Orbit, 2014; 33(1): 5–12 ! Informa UK Ltd. ISSN: 0167-6830 print / 1744-5108 online DOI: 10.3109/01676830.2013.842250

REVIEW

General Anaesthetic Considerations for Haemostasis in Orbital Surgery David Ik Tuo Sia1,2, Alison Chalmers3, Varjeet Singh4, Raman Malhotra5, and Dinesh Selva1,2 South Australian Institute of Ophthalmology, Adelaide, Australia, 2Discipline of Ophthalmology & Visual Sciences, University of Adelaide, Adelaide, Australia, 3Department of Anaesthesia, Queen Victoria Hospital, East Grinstead, West Sussex, United Kingdom, 4Adelaide Anaesthetic Services, Dulwich, South Australia, Australia, and 5Corneoplastic Unit, Queen Victoria Hospital, East Grinstead, West Sussex, United Kingdom

ABSTRACT Orbital surgery is often conducted in areas with limited exposure where vital structures are tightly crowded together. A bloodless field is paramount in orbital surgery for the proper identification of normal and pathologic tissue and even minimal bleeding can obscure the surgical field, making surgery more difficult and increasing the risk of complications. Surgery for highly vascular orbital lesions is an additional situation where maintaining an adequate surgical field is often challenging but paramount. The role of the anaesthetist in controlling surgical blood loss has been increasingly recognized in the last few decades. Various techniques including hypotensive anaesthesia have been described, but the control of intraoperative bleeding does not rely on a single particular technique, but a series of well-designed interventions that result in optimal conditions. An understanding of the anaesthetic considerations pertinent to haemostasis is invaluable for oculoplastic surgeons. Additionally, with the growing use of endonasal approaches to medial wall decompression and accessing the medial orbit, it has become increasingly important that orbital surgeons understand the anaesthetic requirements of their colleagues in other disciplines. Keywords: Anaesthetics, haemostasis, hypotensive anaesthesia, orbital surgery, oculoplastics

INTRODUCTION

A bloodless field is paramount in orbital surgery for the identification of subtle differences in coloration and texture of normal and pathologic tissue. Orbital surgery is often conducted in areas with limited exposure where vital structures are tightly crowded together. Even minimal bleeding can obscure the narrow surgical field, making surgery more difficult and increasing the risk of complications.3 With the growing use of endonasal approaches to medial wall decompression and accessing the medial orbit, it has become increasingly important that orbital surgeons understand the anaesthetic requirements of their colleagues in other disciplines. Furthermore, medial wall and deep lateral wall decompression via trancaruncular or skin incisions also may at times benefit from anaesthetic measures to help control bleeding in

Since Gardner1 first used arteriotomy during anaesthesia in 1946 to improve visibility in the surgical field, various techniques and pharmacological agents have been described for the reduction of intraoperative blood loss. These techniques appeal mainly to two groups of surgeries: those with moderate or high haemorrhagic potential such as orthopaedic, cardiothoracic, urologic and hepatic transplantation surgeries, with the goal of decreasing transfusion requirements and surgeries with low haemorrhagic potential but stringent requirements on quality of surgical field, these include surgery of the middle ear, endoscopic sinus surgeries, plastic and reconstructive microsurgery, ophthalmologic surgery and neurosurgery.2

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Received 28 February 2013; Accepted 30 August 2013; Published online 18 October 2013 Correspondence: David Ik Tuo Sia, South Australian Institute of Ophthalmology, Royal Adelaide Hospital, North Terrace, Adelaide, South Australia 5000, Australia. E-mail: [email protected]

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selected cases. Surgery for highly vascular orbital lesions is an additional situation where anaesthesia can be a factor in maintaining an adequate surgical field. Finally, neophyte endonasal surgeons performing endonasal dacryocystorhinostomy may on occasion encounter significant bleeding, which obscures the visual field and may require the assistance of their anaesthetist. Hence, an understanding of the anaesthetic considerations pertinent to haemostasis is invaluable for oculoplastic surgeons.

