INTRODUCTION
Point-of-care ultrasonography (POCUS) has become widely used in clinical anesthesiology for a range of procedures. Its routine application in central venous catheterization and established utility in diagnosing conditions such as pneumothorax demonstrate its clinical versatility [1,2].
In airway management, POCUS provides several distinct advantages. Preoperative airway assessment using ultrasound allows clinicians to anticipate difficult airways and plan appropriate management strategies. Endotracheal intubation can also be effectively confirmed by direct visualization of the tracheal tube and vocal cords. Real-time airway imaging enables prompt intervention and may shorten procedural time. During critical “cannot intubate, cannot ventilate” scenarios, POCUS allows rapid and accurate identification of the cricothyroid membrane (CTM), improving the precision of emergency cricothyrotomy.
In pediatric patients, assessing the relationship between the tracheal tube and vocal cords helps determine the optimal tube size and reduces intubation-related complications. The portability of POCUS makes it particularly valuable in non-operating room anesthesia (NORA), where it allows quick assessment of both gastric emptying and airway anatomy—two factors that significantly influence patient safety and outcomes [3-6].
This review provides a comprehensive overview of the clinical applications of POCUS in airway management and describes scanning techniques that facilitate its practical use in anesthetic practice.
LITERATURE SEARCH
A literature search was conducted in PubMed, ScienceDirect, and Google Scholar for articles published between 2015 and 2025 (primarily, though not exclusively). Keywords included “ultrasound,” “ultrasonography,” “POCUS,” “anatomy,” “airway,” “difficult airway,” “endotracheal intubation,” “esophageal intubation,” “laryngeal edema,” “cricothyrotomy,” “gastric ultrasound,” “aspiration,” “NORA,” “pediatric,” “geriatric,” and “supraglottic airway.”
Only peer-reviewed articles written in English and involving human subjects were included. Conference abstracts, editorials, and non-English publications were excluded. The most recent systematic reviews and meta-analyses were prioritized, along with well-designed randomized controlled trials and published guidelines. Reference lists of relevant reviews and original articles were also screened for additional studies.
The final search was completed on July 29, 2025. HS, CSO, GJC, and JBP who were experienced in POCUS or airway management reviewed articles and determined their inclusion in this review.
PROBE SELECTION AND PATIENT POSITIONING
Both linear and curvilinear probes are commonly used for upper airway imaging, depending on the depth of the target structures. A high-frequency (5-15 MHz) linear probe provides excellent resolution for superficial structures such as the vocal cords and epiglottis. In contrast, a high-frequency curvilinear probe is preferred for imaging deeper structures around the tongue base or when measuring the hyomental distance (HMD).
For gastric ultrasonography, a low-frequency (2-5 MHz) curvilinear probe is generally appropriate, except in low-body-weight adults or pediatric patients (< 40 kg). Upper airway ultrasonography is typically performed with the patient in a supine position and the neck in a neutral or slightly extended posture. Although longitudinal views are particularly useful for identifying the CTM, the probe may also be positioned in the transverse plane as required.
For gastric ultrasonography, scanning is performed in both the supine and right lateral decubitus (RLD) positions using a longitudinal approach. The supine view provides qualitative information about gastric contents, whereas the RLD position allows more accurate quantitative assessment.
UPPER AIRWAY ANATOMY
Key upper airway structures identifiable via POCUS include the hyoid bone, tracheal rings, cricoid cartilage, CTM, thyroid cartilage, vocal cords, epiglottis, and tongue. Upper airway ultrasonography typically focuses on four anatomical levels: suprahyoid, thyrohyoid, thyroid, and cricothyroid. Depending on the clinical objective, specific ultrasonographic views may be selected [4,5].
Suprahyoid level
At the suprahyoid level, the relevant anatomical landmarks include the mandibular mentum, hyoid bone, tongue, and the mylohyoid and geniohyoid muscles. A curvilinear probe in the longitudinal plane is preferred to capture both the mandibular mentum and the hyoid bone (Fig. 1). The mandible and hyoid bone appear as hyperechoic structures with posterior acoustic shadowing. The mylohyoid and geniohyoid muscles appear as hypoechoic areas between these bony landmarks, while the tongue—located deep to the suprahyoid muscles—also appears hypoechoic.
