The nasal and paranasal sinus mucosa is extremely well supplied with blood. Thanks to high blood flow through the thick network of capillaries, the inspired air can be quickly moistened and warmed. Injuries to this region are likely to be characterized by intensive bleeding; spontaneous bleedings are also observed, e.g. related to arterial hypertension.

Surgeries involving this anatomico-functional region are thus associated with intensive and difficult to stop bleeding from the capillaries [1], which is particularly difficult to manage during functional endoscopic sinus surgery (FESS), when precise manoeuvres under the guidance of a video camera introduced through the nose, magnifying and illuminating the area operated on, are essential. This technique may be used for the removal of tumours, polyps, the post-inflammation hypertrophied mucous membrane closing the sinus cavity entrance, or for surgery of the pituitary or other structures of the middle cranial fossa. Bleeding is a serious impediment increasing the risk of damage to the orbit, optic nerve, unintended penetration of the middle cranial fossa or even damage to the internal carotid artery. For this reason, after the introduction of endoscopic sinus procedures under general anaesthesia to clinical practice, several methods were designed to reduce surgical field bleeding.

The basic method to reduce the bleeding from the nasal mucous membranes operated on is to constrict the capillaries of the area involved.

This can be accomplished by:

• local anemization of the mucosa with vasoconstrictors

• positioning the patient in the anti-Trendelenburg position

• pharmacological cardiodepression with the heart rate stabilized within lower physiological limits (about 60 min-1) and the mean arterial pressure reduced to about 65 mm Hg,

• preoperative steroids to reduce the inflammation in the paranasal sinuses.

LOCAL ANEMIZATION

Local anemization is provided by an operator by insertion of gauze pads infiltrated with adrenaline or a beta-blocker to the nasal passages and by submucosal administration of 1-2% lidocaine with adrenaline in the concentration of 1:80 000-1:200 000. The reluctance of some anaesthesiologists to this management results from historical determinants. In the past, halothane used for general anaesthesia sensitized the myocardium to catecholamines, especially in the initial, light stage of anaesthesia, which could have resulted in arrhythmia. At present, when propofol or other novel inhalation agents, less sensitizing the myocardium, are used and anemization is produced only once the patient is well saturated with an inhalation anaesthetic, adrenaline in the concentration of 1:1000-1:50 000 can be administered without severe side effects [2, 3, 4]. The majority of patients experience only short-term accelerated heart rate or increased arterial blood pressure if the adrenaline concentration in swabs is high [5]. After submucosal injection, arterial blood pressure may decrease and heart rate accelerate [6, 7].

BODY POSITIONING

Head elevation causes a decrease in mean arterial pressure within the elevated region by about 2 mm Hg for each 2.5 cm above the heart level [8]. Moreover, blood supply to this area improves. Reduced venous return from the lower body part reduces cardiac output [9]. In patients in the anti-Trendelenburg position the surgical conditions are better compared to those in the supine position, even if the arterial pressure measured at the heart level does not decrease [10]. This may be explained by the fact that in the anti-Trendelenburg position lower volumes of blood at lower pressure flow through the surgical field per unit time; moreover, a higher proportion of cardiac output directs to the lower body part than in the horizontal position. Thus, appropriate surgical conditions are provided at higher arterial pressure at the heart level, which is essential for coronary perfusion. Considering the fact that during general anaesthesia the myocardial oxygen consumption is not decreased to such an extent as in e.g. the brain, the anti-Trendelenburg position protects the patient against coronary incidents. For the safety of cerebral flow it is important that the capacity of veins and intracranial venous sinuses in this position decreases and part of the cerebrospinal fluid passes to the spinal sac, which reduces intracranial pressure and enables cerebral perfusion despite lower mean arterial pressure [10, 11].

ARTERIAL BLOOD PRESSURE

Once endoscopic sinus surgery under general anaesthesia was introduced into clinical practice, it became obvious that such procedures cannot be performed without the decrease in arterial blood pressure. To reduce the surgical field bleeding, controlled hypotension was induced using various drugs, e.g. trimetaphan, magnesium sulphate, nitroglycerine, beta-blockers, convertase inhibitors, labetalol, sodium nitroprusside and large doses of inhalation anaesthetics – halothane or isoflurane [12, 13, 14]. Sodium nitroprusside gained special popularity [8]. However, with this drug, despite a decrease in arterial pressure, haemorrhaging was still too intensive in many cases; the necessity to induce deep hypotension disqualified patients with the diagnosed contraindications for this method [12, 13].

The need for other systemic methods reducing bleeding resulted in numerous clinical trials. In the majority of trials, authors focused on the comparison of surgical field bleeding and total volume of blood loss or the surgical field quality during administration of various hypotensive drugs or anaesthetics inducing hypotension and maintenance of the assumed mean or systolic arterial blood pressure. Despite a firm conviction that decreased arterial pressure reduces bleeding in the surgical field, the results of clinical studies were inconclusive and correlation between arterial pressure and bleeding was not always observed [12, 13, 14].

