Introduction

Intravenous access can be challenging when our patients are small or veins are constricted or collapsed as a result of severe hypovolaemia, shock or even cardiovascular standstill, i.e., death. With a venous cut-down the vein can be visualised, which helps with the introduction of the catheter. With some training and experience this can be a very effective technique. However, even this technique is not always successful.

Some alternative routes have been suggested with some considered to be better than others.

Intratracheal / Endobronchial

Especially in cardiopulmonary resuscitation (CPR) the administration of resuscitation drugs via the bronchial tree has been advocated for decades in the absence of venous access. However, the limited number of studies looking at effectiveness suggest that even a dose ten times the intravenous dose does not always result in effective plasma levels. This route should be abandoned.

Intracardiac

Also in CPR intracardiac administration of drugs has been used to deliver the resuscitative drugs directly to the heart. The intracardiac route should be considered obsolete for several reasons: interruption of thoracic/cardiac massages; myocardial trauma or damage to the coronary arteries with risk of cardiac tamponade; refractory ventricular fibrillation if epinephrine is injected in the myocardium.

Intraperitoneal

The interperitoneal route is still used by many veterinarians, especially in exotic animals. The peritoneum certainly has a large surface area that is well vascularised and has the potential to absorb fluids and medications. However, in hypovolaemia or shock, perfusion is severely reduced and there is also the risk of damaging internal organs, especially the intestinal tract.

Mucosal: Sublingual and Conjunctival Sac

This route has been developed for only a limited number of drugs such as nitroglycerine spray sublingually or the apomorphine tablets via the conjunctival sac.

Intraosseous or Intramedullar

Intraosseous (IO) access has become a recommended alternative in paediatric medicine and advanced life support. First described in 1922, a lot of experience was gained during World War II. However, this knowledge was lost after the war, only to be rediscovered in the 1980s. In veterinary medicine this technique is also gaining ground: it is, besides a venous cut-down, the only real alternative to venous catheterisation.

Protected by the bone, bone marrow vessels do not collapse during circulatory failure. Drugs and fluids administered find their way easily through the medullary capillaries, the large medullary veins, and the nutrient and emissary channels into the venous circulation.

Indications

In humans, IO access is the first alternative to failed intravenous access in small neonates and babies. In an emergency situation (cardiac arrest) the IO route is becoming the route of choice after an unsuccessful intravenous access attempt. In veterinary medicine similar considerations may apply. Certain medical conditions may favour the IO route even further: peripheral thrombosis, peripheral oedema, status epilepticus, obesity and burns. Furthermore IO access also offers an alternative for intravenous blood sampling.

Materials

 Hypodermic or epidural needle with trocar (18–30 gauge (neonate); 18–22-gauge (cat, small dog, bird): they can be used in younger animals with relatively 'soft' bones. However, the absence of a trocar can cause the bone cortex to obstruct the hypodermic needle. Replacing the needle with one that has a slightly larger diameter often resolves this problem.

 Bone marrow needle with trocar: they have a handle which makes it easier to introduce them. Significant effort can be required from the clinician placing the needle when used in adult animals.

 F.A.S.T.1 (Bed of Nails) (Pyng Medical, Richmond, BC, Canada): only used in sternum of adult humans.

 Bone injection gun (B.I.G.) (WaistMed Ltd, Houston, TX, USA): this gun shoots the bone marrow needle into the medulla. Although this makes access effortless, the diversity in bone size and strength makes it difficult to choose the right needle size and choose the power of the shot.

 Battery Powered Drill (EZ-IO) (VidaCare, San Antonio, TX, USA; available via Mila International Inc.): this device drills the needle into the medulla through the cortex. It is easy and effortless to use and placement is well controlled.

All dedicated access devices are relatively expensive but when it is possible to reuse them, this disadvantage can be resolved easily.

Access Points

 The flat craniolateral plane distal to the greater tubercle of the humans and proximal to the attachment of the deltoid muscle (CPR)

 Advantages: no muscle over the insertion point; close to the heart; easy access

 The flat medial surface of the tibial tuberosity (1–2 cm distal to the tibial plateau)

 The trochanteric fossa of the femur (young animals for fluid resuscitation).

