Veterinary Point of Care Ultrasound (POCUS) Practice Flashcards

INTRODUCTION TO VETERINARY POINT OF CARE ULTRASOUND (POCUS)

  • Definition of POCUS: The acquisition, interpretation, and immediate clinical integration of ultrasonographic imaging performed patient-side by an attending clinician. It is a problem-based assessment based on Bayes’ theorem of pre-test probabilities. In contrast to consultative specialist exams, POCUS answers focused questions rather than assessing all structures of an organ.

  • POCUS vs. FAST: The Focused Assessment with Sonography for Trauma (FAST) was developed at Tufts in 19991999 and published in 20042004 by Boysen et al. FAST primarily searches for free fluid and pneumothorax. POCUS is broader, incorporating assessments of lung pathology, basic cardiac function, volume status, renal pelvic dilation, and ultrasound-guided procedures.

  • Comparison of Specialists vs. POCUS:     * Formal Ultrasound: Consultative, assesses all organs/anatomy, requires years of training, takes > 30-60\min, performed by specialists, patients are often stable, requires fur clipping and lateral/dorsal recumbency, uses gel.     * POCUS: Focused on binary questions, requires minimal experience, performed in < 5-10\min, performed by non-specialists (ER/General Practitioners), machine is taken to the patient, fur is rarely clipped, uses alcohol as a coupling agent, and patients are scanned in the most comfortable position.

  • Evidence and Clinical Impact: Human studies support that POCUS improves clinical decision-making. Combined with other findings, it confirms suspected diagnoses in up to 50%50\% of cases and supports diagnostic changes in 23%23\% of cases.

  • The 5 T’s of POCUS:     1. Trauma: Focused on injury detection.     2. Triage: Identifying immediate life-threatening conditions. Do not compromise patient safety; find the injury and correct it ASAP.     3. Tracking: Serial monitoring of progression/resolution or response to therapy.     4. Treatment/Therapeutic: Reducing complications during interventions.     5. Total Systemic POCUS: Screening of asymptomatic/stable patients prior to procedures or discharge.

  • Binary Questions: A key approach to POCUS is asking Yes/No questions. This reduces false positives and negatives. Examples include: "In this dyspneic cat, is there pleural effusion?"

MACHINE FUNCTIONS AND PROBE MANIPULATIONS

  • Essential Machine Functions:     1. Gain: Controls overall brightness. For lung scans, adjusting gain helps visualize the glide sign (easier to see if the pleural line looks "grainier"). Abdominal scans usually require higher gain than lung scans.     2. Depth: Determines how deep the beam penetrates. For lung scans, the pleural line should be in the proximal 1/31/3 of the image. For heart/abdomen, the organ of interest should be the middle 2/32/3 of the screen.     3. Frequency: Affects image quality and depth. High frequency provides better superficial resolution; low frequency penetrates deeper. Micro-convex curvilinear transducers often have adjustable frequencies.

  • Transducer Orientation: Every probe has an orientation marker corresponding to a symbol on the screen. The end with the cable is the "tail," and the contact surface is the "head."

  • The 5 Key Transducer Movements:     1. Fanning: Tail moves side-to-side (widest axis) while the head stays stationary.     2. Rocking: Tail moves side-to-side (shortest axis) like a rocking chair.     3. Sweeping: The entire probe moves in the short axis direction with a constant angle.     4. Sliding: The entire probe moves in the long axis direction across the body.     5. Rotating: Turning the probe on its axis (clockwise or counter-clockwise).

  • Scanning Axis:     * Longitudinal (Long): Long view relative to the organ.     * Transverse (Short): Short view relative to the organ, obtained by rotating the probe 90∘90^{\circ}.

ABDOMINAL POCUS

  • IndicATIONS: Trauma, unstable/emergency patients, triage, post-surgery monitoring, difficult anesthesia cases, and routine daily assessments.

