10. PROCEDURAL POCUS

10.1 Universal procedural principles

Three phases:

  • Pre-procedural assessment.

  • Real-time guidance.

  • Post-procedural verification.

Sterile technique for invasive procedures: probe cover, sterile gel, handle outside field [1]. In-plane needle visualization is preferred. Visualize needle shaft and tip [2]. If the tip is lost, stop and re-image [3]. Do not advance blindly [2,3]. Flashback does not equal venous confirmation [2]. Post-procedure imaging is required [2]. Know when to stop: loss of tip, unexpected anatomy, instability, suspected intravascular or intraneural injection [2,3].

10.2 Central venous catheterization

Pre-procedure

  • IVC status.

  • LVOT VTI if fluid question.

  • RV/LV if PE.

  • Access site anatomy: vein diameter, depth, compressibility, thrombus, artery location, thyroid [2,4].

Real-time

  • IJV: longitudinal, lateral to carotid.

  • Subclavian: low clavicular, avoid pleura.

  • Femoral: vein medial to artery.

  • Short increments, tip visualized [2,3].

Post-procedure

  • Catheter tip at SVC/RA junction.

  • Pneumothorax, especially subclavian.

  • Hemothorax.

  • Haematoma.

  • Arterial malposition.

  • Venous malposition: contralateral brachiocephalic, azygos, internal mammary.

POCUS supports positioning. Institutional standards may still require radiographic confirmation [2].

10.3 Thoracentesis

Pre-procedure

  • Effusion depth.

  • Safe pocket 1–2 cm or greater preferred.

  • Lung apposition.

  • Pleural thickening.

  • Loculations.

  • Adjacent vessels.

Complex or loculated effusion: consider CT/radiology [5].

Real-time

  • Posterior or axillary approach.

  • Probe lateral to needle.

  • Visualize needle entering pleural space [5].

  • Stop if pain, instability, or lost tip.

Post-procedure

  • Residual effusion.

  • Pneumothorax [5].

  • Hemothorax.

  • Lung sliding [5].

  • B-lines [5].

10.4 Paracentesis

Pre-procedure

  • Fluid depth 1–2 cm or greater preferred.

  • Avoid liver, spleen, bowel, omentum, varices, vessels.

  • Minimal, complex, or post-surgical collections: alternative guidance.

  • Use a low-frequency curvilinear probe; optimize gain and depth to visualize the full fluid pocket and its deep boundary; scan multiple abdominal quadrants to select the safest entry; use colour Doppler when needed to identify superficial or inferior epigastric vessels; mark the site after confirming a stable pocket; re-image if the patient moves, coughs, or the pocket changes [6].

Real-time

  • Subcostal, in-plane, short increments.

  • Stop if resistance, solid organ, or bleeding.

  • Prefer real-time needle visualization when the pocket is small, complex, or mobile; otherwise a static-guided marked-site approach is acceptable after stable imaging [6].

Post-procedure

  • New collection.

  • Haematoma.

  • Visceral injury suspicion.

  • Re-accumulation.

  • Repeat scanning if haemodynamic change, increasing abdominal pain, or suspected visceral injury [6].

10.5 Nerve block / regional

Define target nerve. Identify adjacent lung, artery, vein, bone, plexus, and pleura. Measure depth to target. Use in-plane needle. Aspirate before injection [7]. Observe local anaesthetic spread qualitatively; it is not a validated numeric score [7]. Stop for intravascular injection, intraneural injection, unexpected anatomy, or signs of toxicity [7]. Monitor hypotension, bradycardia, high spinal, respiratory depression, and local anaesthetic systemic toxicity [7].

10.6 Lumbar puncture / neuraxial

Midline: spinous processes, interspinous space, subarachnoid space, depth [8]. Paramedian if stenosis, lipoma, malalignment, or prior surgery [8]. Use colour Doppler for paraspinal vessels [8]. Confirm needle entry into subarachnoid space when possible [8]. Anticoagulation/coagulopathy: special caution. Post-procedure: puncture site bleeding, haematoma if anticoagulated, neurological deficit.

