Sub-Tenon's Block Technique

Faculty of Medicine Department of Anesthesia Intensive Care & Pain Management

Efficacy of Clonidine as an Adjuvant to Mepivacaine in Sub-Tenon’s Block for Ophthalmic Anterior Segment Surgery A Thesis Submitted For Partial Fulfillment of M.D. Degree in Anesthesiology

Presented By

Ramy Ahmed Gouda Hassan M.B.B.Ch., M.Sc. Ain Shams University

Under Supervision of

Prof. Dr. Ahmed Ibrahim Ibrahim Professor of Anesthesia, Intensive Care and Pain Management Faculty of Medicine, Ain Shams University

Prof. Dr. Amr Essam Eldin Abd El-Hamid Professor of Anesthesia, Intensive Care and Pain Management Faculty of Medicine, Ain Shams University

Prof. Dr. Hazem Mohamed Fawzy Professor of Anesthesia, Intensive Care and Pain Management Faculty of Medicine, Ain Shams University

Dr. Sanaa Farag Mahmoud Lecturer of Anesthesia, Intensive Care and Pain Management Faculty of Medicine, Ain Shams University

Dr. Ashraf Hassan Soliman Lecturer of Ophthalmology Faculty of Medicine, Ain Shams University

Faculty of Medicine Ain Shams University 2015

‫َّب زِدْنِي عِلْماً)‬ ‫(وقُل ر ِّ‬ ‫سورة طه اآلية‪111 :‬‬

Acknowledgment First and foremost thanks to ALLAH, the most beneficent and merciful. I wish to express my deep appreciation and sincere gratitude to Prof. Dr. Ahmed Ibrahim Ibrahim, Prof. of anesthesiology, intensive care medicine and pain management, Ain Shams University, who suggested this subject for reviewing and for his supervision, continuous help and patience. It was a great honor to me to work under his supervision. I wish to express my sincere thanks and deepest gratitude to Prof. Dr. Amr Essam Eldin Abd El-Hamid,Prof. of anesthesiology , intensive care medicine and pain management ,Ain Shams University for his eminent guidance, encouragement and revision throughout the work. Also, I would like to express my sincere thanks and deep gratitude to Prof. Dr. Hazem Mohamed Fawzy, Prof. of anesthesiology, intensive care medicine and pain management, Ain Shams University, for his keen and valuable guidance. Special appreciation to Dr. Sanaa Farag Mahmoud ,Lecturer of Anesthesiology ,intensive care medicine and pain management, Ain Shams University, for her kind advice, valuable instructions and continuous support in the completion of this work. Also, I would like to express my sincere thanks and deep gratitude to Dr. Ashraf Hassan Soliman, Lecturer of Ophthalmology, Ain Shams University, for his keen and valuable guidance and encouraging for applying some of these techniques. Last but not least, I would like to present a lot of thanks to my family, friends, and to my colleagues, whose without their help and support, this work could not come to birth. Ramy Ahmed Gouda

Contents List of abbreviations ..........................................................

i

List of tables ......................................................................

ii

List of figures ....................................................................

iii

Introduction and aim of the work ..................................

1

Review of literature ..........................................................

6

Anatomical considerations for ophthalmic regional anesthesia .............................................................

6

Physiological Aspects Related to Ophthalmic Anesthesia

20

Sub-Tenon’s Block Technique...........................................

24

Complications of Sub-Tenon’s Block Technique ..............

30

Local Anesthetic Mixture ..................................................

38

Patients and Methods .........................................................

45

Results ...............................................................................

52

Discussion ..........................................................................

64

Summary ...........................................................................

73

References .........................................................................

76

Arabic Summary ..............................................................

--

List of abbreviations ASA

: American Society of Anesthesiologists

CBC

: Complete blood count

CSF

: Cerebrospinal fluid

CT

: Computerized tomography

DBP

: Diastolic blood pressure

ECG

: Electrocardiogram

Fig

: Figure

HR

: Heart rate

I.U.

: International unit

IOP

: Intraocular pressure

IQR

: Interquartile range

LA

: Local anesthetic

LPS

: Levator palpebrae superioris

Min

: Minute

PCO2

: Partial pressure of carbon dioxide

PO2

: Partial pressure of oxygen

RBS

: Random blood sugar

RR

: Respiratory rate

SBP

: Systolic blood pressure

SD

: Standard deviation

SPSS

: Statistical Package for the Social Science

VPS

: Verbal pain score i

List of tables Table No. 1 2 3 4 5 6 7 8 9 10

Title

Page 52

Patient characteristics Comparison of motor block score the two groups Comparison of patient-reported pain the two groups Comparison of systolic blood between the two groups Comparison of diastolic blood between the two groups

between

53

between

55

pressure

56

pressure

57

Comparison of heart rate between the groups Comparison of oxygen saturation between the two groups Comparison of respiratory rate between the two groups Comparison of patients number according to sedation score between the two groups Comparison of satisfaction level between the two groups

ii

58 59 60 62 63

List of figures Figure No. Title 1 Geometry of the orbits and the eye globes 2 Subdivisions of the orbit 3 Extra-occular muscles 4 Tenon’s fascia 5 Nerve supply of the orbit and globe 6 Arterial blood supply and Venous drainage of the Orbit 7 Globe position and inferonasal direction using forceps and scissors during subTenon’s block 8 Cannula advancement in Sub-Tenon’s Block 9 Different types of sub-Tenon’s cannulas 10 Algorithm for the management of local anesthetic systemic toxicity 11 Patients number according to sedation score

iii

Page 6 9 11 13 15 18 25

27 29 36 62

Introduction and Aim of the Work

Introduction Regional anesthesia is commonly used for ophthalmic surgery. Various ophthalmic surgeries require a potent motor blockade (akinesia) of the eyeball and eyelids. Retrobulbar anesthesia was the only technique used for many years since the late 1800s, but became more widely used in the 1940s (Ripart et al., 2000). Rare but serious complications as globe perforation, brain stem anesthesia, postoperative strabismus, retrobulbar hematoma and optic nerve injury have led many physicians to abandon this technique (Hamilton, 1998). In an attempt to reduce some of the complications of retrobulbar anesthesia, peribulbar anesthesia was introduced in the 1960s. However, peribulbar anesthesia has some limitations. The complications associated with retrobulbar anesthesia have been subsequently described with peribulbar anesthesia with less, but still unacceptable frequency (Edge and Navon, 1999). Another thing is even with a twoinjection technique, peribulbar anesthesia has sometimes an excessive rate of imperfect blockade. This necessitates supplemental injection, with a rate of up to 50% in certain series.

