Showing papers in "Canadian Journal of Anaesthesia-journal Canadien D Anesthesie in 1994"

The airway: problems and predictions in 18,500 patients

Abstract: The purpose of this study was to describe methods, risk factors, and outcomes of airway management in all patients (obstetrics excluded) attended by anaesthetists over 27 months. Preoperatively, anaesthetists recorded patient factors and assessed four airway characteristics. Methods of tracheal intubation and ease of direct laryngoscopy following general anaesthesia (easy, awkward, difficult) were noted. Factors predictive of poor outcome and the value of the preoperative airway examination were determined. For 18,205 patients following a direct laryngoscopy, (GA), tracheal intubation was difficult (> 2 laryngoscopies) in 1.8% and awkward ( 200 mm Hg) and dental damage on induction of anaesthesia. It is concluded that difficult tracheal intubations occurred infrequently but were associated with increased morbidity. Patient factors and four physical airway characteristics were useful predictors but limited in identifying all problems.

The prevention of postoperative pain

Abstract: Patients want safe and effective analgesia Our goal is to prevent postoperative pain in an efficient and cost effective manner For most patients, the pain can be managed using simple, non-invasive and inexpensive analgesic techniques Given the current economic climate, cost will become increasingly important There will be financial pressure to expand the scope of ambulatory surgery There will be pressure to discharge patients as soon as they are able to take oral medications Outpatient analgesia is the oldest and most widespread form of patient-controlled analgesia--We already have the knowledge and the analgesics necessary to prevent postoperative pain What we need now is logical, rational, and universal application of this information

Respiratory depression associated with patient-controlled analgesia: a review of eight cases

Abstract: Patient-controlled iv delivery of opioids for postoperative pain management is a popular alternative to the traditional im route of administration. However, occasional patients receiving opioids in this manner develop severe respiratory depression. The purpose of this paper is to determine the incidence of, and factors contributing to, the development of this complication. To do this, the Office of Medical Quality Improvement retrospectively searched for reports of respiratory depression in a database compiled from the charts of approximately 1600 patients who had received PCA at the University of Alberta Hospitals in 1992. Eight cases of serious respiratory depression were detected. Factors associated with the occurrence of respiratory depression included the concurrent use of a back-ground infusion, advanced age, concomitant administration of sedative/hypnotic medications, and pre-existing sleep apnoea syndrome. No cases were attributed to operator error or equipment malfunction. In conclusion, the risk of respiratory depression with patient-controlled opioid administration is similar to that observed when opioids are delivered by the traditional im or spinal routes. The safe and effective use of patient-controlled analgesia depends upon knowledgeable medical and nursing staff, clearly defined nursing policy and procedures, and frequent patient follow-up.

The laryngeal mask airway: its features, effects and role

Abstract: The laryngeal mask airway was designed as a new concept in airway management and has been gaining a firm position in anaesthetic practice. Numerous articles and letters about the device have been published in the last decade, but few large controlled trials have been performed. Despite widespread use, the definitive role of the laryngeal mask has yet to be established. In some situations, such as after failed tracheal intubation or in anaesthesia for patients undergoing laparoscopic or oral surgery, its use is controversial. There are a number of unresolved issues, for example the effect of the laryngeal mask on regurgitation and whether or not cricoid pressure prevents placement of the mask. We review the techniques of insertion, details of misplacement, and complications associated with the use of the laryngeal mask. We discuss the features and physiological effects of the device, including the changes in intra-cuff pressure during anaesthesia and effects on blood pressure, heart rate and intra-ocular pressure. We then attempt to clarify the role of the laryngeal mask in airway management during anaesthesia, based on the current knowledge, by discussing the advantages and disadvantages as well as the indications and contraindications of its use. Lastly we describe the use of the laryngeal mask in circumstances other than airway maintenance during anaesthesia: fibreoptic bronchoscopy, tracheal intubation through the mask and its use in cardiopulmonary resuscitation.

