Abstract
Objectives
The aim of the present study was to identify patient, vein and operator factors associated with first-attempt success of peripheral intravenous catheter (PIVC) insertion in cats presenting to an emergency room.
Methods
A prospective study was conducted in the emergency room of a university small animal hospital between February and April 2024. Cats requiring PIVC insertion were enrolled. Data collected included patient signalment, vein visibility and palpability, catheter size, indication for catheterization and operator characteristics (role, years of experience and estimated number of previous PIVC insertions). First-attempt success was defined as catheterization with visible blood flashback and successful flushing without extravasation or discomfort. Univariable and multivariable logistic regression analyses were performed to assess associations with first-attempt success.
Results
A total of 97 PIVC insertions in 95 cats were analyzed. Overall, first-attempt success was 85.6% (n = 83/97). Most insertions involved the cephalic vein (96.9%) and 22 G catheters (57.7%). Neither catheter size, target vein nor indication for insertion was significantly associated with success. Operators with 8–15 years of experience had significantly higher odds of success compared with those with 2 years or less (P = 0.03). Operators who had inserted more than 500 intravenous catheters had greater odds of success than those with fewer than 100 insertions (odds ratio [OR] 8.63, 95% confidence interval [CI] 1.48–50.12; P = 0.02). Vein visibility was strongly associated with first-attempt success (OR 7.78, 95% CI 2.29–26.42; P = 0.001), while palpability was not. In the final multivariable model, both vein visibility (OR 8.0, 95% CI 2.16–30) and more than 500 prior insertions (OR 13.24, 95% CI 1.54–144) remained independently associated with success.
Conclusions and relevance
First-attempt intravenous catheter insertion success in cats was strongly influenced by operator experience and vein visibility. These findings highlight the clinical importance of operator training and vein assessment during catheter insertion in feline emergency patients.
Plain language summary
Intravenous catheters are commonly used in hospitalized cats, but inserting the catheter can be stressful to cats. Factors that determine first-attempt success rates for insertion have not been evaluated in cats. This study was performed in an emergency room in cats requiring catheters for various reasons. Veterinary professionals who have inserted more than 500 catheters are more likely to successfully place peripheral intravenous catheters in cats compared with those who have inserted fewer catheters. Peripheral intravenous catheters are also more likely to be successfully inserted in cats with visible veins. Being aware of these factors will minimize unsuccessful intravenous catheter insertions in hospitalized cats.
Keywords
Introduction
Peripheral intravenous catheters (PIVCs) are the most common invasive devices used in hospitalized cats for the delivery of fluids, medications or blood products.1,2 Their use can be lifesaving in critically ill cats requiring urgent intervention. Despite their ubiquity, PIVC insertion can be challenging in cats even for experienced veterinary professionals. 3 The rate of successful first-attempt insertion of PIVC insertion in humans varies widely, reported to be in the range of 23–98%.4–8 Difficult intravenous access (DIVA) is defined as two or more failed insertion attempts, characterized by non-visible and non-palpable veins. 9 Patients with DIVA may undergo repeated failed insertion attempts, increasing pain and discomfort, formation of hematoma, risk of infection, vessel damage and venous depletion.9–11 Failed PIVC attempts can result in treatment delays, missed administration of medication or escalation to more invasive devices, such as central venous catheters. 9 In addition, failed PIVC attempts may lead to a traumatic experience for cats and may also cause discomfort and distress in veterinary professionals; therefore, effective PIVC insertion in cats is an important consideration in hospitalized cats.
Extensive studies in humans have identified reasons for catheter insertion failure and these findings have led to established standards of care for PIVC cannulation, improving patient safety and comfort. Recently, a study evaluated PIVC insertion success rates in dogs. 12 Specific reasons for failure in dogs were identified as operator inexperience, and poorly visible and poorly palpable veins. 12 These findings have not been evaluated or established in cats. The goal of this study was to identify reasons for PIVC insertion in cats while evaluating success rates for insertion on the first attempt. Our hypothesis was that operators with more experience placing PIVCs would be more successful than those with less experience.
