability of the ETT; however, if there is no further increase in the difference between the ITV and ETV, the ETT is deemed an oversized one. In this situation, we replace the ETT with a one size small (0.5 mm) ETT and repeat the test sequence to ensure suitability of the replaced ETT.
Application of PEEP increases intrathoracic pressure and PIP; these changes increases leak around ETT that is detected as difference in ITV and ETV. Finholt et al (2), in an experimental study found that leak pressure testing gives an excellent indication of fit between ETT and trachea. By ensuring minimal air leak around the ETT at 25 cm H2O, it is believed that the pressure-related tracheal injury can be avoided. In pediatric cardiac surgical practice, patients are often subjected to overnight ventilation; in these patients, PEEP is recommended for various reasons. Evaluation of appropriate size of ETT by application of PEEP further ensures that erratic ventilation would be unlikely in the postoperative period. However, changes in the lung compliance can still cause erratic ventilation (by raising PIP) with an ETT that was appropriate at the time of intubation. Similarly, an appropriate ETT can become oversized because of airway edema and may cause pressure-related airway injury.
The method we have described allows an objective evaluation of leak around the ETT. PEEP is usually well tolerated by patients; however, it is desirable that the hemodynamics is monitored during its application. We have been practicing this method for the last 4 years and have never faced any complication related to the method or intubation with an oversized ETT.
Praveen Kumar Neema, MD
Prabhat Kumar Sinha, MD
Manikandan S, MD
Ramesh Chandra Rathod, MD
1. Eckenhoff JE. Some anatomic considerations of the infant larynx influencing endotracheal anesthesia. Anesthesiology 1951; 12: 401–10.
2. Finholt DA, Audenaert SM, Stirt JA, et al. Endotracheal tube leak pressure and tracheal lumen size in swine. Anesth Analg 1986; 65: 667–71.
3. Penlington GN. Endotracheal tube sizes for children. Anaesthesia 1974; 29: 494–5.
4. Cote CJ. Pediatric anesthesia. In: Miller RD, ed. Anesthesia. Philadelphia: Churchill-Livingstone, 2000: 2088–117.
5. Dunne NM. Paediatric intubation. In: Latto IP, Vaughan RS, ed. Difficulties in intubation. London: WB Saunders, 1997: 241–53.