Are ultrasound-guided ophthalmic blocks injurious to the eye? a comparative rabbit model study of two ultrasound devices evaluating intraorbital thermal and structural changes

Howard Palte, Steven Gayer, Esdras Arrieta Quintero, Eric Scot Shaw, Izuru Nose, Elizabete Lee, Kristopher Arheart, Sander Dubovy, David Birnbach, Jean-Marie A Parel

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

BACKGROUND:: Since Atkinson's original description of retrobulbar block in 1936, needle-based anesthetic techniques have become integral to ophthalmic anesthesia. These techniques are unfortunately associated with rare, grave complications such as globe perforation. Ultrasound has gained widespread acceptance for peripheral nerve blockade, but its translation to ocular anesthesia has been hampered because sonic energy, in the guise of thermal or biomechanical insult, is potentially injurious to vulnerable eye tissue. The US Food and Drug Administration (FDA) has defined guidelines for safe use of ultrasound for ophthalmic examination, but most ultrasound devices used by anesthesiologists are not FDA-approved for ocular application because they generate excessive energy. Regulating agencies state that ultrasound examinations can be safely undertaken as long as tissue temperatures do not increase >1.5°C above physiological levels. METHODS:: Using a rabbit model, we investigated the thermal and mechanical ocular effects after prolonged ultrasonic exposure to single orbital-and nonorbital-rated devices. In a dual-phase study, aimed at detecting ocular injury, the eyes of 8 rabbits were exposed to continuous 10-minute ultrasound examinations from 2 devices: (1) the Sonosite Micromaxx (nonorbital rated) and (2) the Sonomed VuMax (orbital rated) machines. In phase I, temperatures were continuously monitored via thermocouples implanted within specific eye structures (n = 4). In phase II the eyes were subjected to ultrasonic exposure without surgical intervention (n = 4). All eyes underwent light microscopy examinations, followed at different intervals by histology evaluations conducted by an ophthalmic pathologist. RESULTS:: Temperature changes were monitored in the eyes of 4 rabbits. The nonorbital-rated transducer produced increases in ocular tissue temperature that surpassed the safe limit (increases >1.5°C) in the lens of 3 rabbits (at 5.0, 5.5, and 1.5 minutes) and cornea of 2 rabbits (both at 1.5 minutes). A secondary analysis of temporal temperature differences between the orbital-rated and nonorbital transducers revealed statistically significant differences (Bonferroni-adjusted P < 0.05) in the cornea at 3.5 minutes, the lens at 2.5 minutes, and the vitreous at 4.0 minutes. Light microscopy and histology failed to elicit ocular injury in either group. CONCLUSIONS:: The nonorbital-rated ultrasound machine (Sonosite Micromaxx) increases the ocular tissue temperature. A larger study is needed to establish safety. Until then, ophthalmic ultrasound-guided blocks should only be performed with ocular-rated devices.

Original languageEnglish
Pages (from-to)194-201
Number of pages8
JournalAnesthesia and Analgesia
Volume115
Issue number1
DOIs
StatePublished - Jul 1 2012

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Hot Temperature
Rabbits
Equipment and Supplies
Temperature
Eye Injuries
United States Food and Drug Administration
Transducers
Ultrasonics
Cornea
Lenses
Microscopy
Histology
Anesthesia
Light
Nerve Block
Peripheral Nerves
Needles
Anesthetics
Guidelines
Safety

ASJC Scopus subject areas

  • Anesthesiology and Pain Medicine

Cite this

Are ultrasound-guided ophthalmic blocks injurious to the eye? a comparative rabbit model study of two ultrasound devices evaluating intraorbital thermal and structural changes. / Palte, Howard; Gayer, Steven; Arrieta Quintero, Esdras; Scot Shaw, Eric; Nose, Izuru; Lee, Elizabete; Arheart, Kristopher; Dubovy, Sander; Birnbach, David; Parel, Jean-Marie A.

In: Anesthesia and Analgesia, Vol. 115, No. 1, 01.07.2012, p. 194-201.

Research output: Contribution to journalArticle

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author = "Howard Palte and Steven Gayer and {Arrieta Quintero}, Esdras and {Scot Shaw}, Eric and Izuru Nose and Elizabete Lee and Kristopher Arheart and Sander Dubovy and David Birnbach and Parel, {Jean-Marie A}",
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AU - Scot Shaw, Eric

AU - Nose, Izuru

AU - Lee, Elizabete

AU - Arheart, Kristopher

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AU - Birnbach, David

AU - Parel, Jean-Marie A

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N2 - BACKGROUND:: Since Atkinson's original description of retrobulbar block in 1936, needle-based anesthetic techniques have become integral to ophthalmic anesthesia. These techniques are unfortunately associated with rare, grave complications such as globe perforation. Ultrasound has gained widespread acceptance for peripheral nerve blockade, but its translation to ocular anesthesia has been hampered because sonic energy, in the guise of thermal or biomechanical insult, is potentially injurious to vulnerable eye tissue. The US Food and Drug Administration (FDA) has defined guidelines for safe use of ultrasound for ophthalmic examination, but most ultrasound devices used by anesthesiologists are not FDA-approved for ocular application because they generate excessive energy. Regulating agencies state that ultrasound examinations can be safely undertaken as long as tissue temperatures do not increase >1.5°C above physiological levels. METHODS:: Using a rabbit model, we investigated the thermal and mechanical ocular effects after prolonged ultrasonic exposure to single orbital-and nonorbital-rated devices. In a dual-phase study, aimed at detecting ocular injury, the eyes of 8 rabbits were exposed to continuous 10-minute ultrasound examinations from 2 devices: (1) the Sonosite Micromaxx (nonorbital rated) and (2) the Sonomed VuMax (orbital rated) machines. In phase I, temperatures were continuously monitored via thermocouples implanted within specific eye structures (n = 4). In phase II the eyes were subjected to ultrasonic exposure without surgical intervention (n = 4). All eyes underwent light microscopy examinations, followed at different intervals by histology evaluations conducted by an ophthalmic pathologist. RESULTS:: Temperature changes were monitored in the eyes of 4 rabbits. The nonorbital-rated transducer produced increases in ocular tissue temperature that surpassed the safe limit (increases >1.5°C) in the lens of 3 rabbits (at 5.0, 5.5, and 1.5 minutes) and cornea of 2 rabbits (both at 1.5 minutes). A secondary analysis of temporal temperature differences between the orbital-rated and nonorbital transducers revealed statistically significant differences (Bonferroni-adjusted P < 0.05) in the cornea at 3.5 minutes, the lens at 2.5 minutes, and the vitreous at 4.0 minutes. Light microscopy and histology failed to elicit ocular injury in either group. CONCLUSIONS:: The nonorbital-rated ultrasound machine (Sonosite Micromaxx) increases the ocular tissue temperature. A larger study is needed to establish safety. Until then, ophthalmic ultrasound-guided blocks should only be performed with ocular-rated devices.

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