Age and the onset of desaturation in apnoeic children

Abstract: Most patients undergoing general anaesthesia are apnoeic during laryngoscopy and tracheal intubation. This study determined the time until the onset of desaturation following pre-oxygenation in apnoeic infants, children, and adolescents. Fifty ASA physical status I patients, 2 days to 18 yr of age, were studied. The patients were stratified into one of five groups according to age: Group I, 0-6 mo; Group II, 7-23 mo; Group III, 2-5 yr; Group IV, 6-10 yr; and Group V, 11-18 yr. Following induction of anaesthesia with halothane via mask or intravenous barbiturates, the ability of the anaesthetist to ventilate the lungs via the mask was ascertained and paralysis was accomplished with vecuronium 0.1 mg.kg-1. Manual mask ventilation was maintained with oxygen and halothane. When end-tidal N2 decreased below 3% (minimum time two minutes), the face mask was removed. The time between the removal of the face mask and a decrease in oxygen saturation (SpO2) from 99-100% to 90% was measured. Manual ventilation was then resumed and the trachea intubated. Desaturation started earlier in infants than in two- to five-year-old children (96.5 +/- 12.7 sec vs 160.4 +/- 30.7 sec, P < 0.0001). Children became desaturated faster than adolescents (160.4 +/- 30.7 vs 382.4 +/- 79.9 sec, P < 0.0001). The time required to reach 90% saturation correlated well with age by linear regression analysis (r2 = 0.88, P < 0.0001). We conclude that the time to onset of desaturation following pre-oxygenation with mask ventilation increases with age in healthy apnoeic children.(ABSTRACT TRUNCATED AT 250 WORDS)

Difficult laryngoscopy: obtaining the best view

Abstract: The anaesthesia community is now well aware that respiratory-related events are the most common cause of brain death and whole body death due to anaesthesia and that difficulty/failure to establish the airway is the most common cause of these respiratory-related events. This issue of the Canadian Journal of Anaesthesia contains an excellent description of the experience of one major teaching hospital with establishing the airway; this experience likely "reflects the reality of the actual practice setting" for many anaesthesia caregivers.2 The paper by Drs. Rose and Cohen greatly strengthens several understandings that were suggested by previous studies and are summarized in several recent reviews. 3-5 First, the incidence of "troublesome" or "awkward" intubation requiting "less than or equal to two laryngoscopies" is relatively common and is approximately 1-18% (the authors found 2.5%). Second, the incidence of "difficult" intubation requiring "more than two laryngoscopies" is approximately 1-4% (the authors found 1.8%). Third, the incidence of "abandoned/failed intubation" is approximately 0.05-0.35% (the authors found 0.30%). Fourth, the incidence of "cannot ventilate by mask, cannot intubate" is somewhere around 0.0001-0.02% (the authors had a near miss incidence of 0.01%). The wide range of incidences cited above for all degrees of difficulty generally reflect the difference between the obstetrical and general surgical population of patients. Fifth, the greater the degree of intubation difficulty, the greater the incidence and severity of complications. Sixth, simple noninvasive tests can predict difficult intubation. Seventh, use of/combining multiple noninvasive tests results in more powerful prediction of difficult intubation than any test alone. Eighth, and most important, prediction of ease/ difficulty of intubation remains an imperfect science since the tests fail to predict some difficult intubations and many predicted intubations turn out to be easy. Rose and Cohen use the qualitative terms (1) "easy"; (2) "troublesome," "awkward," and "less than or equal to two laryngoscopies"; (3) "difficult" and "more than

Predicting blood loss in surgery for idiopathic scoliosis

Abstract: The authors attempted to determine the relative importance of factors that influence bleeding during and after spinal fusion. Data from 30 ASA I patients with idiopathic scoliosis were prospectively collected and analyzed. Intraoperative bleeding was 1971 ± 831 ml (mean ± SD) (61.5 ± 27% of estimated blood volume (EBV) and correlated with the number of fused vertebrae (r = 0.66, P < 0.0001) and the duration of surgery (r = 0.46, P = 0.0105). There was no correlation between intraoperative bleeding and the Cobb curve angle (43 to 86°), the mean arterial blood pressure (MAP) (63 to 86 mmHg), the central venous pressure (CVP), the quantity of epinephrine infiltrated, muscle relaxants or opioids used, nor in the type of opioids used, the minimal body temperature or whether stored or autologous blood was used. Postoperative bleeding was 1383 ± 369 ml (43.1 ± 11.7% of EBV) and correlated with the length of time the Hemovac drain was in place (r = 0.40, P = 0.0285) and MAP (r = 0.40, P = 0.0285). There was no correlation between postoperative and intraoperative bleeding nor in the number of fused vertebrae. Six patients had greater postoperative than intraoperative bleeding. The total bleeding (intra-plus postoperative) was 3347 ± 920 ml (104.2 ± 30.6 of EBV) and correlated with the number of fused vertebrae (r = 0.63, P = 0.0001) and with the duration of surgery (r = 0.42, P = 0.0208). We conclude that the number of fused vertebrae is the key factor in predicting intraoperative and total bleeding. Postoperative bleeding is considerable (up to 76.9% of EBV). No other factors allow for adequate prediction of postoperative bleeding and these patients must be kept under strict surveillance after surgery.

