The endotracheal tube cuff is a critical component of the tracheal intubation system. Its primary functions include sealing the airway to prevent gas leakage and minimizing the risk of aspiration by creating a barrier against gastric content reflux, thereby ensuring effective ventilation and oxygenation. The cuff is typically positioned at the distal end of the endotracheal tube, adhering closely to the tracheal wall to establish an airtight seal.

From an anatomical perspective, the design of the cuff must account for variations in tracheal structure and physiological characteristics. The inner diameter of the trachea exhibits significant variability among individuals, particularly in pediatric and geriatric populations. Consequently, the structural design of the cuff must accommodate diverse tracheal diameters while avoiding excessive pressure-induced mucosal injuries.

In terms of design, cuffs are primarily classified into two types: high-volume low-pressure (HVLP) and low-volume high-pressure (LVHP). The HVLP cuff achieves airway sealing through a larger volume and lower pressure, thereby reducing compression on the tracheal mucosa and minimizing the incidence of complications [3] . In contrast, the LVHP cuff requires higher pressure to achieve sealing. Upon inflation, the LVHP cuff assumes a spherical shape, resulting in a smaller contact area with the tracheal wall. Consequently, the localized pressure exerted on the tracheal mucosa can reach 50 - 100 mmHg, far exceeding the capillary perfusion pressure of the tracheal mucosa (normally 25 - 35 mmHg). This significantly increases the risk of tracheal mucosal ischemia, hemorrhage, and ulceration, ultimately leading to tracheal dilation, collapse, tracheal wall necrosis, and stenosis. In some cases, tracheoesophageal fistula may also develop. Due to these adverse effects, LVHP cuffs have been phased out in clinical practice.

The inflation mechanism is critical for the proper functioning of the cuff. The inflation process is typically performed via an inflation tube connected to the cuff, through which air is introduced using a syringe. The volume of inflation directly influences cuff pressure and sealing efficacy.

In clinical practice, cuff inflation pressure must be strictly controlled. Excessive pressure may lead to tracheal mucosal ischemia and injury, whereas insufficient pressure compromises airway sealing, increasing the risk of aspiration. Therefore, the use of a manometer to measure intracuff pressure is recommended [4] .

Cuff inflation is performed to seal the gap between the tracheal tube and the tracheal wall, ensuring the tidal volume required for mechanical ventilation during general anesthesia while preventing the aspiration of respiratory secretions or gastric contents into the airway.

Currently, four primary inflation methods are commonly employed: 1) Palpation Method: A syringe is used to inflate the cuff via the pressure-indicating pilot balloon, with the anesthesiologist assessing cuff pressure based on finger palpation of the pilot balloon. The optimal pressure corresponds to a firmness similar to that of a normal human nasal tip. Although this method is the simplest in clinical practice, it heavily relies on the anesthesiologist’s tactile sensitivity and experience. Studies have demonstrated that variations in cuff wall tension may influence tactile perception and judgment, and even experienced anesthesiologists cannot achieve 100% accuracy [5] [6] . 2) Minimal Occlusive Volume (MOV) Method: The cuff is inflated to the minimal pressure required to prevent air leakage. A stethoscope is placed over the trachea, and a 5 mL syringe is used to inflate the cuff until no air leak is audible. Subsequently, 0.5 mL of air is withdrawn at a time until slight leakage is detected, followed by incremental 0.5 mL reinflation until leakage ceases. This method ensures a tight seal between the cuff and tracheal wall, minimizing aspiration risk, preventing air leakage, maintaining tidal volume, and enhancing tube stability. However, the procedure is cumbersome and time-consuming, limiting its widespread clinical application. 3) Minimal Leak Technique (MLT): A stethoscope is positioned over the trachea, and the cuff is inflated until no air leak is audible. Air is then withdrawn in 0.1 mL increments until slight leakage is detected. This technique permits minor air leakage during ventilation, potentially reducing airway trauma compared to the MOV method. However, it increases aspiration risk, compromises tidal volume, and may lead to tube displacement due to reduced fixation stability. 4) Manometer Inflation Method: A dedicated manometer is connected to the cuff inflation port via a three-way connector, allowing real-time pressure monitoring during inflation. The cuff pressure is adjusted to 25 - 30 cmH₂O. This method is straightforward and provides accurate, reliable measurements. Comparative clinical studies have confirmed that this approach enables precise cuff pressure monitoring, effectively reducing mucosal injury and aspiration incidence [6] .

