Procedural Anatomy: Lines, Taps & Airway Access
Where the needle goes, and which structure it must miss
Central venous access
Principles. Each site trades accessibility against the neighbors it lies beside. Real-time ultrasound guidance is standard. For internal jugular and subclavian lines, the patient is placed head-down to distend the vein and prevent air embolism, and a chest x-ray confirms the tip position (lower SVC near the cavoatrial junction) and excludes pneumothorax.
Internal jugular vein. The central approach enters at the apex of the triangle formed by the sternal and clavicular heads of sternocleidomastoid and the clavicle, aiming toward the ipsilateral nipple. Within the carotid sheath the IJ lies lateral to the common carotid artery, with the vagus nerve posterior between them, so a needle straying medially enters the carotid. The right IJ is preferred for its short, straight course through the right brachiocephalic vein to the SVC, and because the thoracic duct, draining into the junction of the left subclavian and internal jugular veins, is a left-sided hazard (chylothorax).
Subclavian vein. The infraclavicular approach passes beneath the clavicle at the junction of its middle and medial thirds, aimed toward the sternal notch. The vein runs anterior to the anterior scalene muscle, whereas the subclavian artery passes behind it. It has the lowest infection and thrombosis rates but the highest pneumothorax risk, because the lung apex lies just beneath, and bleeding behind the clavicle cannot be compressed, so it is avoided in coagulopathy.
Femoral vein. Just below the inguinal ligament, in the femoral triangle, the structures from lateral to medial are the femoral nerve, femoral artery, femoral vein, an empty space (the femoral canal), and lymphatics. The needle enters just medial to the palpated pulse; puncture above the ligament risks uncompressible retroperitoneal hemorrhage. The site avoids pneumothorax and stays clear of the chest and airway during resuscitation, but has higher infection and deep-vein thrombosis rates.
| Site | Landmark | Structure at risk | Key trade-off |
|---|---|---|---|
| Internal jugular | Apex of the SCM triangle, lateral to the carotid | Carotid artery, pleura | Compressible; right side preferred |
| Subclavian | Below the clavicle, middle–medial third junction | Pleura and lung apex, subclavian artery | Highest pneumothorax risk, lowest infection; noncompressible |
| Femoral | Below the inguinal ligament, medial to the pulse | Femoral artery; retroperitoneum if too high | No pneumothorax; more infection and DVT |
Pleural procedures
Over the top of the rib. The intercostal vein, artery, and nerve run together in the costal groove on the inferior border of each rib, in that order from top to bottom, with the nerve lowest and least protected. Needles and tubes therefore pass just over the superior border of the rib below the chosen space. For thoracentesis, the patient sits leaning forward and the needle enters posteriorly, below the top of the effusion but not so low as to meet the diaphragm, liver, or spleen.
Chest tube. Tubes go in the 4th–5th intercostal space at the anterior-to-mid-axillary line, inside the triangle of safety bounded by the lateral border of pectoralis major, the anterior border of latissimus dorsi, and a horizontal line at the nipple (5th intercostal space); lower placement risks the diaphragm, liver, or spleen. The long thoracic nerve descends along the mid-axillary line on serratus anterior, and injury to it produces a winged scapula.
Tension pneumothorax. This is a clinical diagnosis (hypotension, absent breath sounds, tracheal deviation away from the affected side), and decompression precedes imaging. Current trauma guidance places the adult needle in the 4th–5th intercostal space just anterior to the mid-axillary line, where the chest wall is thinner than at the 2nd intercostal space midclavicular line (often too thick for standard catheters); that 2nd-space site remains the choice in children. A chest tube follows, with a chest x-ray to confirm re-expansion and tube position.
Pericardiocentesis and paracentesis
Pericardiocentesis. In the subxiphoid approach, the needle enters between the xiphoid process and the left costal margin and is advanced upward and posteriorly toward the left shoulder, ideally with echocardiographic guidance to choose the shortest path to the fluid. Complications include right ventricular puncture, coronary artery laceration, arrhythmia, liver injury, and pneumothorax. Approaches beside the sternum must avoid the internal thoracic (mammary) artery, which descends just lateral to the sternal border.
Paracentesis. Ascites is sampled in a lower quadrant lateral to the rectus sheath, a few centimeters medial and superior to the anterior superior iliac spine (usually on the left, where the wall is thinner and fluid pools deeply), or in the midline through the relatively avascular linea alba below the umbilicus. Both routes avoid the inferior epigastric vessels, which arise from the external iliac vessels and ascend behind the rectus abdominis.
Airway access
Cricothyrotomy. In a "can't intubate, can't oxygenate" emergency, the fastest surgical airway runs through the cricothyroid membrane, felt as a soft notch between the thyroid cartilage above and the cricoid cartilage below. The membrane is superficial, relatively avascular, and below the vocal cords. A cricothyrotomy that must stay in place is usually converted to a formal tracheostomy.
In young children (roughly under 12 years), the cricothyroid membrane is tiny and the cricoid, the only complete cartilaginous ring in the airway, is easily injured, risking subglottic stenosis. Needle cricothyrotomy with jet insufflation is used as a temporizing bridge instead.
Tracheostomy. A planned tracheostomy, as for prolonged ventilation, enters through the 2nd to 4th tracheal rings, where the thyroid isthmus is retracted or divided; anterior jugular and inferior thyroid veins and, when present, a thyroid ima artery are further hazards. Staying below the first ring spares the cricoid. A stoma placed too low can erode into the brachiocephalic (innominate) artery crossing in front of the trachea: a tracheo-innominate fistula, often heralded by a sentinel bleed before massive hemorrhage.
Arterial puncture and intramuscular injections
Radial artery. The radial artery is the usual site for arterial lines and blood gases because the ulnar artery also supplies the hand through the palmar arches. Its pulse lies just lateral to the flexor carpi radialis tendon. Collateral flow is checked first with the modified Allen test:
- Compress both arteriesradial and ulnar, at the wrist
- Clench and open the fistthe palm blanches
- Release the ulnar arterykeep the radial compressed
- Watch the palmprompt return of color indicates adequate ulnar collateral flow
Gluteal injections. The sciatic nerve leaves the pelvis below piriformis and runs through the inferomedial buttock, so dorsogluteal injections go in the upper outer quadrant. An injection placed too high and medial can injure the superior gluteal nerve, weakening gluteus medius and producing a Trendelenburg gait. The ventrogluteal site (gluteus medius and minimus, between the anterior superior iliac spine and the iliac crest) avoids major nerves and vessels; in infants, the anterolateral thigh (vastus lateralis) is preferred.
Deltoid injections. Injections go into the upper deltoid, 2–3 finger-breadths (about 5 cm) below the acromion. The axillary nerve wraps horizontally around the surgical neck of the humerus beneath the deltoid; injury paralyzes the deltoid and numbs the lateral shoulder. Injections placed low and posterior on the arm risk the radial nerve in the spiral groove.