FLOW Trial
A Trial of Wound Irrigation in the Initial Management of Open Fracture Wounds
FLOW Investigators · N Engl J Med · 2015
In this international 2x3 factorial randomised trial of 2,447 patients with open fractures, normal saline demonstrated lower reoperation rates than castile soap, while irrigation pressure (high, low, or very low gravity flow) showed no significant difference in clinical outcomes.
Citation & links
FLOW Investigators, Bhandari M, Jeray KJ, Petrisor BA, Pinto R, Devereaux PJ, et al. A Trial of Wound Irrigation in the Initial Management of Open Fracture Wounds. N Engl J Med. 2015 Dec 31;373(27):2629-41.
Key findings
- 1.Reoperation rates within 12 months were significantly higher in the castile soap cohort compared to the normal saline cohort (14.8% vs. 11.6%; hazard ratio 1.32; 95% CI, 1.06 to 1.65; p = 0.01).
- 2.No significant difference in reoperation rates was identified across irrigation pressures: high pressure (13.2%), low pressure (12.7%), and very low gravity flow (13.7%) showed comparable outcomes.
- 3.Pairwise comparisons between pressures demonstrated no statistical divergence: high vs. low pressure (HR 1.02; 95% CI, 0.78 to 1.33), high vs. very low pressure (HR 0.96; 95% CI, 0.73 to 1.25), and low vs. very low pressure (HR 0.94; 95% CI, 0.72 to 1.23).
- 4.Surgical site infection rates were similar across all pressure groups, confirming that pulsatile high-pressure lavage does not reduce clinical infection rates over gravity flow.
- 5.Castile soap was associated with a higher incidence of repeat surgical procedures specifically for wound healing complications, likely secondary to local cellular toxicity and tissue irritation.
- 6.The volume of irrigation remained standard across groups according to Gustilo-Anderson classification (minimum 3L for Type I, 6L for Type II, and 9L for Type III), demonstrating that volume and thorough debridement matter more than delivery pressure.
Background
Wound irrigation is a foundational component of the initial surgical management of open fractures, aiming to reduce bacterial contamination and remove foreign debris. However, considerable debate persisted regarding the optimal hydrostatic pressure required (pulsatile high-pressure vs. low-pressure vs. gravity flow) and whether additive solutions like surfactants (castile soap) offered superior outcomes compared to standard isotonic normal saline. The FLOW trial sought to determine whether irrigation pressure and fluid type affected the rate of unplanned reoperations within 12 months.
Methods
The Fluid Lavage of Open Wounds (FLOW) study was a multicentre, blinded, randomised controlled trial employing a 2-by-3 factorial design conducted across 41 clinical sites in the United States, Canada, Australia, Norway, and India. A total of 2,447 adult patients presenting with operatively treated open extremity fractures were randomised to receive irrigation with either castile soap solution or normal saline delivered via high pressure (>20 psi), low pressure (1–2 psi), or very low pressure (gravity flow). Standardised volumes of irrigation fluid were delivered according to fracture severity based on the Gustilo-Anderson classification (typically 3 L for Type I, 6 L for Type II, and 9 L for Type III). The primary outcome was reoperation within 12 months for wound infection, soft-tissue healing problems, or bone-healing complications.
Clinical implications
The FLOW trial fundamentally reshaped clinical guidelines (such as BOA/BAPRAS and OTA standards) for open fracture management. It demonstrated that castile soap should not be used in open fracture lavage due to increased reoperation rates, cementing normal saline as the irrigant of choice. Furthermore, it refuted the dogma that expensive, high-pressure pulsatile lavage systems are necessary, showing that simple, cost-effective low-pressure or gravity-flow irrigation achieves equivalent outcomes without risking collateral soft-tissue damage or bacterial seeding deeper into bone canal architecture.
Critical appraisal
Strengths include the large sample size (>2,400 patients), pragmatic international multicentre execution across diverse healthcare systems, factorial design, blinding of outcome adjudicators, and robust 12-month follow-up with high retention (>90%). Limitations include the inability to completely blind operating surgeons to the delivery pressure (though outcome assessors remained blinded) and heterogeneous injury types across the cohort, ranging from low-energy Gustilo Type I injuries to severe Type IIIB/C open fractures.
Teaching note
For fellowship and exit examinations (FRCS Orth/EBOT/FRACS), remember the core message of FLOW: use normal saline, avoid soap, and low pressure or gravity flow is completely acceptable. High-pressure pulsatile lavage adds substantial expense with zero clinical benefit and potential cellular trauma.
Exam-tested points
- ›Trial acronym and publication: FLOW trial (Fluid Lavage of Open Wounds), NEJM 2015.
- ›Study design: 2x3 factorial international randomised controlled trial with 2,447 open fracture patients.
- ›Interventions tested: Castile soap vs. normal saline; high pressure vs. low pressure vs. very low (gravity flow) pressure.
- ›Primary endpoint: Composite reoperation rate within 12 months for infection, wound healing, or nonunion.
- ›Main fluid finding: Castile soap significantly increased reoperation risk compared to normal saline (HR 1.32; p = 0.01).
- ›Main pressure finding: Irrigation pressure made no statistical difference to reoperation or infection rates.
- ›Clinical takeaway: Open fracture debridement is best served by copiously irrigating with plain normal saline via low pressure or gravity flow, avoiding additive soaps and unnecessary pulsatile high-pressure devices.
- ›Standard volumes used in protocol: 3 Litres for Gustilo Type I, 6 Litres for Type II, and 9 Litres for Type III fractures.
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