◊ BACKGROUND:
Retrobulbar anaesthesia allows eye surgery in awake patients. Severe complications of the blind techniques are reported. Ultrasound-guided needle introduction and direct visualization of the spread of local anaesthetic may improve quality and safety of retrobulbar anaesthesia. Therefore, we developed a new ultrasound-guided technique using human cadavers.
◊ METHODS:
In total, 20 blocks on both sides in 10 embalmed human cadavers were performed. Using a small curved array transducer and a long-axis approach, a 22 G short bevel needle was introduced under ultrasound guidance lateral and caudal of the eyeball until the needle tip was seen 2 mm away from the optic nerve. At this point, 2 ml of contrast dye as a substitute for local anaesthetic was injected. Immediately after the injection, the spread of the contrast dye was documented by means of CT scans performed in each cadaver.
◊ RESULTS:
The CT scans showed the distribution of the contrast dye in the muscle cone and behind the posterior sclera in all but one case. No contrast dye was found inside the optic nerve or inside the eyeball. In one case, there could be an additional trace of contrast dye behind the orbita.
◊ CONCLUSIONS:
Our new ultrasound-guided technique has the potential to improve safety and efficacy of the procedure by direct visualization of the needle placement and the distribution of the injected fluid. Furthermore, the precise injection near the optic nerve could lead to a reduction of the amount of the local anaesthetic needed with fewer related complications.
◊ Reviewed by C. M. Kumar, MD
Professor, Consultant Anaesthesist,
The James Cook University Hospital, Middlesborough, United Kingdom
The authors have performed a study in cadaveric eyes where the tip of the retrobulbar needle was visualised and the spread of dye substituted for local anaesthetic agents was seen very close to the nerve. Authors concluded that the use of ultrasound has the potential to improve safety and efficacy of the retrobulbar block by direct visualization of the needle placement and the distribution of the injected fluid. They also concluded that the precise injection near the optic nerve could lead to a reduction of the amount of local anaesthetic needed with fewer related complications.
Is the study methodology sound? Can the technique performed in cadavers translate clinically and change practice of clinicians? The answer to both questions is not favourable.
The use of local anaesthesia is common during eye surgery and patients are mostly elderly who suffer from systemic diseases and receive multiple drugs. Local anaesthesia ranges from invasive technique such as retrobulbar needle block which produces akinesia and good anaesthesia to topical anaesthesia without akinesia. If akinesia is required, the blunt cannula technique “sub-Tenon’s block” has been introduced which is effective, and relatively simpler and safer 1.
The classical retrobulbar technique, as described by Atkinson2, utilises a 3.8 cm long needle which is inserted at medial 2/3rd and lateral 1/3rd junction of the inferior orbital margin and directed upwards and medially in a rotated eye. A small volume of local anaesthetic is injected into the apex where major structures are present. Many published studies have confirmed that the injection of a small volume of local anaesthetic very close to nerves of the orbit is undesirable 3. Retrobulbar block has undergone changes based on evidence and similar results can be obtained by injecting relatively higher volume of local anaesthetic agent but away from the nerves 4. The use of retrobulbar block has declined too in favour of sub-Tenon’s block and topical anaesthesia. The complications of retrobulbar block ranging from simple to major and from sight threatening to life threatening are very well documented 3. These complications have mostly occurred due to inappropriate technique, injection of local anaesthetic very close to nerve in pursuit of obtaining good block. Authors have used a 5 cm long needle for retrobulbar block and the direction of needle is not well described in this study.
However, the use of ultrasound during eye block in real patients is very difficult. Placing a probe and inserting a needle in a small area such as orbit is very difficult. Knowledge of the ultrasound mechanism is required and appropriate training in using ultrasound probe is very difficult. Finally, visualisation of the metal needle may be very difficult and the cost of the ultrasound machine is an added disadvantage.
Classical retrobulbar technique is reserved for special situations such as management of chronic orbital pain where the neurolytic agent is injected deliberately very close to the nerves5. The use of an ultrasound can be advantageous in visualising the needle tip close to the target nerve and injection of the neurolytic agent which then lead to a maximum intentional damage to the nerve. The use of ultrasound in orbital regional anaesthesia is at present limited but definitely will be of value in teaching and research 6.
It is very unlikely to completely eliminate the complications of retrobulbar block. However, a good knowledge of anatomy, education and training in retrobulbar block as well as training in the use of ultrasound may prove beneficial. In my view the use of ultrasound in routine clinical practice during retrobulbar block in eye surgery where safer alternatives exist, is difficult to prove at present.
◊ REFERENCES
1. Stevens JD.
A new local anaesthesia technique for cataract extraction by one quadrant sub-Tenon’s infiltration. Br J Ophthalmol 1992; 76:670-4.
2. Atkinson WS.
Retrobulbar injection of anesthetic within the muscular cone. Arch Ophthalmol. 1936; 16:494-503.
3. Kumar CM, Dowd TC.
Orbital regional anaesthesia. Current Opinion in Anesthesiology. 2008 Oct;21(5):632-7
4. Kumar CM, Dowd TC.
Complications of ophthalmic regional blocks: their treatment and prevention. Ophthalmologica.2006; 220: 3-82.
5. Kumar CM, Dowd TC, Hawthorne M.
Retrobulbar alcohol injection for orbital pain relief under difficult circumstances: a case report. Ann Acad Med Singapore. 2006 Apr;35(4):260-5.
6. Kumar CM.
Ultrasound in ophthalmic anaesthesia in “Ultrasound in anaesthetic practice” edrs Arthurs G, Nicholls. Cambridge University Press, Cambridge 2009 (pages169-177) |
