Prevention of retained surgical sponges: a decision-analytic model predicting relative cost-effectiveness

Abstract

Background: New technologies are available to reduce or prevent retained surgical sponges (RSS), but their relative cost effectiveness are unknown. We developed an empirically calibrated decision-analytic model comparing standard counting against alternative strategies: universal or selective x-ray, bar-coded sponges (BCS), and radiofrequency-tagged (RF) sponges.

Methods: Key model parameters were obtained from field observations during a randomized-controlled BCS trial (n = 298), an observational study of RSS (n = 191,168), and clinical experience with BCS (n approximately 60,000). Because no comparable data exist for RF, we modeled its performance under 2 alternative assumptions. Only incremental sponge-tracking costs, excluding those common to all strategies, were considered. Main outcomes were RSS incidence and cost-effectiveness ratios for each strategy, from the institutional decision maker's perspective.

Results: Standard counting detects 82% of RSS. Bar coding prevents > or =97.5% for an additional $95,000 per RSS averted. If RF were as effective as bar coding, it would cost $720,000 per additional RSS averted (versus standard counting). Universal and selective x-rays for high-risk operations are more costly, but less effective than BCS-$1.1 to 1.4 million per RSS event prevented. In sensitivity analyses, results were robust over the plausible range of effectiveness assumptions, but sensitive to cost.

Conclusion: Using currently available data, this analysis provides a useful model for comparing the relative cost effectiveness of existing sponge-tracking strategies. Selecting the best method for an institution depends on its priorities: ease of use, cost reduction, or ensuring RSS are truly "never events." Given medical and liability costs of >$200,000 per incident, novel technologies can substantially reduce the incidence of RSS at an acceptable cost.

FIGURE 1

Structure of the sponge-tracking model in a standard counting protocol. Each pair of yes/no arrows represents a chance node in the decision model. Chance probabilities for each strategy were derived from previous research and from algebraic back-computation from epidemiologic data. Costs are accrued both from the intrinsic cost of the technologies employed and from any X-rays incurred as a result of unreconciled discrepancies. In accordance with a previously described taxonomy, we consider discrepancies to be instances in which a subsequent count does not agree with a previous one (this definition differs from that of Egorova et al. who refer to unreconciled incorrect final counts as discrepancies). Misplaced sponges are those unintentionally lost in the OR, either on the floor, in the trash, in the drapes, or elsewhere. Misplaced sponges may or may not be subsequently found. Those misplaced within the patient’s body cavity may be found either before the patient leaves the operating room (a “near miss”) or post-operatively (an RSS adverse event). Universal use of X-ray decreases the RSS rate primarily by detection of most sponges that are left in the patient, in the absence of a discrepancy (*) For the selective mandatory radiography strategy, obesity is assumed to decrease the likelihood of discovering a sponge misplaced in the patient (†) and decrease the sensitivity of X-rays (§). Emergencies and unexpected procedure changes are assumed to increase the likelihood of misplacing a sponge (£). The bar-coded sponge (BCS) system affects the RSS rate by increasing detection of incidents of misplaced sponges (#). Radiofrequency-tagged (RF) sponges would be expected to increase reconciliation of discrepancies (@) and increase discovery of sponges misplaced in the patient (¥). The RFID system is expected to have effects common to both BCS and RF.