The Pinprick Test: Key Considerations in Execution of Skin Flap Perfusion Testing

Effective pinprick test, a method of testing skin free flap perfusion, is essential to establish and confirm blood inflow in free tissue transfer. Free flap monitoring is essential and comprises several methods, specifically, Acland test for the microvascular anastomoses and clinical bedside evaluations based on skin flap colour, capillary refill time, flap temperature, tissue turgor and texture, and peripheral bleeding on pinprick testing.1,2 Novel methods using the gold standard traditional bedside assessment, pinprick testing, combined with indocyanine green (ICG) near-infrared angiography has been reported to be useful in evaluating the distribution of flap blood flow.3,4 The combined ICG-pinprick flap perfusion test demonstrated effective perfusion-related outcomes in intra-oral free flaps monitoring; however, the effectiveness in execution of the pinprick test may have divergent outcomes in inexperienced hands. Especially during flap congestion, troubleshooting, or when ICG-pinprick test is performed in a very brightly perfused area.5 We describe some key considerations during execution of the pinprick test, in the attempt to eliminate technical performance doubts when skin free flap distal perfusion is equivocal.

The Pinprick Testing

A hollow straight 20-24G needle is used, in close to 90 degrees’ insertion angle, to the more distal to the anastomosis pedicle skin paddle, on non-previously pinpricked or bruised skin. The needle is inserted through the dermis to the subcutaneous fat of the flap. A slower extraction speed of the needle allows fresh blood to enter the lumen, as the oblique beveled shaped proximal needle side is exiting the skin surface. A drop of blood (above a millimeter) appears on the flap skin surface within maximum 5 seconds after full needle extraction (Fig. 1).

Fig. 1.

The pin-prick test: A step-by-step guide and key considerations for effective skin flap perfusion testing. 1: 20-24 Gauge hollow straight needle, 2: Slow needle extraction speed, 3: 90 degrees angle of insertion, 4: Wait up to five seconds until physiological fresh blood appears.

Conventional clinical bedside evaluations of flap are based on observations (capillary refill time, temperature, turgor and texture) and bleeding which may prove to be subjective; strictly technique and experience dependent. (5) The pinprick test, a traditional gold standard reliable method to establish fasciocutaneous flap blood perfusion, is likewise technique dependent; especially in congested flaps or when the survival is puzzling. We demonstrated a hierarchical task analysis in pinprick testing execution and presented reasoning of the rationale of each described consideration. We advocate that the needle hollowness and size, area and angle of insertion, speed of needle extraction through the dermal and subdermal plexuses and expected fresh bleeding time are essential during pinprick perfusion testing, especially in the hands of inexperience surgeons, to enable reliability, reduce multiple punctures and increase specificity of this test.