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THE ROLE OF THE ANAESTHETIST The role of the anaesthetist in controlling surgical blood loss has been increasingly recognised in the last few decades. Aside from physical manoeuvres and local agents to control intraoperative bleeding, controlled hypotension has been utilised. The development of newer pharmacological agents that are safer, more predicable and effective has allowed for excellent intraoperative conditions to be achieved.2

PHYSIOLOGY Intraoperative bleeding can be defined as the quantity of blood that appears in the operative field in a given time, expressed mathematically as flow. Flow (F; volume/unit of time) is directly related to pressure by the relationship F = P/R, where P is the pressure and R represents vascular resistance. If pressure P decreases, and resistance R remains constant or increases (vasoconstriction), then flow D decreases. On the other hand, if the pressure P decreases, as well as the resistance R (vasodilation), then flow D remains constant or varies little. Therefore, the result of hypotension in terms of bleeding also depends on the change in vascular resistance R. Mean arterial blood pressure (MAP) is governed by cardiac output (CO) and systemic vascular resistance (SVR), MAP = CO*SVR. CO itself can be further defined as CO = SV*HR, where SV is stroke volume and HR is heart rate. SV is determined by venous return and afterload, and is affected by myocardial contractility. When the surgery is performed under general anaesthesia, the anaesthetist is able to induce hypotension by reducing cardiac output through the lowering of venous return and heart rate, and or by reducing SVR through peripheral vasodilation of resistance vessels. Myocardial contractility often reduces due to effect of the anaesthetic agent but this is not usually titratable or desirable particularly in the elderly patient.

CONTROLLED HYPOTENSION Surgical bleeding can be classified into arterial, venous and capillary.4 Deliberate controlled hypotension is a well-described technique for the reduction of intraoperative bleeding. It is defined as a reduction of the systolic blood pressure to 80–90 mmHg, a reduction of MAP to 50–65 mmHg or a 30% reduction of baseline MAP.2 Its use has been shown to reduce intraoperative blood loss in orthopaedic, oromaxillofacial, otorhinolaryngologic, neurosurgical, urologic, and spinal procedures, although there continues to be much debate in the anaesthetic community as to the degree of induced hypotension that can be considered safe.2,5 The target MAP is measured at the level of the large vessels, and this is different from the pressure at the level of tissue circulation in the operated zone. Consequently, a number of studies have demonstrated that a reduction of MAP may not necessarily reduce intraoperative blood loss.6–9 The heart rate (HR) may be a more important variable especially for venous and capillary bleeding.10–12 Nair et al. reported that optimal surgical fields in endoscopic sinus surgery (ESS) were achieved when HR was 560 beats/min.10 Changes in heart rate proportionately affect diastolic time to a greater extent than systolic time. They postulated that decreasing the HR increases the diastolic time, resulting in greater filling of the venous capacitance vessels, lowering venous tone and consequently, resulting in decreased venous oozing.10 Furthermore, the use of inhalational agents such as isoflurane to decrease MAP to less than 70 mmHg may increase intraoperative blood loss and worsen surgical field because of peripheral vasodilation and tachycardia.8,13 The mechanisms responsible for the reduction of intraoperative bleeding depend on the intricate interplay between the technique used (effect of agents on the heart and vascular network), the mechanisms of regulation that these agents antagonise and the counter-regulatory mechanisms that they cause (Figure 1).