  • Patient Positioning: Sternal or standing for unstable patients to avoid cardiovascular collapse. Lateral recumbency is preferred for stable patients. Dorsal recumbency is avoided in unstable patients.

  • Probe Selection: Micro-convex/curvilinear probe at 5 MHz5\,MHz (for patients > 15\,kg) and 7.5 MHz7.5\,MHz (for patients < 15\,kg).

  • Abdominal POCUS Protocol (5 Sites):     1. Subxiphoid / Diaphragmatico-Hepatic (DH): Caudal to the xiphoid. Targets: Diaphragm, liver, gallbladder, ventral stomach wall, caudal vena cava, pleural/pericardial space. Mirror image artifact distal to the diaphragm rules out pleural effusion.     2. Urinary Bladder / Cysto-Colic (CC): Long axis between pelvic limbs. Targets: Bladder (apex and body wall), colon. Fluid often gathers at the apex or between the bladder and body wall.     3. Right Paralumbar / Hepato-Renal (HR): Mid-lateral. Targets: Right caudal liver lobe, right kidney, intestines. Often requires intercostal scanning.     4. Left Paralumbar / Spleno-Renal (SR): Lateral. Targets: Spleen, left kidney, intestines. The kidney is usually found where the last rib meets the lumbar muscles.     5. Umbilical (5th View): Placed at the umbilicus at a 45∘45^{\circ} angle towards the table. Best for identifying small quantities of gravity-dependent free fluid.

  • Abdominal Fluid Score (AFS): Validated for post-trauma hemorrhage in lateral recumbency. AFS 11 means fluid at 1/41/4 sites; AFS 44 means fluid at all 4/44/4 sites. Patients with AFS 33 or 44 are significantly more likely to require blood transfusions.

  • Specific Abdominal Findings:     * Free Fluid: Appears as hypoechoic/anechoic triangles/sharp angles between organs.     * Pneumoperitoneum: Requires identifying the peritoneal lining, reverberation artifact, and the "enhanced peritoneal stripe sign" (hyper-echoic lining where air meets the peritoneum).     * Ileus: Cessation of motility. Normal motility is 4−54-5 contractions per minute at the stomach/duodenum. To diagnose, record for 1−31-3 minutes.     * Urine Production: Estimated via the formula Length×Width×Height (avg)×0.625\text{Length} \times \text{Width} \times \text{Height (avg)} \times 0.625. Height is averaged from transverse and longitudinal views.     * Gallbladder Halo Sign: Thickened edematous wall (double-rimmed). Indicators: Anaphylaxis, right-sided heart failure, pericardial effusion, or sepsis.     * Renal Pelvis Dilation (Cats): Short axis measurements. > 13\,mm is highly indicative of ureteral obstruction (e.g., ureteroliths). Grey zone is 7−13 mm7-13\,mm (may be pyelonephritis). Normal is 1−3 mm1-3\,mm.

PLEURAL SPACE AND LUNG POCUS (PLUS)

  • Scanning Protocol: The "S" shaped sliding pattern covers the dorsal, middle, and ventral thirds of the thorax bilaterally, plus the subxiphoid site.

  • The 5 PLUS Borders:     1. Caudal: Curtain sign.     2. Dorsal: Hypaxial muscles.     3. Cranial: Thoracic limb/scapula.     4. Ventral Pleural Border.     5. Ventral Lung Border (separated due to cardiac notch).

  • Normal PLUS Findings:     1. Bat Sign / Gator Sign: Identification of the pleural line between rib heads (ribs = wings, pleural line = body). Mnemonic BAT: Bone, Air, Transverse.     2. Glide Sign: Shimmering movement along the pleural line. Indicates the visceral and parietal pleura are in contact.     3. A-lines: Horizontal hyper-echoic reverberation artifacts equidistant from the pleural line. Indicates air below the pleural line (normal lung or pneumothorax).     4. B-lines: Vertical, laser-like white projections from the pleural line to the far field, moving with respiration, obscuring A-lines. ≤3\le 3 at a single site is normal.     5. Dry Lung: Presence of a glide sign and ≤3\le 3 B-lines.     6. Curtain Sign: The interface between the air-filled thorax and soft-tissue abdomen. Moves caudally during inspiration.     7. Lung Pulse: Mini-shimmering caused by the heartbeat radiating through lung tissue. Rules out pneumothorax.