Thyrohyoid level
At the thyrohyoid level, a linear probe is used to visualize the strap muscles, thyrohyoid membrane, and epiglottis. In the transverse plane, these structures together create a characteristic “small face” appearance (Fig. 2) [7]. The strap muscles appear hypoechoic, with the thyrohyoid membrane lying between them. The epiglottis is seen as a curved, hypoechoic structure lying deep to the thyrohyoid membrane.
Thyroid level
At the level of the thyroid cartilage, both the vocal cords and arytenoid cartilages can be identified (Fig. 3). The strap muscles are located superficial to the thyroid cartilage. The vocal cords appear as triangular hypoechoic structures deep to the thyroid cartilage, with the arytenoid cartilages positioned posteriorly. In cases where calcification of the thyroid cartilage results in posterior acoustic shadowing, tilting the probe at the superior thyroid notch or repositioning it to the cricothyroid level can enhance visualization [8].
Cricothyroid level
This anatomical level corresponds to the region between the thyroid and cricoid cartilages and includes the CTM, which can be visualized in both transverse and longitudinal planes (Fig. 4). In the transverse plane, scanning caudally from the thyroid cartilage reveals the CTM as a linear hyperechoic band situated between the triangular-shaped thyroid cartilage and the inverted U-shaped cricoid cartilage [9].
In the longitudinal plane, the tracheal rings appear as small ovoid hypoechoic structures (“beads on a string”) inferior to the cricoid cartilage, aiding in the identification of the CTM. The CTM lies between the thyroid cartilage—characterized by a thick, angular-shaped inferior border—and the cricoid cartilage, which appears as a hypoechoic ovoid structure.
In addition to these four anatomical levels, the suprasternal view—obtained using a curvilinear probe—provides valuable information on the position of the trachea and esophagus, as well as adjacent structures such as the thyroid gland, sternocleidomastoid muscles, and cervical vessels. In the transverse plane, the trachea appears as a hyperechoic semicircular structure with posterior reverberation artifacts, while the esophagus is typically located posterior and slightly to the left or right of the trachea. Visualization of both structures is critical for confirming endotracheal tube (ETT) placement and detecting misplacement into the esophagus (i.e., the “double tract sign,” produced by the air-mucosa interface within the esophagus) [10]. The use of POCUS for detecting tracheal tube misplacement will be discussed in a later section.
POCUS FOR DIFFICULT AIRWAY PREDICTION
A difficult airway is a clinical situation in which a trained anesthesiologist encounters difficulty with facemask ventilation, tracheal intubation, or both [11]. The incidence of difficult facemask ventilation ranges from 1.4% to 5.0%, while difficult intubation occurs in approximately 5-8% of cases. The “cannot intubate, cannot oxygenate” scenario—one of the most critical emergencies in airway management—has a reported incidence of 0.002-0.04% [6].
Despite the use of various screening tests and physical predictors, their diagnostic accuracy remains limited because of subjective landmark identification and inconsistent scoring methods [12]. POCUS provides a real-time, objective assessment of airway anatomy and has shown promise in improving the prediction and preparation for difficult airways.
Ultrasound-based airway evaluation focuses on three main anatomical domains: soft tissue thickness, anatomical positioning, and oral cavity space [13].
• Soft tissue thickness: The distance from the skin to the epiglottis (DSE), measured at the thyrohyoid level in the transverse plane, reflects pre-epiglottic tissue thickness. A DSE of ≥ 2.36-2.54 cm is associated with difficult laryngoscopy and higher Cormack-Lehane (C-L) grades. A meta-analysis reported that this measurement has a sensitivity and specificity of 82% and 79%, respectively, for predicting difficult laryngoscopy [14].
• Anatomical positioning: The HMD, measured in the longitudinal plane as the distance from the hyoid bone to the mandibular symphysis, is assessed using a curvilinear probe. Measurements can be obtained in the supine, ramped, or extended neck positions. Recent evidence suggests that HMD is among the most reliable predictors of difficult laryngoscopy, difficult intubation, and higher C-L grades. An HMD ≤ 5.29 cm predicts a C-L grade ≥ 3 with 96.7% sensitivity and 71.6% specificity [13,15,16]. Some studies have proposed using the ratio of HMD in the extended or ramped position to that in the supine position to enhance predictive accuracy, although its clinical utility remains debated [17].
• Oral cavity space: Tongue thickness, measured as the distance from the skin to the dorsal surface of the tongue at the suprahyoid level, has also been explored as a predictor of difficult intubation. A thickness greater than 6.1 cm has been associated with difficult intubation, although its sensitivity and specificity (75% and 72%, respectively) are lower compared with other parameters [5,18].