Materials and methods
Study design and ethical approval
This prospective study was reviewed and approved as exempt by the Institutional Animal Care and Use Committee. Approval from the Institutional Review Board was also obtained for the collection of data involving clinical personnel. The study was conducted in the Emergency Room (ER) of the Small Animal Hospital at the University of Florida between 1 February and 30 April 2024.
Study population
Cats evaluated in the ER requiring a PIVC were eligible for inclusion. Cats were excluded if catheter insertion was not indicated, if a non-routine site was used for PIVC insertion or if the data collection form was substantially incomplete. Records with missing data for the primary outcome variable (successful first-attempt insertion) were excluded. Records with missing data for other variables were retained for analysis.
Catheter insertion procedures
Once the need for venous access was established, the catheter insertion site was selected at the discretion of the operator. Fur at the selected site was clipped and the skin was aseptically prepared using chlorhexidine swabs. After successful insertion, the catheter was secured with tape.
First-attempt success was defined as catheterization of a vein on the first attempt, confirmed by blood flashback and the ability to flush the catheter without evidence of extravasation or patient discomfort. Redirection of the catheter without withdrawal from the skin was considered part of the same attempt. First-attempt failure was defined as inability to flush the catheter, swelling at the insertion site during flushing (extravasation) and/or inability to obtain blood flashback on the first attempt.
Patient information
Data were recorded immediately after each insertion attempt using a standardized form. Variables collected included signalment, indication for catheter insertion, catheter size, whether the vein was visible and/or palpable, and the vein utilized for catheterization. Patient age (years) and body weight (kg) were recorded as continuous variables, whereas all other patient characteristics were recorded as categorical variables. Vein visibility and palpability were recorded as binary (yes/no) variables. Indications for catheter placement were initially recorded as free-text entries (eg, anemia, abdominal effusion, dehydration, urethral obstruction, euthanasia, sedation for imaging). For analytical purposes, these indications were consolidated into three categories: hospitalization, euthanasia and sedation.
Operator information
The first available operator inserted each catheter; no selection criteria were used to assign operators. Information collected included the operator’s years of veterinary experience, estimated number of intravenous catheters (IVCs) previously inserted in dogs and cats (0–100, 100–500 or >500) and hospital role (veterinary assistant, veterinary technician, veterinary student or veterinarian). Operator experience was recorded as years in practice (continuous scale), and operators selected one of three categories to estimate the number of previously placed IVCs: 0–100, 100–500 or >500. For unsuccessful attempts, operators were asked to report perceived reasons for failure. Individual operators were not uniquely identified or tracked, and operators could therefore have contributed more than one catheter insertion to the data set.
Statistical analysis
Data were analyzed using SAS 9.4 (SAS Institute). Variables evaluated for association with first-attempt success included the target vein, catheter size, indication for insertion, operator role, operator experience, estimated number of previous IVC insertions, and vein visibility and/or palpability.
The Kolmogorov–Smirnov test was used to assess normality of continuous variables, including patient age, body weight and operator years of experience. Descriptive statistics were reported as frequencies and percentages for categorical variables and as medians with interquartile ranges (IQRs; Q1–Q3) for continuous variables. Univariable and multivariable logistic regression analyses were performed to calculate odds ratios (ORs) and 95% confidence intervals (CIs) and to identify factors associated with successful first-attempt catheterization. All variables identified in univariable analyses were considered for inclusion in the multivariable model. Potential interactions among categorical variables were assessed. A variable was considered a confounder if its inclusion altered the coefficient of a previously significant variable by 20% or more on the log scale. Selection of the final multivariable logistic regression model was guided by Bayesian Information Criterion values. P <0.05 was considered statistically significant.