  • Pathology Findings:     * Alveolar Interstitial Syndrome (AIS): "Wet Lung." Defined by > 3 B-lines at one site. Differentials include edema (CHF), contusions, or pneumonia. "Dry" B-lines can be caused by atelectasis or cellular infiltration.     * Pneumothorax: Diagnosis based on the absence of a glide sign and absence of B-lines at that site. The Lung Point is pathognomonic; it is the specific location where the lung re-contacts the parietal pleura, causing an intermittent glide sign.     * Pleural Effusion: Anechoic fluid between the chest wall and lung. Signs include the "Sail Sign" (lung flapping like a sail in fluid) or "Ski Slope Sign" (absence of fluid where the pleura slopes down).     * Lung Consolidation: Tissue-like patterns (hepatization). Findings include the "Shred Sign" (irregular border where air meets consolidation), air bronchograms (white dots/lines in tissue), and nodules (smooth circular consolidation).

CARDIAC POCUS

  • Key Windows:     1. Mushroom View: Right parasternal short axis at the level of the papillary muscles.     2. Fish Mouth View: Short axis at the mitral valve level.     3. Mercedes and a Whale View: Short axis at the heart base (Aorta = Mercedes sign, Left Atrium = Whale).

  • Left Atrium to Aorta Ratio (LA:Ao):     * Measured when the aortic valve is closed and the atrium is at its largest during systole.     * Normal: < 1.3 in cats; < 1.5 in dogs.     * Large: > 2.0 indicates significant cardiac disease. In dyspneic cats, a literal LA diameter > 16.5\,mm suggests heart failure.

  • Pericardial Effusion: Anechoic fluid surrounding the heart. Best seen at the subxiphoid window (rocking the probe until parallel to the dog) or the right parasternal view.

  • Volume Status (Mushroom View):     * Hypovolemia: "Pseudohypertrophy." The left ventricular lumen is small, and walls appear thick. LA:Ao≤1:1LA:Ao \le 1:1.     * Hypervolemia: Ventricular lumen is enlarged with normal contractility. LA:Ao≥2:1LA:Ao \ge 2:1.

  • Contractility: Subjectively assessed. Decreased contractility (e.g., DCM) is suspected if the LV walls look thin and the lumen decreases by ≤20%\le 20\% during contraction.

VASCULAR POCUS AND VASCULAR ACCESS

  • Caudal Vena Cava (CVC): Evaluated at the subxiphoid site, fanned to the right of midline.     * Euvolemia: Diameter varies by 20−60%20-60\% during respiration.     * Hypovolemia: Diameter changes by > 60\% or is severely collapsed/flat.     * Hypervolemia / Right Heart Failure: "Fat CVC." Diameter changes by < 20\%. Often associated with distended hepatic veins.

  • Vascular Access: Ultrasound guidance reduces attempts and time (4min⁡4\min vs 15min⁡15\min in human studies).

  • Techniques:     * In-Plane (Longitudinal): Catheter stylet followed in its entirety through the tissues. Excellent for keeping the tip in view but harder to master.     * Out-of-Plane (Transverse): Stylet appears as a white dot. The probe is slid distally to "chase" the needle tip until it enters the vessel lumen.

  • Chicken Phantom Model: A teaching tool made of a raw chicken breast sandwich. A modelling balloon (vessel) is placed between two breasts, wrapped in saran wrap. Used to practice the Seldinger technique (advancing a guide wire through a catheter into the vessel).