Main characteristics Advantages of the MinimalIOP system Why the MinimalIOP system offers these advantages Change in IOP depending on the irrigation system used Composition of the balanced saline solution Characteristics of the solution Apparatus to which this device can be connected

 

The device consists of: PVC bag, complete with tube connecting with the air source at controlled pressure and transparent flip-off vial seal, containing 500 ml of sterile balanced saline solution; a colored band printed inside the bag alerts the user that the remaining solution is less than 100 ml and that the bag must be replaced shortly. drip chamber (irrigator) with tube connecting to the irrigation line of the equipment tubes The equipment to which the bag is connected provides compressed air at low pressure (max. 80 mmHg) and causes saline solution to flow within the irrigation line.

Low-pressure irrigation
  Modern phacoemulsification techniques require strong vacuums in the aspiration line, this implies the need for high irrigation flows which, with the traditional gravity-irrigation system (bottles of solution), can be obtained only by raising the height of the irrigation bottle with the consequential increase in Intraocular Pressure (IOP).
If the irrigation pressure increases, the patient can feel pain. Furthermore, pressures greater than 100 mmHg (bottle located at a height of 130 cm above the patient's eye), if held for an extended period, can cause retinal damage which may also be permanent.
The forced irrigation kit allows the surgeon to safely perform surgery using lower IOPs.
To obtain the same fluid balance with the traditional system (gravity irrigation) it's necessary to work at intraocular pressures that go even up to 40% higher than the system.

Stability of the anterior chamber
  The system guarantees a stable anterior chamber with a low IOP even with strong vacuums (both with the peristaltic pump and with the Venturi pump). In order to use the same vacuum level, it would be necessary to position the gravity irrigation bottle at higher level, even higher than 120 cm, which would produce high intraocular pressures.
Such pressures produce dimensional variations of the anterior chamber and turbulence that hinder the removal of nucleus fragments during phaco emulsification.

Repeatability and Standardization
 With the system variations in environmental factors (the altitude of the location where the operation is performed) and technical factors(the difference between the irrigators, between the calipers of the irrigation tubes, etc.) are no longer variables that can influence the progression of the surgical operation.

Guarantee of sterility
  The air compressed at low-pressure used to pressurize the system, unlike other pressurized systems, does not come into contact with the irrigation liquid, therefore the irrigation liquid cannot lose its sterility as a consequence of erroneous maneuvers. Furthermore, the absence of antibacterial filters ensures a quicker system response. 

Transport and Storage
  The packages containing the forced irrigation kits are less fragile and require less attention during handling as compared to the irrigation solution in glass bottles.

Total length of the irrigation tube

 The pressurized bag is placed in the immediate vicinity of the I/A cassette, the solution bottle (standard or pressurized as prescribed by other systems) must be placed at least 110 cm above the height of the equipment.

  The length of the irrigation circuit is therefore, for the bag, approximately 240 cm (20 cm bag drip chamber + 20 cm tubing in the cassette + 200 cm from cassette to handpiece).
The length of the irrigation circuit in the case of the bottle (standard or pressurized) is approximately 350 cm (130 cm drip chamber bottle + 20 cm tubing in the cassette + 200 cm from cassette to handpiece). See figure.


  

The surges in the IOP when the occlusion is created and removed are due to the inertia of the saline solution in the irrigation circuit: the delay in the stoppage of the fluid column when the occlusion is created causes a pressure surge (water hammer). The delay in the restarting of fluid flow when the occlusion is removed is one of the reasons for the collapse of the anterior chamber.
These two effects are directly proportional to the mass of water in the irrigation tubing and, therefore, to its length.


Available irrigating flow - Overpressure and collapses

  Since the ratio of the two lengths is 350/240=1.46, the bag, with pressure being equal, can provide a higher flow:

 Consequence of the higher flow is that the water hammers (surges and collapses), for the same irrigation level settings (and, hence, same IOP settings), is around 46% higher using gravity irrigation than those that occur with the bag. This value is perfectly borne-out by the experimental data.

Summarizing, the pressurized bag does reduce significantly collapsing and pressure surges.


Static and dynamic IOP

  Because of the shorter length of irrigation tube, the bag, with irrigating flow being equal, can maintain the anterior chamber stable at lower static IOP.

  Even the difference of IOP between the static situation (occlusion, or aspiration OFF) and the dynamic situation (aspiration ON) is much less if the bag is used.

  For example, if a peristaltic pump is used, with the bottle at 80 cm, there will be 60 mmHg in a static situation and approximately 30 mmHg in dynamic situation (flow adjusted to 50 cc/min).
If instead the bag is used, setting a pressure of 60 mmHg, the IOP will be 60 mmHg under static conditions and approximately 40 mmHg under dynamic conditions (flow at 50 cc/min).

  The smaller jump in pressure is reflected in less turbulence and greater stability in the anterior chamber.

  If the Venturi pump is used, where the flow is proportional to the vacuum set, the pressurized bag allows a stronger vacuum to be used for the same set value of IOP or it allows a smaller IOP (30%), holding the vacuum value constant.

  For example, with a 19 G phaco tip, and the bottle at 80 cm, the static IOP is 60 mmHg and a maximum vacuum of 50 mmHg can be set.
Holding IOP constant, with the pressurized bag, a 75 mm Hg vacuum can be used, or also a 50 mmHg vacuum could be used with and IOP of just 40 mmHg (instead of 60).

  The eye is under internal physiological pressure due to the hydrodynamics of the aqueous humor.
During cataract surgery by means of phacoemulsification technique, because the fragments must be aspirated together with the liquid in the anterior chamber, it is necessary to infuse saline solution to replace what is removed and to attempt to maintain the pressure as constant as possible.
However, changes in IOP and turbulence, which are damaging for the ocular structure and make surgery more difficult, are inevitable.
Therefore, it is necessary to attempt to limit as much as possible the changes in IOP by means of the method of irrigation.
Below are shown two graphs that compare the behavior of the two irrigation systems during cataract surgery.
The following are the conditions of surgery and the parameters set during phacoemulsification:

 

  In Graph 1 it can be seen how, by means of forced irrigation at a value of 35 mmHg, it is possible to perform the operation without any collapses (during aspiration the IOP remains above 8 mmHg, and even following disocclusion of the tip the pressure does not ever fall below 5 mmHg). With the bottle (gravity irrigation) placed at 50 cm above the patient’s eye level (which corresponds to an identical pressure of 35 mmHg), the eye is emptied (collapse) during aspiration.

  From Graph 2 it can be seen that, to perform an operation using the bottle without collapses (that is, with a minimum pressure of 5 mmHg resulting from disocclusion, as in the case of forced irrigation), it is necessary to position the bottle at a height of 74 cm, which is equivalent to a static IOP of 54 mmHg.
Now let’s take into consideration the pressures of the two systems in the various phases of the operation:

  Examining the extreme values reached, the pressure variations are 35 mmHg with the bag and 58 mmHg with the bottle.
Therefore, the pressure variations with the bottle are 65% higher than with the bag.
If the extreme values are disregarded and only the static and dynamic pressures (during aspiration) are taken into account, the pressure variations are 27 mmHg with the bag and 39 mmHg with the bottle, that is, 44% higher in the latter case.

  The same advantages obtained by means of the use of the Venturi pump are equally evident if the peristaltic pump is used, as can be seen in Graphs 3 and 4.

 

1000 ml contain: