The effect of hypotensive anaesthesia on cognitive functions and recovery at endoscopic sinus surgery

EDITOR: Controlled hypotensive anaesthesia has been used during surgical procedures in an attempt to reduce intraoperative haemorrhage and the resultant need for transfusion. Previous reports show that hypotension with a mean arterial pressure (MAP) between 50 and 60 mmHg affects cognition [1]. A prospective, randomized, blinded clinical trial was performed to compare blood loss, cognitive function and recovery after moderate hypotensive or normotensive anaesthesia for endoscopic sinus surgery. After obtaining approval from the Ethics Committee of our university hospital and informed consent from all patients, 46 adults undergoing endoscopic sinus surgery were recruited to the study. Patients under 17 or over 55, with anaemia (Hb < 10g dL−1), poorly controlled arterial hypertension, pre-existing coagulation defects or anticoagulatory medication were excluded. Patients were randomly assigned via computer-generated numbers to the normotensive group (Group N, n = 23) or the hypotensive group (Group H, n = 23). Patients were monitored using continuous ECG, pulse oximetry (SPO2) and invasive arterial pressure via a 20 G catheter inserted into the radial artery of the non-dominant hand after induction of anaesthesia. Anaesthesia was induced with propofol 2 mg kg−1 and fentanyl 1 μg kg−1, and endotracheal intubation was facilitated with atracurium 0.2 mg kg−1. Anaesthesia was maintained in both groups with propofol infused at rates between 3 and 8 mg kg−1 h−1 as the anaesthetist deemed clinically necessary. In the hypotensive group, a nitroglycerine infusion (1 mg mL−1 in 5% dextrose) was titrated to maintain MAP between 60 and 70 mmHg. The trachea was extubated when a regular spontaneous breathing pattern was re-established and when the patients responded to verbal commands (open eyes, squeeze hand). The times to eye opening and extubation were defined as emergence criteria. Heart rate and MAP were recorded before induction of anaesthesia, at 5, 10, 20, 30, 40, 50 and 60 min after beginning of surgery and at the end of the operation. Intraoperative bleeding was assessed by collecting shed blood with a flush suction device integrated in the endoscope. The neuropsychological tests were conducted by the same anaesthesiologist who was trained in their use and blind to the patient group allocation. The baseline neuropsychological test results were obtained 2 h prior to surgery. Neurocognitive outcome was assessed 2 and 24 h after extubation. The tests at both times consisted of the Mini Mental State Examination (MMSE) and the Visual Aural Digit Span Test (VADST) [2,3]. The first tests cognitive function simply and quickly and the second alertness, attention, concentration and short-term memory. Recovery was assessed using the modified postanaesthesia recovery score (PARS) of Aldrete and Kroulik at 15, 30 and 45 min after extubation [4]. This records vital signs with patients receiving 0-13 points for five physiological variables (consciousness, ventilation, circulation, horizontal nystagmus and count down test). Data are presented as means ± SD and ranges. Differences were analysed using one-way analysis of variance (ANOVA) for repeated measures after testing for a normal distribution and equal variance (Kolmogorov-Smirnov test). A P-value of 0.05 or less was considered statistically significant. The duration of anaesthesia did not differ significantly between the two groups nor did the times from the end of infusion to opening eyes on command and giving correct date of birth. There were no significant differences in the total dose of propofol or fentanyl. The hypotensive group received 1.34 ± 0.65 μg kg−1 min−1 nitroglycerine between intubation and the end of surgery. Blood loss was significantly lower in the hypotensive group (Table 1).Table 1: Patient characteristics data.Although induction of anaesthesia resulted in a significant drop in MAP in both groups there was no difference between groups. At the beginning of surgery, MAP increased significantly in the control group but not in the other. Intraoperative MAP was significantly lower in the hypotensive group. Recovery scores at 15 min were significantly lower in the control group but there were no differences at 30 min and later. There were no significant differences between the two groups in cognitive test scores at any measurement time (Fig. 1).Figure 1.: VADST and MMSE scores. □: hypotensive; Symbol : normotensive.SymbolThe aetiology of postoperative cognitive dysfunction (POCD) is likely to be multifactorial. General anaesthesia, anaesthetic agents or the postoperative analgesic regiment can cause POCD. Other factors such as the inflammatory or metabolic endocrine stress responses associated with major surgery and hypotension may also be important. In a recent study, attention and cognitive performance was assessed in 26 hypotensive (systolic blood pressure <100 mmHg, diastolic blood pressure < 60 mmHg), and 22 normotensive female university students. Hypotensive individuals remembered fewer words than the normal subjects [5]. Induced hypotension has been used to reduce blood loss and improve surgical conditions. A targeted MAP that is 30% below the usual blood pressure, but not lower than 50 mmHg in ASA I patients and 80 mmHg in elderly patients is thought to be clinically acceptable. The margin of safety for controlled hypotension with regard to the integrity of the central nervous system is still uncertain. In a recent study of 1802 otorhinolaryingological procedures performed under controlled hypotension, four patients had postoperative symptoms of cerebral damage. One patient with a preoperatively unrecognized stenosis of the internal carotid artery died of generalized ischaemic brain damage. In two patients, the symptoms of cerebral ischaemia did not occur until 3 and 11 days later so that the causative role of hypotension is questionable [6]. No postoperative neurological disorder was observed in this study. We prefer moderate hypotension and our patients were all in ASA I group to minimize the risk of cerebral hypoperfusion. Postoperative cognitive impairment is a major problem among older patients. Our patients were young with no cardiac or cerebral impairment, and surgery was not long. Prolonged cerebral hypoperfusion might lead to cognitive impairment even in young and healthy patients. In our study, there were no differences in early cognitive functions between the two groups. MMSE examines attention, orientation, registration, recall, calculation and language. VADST is a sensitive measurement of the late stage recovery of cortical function. Our results may be due to the fact that only moderate hypotension was used, since no patient had a MAP of <50 mmHg. Although the MMSE scores were higher at 24 h this might be due to a practice effect. Various techniques and pharmacological agents have been used to induce hypotension but we prefer nitroglycerine and propofol. Nitroglycerine is a nitric oxide donor that dilates both veins and arteries with little effect on the smaller resistance vessels [7] and provides improved intraoperative stability of MAP levels. Reflex tachycardia was not observed in the hypotensive group, probably due to the low dose of nitroglycerine employed. The hypotensive group had a higher PARS score at 15 min after extubation, but there were no differences between the groups at other measurement times. This higher score might result from the propofol infusion rate being reduced because of the low blood pressure in some of the patients in the hypotensive group. On the basis of these results we conclude that moderate hypotension reduces blood loss without causing postoperative cognitive deficits. F. Sarıcaoglu V. Celiker E. Basgul O. Yapakcı U. Aypar Department of Anesthesiology, Hacettepe University Faculty of Medicine, Ankara, Turkey