13.1 Central Venous Catheterization, Arterial Lines & Intraosseous Access

Central Venous Catheterization, Arterial Lines & Intraosseous Access

VTS Critical Concept: In the Veterinary Emergency and Critical Care (VECC) setting, vascular access is the primary lifeline for resuscitation, advanced hemodynamic monitoring, and metabolic support. When standard peripheral intravenous catheters fail or are physiologically inadequate, critical care veterinary technicians must rapidly execute and maintain advanced vascular access—including Central Venous Catheters (CVCs), direct continuous arterial lines, and intraosseous (IO) infusion lines.

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1. Central Venous Catheterization (CVC)

Clinical Indications for Central Venous Access

A Central Venous Catheter (CVC) is defined as an intravenous catheter whose distal tip resides in the cranial or caudal vena cava immediately adjacent to the right atrium. Standard peripheral veins (cephalic, saphenous) are prone to phlebitis, thrombosis, and extravasation when exposed to extreme osmolarities or vasoactive compounds. The major clinical indications for CVC placement include:

• Hyperosmolar Infusions ($>600\text{ mOsm/L}$): Peripheral veins rapidly develop chemical thrombophlebitis and endothelial sloughing when exposed to solutions exceeding $600\text{ mOsm/L}$. Central veins exhibit high blood flow velocity, rapidly diluting hypertonic solutions.
• Total Parenteral Nutrition (TPN): Standard complete TPN formulations frequently exhibit osmolarities between $1,000-1,500\text{ mOsm/L}$ (due to concentrated dextrose, amino acids, and lipids) and must strictly be administered via a dedicated central venous lumen.
• Concentrated Potassium Infusions: Potassium chloride infusions exceeding $0.5\text{ mEq/kg/hr}$ or peripheral concentrations $>60\text{ mEq/L}$ cause severe peripheral vein pain and sclerosis; central lines allow safe, rapid dilution.
• Central Venous Pressure (CVP) Monitoring: Direct hydrostatic pressure measurement within the cranial vena cava / right atrial junction.
• Serial Blood Draws: Eliminates repetitive venipunctures in coagulopathic, critically stressed, or hematoma-prone patients.
• Multiple Incompatible Continuous Rate Infusions (CRIs): Multi-lumen CVCs provide anatomically separate channels (e.g., proximal, medial, distal ports) that exit at different levels along the catheter, allowing concurrent infusion of physically or chemically incompatible drugs (such as vasoactive catecholamines, insulin, and calcium gluconate) without lumen mixing.

Catheter Selection & Anatomic Routes

[ Multi-Lumen CVC Port Architecture & Staggered Exit Points ]

 Proximal Port (18-20G)  ──► Exits 4-5 cm from tip  ──► Vasoactive CRIs / Sedation
 Medial Port (18-20G)    ──► Exits 2-3 cm from tip  ──► TPN / Hyperosmolar Fluids
 Distal Port (14-16G)    ──► Exits at catheter tip  ──► CVP Monitoring / Blood Sampling / Colloids
 ═══════════════════════════════════════════════════════════════════════════════════════════════►

The Modified Seldinger Technique (Guidewire-Assisted)

The Modified Seldinger Technique is the clinical standard for placing multi-lumen central venous catheters:

