Comparison of Intubation and Laryngeal Mask for Pars Plana Vitrectomy

Usually eye surgery can be safely performed under local anesthesia. However, if the eye is opened during the procedure, general anesthesia may be a safer alternative. The intraocular pressure is less stable in wake patients than in anesthetized patients and increasing intraocular pressure can lead to prolapse of vitreous. Moreover, wake patients may move during the procedure and movement during surgery can cause serious lesions of the retina with consecutive loss of vision due to intraocular instruments.

A typical intraocular procedure is vitrectomy. During vitrectomy the vitreous body is removed and substituted by silicon oil or gas. Vitrectomy is usually performed by inserting instruments through the pars plana in the eye. The pars plana, an area between iris and retina, contains no structures essential for vision. On one side of the eye a light source and access for intraocular infusion is introduced into the eye through the pars plana. An infusion is connected and fixed at 60 cm above eye level thus maintaining intraocular pressure by gravity. On the opposite side of the eye instruments like scalpels, scissors or an instrument combining cutting and suction of vitreous can be inserted through a tube. Common indications for vitrectomy are vitreous body bleedings or retinal detachment.

Reliable immobilization by anesthesia is mandatory for vitrectomy. However, anesthesia for vitrectomy is complicated by the fact that the anatomical structures at risk are reached very early during operation and consequently there is not much time to adopt anesthesia dosage to individual patient's needs. At the end of the procedure the critical area is left a few minutes before conjunctival suture leaving a relatively short period of time for recovery from anesthesia until extubation.

Possibly due to these difficulties deviation of vision axis and patient movements are not uncommon during general anesthesia for eye operations. Usually these events can be dealt with by supplementation of anesthesia and muscle relaxation, but they can lead to impairment of operation conditions and put the patient at risk of eye damage and loss of vision. Rossiter and co-workers investigated quality of immobilisation in 52 patients during eye surgery. Even small eye movements like upward deviation of the vision axis have been regarded as incomplete immobilisation in this study because they interfere with surgery and thereby increase the risk of complications.

In four of these 52 patients (7.6 %) eye movements have been observed during surgery (Rossiter 2006). It has been shown by a further study that these deviations can be quantified and depend from the patient's preoperative findings (Daien 2013).

Vitrectomy is performed as 20-gauge- or 23-gauge sutureless transconjunctival vitrectomy, depending of the diameter of the intraocular access channel (Aylward 2011)3. Generally, operation time is considerably shorter for 23-Gauge-vitrectomie, because no conjunctival suture is needed. Hence, 23 Gauge-vitrectomies are performed under general anesthesia using a laryngeal mask without muscle relaxation at our institution. 20-Gauge-vitrectomies are performed under general anesthesia with endotracheal intubation due to longer operation times. However, total muscle relaxation is maintained only during the first 30 - 45 min of surgery until reliable immobilization is reached by volatile anesthetics. The results of Rossiter and co-workers showed that eye movements occurred only during surgery without muscle relaxation in their study. Hence, it may be argued that immobilization by balanced anesthesia only during 23 Gauge-vitrectomy and during the second half of 20 Gauge-vitrectomy may be inferior to immobilization by addition of muscle relaxants.

Objective of this prospective observational study is the comparison of immobilization quality during general anesthesia for pars plana-vitrectomy with and without neuromuscular blockade and endotracheal intubation.