PREOPERATIVE CONSIDERATIONS Although controlled hypotension has an ascribed mortality similar to other types of anaesthesia and a low reported incidence of morbidity,5,14 patient selection is still vitally important due to the risk of endorgan ischaemia. This applies particularly to patients with pre-existing co-morbidities that predisposes to vital organ hypoperfusion (ischaemic cerebrovascular disease, anaemia, severe pulmonary, heart, renal and hepatic disease, severe systemic hypertension).5 As the ischaemic threshold differs for every patient, there Orbit

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FIGURE 1 Mechanisms of regulation of blood pressure and vasomotor tone responsible for the reduction of intraoperative bleeding. Adapted from Degoute et al.2.

are no rigorous guidelines and the decision for controlled hypotension has to be individualized in each case following discussion between the surgeon and anaesthetist.5 This is a particularly important point as only gross measurements of cardiac and/or renal ischaemia are measured from 3-lead ECG analysis and urinary output studies, whereas ischaemia in other tissue beds are not monitored. Clonidine, a central a2-adrenoceptor agonist, has been successfully used as a premedication adjunct to hypotensive anaesthesia. It allows a reduction of the concentrations of the other agents while reinforcing their hypotensive effect in reducing intraoperative bleeding.15–18 Angiotensin converting enzyme inhibitors (captopril and enalapril) have also been used successfully as premedication adjuncts for controlled hypotension.19–21 However, they have recently fallen out of favour due to the risk of producing profound hypotension on induction which can be difficult to treat and may be associated with potentially lethal outcomes. A full discussion and explanation by an anaesthetist at the preoperative visit will help allay any fears and anxieties that the patient may have and reduce circulating catecholamines. The use of a sedative and/or anxiolytics may be helpful in the anxious patient and can be an important premedication for lowering HR and BP. In general, anticholinergic agents are best avoided as they may produce tachycardia.22 Cessation of anticoagulation and antiplatelet medication is recommended for reduction of intraoperative bleeding, but the risks of stopping these medications must be carefully considered particularly in the setting of coronary stenting (especially drug-eluting stents where patients are often on combination therapy).23,24 Consultation with cardiology is recommended before altering these medications perioperatively.25–29 Recent recommendations with new anticoagulants such as Dabigatran and Rivaroxaban suggest interruption 48 h preoperatively for high risk procedures and 24 hours preoperatively for procedures with low !

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risk of bleeding. With decreasing renal function, the period of interruption should be longer.30

INTRAOPERATIVE CONSIDERATIONS Physical Measures Simple measures of elevating the head of the operating table by 10–15 in the reverse Trendelenburg position can increase venous return to the heart by a gravitational effect, hence reducing venous congestion in the upper part of the body.31,32 This position has been shown to reduce blood loss and improve operating conditions in endoscopic sinus surgery (ESS).33 The potential complications of this position include cerebral hypoperfusion and venous air embolism.31,34 It is also important to be aware of things that might occlude venous return from the head, such as by ties used to secure endotracheal tubes. Endotracheal tubes should ideally be taped in place at a suitable position.

Endotracheal Tube (ETT) VS Laryngeal Mask Airway (LMA) The effect of LMA on blood loss and quality of operative field was studied by Atef and Fawaz35 under propofol/remifentanil anaesthesia for ESS. They found that the LMA group was associated with a better quality of operative field in the first 15 min and a statistically reduced total blood loss. Similar operating conditions were seen in both groups after 15 min, although the ETT group required higher infusion rates of remifentanil to produce the target systolic arterial blood pressure (80 mmHg).35 Heart rate and MAP were significantly lower in the first 15 min of the procedure in the LMA group, which likely explained the better quality of operative field during that period. The investigators suggested that the decreased sympathetic stimulation associated with the insertion of an LMA compared with