Results
A total of 101 PIVC insertions were recorded. Topical analgesia was not utilized for any PIVC insertion. Three catheters were inserted in the jugular vein; because this is not a routine site for peripheral catheterization in cats, these catheters were excluded from analysis. One record was missing the primary outcome variable (successful first-attempt insertion) and was removed from analysis. Additional missing data included operator experience (n = 2), vein palpability (n = 1) and vein visibility (n = 1); however, these variables were retained because they were not dependent variables. After exclusions, 97 PIVC insertions in 95 cats were analyzed. Two cats each had two PIVCs inserted during a single visit; all other cats received one PIVC. Domestic shorthair cats were most commonly represented (66/97, 68%), followed by domestic longhair, domestic mediumhair (7/97 each, 7.2%) and Siamese cats (4/97, 4.1%). The median age was 7.0 years (IQR 3–12) and the median body weight was 4.4 kg (IQR 3.3–5.8).
Catheter characteristics and insertion success
Overall, 83/97 (85.6%) PIVCs were successfully inserted on the first attempt. In total, 14 (14.4%) PIVCs were unsuccessful. There was no significant association between first-attempt success and target vein, catheter size or indication for insertion (Table 1).
Summary data and results of univariable logistic regression model of factors associated with successful intravenous catheter (IVC) insertions in 97 catheters inserted in 95 cats during a visit to a veterinary teaching hospital emergency room
Data are n (%). Referent is the group used for comparison in the calculation of the reported ORs
CI = confidence interval; OR = odds ratio
The cephalic vein was the most common vein utilized for PIVC insertions (94/97, 96.9%) (Table 1). The most frequently used catheter size was 22 G (56/97, 57.7%), followed by 20 G (39/97, 40.2%). Indications for PIVC insertion included hospitalization (83/97, 85.6%), euthanasia (11/97, 11.3%) and sedation (3/97, 3.1%).
Operator characteristics
Most PIVCs were inserted by veterinary technicians (83/97), followed by veterinary students (11/97) and veterinarians (3/97). First-attempt success rates were 86.7% (n = 72/83), 81.8% (n = 9/11) and 66.7% (n = 2/3), respectively (Table 1). Operators had a median experience of 8 years (IQR 3.5–13).
Univariable logistic regression did not reveal a significant association between operator type and success (P = 0.6063); however, operator experience was significantly associated with outcome. Operators with 8–15 years of experience had nearly seven-fold greater odds of success compared with those with 2 years of experience or less (P = 0.0257). Operators with more prior PIVC insertions were also more successful. Those who had previously inserted more than 500 IVCs had significantly greater odds of first-attempt success compared with those who had inserted fewer than 100 IVCs (OR 8.63, 95% CI 1.48–50.12; P = 0.0191).
Vein visibility and palpability
Vein visibility was reported in 96 insertions: 76 veins were visible and 20 were not visible. First-attempt success occurred in 92.1% (n = 70/76) of visible veins vs 60% (n = 12/20) of non-visible veins. Vein palpability was reported in 96 insertions; veins were palpable in 73 and non-palpable in 23. First-attempt success occurred in 87.7% (n = 64/73) of palpable veins and 78.3% (n = 18/23) of non-palpable veins (Table 1). Vein visibility was significantly associated with successful catheterization (OR 7.78, 95% CI 2.29–26.42; P = 0.001). Palpability was not significantly associated with success (P = 0.2709).
Reasons for catheterization failure
Operator-reported reasons for unsuccessful insertions are reported in Table 2. Three insertions had two reported reasons and one insertion had three. The most common operator-reported reasons for PIVC insertion failure included hypotension, operator inexperience and scar tissue or tough skin at the intended site.
