Philip R Judge BVSc MVS PG Cert Vet Stud MACVSc (Vet Emergency and Critical Care; Medicine of Dogs)
Introduction
Lung ultrasound (LUS) has become an indispensable extension of the physical exam. Using lung ultrasound, we are able to determine the presence of absence of intra-pulmonary fluid – represented by B-lines), consolidation of lung (shred sign or tissue/hepatisation of lung appearance), or pleural space disease, such as pneumothorax – indicated by loss of the glide sign – or pleural effusion. But how do we move from a simple qualitative assessment to a quantitative, repeatable metric for monitoring our patients?
A recent reliability study published in the Journal of Veterinary Internal Medicine by Oricco et al., titled “Lung ultrasound score in dogs and cats: A reliability study,” validates a new Lung Ultrasound Score (LUSS) for veterinary medicine. This score, adapted from human medicine, allows semi quantification of lung aeration loss with good reliability, regardless of the operator’s experience level. This provides a new tool to track patient progress more objectively.
What is the Lung Ultrasound Score (LUSS)?
The LUSS is a numerical system designed to quantify the loss of lung aeration. Instead of just noting the presence of B-lines, the LUSS evaluates the percentage of the pleural surface occupied by different ultrasound patterns. The total score assists with monitoring patient progress (improving = score decreases, vs. deteriorating = score increasing) over time.
The scoring system is based on four distinct levels of aeration loss, ranging from 0 (normal) to 3 (complete loss).
Scoring Key
LUSS 0: Normal aeration. The pleural surface is occupied by horizontal A-lines or a maximum of 2 individual B-lines.
LUSS 1: Mild loss of aeration. Vertical artifacts (B-lines), an irregular pleural line (IPL), or small subpleural consolidations involve ≤50% of the visualized pleural line.
LUSS 2: Moderate to severe loss of aeration. Coalescent B-lines, subpleural loss of aeration, or pleural effusion (causing atelectasis) involve >50% of the visualized pleural line.
LUSS 3: Complete loss of aeration. A trans-lobar tissue-like pattern (consolidation/atelectasis) or a large pleural effusion occupies the entire visualized field, with no aerated lung visible.
Image showing representative characteristics of each grade within the LUSS system, from LUSS grade 0 (left) to LUSS grade 3 (right) (Image: Oricco et al 2024)
The 8-Quadrant Protocol: Probe Placement
To ensure consistency, the study uses a standardized 8-quadrant protocol. The patient is positioned in sternal recumbency or standing. The hair is clipped, and ultrasound gel and alcohol are applied. The probe used should ideally be a high-frequency linear transducer.
The Map: Each hemithorax is divided into 4 quadrants. The 6th intercostal space is the boundary between cranial and caudal. The elbow is the boundary between dorsal and ventral.
The Scan Order:
Left Side: Caudal-dorsal -> Cranial-dorsal -> Cranial-ventral -> Caudal-ventral
Right Side: Caudal-dorsal -> Cranial-dorsal -> Cranial-ventral -> Caudal-ventral
The Technique:
Place the probe in each intercostal space, aligning it parallel to the ribs (transverse scan) – to reduce the interference of ribs in assessing lung structure. For each quadrant, a single cine loop is recorded by scanning each intercostal space within that quadrant in a zig-zag pattern. The goal is to explore the entire pleural surface of that quadrant.
Image showing the 4 quadrants of the chest wall for lung ultrasound evaluation
How to Assign the Score: A Step-by-Step Guide
When you review the video loop for a single quadrant, you are assessing the dominant pattern and its extent along the pleural line.
Watch the Entire Quadrant Loop: Do not dwell on a single “hot spot.” You are assessing the whole pleural surface within that quadrant.
- Identify the Dominant Pathology: Is it B-lines? An irregular line/shred sign? A consolidation?
- Estimate the Percentage: Estimate what percentage of the pleural line in that loop is affected by the pathology. This is the key distinction in this scoring system.
The study emphasizes that the distinction between a score of 1 and 2 is based on the extent of pleural involvement, not just the “coalescence” of B-lines.
LUSS 1 (≤50% involvement): This quadrant might show a few isolated B-lines, or even a small pocket of coalescent B-lines, as long as that pocket occupies less than half of the pleural line seen in the loop.
LUSS 2 (>50% involvement): This quadrant could have multiple single B-lines spread out over the majority of the pleural surface. Crucially, you don’t need coalescent B-lines to get a score of 2 if the single B-lines are widespread. Conversely, if you have coalescent B-lines confined to a very small area (<50%), the score remains 1.
Scoring Special Cases
Pleural Effusion and Atelectasis: If effusion is present but you still see aerated lung (even if atelectatic) touching the chest wall, score it based on the percentage of aerated lung affected. If the effusion lifts the entire lung lobe away from the chest wall, and you see no aerated lung in that quadrant (only fluid and possibly a tissue-like pattern), it is a LUSS 3.
Tissue-like Pattern: A small, peripheral subpleural consolidation is LUSS 1 if it occupies ≤50% of the pleural line. A large, trans-lobar consolidation filling the entire quadrant is LUSS 3.
Calculating the Total Score
Once you have scored all 8 quadrants (0-3 each), you simply add them together.
Minimum Score: 0/24 (all quadrants are normal)
Maximum Score: 24/24 (complete loss of aeration in all quadrants)
Summary
The LUSS offers a robust, reliable way to quantify pulmonary pathology. By focusing on the percentage of pleural involvement rather than just counting B-lines, a more physiologically relevant measure of aeration loss is obtained. There is good inter- and intra-rater reliability shown for this technique.
References:
Oricco, S., Medico, D., Tommasi, I., Bini, R. M., & Rabozzi, R. (2024). Lung ultrasound score in dogs and cats: A reliability study. Journal of Veterinary Internal Medicine, 38(1), 336-345.
Rademacher, N., Pariaut, R., Pate, J., Saelinger, C., Kearney, M. T., & Gaschen, L. (2014). Transthoracic lung ultrasound in normal dogs and dogs with cardiogenic pulmonary edema: a pilot study. Veterinary Radiology and Ultrasound 55(4), 447-452.