1. Patient Preparation & Maximal Sterile Barrier Precautions: Place the patient in lateral recumbency with the neck extended. Prepare a wide surgical field centered over the external jugular vein with a $2%$ Chlorhexidine gluconate in $70%$ isopropyl alcohol surgical scrub. The veterinary technician wears a surgical cap, mask, sterile gown, and sterile gloves, and places a full-body sterile drape over the field.
2. Introducer Needle Venipuncture: Insert the introducer needle (or over-the-needle catheter, typically 18-20G) into the jugular vein at a $30-45^\circ$ angle while applying gentle negative pressure with a syringe until flash of dark venous blood confirms intraluminal entry.
3. J-Tip Guidewire Insertion: Remove the syringe and advance the flexible "J-tip" guidewire through the needle into the vein. The wire should advance smoothly without resistance. Never force the guidewire against resistance, which can perforate the vessel wall or induce cardiac dysrhythmias if advanced too deeply into the right ventricle.
4. Introducer Removal & Skin Nick: While maintaining continuous manual control of the guidewire, remove the introducer needle. Make a small #11 scalpel stab incision at the skin entry site directly adjacent to the wire to ease passage through the dermis.
5. Vessel Dilator Passage: Advance the rigid vessel dilator over the guidewire through the skin and vein wall with a gentle twisting motion to create a subcutaneous tract. Advance only into the vessel lumen; do not advance the dilator its full length. Remove the dilator while maintaining wire position.
6. CVC Advancement Over Guidewire: Thread the multi-lumen catheter over the guidewire. Ensure the distal tip of the guidewire emerges from the distal catheter hub before the catheter tip enters the skin (the "Never Let Go of the Wire" cardinal rule). Advance the catheter over the wire into the cranial vena cava.
7. Guidewire Removal & Port Verification: Withdraw the guidewire completely. Aspirate dark venous blood from all lumens, flush with heparinized saline (1-2 U/mL), and attach injection caps or needleless connectors.
8. Securing & Radiographic Confirmation: Secure the catheter wings to the skin using non-absorbable monofilament suture (2-0 or 3-0 nylon) using a Chinese finger-trap or purse-string technique. Apply a sterile chlorhexidine-impregnated sponge patch (Biopatch) over the insertion site and cover with a transparent occlusive dressing (Tegaderm). Confirm catheter tip placement via thoracic radiography: the tip should sit within the cranial vena cava at the level of the 4th to 5th intercostal space, strictly cranial to the cardiac silhouette.

Catheter-Related Bloodstream Infection (CRBSI) Prevention

Catheter-Related Bloodstream Infections (CRBSI) represent one of the most severe iatrogenic complications in veterinary critical care, carrying high morbidity and mortality. Veterinary technicians are the primary defenders against CRBSI through rigorous aseptic catheter bundle practices:

• "Scrub the Hub" Protocol: Every access of any catheter port, stopcock, or needleless connector must be preceded by vigorous mechanical scrubbing for at least 15 to 30 seconds using a sterile $2%$ Chlorhexidine gluconate in $70%$ isopropyl alcohol wipe, followed by allowing 30 seconds of active air-drying time. Wiping with dry gauze or touching ports with non-sterile hands introduces skin flora directly into the central circulation.
• Lumen Dedication: Maintain strict separation of infusions. Never aspirate blood or administer intermittent boluses through a designated TPN line.
• Heparin Flushes vs. Normal Saline: Maintain unused lumens with $1-2\text{ U/mL}$ heparinized saline (or preservative-free $0.9%$ NaCl) every 4 to 8 hours using a positive-pressure flush technique (closing the clamp while still depressing the syringe plunger to prevent backward aspiration of blood into the catheter tip).
• Daily Site Surveillance: Inspect the insertion site daily through the transparent dressing for erythema, purulent exudate, swelling, or pain. Replace dressings immediately if soiled, loose, or wet.

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2. Arterial Lines (Invasive Direct Arterial Monitoring)

Clinical Indications & Anatomic Sites

Direct arterial catheterization connects an indwelling arterial cannula to an electronic pressure transducer or sampling system. It is indicated for:

1. Continuous Beat-to-Beat Arterial Blood Pressure Monitoring: Real-time systolic, diastolic, and mean arterial pressure assessment during severe hemodynamic instability (e.g., septic shock, polytrauma, cardiogenic shock, high-dose vasopressor titration).
2. Serial Arterial Blood Gas (ABG) Sampling: Evaluating pulmonary gas exchange ($PaO_2$, $PaCO_2$, $PaO_2/FiO_2$) and acid-base kinetics in mechanically ventilated or acute respiratory distress syndrome (ARDS) patients without repeated painful arterial punctures.

[ Primary Arterial Catheterization Sites in Small Animals ]

1. Dorsal Pedal Artery (Most Common & Preferred)
   • Located along the dorsomedial aspect of the metatarsus
   • Excellent collateral flow via plantar arches; easily palpated and immobilized

2. Palmar / Radial Artery
   • Medial aspect of the distal antebrachium
   • Used when hindlimbs are traumatized or inaccessible

3. Auricular Artery (Intermediate Branch)
   • Dorsal surface of the pinna in large dogs with long ears
   • Common in calves, pigs, and floppy-eared canine breeds

Continuous Pressurized Flush System Setup

Arterial pressure easily overcomes simple gravity drip sets. A specialized continuous flush system is mandatory:

• Pressurized Bag: A $500\text{ mL}$ or $1,000\text{ mL}$ bag of $0.9%$ Sodium Chloride with $1-2\text{ U/mL}$ heparin is placed inside an inflatable pressure infuser bag pumped to $300\text{ mmHg}$.
• Continuous Micro-Flow Restrictor: The system delivers a continuous micro-flush of $3-4\text{ mL/hr}$ through rigid, non-compliant pressure tubing to maintain catheter patency and prevent micro-thrombi formation without volume overloading small patients.