The most common primary, secondary and tertiary reasons for peripheral intravenous catheter (PIVC) insertion failure in 14 catheters in cats requiring intravenous access during a visit to a veterinary teaching hospital emergency room
Data are n (%)
Multiple reasons for failure could be selected per catheter
Multivariable analysis
In the final multivariable logistic regression model (Table 3), two variables remained independently associated with first-attempt success: operator experience (number of previous IVC insertions) and vein visibility. After adjustment, operators who had inserted more than 500 IVCs had 13.24-fold greater odds of success compared with those who had inserted fewer than 100 (95% CI 1.54–144; P = 0.0182). Vein visibility also remained significant. Visible veins were associated with higher odds of success compared with non-visible veins (OR 8.0, 95% CI 2.16–30).
Final multivariable logistic regression model of factors associated with successful intravenous catheter (IVC) insertions in 97 catheters inserted in 95 cats during a visit to a veterinary teaching hospital emergency room
CI = confidence interval; OR = odds ratio
Discussion
The results of the present study suggest that operators who have inserted more than 500 catheters and the presence of visible veins are two factors strongly associated with PIVC first-attempt insertion success in cats. The results of this study are similar to studies in humans and dogs, where operators with more experience inserting PIVCs are more likely to be successful compared with those with less experience. 13 Veterinary technicians inserted the most PIVCs in the present study, and though not statistically significant, had the highest first-attempt insertion success rates compared to other operator groups. Although operator type was not significantly associated with first-attempt success, the number of catheter insertions performed by each operator group was highly imbalanced, with most insertions performed by veterinary technicians and relatively few by veterinarians or students. This unequal distribution may have limited the statistical power to detect differences between groups. In a human study based out of Australia, PIVC failure tends to be higher in generalists who place fewer PIVCs (27/50, 54%), compared with vascular access specialists (33/69, 48%). 14
Although visible veins had a higher incidence of first-attempt insertion success in cats (similar to humans and dogs),12,15–18 vein palpability surprisingly did not have a correlation to first-attempt insertion success in this group of cats. Non-palpable veins may be associated with veins with smaller diameter, reduced venous filling (hypovolemia, dehydration, shock, hypothermia, etc), greater vein depth from the surface, edema, increased subcutaneous tissue or veins with poor integrity. 19 These factors are associated with why non-palpable veins increase the risk of DIVA in human patients; 19 thus, ultrasound-guided access has been used more commonly to increase the success rate of PIVC, especially in patients without visible or palpable veins.20–23 It is possible that in cats, vein palpability may be a weaker surrogate of first-attempt insertion success compared with dogs and humans. This may be because the most commonly used peripheral veins in cats (cephalic and medial saphenous) are small caliber, highly compliant and are more likely to collapse under minimal pressure.24,25 Thus, palpability may not reflect the functional lumen size of the vessel. It is also possible that the study population may have had an under-represented number of cats with shock, thus vein palpability may not have captured meaningful physiologic extremes. The highly skilled operators may also have had excellent anatomic vein prediction, masking any effect of palpability. The lack of association between vein palpability and first-attempt success may also reflect anatomical differences between species. Cats have relatively thin skin and minimal subcutaneous tissue, which may make visual identification of superficial veins more important for successful catheter placement. In contrast, in dogs with thicker skin and greater subcutaneous tissue, palpation may play a more important role in locating peripheral veins.
Based on the results of this study, cats with non-visible veins requiring PIVC insertion should have the procedure performed by the most skilled operator available, whenever possible, to reduce the risks of DIVA and multiple venipuncture attempts. The present study indicates that operator experience, particularly with a high volume of prior IVC placements (>500), is associated with greater success in cats. These findings suggest that veterinary practices may benefit from providing technicians with more opportunities to place PIVCs, to enhance their skill development and maintain proficiency. Structured hands-on practice for veterinary technicians could improve overall efficiency and patient outcomes, while supporting team-based clinical competency.
