Procedural POCUS

10.1 Universal procedural principles

Three phases:

  1. Pre-procedural assessment.

  2. Real-time guidance.

  3. Post-procedural verification.

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

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.

Real-time

  • IJV: longitudinal, medial to carotid.

  • Subclavian: low clavicular, avoid pleura.

  • Femoral: vein medial to artery.

  • Short increments, tip visualized.

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.

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.

Real-time

  • Posterior or axillary approach.

  • Probe lateral to needle.

  • Visualize needle entering pleural space.

  • Stop if pain, instability, or lost tip.

Post-procedure

  • Residual effusion.

  • Pneumothorax.

  • Hemothorax.

  • Lung sliding.

  • B-lines.

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.

Real-time

  • Subcostal, in-plane, short increments.

  • Stop if resistance, solid organ, or bleeding.

Post-procedure

  • New collection.

  • Haematoma.

  • Visceral injury suspicion.

  • Re-accumulation.

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. Observe local anaesthetic spread qualitatively; it is not a validated numeric score. Stop for intravascular injection, intraneural injection, unexpected anatomy, or signs of toxicity. Monitor hypotension, bradycardia, high spinal, respiratory depression, and local anaesthetic systemic toxicity.

10.6 Lumbar puncture / neuraxial

Midline: spinous processes, interspinous space, subarachnoid space, depth. Paramedian if stenosis, lipoma, malalignment, or prior surgery. Use colour Doppler for paraspinal vessels. Confirm needle entry into subarachnoid space when possible. 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. POCUS does not replace Allen test or collateral perfusion assessment. Use in-plane needle. Confirm pulse or flashback. Avoid adjacent vein. Post-procedure: haematoma, arterial flow, venous puncture, pseudoaneurysm.

10.8 Pericardiocentesis

Identify the largest fluid pocket. Avoid lung, liver, and intercostal vessels. Use subxiphoid or subcostal approach with real-time needle trajectory. 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.

DARES workflow

DARES is explicitly defined in v4 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. 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.

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

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

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

  • 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.

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

  1. 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.

  2. Thyrohyoid view

    • Thyrohyoid membrane.

    • Epiglottis.

    • Pre-epiglottic space.

    • Strap muscles.

  3. 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.

  4. 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.

  5. 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:

  • 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.

  • 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:

  • 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.

  • 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.

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

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.

  • 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:

  • 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.

Ultrasound can:

  • 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.

Airway POCUS pitfalls

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

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

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

  • Misidentifying esophagus, vessels, or strap muscles.

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

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