10.7 Arterial line

Pre-procedure: artery size, depth, adjacent vein, calcification [9]. POCUS does not replace Allen test or collateral perfusion assessment. Use in-plane needle [9]. Confirm pulse or flashback. Avoid adjacent vein. Post-procedure: haematoma, arterial flow, venous puncture, pseudoaneurysm [9].

10.8 Pericardiocentesis

Identify the largest fluid pocket. Avoid lung, liver, and intercostal vessels. Use subxiphoid or subcostal approach with real-time needle trajectory [5]. Correlate with clinical response. Surgical intervention is preferred for traumatic, post-operative, or unsuitable-for-percutaneous tamponade. This is a high-risk procedure requiring trained operator, supervision, and escalation support.

10.9 Airway POCUS

Airway POCUS is a procedural POCUS domain spanning pre-intubation difficult-airway assessment, endotracheal tube confirmation, post-extubation risk assessment, and front-of-neck access planning. It is an adjunct to clinical judgment, capnography, and established airway algorithms, not a replacement [10].

DARES workflow

DARES is defined as:

  • D — Difficult-airway risk assessment.

  • A — Airway device placement confirmation.

  • R — Rescue/front-of-neck access planning.

  • E — Extubation-risk assessment.

  • S — Stridor/laryngeal oedema prediction.

DARES is a workflow mnemonic, not a diagnostic algorithm [10]. Each element should be tied to a specific clinical question.

Evidence context

  • Up to 12% of ED intubations may be complicated.

  • Failed intubation occurs in approximately 1 in 50 to 1 in 100 patients in ED, ICU, and prehospital settings [10].

  • More than 90% of difficult airways may be unanticipated in some studies [10].

  • Traditional difficult-airway screening tools generally have low sensitivity and specificity [10].

  • Sonographic identification of upper airway anatomy outperforms palpation and correlates well with CT measurements [10].

  • Ultrasound improves cricothyrotomy success in cadaveric models with poorly defined neck anatomy.

  • Sonographic laryngeal air column width difference has been evaluated for predicting post-extubation stridor [10].

Probe selection

  • Linear probe approximately 5–14 MHz: cricothyroid membrane, vocal cords, epiglottis, thyrohyoid membrane, tracheal air-mucosa interface.

  • Curvilinear probe approximately 4–10 MHz: tongue base, submandibular/infrahyoid tissues, hyomental distance.

Patient positioning

  • Supine is default.

  • Neck neutral, ramped, or hyperextended as appropriate.

  • Ramped positioning with head extension often improves probe manipulation and imaging quality.

  • In respiratory distress, semi-recumbent or seated position may be safer.

  • Use ample gel to minimize probe pressure and reduce acoustic air gaps.

  • Avoid probe compression of compressible structures when measuring dimensions.

  • Measurements vary with neck position, habitus, probe pressure, respiration, swallowing, and phonation.

Standard views

Suprahyoid view:

  • Hyomental distance.

  • Tongue thickness.

  • Distance to tongue.

  • Submandibular soft tissue depth.

  • Hyoid and mentum appear hyperechoic with posterior shadowing.

  • Tongue is hypoechoic between hyoid and mentum.

Thyrohyoid view:

  • Thyrohyoid membrane.

  • Epiglottis.

  • Pre-epiglottic space.

  • Strap muscles.

Thyroid/tracheal view:

  • Trachea: hyperechoic air-mucosa interface with posterior reverberation artifact.

  • Thyroid lobes lateral to trachea.

  • Thyroid isthmus may bridge anteriorly.

  • Common carotid arteries and internal jugular veins posterior to thyroid lobes.

  • Esophagus posterior and slightly left of trachea.

  • Double tract sign: two hyperechoic air-mucosa interfaces suggesting esophageal intubation.

Cricothyroid view:

  • Cricothyroid membrane.

  • Thyroid cartilage.

  • Cricoid cartilage.

  • Trachea at the level of the cricothyroid membrane.

  • Critical for cricothyrotomy planning and emergency front-of-neck access [10].