 Advantages: possible to stabilise and leave for a longer period; easy access

 Disadvantage: damage to ischiadic nerve

 The cranial dorsal iliac spine

 The sternal manubrium

The choice of a particular site depends on the experience and preference of the clinician, accessibility of the insertion site and the mobility of the patient.

Technique

Surgically prepare the insertion site and, if the situation allows for a 5–10 minute wait, deposit some lidocaine subcutaneously along the path the needle will traverse to reach the bone cortex. This may also numb the periosteum. Puncture of the skin can be facilitated by making a small stab incision.

The needle must be positioned perpendicular to the surface of the bone. When placed manually it is important to hold the wrist rigid and rotate the length of the needle in a clockwise/counterclockwise manner; keep the needle and lower arm in one straight line. Use your other hand to stabilise the bone or limb and for orientation. First apply minimal pressure to establish grip; then increase pressure to pass the needle through the cortex. There is a clear loss of resistance when the medulla is reached.

Needle position can be checked in several ways:

 The needle is stable in the bone (follows the movement of the limb)

 Bone marrow at the tip of the trocar when it is removed from the needle

 Aspiration of bone marrow

 Bone marrow comes out of the needle

 Injection without resistance

 Effect of IO-administered medication

The needle has to be fixed if it has to stay in place for a longer period and the patient is/will be mobile. Different techniques can be used depending on the type of needle, the location and size of the animal including suture, tape butterfly and dedicated fixation devices. For maintenance of the catheter the same stringent guidelines apply as for intravenous catheters.

Pain can be an issue in awake patients. Pain during placement is minimal but pain can be significant with flushing, aspiration and infusion. This pain can be reduced by administering a bolus of lidocaine before use of the needle (0.5 mg/kg lidocaine in small steps: 0.2 ml per step, one step per 15 seconds).

Use

Always flush to check patency before starting the infusion. An IO catheter can be used for administration of fluids, drugs and blood sampling for analysis. How efficient the route in animals is compared to central or peripheral venous access is not known. In humans drugs reach the heart via the proximal humerus and sternum more quickly than via a peripheral venous catheter.

In combination with a pressure bag, access via the tibial tuberosity compares to a 21-gauge and via the proximal humerus or sternum with a 16-gauge needle. With 300 mmHg of pressure speeds of 29 ml/min (proximal tibia) in puppies, 47 ml/min in foals, 44 (proximal tibia) to 77 (proximal humerus) ml/min in pigs and 15 (proximal tibia) to 83 (proximal humerus) ml/min in human adults can be reached.

Anything that can be administered safely through a peripheral catheter can be given via an IO needle. The dose is the same as for the venous route. To aid in moving the drug out of the medulla into the venous system during CPR the needle is flushed after drug administration with 5–50 ml of an isotonic crystalloid.

Samples for laboratory examination can also be taken from the needle. As with a venous catheter the initial aspirate has to be discarded.

Reference ranges are similar to venous sampling. Potassium and glucose need to be interpreted with some caution. White blood cell count is higher. Blood gas results are between the arterial and venous values. The infusion of fluids and drugs may have influence on the biochemical results.

Complications

Complications are limited: extravasation (leakage, wrong position of the needle during insertion, needle displacement, or penetration of the cortex on a previous attempt), compartment syndrome (infusion rate too high), bone fracture, failure (needle or operator), infection (< 0.6%). Fat emboli and growth plate damage do not occur in humans.

Contraindications

Contraindications are limited and consist of local infection (including skin infections), fractures, prostheses, absence of anatomical orientation points (obesity), recent IO (< 24 hours) use at the same insertion point/bone.

Acknowledgement

The author would like to acknowledge Dr C. Valtolina DipACVECC for her help in the preparation of these notes.

References

1.  Giunti M, Otto CM. Intraosseous catherization. In: Silverstein DC, Hopper K, eds. Small Animal Critical Care Medicine. St Louis, MI: Saunders Elsevier, 2009:263–267.

2.  Otto CM, Kaufman MG, et al. Intraosseous infusion of fluids and therapeutics. Compendium on Continuing Education for the Practicing Veterinarian 1989;11:42.