Epidrum replaces the Loss of Resistance Syringe as a means of identifying the epidural space, whilst performing epidural anaesthesia. Epidrum is an optimal pressure loss of resistance device that is designed to operate at a high enough pressure to discharge into the epidural space but a low enough pressure to minimise premature leaking into the patients' tissues.
This optimal pressure is generated by the extremely thin diaphragm on top of the device that acts as the meniscus of a manometer, so allowing the operator to interpret the diaphragm's signal to identify the position of the tip of the needle.
By decoupling the means of advancement of the needle from the means of detecting the epidural space, Epidrum offers the following benefits:
- Two hands on the needle (instead of one) for better directional and depth control.
- Visual endpoint.
- Optimised, low, constant pressure - minimises false positive error.
- Allows the use of a smaller needle to:
- reduce post dural puncture headache
- reduce epidural haematoma formation
- Shorter training periods.
- Supervisor can monitor the signal when the trainee is performing the procedure.
- Easily observed csf (cerebral spinal fluid) in the event of a dural tap.
- Optimal operating parameters established by original research / clinical investigation.
Epidrum offers certain important advantages over existing methods of delivering epidural anaesthesia.
Epidrum enables the user to have both hands on the needle, which makes for better control of its direction and depth. It also permits the epiduralist to maintain continuous pressure on the needle and heightens the 'feel' as its tip passes through the successive layers of tissue. It is particularly useful in difficult cases.
In those patients whose interspinous ligaments are very soft or characterised by voids, i.e. the so-called 'boggy backs', the much higher pressures generated in other devices, e.g. Loss of Resistance Syringe, will discharge into the tissues, so potentially giving the user a false positive signal that the needle's tip has entered the epidural space.
In tests with the LOR syringe the following output pressure data were recorded: mean 687; range 176-1127 (cm H2O).
N.B. Epidrum, by contrast, is fully inflated at 51 cm H2O.
Note: leaking into 'boggy backs' occurs at about 120 cm H2O which means that th low pressure Epidrum is much less likely to leak into a 'boggy back' - nor will it discomfort the patient when discharging into the epidural space.
Source: Dr. Jim Roberts' Epidrum presentation at the 9th Current Controversies in Anaesthesia and Peri Operative Medicine.
- Endpoint Signal:
The signal transmitted via the sense of touch is self-evidently more vague than the highly specific, visual signal delivered to the user by Epidrum. This is borne out by the results of the clinical investigation to be seen below.
Note: the 'Hanging Drop' technique has not been included in these comparisons because it depends on negative pressure in the epidural space, relative to atmosphere.
- Smaller Needle:
The traumatic 16 swg needle is used by anaesthetists only in epidural anaesthesia - and selected for these procedures because a smaller gauge of needle does not afford the same degree of 'feel', on which the LOR technique depends. Since the user has the benefit of a visual endpoint signal when using Epidrum, a smaller, less traumatic needle might be employed (which initial in vivo trials indicate will work satisfactorily) so reducing the incidence of serious post dural puncture headache, epidural haematoma and nerve damage.
Epidrum's design and, in particular, its operating perameters, have been informed by original anatomical research, derived from clinical investigation.
A further trial was undertaken in which nurses, with no history of performing epidural anaesthesia, were invited to compare their experiences of using Epidrum and Loss of Resistance Syringe (on a similulator, of course). The results of the 'Model Trial' were as follow:
Note: from the foregoing, there is a clear indication that it is easier and quicker for anaesthetists to learn to perform epidural anaesthesia procedures with Epidrum, not least because they can be more confident of the endpoint signal. It is also much less stressful for the consultant trainer, who has more control over the procedure when Epidrum is used, as he also can observe the endpoint signal. By contrast, when the Loss of Resistance Syringe is employed, the trainer must simply trust in the trainee that the endpoint signal will be recognised by sense of touch.
A scientifically rigorous, clinical investigation has been undertaken to compare Epidrum and Loss of Resistance Syringe techniques for the delivery of epidural anaesthesia. From the full results of that investigation, the following data have been extracted:
N.B. By adopting Epidrum for this procedure, these strong clinical indications (p = 0.068) are that the failure rate may reasonably be expected to be reduced by 4.2%, i.e. 83 - 41 = 42 (4.2%). This would save the cost of delays in the operating theatre (typically one hour?).