Performing

multiple 1

supplemental

injections

Introduction and Aim of the Work theoretically increase the risk of complications (Davis and Mandel, 1994). Sub-Tenon’s (Episcleral) anesthesia was reported as early as 1884 by Turnbul and subsequently by Swan in 1956. Since then, the place for this technique in ophthalmic surgery has been reaffirmed as a well tolerated, effective, quicker, safer alternative to peribulbar, retrobulbar, or topical anesthesia in anterior and posterior segment eye surgery and even for the therapeutic delivery of drugs to the eye (Swetha et al., 2009). Sub-Tenon’s

anesthesia,

sometimes

also

called

parabulbar anesthesia, places the injection into the episcleral space. This allows the local anesthetic (LA) to spread circularly all around the scleral portion of the globe, thus accounting for high-quality analgesia of the whole globe with relatively low volumes injected (usually 3-5 mL) (Ripart et al., 1998). Injection of local anesthetic agent under the Tenon capsule blocks sensation from the eye by action on the short ciliary nerves as they pass through the Tenon capsule to the globe, akinesia is obtained by direct blockade of anterior

2

Introduction and Aim of the Work motor nerve fibers as they enter the extraocular muscles (Ripart et al., 2000). Additives have been used to prolong the duration of ophthalmic regional blocks. Clonidine (a centrally acting α 2

agonist) has been used in ophthalmic anesthesia several years ago. It was initially used as an oral premedication at a dose of 100 - 150μg. It resulted in a reduction in intraoperative stress associated with surgery and a decrease in intraocular pressure (IOP) (Weindler et al., 2000). Clonidine is a selective partial agonist for α 2

adrenoreceptors, with a ratio of approximately 200:1 (α to 2

α ). Clonidine is lipid soluble so, it penetrates the blood1

brain barrier to reach the hypothalamus and medulla. Although experience with α -agonists as sole anesthetics is 2

limited (Richard et al., 1990), data suggest that oral, intravenous, epidural, and intrathecal administration of clonidine potentiates the anesthetic action of other anesthetics, volatile or injectable, and reduces general and regional anesthetic requirements with correspondingly fewer side effects. In addition to its use in the operative setting, the addition of clonidine to local anesthetic increases the

3

Introduction and Aim of the Work duration of analgesia and reduces dose requirements for local and narcotic pain medications (Rockemann et al., 1995). The mechanism of action of clonidine in regional blocks is not completely understood. It may have a direct local anesthetic action on C fibres, act via imidazole receptors on the peripheral nerve or act as a local vasoconstrictor to prolong the action of concomitantly injected local anesthetic (Ge et al., 2006). Addition

of

Clonidine

to

local

anesthetic

in

retrobulbar block has several advantages: it decreases IOP, enhances

anesthesia

and

akinesia

and

increases

intraoperative sedation (Bahy Eldeen et al., 2011). The duration of lid and globe akinesia, globe analgesia and anesethesia was significantly increased with clonidine in peribulbar block (Madan et al., 2001). A dose-response study by Madan et al. (2001) looked at adjuvant

clonidine to peribulbar blockade for cataract

surgery, the authors concluded that clonidine enhances the duration of anesthesia and analgesia in the 1 µg/kg dose without significant side effects (Madan et al., 2001).

4

Introduction and Aim of the Work

Aim of the work The aim of this work is to study the effect of addition of clonidine to mepivacaine 3% in sub-tenon’s block as regard efficacy, safety and satisfaction of the patient

5

Review of Literature

Anatomical Considerations for Ophthalmic Regional Anesthesia I) Anatomy of the orbit: 1) Structure: The orbit functions to protect, support, and maximize function of the eye. The orbit is an irregular four-sided pyramid with its apex pointing posteromedially and its base facing anteriorly. The annulus of Zinn, a fibrous ring arising from the superior orbital fissure, forms the apex. The base is formed by the surface of the cornea, the conjunctiva and the lids. It contains the globe, orbital fat, extraocular muscles, nerves, blood vessels and part of the lacrimal apparatus (Kumar and Dodds, 2006).

Fig.1: Geometry of the orbits and the eye globes (Rubin 2003).

6

Review of Literature The orbits are aligned so that the medial walls are parallel to the sagittal plane and lines drawn along the lateral walls join behind the nose and very nearly form a right angle. The arc from medial to lateral wall in each orbit is 45° (Fig.1). The orbital floor rises about 5 degrees while the roof is horizontal (Rubin, 2003). The orbital axis thus run from behind forwards laterally and slightly downwards towards the base. The orbital axis and visual axis (the position of the eye when in straight, or primary, gaze) do not coincide (Fig.1) and the anesthetist must be quite clear as to which one he or she is referring to when describing angles for insertion of needles (Chishti and Varvinskiy, 2009). The average dimensions of the orbit are as follows (Fig.1): 

Height of orbital margin - 40 mm



Width of orbital margin - 35 mm



Depth of orbit - 40-50 mm. The orbital depth measured from the hind surface of the eyeball to the apex is approximately 25 mm (range 12-35 mm).



Interorbital distance - 25 mm



Volume of orbit - 30 cm3 (Petruzzelli and Hampson, 2008).

7

Review of Literature Because of the irregular shape of the orbit, the lateral wall is longer than the medial wall. As a result, a long (1.5 inch) needle that is inserted along the medial wall can easily reach the optic canal in most patients (Fanning, 2006). 2) Relations: Above the roof are the frontal air sinuses anteriorly and the meninges and frontal lobe of the cerebral hemisphere. Inferior to the floor is the maxillary air sinus. The infraorbital nerve and blood vessels lie within the infraorbital canal. Laterally the orbit is related to the temporal fossa in its anterior portion and the middle cranial fossa containing the temporal lobe of the cerebral hemisphere and its investing meninges posteriorly. The orbital septum forms its anterior boundary (Johnson, 1995). Medially, the orbital wall is related to the nasal cavity anteriorly, the ethmoid sinuses in the middle part and the sphenoid sinus posteriorly. The bony walls may be very thin in some individuals and

needle penetration

is possible.

Perforation of the medial wall by a block needle may result in orbital cellulitis or abscess (Wong, 1993).

8

Review of Literature 3) The subdivisions of the orbit The orbit is divided into four areas:

Fig.2: Subdivisions of the orbit (Ellis et al., 2004). 1 - The eyeball. 2 - The preseptal space, defined as anterior to a vertically aligned orbital septum. This is a thin sheet of connective tissue that encircles the orbit as an extension of the periosteum (as shown in fig.2). The septum provides an important barrier to the anterior or posterior extravasation of blood or spread of infection.

