Comparison of 3 intraosseous catheter sites and methods of determining placement success in cadaver rabbits

Abstract

The study goals were to determine if intraosseous (IO) catheters can be placed with greater success into the humerus, femur, or tibia of cadaver rabbits, and to evaluate the accuracy of perceived success (PS) and objective clinical success (OCS) criteria against true intramedullary catheterization confirmed by fluoroscopy. This was a prospective study utilizing 12 rabbit cadavers. Twenty-two participants attempted IO catheter placement at 3 sites. Perceived success, OCS, and fluoroscopic true success (FTS) were recorded. A Fisher’s exact test was used to compare PS, OCS, and FTS, and FTS rates between sites (P < 0.05). A Wilcoxon test was used to compare speed of placement (P < 0.05). Overall, of 66 attempts, PS was reported in 86.4%, OCS was documented in 62.1%, FTS was confirmed in 43.9%. Perceived success and OCS overestimated FTS (P ≤ 0.01 and P = 0.027, respectively). Confirmation of FTS occurred in 10/22 (45.5%) humeral, 5/22 (22.7%) femoral, and 14/22 (63.6%) tibial (P = 0.03) attempts.

Median time until placement for the humerus was 37.5 seconds (range: 15 to 125 seconds); the femur 135 seconds (range: 91 to 148 seconds); the tibia 49 seconds (range: 19 to 150 seconds). The humerus and tibia were faster to catheterize than the femur (P = 0.01 and 0.03, respectively). Participant PS and OCS criteria overestimated FTS. The humerus or tibia may be more successful and are faster to catheterize.

Introduction

Intraosseous (IO) catheterization may be used to obtain vascular access in rabbits. For debilitated rabbits presenting with circulatory collapse, or those at imminent risk of cardiopulmonary arrest, IO catheters may be considered as an alternative or in preference to, intravenous catheters.

Any long bone can be used for IO catheterization in small mammals. The ideal IO placement site is unknown, although the humerus, femur, and tibia have all been recommended (1). Despite a wealth of anecdotal recommendations, there is little supporting literature related to IO catheters in veterinary medicine and much less in exotic animals. A recent canine cadaver study demonstrated that placement of a humeral IO catheter compared favorably to jugular venous catheters and suggested IO use in emergent dogs (2). A report of successful cardiopulmonary resuscitation in a geriatric chinchilla included the use of an IO catheter placed in the humerus (3).

Intraosseous catheters were successfully placed in the craniomedial aspect of the tibial plateau of rabbits in a study comparing IO versus IV propofol administration (4). Insertion of a bone marrow needle was reported to be well-tolerated in these animals after infiltration of a local anesthetic. Clinical recommendations for the ideal IO catheter placement site vary amongst clinicians, with the tibial crest site often recommended for rabbits and most other small mammals (5). Based on extrapolations from IO recommendations in neonatal dogs and cats, some clinicians favor the proximal femur. Knowing which bone may be catheterized the fastest and most successfully, especially for the novice placer, will likely help optimize patient care and reduce the impact of restraint on critically ill rabbits.

No current studies have evaluated the ideal IO catheter placement site in rabbits. Confirmation of successful urgent IO catheter placement has not been previously evaluated. Currently bedside clinical indicators of successful IO catheterization include loss of resistance when the cortex is penetrated, the perception of firm seating of the catheter at the insertion site with the ability to manipulate the limb via the catheter, a slight resistance to catheter flushing, and the absence of post-flush subcutaneous fluid accumulation (1). No studies have evaluated the accuracy of these criteria. Although radiographic confirmation is often recommended, it may not be practical in an impending cardiopulmonary arrest situation. Once stable, radiographs are important for confirmation of placement and further patient diagnostics. Validating bedside clinical indicators of IO catheter placement success would be useful for clinicians treating emergent rabbits.

The goals of this study were to determine if IO catheters can be placed faster and with greater success into the humerus, femur, or tibia of cadaver rabbits, and to evaluate the accuracy of perceived success and commonly used clinical criteria for success, against true intramedullary catheterization confirmed by fluoroscopy.

Materials and methods

Twenty-two participants were recruited (veterinary students and house officers) with limited (≤ 5 prior attempts at IO catheter placement) experience. Participants underwent a 15 min training session on IO catheter placement techniques immediately before the study.