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endotracheal intubation was the likely explanation for these findings.35 The use of LMA was shown to offer a smoother emergence from general anaesthesia and is associated with a lower risk of airway complications such as laryngospasm and coughing compared to ETT.36 This is a significant benefit as coughing and straining during emergence may produce venous engorgement and increase bleeding from the surgical site. Traditionally, the ETT has been considered the gold standard when protecting the airway from aspiration (coming from the oesophagus below). However, the LMA’s shape allows it to sit like an umbrella over the laryngeal inlet and protect the airway from blood coming from above. This is particularly useful for orbital/sinus surgery where it has been shown to protect the upper airway from contamination when compared with ETT.37 Some anaesthetists also insert a throat pack over the top of the LMA to further augment this protection of upper airway contamination. Direct comparisons of lower airway contamination by fiberoptic examination at the end of nasal surgery have shown that patients managed with a flexible LMA, using spontaneous ventilation, are less or at least as likely to have blood in the airway compared with patients managed with an ETT.37–40 The LMA’s most limiting feature remains the risk of aspiration and the inability to apply positive pressure ventilation in patients with high lung inflation pressures. Although the evidence to date suggests that pulmonary aspiration with the LMA is comparable to that for outpatient anaesthesia with the face mask and ETT, meticulous selection of low-risk patients and adherence to usage guidelines is still encouraged to minimise the risk of aspiration.41 The reinforced flexible LMA offers the advantage that it can be secured away from the surgical field and provides a similar seal to a conventional LMA when the head is flexed or rotated.42 Such an advantage comes in handy with procedures such as endoscopic dacryocystorhinostomy where the ventilation tube is often secured away from the side of the surgeon.

Modes of Ventilation Different modes of ventilation may potentially affect surgical bleeding and operating conditions independently. Spontaneous ventilation is usually not recommended for head and neck surgeries, for fear that rapidly ensuing hypercapnia will promote microvascular and mucosal bleeding due to the CO2induced peripheral vasodilation.43,44 However, Nekhendzy et al. studied the effect of end tidal CO2 on blood loss and quality of operative field during ESS under propofol/remifentanil. They found that mild hypocapnia and hypercapnia did not have a significant effect on blood loss and quality of surgical

field during ESS when MAP and HR were controlled.45 Remifentanil is commonly used in controlled hypotension and appears to provide superior operating conditions compared to other opioid analgesics. It is also a potent inhibitor of spontaneous ventilation, therefore, most authors advocate intermittent positive pressure ventilation with its use.46 Intermittent positive pressure ventilation (IPPV) has its purported drawbacks in high intra-thoracic pressures transmitted to blood vessels resulting in decreased venous return, venous congestion and increased bleeding.47,48 The deleterious effects of IPPV may be partially overcome by carefully setting the ventilation parameters and by minimising PEEP (positive end-expiratory pressure) and/or auto-PEEP in order to reduce the amount of positive pressure exerted in the thorax. Another possibility is the high frequency jet ventilation (HFJV) method, which employs small-volume high flow ventilation resulting in adequate gas exchange at lower airway pressures than IPPV. It has been used in ESS with reduced intraoperative bleeding and improved quality of operative field when compared with IPPV.49 The suggested mechanism is increased venous return from lower intrathoracic pressures.49 However, the suitability of this technique in orbital surgery is uncertain, due to the awkward positioning of tube, degree of skill requirement and significant risks surrounding barotrauma from inappropriate airway pressure monitoring and necrotizing tracheobronchitis from inadequate humidification due to high gas flows.48

INTRAVENOUS VS. INHALATIONAL ANAESTHESIA Anaesthetic agents can influence the amount of blood loss and condition of the surgical field through their hypotensive and vasodilatory action. A large number of studies done in ESS have shown that total intravenous anaesthesia (TIVA) with propofol/remifentanyl results in a better surgical field.11,50–55 and reduced amount of bleeding 11,50,51,53–57 than inhalational anaesthesia with isoflurane or sevoflurane. Both propofol and inhalational agents have a vasodilatory effect in a concentration-dependent manner.58,59 Systemic vasodilatation with propofol is less significant compared to anaesthesia with isoflurane.4 Propofol’s effect on systemic vascular resistance is via suppression of central (cerebral) sympathetic vascular tonicity, whereas isoflurane has a direct relaxing effect on smooth muscles of blood vessels.4 All inhalational agents cause reflex tachycardia to variable extents due to lack of baroreceptor reflex inhibition.58 On the other hand, propofol has the additional advantage of reducing sympathetic brainstem activity and Orbit

