Optimization of Orbital Retraction During Endoscopic Transorbital Approach: Quantitative Measurement of Intraocular Pressure - SevEN 006

doi:10.21203/rs.3.rs-48936/v1

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Optimization of Orbital Retraction During Endoscopic Transorbital Approach: Quantitative Measurement of Intraocular Pressure - SevEN 006

https://doi.org/10.21203/rs.3.rs-48936/v1

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Background: Increased utilization of transorbital approach (TOA) necessitates study of the risk of increased intraocular pressure (IOP) and intraorbital pressure (IORP) due to orbital compression. We aimed to investigate the changes in IOP and IORP in response to orbital retraction in TOA and establish a method for continuous measurement of intraoperative IORP.

Methods: We investigated nine patients who underwent TOA surgery from January 2017 to December 2019, and five cadavers. IORP and IOP were measured using a cannula needle monitor, tonometer, cuff manometer, and micro strain gauge monitor.

Results: In all nine clinical cases and five cadavers, increased physical compression of the orbit increased the IOP and IORP in curvilinear pattern. In clinical cases, when the orbit was compressed 1.5 cm from the lateral margin in the sagittal plane, mean IOP and IORP levels were measured at 25.4±5.2 mmHg and 14±9.2 mmH₂O, respectively. The IORP reflected the IOP satisfactorily (Pearson correlation coefficient=0.824, p<0.001).

Conclusion: We measured IOP and IORP simultaneously during orbital compression offering the basic information of the pressure change. In clinical cases, we found that the change in IOP can be monitored conveniently and noninvasively using continuous IORP measurement.

Ophthalmology

Intraocular pressure

Intraorbital pressure

Orbital compression

Transorbital approach

Recent focus has been on the transorbital approach (TOA) as a minimally invasive approach for skull base lesions in the frontal and middle cranial fossa. TOA has several advantages: lesser wounds, minimal brain retraction, reduced cerebrospinal fluid (CSF) leakage, and shorter and lesser time-consuming access to skull base lesions.[1]

However, thus far, the TOA has been applied in a limited number of clinical cases, and little is known about its side effects. The possible ophthalmic complications of TOA surgery include enophthalmos, epiphora, ptosis, and diplopia.[2] Several factors such as direct cranial nerve injury or extraocular muscle injury due to surgery may contribute to ocular abnormalities.[3] These complications can also occur when the intraocular pressure (IOP) and intraorbital pressure (IORP) increases due to the increased physical traction by retraction of orbit and venous pressure during surgery.[4–7] This can lead to visual loss. When IOP is too high or low for a while, it permanently damages the optic nerve or causes detachment of retina.[8] Therefore, testing IOP and IORP is critical in TOA surgical patients, and their accurate measurement is essential.

Continuous measurement of IOP and IORP with a retracted orbit remains challenging, despite several measuring methods. We investigated how IOP and IORP change in TOA surgery. Furthermore, we propose a useful measurement method for continuous intraoperative IORP monitoring.

This prospective study included consecutive patients who underwent transorbital endoscopic operations from March 2019 to December 2019. Cadaver studies were performed in the Surgical Neuroanatomy Laboratory.

Cadaver studies

Five cadaveric specimens (10 eyeballs) without eye damage, including orbital disease, periorbital disease, and head trauma were examined. Cadavers with enophthalmos due to premortem or postmortem dehydration were excluded. Cadaveric specimens were processed based on previously described methods.[9] The blade was withdrawn from 0 to 2.5 cm in 0.5 cm increments for orbital retraction from orbital rim to coronal plane, the average value of three IOP and IORP measurements were obtained.

A handheld tonometer (Tono-Pen AVIA® Handheld Tonometer, Reichert Inc., USA) and direct cannulation to the eyeball using a Philips IntelliVue MP30 monitor (Philips Medical Systems, Eindhoven, The Netherlands) was used to measure IOP. Tono-Pen AVIA® was utilized cautiously without applying orbital pressure, and calibrated according to the manufacturer’s manual. IOP was measured using right-angle contact with corneal surface and average value was recorded thrice.