The choice of cuff inflation medium is a critical factor influencing its performance. The most commonly used medium is air. Currently, the cuffs of clinically employed endotracheal tubes are predominantly composed of hydrophobic polyvinyl chloride (PVC). As lidocaine is a lipophilic drug, it can permeate through the cuff material and exert localized effects on the tracheal mucosa via sustained release. Based on this principle, Shroff et al. [7] demonstrated that intracuff injection of lidocaine effectively alleviated postoperative sore throat.

The factors affecting cuff pressure can be categorized into three main aspects: patient-related factors, anesthesiologist-related factors, and perioperative factors.

Accumulation of subglottic secretions above the endotracheal tube cuff during cuff inflation is inevitable. Aspiration of these secretions is a major cause of pulmonary infection following endotracheal intubation [17] . Residual subglottic secretions after extubation may also trigger laryngospasm, and their retention in the airway significantly increases the risk of patient asphyxiation. Therefore, prior to cuff deflation, thorough suctioning of secretions via the nasal and oral cavities must be performed. Additionally, positive pressure may be applied during cuff deflation to prevent aspiration.

The method for clearing secretions above the cuff using positive pressure is as follows:

1) Disconnect the ventilator and attach a manual resuscitation bag to the endotracheal tube.

2) Deliver several ventilations to facilitate deep inspiration by the patient.

3) Deflate the cuff while simultaneously compressing the resuscitation bag rapidly to generate positive airway pressure, propelling gas upward through the space between the cuff and the tracheal wall to expel accumulated secretions into the pharynx.

4) Immediately reinflate the cuff to prevent reflux of secretions, followed by prompt suctioning with a catheter.

Alternatively, without disconnecting the ventilator, tidal volume may be increased appropriately. The cuff is released at the onset of ventilator-delivered inspiration, utilizing the positive pressure to propel secretions from above the cuff toward the oropharynx, while concurrent suctioning is performed via the oral or nasal route [18] .

The tapered-cuff endotracheal tube (ETT) is a novel type of endotracheal tube recently introduced into clinical practice. The diameter and taper angle of the cuff can be adjusted according to the tracheal diameter, ensuring an effective seal for tracheas of varying shapes and sizes. This design prevents cuff folding and the formation of leakage channels, thereby effectively reducing the incidence of microaspiration [23] . The tapered-cuff suction-irrigation endotracheal tube integrates a novel tapered cuff with a separate suction-irrigation channel positioned above the cuff. This design not only ensures an effective seal between the cuff and the tracheal wall but also enables timely and efficient aspiration and irrigation of subglottic secretions, thereby further preventing microaspiration. Mahmoodpoor et al. [24] demonstrated that in critically ill patients requiring prolonged mechanical ventilation, the use of tapered-cuff suction-irrigation endotracheal tubes with intermittent subglottic suctioning significantly reduces the incidence of ventilator-associated pneumonia (VAP). Additionally, the researchers observed that the mean cuff pressure in the experimental group was lower than that in the control group, further highlighting the advantages of the cuff design and subglottic secretion drainage. Li et al. [25] found that during anterior cervical spine surgery, the use of a tapered-cuff endotracheal tube minimized the impact of surgical manipulation on cuff pressure when retracting neck tissues to expose the vertebrae, thereby reducing the incidence of postoperative intubation-related complications. Chen et al. [26] reported that the use of a tapered-cuff endotracheal tube reduced the incidence and severity of postoperative sore throat in patients undergoing breast surgery and improved satisfaction with anesthesia. This may be attributed to the smaller cuff–mucosa contact area of the tapered cuff. However, as the study exclusively enrolled female patients undergoing breast surgery, the findings may not be generalizable to other types of surgery.

Management and maintenance of the endotracheal tube cuff play a critical role during the establishment of an artificial airway, which has garnered significant attention from clinicians. Consequently, numerous novel cuff pressure monitoring techniques have emerged. Farre et al. [27] employed a glass-chamber air pump to achieve continuous cuff pressure control. This system maintained a constant endotracheal tube cuff pressure under various influencing factors, including endotracheal tube displacement, tracheal wall tension changes, diffusion of anesthetic gases, or hypothermic surgical procedures.