Pulmonary hypertension and pregnancy: a series of eight cases

Abstract: This is the report of a series of eight patients with pulmonary hypertension (primary and secondary) who delivered at the McMaster University Medical Centre between 1978 and 1987. Seven of the eight patients delivered vaginally and had a successful outcome. The eighth patient was admitted as an emergency and died shortly after Caesarean section under general anaesthesia, performed to save the infant. The other seven patients were all managed by a team, including anaesthetists, cardiologists and obstetricians, from about 25 wk. The patients were hospitalized pre-partum and received oxygen therapy and anticoagulation with heparin. Analgesia in labour was managed, once anticoagulation was reversed, by low concentrations of epidural bupivacaine (0.125% – −0.375%) and fentanyl. The patients were monitored during labour and delivery with oximetry and arterial and central venous pressure lines. Pulmonary arterial lines were not used because of increased risk and questionable usefulness. Vaginal delivery was managed with vacuum extraction or forceps lift-out to minimize the stress of pushing. After delivery, all patients were monitored in an intensive care unit for several days, anticoagulation was restarted, and all patients were discharged home taking oral anticoagulant therapy. The successful management of pulmonary hypertension in pregnancy should include team management started early in pregnancy and controlled vaginal delivery utilizing epidural analgesia.

Complications of continuous epidural infusions for postoperative analgesia in children

Abstract: To determine the incidences of side effects and complications associated with the use of epidural analgesia for infants and children at the Alberta Children’s Hospital, we reviewed our experience over a two-year period. A database was established for recording management, side effects and complications of each epidural, and this is a retrospective review ofthat database. Problems were identified as complications if there was a need for medical intervention related to the patient complaint, and if the intervention was documented in the patient record. Continuous epidural analgesia with bupivacaine 0.125% or bupivacaine 0.1% with epinephrine was used for managing postoperative pain in 190 children with mean age 5.6 yr (range 1 mo to 18 yr) and the mean weight 22 kg (range 4–88 kg). Mean duration of the epidural infusions was 4.7 days (range 1–16 d). In 127 patients, 203 complications were recorded. Complications, in order of frequency, were nausea and vomiting (23% of patients), motor blockade (15.8% of patients), oversedation (6.3% of patients), and pruritus (5.2% of patients). Four patients had complications which were potentially related to toxic effects of, or resistance to, bupivacaine, and serum levels of bupivacaine were measured at 3.86, 5.5, 2.1 and 2.34 μg · ml−1. Early discontinuation of the epidural occurred in 41 cases, technical problems with the epidural catheter being the commonest reason (21 cases). Although three potentially serious complications were identified (one catheter site infection, one seizure, one respiratory depression) none was associated with lasting consequences. The majority of complications associated with the use of epidurals were minor and easily remedied. With increased experience using continuous epidurals, technical problems should diminish and consistency and reliability of the technique should improve.

Anatomy of the posterior approach to the lumbar plexus block.

Abstract: The purpose of this study was to describe the relation of the lumbar plexus with the psoas major and with the superficial and deep landmarks close to it. Four cadavers were dissected and 22 computed tomography files of the lumbosacral region studied. Cadaver dissections demonstrated that the lumbar plexus, at the level of L5, is within the substance of the psoas major muscle rather than between this muscle and the quadratus lumborum. The femoral nerve lies between the lateral femoral cutaneous and obturator nerves. However, while the lateral femoral cutaneous nerve is in the same fascial plane as the femoral nerve, the obturator nerve can be found in the same plane as the two other nerves or in its own muscular fold. Radiological data provided the following measurements: the femoral nerve is at a depth of 9.01 +/- 2.43 cm; the psoas major medial border is at 2.73 +/- 0.64 cm from the median sagittal plane; and its lateral border is at 6.41 +/- 1.61 cm from the same plane. It is concluded that the lumbar plexus is within the psoas major, that the obturator nerve localization within the psoas major varies and that computed tomography data define precisely the relationship of the lumbar plexus with superficial and deep landmarks.