Although these ultrasound-derived parameters are helpful in predicting difficult airways and are supported by meta-analyses, clinicians should recognize that no single measurement can reliably predict a difficult airway. By incorporating multiple ultrasound-based assessments, clinicians can more accurately identify patients at risk and tailor airway management strategies accordingly.
POCUS FOR EMERGENCY AIRWAY INTERVENTION
Difficult tracheal intubation
Ultrasound is an effective adjunct in managing difficult tracheal intubation, as it facilitates identification of airway structures and confirmation of ETT placement [19]. In cases with C-L grade IV views, where the vocal cords are not visible, real-time ultrasound-guided intubation can assist in blind intubation attempts [20].
At the thyrohyoid level in the transverse plane, the thyrohyoid membrane appears as a hypoechoic band between the thyroid cartilage and the hyoid bone. Slight caudal movement of the probe reveals the vocal cords as hyperechoic structures [21]. During mask ventilation, dynamic movement of the vocal cords can be observed. Passage of the ETT results in visible abduction of the cords, and cuff inflation further accentuates the acoustic shadow of the tube, confirming intratracheal placement [22]. This provides clear, real-time confirmation of successful tracheal intubation.
Cricothyrotomy
The CTM is a key anatomical landmark for emergency airway access [23]. However, palpation alone is often unreliable, particularly in individuals with obesity or those with short necks [24]. POCUS enables rapid and accurate identification of the CTM, often within 25 seconds [25], facilitating pre-procedural marking and expeditious airway access.
To identify the cricothyrotomy site, the patient is positioned supine, and the operator typically stands on the patient’s right side to perform ultrasonography. A linear transducer placed in the transverse plane just above the suprasternal notch allows visualization of the tracheal ring. Clockwise rotation of the probe followed by cephalad advancement reveals a series of tracheal rings that appear continuous, often described as a “string of pearls.” In this view, further cephalad advancement of the probe reveals the cricoid cartilage, which appears as a flat, circular, hypoechoic structure situated anterior to the trachea. The CTM appears as a hyperechoic band between the cricoid and thyroid cartilages and lies immediately cephalad to the cricoid cartilage, characterized by a strong air-mucosa interface (Fig. 4B).
Marking the CTM using a blunt needle to create an acoustic shadow enhances procedural accuracy. In patients with obesity or those with distorted neck anatomy, a caudal-to-cephalad scanning approach from the thyroid cartilage in the transverse plane can also be effective.
Tracheostomy
POCUS plays a pivotal role in both surgical and percutaneous tracheostomy [26], enabling precise identification of the trachea, assessment of tracheal depth, and evaluation of adjacent vascular structures [27]. Ultrasound-guided percutaneous tracheostomy improves safety and success rates by providing real-time visualization of anatomical landmarks and vascular structures, thereby reducing complications such as subglottic injury, hemorrhage, and pneumothorax [28]. Compared with fiberoptic bronchoscopy-guided techniques, ultrasound-guided tracheostomy is associated with a higher likelihood of achieving a midline puncture [29]. Moreover, POCUS allows accurate measurement of the distance from the skin to the tracheal lumen, minimizing the risk of posterior tracheal wall injury [27,30].
Longitudinal ultrasonographic imaging helps visualize the tracheal rings. Once the “string of pearls” pattern is observed, the specific space between the second and third tracheal rings can be clearly identified (Fig. 4C). After marking the precise inter-ring space on the skin, the ultrasound probe is rotated into the transverse plane, allowing an out-of-plane view of the trachea [31]. Following a midline puncture under real-time ultrasonographic guidance, a guidewire is inserted into the tracheal lumen through the needle. Ultrasound can then be used again to confirm proper guidewire placement. After needle removal, the tract is dilated, and a tracheostomy tube is inserted over the guidewire in accordance with standard percutaneous dilatational tracheostomy protocols.
POCUS FOR ASPIRATION RISK ASSESSMENT AND APPLICATION IN NORA
Evaluation of aspiration risk before intubation is a critical component of safe airway management. While conventional physical examination remains fundamental, POCUS has become a valuable adjunct by providing real-time anatomical and physiological insights. Recent advancements have expanded its use to include assessment of gastric contents and aspiration risk, as well as rapid evaluation in emergent or remote settings.
