Hemostasis Strategy in UBE

#Bleeder Source Classification

To respond effectively to bleeding, the source must first be classified. Bleeders encountered in UBE fall into four broad categories.

(a) Epidural venous plexus
The most common — and the greatest challenge of UBE. Bleeding from this source begins the moment the epidural space is entered after ligamentum flavum removal, appearing as small spurts above and lateral to the dura. Pressure is low and the bleeding tends to be self-limited, but it clouds the visual field and impedes the next step.

(b) Bone bleeders
Arise from cancellous bone of the lamina, facet, or spinous process base. Often observed following decompression with the burr, with an oozing character. If neglected at closure, they are a frequent source of postoperative subcutaneous or epidural collection.

(c) Muscle bleeders
Occur during initial dissection or around the lateral facet, from the paraspinal musculature. They include vasculature within the multifidus and similar muscles and are most commonly encountered while creating the initial working space.

(d) Arterial bleeders
Rare but emergent. A spurting arterial bleeder may arise from injury to a segmental artery branch or a foraminal vessel. If immediate coagulation fails, the threshold for conversion to open surgery must be recognized and acted on quickly.

Each source differs in the timing of its appearance, its character, and the appropriate method of control. When bleeding begins, the first task is to identify which source it is.

#RF Coagulation: Tools and Principles

Hemostasis in UBE is centered on radiofrequency (RF) coagulation. The fundamentals are identical to those of bipolar electrocautery in open surgery, but it is critical to recognize that the operating environment is different.

Bipolar vs monopolar
In UBE, bipolar is preferred, for two reasons: (1) thermal energy can be precisely localized, protecting the adjacent dura and nerve roots, and (2) stable coagulation is achievable even in a saline environment. Monopolar may be used for deep oozing during muscle dissection, but its use near the dura must be avoided.

Tip types
RF tips come in several configurations — flexible, curved, hooked — and are chosen by target location: (1) Flexible / straight — for vessels or muscle in an open area. (2) Curved — for approaches inside the foramen or to the contralateral side. (3) Hooked — for hooking tissue while coagulating, exploiting the mass effect.

Power settings & contact technique
Begin with a low setting of 20–30 W, increasing in 5–10 W increments only when effect is inadequate. Starting at high power increases collateral tissue damage. Activate the tip in short bursts of 1–2 seconds while in light contact with the bleeder. Do not push; a "tap and release" pattern is safer. Prolonged contact causes tissue charring, and rebleeding occurs as charred tissue detaches.

Saline environment considerations
Saline disperses thermal energy. With adequate irrigation flow, thermal damage to adjacent tissue is reduced; with insufficient flow, local heat accumulation can occur. When using RF, consciously verify that irrigation flow is being maintained.

Adjunct: epinephrine-saline irrigation
Some reports suggest that adding epinephrine to the irrigation saline contributes to intraoperative hemodynamic stability. However, because epinephrine carries the possibility of systemic absorption, prior consultation with the anesthesia team is required.

#Step 1. Source Identification

When bleeding begins, the first question to ask is a single one: where is the blood coming from?

Caution under pump pressure
High pump pressure can temporarily tamponade a venous bleeder, hiding it from view. This is the risk of false hemostasis emphasized within fluid management principles. If the visual field suddenly clouds without a clearly visible bleeder, first reduce pump pressure transiently — or switch to gravity. As the pressure drops, the masked bleeder reveals itself.

Bleeder isolation
(1) Briefly reduce or stop irrigation flow. (2) Rotate the scope tip slowly, tracing where the bleeding column begins. (3) Once the bleeder is noted, approach it and identify the source type (vein vs bone vs muscle). (4) When the source is identified, transition to a source-specific strategy.

The trap: indiscriminate RF before source identification
The most common mistake. Applying RF reflexively to every visible area while panicked by an obscured field causes two problems: (1) the source goes untouched while surrounding tissue is damaged and bleeding continues, and (2) the dura or nerve root sustains thermal injury. "Identify before you cauterize" is the first principle of hemostasis.

#Step 2. Source-specific Hemostasis

Once the source is identified, control proceeds with the method matched to its type.

Epidural venous plexus
Gentle bipolar RF coagulation in short bursts of 1–2 seconds. If there is no active bleeder and only oozing, press with a saline-soaked patty for 30 seconds and reinspect (most are self-limited). Maintain a 1–2 mm distance from the dura to avoid direct contact. Overly aggressive coagulation increases the risk of rebleeding from venous wall thickening.

