Imagine this clinical scenario: you are presented with a lethargic, anorexic rabbit whose owner brought in for examination after a sudden change in demeanour. During clinical examination, you notice the mucous membranes are pale and the cranial abdomen is firm and painful. Blood analysis reveals severe anaemia with raised liver enzymes, and you suspect a liver lobe torsion, which is confirmed via ultrasonography. You identify a swollen liver lobe with no blood flow on a colour Doppler. You recommend carrying out surgical intervention under general anaesthesia to treat the issue, but the owner is concerned about the risks involved. An alternative is to manage the issue medically, but you are unsure how this compares to surgical intervention. You consult the evidence to find out more.
The evidence
Six papers were evaluated that relate to the research question. All are retrospective in nature: three are case series (Leonard et al., 2022; Stanke et al., 2011; Wenger et al., 2009), and three are cohort studies (Graham et al., 2014; Ozawa et al., 2022; Sheen et al., 2022).
In terms of the case series, Leonard et al. (2022) studied 22 rabbits, all of which underwent surgical intervention. None were treated using medical treatment alone. Outcomes studied were mortality rate, time to eating and anaesthesia/surgical time. Stanke et al. (2011) studied four rabbits, all of which were treated surgically. The outcomes studied were surgical success, measured via wellness post-operatively, and survival. Finally, Wenger et al. (2009) studied three rabbits, one of which was treated surgically and two that were treated medically. The outcome studied was mortality.
The details of the cohort studies are as follows. Graham et al. (2014) studied 16 rabbits, nine of which underwent surgical intervention, and seven of which received supportive medical treatment only. The outcome studied was mortality rate. Ozawa et al. (2022) studied 82 rabbits: 50 underwent surgical intervention, 23 received medical treatment only and nine were euthanised or died on presentation. Outcomes studied were clinicopathological findings, prognostic indicators and mortality rate. Lastly, Sheen et al. (2022) studied 40 rabbits, 15 of which were treated medically and 23 of which were treated surgically. Outcomes studied were improvement of packed cell volume and biochemical parameters, and survival four weeks after diagnosis.
Limitations of the evidence
The papers reviewed have many limitations, and the overall strength of evidence is weak. All six papers were retrospective studies, which is a weak study design. Retrospective studies can lack control for chance, bias and confounders, and as the interventions differed between patients, the data included was reliant upon accurate record keeping and reporting.
Two papers (Leonard et al., 2022; Stanke et al., 2011) only studied rabbits that were treated surgically; this limits their relevance to the research question, which aims to compare surgery against medical intervention. Leonard et al. compared two different surgical techniques, but information was not provided on how each surgical approach was selected for each patient. Stanke et al. also failed to provide selection criteria, which could lead to selection bias.
The evidence indicates that medical management does not reduce the mortality rate compared with surgery
Both Stanke et al. (2011) and Wenger et al. (2009) had small sample sizes, with four and three cases, respectively. All three of the rabbits studied by Wenger et al. died, making the outcome of the study unclear.
Three papers (Graham et al., 2014; Sheen et al., 2022; Ozawa et al., 2022) did not specify whether every patient was offered equal opportunity for surgical or medical treatment.
Thirty-five percent of patients studied by Ozawa et al. (2022) were referred by other practices, which may have created a bias towards more serious cases being included in the study. Sheen et al. (2022) failed to include details on whether patients were referrals or not, which creates the possibility for bias.
Summary of findings
The evidence indicates that medical management does not reduce the mortality rate compared with surgery. However, this analysis must be considered alongside the limitations set out above.
Both larger cohort studies (Ozawa et al., 2022; Sheen et al., 2022) provided a moderate strength of evidence and found that the seven-day survival rate did not differ significantly between the medical and surgical groups, indicating medical management does not reduce mortality compared with surgery. The other cohort study, Graham et al. (2014), found that 100 percent (9/9) of surgically treated rabbits survived, while 42 percent (3/7) of medically treated rabbits survived.
Leonard et al. (2022) and Stanke et al. (2011) only studied rabbits that were treated surgically, so their applicability to the research question is limited. All four rabbits studied by Stanke et al. survived, while the survival rate noted by Leonard et al. was 77 percent (17/22). All three rabbits studied by Wenger et al. (2009) died, which makes the significance between the intervention and outcome difficult to quantify.
Conclusion
There is a need for randomised, blinded control studies that directly compare medical management against surgical management to improve the strength of evidence
There is weak evidence to suggest that medical management does not reduce the mortality rate when compared with surgical intervention for liver torsion in rabbits. However, the quality of the evidence is weak. There is a need for randomised, blinded control studies that directly compare medical management against surgical management to improve the strength of evidence.
Additionally, not all liver lobe torsions have the same degree of severity. From a clinical perspective, the decision to go to surgery versus medical treatment depends on the lobe affected and the degree of severity of the clinical signs (itself related to the lobe affected). This means that any future research may require more nuance than directly comparing surgical versus medical treatment in cases of differing severity levels.
Finally, it may be appropriate for future research to include euthanasia as an alternative to surgery or medical management, and explore where and when this may be the best option.
| The full Knowledge Summary can be read in RCVS Knowledge’s open access journal Veterinary Evidence. |
Disclaimer
The application of evidence into practice should take into account multiple factors, not limited to: individual clinical expertise; patient’s circumstances and owner’s values; country, location or clinic where you work; the individual case in front of you; and the availability of therapies and resources.