Patient satisfaction with intravenous PCA or epidural morphine

Abstract: In many institutions postoperative patients may receive morphine for analgesia administered into the epidural space, epidural opioid analgesia (EOA), or through intravenous self-administered patient-controlled analgesia pumps (PCA). Although a number of studies have compared the two approaches with regard to efficacy and side effects, there is less known with regard to patient satisfaction and its sources. In this study, 711 patients using PCA morphine and 205 patients receiving epidural morphine following a variety of gynaecological, urological, orthopaedic, and general surgical procedures rated their satisfaction with the method they used on a 0–10 verbal analogue satisfaction scale (0 = very dissatisfied; 10 = very satisfied). A consecutive subset of 100 patients (50 from EOA group and 50 from the PCA group) underwent further evaluation to identify advantages and disadvantages of the technique used which contributed to their satisfaction and /or dissatisfaction. Overall satisfaction (mean ± SD) in the two large groups was 8.6 ± 1.8 for PCA and 9.0 ± 1.5 for EOA (P < 0.01). In the subset of 100 patients, there were differences between the EOA and PCA groups with regard to the advantages and disadvantages selected. Patients in the PCA group identified “personal control” and “method worked quickly” as advantages whereas patients receiving EOA selected “clear mind,” “effective relief resting,” and “effective relief while moving or coughing.” The single disadvantage identified more frequently by PCA patients was “pain immediately after surgery before method became effective.” Disadvantages identified more frequently by EOA patients were “side effects” and “poor pain relief.” We conclude that overall patient satisfaction was high whether patients received PCA or EOA. The reasons for satisfaction or dissatisfaction differ depending on the method used.

An anaesthetic drug error: minimizing the risk.

Abstract: A medication error caused a near fatal cardiac arrest in a previously healthy patient undergoing elective surgery. Inadvertent epinephrine injection induced ventricular dysrhythmias, hypertension, hypotension and pulmonary oedema. The case was investigated using critical-incident technique and was reviewed by the Risk Management Team of the Department of Anaesthesia. The purpose of this report is to present the recommendations resulting from the investigation. These include: improved resident training in intravenous drug management, the use of anaesthetic drug ampoules with distinct labels, and the development of a standardized colour code system for labels on anaesthetic drug ampoules. Furthermore, it is recommended that all anaesthetic drug errors be reported to the Canadian agencies responsible for drug packaging in order to identify patterns in anaesthetic drug errors, and to facilitate the implementation of effective drug identification systems.

Lateral popliteal sciatic nerve block compared with subcutaneous infiltration for analgesia following foot surgery

Abstract: A new lateral approach to blocking the sciatic nerve in the popliteal fossa is described. In a prospective study, 40 patients scheduled for foot surgery involving osteotomies were allocated randomly into one of two groups following induction of general anaesthesia: group PS (n = 21) received a lateral popliteal sciatic nerve block and group SC (n = 19) received subcutaneous infiltration of the wound. Both groups received 20 ml bupivacaine 0.5% plain. The lateral approach to the popliteal sciatic nerve was found to be an effective, quick, and easy to perform, block. Postoperative analgesia in groups PS lasted a median of 18.0 hr and in group SC lasted 6.3 hr (P < 0.05). The lateral popliteal sciatic nerve block provided effective analgesia following foot surgery and had a high level of patient satisfaction.

Oral premedication for paediatric ambulatory anaesthesia: a comparison of midazolam and ketamine.

Abstract: To compare the clinical characteristics of two oral premedicants, midazolam and ketamine, 40 healthy children, one to six years of age, who were scheduled for ambulatory dental surgery, were assigned to receive either oral midazolam 0.5 mg.kg-1 or oral ketamine 5.0 mg.kg-1 in a double-blind, randomized study. Sedation and anxiolysis scores before induction, cooperation at induction of anaesthesia and recovery times and complications were assessed. We found that both drugs effectively sedated the children within 20 min of administration. Although sedated, 10% of the children in the midazolam group and 20% of those in the ketamine group became tearful on separation from their parents and 20% of those in the midazolam group and 35% of those in the ketamine group became tearful when the facemask was applied. No important side effects were attributable to either premedication. The time until the children were fit for discharge from the hospital after midazolam was approximately 20 min less than after ketamine. In conclusion, midazolam and ketamine offer similar clinical characteristics when used as oral premedications for children undergoing ambulatory surgery, although the time to discharge from hospital may be more rapid after midazolam than after ketamine.

Posterior approach to the lumbar plexus combined with a sciatic nerve block using lidocaine.

