Vitrectomy Machine Parameters Impact

In this part, we focus on the influence of the vitrectomy machine parameters on the effective failure rate. As for the clinical findings, first a univariate analysis was performed in order to select the major explanatory variables, then bivariate analysis and finally, a multivariate analysis with a logistic regression, using a step by step method in order to get the model that fits the best the data. The results of the multivariate analysis are presented at the end of this part.

When comparing failure rates for 20 and 23 gauge for a given PVR stage, the trend remains the same : 20 gauge provides both a higher true failure and a higher remaining silicone rate. Although, none of these differences are statistically significant, these variables were considered in the multivariate analysis.

At first sight, when looking at the failure rates depending on the pump used, it appears that a flow control pump is better than a vacuum control pump both in relation to the true failure rate as well as the remaining silicone rate. However, this difference may be explained by the differences in the treated cases with each of these pumps.

If we exclude the aggravating factors and consider the PVR distribution in relation to the pump used we can see that the cases are about the same with a little bit more easy cases stage 0 and difficult cases stage C1 in the venturi pump group. This cannot entirely explain entirely the statistically significant difference.

If we compare the failure rates without choroidal detachment and hypotony for each stage of PVR stage, we can notice that peristaltic pump still gets better results than the venturi pump, however these differences are not statistically different anymore. Yet, the pump was selected to enter the multivariate analysis, the results of which will be presented at the end of this presentation.

The result of this logistic regression shows that 2 vitrectomy machine parameters are independently significant. Venturi pump delivers a poorer surgical result whatever the initial findings of the eye : there are three times as much risk of a failure with a venturi pump than with a peristaltic one. Moreover, the multivariate analysis shows that using a high cutting frequency can counterbalance a little bit this tendency. However the combination venturi plus high speed is still worse than peristaltique whatever the cutting frequency.