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baroreflex so the heart rate does not increase.22 In certain cases, it can even result in bradycardia.59 The lower intraoperative heart rate and less significant peripheral vasodilation seen in TIVA with propofol/ remifentanil is thought to be responsible for reduced intraoperative blood loss and better quality of operative field compared to inhalational anaesthesia.11,51,55 Additionally, TIVA also has the potential to decrease coughing on emergence and postoperative nausea and vomiting, which speeds discharge from the hospital. A systematic analysis comparing TIVA with propofol with inhalational anaesthesia in ambulatory surgical procedures found a significantly reduced incidence of postoperative nausea and vomiting in the TIVA group.60

Adjunctive Drugs Remifentanil Remifentanil is an ultra-short-acting m-opioid agonist with a short elimination half-life (10 min).11 It is a fentanyl derivative and differs from other opioids in that it possesses an ester linkage that can be broken down by nonspecific plasma esterases. This makes clearance of the drug independent of gender, age, weight, hepatic or renal impairment.11,61 Remifentanil also causes hypotension and bradycardia, without peripheral vasodilatation.62 This feature combined with its easy titratability makes it particularly useful in controlled hypotension combined with an inhalation agent or propofol. It has been associated with reduced intraoperative blood loss and improved surgical conditions in middle ear surgery and endoscopic sinus surgery.11,53,62,63 Due to its faster elimination characteristics, it has been suggested that intraoperative remifentanil may also be associated with reduced postoperative nausea and vomiting. However, a recent systematic review concluded that remifentanil had no overall impact on postoperative nausea and vomiting compared to other short-acting opioids (fentanyl, alfentanil and sufentanil).64 -blockers Although labetalol has been shown to achieve quality operative fields, titration is not easy and its half-life extends long past the completion of surgery.12.65 On the other hand, esmolol is a cardioselective 1– blocker, with fast onset and short half-life, making it easily titratable. It also has the valuable effect of lowering the HR while causing hypotension, instead of causing reflex tachycardia.12 Intraoperative esmolol has been shown to produce better operating conditions than sodium nitroprusside in middle ear surgery.8 It has also been used successfully to improve the quality of the surgical field in mandibular surgery and endoscopic sinus surgery.12,65,66 !

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Magnesium Magnesium sulphate infusion produces hypotension by a reduction in CO and SVR. It has been shown to provide a significantly better operative field, decrease blood loss and reduce the duration of the surgery in ESS, but this comes at the expense of a longer emergence time, causing drowsiness postoperatively and potentiating the action of opioids and neuromuscular-blocking drugs.67 Tranexamic acid Tranexamic acid (TXA) is a synthetic derivative of the amino acid lysine. It exerts an antifibrinolytic effect via its reversible blockade of lysine-binding sites on plasminogen molecules. TXA has been shown to have a beneficial effect on intraoperative bleeding in patients undergoing cardiac, major orthopaedic, transplantation, oral and prostate surgeries.68–71 In ESS, topical and oral TXA was shown to improved surgical field and decrease blood loss.72,73 Intravenous TXA was shown to also reduce bleeding and improve surgical field in an ESS study that did not use local vasoconstrictors and microdebriders.74 However, a recent ESS study that utilised local vasoconstrictors and microdebriders failed to show any benefit for blood loss and intraoperative visualisation.75

POSTOPERATIVE CONSIDERATIONS Post-Op Nausea and Vomiting Postoperative nausea and vomiting should be minimised and if present, be treated promptly with antiemetics. Excessive valsalva from nausea and vomiting may increase the risk of bleeding from the surgical site. As mentioned previously, TIVA with propofol has been associated with lower risk of postoperative nausea and vomiting compared to inhalational anaesthesia.60