Cannulation method involved insertion of a 26-gauge needle into the anterior chamber through the limbus (superomedial position) for each eye.[10, 11] Cannulation was done based on manufacturer’s instruction and as previously described.[12]

The IORP was measured using a cuff manometer (Cufflator, JT Posey Company, Arcadia, CA, USA) and 3-mm tracheal tube, by placing a pressure measuring cuff on the tracheal tube between retractor blade and periorbit.

Clinical cases

The inclusion criteria were: (1) TOA surgery to treat intracranial pathology, (2) written informed consent by patient, (3) no CSF leakage prior to IOP and IORP measurement. The exclusion criteria were: (1) preoperative visual field defect and visual acuity less than 0.05, (2) IOP more than 20 mmHg preoperatively, (3) any ophthalmological disease, particularly glaucoma. All patients were tested for IOP, visual acuity, and visual field before and after surgery by the ophthalmologist.

After induction of general anesthesia and intubation, the patient was positioned in intraoperative supine state with reverse Trendelenburg at 30 degrees. An oculoplastic surgeon performed the TOA protocol similar to previous cadaver studies.[9] An ophthalmologist measured IOP at the beginning of surgery. Pressure measurement was taken at intervals of 10 minutes. A skilled inspector of each measuring instrument, blinded to the results of other tools measured the parameters.

IOP and IORP were measured individually according to the degree of orbital retraction during surgery. During orbital retraction from the orbital rim to the coronal plane, the blade were withdrawn from 0 to 2.5 cm in 0.5-cm increments, average value was obtained after measuring the IOP and IORP thrice.

The iCare pro (iCare Finland Oy, Helsinki, Finland) tonometer was used to measure the IOP. Similar to the cadaver studies, the average of three final measurements was analyzed (Fig. 1A).

A micro strain gauge monitor system (CODMAN MICROSENSOR Transducer & CODMAN® MICROSENSOR® Basic Kit, Codman, Raynham, MA, USA) was used for measuring IORP in clinical cases based on the manufacturer’s instructions (Fig. 1B). The distal catheter tip was placed between periorbit and retraction blade.

Statistical analysis

A paired Student t-test was used for statistical analysis of IOP and IORP changes. Pearson correlation coefficient was calculated with linear regression model to test the correlation between IOP and IORP. SPSS version 22.0 (Statistical Package for Social Sciences, SPSS Inc., Chicago, IL, USA) was employed for statistical analysis, with signiﬁcance level at p<0.05.

Cadaver studies

The mean IOP±SD values measured by Tono-Pen AVIA® for every 0.5-cm retraction from 0 to 2.5 cm were 4.9±5.78, 8.2±6.92, 17.2±9.59, 24.1±12.08, 34.1±10.32, and 41.9±9.04 mmHg. Greater degree of retraction increased the IOP proportionately (Fig. 2A).

IOP measured by cannula needle was set to 0 mmHg before orbital retraction. The mean IOP±SD values measured by cannula pressure monitoring method were 0, 6.6±3.72, 12.8±6.58, 19.5±10.75, 32.9±32.00, and 54.6±40.49 mmHg at each retraction (Fig. 2B).

The mean IORP±SD values measured by cuff manometer were 8.5±2.55, 10.1±2.33, 12.4±3.44, 15.3±4.19, 24.4±9.44, and 35.2±12.99 cmH2O, when the orbit was retracted from 0 to 2.5 cm with an interval of 0.5 cm (Fig. 2C).

Patient characteristics

The demographic data of clinical subjects and their IOP are presented in Table 1. One patient out of 9 was male. Mean age was 44.5±14.3 years (range, 23-70 years). The pathological findings were 5 schwannomas, 3 meningiomas, and 1 glioma. The sites of tumor differed, but were accessible through TOA surgery. Mean tumor size (±SD, range) was 26.6 mm (±7.4, 20-41.7, max diameter). The mean preoperative and postoperative IOP values (±SD, range) were 13.2 mmHg (±1.7, 11-16) and 13 mmHg (±1.3, 11-14) on the left side. There was no difference in visual acuity and visual field before and after the operation.