Twelve donated rabbit cadavers were obtained from a combination of an owner-initiated donation program (6) and the department of laboratory animal medicine. Each participant attempted timed placement of a hypodermic needle into the humerus, femur, and tibia of a cadaver rabbit. A choice of 18- to 20-gauge hypodermic needles was provided for catheterization. Each placement attempt was timed and evaluated by a single assessor (CK). Each participant was allowed up to 3 min per site. Time until perceived success (PS) was recorded. Perceived success was recorded if the participant believed the catheter to be correctly placed. Once PS was noted by the participant, the IO catheters were further assessed by a single investigator (CK) using the following objective clinical success (OCS) criteria: perception of firm seating of the catheter at the insertion site; ability to manipulate the limb via the catheter; a slight resistance to catheter flushing (i.e., in excess of subcutaneous placement); and the absence of post-flush subcutaneous fluid accumulation after infusing 0.5 mL saline in the IO catheter. Meeting all 4 criteria was required to claim OCS. After being assessed for these criteria, the IO catheters were further assessed via fluoroscopy by a second investigator (ER), blinded to the previous results. Fluoroscopic True Success (FTS) was determined by infusion of iohexol (Omnipaque, GE Healthcare, Oslo, Norway) and subsequent identification of intramedullary flow via fluoroscopy (Fluoroscopy/DR Unit [Model# UD150L], Shimadzu, Kyoto, Japan) (Figure 1). Presence of contrast material within the medullary cavity represented truly successful intramedullary catheterization. Data collected included: site of placement, time (seconds), perceived success (PS), objective clinical success (OCS), and fluoroscopic true success (FTS). A Fisher’s exact test was used to compare success between the 3 placement sites: humerus, femur, and tibia; (P < 0.05) and the different methods of success determination: PS, OCS, FTS (P < 0.05). Individual 2 × 2 Fisher’s exact tests were used to compare variables when significance was found with a 3 × 3 test (P < 0.05). A Mann-Whitney test was used to compare speed of placement between sites where applicable.

Figure 1.

A — Correctly placed intramedullary tibial IO catheter. B — Incorrectly placed humeral IO catheter with accumulation of radiopaque contrast material outside of the medullary cavity.

Results

The median weight of the 12 rabbit cadavers was 2.26 kg (range: 1.04 to 5.44 kg). There was a total of 66 placement attempts; 29 (43.9%) were true intramedullary catheterizations confirmed by fluoroscopy. Participants reported PS in 57/66 (86.4%) attempts, although only 41/66 (62.1%) attempts met the criteria for OCS. Two catheters placed were assessed as truly successful via fluoroscopy, but clinically unsuccessful based on an initial inability to flush (i.e., did not meet the all of the OCS criteria). Of the 2 catheters that were incorrectly assessed by OCS, both placers had reported PS. One attempt at a tibial catheter was successfully placed in the distal femur but counted as a failure as it was not the intended bone. There was an overall significant difference between PS, OCS, and FTS (P ≤ 0.01) for all sites together. Both participant PS and OCS overestimated true intramedullary placement of catheters (P ≤ 0.01 and P = 0.027, respectively).

Confirmation of FTS occurred in 10/22 (45.5%) humeral, 5/22 (22.7%) femoral, and 14/22 (63.6%) tibial (P = 0.03) attempts. These results were significantly different between attempted sites (P = 0.03). The tibia was more successful than the femur (P ≤ 0.01); the tibia was not different from the humerus (P = 0.18); the humerus was not different from the femur (P = 0.1).

For catheters that had confirmed FTS, median time until placement for the humerus (n = 10) was 37.5 s (range: 15 to 125 s); the femur (n = 5) 135 s (range: 91 to 148 s); the tibia (n = 14) 49 s (range: 19 to 150 s). There was a significant difference in time until placement between the humerus versus the femur (P = 0.01). There was a significant difference between the tibia versus the femur (P = 0.03). There was no significant difference in speed of placement between the humerus and the tibia (P = 0.9).

Considering only catheters with confirmed FTS, only 1 participant was successful at 0 sites. Fifteen (68.2%) participants were successful at 1 site. Four (18.2%) participants were successful at 2 sites. Two (9.1%) participants were successful at all 3 sites. See Table I for a complete summary table outlining methods of determining IO catheter placement success by catheter site reported as success/total attempts.

Table I.

Methods of determining IO catheter placement success by catheter site (reported success/total attempts).

IO catheter site	Perceived success	Objective clinical success	Fluoroscopic true success
Humerus	20/22	15/22	10/22
Femur	17/22	10/22	5/22
Tibia	20/22	16/22	14/22
Total	57/66	41/66	29/66

Discussion

This study confirms that inexperienced clinicians can place IO catheters in rabbits with moderate success. A recent canine cadaver study did not find that experience influenced success rates nor impacted time to placement with IO catheters (2). In humans, the superiority of IO catheterization over peripheral IV catheterization was demonstrated amongst inexperienced dental medicine students, supporting the role of the IO catheter for the novice placer in emergency settings (7).

The results of this study indicate that either the humerus or the tibia should be used for emergent IO catheterization in rabbits. The femur should not be used in the emergent setting by the novice placer. Superiority of the tibia over the radius has been demonstrated in a neonatal foal study (8). Both the humerus and the tibia were desirable for IO catheterizations in humans (9). Tibial IO catheters had less longevity than humeral IO catheters in goats (10). However, these studies were performed in larger animals with significant morphological differences. A feline IO catheterization study showed similar results to the study herein, with no difference in success between the humerus versus the tibia (11). In obese human patients, the tibia has been recommended over the humerus (12); whether this is also true for obese rabbits is unclear.