9

Review of Literature 3- The retrobulbar (intraconal) space, defined as the area posterior to the septum and within a ring formed by the rectus muscles. The retrobulbar space encloses cranial nerves II, III and VI, the nasociliary nerve (V), the autonomic ciliary ganglion and the ophthalmic vessels. As a consequence, the injection of local anesthetic into this space (retrobulbar injection) provides rapid and effective anesthesia. 4 - The peribulbar space is defined as an area posterior to the septum and lying outside the rectus cone. This space contains fewer nerves: the lacrimal (V), frontal (V), and trochlear (IV). As a consequence, injection of local anesthetic into this area requires a larger volume and acts by diffusion into the retrobulbar space. (Ellis et al., 2004)

10

Review of Literature

II) The Orbital Muscles

Fig.3: Extra-occular muscles (Dutton, 1994). These are the levator palpebrae superioris (LPS) and the extra-ocular muscles: the medial, lateral, superior and inferior recti and the superior and inferior obliques. Together, the four rectus muscles form a "cone" with the point at the orbital apex and the base at the equator of the globe. Within this cone lie the optic nerve, artery, vein and the ciliary ganglion. When performing local anesthesia blocks, the tip of the needle is inserted inside this muscle cone in retrobulbar blocks, and outside it in peribulbar blocks (Wong, 1993). The four rectus muscles originate from the annulus of Zinn (as shown in fig.3). They travel anteriorly along the orbital walls, inserting 5.5 - 7.7 mm from the limbus. The 11

Review of Literature superior oblique muscle originates from the orbital apex and passes anteriorly along the superomedial orbital wall. The tendon then passes through the trochlea and is reflected inferiorly, posteriorly, and laterally before inserting posterior to the equator on the superior and lateral aspect of the globe. The inferior oblique muscle originates from the maxillary bone slightly posterior to the orbital rim. It passes posteriorly and laterally in the orbit and inserts posterior to the equator on the inferior and lateral aspect of the globe (Graham, 2009). The combined actions of the four rectus and two oblique muscles on each eyeball allow elevation, depression, adduction and abduction. Intortion is otherwise termed inward or medial rotation, and extortion may be termed external or lateral rotation (Chishti and Varvinskiy, 2009). The medial and lateral recti move the eyeball in one axis only. The four other muscles move it in all three axes:  Superior rectus: elevation, adduction and intorsion. 

Inferior rectus: depression, adduction and extorsion.

 Superior oblique: depression, abduction and intorsion.  Inferior oblique: elevation, abduction and extorsion. (Ellis et al., 2004).

12

Review of Literature Pure elevation and depression of the eyeball is produced by one rectus acting with its opposite oblique, i.e. superior rectus with inferior oblique produces pure elevation and inferior rectus with superior oblique produces pure depression (Ellis et al., 2004).

III) Intra-Orbital Fascia: In general, the connective tissue boundaries can be divided into 4 main units as follows:

Fig.4: Tenon’s fascia (Petruzzelli and Hampson, 2008). A thin fascial membrane, the vagina bulbi, or Tenon’s fascia, ensheaths the eyeball from the corneo-scleral junction to the optic nerve; here it fuses with the dural sheath of the 13

Review of Literature nerve as it enters the eyeball. This fascia separates the eyeball from the surrounding orbital fat, allowing free motion of the globe. The tendons of the muscles perforate the fascial membrane, which is reflected onto each of these muscles as its fascial sheath (Petruzzelli and Hampson, 2008). A potential space exists between Tenon’s capsule and the episclera. A cannula can be placed into this space and solution injected.

As some of the injected solution can

diffuse along the sheaths of the extraocular muscles and as the posterior ciliary nerves enter the globe directly through this space, excellent anesthesia and akinesia will occur if adequate volumes are injected (Fanning, 2008).

IV) The Eyelids The eyelids are protracted by the orbicularis muscle which is innervated by the facial nerve. This muscle may not be paralysed by anesthetic solutions deposited behind the globe. The upper eyelid is retracted by the LPS. The lower eyelid is retracted by the capsulopalpebral fascia which is a direct extension of the inferior rectus muscle (Wong, 1993).

14

Review of Literature

V) Nerve supply of the orbit and globe

Fig.5: Nerve supply of the orbit and globe (Kumar, 2007). Four cranial nerves are responsible for the innervation of the extraocular muscles and the orbicularis oculi:

The

superior branch of the oculomotor nerve supplies the superior rectus and the LPS muscles. The inferior branch of oculomotor nerve supplies the medial rectus, the inferior rectus, and the inferior oblique muscles. The abducent nerve supplies the lateral rectus. The trochlear nerve runs outside and above the annulus, and supplies the superior oblique muscle (retained activity of this muscle is frequently observed as anesthetic agents often fail to block this nerve). The facial nerve supplies the orbicularis oculi (Kumar, 2007).

15

Review of Literature The oculomotor and abducent nerves enter the orbit within the annulus of Zinn and are distributed to their muscles on their intraconal aspects. The branch of the oculomotor nerve to the inferior oblique has a very long intraorbital course along the lateral aspect of the inferior rectus. It is especially vulnerable to damage by needles. The trochlear nerve is extraconal, running along the periorbital and entering the superior aspect of the superior oblique (Fanning, 2008). The most important sensory nerve in the orbit is the optic nerve, which enters through the optic canal along with the ophthalmic artery. The optic nerve extends from the optic chiasma to enter the orbit through the optic canal. The intraorbital portion of the optic nerve is 30 mm in length and 4 mm in diameter. The optic nerve is completely covered by dura, arachnoid, along with the subarachnoid space containing cerebrospinal fluid (CSF) and pia from the sclera to the canal, where the fibers of the dural sheath intermix with the fibers of Tenon’s capsule (Petruzzelli and Hampson, 2008). All somatosensory inputs from the eye are transmitted mainly through the ophthalmic nerve and, to a much less extent, the maxillary nerve, to the sensory root of the trigeminal nerve. The ophthalmic nerve divides into three branches, the frontal, lacrimal, and nasociliary nerves. These 16

Review of Literature branches enter the orbit through the superior orbital fissure, and provide the innervation of the eye and surrounding tissues (Wong, 1993). The sensations arising from the cornea, iris, conjunctiva, and sclera, unlike other parts of the body, are principally pain or irritation. The retina and optic nerve, like the rest of the brain tissue, lack direct sensitivity to somatosensory stimuli. However, the optic nerve dural sheaths are densely innervated with free nerve endings, and a needle puncture of the optic nerve will be painful (Wong, 1993). Injection of local anesthetic solution into the lateral adipose compartment from an inferotemporal needle insertion normally blocks the nasociliary, lacrimal, frontal, supraorbital and supratrochlear branches of the ophthalmic division of the trigeminal nerve and the infraorbital branch of the maxillary division. Injection into the medial compartment through a needle placed between the caruncle and the medial canthal angle usually blocks the medial branches of the nasociliary nerve, the long ciliary nerves, the infratrochlear nerve and medial components of the supraorbital and supratrochlear nerves (Chishti and Varvinskiy, 2009).