Gastric ultrasonography and aspiration risk
Gastric ultrasonography enables a direct, real-time, bedside assessment of gastric contents and volume. Scanning is typically performed using a low-frequency curvilinear transducer, targeting the gastric antrum in both the supine and RLD positions. The antrum is visualized in a longitudinal plane between the left lobe of the liver anteriorly and the aorta or inferior vena cava posteriorly. In fasted individuals, the antrum appears flat or collapsed; with increasing gastric content, it becomes round and distended [32].
A commonly used qualitative grading system classifies antral findings into three grades:
Grade 0, an empty stomach (no contents in either position); Grade 1, a small volume of clear fluid visible only in the RLD position (considered low risk); Grade 2, fluid visible in both positions, corresponding to a “full stomach” and indicating a higher aspiration risk.
Solid or particulate content, regardless of volume, is associated with a high aspiration risk [33,34]. In selected cases, quantitative assessment is performed using the antral cross-sectional area in the RLD position, which correlates closely with gastric volume [35]. Volumes exceeding 1.5 ml/kg are often cited as a threshold above which aspiration risk becomes clinically significant [36].
Despite routine preoperative fasting to minimize aspiration risk, delayed gastric emptying may still occur in a variety of patients. Contributing factors include diabetes, chronic kidney or liver disease, neurological disorders, pregnancy, and the use of medications such as opioids and glucagon-like peptide-1 (GLP-1) receptor agonists [37]. Notably, GLP-1 receptor agonists—including semaglutide and tirzepatide, a dual glucose-dependent insulinotropic polypeptide (GIP)/GLP-1 receptor agonist—are increasingly prescribed for obesity and type 2 diabetes and are known to delay gastric emptying through both central and vagally mediated mechanisms [38]. This effect may persist for several days after the last dose, potentially exceeding standard preoperative fasting intervals [39].
Patients receiving GLP-1 receptor agonists are significantly more likely to present for anesthesia with residual gastric contents despite adherence to fasting guidelines [40]. This presents a clinically relevant concern, particularly in procedures where gastric visualization or aspiration prevention is critical [41]. Further research is needed to better define optimal perioperative management in such patients. Current expert consensus recommends withholding daily GLP-1 receptor agonists on the day of surgery, and withholding weekly formulations such as semaglutide or tirzepatide for at least one week before elective procedures to reduce aspiration risk [42,43].
Gastric ultrasonography provides an individualized and objective approach to aspiration risk assessment, surpassing reliance on fasting history alone. Its utility is especially evident in patients with known or suspected delayed gastric emptying. By enabling direct visualization and grading of gastric contents, POCUS supports informed decision-making regarding anesthetic management, airway protection, and procedural timing.
Gastric assessment in emergency and non-operating room settings
In emergency surgeries and NORA environments—such as endoscopy units, interventional radiology suites, and magnetic resonance imaging rooms—POCUS enables rapid, noninvasive evaluation of gastric contents when preoperative assessment is limited. Gastric ultrasonography can detect residual gastric contents and guide decisions regarding the need for rapid sequence induction or adjustments to the airway management strategy, particularly when fasting status is unknown [19,44].
Additionally, POCUS facilitates evaluation of anterior neck anatomy, aiding in emergency front-of-neck access when physical examination is restricted. The availability of portable ultrasound devices has increased the practicality of POCUS in both NORA and trauma settings, enhancing patient safety and supporting timely clinical decision-making.
POCUS FOR AIRWAY MANAGEMENT IN SPECIAL CONDITIONS
POCUS has proven effective for airway assessment in several special situations, including pediatric and geriatric patients. It is also useful for confirming tracheal tube placement, estimating tube depth and size, and detecting supraglottic airway (SGA) malposition [45,46].
Detection of esophageal intubation
In clinical situations where conventional confirmation methods such as capnography may be unreliable [47-50], upper airway POCUS enables immediate identification of esophageal intubation before the initiation of positive pressure ventilation. Early detection is particularly valuable, as it reduces the risk of gastric insufflation and aspiration.
In transverse suprasternal views, a single air-mucosa interface suggests correct tracheal placement (the “bullet sign”), whereas a double interface indicates esophageal intubation (the “double tract sign”) (Fig. 5A) [51]. Studies have shown that POCUS is faster and more accurate (90.6-100%) than chest radiography for identifying esophageal intubation [52,53], and it outperforms both auscultation and capnography in diagnostic reliability [54-56].
