Example

“All participating centres . . . were major neurosurgical centres, treating large numbers of patients after aneurysmal subarachnoid haemorrhage (SAH), each centre treating between 60 and 200 cases annually . . . Centres had to have expertise in both neurosurgical and endovascular management of ruptured aneurysms. Only accredited neurosurgeons with experience of aneurysm surgery were permitted to manage patients in the trial. Endovascular operators had to have done a minimum of 30 aneurysm treatment procedures, before they were permitted to treat patients in the trial” [187].

 

Explanation

For all types of trials, it is important to define the eligibility criteria for clinical sites, and to consider the characteristics of the treatment providers who will provide both the experimental and comparator interventions [22, 188]. Evidence suggests that patient outcomes can be associated with hospital and care provider volume [188]. A systematic review of 135 trials found that 71% observed a positive association between hospital volume and outcomes, and 70% observed an association between care provider volume and outcomes [189]. Different levels of expertise of care providers in each intervention group can bias treatment effect estimates [190]. Furthermore, an intervention might be found to be safe and effective in a trial performed in high volume sites by high volume care providers but could have different results in low volume sites. For example, in an analysis of Medicare National Claim files of 167 208 patients who had undergone coronary stent surgery, patients treated by high volume physicians and at high volume sites experienced better outcomes than those treated by low volume physicians at low volume sites [191]. Similar studies show that in most non-pharmacological trials, care provider expertise and site volume will influence treatment effects [192-194].

 

Eligibility criteria for care providers and sites are often poorly reported. A systematic review of randomised trials in surgery found that the setting and the site volume of activity were reported in only 7% and 3% of articles, respectively. Eligibility criteria were reported for care providers in 41% of the articles, and the number of care providers performing the intervention was reported in 32% [195]. A careful description of care providers involved in the trial, as well as details of the sites in which participants were treated, helps readers appraise the risk of bias and the applicability of the results [22 188]. Eligibility criteria for sites typically relate to site volume for the procedure under investigation or similar procedures. Eligibility criteria for care providers might include professional qualifications, years in practice, number of interventions performed, skill as assessed by level of complication when performing the intervention, and specific training before trial initiation. Exclusion criteria should be justified because they will influence the applicability of the trial results [188].