Letters to the Editor: Letter to the Editor
To the Editor
We read with interest the study published by Wang et al1 on optimal depth for nasopharyngeal temperature probe positioning for standard temperature monitoring during anesthesia. It involved nasopharyngeal temperature probes at different insertion depths, concluding that “any nasopharyngeal probe insertion depth between 10 and 20 cm well represents core temperature in adults having noncardiac surgery.” Direct laryngoscopy confirmed that when the probe was inserted 20 cm, the tip was in the pharynx, with subsequent estimation of the accuracy of positioning of the nasopharyngeal probes at varying depths. We would suggest that, when these probes were inserted between 14 and 20 cm, they were positioned in the oropharynx or laryngopharynx, not the nasopharynx. Lee et al2 studied optimal nasopharyngeal temperature probe placement and concluded “the closest portion of the nasopharyngeal mucosa to the internal carotid artery is within the upper or mid-nasopharynx. The depth from the nares to the upper one-third of the nasopharynx is approximately 10 cm. Less than half of nasopharyngeal temperature probes placed blindly by practitioners were optimally positioned.” It is customary that these probes are inserted blindly, once the endotracheal tube is placed by using direct laryngoscopy. Little is known about complications following blind insertion of nasopharyngeal tubes, although, Abu-Gazala et al3 report on too deep insertions with morbidity following bariatric surgery. One of the authors of this letter (A.V.Z.) utilizes videolaryngoscopy as a standard technique to insert anesthesia equipment into the airway and oropharynx, and his research has found malpositioning of supraglottic airway devices can lead to ineffective airway management.4
We provide evidence that temperature probes must be inserted under direct vision, to ensure that they are in the oropharynx and the esophagus. We have demonstrated that temperature probes can be positioned wrongly in the trachea (Figure 1, A–C), although optimal position should be in the esophagus (Figure 1, D–E). We were also surprised to discover that malpositioning of the tip can occur, as demonstrated in Figure 1F, whereby the tip of the temperature probe took a 180° turn in the esophagus and ended up in the oropharynx. The latter did not provide the correct temperature of the patient.
Visualization of the airway is key to provide: (1) correct insertion of the airway device and adequate ventilation of the lungs, (2) optimal separation of the ventilator and esophageal-gastric channels, and (3) correct positioning and accurate monitoring. Measurement markings are suggested to prevent insertions that are too deep.
We suggest the following simple recommendations for children and adults for temperature probe placement and positioning: (1) insertion via the mouth and the tip placed in the pharynx under direct laryngoscopic vision, after the endotracheal tube or laryngeal mask has been placed and secured, and (2) if the pharynx is unsuitable for temperature probe placement, the probe should be placed as distally as possible in the nasopharynx. This would be achieved by insertion through the nares and nasopharynx until the probe is observed under direct vision to emerge behind the soft palate and then withdrawn a short distance to be in proximity to the internal carotid artery.
André van Zundert, MD, PhD, FRCA, EDRA, FANZCAKerstin Wyssusek, MSc, PhD, FANZCADepartment of Anaesthesia and Perioperative MedicineRoyal Brisbane & Women’s HospitalThe University of QueenslandBrisbane, QLD, Australiavanzundertandre@gmail.com
Vernon Vivian, MDDepartment of AnaesthesiaGympie General HospitalGympie, QLD, Australia
1. Wang M, Singh A, Qureshi H, Leone A, Mascha EJ, Sessler DI. Optimal depth for nasopharyngeal temperature probe positioning. Anesth Analg. 2016;122:14341438.
2. Lee J, Lim H, Son KG, Ko S. Optimal nasopharyngeal temperature probe placement. Anesth Analg. 2014;119:875879.
3. Abu-Gazala S, Donchin Y, Keidar A. Nasogastric tube, temperature probe, and bougie stapling during bariatric surgery: a multicenter survey. Surg Obes Relat Dis. 2012;8:595600.
4. Van Zundert AA, Kumar CM, Van Zundert TC. Malpositioning of supraglottic airway devices: preventive and corrective strategies. Br J Anaesth. 2016;116:579582.