Bone bleeders
Apply a small amount of bone wax with an RF probe or small curette. For oozing at the lamina edge, smooth the surface with a high-speed burr and achieve cortical sealing. At the end of the case, inspect every bone surface one more time (a common source of postoperative epidural collection).

Muscle bleeders
Large vessels: bipolar RF. Diffuse oozing: surface coagulation with monopolar RF. However, monopolar is not used near the dura.

Arterial bleeders
Isolate the source immediately with bipolar. If the field does not recover, apply temporary control with patty packing, then re-confirm the anatomic context with fluoroscopy. If coagulation does not control it, recognize the conversion threshold and decide quickly.

After source-specific control is complete, observe the same area for at least 30 seconds to confirm no rebleeding.

Systemic adjunct: Tranexamic acid (TXA)
Beyond source-specific bleeder control, the antifibrinolytic agent tranexamic acid (TXA), used as a systemic or topical adjunct, can further reduce perioperative blood loss and postoperative hematoma formation. The mechanism is inhibition of plasmin-mediated fibrinolysis, preserving the stability of clots already formed.

#Evidence:

A systematic review of topical TXA alone (18 studies, 2,045 patients) demonstrated significant reductions in intraoperative/postoperative blood loss and hospital stay, with no differences in rates of thromboembolism or infection compared with controls. A cervical spine meta-analysis showed the same pattern (reduced intraoperative/total blood loss, no difference in complications). Extending evidence established in open spine surgery to UBE is a reasonable approach.

Three regimens are applicable in UBE. (1) Pre-operative IV bolus (standard) — 10–15 mg/kg IV bolus before skin incision. Administered by the anesthesia team at the time of anesthesia induction. The regimen with the most evidence and the established standard practice. (2) Topical TXA at closure — Just before closure, add 1–3 g of TXA to the saline irrigation to irrigate the working space, or apply TXA-soaked Gelfoam onto the surgical bed. Systemic absorption is lower, conferring a lower thromboembolism risk. (3) UBE-specific consideration — Adding TXA directly to the continuous saline irrigation is reported in only a small number of cases, and because of the possibility of systemic absorption with the large irrigation volume used in UBE (median 9 L), prior consultation with the anesthesia team is required. For now, the combination of (1) pre-op IV and (2) topical at closure is the most practical.

#Contraindications:

Active intravascular thrombosis, recent thromboembolic event, severe renal impairment (with dose reduction), and prior seizure with TXA exposure. With high-dose regimens (> 30 mg/kg), additional seizure risk must be considered.

In particular, in bilateral decompression or multilevel cases — where securing adequate hemostasis time is most challenging — TXA is an option that should be actively decided together with the anesthesia team at the case-planning stage.

#Common Pitfalls

(a) Pump pressure masking a venous bleeder
Recognition: The intraoperative field appeared clean and hemostasis seemed perfect, yet an epidural hematoma is found on postoperative MRI or the patient complains of postoperative leg pain.

Recovery (= prevention): (1) When using a pump, switch it off before closure without exception. (2) Wait at least 30 seconds, then reinspect the working space (identical to the fluid management end-of-case routine). (3) Explicitly confirm every venous bleeder. (4) In bilateral decompression cases, extend the wait time to at least 60 seconds.

(b) Bipolar tip in direct contact with the dura
Recognition: During coagulation, the dura suddenly contracts or a small CSF leak appears.

Recovery: (1) Deactivate the RF immediately. (2) For a small CSF leak, fibrin sealant or a small patch repair. (3) For larger dural tears, microsuture or tissue glue. (4) Re-review the coagulation position and re-learn the technique of maintaining 1–2 mm distance from the dura.

(c) Underestimating bone bleeders
Recognition: Postoperative swelling around the wound, subcutaneous hematoma, or an epidural collection found on imaging.

Recovery (= prevention): (1) Explicitly inspect every cancellous bone surface immediately after bone work. (2) Apply bone wax or burr smoothing to oozing surfaces. (3) When placing a drain, position the tip near the most active bone bleeder. (4) For bilateral or multilevel cases, plan hemostasis time separately.

#Pearls for the First Cases

Hemostasis in UBE is not a separate step. It is the procedure itself, woven into every moment from initial dissection to closure. If working portal triangulation builds the geometry of the working zone and fluid management determines its hydrodynamics, then hemostasis is the final layer that allows both to operate safely.

#Author Note

This article provides technical instruction on hemostasis principles in unilateral biportal endoscopic (UBE) surgery and does not substitute for individual clinical judgment. Bleeder management, RF power settings, tranexamic acid dosing and route of administration, and conversion thresholds should be individualized based on patient factors, surgical context, anesthesia team consultation, and surgeon experience.