Compared with adults, children have significant differences in the organization system of anatomy, physiology, and pharmacological change. The intracorporeal environment of children is more likely to be altered by the various procedures used in clinical anesthesia. The smaller the age, the more obvious this kind of difference, the influence of clinical anesthesia is also more significant [15–19]. Therefore, the theory of adult anesthesia can’t be directly applied to children. In clinical practice, the device for adults can’t be directly used in children after being reduced in size. This requires that on the basis of the mature concept system of adult anesthesia, it should be improved aiming at the characteristics of children themselves. Then, the anesthesia method that has little influence on children and is easy to implement is selected, the instruments and equipment that matches children are applied, and a unique theoretical system can be formed.
At present, there are two types of ETTs used for TI under GA in children, namely uncuffed and cuffed ETTs. For children under 6 years old, it is still controversial whether to use cuffed or uncuffed ETTs. Both of the types can be safely used in children clinically, but each has the advantages and disadvantages [20–23]. With a cuff, the outer diameter of ETT is a bit larger than that of uncuffed ETT. During GA, a good pulmonary ventilation should be maintained, and the incidence of airway resistance and lung injury in children should also be reduced. Thus, when the cuffed ETT is selected, those with the with ID as larger as possible should be used. Clinically, it’s advised that children under 6 years old should be given uncuffed ETT [24–26]. The disadvantage of uncuffed ETT is that the catheter is too thick, which will lead to failure of TI. The pressure on the inner mucosa of trachea will result in ischemia necrosis of tissues, and too thin ETT will lead to leakage of anesthetic gas, reflux, and aspiration. Therefore, the emergence of ultrasound technology offers a method to explore the selection of optimal ETT model in clinical practice.
The common methods for selecting ETT type in clinical practice include weight equation method, body length equation method, maximum width of the fifth finger nail, multi-parameter estimation method, and age equation method [27–30]. Scholars in the world have compared the above five methods, and the results show that age equation method is the most accurate among these methods, followed by the maximum width of the fifth finger nail. However, with the continuous improvement of people’s living standards, the parameters of children’s growth and development have also produced huge differences from the past data. If it is still calculated according to the various growth indicators of children in the past, it needs to be explored whether it can still be accurately applied to the current. In this work, the method of measuring TD of the narrowest subglottic airway by ultrasonography was applied to children aged 4–14 years old who underwent TI under GA. The correlations of their age, height, weight, and the TD of the narrowest subglottic airway measured by ultrasonography with the ID of ETT were analyzed. The Spearman rank correlation coefficients (rs) between age, height, weight, TD of subglottic airway and ID of clinical optimal uncuffed ETT turned out to be 0.6251, 0.6832, 0.6143, and 0.8153, respectively (P < 0.05). The Spearman rank correlation coefficients (rs) of these indicators with ID of cuffed ETT were 0.6238, 0.5723, 0.5624, and 0.8723, respectively (P < 0.05). These suggested that the above indicators were correlated with ID of the clinical optimal ETT. The correlation between TD of subglottic airway and the ID of the clinically optimal ETT was significantly higher than that of other parameters, which was consistent with the findings of Öztürk et al. (2021) [31]. Compared with other parameters, the TD of subglottic airway under ultrasonic measurement could be taken as a great indicator with predictive value for predicting the model of ETT.
In this work, the results of ultrasonic measurement were compared with those calculated by the age equation method in the TD of the narrowest part of subglottic airway. The accuracy of ultrasonic measurement method was 91.42%, while that of the age equation method was 54.28%. The accuracy of ultrasonic measurement was remarkably higher than that of age equation method, with a difference having statistical significance (P < 0.05). This was consistent with the results reported by Chang et al. (2021) [32]. The uncuffed and cuffed ETTs were utilized respectively, which reduced the tube replacement rate to a certain extent and made up for some defects of the two types of ETTs. Thus, the safety of ETTs in clinical application was enhanced.
The shortcomings of this work were considered as follows. First, due to the influence of diagnosis and treatment conditions of children, infants and newborns under 6 months of age were not included. However, GA on these children is more special with significant individual differences, and they are more sensitive to the changes of external environment. In particular, neonates who need to undergo TI surgery are usually premature, deformed, and critically ill infants. Second, the accuracy of ultrasonic measurement and age equation method was compared, from which it was concluded that the accuracy of ultrasonic measurement was higher. Nevertheless, such a speculation still needed to be supported by more perfect data.