We thank Drs. Palte and Gayer for their thoughtful response to our recently published article.1
We appreciate their input and would like to respond to their comments.
Patient’s safety in anesthesiology is a critical point and becomes even more important in the context of medical research. We totally agree that ocular sonography can be detrimental by either thermal or mechanical injuries. Palte et al.
in an animal study on four rabbits, have clearly demonstrated that significant increase in ocular temperature (more than 1.5°C) may occur in subcutaneous, corneal, cameral, or vitreal areas after 90 s of direct application to the cornea of a Micromaxx® 10 MHz probe (Sonosite, Bothell, WA); the latter been used in our study. They have also shown that this thermal effect is time dependent. In our study, two trained investigators made all measurements, and strict attention was paid to decrease exposure time to ultrasound to less than 60 s. As has recently been highlighted,3
“minimizing the exposure time is probably the most important factor for ensuring patient safety from thermal injury.” Moreover, in our study, applying the probe on a thick layer of ultrasound gel over the closed upper eyelid could have decreased the heat transfer.
Anesthesiologists who want to train for ocular ultrasonography should, however, be aware of the risk of prolonged exposure to ultrasounds. In the view of current knowledge in the topic, limiting the examination time to less than 90 s seems to be safe. It would be of great interest to develop ocular phantoms modelizing the eye and optic nerve sheath to allow training in ocular ultrasound without unnecessary human exposure to ultrasound. We also strongly encourage manufacturers to develop specific ocular settings or dedicated probes for ocular ultrasonography with low power output and mechanical and thermal indexes less than 1, allowing nonspecialists in ocular sonography to study in full safety the incidence of raised intracranial pressure in pathologies as preeclampsia or others.
Clément Dubost, M.D.,* Agnès Le Le Gouez, M.D., Viridiana Jouffroy, M.D., Sandrine Roger-Christoph, M.D., Dan Benhamou, M.D., Frédéric J. Mercier, M.D., Ph.D., Thomas Geeraerts, M.D., Ph.D.
*Hôpital d’Instruction des Armées Val-De-Grace, Paris, France. firstname.lastname@example.org
1. Dubost C, Le Gouez A, Jouffroy V, Roger-Christoph S, Benhamou D, Mercier FJ, Geeraerts T. Optic nerve sheath diameter used as ultrasonographic assessment of the incidence of raised intracranial pressure in preeclampsia: A pilot study. ANESTHESIOLOGY. 2012;117:1066–71
2. Palte HD, Gayer S, Arrieta E, Scot Shaw E, Nose I, Lee E, Arheart KL, Dubovy S, Birnbach DJ, Parel JM. Are ultrasound-guided ophthalmic blocks injurious to the eye? A comparative rabbit model study of two ultrasound devices evaluating intraorbital thermal and structural changes. Anesth Analg. 2012;115:194–201
3. Shankar H, Pagel PS. Potential adverse ultrasound-related biological effects: A critical review. ANESTHESIOLOGY. 2011;115:1109–24
© 2012 American Society of Anesthesiologists, Inc.