Medical

Anterior Axillary Line (AAL)

A vertical anatomic landmark running from the anterior axillary fold downward along the chest wall. The 5th intercostal space at the anterior axillary line is the TCCC-doctrine site for needle decompression of tension pneumothorax and the standard site for finger thoracostomy and chest tube placement.

In the Field

The AAL site for needle decompression supplanted the older midclavicular line (MCL) site at the 2nd intercostal space as the TCCC-preferred location. The AAL site has thinner chest wall in most patients (especially muscular males), better needle penetration to the pleural space, and is the same anatomic location used for chest tube placement, which simplifies the transition to definitive care. TCCC 2026 lists both AAL and MCL sites as acceptable, but doctrinal preference and recent military trauma research favor the AAL site.

Common Mistake

Going too far posterior past the AAL toward the mid-axillary line, where chest wall thickness increases and there is no benefit. The other mistake is locating the 5th intercostal space too inferiorly. The 5th ICS at the AAL is approximately at nipple level in males and inframammary fold in females; lower locations risk diaphragm or upper abdominal injury, particularly during exhalation when the diaphragm rises.

Technical Detail

The anterior axillary line is one of the standard chest wall vertical landmarks. From anterior to posterior: midclavicular line (MCL), anterior axillary line (AAL), mid-axillary line (MAL), posterior axillary line (PAL), scapular line. The AAL runs vertically downward from the anterior axillary fold (the lateral edge of the pectoralis major muscle as it forms the anterior wall of the axilla). The 5th ICS at the AAL is identified by counting down from the sternal angle (2nd rib level) or by locating the nipple line in adult males (approximate level of 5th ICS). TCCC 2026 lists either the 5th ICS in the AAL or the 2nd ICS in the MCL for needle decompression; the AAL site is preferred by current evidence and is the same site as finger thoracostomy and chest tube placement.

Related Equipment

ARS for Needle Decompression (3.25 in.) image 0

ARS® Needle Decompression Kit (14 Ga x 3.25 in)

$12.99

Needle Decompression Indicator Kit (N.I.K.)

$35.00

SPEAR (Simplified Pneumothorax Emergency Air Release)

$41.99

Browse Categories

Needle Decompression Respirations

Related Terms

Midclavicular Line / Mid-Axillary Line Intercostal Space Needle Decompression Tension Pneumothorax

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