Suprasternal view:

  • More inferior airway assessment.

  • ETT confirmation.

  • Distal cervical airway structures.

D — Difficult-airway risk assessment

Airway ultrasound provides objective measurements in domains that correlate with laryngoscopy difficulty [10]:

  • Anterior neck soft tissue thickness domain: submandibular and anterior soft tissue depth; reflects curvature and resistance to laryngoscopy.

  • Anatomic position domain: dynamic measurements that vary with positioning; reflects alignment of oral, pharyngeal, and laryngeal axes.

  • Oral space domain: oral cavity and tongue dimensions; larger tongue volume or reduced oral space may contribute to difficult laryngoscopy.

Interpretation:

  • Ultrasound-derived measurements differ significantly between patients with and without difficult laryngoscopy [10].

  • Ultrasound is risk stratification, not a binary diagnosis.

  • Integrate with clinical history, comorbidities, aspiration risk, physical examination, and anticipated course of care.

  • May prompt early planning for video laryngoscopy, supraglottic airway availability, difficult airway cart, and early escalation.

  • Particularly useful in obesity, obscured landmarks, limited neck mobility, or prior difficult intubation.

A — Airway device placement confirmation

Capnography remains the primary method for confirming ETT placement. Ultrasound is useful when capnography is unreliable or equivocal [10]:

  • Cardiac arrest.

  • Severe hypoperfusion.

  • Obstructed airway.

  • Certain ventilatory pathophysiologies.

Key findings:

  • Tracheal intubation: tracheal air-mucosa interface present; trachea noncompressible; dynamic air artifact; absence of second hyperechoic air interface in expected esophageal location [10].

  • Esophageal intubation: double tract sign; two hyperechoic air-mucosa interfaces; one from trachea, one from esophagus containing the ETT; esophagus may appear as compressible air-containing structure posterior and slightly left of trachea [10].

  • Mainstem intubation: ultrasound may help detect unilateral airway obstruction or asymmetric air transmission with appropriate planes and clinical context [10].

Practical advantages:

  • Rapid.

  • Repeatable.

  • Useful when capnography is equivocal.

  • Can be performed at bedside with minimal interruption of resuscitation.

Limitations:

  • Should not fully replace capnography in stable patients [10].

  • Interpretation depends on image quality and operator familiarity.

  • ETT twisting, positioning, and anatomy may affect image clarity.

E/S — Extubation-risk assessment and stridor prediction

Post-extubation stridor and laryngeal oedema can lead to reintubation, airway emergency, and increased morbidity. The cuff leak test is commonly used; low cuff leak volume suggests higher risk.

Airway ultrasound may provide a noninvasive, repeatable alternative or adjunct by evaluating [10]:

  • Laryngeal air column dimensions.

  • Airway calibre.

  • Soft-tissue changes associated with oedema.

  • Laryngeal air column width difference before and after cuff deflation.

Ultrasound may be particularly attractive when serial assessment is needed or cuff leak testing is impractical. It is best viewed as an adjunct to cuff leak testing and clinical judgment, not a complete replacement. It may help monitor response to interventions such as steroids, but interpretation must remain within the full clinical context.

R — Rescue/front-of-neck access

In cannot-intubate, cannot-ventilate scenarios, cricothyrotomy may be required. Accurate identification of the cricothyroid membrane is essential, especially when anatomy is obscured by obesity, oedema, trauma, haematoma, body habitus, or neck mass [10].

Ultrasound can [10]:

  • Identify the cricothyroid membrane.

  • Distinguish thyroid and cricoid cartilages.

  • Identify adjacent vasculature.

  • Guide needle or blade placement.

  • Improve precision in difficult anatomic settings.

Practical advantages:

  • Useful when palpation is unreliable.

  • May reduce time spent searching for landmarks in a crisis.

  • Supports safer procedural planning in high-risk patients.

Practical caveat

  • Speed remains paramount in a true emergency.

  • Ultrasound should not delay definitive access if the patient is critically unstable.