IOP and IORP in clinical cases

The initial mean value of intraoperative IOP of the tumor side measured by iCare was 12.7±2.33 mmHg. Mean IOP values measured consecutively by increasing the distance of retraction blade from 0 to 2.0 cm with an interval of 0.5 cm from the lateral orbital wall were 15.8±1.8, 21.1±4.5, 25.4±5.2, and 46.6±8.8 mmHg showing a curvilinear pattern (Fig. 3A). IORP was continuously measured using a micro strain gauge monitor, increasing the retraction by 0.5 cm from 0 to 2.0 cm. The mean IORP values were 0, 3.5±2.9, 7.8±5.7, 14±9.2, and 24.8±15.6 mmHg. As retraction increased, IORP also increased in a curvilinear pattern (Fig. 3B). The pressure increased gradually when retraction was less than 1.5 cm but increased abruptly when retraction was greater than 1.5 cm. Finally IOP and IORP increased to 46.6 mmHg from 12.7 mmHg and 24.8 mmHg from 0.0 mmHg, respectively, when the orbit was compressed to 2.0 cm. In a linear regression analysis of difference between IOP and IORP, there was a significant correlation between IOP and IORP (Pearson correlation coefficient=0.824, p<0.001) (Fig. 4).

Risk of the increased IOP and IORP

IOP is a dynamic balance between aqueous humor formation and outflow, which are normally nearly equal.[13] The mean IOP is approximately 14-16 mmHg (±3.5 mmHg during a 24-h cycle) in a general population, and IOP between 7 and 21 mmHg is considered statistically normal.[13-15]

Normal IORP is considered as 3-6 mmHg.[16, 17] Rapid increase of IORP is associated with orbital structural damage causing irreversible vision loss.[18] The proposed mechanism of this ophthalmologic complication is a rapid increase in IORP within the rigid confines of the orbit, resulting in hypoperfusion of critical neural structures. This is defined as orbital compartment syndrome (OCS). In OCS, optic nerve and retinal damage may develop into rapidly irreversible vision loss.

An elevated IOP due to orbit retraction during TOA surgery might lower eye perfusion pressure leading to perioperative visual loss (POVL). High IOP is still the most important risk factor for untreated glaucomatous eye (>21 mmHg) to progress to a severe stage. Glaucoma is characterized by atrophy of optic nerve and impaired vision, and the main cause of increased IOP causing neuropathy.[19-22]

There are no reports on OCS complications in the application of TOA; even if they are likely to occur. Although serious adverse events such as temporary or permanent POVL or visual disturbance due to an increase in IOP during surgery is not reported in TOA surgery; neurosurgeons should be cautious of the risks.

IOP and IORP measurement

Currently, the most accurate clinical tonometer is Goldmann applanation tonometer (GAT). When measuring the IOP, iCare has high values compared to GAT but has similar results and therefore it can be used alternately when it is difficult to use GAT because of its high correlation.[23] In clinical cases of this study, GAT was replaced with iCare for ease of measurement of intraoperative IOP.

Surgical considerations

Increased orbital pressure for over 60-100 minutes can cause permanent visual complications.[18, 24] Although there may be differences depending on the applied pressure, position, and contact area, the mean recovery time of IOP was 22.3±2.2 minutes when a 15-g weight was applied for 1 minute.[25]Therefore, it is necessary to consciously relieve the pressure on the orbit during TOA surgery. We wanted to find the basic information about range of possible retraction extent that would not cause complications during TOA surgery.

We intended to validate an instrument for measuring IOP, IORP and quantify pressure increment due to external ocular compression during TOA surgery. Our results show that as the orbit was retracted, IOP and IORP increased in curvilinear pattern (Fig. 3). In the cadaver study, we found that both IOP and IORP increased rapidly when pulled over 2 cm on inspection using a cuff manometer and a cannula needle monitoring system (Fig. 2). The slope of the ascending curve of the iCare measurement show a gradual rise in IOP when retracting the orbit to less than 1.5 cm, and an abrupt rise above 1.5 cm. Furthermore, it was observed that the highest IOP was 64.2 mmHg in iCare when the orbit was compressed to 2 cm during TOA surgery.

The method of choice for measuring IOP is iCare tonometry through direct contact with the cornea. If measured during TOA surgery, it is impossible to detect increased IOP induced by the excessive traction of the orbit continuously. However, IORP could be measured continuously using a micro strain gauge monitor system. And IORP measured using a micro strain gauge shows high correlation with IOP measured by the iCare tonometer (Fig. 4). This IORP measurement method could be a useful compensate for the shortcomings of the tonometer.