The mean arterial pressure providing good surgical conditions is different for various methods of inducing hypotension. The use of vasodilating drugs was effective once the pressure was decreased ≤60 mm Hg. Mild hypotension induced with sodium nitroprusside did not result in reduced blood loss or improved visibility in the surgical field compared to procedures without hypotensive drugs. This was likely to be caused by decreased arterial pressure (relaxation of the muscular layer of capillaries) and reflex tachycardia, which increased cardiac output and blood flow to the tissues operated on [1, 13]. The maintenance of mean arterial pressure at the level of 50 mm Hg, on the other hand, was associated with increased mortality estimated at 20-60 cases per 100 000 patients [12].

Esmolol, the drug of extremely short half-life (about 9 min), which administered in a continuous infusion provides stable and controllable beta-adrenergic block, reduces bleeding in a different way [15]. Decreased heart rate and strength of contractions leads to reduced arterial pressure and impulsation from the carotid sinus baroreceptors and stimulates the sympathetic system simultaneously inhibiting the activity of cardiac branches of the vagus nerve. However, the cardiac component of the reflex is blocked by esmolol thus heart rate is not accelerated; the vascular component – vasoconstriction – is active, which decreases the tissue perfusion and enhances local anemization [4]. Thanks to that, surgery may be efficiently performed at the mean arterial blood pressure decreased to 60-65 mm Hg; when nitroprusside is used – to 50-55 mm Hg [4, 14].

A similar effect as the one after esmolol is obtained thanks to cardiodepressive anaesthetics – remifentanil or propofol or their combination under TIVA. Thus, in the majority of cases, the use of hypotensive drugs becomes unnecessary, the bloodless surgical field may be provided at moderate hypotension of 60-65 mm Hg [3,16, 17, 18]. Thanks to moderate and not deep hypotension, the risk of myocardial or cerebral hypoxia is lower as the risk of total loss of vascular flow is lower; vessels, due to a local pathological change, generate higher resistances hence higher pressures are required. Thus, moderate hypotension with low cardiac output causes an evener decrease in tissue flow and prevents the steal phenomenon.

HEART RATE

The effect of heart rate on surgical bleeding has been underestimated, although many comparative studies demonstrated lower blood loss in patients with decreased heart rate and the same arterial blood pressure [1, 3, 4, 14, 18, 19]. Moreover, there were no significant differences in intraoperative bleeding, irrespective of the agents used when the mean arterial blood pressure and heart rate did not differ significantly among groups [16, 17]. In patients with slight intraoperative bleeding, the heart rate was within 55-75 min-1, i.e. corresponded to the heart rate at rest [1, 3, 4, 19, 20, 21]. It was conclusively demonstrated that during general anaesthesia for FESS, the heart rate should be maintained at 60 min-1, as there is correlation between its value and surgical  bleeding [19, 20]. A decrease in heart rate enables to administer anaesthesia under moderate and not deep hypotension.

CARDIAC OUTPUT

The findings of studies concerning cardiac output under the conditions of controlled hypotension remain inconclusive: on the one hand, a correlation was demonstrated between decreased cardiac output and surgical field bleeding using trimetaphan during mastectomy; on the other hand, there was no correlation found between increased cardiac output and bleeding during maxillofacial surgery [22, 23]. The lack of intensive bleeding during controlled hypotension at increased cardiac output may be associated with, among other things, the anti-Trendelenburg position, which at markedly decreased systemic vascular resistance is likely to direct the blood to the lower body part and reduce the inflow to the operating site located below the heart [23]. Non-invasive determinations of cardiac output during nasal septum procedures under intravenous anaesthesia with propofol and remifentanil or propofol, remifentanil and esmolol showed proper values despite the mean arterial pressure decreased to 60 mm Hg and heart rate to 60-75 min-1 [21]. Nevertheless, it is difficult to refer those results to sinus endoscopic surgery as high blood supply to this region hinders the provision of bloodless surgical field during FESS compared to any other surgical procedure.

It is noteworthy that as far as the method of anaesthesia for such procedures is concerned, an intravenous infusion of remifentanil and propofol – two cardiodepressive agents, is found beneficial. An increase in cardiac output in such a case is unfavourable [24, 25, 26, 27, 28, 29, 30]. Further studies are needed to determine whether and to what extent the cardiac output should be decreased during such procedures. Based on the available results, it should be assumed that the optimal measure is to maintain cardiac output values within the lower physiological range [21]. 

STEROID THERAPY

Beneficial effects of steroids administered over several preoperative days on intraoperative bleeding may result from inhibition of the inflammatory process and activation of adrenergic receptors [31]. Steroids, decreasing the number of inflammatory reaction mediators in the nasal and sinus mucosa, limit the damage to blood vessels, tissue transudates and oedema as well as inflammatory congestion. Moreover, they increase the systolic reactivity of smooth muscles and enhance the action of endogenic adrenaline and noradrenaline [32, 33, 34].

