PREFACE
In daily practice, worldwide, the veterinarian faces conditions where the need for personnel (especially skillful) or specialized equipment is imperative. Because of such shortages, some cases are not treated adequately or even mistreated. We could mention problems in newborn animals, accidents, animals in shock, or the inability to administer fluids after several days of hospitalization. The classical approach to the circulatory system via venous access, some times has been proved impossible or time consuming. And there are cases where time or the unhampered fluid administration is of vital importance.
The veterinarian or his staff considers the intraosseous approach as a dangerous or complicated way of administering fluids and faces the method as an intraoperative procedure. The purpose of t his lecture is to render the relevant medical staff familiar with the method and the techniques of the intraosseous infusion.
DEFINITION
The intraosseous or intramedullary infusion is a rapid, safe and effective alternative for delivering fluids and medications to the systemic circulation especially when peripheral circulatory collapse makes venous access difficult or impossible.
OPTIONS
If peripheral venipuncture cannot be accomplished, central venous catheterization or venous cutdown procedures are the options. But both are time consuming and hematoma formation, thrombosis, thrombophlebitis and hemorrhage are potential complications. Animals in shock, neonate animals, cats or even birds are the common patients we use intraosseous techniques on.
ADVANTAGE
The marrow cavity is comprised of a fibrous stroma supporting bone marrow elements, interspersed with an extensive collection of venous sinuses. These intramedullary blood vessels are held open by the rigid non-collapsed bony wall. During hypovolemic conditions the intramedullary blood vessels do not collapse. Another vital parameter is the certain dimensions (diameter) of the shaft of the bones, which make the rapid access to the circulation more feasible. This is quite useful in small animals like newborn, cats or birds. The rigid construction of the bony wall renders it durable to the irritation from fluids such as hypertonic or parenteral feeding solutions, saving places for future intravenous usage. Finally, some preferable places, as the inter-trochanteric fossa of the proximal femur, give moveability or even comfort to the animals during their hospitalization especially when they are confined inside a cage.
PREFERABLE SITES
Bone marrow access sites in the dog and cat include:
The inter-trochanteric fossa of the proximal femur
The flat medial aspect of the proximal tibia distal to the tibial tuberosity and the proximal tibial growth plate (The proximal tibia is the most frequently used site for intraosseous infusion in human pediatric medicine.)
The proximal shaft (cranial aspect of the greater tubercle) of the humerus
The cranial aspect of the mid-diaphyseal ulna
The first two and especially the first one are the most convenient sites for the veterinarian performing the procedure and the less distressful site for the hospitalized animal.
IMPLEMENTS
Various infusion needles or catheters can be used for that purpose.
In the very young animal, the cortical bone may be soft enough to allow the use of a standard hypodermic needle. In mature animals either a spinal needle or a commercially available intraosseous needle (Cook products) is used. The bone marrow needles used for diagnostic collection of bone marrow work equally well. There are cases in which even a combination of a large bore metal needle with a plastic--shorter bore--one placed inside can be used quite efficiently.
In one experimental study the Bone Injection Gun (BIG) was used as an alternative way for placement of intraosseous cannulas with positive results concerning the rapidity of the placement.
PRECAUTIONS
Bones used for intraosseous infusion should be intact (not fractured) and the skin over the insertion site should be healthy and unbroken to avoid contamination of the site and especially the bone (osteomyelitis) with bacteria.
PROCEDURE
At one of the above mentioned sites, the skin is clipped and prepared aseptically.
Local anaesthetic (2% Lidocaine) is injected into the skin, to the subcutis over the insertion point and then down onto the periosteum.
A small stab incision is made in the skin.
The needle or device is inserted, pointing in a distal direction. Sometimes rotation may facilitate the entrance (About a quarter turn at a time). An initial opening of the periosteum with a smaller drill or a Steinmann pin can be made in some mature patients. Certain commercially available devices reduce the amount of axial pressure that is needed and therefore reduce the complication of leakage at the insertion site.
When the needle enters the near cortex it must be firm and steady.
The stylet or the inside plastic needle is removed.
The needle is aspirated and flushed with heparinized saline.
An infusion set or T-connector is connected and the needle is secured and bandaged in place.
The normal rate should not exceed 11ml/min with gravity flow. Gravity flow through a single catheter is used for animals that weigh up to 10 kg.
With pressurized infusion systems ( up to 300 mmHg), the flow rate should not exceed 24 ml/min Pressurized flow through a single catheter or gravity flow through multiple catheters is used for animals that weight between 10-20 Kg. Pressurized flow through multiple catheters is reserved for animals above 10 kg in shock.
When not in use, the system should be flushed periodically (every 6 hours) with heparinized saline. The bone marrow needle can be left in place for the same duration as IV catheters. (A new needle should be placed into a different bone every 72 hours.) The same bone, under extreme conditions, can be reused at another location once the original site has occluded and healed. This will occur after approximately 36 hours. But this is something that should be avoided since the risk of infection or damage (even fracture) of the bone increases dramatically. Most often the administration route is changed to the intravenous one once the acute phase (shock) has been successfully treated.
COMPLICATIONS
Infection (osteomyelitis).
Damage to the growth plates (juvenile patients).
Leakage of administered fluids into the surrounding tissues (subcutaneous or subperiosteal) following poor needle placement technique.
Fat embolization.
Malposition. In neonatal animals one has to be careful not to introduce the needle into the proximal portion of the bone and exit the distal aspect of the bone into the joint cavity.
Partial occlusion of the intraosseous needle.
Inability to enter the marrow cavity.
Damage to the local nerves (sciatic).
Localized cellulitis.
Subcutaneous abscesses (especially in human patients).
INTRAOSSEOUS USED AGENTS
Most drugs and fluids that can be administered intravenously can be given by this route. Drugs administered via this route enter the systemic circulation rapidly. Numerous pharmacokinetic and clinical studies have shown no significant differences in plasma levels when medications were given by either the intravenous or intraosseous route.
OUR OWN EXPERIENCE
According to the experience in our clinic, the most common side effect is the leakage of the fluids (even in a properly positioned needle) especially when a very rapid infusion rate is used. But this can work as a safety valve to avoid the accidental administration of excessive amounts of fluids. No animal suffered infection or exhibited lameness of any cause. Only in one case the animal died with symptoms similar to those of fat embolism following the administration of parenteral feeding solution. We have faced no cases of infection even in severely debilitated animals or in bad hygiene conditions. The typical way of using this method is the initial intraosseous administration and change to the intravenous administration as soon as the condition of the animal permits. But it is the preferable route when hypertonic fluids and especially the parenteral solutions are used.
References
1. Lesley king and Richard Hammond: BSAVA Manual of Canine and Feline Emergency and Critical Care
2. Veterinary Clinics of North America: Critical Care/Nov 89: Advances in Fluid and Electrolyte Disorders/May 98
3. Olsen D, Packer BE, Perrett J, Balentine H, Andrews CA: Evaluation of the bone injection gun as a method for intraosseous placement for fluid therapy in adult dogs.