Estimating blood loss

Why it matters (in theatre and recovery)

• Underestimating blood loss delays resuscitation and transfusion; overestimating can lead to unnecessary fluids/blood and complications.
• Blood loss estimation is part of a bigger picture: patient physiology, surgical field, suction/drains, swabs, and lab results.
• Trend matters more than a single number: repeated estimates + observations help you spot ongoing bleeding early.

Core concepts and definitions

• Estimated Blood Loss (EBL): a best estimate from suction, swabs, drapes, and the surgical field (often imprecise).
• Measured Blood Loss (MBL): what you can actually measure (e.g., suction volume minus irrigation; weighed swabs).
• Hidden blood loss: blood in tissues/cavities or on the floor/drapes; can be significant in major surgery/trauma.
• Haemodilution: Hb may look “okay” early if bleeding is acute and fluids are given; interpret Hb in context and repeat if concerned.

Step-by-step approach in theatre (simple and repeatable)

• Start with a baseline: note pre-op Hb, weight, comorbidities, anticoagulants/antiplatelets, and expected surgical blood loss.
• Suction: record total in canister and subtract irrigation/flushes (ask the scrub team what has been used).
• Swabs: estimate by counting and (if available) weighing; if not weighed, use a consistent local rule of thumb and document it.
• Drapes/floor/gowns: acknowledge “unmeasured loss” if significant; do not ignore it when the patient is unstable.
• Drains: note output and whether it is fresh blood vs serosanguinous; sudden increases are important.
• Reassess frequently: update EBL at key points (after incision, after major dissection, at closure, on arrival to recovery).

Practical rules of thumb (use with caution and consistency)

• Suction canister: 1 mL volume ≈ 1 mL blood, but only after subtracting irrigation accurately.
• Weighing swabs: 1 g increase in weight ≈ 1 mL blood (because blood density is close to 1 g/mL).
• Visual estimation is unreliable: bright lighting, dilution with saline, and soaked drapes can mislead—prefer measured methods where possible.
• If you must use visual cues, standardise: agree with the team what “half soaked” or “fully soaked” means locally, and document the method.

Linking blood loss to physiology (what to watch)

• Early signs of significant loss: rising heart rate, falling blood pressure, narrowing pulse pressure, cool peripheries, reduced capillary refill.
• Anaesthesia can mask signs: vasodilation, beta-blockers, neuraxial block, and controlled ventilation may blunt tachycardia/hypotension.
• Look for end-organ clues: falling urine output, rising lactate/base deficit, increasing vasopressor requirement, worsening peripheral perfusion.
• Check the surgical field: ask directly if bleeding is controlled and whether loss is ongoing or expected to worsen.

What to do with your estimate (actions and communication)

• Communicate early: tell the surgeon and ODP/anaesthetic assistant your current EBL/MBL and whether it is ongoing.
• Escalate appropriately: call for senior help early if bleeding is brisk, ongoing, or physiology is deteriorating.
• Use EBL to guide planning: IV access, warming, blood availability, and whether to activate local major haemorrhage processes if needed.
• Document clearly: include method (e.g., suction minus irrigation, swab weights), time points, and key interventions.

Common first-time scenarios

• Tonsillectomy/ENT: small volumes can look dramatic; focus on suction minus irrigation and patient physiology, especially in children.
• Obstetrics: postpartum haemorrhage can be rapid; blood mixes with amniotic fluid—use weighed swabs, suction minus irrigation, and clinical signs; escalate early.
• Orthopaedics (hip/knee): hidden loss can be large; tourniquet release may cause sudden bleeding; expect Hb to fall later.
• Laparoscopy: blood can pool out of sight; unexplained tachycardia/hypotension with low suction volumes should prompt concern for concealed bleeding.