Limitations

There are some limitations to this study. First, a small number of patients who have normal IOP have been investigated in the clinical study. Second, we did not consider the geometry of the retractor and contact surface. Third, since the micro gauge catheter tip has a very small contact area, IORP may not be reflected accurately based on the position of the catheter tip. Finally, we did not consider the changes in IOP due to delayed surgical time, damage of the periorbita, CSF leakage, and did not compare the blood pressure and the reverse Trendelenburg level at the time of IOP measurement. We are continuing to collect data and these limitations will be addressed in future.

We measured IOP and IORP simultaneously in cadaver and clinical cases for transorbital surgery. The IOP and IORP rise in a curvilinear pattern when the orbit is retracted. Retracting the orbit medially more than 1.5 cm from the lateral orbital wall can increase IOP to a critical level. The change in IOP can be monitored conveniently and noninvasively using continuous IORP measurement.

CSF: Cerebrospinal fluid; GAT: Goldmann applanation tonometer; IOP: Intraocular pressure; IORP: Intraorbital pressure; TOA: Transorbital approach; OCS: Orbital compartment syndrome; POVL: Perioperative visual loss

Ethics approval and consent to participate: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional research committee (Yonsei University Health System, Severance Hospital, Institutional Review Board, 4-2019-0181) and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. This study was approved by the local institutional research committee. All the subjects gave informed consent, and we followed the principles outlined in the Declaration of Helsinki in the current study.

Consent for publication: Informed consent for publication was obtained from all individual participants included in the study.

Availability of data and materials

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

Competing interests: All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers' bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript.

Funding - No funding was received for this research.

Authors' contributions
Woo Hyun Kim, MD,1 Ju Hyung Moon, MD,2 Eui Hyun Kim, MD, PhD,2 Ji Sang Han, MD,3 Chang Ki Hong, MD, PhD,1 Je Beom Hong, MD4

WHK, JHM, EHK, JBH were responsible for the conception and design of this study. WHK, JSH, JBH acquired the data. WHK and CKH analyzed and interpreted the data. WHK and JBH wrote the draft. EHK and CKH revised the manuscript critically. All authors have read and approved the final manuscript.

Acknowledgments: The authors thank Mi-Yeon Lee for assistance with statistical analysis and Hye Won Min for designing the graphics.

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Table 1

Patient data in clinical cases
No.	Sex	Age	Pathology	Location	Tumor size (mm)	Surgical position, head position	Preop. IOP		Postop. IOP
No.	Sex	Age	Pathology	Location	Tumor size (mm)	Surgical position, head position	Lt	Rt	Lt	Rt
1	F	39	Schwannoma	V2, PPF, Lt.	12.5 × 23.4 × 24.4	Supine, neutral	14	16	14	19
2	F	42	Schwannoma	Trigeminal, Lt.	21 × 18.8 × 23.2	Supine, neutral	16	15	14	16
3	F	42	Meningioma	CS wall, Lt.	31.1 × 32.6 × 35.2	Supine, neutral	15	12	11	12
4	F	42	Meningioma	Temporal tip, Lt.	17.5 × 20.3 × 19.5	Supine, neutral	11	14	12	13
5	F	47	Schwannoma	Trigeminal, Rt.	30 × 21.4 × 24.9	Supine, neutral	12	11	13	13
6	F	35	Schwannoma	Trigeminal, Rt	41.7 × 31.5 × 27.3	Supine, neutral	11	12	11	13
7	F	70	Meningioma	ACP, Lt.	28 × 19.1 × 22.2	Supine, neutral	14	15	14	17
8	M	58	Schwannoma	CS, Rt.	25.1 × 23 × 22.4	Supine, neutral	13	14	14	15
9	F	23	Glioma	Temporal tip	20.3 × 21.2 × 18.6	Supine, neutral	13	11	14	11
ACP = anterior clinoid process; CS = cavernous sinus; F = female; IOP = intraocular pressure; Lt = left; M = male; Postop.=postoperative; PPF = pterygopalatine fossa; Preop.=preoperative; Rt = right.

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Optimization of Orbital Retraction During Endoscopic Transorbital Approach: Quantitative Measurement of Intraocular Pressure - SevEN 006

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