Abstract: A combination of lumbar plexus block, by a posterior technique, and sciatic nerve block can be a useful technique for outpatient anaesthesia. The purpose of this study was to examine the clinical characteristics of these blocks using lidocaine and to measure the serum lidocaine concentrations. Forty-five patients, undergoing lower extremity surgery, were studied. Sciatic nerve and lumbar plexus blocks were made with lidocaine, 680 mg with adrenaline 0.3 mg. For each patient the following data were collected: weight, age, sex, site of surgery, time to perform each block, needle depth, speed of onset of the sensory and motor blocks in the territories of the sciatic, femoral, obturator and lateral cutaneous (sensory) nerves and postoperative analgesic requirements. Lidocaine serum concentrations were measured in ten of these patients at 0, 2, 5, 10, 30, 60, 90 and 120 min after the second block. Analgesia was complete in 88% (40/45) of the patients. The remaining five patients needed analgesics (fentanyl 150 μg or less). Despite the high dose of lidocaine, the serum concentrations were within safe limits (mean ± SD) (CMAX = 3.66 ± 2.21 μg · ml−1). Only one patient had a serum concentration > 5 μg · ml−1 (CMAX = 9.54 μg · ml−1). This was associated with a contra-lateral extension of the block. We conclude that this combination of blocks is a valuable alternative for unilateral lower extremity anaesthesia. However, clinicians must be aware of the implications of a contra-lateral extension of the block.

Awake intubation increases intracranial pressure without affecting cerebral blood flow velocity in infants

Abstract: Tracheal intubation is frequently required in neonatal anaesthetic practice. Awake intubation is one method of securing the airway and in certain circumstances, for many anaesthetists, can be preferable to intubation following induction of anaesthesia. Previous studies have inferred that the elevation in anterior fontanelle pressure observed during tracheal intubation in neonates was caused by an increase in cerebral blood flow although it was never measured. In this study, direct methods were used to observe changes in the cerebral circulation. Thirteen neonates, ASA I to III (E), aged from 1 to 34 days of age were studied. Patients were randomized to receive either tracheal intubation awake or following induction of anaesthesia with thiopentone 5 mg.kg-1 and succinylcholine 2 mg.kg-1. Heart rate, systolic arterial blood pressure, anterior fontanelle pressure, cerebral blood flow velocity (using transcranial Doppler sonography) and oxygen saturation were recorded at the following intervals: baseline (not crying), after intravenous atropine 0.02 mg.kg-1, during laryngoscopy, immediately after insertion of the endotracheal tube, one and five minutes later. The use of atropine masked the cardiovascular responses to intubation. Whereas the change in anterior fontanelle pressure from baseline was different between the groups (P < 0.05), the cerebral blood flow velocity variables were not. The rise in anterior fontanelle pressure seen in the awake group may be attributed to a reduction of the venous outflow from the cranium thereby increasing cerebral blood volume and subsequently the intracranial pressure.

Propofol anaesthesia in paediatric ambulatory patients: a comparison with thiopentone and halothane

Abstract: The purpose of this study was to evaluate the haemodynamic changes during induction, as well as the speed and quality of recovery when propofol (vs thiopentone and/or halothane) was used for induction and maintenance of anaesthesia in paediatric outpatients. One hundred unmedicated children, 3–12-yr-old, scheduled for ambulatory surgery were studied. The most common surgical procedures performed were eye muscle surgery (42%), plastic surgery (21%), dental restoration (15%), and urological procedures (15%). The children were randomized to an anaesthetic regimen for induction/maintenance as follows: propofol/propofol infusion; propofol/halothane; thiopentone/halothane; halothane for both induction and maintenance. Succinylcholine 1.5 mg · kg−1 was used to facilitate tracheal intubation and N2O/O2 were used as the carrier gases in each case. All maintenance drugs were titrated according to the clinical response of the patient to prevent movement and/or maintain BP ± 20% of baseline. Two patients (4%) who received propofol expressed discomfort during injection. The mean propofol dose required to prevent movement was 267 ± 83 μg · kg−1 · min−1. The overall pattern of haemodynamic changes, as well as awakening (extubation) times were not different among the four groups. Children who received propofol recovered faster (22 vs 29–36 min) (P < 0.05), were discharged home sooner (101 vs 127–144 min) (P < 0.05), and had less postoperative vomiting (4 vs 24–48%) (P < 0.05) than all others. There were no serious complications or adverse postoperative sequelae in any of the patients in the study. It is concluded that induction and maintenance of anaesthesia with propofol is a well-tolerated anaesthetic technique in children, and is associated with faster recovery and discharged as well as less vomiting than when halothane is used.

The role of vasopressors in the management of hypotension induced by spinal and epidural anaesthesia.