17

Review of Literature

VI) Blood supply of the orbit and globe

Fig.6: Arterial blood supply and Venous drainage of the Orbit (Dutton, 1994).

The main arterial supply to the globe and orbital contents is from the ophthalmic artery (Fig. 6) which is the first major branch of the internal carotid artery originating as it exits the cavernous sinus and passes into the orbit through the optic canal inferolateral to the optic nerve and within the meningeal sheath of that nerve (Petruzzelli and Hampson, 2008). Venous drainage of the orbit occurs through 2 major veins, the superior and inferior ophthalmic veins (Fig. 6). The orbital veins are valveless; therefore, direction of venous

18

Review of Literature drainage depends on pressure gradients (Petruzzelli and Hampson, 2008). It is important to note that both the largest arteries and largest veins lie in the superior half of the orbit. In addition, the vessels that have the largest diameter lie in the deep portion of the orbit. To avoid a major retrobulbar hemorrhage or intravascular injection, the needle tip should be kept out of the upper half and out of the deep portion of the orbit. The superonasal quadrant of the orbit is an especially dangerous place to put a needle. The terminal branches of the ophthalmic artery are there, an artery that is often large and tortuous in elderly, hypertensive individuals. A needle placed in this artery may result in a sight-threatening hematoma or intravascular injection of anesthetic that causes immediate seizure activity (Fanning, 2006).

19

Review of Literature

Physiological Aspects Related to Ophthalmic Anesthesia Intraocular pressure (IOP): It is defined as the tension exerted by the contents of the globe on the surrounding corneo-scleral envelope. Normally it ranges between 10-20 mmHg and there is diurnal variation of 2-3 mmHg with higher pressures in the morning. It may differ by up to 5 mmHg between eyes. It increases with age and there is a positive correlation between IOP and axial length. IOP changes from sitting to supine position from between 0.3-6 mmHg. Transient rises in IOP are seen with coughing, straining and vomiting, but are of no consequence to the intact eye. Prolonged rises in IOP however, may cause progressive loss of vision (Chishti and Varvinsky, 2009).

Aqueous humor: Its volume is about 250μL and is produced at a rate of 2.5μL/min. Its composition is similar to that of plasma except for a much higher concentration of ascorbate, pyruvate and lactate and a lower of concentration of protein, urea and glucose. IOP is a function of the rate at which aqueous humour enters the eye (inflow) and leaves it (outflow). When these

20

Review of Literature flow rates are equal the IOP remains fairly constant. Inflow is related to the rate of aqueous humor production, whilst outflow depends on the resistance to flow of aqueous from the eye and the pressure in the episcleral veins (Murgatroyd and Bembridge, 2008).

Factors affecting IOP: 1. Arterial blood pressure- A fall in systemic blood will reduce IOP, but only becomes significant at pressures below 90 mmHg. A decrease in choroidal blood volume is thought to cause the reduction in IOP. 2. Venous pressure- Coughing, straining, vomiting and Valsalva manoeuvre will cause venous congestion thereby increasing intraocular vessel volume and reducing episcleral venous drainage causing a rise in IOP. Head up tilt decreases venous congestion reducing IOP and vice versa. 3. Partial pressures of oxygen (PO2) and carbon dioxide (PCO2) affect intraocular tone and hence IOP. A rise in

PCO2 results in dilation of the choroidal vessels and a rise in IOP, the converse is also true. Metabolic acidosis decreases IOP and metabolic alkalosis increases IOP. 4. Drugs- Opioids, hypnotics, major tranquilizers and volatile agents are associated with a fall in IOP with the exception 21

Review of Literature of ketamine which causes a rise. Depolarising muscle relaxants cause a small, transient, but consistent rise in IOP whilst non-depolarisers produce no change or a decrease in IOP. Other drugs which reduce IOP include mannitol (0.5mg/kg IV) which works by removing fluid from the vitreous and acetazolamide (500mg IV) which acts to decrease aqueous humor production by the ciliary body. 5. Anesthesia - Local anesthesia injections cause a definite, although variable, rise in IOP. This increase in pressure is transient and depends on the rate and volume of injection. General anesthesia and the physical intervention by the anesthetist also affect IOP. Laryngoscopy and intubation causes a rise in IOP and to a lesser degree the insertion of a laryngeal mask airway. Any coughing or gagging during extubation also causes a rise in IOP (Murgatroyd and Bembridge, 2008)

Oculomedullary reflexes: 1. Oculocardiac reflex - causes bradycardia, nodal rhythms, ectopic beats or sinus arrest due to pressure, torsion or traction on the extraocuar muscles. It is a trigemino-vagal reflex - the afferent arc is via long and short ciliary nerves to the ciliary ganglion and the ophthalmic division of the trigeminal nerve with the efferent impulses conveyed by 22

Review of Literature the vagus. This reflex most commonly occurs in pediatrics squint patients. LA blocks may attenuate the afferent arc and muscarinic antagonists block the efferent limb at the level of the heart. Hypercarbia sensitises the reflex and should be avoided. 2. Oculorespiratory reflex - may cause shallow breathing, reduced respiratory rate and even full respiratory arrest. The afferent pathways are similar to the above reflex and it is thought that a connection exists between the trigeminal sensory nucleus and the pneumotactic centre in the pons and medullary respiratory centre. Again this reflex is commonly seen in strabismus surgery and atropine has no effect. If controlled ventilation is not routinely employed then extra attention is needed. 3. Oculoemetic reflex - is likely responsible for the high incidence of vomiting after squint surgery (60-90%). Again this is a trigemino-vagal reflex with traction on the extraocular muscles stimulating the afferent arc. Whilst antiemetics may reduce the incidence, a regional block technique provides the best prophylaxis (Chishti and Varvinsky, 2009).