Tracheal tube depth
In pediatric patients, POCUS demonstrates excellent sensitivity (98.8%) and specificity (96.4%) in confirming tracheal tube depth [57]. Longitudinal scanning of the anterior neck reveals the tube shaft within the trachea as a hyperechoic structure with posterior shadowing (Fig. 5B). In ambiguous cases, gentle manual compression of the pilot balloon may help identify the cuff through dynamic shadowing artifacts. The depth of the tracheal tube can be assessed by locating the cuff or tip at the level of the suprasternal notch [58,59].
Determination of tracheal tube size
POCUS of the subglottic airway can reliably estimate the appropriate tracheal tube size in pediatric patients. This technique is particularly useful in cases of subglottic stenosis or tracheal narrowing due to mass effect. POCUS also improves diagnostic precision in detecting subglottic narrowing and helps select the optimal tube size, thereby reducing the need for multiple intubation attempts [60].
SGA device malposition
Airway ultrasonography can detect SGA malposition through transverse glottic views by identifying abnormal arytenoid positioning, asymmetric cuff shadows, or air artifacts. This technique is especially useful when fiberoptic bronchoscopy is unavailable or when continuous ventilation must be maintained [46,65]. It provides a rapid, noninvasive means of assessment without interrupting airway management.
POCUS for airway management in elderly patients
In elderly patients, anatomical and physiological changes can complicate airway management. Age-related alterations in dentition and musculoskeletal structures often increase the difficulty of airway interventions [66]. Alveolar bone atrophy and tooth loss in the lower jaw can result in a thinner mandible, cheek retraction, and the characteristic appearance of an aged face. In addition, loss of masseter and pterygoid muscle volume can make bag-mask ventilation more difficult. Age-related changes in the temporomandibular joint, such as disc displacement, may also limit mouth opening and contribute to difficult intubation [67].
For airway POCUS in elderly patients, calcification of the thyroid cartilage should be considered. With advancing age, the thyroid cartilage may become calcified, producing posterior acoustic shadowing. Because the thyroid cartilage serves as a key landmark for identifying the CTM, such calcification can make localization challenging. As discussed earlier, slight probe tilting at the thyroid or cricothyroid level can facilitate CTM visualization [5].
LUNG ULTRASONOGRAPHY FOR POST-INTUBATION PERIOD
Lung ultrasonography complements airway POCUS by providing reliable confirmation of tracheal tube placement and enabling immediate detection of esophageal intubation following airway instrumentation. In addition, it supports rapid evaluation and diagnosis of pulmonary conditions such as pneumothorax, atelectasis, and pulmonary edema in both adult and pediatric populations [68-70].
Although lung ultrasonography is a powerful adjunct for post-intubation assessment, a comprehensive discussion of sonographic techniques for evaluating pulmonary pathology is beyond the scope of this review and will be addressed in future research.
CONCLUSIONS
Airway management is a critical component of patient safety. Despite advances in tools and guidelines, challenges related to bag-mask ventilation, laryngoscopy, and endotracheal intubation continue to occur. Although POCUS is widely recognized as a valuable tool for assessing airway anatomy and predicting difficult intubation, its effectiveness remains limited by operator dependence, and some studies report substantial inter-observer variability.
The current body of evidence on airway POCUS is characterized by considerable heterogeneity. Clinical decision-making may be influenced by factors such as operator skill level, probe selection, ultrasound equipment, and imaging settings. Patient populations also vary widely, encompassing pediatric, geriatric, and individuals with obesity, as well as those undergoing NORA. Threshold criteria for key diagnostic parameters have yet to be clearly defined. Furthermore, much of the existing research consists of observational rather than randomized controlled trials, and reported performance measures are often limited by inconsistent presentation of confidence intervals, which restricts both precision and generalizability.
POCUS enhances airway management by enabling objective anatomical assessment, reliable confirmation of tube placement, real-time guidance during emergency procedures, and dynamic evaluation of gastric contents. In pediatric patients, it offers additional advantages, including confirmation of tracheal intubation, selection of appropriate tube size, and assessment of SGA devices.
Future research should prioritize well-designed randomized controlled trials with rigorous and clinically relevant endpoints, such as first-pass intubation success and aspiration events. Standardization of imaging protocols and clinical assessment criteria will be essential to improve reproducibility and validity across studies. The role of airway POCUS should also be further investigated in diverse clinical contexts, including thoracic surgery, extremes of age, and obesity.
Tailoring airway management protocols to specific patient populations—such as pediatric, geriatric, NORA, and emergency department settings—and integrating POCUS-based evidence into these protocols may further enhance patient safety and clinical outcomes.
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