Abstract: Although spinal and epidural blocks provide excellent anaesthesia for many operations, they are frequently accompanied by hypotension. This is largely the result of sympathetic nerve blockade. Excessive hypotension may potentially produce myocardial and cerebral ischaemia, and is associated with neonatal acidaemia in obstetric practice. How to prevent and treat this hypotension has been the subject of much investigation and controversy. One of the mainstays of management is the use of vasopressor agents and those currently available are not perfect. In this review, the role of vasopressor agents is discussed and possible future management strategies are commented upon. Ephedrine was the first agent used for this purpose and it has withstood the test of time: it is the agent against which all others are compared. It remains the first-line agent in obstetric anaesthesia as it does not affect the fetus adversely, but it cannot be relied upon to be 100% successful and other agents must be considered when it is inadequate. It is best given by infusion. In non-obstetric practice, ephedrine has a good track record but again its success rate is less than 100%. As there is no fetus to consider, it may be more appropriate to consider using a pure vasoconstrictor agent such as methoxamine or phenylephrine as a first-line therapy in such cases. This judgment can only be made on an individual patient basis as ephedrine produces a tachycardia while phenylephrine and methoxamine both produce bradycardia.

Sugarless gum chewing before surgery does not increase gastric fluid volume or acidity

Abstract: Patients occasionally arrive in the operating suite chewing gum despite instructions to avoid oral intake for a specific number of hours before surgery. Some anaesthetists are hesitant to proceed with these patients fearing an increase in gastric volume and acidity. This study was undertaken to determine if gum chewing increased gastric volume and acidity. Seventy seven patients were recruited and informed consent obtained. Thirtyone patients who fasted overnight were randomly assigned either to serve as control (Group 1) or to chew sugarless gum prior to anaesthesia (Group 2). The remaining 46 patients fasted overnight but were given sugarless gum and allowed to chew it until immediately before induction of anaesthesia if they desired (Group 3). Volume and pH of gastric content were determined immediately after induction of anaesthesia and tracheal intubation. Results revealed mean values (range) of gastric volume for Group 1 — 26 ml (9–60), Group 2 — 40 ml (5–93), and Group 3 — 28 ml (4–65). Mean values for pH (range) were Group 1 — 1.8 (1.0–4.6), Group 2 — 1.6 (1.3–1.9), Group 3 — 1.7 (1.0–4.4). There was no difference between groups in terms of gastric volume or pH. In addition, there was no relationship between gastric content and the length of time from gum discard to induction or the length of time gum was chewed. In conclusion, the data suggest that induction of anaesthesia is safe and surgery does not need to be delayed if a patient arrives in the OR chewing sugarless gum.

RETRACTED ARTICLE: Optimal anti-emetic dose of granisetron for preventing post-operative nausea and vomiting

Abstract: In order to determine the optimal effective dose of granisetron for preventing postoperative nausea and vomiting, the drug was administered in doses of either 20, 40 or 60 μg sd kg−1. The efficacy of granisetron was evaluated in a randomized, double-blind comparison with placebo in 100 patients undergoing general anaesthesia for major gynaecological surgery. The patients received a single dose of either granisetron or placebo (saline) iv immediately after recovery from anaesthesia. The effects were assessed during the 24 hr after recovery from anaesthesia by means of a nausea and vomiting score; 0 = no emetic symptoms, 1 = nausea, 2 = vomiting. The treatment groups were similar for patient characteristics, surgical procedures and anaesthetics administered. The mean scores were 0.7, 0.6, 0.2 and 0.2 after administration of placebo, granisetron 20, 40 and 60 μg · kg−1, respectively. Granisetron 40 μg · kg−1 was as effective as 60 μg · kg−1 and both resulted in reduction of the scores compared with placebo and granisetron 20 μg · kg−1 (P < 0.05). In conclusion, granisetron 40 μg · kg−1 is considered to be the appropriate dosage for preventing postoperative emesis after anaesthesia.