23

Review of Literature

Sub-Tenon’s Block Technique Akinetic

blocks

include

injection

of

the

local

anesthesetic in (intraconal, retrobulbar) or around (extraconal, peribulbar) the muscle cone through a needle or by instilling the local anesthesetic under the Tenon’s capsule (subtenon, parabulbar, pinpoint, episcleral) using a blunt cannula or needle (Gayer and Kumar, 2008). Sub-Tenon’s block become the most popular technique for regional anesthesia in eye surgery in UK and has largely replaced peribulbar blocks and general anesthesia for many types of eye surgery. It has been used increasingly for cataract surgery, vitreoretinal surgery, panretinal photocoagulation, strabismus surgery, retinopathy of prematurity, uveitis, glaucoma, optic nerve sheath fenestration, chronic pain management, and for the therapeutic delivery of drugs (Jeganathan and Jeganathan, 2009). Due to the relatively higher risks of retrobulbar blocks this technique is quickly becoming obsolete. Whilst the subtenon approach is arguably safer than the peribulbar block, the latter still has its place as a regional technique for those patients

in

whom

a

subtenon

block

is

relatively

contraindicated. These include patients with previous scleral 24

Review of Literature banding and detachment surgery, medial rectus or pterygium surgery (Chishti and Varvinsky, 2009). A) Classic technique: After topical anesthetic eye drops have been instilled, Tenon’s capsule is cut apart. Then, a blunt, curved cannula is advanced into the sub-Tenon’s space, and a preferred LA agent is administered (Mather and Kirkpatrick, 2003). Ophthalmic surgery can begin almost immediately afterwards. Because the sub-Tenon’s approach uses blunt dissection along tissue planes and avoids sharp needles, it is of particular value in patients with long globe or posterior staphylomas and in those taking anticoagulants or antiplatelet agents as long as their clotting results remain within the normal therapeutic range (Konstantatos, 2001).

Fig.7: Globe position and inferonasal direction using forceps and scissors during sub-Tenon’s block (Kumar and Dodds, 2006).

25

Review of Literature Sensory blockade is achieved through the short ciliary nerves passing through Tenon’s capsule to the globe. The analgesic

effect

is

immediate,

and

akinesia

follows.

Furthermore, a sub-Tenon’s block can be augmented for prolonged anesthesia and postoperative pain relief (Gayer and Kumar, 2008). B) Variations of sub-Tenon’s technique: There are many variations of sub-Tenon’s block that relate to approach, cannula type, LA agent, and adjuvant used. i) Approach to sub-Tenon’s space: Access

to

all

quadrants

-

the

superotemporal,

superonasal, inferotemporal, and medial canthal side - has been described, with the most common approach being through the inferonasal quadrant, approximately 3-5mm from the limbus. The superonasal approach is unsafe because of its vascular, neuronal, and muscular contents (Jeganathan and Jeganathan, 2009).

26

Review of Literature

Fig.8: Cannula advancement in Sub-Tenon’s Block (Ripart et al, 2000). Access to sub-Tenon’s space through the medial canthal area has been reported using needles without dissection by Jacques Ripart and his colleagues in Nimes, France. The bevel of a short (0.5 inch) needle is inserted in the conjunctiva between the semilunaris fold and the globe. Before advancing, the needle is shifted medially to go away from the globe and pull the fascial sheath of the orbit (Tenon’s capsule) and the conjunctiva, which are joined at this level. The needle is advanced strictly posteriorly. The traction on the fascial sheath of the eyeball causes the globe to rotate nasally. After a “click” is perceived, the globe returns to the primary gaze position. This indicates the passage through the fascial sheath of the eyeball to enter into the episcleral space, injection then is 27

Review of Literature performed. In their study Episcleral anesthesia provided a quicker onset of anesthesia, a better akinesia score, and a lower rate of incomplete blockade necessitating reinjection and more constancy in effectiveness (Ripart et al., 2000). In 2005, Rizzo and colleagues presented a more recent approach to medial episcleral block through the skin below the inferior lacrimal canaliculus using a 16 mm needle and low volume of LA. The needle was advanced percutaneously in an antero-posterior direction for half of its length (never more than 10 mm) and later obliquely in the direction of the optical foramen until the needle was on the same plane of the bony margin of orbit. Excellent results were reported using this method (Rizzo et al., 2005) ii) Cannula type: Several different cannulae are available for delivering sub-Tenon’s anesthesia (Fig. 9), and selection of a given type depends on the availability, cost, and skills of the performer. These cannulae may be either metallic or plastic. The metal form varies in gauge, length, curvature, and the position of its end holes. The commercially manufactured, posterior metal sub-Tenon’s cannula is the most common type referred to in published research (Kumar and Dodds, 2006).

28

Review of Literature

Fig.9: Different types of sub-Tenon’s cannulas (Kumar and Dodds, 2006).

iii) Volume: There is substantial variance in the volume of LA agent used in sub-Tenon’s block, ranging from 1 to 11 ml. Only 3-5 ml of local anesthesia is safely used. Smaller volumes usually provide globe anesthesia and less akinesia, but larger volumes are required if akinesia is preferable (Jeganathan and Jeganathan, 2009).

29

Review of Literature

Complications of Sub-Tenon’s Block Technique Complications arising from orbital regional anesthesia may be local or may manifest systemically and may arise immediately or may be delayed. Complications are related to the method of administration or LA agent and adjuvant used (Rubin, 1995).

A) General measures which may reduce SubTenon’s block complications:  Always check the globe for anatomical abnormality and surgical intervention.  Use a technique based on anatomical knowledge.  Always check the axial length.  Never use a needle longer than 31 mm.  Always insert the needle with the eye in primary gaze.  Needle should always remain tangential to the globe.  Avoid insertion of needle into the vascular quadrant.  Avoid placement of needle into the muscle belly.  Never inject local anesthetic agent without aspirating.  If there is any resistance to injection, consider repositioning of the needle.

30

Review of Literature  Beware the patient with a long eye, staphyloma, coloboma or scleral buckle.  Never use sedation to cover inadequate block (Kumar and Dowd, 2006).

B) Minor complications: 1) Pain during injection: Sub-Tenon’s block is less painful than retrobulbar or peribulbar block (Jeganathan and Jeganathan, 2009). Evidence from the Cochrane Database Systematic Review shows that sub-Tenon’s anesthesia provides better pain relief than topical anesthesia for cataract surgery (Davison et al., 2007). Up to 44% of patients report pain during sub-Tenon’s injection in which a posterior metal cannula is used. Pain scores on a visual analog scale have been reported as high as 5, the cause is multifactorial, for example, cannula design, position, and temperature of the LA agent used. The use of sharp bevel needles 25 G or less or smaller cannulae can reduce the incidence of pain. To reduce the patient’s discomfort and anxiety, it is important to give a thorough preoperative explanation of the procedure, use a good surface anesthesia, use gentle technique, slowly inject the warm LA agent, and provide reassurance (Kumar and Dodds, 2006).