The first-attempt insertion success rate of 86% (n = 83/97) is similar to that of a recent study in dogs (86%, 309/361). 12 The authors believe that this finding emphasizes that cats are not necessarily more challenging for PIVC and success rates can be comparable to dogs. This is especially true in an emergency and critical care setting where cats are often stressed and are unlikely to have had any pre-visit pharmaceuticals (eg, gabapentin) before the ER visit although the fear, anxiety and stress scores of the cats were not evaluated in the present study. 26 Anecdotally, although most catheters were placed in the cephalic vein with an 85% first-attempt insertion success (n = 80/94), all three catheters placed in the medial saphenous vein were 100% successful. Although the small sample size limited statistical evaluation, the medial saphenous vein may offer potential advantages over the cephalic vein. Its greater size, visibility and palpability likely contributed to improved success with PIVC placement in cats, suggesting that this vessel may represent a preferable site for catheterization in cats with DIVA.
There was no difference in first-attempt insertion success when catheter size was evaluated. In humans, the catheter:vein ratio (CVR) is significantly associated with first-attempt insertion success rates, where a lower CVR was correlated to success. 27 Oversized PIVCs relative to the vein are thought to decrease first-attempt success in humans. 27 The present study did not evaluate the CVR and it is possible that most catheters used (20 and 22 G) were of an appropriate CVR for the cats in the study.
Hypotension, vein resistance to threading and the operator needing more experience were reported as the most common reason for insertion failure by the operators. Although these variables were not independently assessed, their identification by operators highlights potential areas for targeted intervention. Hypotension may reduce vein turgor and visibility, making catheter advancement more difficult, whereas vein resistance to threading could reflect small caliber, high compliance or underlying vascular spasm. Hypotension was reported by operators as a perceived contributor to catheter insertion failure; however, blood pressure measurements were not consistently recorded and hypotension was not systematically assessed in this study. Therefore, this finding reflects operator perception rather than objectively confirmed hypotension and should be interpreted with caution. Operator experience appears to play an important role, suggesting that focused training and repeated practice may improve first-attempt success rates. Future studies should aim to quantify the independent impact of these factors to better guide clinical strategies for DIVA in cats.
The limitations of the present study include a smaller number of certain variables (medial saphenous catheters, veterinarian and veterinary student operators) that might have contributed to the inability to observe a difference in success rates, if one were present. In addition, not every PIVC inserted during the study period was enrolled in the study owing to benign neglect or acuity of the caseload. This study did not utilize fear, anxiety and stress scoring, which may have contributed to first-attempt failure in some cats. Further, the study was conducted at a single institution, which may limit generalizability. Finally, specific medical conditions associated with the cats were not tracked (eg, hypothermia, hypotension, use of sedatives that cause vasoconstriction, etc), which may have affected the first-attempt success rates in the cats in the present study.
Conclusions
Of the PIVCs inserted, 86% were successful on the first attempt in cats in a veterinary ER. The previous number of PIVCs inserted by the operator and vein visibility influenced first-attempt success rates in the cats in this study, while vein palpability did not appear to have an influence. Although not statistically significant, veterinary technicians had the highest first-time success rates compared with other operators and veterinary practices should consider leveraging technicians for acquiring venous access to improve their PIVC insertion skills and practice workflow.
Footnotes
Acknowledgements
The authors would like to thank the emergency and critical care team at the University of Florida for their help in data collection.
Conflict of interest
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Ethical approval
The work described in this manuscript involved the use of non-experimental (owned or unowned) animals. Established internationally recognized high standards (‘best practice’) of veterinary clinical care for the individual patient were always followed and/or this work involved the use of cadavers. Ethical approval from a committee was therefore not specifically required for publication in JFMS. Although not required, where ethical approval was still obtained, it is stated in the manuscript.
Informed consent
Informed consent (verbal or written) was obtained from the owner or legal custodian of all animal(s) described in this work (experimental or non-experimental animals, including cadavers, tissues and samples) for all procedure(s) undertaken (prospective or retrospective studies). No animals or people are identifiable within this publication, and therefore additional informed consent for publication was not required.