Post-Op Analgesia Uncontrolled postoperative pain is a common cause of postoperative tachycardia and hypertension. There is currently no data on what provides the optimum analgesia following orbital or sinus surgery. Early discharge necessitates the use of oral medications postoperatively, and multimodal analgesic regimes combining nonopioid analgesics and/or regional analgesics with an opioid are commonly used.76–79 Local anaesthesia and preoperative or intraoperative analgesia normally provides sufficient analgesia at the end of surgery.46 However, as remifentanil is rapidly metabolised, it does not provide postoperative analgesia, and further opioid analgesics may need to be administered in the early postoperative period.46

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10 D.I.T. Sia et al. Paracetamol has been shown to reduce pain scores and decrease opioid requirements in other surgeries, while possessing a favourable side-effect profile.46,80 When given alone, it was found to provide adequate postoperative pain relief in most patients after ESS. However, a quarter of the patients needed supplementary opioids.81 Paracetamol is a weak inhibitor of platelet COX-1 and thromboxane A2, but when given at single oral doses of 1 g or up to 1.95 g, it does not inhibit COX-1 enough to affect platelet function.82 The effect on postoperative bleeding was not found to be clinically significant following tonsillectomy.83 Non-selective NSAIDs have also been shown to decrease pain scores and opioid usage after oral, dental and gynaecologic surgery.84 Combinations of NSAIDs with paracetamol has been shown to be more effective than either drug alone in the acute postoperative setting.85 However, as non-selective NSAIDS inhibit the production of thromboxane A2 in platelets and impair their adhesion and aggregation, they are believed to confer an increased risk of severe bleeding in the perioperative period.80,81 COX-2 selective NSAIDs may provide postoperative analgesia without increasing the risk of perioperative bleeding.80 Preoperative COX-2 selective NSAIDs have been shown to reduce postoperative pain, opioid consumption and patient satisfaction without increased intraoperative blood loss.86 Concerns surrounding their use revolves around increased risk of thrombotic cardiovascular complications including myocardial infarction and stroke. However, information related to the cardiovascular risks associated with the use of COX-2 inhibitors is derived from long-term treatment data and may not reflect the risk of short-term use in the acute postoperative setting.80,87

CONCLUSION A bloodless field is paramount in orbital surgery, which is often conducted in a small space, where even minimal bleeding can obscure the surgical field and increase the risk of complications. Various techniques have been described; however, the control of intraoperative bleeding does not rely on a single particular technique, but rather a series of well-designed interventions that result in optimal conditions. Preoperatively, the anaesthetic plan should be individualized, taking into consideration patient comorbidities, severity of disease, surgeon and anaesthesiologist experience. Premedication with clonidine, ACE inhibitors have been used successfully as adjuncts for controlled hypotension. Intraoperatively, simple elevation of the head in reverse Trendelenburg position can decrease venous congestion in the upper body and reduce intraoperative bleeding. Use of the laryngeal

mask may improve early operating conditions and improve the quality of emergence, lowering the risk of laryngospasms, coughing and bleeding postoperatively. Although IPPV may increase intraoperative bleeding by decreasing venous return, its use may be unavoidable in TIVA with propofol/remifentanil due to respiratory depression by remifentanil. TIVA with propofol may produce better surgical conditions compared with inhalational techniques and is associated with reduced postoperative nausea and vomiting. Intraoperative remifentanil and esmolol are useful adjuncts to controlled hypotension and produces improved operating conditions. Postoperatively, nausea and vomiting should be limited and treated promptly if present. Uncontrolled postoperative pain is a common cause of postop tachycardia and hypertension and should be managed with a multi-modal analgesic regime and should be managed with a multi-modal analgesic regime.

DECLARATION OF INTEREST The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

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Orbit

General anaesthetic considerations for haemostasis in orbital surgery.

Orbital surgery is often conducted in areas with limited exposure where vital structures are tightly crowded together. A bloodless field is paramount ...
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