  • The operator should have practiced ultrasound-assisted front-of-neck access in advance.

10.10 Gastric POCUS

Gastric POCUS is a focused, anaesthesia-specific bedside assessment used to estimate gastric content and aspiration risk when fasting status is uncertain or delayed gastric emptying is possible. It is an adjunct to history and examination, not a substitute [11,12].

Indications

Gastric POCUS is indicated when:

  • prandial status is uncertain, unreliable, or cannot be verified;

  • communication is limited (language barrier, cognitive impairment, paediatric patient);

  • delayed gastric emptying is anticipated (diabetes mellitus, chronic kidney disease, obesity, pregnancy, opioid use, acute pain);

  • urgent or emergent induction is planned and the decision between routine induction and RSI is uncertain [11,12].

It is not a routine screening test for all anaesthetics [11,12].

Probe and technique

  • Adults: low-frequency curvilinear probe, approximately 1–5 MHz.

  • Thin habitus or paediatric patients <40 kg: high-frequency linear probe, approximately 5–12 MHz.

  • Epigastric sagittal plane below the xiphoid.

  • Liver serves as the acoustic window.

  • The antrum lies caudal to the left hepatic lobe, anterior to the pancreas/aorta/SMA [12].

Positioning

  • Right lateral decubitus is the validated position for quantitative assessment.

  • Supine position may underestimate content pooled in the fundus.

  • Semi-recumbent is an acceptable alternative when right lateral decubitus is impractical (critically ill, trauma, pregnancy) [11,12].

Interpretation

Qualify content first:

  • Empty

  • Clear fluid

  • Thick fluid

  • Solids

Empty stomach: collapsed “bull’s-eye” in both supine and right lateral decubitus positions.
Solids or thick fluid: high aspiration risk regardless of quantity [11,12].

Perlas qualitative grading:

  • 0: empty in supine and right lateral decubitus.

  • 1: empty supine, fluid in right lateral decubitus.

  • 2: fluid in both positions.

  • 3: solids or thick fluid [11,12].

For clear fluid, quantify antral cross-sectional area:

  • trace serosa-to-serosa measurement;

  • mean of 3 measurements;

  • between peristaltic contractions [12].

Volume model and risk threshold

Perlas model (non-pregnant, BMI <40, right lateral decubitus):

GV (mL) = 27 + 14.6 × CSA (cm²) − 1.28 × age (years) [11,12].

Risk stratification:

  • GV <1.5 mL/kg: low aspiration risk.

  • Clear fluid ≥1.5 mL/kg: elevated risk.

  • Any solid or thick fluid: “full stomach” / elevated aspiration risk [11,12].

Decision-making: routine induction vs RSI

Gastric POCUS supports individualized risk stratification:

  • Empty or low-volume antrum in an unfasted patient: may support a standard titrated induction rather than reflexive RSI.

  • Full stomach (solids, thick fluid, or high-volume clear fluid): supports RSI and aspiration precautions [11,12].

It should not be used in isolation; integrate with NPO history, clinical context, comorbidity, and urgency [11,12].

Special populations — ASRA-PM 2026 recommendations

  • Pregnancy: supported in active labour, urgent caesarean with unclear NPO, and delayed emptying (hyperemesis, pre-eclampsia/eclampsia, gestational diabetes). Not supported for routine use in non-labouring pregnancy or elective caesarean. Gravid uterus displaces the antrum cephalad/right, increasing technical error risk in non-experts [13].

  • Diabetes: supported (higher baseline CSA/residual volume despite fasting) [13].

  • Obesity: conditional support (feasible despite antral depth; volume per kg similar to non-obese) [13].

  • Emergency/urgent care: conditional support (full stomach in >50% despite fasting; fasting time unreliable) [13].

  • GERD: not supported (limited, conflicting data) [13].

  • GLP-1 receptor agonists: conditional support (high residual content) [13].

Paediatric and limitations

  • Paediatric exam is feasible with linear probe; antrum is superficial.

  • Fasting upper limit approximately 1.2–1.5 mL/kg across ages [11].