31

Review of Literature 2) Conjunctival edema (chemosis) and subconjunctival hemorrhage (ecchymosis): Chemosis and ecchymosis are relatively common yet minor complication of sub-Tenon’s block (Kumar, 2007).In subtenon block echymosis can be minimized with careful dissection, the use of a solution containing epinephrine and controlled localized bipolar conjunctival cautery especially in patients on warfarin or aspirin (Gauba et al., 2007). These minor complications usually do not interfere with surgery and resolve spontaneously within few hours. In glaucoma surgery, however, some surgeons believe that chemosis may interfere with construction of the scleral flap (Jeganathan and Jeganathan, 2009). 3) Subjective visual perceptions: Patients undergoing regional anesthesia have been reported to experience visual sensations such as flashes of light, colours, movements or sight of surgical instruments and theatre personnel. Up to 16% of patients can be petrified by such experiences. Furthermore, fear and anxiety may result in hypertension, panic attack, and diminished patient satisfaction. Patients should receive appropriate preoperative information and counselling to allay their nasty experience (Tan et al, 2005). 32

Review of Literature 4) Incomplete Akinesia: Residual muscle movement varies among patients. These are dependent on the type of LA, its volume, and the use of adjuvant. Ocular akinesia was superior with articaine (4%) or Mepivacaine 3% than a mixture of lidocaine (2%) and levobupicaine (0.5%) in subtenon’s block. Furthermore, a 5 ml volume of LA has been shown to provide superior akinesia in comparison with a 3 ml volume. Improved akinesia occurred when hyaluronidase was added to the LA solution. Incomplete akinesia does not cause intraoperative difficulties. However, it is imperative that the eye is not moved at certain times; therefore, the use of stabilizing sutures and forceps is advised (Kumar and Dowd, 2006).

C) Serious Complications: 1) Myotoxicity: Damage to extraocular muscles from orbital blocks can result in strabismus (causing diplopia), ptosis (drooping upper eyelid) and entropion (infolding of the eyelid). However, not all cases of extraocular eye muscle problems are caused by orbital block, such as diplopia from the pre-existing condition that is unmasked after cataract surgery, sensory deviations and optical aberrations. Incidence of post operative diplopia related to anesthetic factors is 0.25% (Gomez et al., 2003). 33

Review of Literature Possible mechanisms of extraocular eye muscle damage include direct needle trauma, ischemic pressure necrosis caused by a large volume of LA, direct myotoxic effects of the LA agent on extraocular muscles and use of high concentrations of Lidocaine. Absence of the enzyme Hyaluronidase mixed with LA has been suggested as another possible risk factor for extraocular muscle damage in several retrospective surveys. Transient strabismus on the first postoperative day is common after eye surgery. The most common permanently injured muscle from an eye block is the inferior rectus, but other muscles can be involved. A 31 mm needle in the extreme inferotemporal quadrant (just above the orbital rim directly below the lateral canthus) is less likely to strike the orbital floor and anterior aspect of the inferior rectus muscle, compared to the traditional insertion point (Kumar and Dowd, 2006). Ptosis is common on the first postoperative day after eye surgery. It occurs in 50% of eye operations. Ptosis resolves in 95% of patients by the 4th postoperative day and in 99%, within 5 weeks. The incidence of ptosis is the same with needle orbital blocks and general anesthesia. It is believed that ptosis can be caused by dehiscence of the levator aponeurosis and is associated with large volume of LA. Therefore, the smallest effective volume of anesthetic agent is advocated. 34

Review of Literature Surgical causes of ptosis include, use of a superior bridal stitch or application of a lid speculum (Nicol, 2003). 2) Central spread of LA agent and brain stem anesthesia: The cerebral dura matter provides a tubular sheath for the optic nerve as it passes through the optic foramen providing a potential conduit for LA to pass subdurally to the brain. Central spread occurs, if the needle tip has perforated the optic nerve sheath and if injection is made. Central spread may also occur if an orbital artery is cannulated by the needle tip. Retrograde flow of LA from a branch of the ophthalmic artery through the internal carotid artery, to the midbrain can occur. An immediate seizure would result and cardiovascular instability is possible. The toxic intra-arterial dose has been estimated to be as low as 3.6 mg of Bupivacaine. To reduce the risk of this complication, one should always aspirate before injecting LAs. If blood is aspirated, the needle must be redirected (Goldberg, 2006). The time of onset of symptoms is variable, but major sequalae develop usually in the first 15 minutes after the injection. The onset of central nervous system toxicity is almost instantaneous, if arterial injection has occurred. A range of different signs and symptoms has been described involving the cardiovascular and respiratory systems, such as 35

Review of Literature temperature regulation, vomiting, temporary hemiplegia, aphasia and generalised convulsions. Palsy of the contralateral oculomotor

and

trochlear

nerves

with

amaurosis,

is

characteristic of central nervous system spread (Kumar, 2007). Treatment consists of respiratory and cardiac support. Bag and mask ventilation is frequently required, but the episode often resolves spontaneously and intubation may not be necessary. Because of the possibility of systemic complications, all patients receiving eye anesthesia must be monitored. It is a good practice to aspirate before injection, to avoid intravascular injection (Dillane and Finucane, 2010).

Fig.10: Algorithm for the management of local anesthetic systemic toxicity (Dillane and Finucane, 2010). 36

Review of Literature 3) Allergic reactions: Allergic reactions from amide anesthetic commonly used for eye anesthesia are rare. There are case reports of allergic reactions following the use of Hyaluronidase mixed with LA agent (Ahluwalia, 2003).

37

Review of Literature

Local Anesthetic Mixture The ideal agent for ophthalmic block should be safe, painless to inject and produce a rapid onset of dense motor and sensory block. All the modern, high-potency LA agents are suitable for ophthalmic blocks and numerous studies have shown little difference in the quality of anesthesia, analgesia and akinesia (Kumar and Dodds, 2006). Mepivacaine hydrocholride is a tertiary amine used as a local anesthetic in ophthalmic regional anesthesia. It stabilizes the neuronal membrane and prevents the initiation and transmission or nerve impulses, thereby effecting local anesthesia. Mepivacaine hydrocholride is rapidly metabolized, with only a small percentage of the anesthetic (5 to 10 %) being excreted unchanged in the urine. Mepivacaine hydrocholride because of its amide structure is not detoxified by the circulating plasma esterases. The liver is the principal site of metabolism, with over 50 % of the administered dose being excreted into the bile as metabolites (McLure and Rubin, 2005).

