Mechanical evacuation of the blood is indicated in either of these two scenarios:10
• Spontaenous blood absorption is too slow to allow treatment of a retinal pathology.
• The IOP cannot be medically controlled and corneal blood staining threatens. Surgery is 20 times more likely to be necessary if there is rebleeding . Several surgical techniques are available. The selection is partially based on whether the blood has clotted and partially on surgeon preference.
8 Must not be used by persons having liver or renal disease; side effects are common and include diarrhea and postural hypotension.
9 These recommendations should be reversed if the patient is a noncompliant child or has sickle cell disease or a rebleeding.
10 The intervention is more pressing if the patient has sickle cell disease.
• The initial step is the preparation of a paracentesis. To be efficient, and reduce the risk of intra- and postoperative complications, the paracentesis must satisfy several criteria (Fig. 2.5.1a,b). The working paracentesis should be on the temporal side to increase convenience and minimize interference from the patient's nose.
• When the blood is liquid, simple irrigation is sufficient. The washout can be accomplished via a single paracentesis or via two.
- If a single paracentesis is used, the irrigation cannula must be relatively small (23 g suffices) to fit the channel and to allow fluid11 to egress (Fig. 2.5.1c). While the cannula is in the AC, it must be angled by the surgeon so as to minimize the risk to the endothelium and to the lens in a phakic eye. The surgeon can use both hands to hold the syringe (5 or 10 ml), and press the lower corneal wound lip down to gape the wound.
- If two paracenteses are used, a larger cannula may be selected; the second paracentesis should be made on the opposite side of the eye where fewer manipulations are required. The surgeon uses a spatula to depress the wound lip here to gape it for easier fluid egress.
• When the blood is clotted, it must be evacuated using the vitrectomy probe or a fine forceps. Especially if the vitrectomy probe is used, an AC maintainer (Fig. 2.5.2) must be placed first to avoid collapse of the AC. Extreme caution is needed to prevent injuring the endothelium, lens, or the irisi2; viscoelastics should not be used until the blood has been removed.
• A fairly thorough evacuation of the blood is recommended, but not all circulating red blood cells need to be removed.
• If a rebleeding is detected, it can be halted with viscoelastics and then the source cauterized if vitrectomy instrumentation is available.
• Whether air or viscoelastics needs to be left in the AC at the conclusion of surgery depends on the specifics of the case. The main goal is to
11 A mixture of blood and BSS, used for irrigation.
12 This can cause severe intraoperative bleeding.
Fig. 2.5.1 The technique of paracentesis and AC irrigation. a The eye is held firmly with forceps (not shown here); ideally, the conjunctiva is grasped at a convenient location on the same side as the paracentesis: this allows the eye to be held against (blue arrow) the force of the MVR (white arrow). The MVR blade should be placed slightly central from the limbus to avoid pushing stem cells into the AC and to reduce the risk of synechia formation. The solid line shows the slice in the epithelium, the dotted line in the endothelium. The channel created by the blade is obviously a slit, yet it allows simultaneous fluid transport in both directions if the irrigation cannula is correctly used.1 b The angle of blade direction is also important: too shallow a path leaves a large scar, limits maneuverability of the instruments introduced through the channel, and causes image distorsion2 by compressing the cornea; too deep a path also limits instrument maneuverability and makes it less likely that the paracentesis will be self-sealing. An angle of 15-20° allows easy manipulations in the AC while alleviating the need for suturing. c The cannula must be kept parallel to the iris (reduce the injury risk both the endothelium the lens in the phakic eye), and its tip is kept over the iris at all times. The jet stream is not too forceful and is roughly parellel with the plane of the iris; the angle is irrigated with a gentle stream. As long as blood flows out from the AC freely, there is little need to modify the cannula's position. If the blood is sticky in certain places, this can usually be "uprooted" with a directly aimed jet stream
1 i.e., the cannula is gently pushing down on the lower lip of the corneal wound to gape the wound, as described in the text and Fig. 2.5.2.
2 This is also true for manipulating any instrument inside the AC whether the paracentesis was performed for blood washout or any other purpose.
have the AC reformatted and the IOP restored. If viscoelastics are left behind, the IOP may rise significantly, and prophylactic antiglaucoma treatment with close follow-up is necessary. Air takes longer to absorb from the AC than from the vitreous cavity.
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