Feline sedation and the spleen part 2

The effects of alfaxalone, alone or with butorphanol, on the ultrasonographic appearance of the feline spleen

Grace McBride 1, Kristen M Fizzano 1, Alison M Lee 1, Marc Seitz 1, Robert Wills 2

Background
Ultrasonography is commonly used to evaluate the feline spleen, with findings influencing decisions about fine-needle aspiration or biopsy. Sedative drugs like alfaxalone and butorphanol are frequently administered to facilitate imaging but may alter the spleen's appearance, leading to potential misdiagnoses. This study aimed to assess the effects of alfaxalone, alone or combined with butorphanol, on the ultrasonographic appearance of the feline spleen.

Methods
Study Design: Randomized, prospective crossover experiment.

Subjects: Eight healthy adult domestic shorthair cats (4 males, 4 females, aged 1–5 years).

Sedative Protocols:
-Protocol A: Alfaxalone 2 mg/kg IM.
-Protocol B: Butorphanol 0.2 mg/kg IM.
-Protocol AB: Alfaxalone 2 mg/kg + Butorphanol 0.2 mg/kg IM.

Each cat received all three protocols, with a minimum 7-day washout period.

Measurements: Ultrasound evaluations were performed before sedation and every 15 minutes post-administration for one hour. Splenic size, margins, shape, echogenicity, echotexture, and blood flow were assessed. Heart rate (HR), respiratory rate (RR), and sedation scores (FMSS) were recorded.

Results
Splenic Appearance:
-All protocols caused a mild, transient increase in splenic size (body height) that peaked at 30–45 minutes, returning to near baseline by 60 minutes.
-No significant changes were observed in splenic margins, shape, echogenicity, echotexture, or blood flow across protocols.
-Splenic rounding was noted in some cases but was not statistically significant.

Sedation:
-Protocol AB (alfaxalone + butorphanol) provided the most consistent and profound sedation, with higher FMSS scores than the other protocols.
-Alfaxalone alone caused unpredictable behavior (e.g., hyperkinesia, aggression) in some cats, making it less suitable for sole use.
-Butorphanol alone resulted in only mild sedation.

Vital Parameters:
All protocols caused a significant decrease in HR and RR, peaking 20 minutes post-administration and returning toward baseline by 60 minutes.
There was a significant negative correlation between FMSS and both HR and RR, indicating that higher sedation levels corresponded to lower vital parameters.

Limitations
The small sample size and the inclusion of only healthy cats limit the generalizability of findings to diseased populations. The lack of a saline control group makes it unclear whether stress from injections influenced splenic changes. The subjective nature of echogenicity and echotexture scoring and the absence of investigation into alternate administration routes (e.g., IV, SC) are additional limitations.

Conclusions
Alfaxalone with butorphanol provides effective sedation for ultrasonographic evaluation of the feline spleen without causing significant alterations in splenic appearance, aside from mild and transient splenomegaly. The combination is preferred over alfaxalone alone, which is associated with undesirable side effects. Practitioners should consider imaging 15–30 minutes post-sedation to balance peak sedative effects and minimal splenic size changes. Monitoring vital parameters is essential when using these sedatives.

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