38

Review of Literature Pharmacokinetic factors affecting onset and duration of local anesthetic: 1. Site of injection, the closer the drug is placed to the nerve, the briefer the time to onset of block because the distance to traverse will be less. 2. Dose, concentration, and volume: It is the total dose of LA, not volume or concentration which determines the onset rate, depth, and duration of nerve block. No further increase in duration of action results when maximal effective concentration is achieved, nothing but greater systemic toxicity. 3. Use of a vasoconstrictor, which will delay onset and prolong duration of action. 4. Nature lipid solubility and (pKa) of the LA. Hydrophobic drugs and higher pKa have more delayed onset of action. Hydrophobic drugs have prolonged duration, intrinsic vasodilator properties shorten the duration 5. Additives: for example epinephrine,hyaluronidase and many other drugs. (Bernards, 2009).

39

Review of Literature Hyaluronidase: Hyaluronidase is an enzyme, which reversibly liquefies the interstitial barrier between cells by depolymerisation of hyaluronic acid to a tetrasaccharide, thereby enhancing the diffusion of molecules through tissue planes. It is commonly added to LA solutions to improve the speed of onset and spread of anesthetic block, and to prevent a sustained rise in orbital pressure. A concentration of 15 IU/mL is recommended in the United Kingdom datasheet. Hyaluronidase has been shown to be useful for retrobulbar, peribulbar and sub-Tenon’s anesthesia (McLure and Rubin, 2005). Clonidine: It is a selective partial agonist for α2-adrenoreceptors, with a ratio of approximately 200:1 (α2 to α₁). General mechanism of action of clonidine:-

 It stimulates central presynaptic 2 receptors (in the hypothalamus

and

locus

caeruleus)

resulting

in

decreased noradrenaline release (i.e. decreased central sympathetic

outflow)

which

in

turn

leads

to

hypotension, bradycardia, sedation and anxiolysis.  It stimulates central postsynaptic 2 receptors and imidazoline (I) receptors (in the medulla) resulting in 40

Review of Literature decreased blood pressure, heart rate and myocardial contractility. This causes reduction of myocardial oxygen consumption.  It stimulates peripheral presynaptic 2 receptors: resulting in decreased noradrenaline release.  It decreases noradrenaline synthesis by inhibition of dopamine

ß-hydroxylase

enzyme

and

N-

methyltransferase enzymes.  It decreases renin activity and renal vascular resistance, therefore; it maintains renal blood flow (Unnerstall et al., 1994)  It has an analgesic action via action on pre- and postsynaptic 2 receptors by: 1. Stimulation of descending inhibitory pathways from the locus caeruleus 2. Inhibition of nociceptive transmission

(and

inhibition of release of substance P) at the spinal cord as clonidine appears to bind to 2 adrenergic receptors in the substantia gelatinosa and the intermediolateral cell column, which inhibits

41

Review of Literature release of substance P and firing of wide dynamic range neurons in the spinal cord dorsal horn (Fleetwood et al., 1995) 3. It potentiates the actions of opioids and local anesthetics (Erlacher et al., 2001). 4. It has been recently hypothesized that clonidine acts at 2 adrenergic receptors in the spinal cord to stimulate acetylcholine release which acts at both muscarinic and nicotinic subtypes for postoperative pain relief (Duflo et al., 2005). Clonidine’s addition to local anesthetic in retrobulbar block has several advantages: it decreases IOP, enhances anesthesia and akinesia and increases intraoperative sedation (Bahy Eldeen et al., 2011). The duration of lid and globe akinesia, globe analgesia and anesethesia was significantly increased with clonidine in peribulbar block (Madan et al., 2001). A dose-response study by Madan et al. (2001) looked at adjuvant clonidine to peribulbar blockade for cataract surgery, the authors concluded that clonidine enhances the duration of anesthesia and analgesia in the 1 µg/kg dose without significant side effects (Madan et al., 2001). 42

Review of Literature Pharmacokinetics: It is lipid soluble and crosses the blood brain barrier and the placenta. Its elimination t1/2 is 9-12 hours except in patients with renal impairment where it may be as long as 41 hours.50% of clonidine is metabolized in the liver resulting in inactive metabolites and 50% is excreted unchanged by the kidney (Frisk, 1993). Side effects: 2 -Adrenergic agonists produce clinical effects after binding to 2 -adrenergic receptors, of which there are three subtypes (2A, 2B and 2C). These receptor subtypes are distributed everywhere, and each may be uniquely responsible for some, but not all, of the actions of 2 agonists; for example, the 2B-adrenoceptor subtype mediates the shortterm hypotensive response to 2 agonists, whereas the 2A adrenoceptor

is

responsible

for

the

anesthetic

and

sympatholytic responses (Kamibayashi and Maze, 2000) It is apparent that there are no subtype-selective agonists; therefore, the goal of producing a single discrete desirable 2 action (e.g., analgesia) without producing another unwanted effect (e.g., hypotension) is elusive. Side effects due to decreased sympathetic activity 43

(Dry mouth,

nasal

Review of Literature congestion,

bradycardia

and

orthostatic

hypotension).

(Kamibayashi and Maze, 2000). Contraindications: 1- History of allergic reaction or sensitization to clonidine. 2- Patients who have any of the following conditions:  Cardiac disease: Severe cardiovascular disease or bradycardia may be worsened due to an increased risk of severe hypotension. Clonidine may also mask the increase in heart rate associated with hypovolemia.  Renal disease: In patients with renal impairment the elimination half-life of clonidine may be prolonged and thus overdosage is a risk. (Kamibayashi and Maze, 2000)

44

Patients and Methods

Patients and Methods This prospective, controlled, randomized, blinded, clinical study was carried out in the ophthalmic surgery unit in Ain Shams University hospital form 2012-2015. After institutional approval and obtaining informed consent form all patients, 60 patients from both sexes, ASA I-III, aged 21-70 years, weighing between 70 - 80 kg and having an axial eye length ranging from 22 to 30 mm

scheduled for elective

ophthalmic anterior segment surgery under sub-Tenon’s block were included in the study. Exclusion criteria:  Patient refusal  Coagulation defect or antiplatelets or anticoagulants medication.  Mental defect or uncooperative patient.  Uncontrolled glaucoma.  Recent surgical procedure on the same eye.  Documented hypersensitivity to study drugs.  Patient on oral clonidine

45

Patients and Methods The 60 patients were allocated randomly in two equal groups 30 patients each using computer generated program.  Group A (Control group): Patients of this group received sub-Tenon’s block using local anesthetic mixture of 5 ml Mepivacaine 3% solution with 1 ml normal saline 0.9% containing hyaluronidase 75 I.U.  Group B (Clonidine group): Patients of this group received sub-Tenon’s block using local anesthetic mixture of 5 ml Mepivacaine 3% solution with 75µg clonidine (0.5 ml) plus 0.5 ml normal saline 0.9% containing hyaluronidase 75 I.U. Operator and patients were blinded to injected local anesthetic mixture which was prepared by a third person.

