Reverse survivor bias in observational studies involving cohorts: a lesson from '1:1' trauma studies

The practice patterns in the management of sebaceous carcinoma of the eyelid in the Asia Pacific region

PURPOSE

To determine the practice patterns of ophthalmic plastic surgeons regarding the management of eyelid sebaceous carcinoma (SC).

METHODS

An electronic survey was distributed to oculoplastic surgical colleagues in the Asia Pacific region requesting clinical information and treatment approaches to SC.

RESULTS

The responses from 192 respondents from the Asia Pacific region was included and analyzed in this study. For initial diagnosis, most surgeons selected incisional biopsy (55%), followed by complete excision (35%). Initial workup was mainly by palpation of lymph nodes, chest X-ray, and computerized tomography scan (CT-scan) of the orbit. Conjunctival map biopsy was done in selected cases. Sentinel lymph node biopsy (SLNB) was done mainly for tumors larger than 10 mm. Management was mainly by surgical excision (5 mm margin) combined with adjuvant therapy in some cases, with radiotherapy being the most common. Margin status was determined most frequently by frozen section as evaluated by the pathologist (57%) followed by Mohs micrographic surgery (18%). Surveillance was based mainly on physical examination alone.

CONCLUSION

The Asia Pacific oculoplastic surgeons prefer incisional biopsy for lesions suspicious of SC prior to definitive surgery. This is in contrast to survey results previously reported in other populations. Frozen section control (done by an oculoplastic surgeon with pathology support) is most commonly used for margin control and conjunctival map biopsies are done only in selected cases. Despite the potential benefits of SLNB, access and expertise in this area is currently lacking in the Asia Pacific region.

Making thawed universal donor plasma available rapidly for massively bleeding trauma patients: experience from the Pragmatic, Randomized Optimal Platelets and Plasma Ratios (PROPPR) trial

BACKGROUND

The Pragmatic, Randomized Optimal Platelets and Plasma Ratios (PROPPR) trial was a randomized clinical trial comparing survival after transfusion of two different blood component ratios for emergency resuscitation of traumatic massive hemorrhage. Transfusion services supporting the study were expected to provide thawed plasma, platelets, and red blood cells within 10 minutes of request.

STUDY DESIGN AND METHODS

At the 12 Level 1 trauma centers participating in PROPPR, blood components transfused and delivery times were tabulated, with a focus on universal donor (UD) plasma management. The adequacy of site plans was assessed by comparing the bedside blood availability times to study goals and the new American College of Surgeons guidelines.

RESULTS

Eleven of 12 sites were able to consistently deliver 6 units of thawed UD plasma to their trauma-receiving unit within 10 minutes and 12 units in 20 minutes. Three sites used blood group A plasma instead of AB for massive transfusion without complications. Approximately 4700 units of plasma were given to the 680 patients enrolled in the trial. No site experienced shortages of AB plasma that limited enrollment. Two of 12 sites reported wastage of thawed AB plasma approaching 25% of AB plasma prepared.

CONCLUSION

Delivering UD plasma to massively hemorrhaging patients was accomplished consistently and rapidly and without excessive wastage in high-volume trauma centers. The American College of Surgeons Trauma Quality Improvement Program guidelines for massive transfusion protocol UD plasma availability are practicable in large academic trauma centers. Use of group A plasma in trauma resuscitation needs further study.

Collider bias in trauma comparative effectiveness research: the stratification blues for systematic reviews

BACKGROUND

Collider bias, or stratifying data by a covariate consequence rather than cause (confounder) of treatment and outcome, plagues randomised and observational trauma research. Of the seven trials of prehospital hypertonic saline in dextran (HSD) that have been evaluated in systematic reviews, none found an overall between-group difference in survival, but four reported significant subgroup effects. We hypothesised that an avoidable type of collider bias often introduced inadvertently into trauma comparative effectiveness research could explain the incongruous findings.

METHODS

The two most recent HSD trials, a single-site pilot and a multi-site pivotal study, provided data for a secondary analysis to more closely examine the potential for collider bias. The two trials had followed the a priori statistical analysis plan to subgroup patients by a post-randomisation covariate and well-established surrogate for bleeding severity, massive transfusion (MT), ≥ 10 unit of red blood cells within 24h of admission. Despite favourable HSD effects in the MT subgroup, opposite effects in the non-transfused subgroup halted the pivotal trial early. In addition to analyzing the data from the two trials, we constructed causal diagrams and performed a meta-analysis of the results from all seven trials to assess the extent to which collider bias could explain null overall effects with subgroup heterogeneity.

RESULTS

As in previous trials, HSD induced significantly greater increases in systolic blood pressure (SBP) from prehospital to admission than control crystalloid (p=0.003). Proportionately more HSD than control decedents accrued in the non-transfused subgroup, but with paradoxically longer survival. Despite different study populations and a span of over 20 years across the seven trials, the reported mortality effects were consistently null, summary RR=0.99 (p=0.864, homogeneity p=0.709).

CONCLUSIONS

HSD delayed blood transfusion by modifying standard triggers like SBP with no detectable effect on survival. The reported heterogeneous HSD effects in subgroups can be explained by collider bias that trauma researchers can avoid by improved covariate selection and data capture strategies.