[ Continuous Arterial Pressure Monitoring Circuit ]
 ┌──────────────────────────┐
 │ 0.9% NaCl + Heparin Bag  │
 │ (Pressurized to 300 mmHg)│
 └────────────┬─────────────┘
              │
              ▼
 ┌──────────────────────────┐     ┌───────────────────────┐
 │ Electronic Pressure      ├────►│ ICU Monitor           │
 │ Transducer (Zeroed)      │     │ (Real-Time Waveform)  │
 └────────────┬─────────────┘     └───────────────────────┘
              │ (Rigid Non-Compliant Tubing)
              ▼
 ┌──────────────────────────┐
 │ Dorsal Pedal Arterial    │
 │ Catheter (20-22G)        │
 └──────────────────────────┘

Strict Arterial Line Safety Rules

VTS Clinical Hazard: Catastrophic Arterial Injection: NEVER, UNDER ANY CIRCUMSTANCES, INJECT MEDICATIONS, ANESTHETIC AGENTS, SEDATIVES, ANTIBIOTICS, OR AIR INTO AN ARTERIAL LINE.

• Intra-arterial drug injection triggers intense, immediate arterial vasospasm, acute endothelial sloughing, massive microvascular thrombosis, distal limb ischemia, compartment syndrome, and severe ischemic necrosis resulting in gangrene and mandatory limb amputation.
• MANDATORY SAFETY PROTOCOL: All arterial lines must be wrapped in bright red or orange warning tape clearly labeled: "ARTERIAL LINE — NO MEDICATIONS / NO AIR". Use dedicated stopcocks with red caps.

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3. Intraosseous (IO) Access

Indications & Pediatric Applications

Intraosseous (IO) infusion involves inserting a specialized rigid cannula directly into the non-collapsible vascular sinusoids of the medullary bone cavity. It is the primary emergency vascular access route when:

• Peripheral IV access cannot be successfully obtained within $90-120\text{ seconds}$ in patients experiencing profound circulatory collapse, cardiopulmonary arrest (CPA), severe hypovolemic/septic shock, or status epilepticus.
• Treating pediatric and neonatal puppies and kittens whose tiny peripheral veins are collapsed, fragile, or inaccessible.
• Severe polytrauma, circumferential burns, or extensive limb edema precludes peripheral catheterization.

Anatomic Insertion Sites & Equipment

[ Intraosseous Needle Insertion Landmarks ]

   1. Proximal Femur (Trochanteric Fossa)
            Greater Trochanter ──► [ Needle Enters Fossa ]
                                        │ (Parallel to shaft)
                                        ▼ Medullary Canal

   2. Proximal Tibia (Tibial Tuberosity)
            Tibial Tuberosity  ──► [ Flat Medial Shelf ]
                                        │ (Angled 60-90° distally)
                                        ▼ Medullary Canal

Equipment, Flow Rates & Delivery Kinetics

• Equipment Options:
  • Manual IO needles with internal stylets (Jamshidi, Illinois sternal/iliac needle, or 18-22G spinal needles with stylets in neonates). The stylet prevents bone cores from plugging the lumen during cortical penetration.
  • Power-driven systems (EZ-IO battery-powered drill driver) utilizing specialized 15-gauge bevel-tipped needles for rapid, controlled cortical penetration within 5-10 seconds.
• Vascular Pharmacokinetics: The medullary bone space is lined with non-collapsible venous sinusoids that drain directly into the central venous circulation via nutrient veins. Drug and fluid pharmacokinetics, bioavailability, and onset of action via IO access are 100% identical to central venous administration.
• Permissible Infusions: ALL resuscitation drugs (epinephrine, vasopressin, atropine), whole blood, packed RBCs, plasma, analgesics, antibiotics, and crystalloid/colloid boluses can be given IO. For rapid fluid boluses, pressure bags must be utilized because rigid bone cortex provides high resistance to passive gravity flow.
• Contraindications & Complications: Never place an IO needle into a fractured bone, an infected skin site (osteomyelitis risk), or a bone where a previous IO attempt failed (fluid extravasates from the prior cortical hole into surrounding muscle, causing compartment syndrome).