Several needle and catheter types exist in the world for use of diferent measurements. Below we discuss each of the types and present the advantages and disadvantages associated with each. (Please note that Gaeltec do not make or offer the majority of these products)
Early compartmental measurement techniques employed a simple 18 gauge needle inserted into the compartment to be measured. The needle was then connected to a mercury pressure manometer for pressure recording. Although the needles are readily available, several studies have shown that they yield the least reliable and least reproducible data. Because there is a single entry port for interstitial fluid, pressures are falsely elevated or depressed if the needle becomes plugged with tissue or is inadvertently inserted into tendon or fibrous tissue.
The wick catheter technique was introduced in 1976 to provide an improved method for pressure monitoring. The catheter contains multiple fibers at its tip which are introduced into a compartment with an introducer needle. The fibers act by capillary action to improve rapid equilibration with intracompartmental interstitial pressures, while preventing ball-valve obstruction at the tip. Furthermore, the catheter may be left in place for up to 8 hours for serial recordings. Disadvantages include the possibility of coagulation and occlusion around the tip, as well as the possibility for fibers to break off and remain within the tissues. Furthermore, wick catheters may only be used to measure a single compartment and cannot be reused.
The slit catheter was introduced in 1981. It is a polyethelene catheter with 5 six-millimeter axially cut slits at the tip to provide a greater open surface area of the catheter for equilibration with interstitial fluid. As with the wick catheter, it may be left in place for serial pressure recordings, but is also susceptible to clotting. Additionally, it may only be used for measurement of a single compartment.
The side-ported needle was introduced in 1988. These needles are inserted into intramuscular compartments perpendicular to the surface, and therefore side ports have low risk of occlusion. This allows for improved accuracy (compared with simple needles) of interstitial pressure measurements along with the additional advantage of being capable of measuring several compartments in the same patient. They have been shown to have similar accuracy to slit catheters. The Stryker Pressure Monitor utilizes this needle type.
Transducer-Tipped Catheters *Made by Gaeltec
The Gaeltec High Pressure Needle transducers have been redesigned in order to improve mechanical robustness and
to reduce the risk of membrane rupture at higher pressures. Initially, only one version is available, the CTN-4F with
domed tip. The transducer body is 140mm long and 1.33mm in diameter. It is supplied with 500mm of flexible
silicone rubber cable terminated in a 6-pin Lemo series 2 connector. A 2m extension cable is available to suite the
Sensor: Thin Film resistive strain gauge
Housing: AISI type 304 surgical steel
Bridge Excitation: 1.5V AC or DC maximum
Bridge Resistance: < 1KΩ nominal
Sensitivity: ca 0.15 mV/V/At.
Pressure Range: up to 3MPa
Compensated Temperature Range: 15 to 40°C
Temperature Coefficient of Zero: <0.05% FS/C°
Temperature Coefficient of Sensitivity: <0.2% FS /C°
Linearity & Hysteresis Error: <±1% FS BSL
Overpressure: Not Known.
They are available from Gaeltec.com.