Evoked potential monitoring during posterior fossa aneurysm surgery: a comparison of two modalities

Abstract: The purpose of this study was to compare and assess the ability of two different evoked potential (EP) modalities, median nerve somatosensory evoked potentials (SSEP) and brainstem auditory evoked potentials (BAEP) in monitoring for cerebral ischaemia and in predicting neurological outcome during posterior fossa aneurysm surgery. During 70 procedures, patients were monitored with both SSEP and BAEP Temporary occlusion of an artery was used in 52 patients and permanent occlusion in 21 patients. A change was defined as a greater than 50% decrease in amplitude and/or an increase in latency greater than 1 msec of the N20 (cortical waveform) for SSEP monitoring and of the fifth peak for BAEP monitoring. Neurological assessment of the patient was performed immediately on emergence, after 24 hr and at the time of discharge. In total, 14 patients had an SSEP change which predicted a neurological deficit in eight patients (57%). Ten patients had a change in BAEP; six had a neurological deficit (60%). Five patients had a change in both, two had a deficit (40%). The incidence of false negative results (a neurological deficit but no EP change) for both modalities was 20% (SSEP 47%, BAEP 60%). The incidence of false positive results (an EP change but no deficit) was 13% overall (SSEP 11%, BAEP 7%). All patients who had a permanent EP change developed a neurological deficit. We did not find a difference in the ability of SSEP compared with BAEP in predicting neurological deficits but, using both modalities, the incidence of false negative results was decreased. In conclusion, dual modality monitoring should be used whenever possible as neither modality alone was better than the other in detecting cerebral ischaemia and in predicting neurological deficits.

Preparing children for the operating room: psychological issues.

Abstract: Children respond psychologically to the prospect of surgery in a variable and age-dependent manner. This review summarizes the psychoanalytic, cognitive, behavioural and family system models of child development. It then reviews studies of hospitalization and anaesthesia in children. These studies suggest that younger children, children previously anaesthetized, and children who experience turbulent anaesthetic inductions are at particular risk for postoperative behavioural disturbances. Strategies of dealing with children and their parents during the perioperative period are discussed. Such strategies include: allowing a parent to be present during induction of anaesthesia, administering sedative premedication, creating a supportive environment, educating children and parents (verbal descriptions, tours, books, videos), and establishing rapport with children and their parents. Age-specific techniques of establishing rapport with children are discussed. If children are less anxious during the perioperative period, not only will they often exhibit less behavioural disturbances postoperatively, but they may face subsequent medical care more easily.

Mechanisms of inhibition of endothelium-dependent relaxation by halothane, isoflurane, and sevoflurane

Abstract: Volatile anaesthetics inhibit endothelium-dependent relaxation, but the underlying mechanism(s) have not been clarified. In an attempt to elucidate the mechanism(s), we determined the effects of halothane, isoflurane and sevoflurane on relaxation induced by acetylcholine and sodium nitro-prusside (SNP) and the cGMP formation elicited by exogenous nitric oxide (NO) and SNP in rat aortas. Acetylcholine (10−7−10−5M) - induced relaxation was attenuated by halothane (2%), isoflurane (2%) and sevoflurane (4%). SNP (10−8 M) - induced relaxation was reduced by halothane (2%), but not by isoflurane (2%) or sevoflurane (4%). The cGMP level of NO-stimulated aorta was reduced by halothane (2%) and sevoflurane (4%), but not by isoflurane (2%). The cGMP level of SNP (10−7 M) - stimulated aorta was reduced by halothane (2%), but not by isoflurane (2%) and sevoflurane (4%). We conclude that the mechanisms responsible for the inhibition of endothelium-dependent relaxation differ among anaesthetics. Isoflurane inhibits the relaxation mainly by inhibiting the formation of NO in the endothelium. In contrast, the effect of halothane on endotheliumdependent relaxation may be largely due to the inhibition of action of NO in the vascular smooth muscle and the effect of sevoflurane may be to inactivate NO or to inhibit the action of NO.

Reduction of postoperative nausea and vomiting with granisetron.

Abstract: The antiemetic effects of granisetron, a selective 5-hydroxy-tryptamine type 3 receptor antagonist, on postoperative nausea and vomiting were studied and compared with placebo and metoclopramide in 60 patients undergoing general anaesthesia for major gynaecological surgery. The patients received a single iv dose of either granisetron (3 mg, n = 20) metoclopramide (10 mg, n = 20), or placebo (saline, n = 20) immediately after recovery from anaesthesia. The effects were assessed during the first three and the next 21 hr after recovery from anaesthesia by means of a nausea and vomiting score; 0 = no emetic symptoms, 1 = nausea, 2 = vomiting. The mean scores during 0–3 hr were 0.8, 0.1 and 0.1 after administration of placebo, metoclopramide and granisetron, respectively; the corresponding scores during 3–24 hr were 0.6, 0.5 and 0.1. The scores of the metoclopramide and the granisetron groups were different from the placebo group in the first three hours (P < 0.05). Although there were no differences in the scores during 0–3 hr between the metoclopramide and the granisetron groups, there were differences during 3–24 hr (P < 0.05). It is concluded that granisetron is superior to metoclopramide in the long-term prevention of postoperative nausea and vomiting after anaesthesia.