PRACTICAL ASPECTS OF ANAESTHESIA

Currently, there is no one recognized method of general anaesthesia for sinus endoscopic surgery. Considering the data presented earlier, particularly the necessity to provide circulatory stability, to eliminate sympathetic pain stimulations and cardiac component of arterial baroreceptors, the anaesthetic of choice is remifentanil. The findings of numerous studies in patients receiving this drug confirm good surgical conditions during its use [28, 35, 36, 37, 38]. A great asset of remifentanil is possible slow, mild introduction into decreased dynamics of the circulatory system and provision of strong and controllable analgesia. In the case of bradycardia or too advanced hypotension, is it sufficient to reduce the rate of drug flow to restore the intended values.

Anaesthesia may be induced with any anaesthetic (except for ketamine). For muscle relaxation before endotracheal intubation, suxamethonium is not recommended due to the risk of bradycardia requiring atropine or elevation in arterial pressure. The most suitable muscle relaxant appears to be cisatracurium as its degradation is independent of the hepatic metabolism and renal function, which is extremely important as reduced arterial pressure weakens the hepatic flow as well as glomerular filtration and prolongs the action of the agents used. [37].

Propofol is the anaesthetic most commonly recommended for FESS. Positive opinions on this agent can be found in studies demonstrating significant differences in heart rate in patients administered propofol vs an inhalation anaesthetic, or in those whose heart rate was not analysed [3, 7, 11, 35, 36, 37, 38]. Moreover, the available literature shows that at the same values of arterial blood pressure and heart rate, surgical bleeding does not differ after remifentanil with sevoflurane or propofol [16, 17]. Although sevoflurane and propofol similarly affect haemodynamics, their effects on microcirculation are different [30]. Inhalation anaesthetics reduce arterial pressure by decreasing the tension of pre-capillary arterioles and cardiodepressive action whereas propofol, with slight influence on the myocardium, exerts similar effects to nitroglycerine: dilating veins hence facilitating the outflow of blood from the surgical field [24]. Furthermore, propofol decreases cardiac output by limiting the venous return, thus reducing the inflow of blood to the surgical field [25]. The decreased density of capillaries during propofol anaesthesia was demonstrated within the oral mucous membranes. Likewise, studies on the tissue flow through the cochlear musoca (a more readily available organ with autoregulation similar to that of the cerebrum) showed its higher decrease during propofol anaesthesia compared to sevoflurane [24, 38]. This difference of action on the cerebral circulation corresponds with the results of studies showing slightly better reduction in bleeding within the ethmoid cells using TIVA [16, 39]. The ethmoid cells are not supplied with blood from the external carotid artery branches, as are other paranasal sinuses, but from the branches of the autoregulated middle cerebral artery.

No significant differences in intraoperative bleeding were found during administration of sevoflurane, isoflurane and desflurane when remifentanil was used as an analgesic [37]. Definitely unfavourable effects were observed using isoflurane and fractionated doses of fentanyl or alfentanil when vasodilation and accelerated heart rate (resulting from decreased concentration of circulating analgesic) led to transiently increased bleeding [18, 32].

The advantage of inhalation anaesthetics, compared to propofol, is the possibility of monitoring their content in the body and fast elimination, which in practice means easy deepening of anaesthesia or otherwise. In this way the arterial pressure can also be regulated. In propofol cases, once excessive cardiodepression develops, the treatment of choice is atropine or ephedrine, which may not be beneficial in all patients. Moreover, if the anaesthetic is administered according to the rule “the full dose until procedure completion“ (movements of a patient should be prevented before the removal of an endoscope from nasal canals), the recovery after propofol anaesthesia will be longer than after sevoflurane or desflurane [17].

We believe that in cases of accelerated heart rate and elevated arterial blood pressure, despite the use of high doses of remifentanil and propofol or inhalation anaesthetic (which results in intensive bleeding), a vasodilator should be administered cautiously and selectively – if the heart rate is slow or a beta-blocker – if rapid heart action maintains. The most appropriate beta-adrenergic blocker is esmolol as its administration in a continuous infusion enables to affect gently the heart rate and reduces the consumption of remifentanil.  

The development of endoscopic surgery of the cranial basis is associated with increasingly longer procedures requiring reduced dynamics of the circulatory system, which raises concerns over the cerebral circulation and oxygen supply to the brain. The phenomena occurring in the cerebral circulation when slow heart rate and hypotension are maintained over several hours should be subjected to further studies assessing the safety margin of anaesthetic methods of intraoperative management.

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address:

*Andrzej Drozdowski
Klinika Anestezjologii i Intensywnej Terapii
Uniwersyteckiego Szpitala Klinicznego w Białymstoku
ul. M. Skłodowskiej-Curie 24A, 15-276 Białystok
tel.: 0-607 748 677
e-mail: optymista678@wp.pl

received: 07.07.2010
accepted: 15.12.2010