Unintentional hypotension from lidocaine infiltration during orthognathic surgery and general anaesthesia.

BACKGROUND: A probable causal relationship between submucosal infiltration of lidocaine, with adrenaline 12.5 microg x mL(-1), and untoward arterial hypotension during general anaesthesia for orthognathic surgery was investigated in two parts. METHODS: The first part of the study was open and non-randomised. The patients served as their own controls, receiving 5.4 mL saline/adrenaline before mandibular or maxillary surgery on the first side of the jaw and 5.4 mL lidocaine (2%)/adrenaline on the other side a minimum of 40 min later. Nine patients received in total 11 pairs of injections of the study drugs. In Part Two, 50 mg or 100 mg of lidocaine with adrenaline was infiltrated in an observer-blinded and randomised order in either side of the jaw in another 13 patients. RESULTS: A significant and dose-dependent blood pressure decrease was observed after infiltration of lidocaine/adrenaline, but not after saline/adrenaline. The heart rate increased significantly after both types of injections, most pronounced after saline/adrenaline. Mean arterial blood pressure decreased on average 11% and 23% with lidocaine 50 mg and 100 mg, respectively (P<0.05, ANOVA). CONCLUSION: Lidocaine induced dose-dependent arterial hypotension when combined with a defined level of general anaesthesia. The causative mechanism is unclear.

Evidence of cerebral dysfunction associated with isoflurane- or propofol based anaesthesia for orthognathic surgery, as assessed by biochemical and neuropsychological methods.

A relationship has previously been described between individual mean isoflurane concentrations and the release of a marker of neuronal injury, adenylate kinase (AK), into the cerebrospinal fluid (CSF) after anaesthesia and orthognathic surgery. Likewise, reduced mental performance has been detected. Twenty-nine patients scheduled for orthognathic surgery were assigned to isoflurane- or propofol based anaesthesia, which was adjusted to a defined level with the aid of processed EEG and quantitative surface EMG. In the case of a mean arterial pressure (MAP) < 50 mmHg a phenylephrine infusion was started to keep the MAP above the minimal level, otherwise no regard was paid to the blood pressure, which never exceeded normal values. A lumbar puncture for CSF sampling was performed approximately 20 h postoperatively. The CSF sample was analysed for AK activity. Neuropsychological tests were performed the day prior to surgery and again in the period 4-8 weeks postoperatively. Five patients were re-examined by psychometry 12-30 months later. A release of AK into CSF was confirmed, equal in both groups. Correlation with the anaesthetic dose given was poor. Five patients from each group failed significantly in the postoperative neuropsychological tests. They differed in several demographic respects from the others. When five of the failed patients were re-examined 12-30 months later, three patients still performed poorly in the tests. Biochemical and neuropsychological disturbances were recorded in several patients objected to orthognathic surgery. The underlying mechanisms are unclear, including the role of the anaesthetic drugs or surgery itself.

Low frequency of adenylate kinase release into cerebrospinal fluid during balanced, normotensive anaesthesia and a non-orthognathic surgical procedure.

Activity of strictly intracellular enzymes in the cerebrospinal fluid (CSF) may indicate leakage from dysfunctional brain cells. Increased activity of adenylate kinase (AK) in the CSF is indicative of brain cell injury arising from several sources, among them orthognathic surgery. The mechanism in the latter case is obscure, but the use of an oscillating saw which generates vibrations, and the site of surgery close to the brain may be contributing factors. Anaesthesia may also play a role. In the present study, CSF-AK activity was measured after hysterectomy and was compared with activity after orthognathic surgery in two other studies. Four of 19 patients (21%) in the present study expressed pathological activity, compared with 34 of 47 (72%) orthognathic patients in the two other studies. No firm conclusion may be drawn from historical comparisons, and the difference in activity seen between the two types of surgery might not necessarily be the result of surgical factors. Until this is investigated further, however, we conclude that there may be a difference in postoperative CSF-AK activity between orthognathic and lower abdominal surgery.

Occurrence of adenylate kinase in cerebrospinal fluid after isoflurane anaesthesia and orthognathic surgery.

UNLABELLED: The study objective was, firstly, to investigate whether anaesthesia with induced arterial hypotension would cause leakage of a biochemical marker of neuronal injury, adenylate kinase (AK), into the cerebrospinal fluid (CSF). ( DEFINITION: arterial hypotension = mean arterial pressure (MAP) 50-65 mmHg during > or = 10 min). Secondly, a subgroup of patients was examined with a limited battery of psychometric tests. Patients, scheduled for orthognathic surgery, were allocated to either hypotension (n = 20) or normotension (n = 20). Seventeen patients were subjected to psychometry. Arterial blood pressure was recorded continuously and controlled by adjustments of the administered concentration of the inhalational anaesthetic isoflurane. Fentanyl, an opioid, was given equally in both groups. A lumbar puncture was performed approximately 20 h post-operatively for a CSF sample, later analysed for AK activity. Neuropsychological tests were performed the day before surgery and the fourteenth day postoperatively. The CSF-AK value was pathologically increased ( > 0.040 U/L) in 24 patients (65%), of whom 9 were normotensive. There was no significant difference between the CSF-AK values in the hypotensive and normotensive groups, mean values were 0.082 (s.d. 0.051) and 0.066 (s.d. 0.059) U/L, respectively. The overall correlation between the 10 min MAP levels and the CSF-AK values was close to zero. In the pilot neuropsychological investigation some abnormalities were observed, indicating clinically significant adverse effects in four hypotensive patients, of whom two displayed pathologically increased CSF-AK values. At the group level, the correlation between the changes in psychometry and the measured CSF-AK values was poor. Increases in CSF-AK activities may be a non-specific occurrence in the perioperative interval, possibly indicating an adverse effect on the brain. Arterial hypotension could not be proven to explain the CSF-AK outcome.

A new hybrid anaesthetic circuit for a low-flow rebreathing technique.

The coaxial Mapleson D (Bain) circuit is close to an ideal anaesthetic breathing circuit but it requires a high fresh gas flow (VF). The CO2 absorber circuit can be used with a low VF but the patient end is clumsy and hyperventilation is common unless a small tidal volume (VT) and a low respiratory frequency (f) is used. To overcome these problems a new hybrid anaesthetic circuit has been constructed. The new system has a slender coaxial patient end, connected to a Y-piece and a CO2 absorber circuit with unidirectional valves. The VF supply runs inside the coaxial tube to the patient end, similar to the Bain circuit. The new circuit was tested with simulated controlled ventilation in a lung model and compared to an absorber circuit, an absorber circuit with an added 300 ml dead space (VD) and a Bain circuit. The fraction of end tidal CO2 (FECO2) was measured as a function of VF. With VF 11 min-1, VT 10 ml.kg-1 and f 12 breaths min-1 a simulated 70 kg patient had an FECO2 of 4.8% and a 40 kg patient 5.5% with VF 21.min-1. At zero VF the new system was equal to an absorber circuit with 300 ml VD. With increasing VF the FECO2 in the new circuit decrease towards the absorber circuit values. The new system combines the benefits of the Bain circuit with those of a low flow CO2 absorber circuit and offers flexibility in the choice of combinations of VT, f and VF.