  • Validated paediatric model (Spencer), 1–18 years, low volumes:
    GV = −7.8 + 3.5 × RLD-CSA + 0.127 × age (months) [11].

  • Inconclusive in approximately 2–3% of scans.

  • Unreliable after prior gastric surgery or large hiatal hernia (content in herniated sac is not visualized → underestimation).

  • Role before extubation is unstudied [11,12].

10.11 Pitfalls

  1. Using airway ultrasound as a replacement for capnography in stable intubated patients.

  2. Over-relying on a single airway measurement for difficult-airway prediction.

  3. Ignoring neck position, habitus, probe pressure, respiration, and phonation.

  4. Misidentifying esophagus, vessels, or strap muscles.

  5. Delaying front-of-neck access in a critically unstable patient for a prolonged scan.

  6. Interpreting airway ultrasound as definitive when clinical probability and anatomy remain uncertain.

  7. Using gastric POCUS as a universal screening test instead of a risk-stratification tool.

  8. Scanning supine only and missing fundal pooling.

  9. Failing to position in right lateral decubitus for quantitative assessment.

  10. Interpreting a single frame without averaging across peristaltic cycles.

  11. Over-relying on volume alone; solids or thick fluid are high risk regardless of quantity.

  12. Underestimating risk in pregnancy, obesity, diabetes, or GLP-1RA use.

  13. Assuming a negative scan excludes aspiration risk in the setting of large hiatal hernia or prior gastric surgery.

  14. Using gastric POCUS to replace clinical judgment, NPO history, or RSI decision-making.

References

  1. Australian and New Zealand Intensive Care Society. Central line insertion and maintenance guideline. 2012.

  2. Karmakar MK, Chuan VW. Ultrasound guided vascular access: efficacy and safety. Baillieres Best Pract Res Clin Anaesthesiol. 2009;23(3):299-311.

  3. Kim KW, Kim JH, Park SH, et al. Guide wire entrapment during central venous catheterization. Korean J Crit Care Med. 2014;29(2):137-140.

  4. Eid MA. Pre-procedure ultrasound as a tool for teaching landmark method for central venous cannulation. Br J Anaesth. 2016;116(1):148-149.

  5. Laursen CB, Clive A, Hallifax R, et al. European Respiratory Society statement on thoracic ultrasound. Eur Respir J. 2021;57:2001519.

  6. Chang AC, et al. Critical care echocardiography review: 1200 questions and answers. Philadelphia, PA: Wolters Kluwer; 2021.

  7. Lopez AM, Balocco AL, Vandepitte C, Hadzic A, eds. Hadzic’s peripheral nerve blocks and anatomy for ultrasound-guided regional anesthesia. 3rd ed. New York, NY: McGraw Hill; 2022.

  8. Luckanachanthachote C, Sivakumar RK, Karmakar MK. Real-time ultrasound-guided lumbar neuraxial blocks using the spinous process-lamina window. A&A Pract. 2026;20(8):e02240.

  9. Min SW, Cho HR, Jeon YT, et al. Effect of bevel direction on the success rate of ultrasound-guided radial arterial catheterization. J Clin Monit Comput. 2016;30(5):709-714.

  10. Lin J, Bellinger R, Shedd A, et al. Point-of-care ultrasound in airway evaluation and management: a comprehensive review. Diagnostics (Basel). 2023;13(9):1541.

  11. Perlas A, Arzola C, Van de Putte P. Point-of-care gastric ultrasound and aspiration risk assessment: a narrative review. Can J Anesth. 2018;65:437-448.

  12. El-Boghdadly K, Wojcikiewicz T, Perlas A. Perioperative point-of-care gastric ultrasound. BJA Educ. 2019;19:219-226.

  13. Haskins SC, Bronshteyn YS, Ledbetter L, et al. ASRA Pain Medicine narrative review and expert practice recommendations for gastric point-of-care ultrasound to assess aspiration risk in medically complex patients undergoing regional anesthesia and pain procedures. Reg Anesth Pain Med. 2026;51:723-745.