Speed of placement is of particular interest in the emergency setting. This study showed no difference in speed of placement between the humerus versus the tibia, again supporting use of either in the emergent rabbit. The femur took significantly longer to catheterize. A recent cadaveric study in dogs demonstrated faster placement of IO catheters versus central venous catheters by cut-down venotomy (2) and recommended early employment of IO catheters. Similar superiority of IO catheters over central venous catheters has been demonstrated in human emergency settings (13,14). Intraosseous catheters in general can be rapidly placed, with human studies reporting short placement times: ≤ 20 s (9); < 60 s (7), and < 72 s (14). Importantly, human IO placement is often facilitated by use of a motorized placement device. A study comparing IO catheterization in humans showed the tibia was catheterized faster with respect to the humerus, though time until placement was significantly longer relative to other studies (median: 4.6 min and 7.0 min, respectively) (15). Faster catheterization of the tibia (mean: 33 s) versus the radius (mean: 63 s) was shown in neonatal foals (8). In a canine cadaver models median time until IO catheterization was 54 s (range: 15 to 153 s), showing similar results to this study in rabbits (2).

This study documented that commonly employed clinical or bedside criteria used to identify successful intraosseous catheterization significantly overestimated truly successful catheterization, i.e., intramedullary placement, as assessed by fluoroscopy. Additionally, participants perceived their catheterizations to be twice as successful as they truly were; this is clinically relevant, as administering drugs or fluids by a periosteal route (i.e., outside of the medullary cavity) would be of limited or no benefit. The perceived success, however, may have been impacted by the relative inexperience of the participants.

While establishing correct catheter placement is essential, both fluoroscopy and radiography may be impractical in the critically ill rabbit. In humans, bedside confirmation of successful intraosseous catheter placement has been described by the following 5 criteria: loss of resistance on entering the medullary cavity; a stable, self-standing needle; easy aspiration of bone marrow or blood via the catheter; administration of 2 mL of saline without subcutaneous tissue swelling; and administration of 8 mL of saline without resistance (12).

In dogs, aspiration of 2 mL of bone marrow via the catheter has been used to confirm intramedullary placement (16). Collection of 3 mL of bone marrow from the femur of anesthetized rabbits has been shown to be possible, suggesting that this criterion may be useful in confirming intramedullary catheter placement (17); this might be difficult in rabbits which have suffered cardiovascular collapse. As defrosted cadaver rabbits were used, no effort was made to aspirate bone marrow in this study. More recently, the use of a bubble study to confirm correct placement of central venous catheters in humans has been described (18). This technique has not been evaluated for IO catheters, but may be useful as a point-of-care determination of success.

This study had a number of limitations. The use of previously frozen cadavers may not accurately represent the tissue characteristics of a living or recently deceased rabbit. These tissue changes may have affected the ability to evaluate success of catheter placement, including perception of success and the ability to manipulate the leg and evaluate for subcutaneous fluid accumulation. The sample size was small. Furthermore, the low number of truly successful catheterizations limits the ability to draw statistically meaningful conclusions, particularly when looking for significance between the humerus and the tibia. The weight of rabbits in this study was variable. Rabbits were a collection of New Zealand white and domestic pet rabbits. New Zealand white rabbits may be larger than rabbits encountered in practice. Intraosseous catheters may be easier to place in larger rabbits due to larger landmarks. Conversely, catheters may be more easily placed in small rabbits due to less cortical resistance to a hypodermic needle. The goal of this study was not to evaluate the effect of rabbit size on successful catheterization and as such was underpowered to draw conclusions; however, in human patients, obesity is known to complicate IO catheter placement. This study did not evaluate the effect of learning. Each participant only attempted each site once. Possibly, more experience would result in greater success. The results of this study may be more applicable to a novice placer.

A key consideration when using hypodermic needles as IO catheters is the risk of a bone core plugging the needle. This can result in an unusable catheter. Bone cores were thought to have occurred in the 2 catheters that were assessed as successful by fluoroscopy, but did not meet clinical criteria, as they did not flush initially. A simple way around this potential complication is to remove the plugged catheter and replace it with a new one: new catheters tend to easily find the previous hole. However, this increases time until successful catheterization. Additionally, catheters placed in previously made holes in the bone tend to leak infusate around the catheter more readily. Based on the criteria used in this study, this may indicate failure of placement. Spinal needles or commercial IO needles readily overcome bone coring due to the presence of a stylet. Spinal needles or commercial IO needles readily overcome bone coring issues due to the presence of a stylet. The typical length of many available spinal needles can predispose them to bending though during placement and placement techniques have to be adjusted to account for this potential issue making rapid placement more challenging. Compared to spinal needles, most commercial IO needles are more appropriate in length; however, they are often only available in larger gauges (15G). Commercial IO needles are also considerably more expensive than hypodermic needles. Hypodermic needles were used in this study, as they are more readily available in practice in a variety of gauges and more appropriate lengths.

In conclusion, IO catheters can be placed in rabbits by inexperienced (novice) clinicians with moderate success. Perceptions of success and selected objective clinical success criteria both overestimated truly successful intramedullary placement of catheters. Better performing clinical criteria for determining correct placement of IO catheters are required. We recommend that either the humerus or the tibia be used for IO catheterization in the emergent rabbit.