Introduction
Fluid therapy is indicated in critical patients. When intravenous catheterization fails or when veins are too small or too fragile, an intraosseous or IO catheter is an excellent option in small mammals.
Video produced by Dr. M. Scott Echols and narrated by Dr. Susan Orosz.
Equipment needed
- Select a 25- to 18-gauge spinal or hypodermic needle long enough to extend one-third to one-half the length of the medullary cavity.
- A 20- to 22-gauge 1 to 1.5 inch spinal needle is appropriate for most ferrets, guinea pigs, and chinchillas.
- If a hypodermic needle is used, thread the needle with cerclage wire or stainless steel suture to serve as a stylet.
- Clippers
- Sterile gloves
- Surgical blade, no. 11 or 15
- Local anesthetic
- Heparinized saline
- Suture, 3-0 to 4-0 non-absorbable
- Needle holders
- Catheter cap or infusion plug
- Porous white tape
- Bandage material
Potential complications
Complications secondary to IO catheter placement are rare.
- A small amount of fluid leakage is considered acceptable.
- In rare instances, infection or fat or bone marrow emboli may develop.
Sites for intraosseous catheter placement in small mammals
- Proximal humerus
Figure 1. Skeletal overlay in a guinea pig (Cavia porcellus). Click image to enlarge
- Proximal tibia
- Proximal femur (placement in this site allows the animal to remain ambulatory)
Step-by-step instructions for proximal femur:
- Intraosseous catheter placement is considered painful so provide preemptive analgesia. Heavy sedation or general anesthesia is also required unless the animal is extremely weak or minimally responsive.
- Place the animal in lateral recumbency.
- Identify landmarks for needle insertion and palpate the limb. Landmarks for the femur include the greater trochanter, the trochanteric fossa, and the body of the femur. Feel for a depression medial to the greater trochanter. Take your time identifying this depression as the extensive amount of muscle that covers this area can make palpation a bit challenging.
Figure 2. Palpate the depression medial to the greater trochanter. Click to enlarge
- Infuse local anesthetic to anesthetize the periosteum and overlying structures.
- Aseptically prepare the site.
- Make a stab incision over the insertion site.
Figure 3. Make a stab incision over the insertion site. Click image to enlarge.
- Grasp the needle securely between the thumb and first finger of your dominant hand. Hold the needle at a point approximately two-thirds down the length of the needle to increase the needle’s steadiness.
- Use a firm twisting motion to penetrate the proximal cortex with the needle as if you are placing an intramedullary pin.
- After entering the cortex, the needle should advance easily.
- Take care not to engage the opposite cortex.
- Remove the stylet and flush the needle immediately with up to 0.5 ml of heparinized saline since the marrow will rapidly clot. Avoid aggressive flushing as this increases the risk of fat or bone marrow emboli formation.
- Secure the catheter with butterfly tape and simple interrupted or horizontal mattress sutures.
Figure 4. Suturing the butterfly tape. Click to enlarge.
- Add additional tape around the hub in a criss-cross pattern as needed.
Intraosseous catheters may be left in place for up to 72 hours. Be sure to check catheter placement regularly.