📝 STANDARD DESCRIPTION:
Clinical Blocking Protocols
1. Bier Block (IVRA): Gold standard for foot surgery. Tourniquet at mid-metacarpus, 20-30mL lidocaine in dorsal common digital vein. Max 90 mins.
2. High Volar Block: Median (medial elbow, cranial to brachial artery + Ulnar (caudal forearm, groove between FCU/Ulnaris Lateralis).
3. Four-Point Block: Blocks dorsal (radial) and palmar (median/ulnar) coverage at fetlock level.
4. Ring Block: Circumferential at mid-metacarpus—simple but fails for deep bone pain.
📚 DETAILED DESCRIPTION:
REGIONAL ANESTHESIA IN BOVINE FORELIMB
Regional anesthesia is critical for digit surgery (amputation, corn removal, septic arthritis lavage). Unlike equine practice (diagnostic lameness localization), bovine blocks are primarily therapeutic—to allow standing surgery.
ANATOMICAL CONSIDERATION:
Cattle stand on TWO digits (III and IV) vs one in horses. Each digit has:
• Axial side: Facing interdigital cleft
• Abaxial side: Facing outward
NERVE DISTRIBUTION TO DIGITS:
• Median: Axial sides of BOTH digits + Abaxial side of medial digit (III)
• Ulnar: Abaxial side of lateral digit (IV)
Implication: Simple ring block insufficient for deep structures—must target specific nerves.
BLOCK TECHNIQUES:
1. INTRAVENOUS REGIONAL ANESTHESIA (IVRA / Bier Block) - GOLD STANDARD
• Target: All distal nerves via vascular delivery
• Landmark: Dorsal Common Digital Vein or any accessible distal vein
• Equipment: Rubber tourniquet (ESmarch bandage or wide rubber tubing) at mid-metacarpus
• Agent: 20-30mL 2% Lidocaine (avoid epinephrine)
• Mechanism: Anesthetic diffuses from vessels to perivascular nerves
• Advantages: Complete desensitization distal to tourniquet, bilateral, reliable
• Limitations: 90-minute maximum (ischemia risk), proximal sites unsafe
2. HIGH VOLAR BLOCK (Proximal Palmar)
Median Block:
• Site: Medial proximal forearm, just distal to elbow
• Landmark: Cranial to brachial artery (palpable pulse)
• Needle: 20G x 1.5 inch
• Volume: 15-20mL
• Critical: ASPIRATE before injection (avoid intra-arterial)
• Effect: Medial digit (III), axial aspects both digits, flexor muscles
Ulnar Block:
• Site: Caudal distal forearm, ~10cm proximal to accessory carpal
• Landmark: Palpable groove between Flexor Carpi Ulnaris and Ulnaris Lateralis
• Volume: 10mL
• Effect: Lateral digit (IV) abaxial aspect, lateral skin
3. FOUR-POINT BLOCK (Bovine Modification)
For complete desensitization at fetlock:
1. Dorsal Metacarpal: Radial branches—subcutaneous infiltration across dorsal fetlock
2. Axial Palmar: Median branches—deep injection in interdigital space/axial groove
3. Abaxial Sesamoid (Medial): Median nerve—abaxial aspect medial proximal sesamoid
4. Abaxial Sesamoid (Lateral): Ulnar nerve—abaxial aspect lateral proximal sesamoid
4. RING BLOCK
• Technique: Circumferential subcutaneous infiltration at mid-metacarpus
• Volume: 30-40mL
• Limitations: Blocks only superficial radial, ulnar, median cutaneous branches. Often fails for deep bone/joint pain. High volume required.
5. SPECIFIC NERVE TARGET BLOCKS
Abaxial Sesamoid Block:
• Single digit procedures (claw amputation)
• Targets: Palmar Digital Nerves (median/ulnar distal continuations)
• Site: Abaxial surface of proximal sesamoid bones at fetlock level
• Volume: 5mL per site
• Effect: Complete anesthesia of specific digit distal to block
// COMPARATIVE ANALYSIS
| HORSE |
IVRA similar but volumes adjusted for size. 'Low 4-point' uses different landmarks (buttons of splint bones). |
| DOG |
Regional blocks less common; general anesthesia preferred. Similar median/ulnar anatomy but different landmarks. |
CLINICAL RELEVANCE
Safety Protocols: IVRA tourniquet must be released SLOWLY to prevent lidocaine toxicity (seizures). Never exceed 4mg/kg lidocaine total dose. Troubleshooting: If block fails, usually due to insufficient volume (bovine tissues require MORE than equine) or injection too proximal (tourniquet effect blocks diffusion). Alternative: When tourniquet contraindicated (infection, dermatitis), use specific nerve blocks rather than IVRA.
