Tuohy needle
From Ganfyd
The Tuohy needle is used in the technique of loss of resistance to injection to gain safe access to the epidural space, typically to produce epidural anaesthesia.
The needle is named after Edward B Tuohy.
It has several defining characteristics which differentiate it from other large needles.
- Gauge: the Tuohy needle tends to be of large gauge (16G or 18G)
- Length: a typical needle is 80mm long from the hub to the tip. Longer needles are available for the obese patient (110mm and 150mm long)
- Depth markings: the barrel of the needle is marked in graduations of 1cm with alternating light and dark bands, called Lee's lines, so that the length of needle already inserted may be deduced.
- Tip: the bevel on the needle is slightly curved superiorly (to direct the catheter cephalad), and the leading edge is curved, not pointed as in a typical needle. This tip, the Huber tip is considerably blunter than another needle of equivalent size with a standard cutting tip (a Quincke tip). The bluntness adds to the force required to advance the needle through the tough ligaments of the spine, but this contributes to its safety, as the "feel" of the needle is improved, and it is less likely to puncture the dura accidentally.
- Wings: in order to apply force to advance the needle, it has wings attached to the hub which make it easier to push on. These are called Mackintosh wings.
- Obturator: the needle has a obturator (originally steel and now plastic) whose offset tip sits flush with the tip of the needle. This is to prevent cores of dermal tissue being introduced into the epidural space, where they may form ectopic keratin (keratin pearls) which can act as space-occupying lesions.
Because of its large gauge and blunt tip, the Tuohy needle may also be used for other applications, such as the insertion of a catheter for a paravertebral block, or single-shot aspiration of pleural effusion fluid.