Preoperative evaluation: History, clinical examination and routine investigations including complete blood count (CBC), random blood sugar (RBS), coagulation profile including (prothrombin time, partial thromboplastin time and international normalized ratio) and electrocardiogram (ECG) were performed to all patients. Explanation

about

pain

assessment

during

administration of anesthesia, during surgery, and after surgery

46

Patients and Methods using verbal pain scores (as none, mild, moderate, and severe, defining none as a score of zero on a 10-point scale, mild as 1 or 2, moderate as 3 to 5, and severe as more than 5)was done

for all patients. Monitoring: Basic monitoring including ECG, pulse oximetry and non-invasive blood pressure were applied to all patients, starting before anesthesia till end of surgery then recovery. Anesthetic technique: All patients after admission to preinduction area were checked for name, medical history, vital signs, fasting for at least 8 hours and operative side. An intravenous access was secured by a peripheral intravenous cannula 20G. Under complete aseptic condition 2-3 drops of topical anesthetic (0.4% benoxinate hydrochloride) were applied to the cornea and conjunctiva. Oxygen supplementation by nasal pronge (24 L/min). All patients received intravenous propofol (0.5- 1 mg/kg) to provide sedation for the placement of the block according to patient’s age and weight. After 2 minutes, a small incision in the inferonasal quadrant approximately 5 mm from the limbus using Wescott (spring) scissors was done by the 47

Patients and Methods same experienced person. An opening was created in the anterior Tenon’s fascia down to bare sclera. Moorfields forceps was then used to grip the conjunctival edge and a blunt subtenon cannula 19-G (used to deliver the local anesthetic mixture) was glided along the contour of the globe. The cannula was then advanced posterior to the equator of the globe. Anesthetic solution was injected slowly over 30 seconds and the cannula was then withdrawn, followed by application of orbital pressure (digital pressure) for 2 minutes (25 second

increments with 5 second release of pressure to allow central retinal vessel flow).

Data collection  Motor blockade (akinesia) was used as the main index of anesthesia effectiveness. It was assessed using a scoring system of globe akinesia as 0 (no movement), 1 (flicker), 2 (full movement) for the four recti muscles, levator palpebrae and orbicularis of the eyelids (total score 12). Globe akinesia was assessed by asking the patient to move their eyes in different directions. When the eye was turned in (nasally) and horizontally, the function of the medial rectus muscle was being tested. When it was turned out (temporally) and horizontally, the function of 48

Patients and Methods the lateral rectus muscle was tested. When it was turned down and out, the inferior rectus was tested. When it was turned up and out, the superior rectus was tested). The actions of the four recti are observed and the degree of movement scored. Also patients asked to close and open their eyes to assess orbicularis oculi and levator palpebrae superioris respectively. Successful block was defined as an ocular motility score between 0 and 6. Recorded score was 1, 5 and 10 min after injection and at the end of the surgical procedures. The incidence of incomplete blockade (after 5min from local anesthetic injection) with a need for supplemental injection was recorded.  Patient-reported

pain

during

administration

of

anesthesia, during surgery, and during the first six postoperative hours was

recorded using verbal pain

score (VPS) as none, mild, moderate, and severe, defining none as a score of zero on a 10-point scale, mild as 1 or 2, moderate as 3 to 5, and severe as more than 5. Postoperatively if patient-reported pain was 3 or more by verbal pain scores, rescue analgesia was given in form of 1 gram intravenous infusion of paracetomal.  Sedation score was monitored by 4-point score (0 = alert, 1 = drowsy, 2 = asleep but easily aroused, 3 = 49

Patients and Methods comatosed) and was checked every 15 minutes during the first hour after propofol injection.  Patients’ global satisfaction level regarding immediate postoperative comfort and pain relief was assessed using a

five-point

scale

(1=

very

unsatisfactory

and

5= excellent). 

Arterial blood pressure, heart rate, respiratory rate and oxygen saturation were evaluated every 5 minutes immediately after local anesthetic injection for the first 15 minutes then every 15 minutes for the next two hours.

 Any complications(intraoperative or postoperative) as regards the general condition of the patient, local anesthetic toxicity or the local condition of the eye as hematoma, postoperative ptosis or diplopia, nerve or globe injuries were recorded .

End points The study was finished at time of recurrence of pain with full data collection.

50

Patients and Methods

Statistical analysis Statistical analysis was done on a personal computer using the Statistical Package for

Social Sciences version 17.0

(SPSS© v. 16.0, SPSS Inc., Chicago, IL, United State of America). Qualitative data were analyzed with pearson Chisquare test and were presented as number [%]. Quantitative data were analyzed using unpaired t-student test for between group comparison and data were presented as mean (standard deviation). Non parametric data were analyzed using Mann Whitney test and was presented as median (IQR). A difference with ″p″ value: P > 0.05 insignificant test P ≤ 0.05 significant test P ≤ 0.01 highly significant

51

Results

Results 1- Demographic data There were no statistically significant difference between the two groups as regards age, sex, weight and axial length Table (1). Table (1): Patient characteristics Group A

Group B

(n=30)

(n=30)

Age (years)

47.7±12.2

50.3 ± 12.4

0.42

Weight (kg)

71.6±3.5

70.1±6.5

0.26

Sex (M/F)

15/15

18/12

0.6

ASAI/II/III

15/9/6

14/11/5

0.85

24.8 ± 2.6

24 .6± 2

Axial Length(mm)

Values are expressed as mean ±SD or ratio P ≤ 0.05 was considered statistically significant

52

P value

0.74

Results 2- Motor Block There was no statistical difference between the two groups of the study as regards motor blockade (akinesia) using scoring system (0-12). This score was compared between the two groups 1, 5 and 10 min after injection and at the end of the surgical procedures. Successful block was defined as an ocular motility score between 0 and 6. Table (2): Comparison of motor block score between the two groups

1

Group A (n=30) 7 (6-8)

Group B (n=30) 8(7-8)

5

1(0-1.25)

0(0-1)

0.31

10

0(0-0)

0(0-0)

1

End of operation

0(0-0)

0(0-0)

1

Min

P value 0.13

Values are expressed as median ± SD P ≤ 0.05 was considered statistically significant

As shown in table (2):- The Vertical Y axis represents number of patients with incomplete motor block (score>6) and the horizontal X-axis represents time at which the motor power has been assessed. One can notice that at the 1st minute, 7 patients in Group A were with score >6 (incomplete akinesia) & 8 patients in Group B were with score > 6 (incomplete akinesia). 53

Results Upon reassessment on the 5th minute after LA administration through subtenon’s technique, One can notice that only 1 out of the 7 patients was still with incomplete akinesia (score >6) while the rest of the patients showed globe akinesia with score