Succinylcholine-induced cardiac arrest in children with undiagnosed myopathy.

Abstract: Two paediatric cases are reported in which unexpected, life-threatening arrhythmias occurred. Routine induction of general anaesthesia with thiopentone, 5 mg · kg−1, in one and with halothane in the other, and succinylcholine 1.25 – −1.5 mg · kg−1 iv was followed by the development of wide complex tachyarrhythmia with hypotension in the first case and asystole in the second case despite pre-treatment with atropine in both cases. The first patient was resuscitated with tracheal intubation, 100% oxygen, manual ventilation and intravenous lidocaine and bicarbonate. The second patient required intubation, manual ventilation, 12 min of CPR and iv calcium, epinephrine and bicarbonate, as well as DC counter shock. Neither patient received dantrolene. Early recovery in both patients was uneventful with no neurological sequelae. Subsequent investigations revealed the presence of a dystrophin-deficient muscular dystrophy, Duchenne muscular dystrophy and Becker muscular dystrophy respectively, previously unsuspected, in both patients. The aetiology of the observed arrhythmias was presumably hyperkalaemia, secondary to succinylcholine-induced rhabdo-myolysis. It is suggested that when faced with sudden, life-threatening arrhythmias following succinylcholine at induction of anaesthesia for paediatric patients, clinicians should include occult myopathy in the differential diagnosis, and thus consider the aggressive management of hyperkalaemia in addition to basic resuscitative efforts.

Isoflurane compared with nitrous oxide anaesthesia for intraoperative monitoring of somatosensory-evoked potentials.

Abstract: Intraoperative monitoring of somatosensory-evoked potentials is a routine procedure. To determine the depressant effect of nitrous oxide relative to isoflurane, the authors recorded the scalp, cervical and brachial plexus-evoked responses to stimulation of the median nerve under different anaesthetic conditions. Eight subjects, age 35 +/- 6 (SD) yr, weight 68 +/- 12 kg, were studied. Following recording of awake control responses, anaesthesia was induced with thiopentone 5 mg.kg-1 and fentanyl 3 micrograms.kg-1 and was followed by succinylcholine 1 mg.kg-1. During normocapnia and normothermia, and with a maintenance infusion of fentanyl 3 micrograms.kg-1.hr-1, evoked potential recording was repeated under three different anaesthetic conditions; 0.6 MAC nitrous oxide, 0.6 MAC nitrous oxide +/- 0.6 MAC isoflurane, and 0.6 MAC isoflurane. Among the anesthetic conditions, the combination of nitrous oxide-isoflurane had the most depressant effect on the cortical amplitude (67 +/- 4% reduction, P < 0.05). Nitrous oxide decreased the cortical amplitude more than an equipotent dose of isoflurane (60 +/- 4% vs 48 +/- 7%, P < 0.05). The latency was unchanged by nitrous oxide, but increased slightly by isoflurane and isoflurane-nitrous oxide anaesthesia (1.0 and 0.9 msec respectively, P < 0.05). We conclude that somatosensory-evoked potential monitoring is feasible both during nitrous oxide anaesthesia and isoflurane anaesthesia, but the cortical amplitude is better preserved during 0.6 MAC of isoflurane alone relative to 0.6 MAC of nitrous oxide alone. The depressant effect is maximal during nitrous oxide-isoflurane anaesthesia but less than the predicted additive effect.

Cerebral arteriovenous malformations in children.

Abstract: The treatment of cerebral arteriovenous malformations (AVM) or vascular anomalies are challenging neurosurgical procedures for an anaesthetist. Large AVMs are uncommon in children. Only 18% of AVMs become symptomatic before the age of 15 yr. This series reviews the experience at this institution during the period of 1982 to 1992. The symptoms at the time of presentation are varied and include haemorrhage (50%), seizures and hydrocephalus (36%) or congestive cardiac failure (18%). Symptoms of congestive heart failure predominate in the new-born whilst neurological symptoms, such as stroke, seizures or hydrocephalus occur more commonly in infants and older children. Approximately one third of AVMs in childhood present acutely. Radiological investigations, e.g., CT scan, MRI and cerebral angiography are essential to identify the precise location of the lesion. Therapeutic intervention in the acute presentation may involve craniotomy for evacuation of haematoma and treatment of increased intracranial pressure (ICP). Control of seizures and congestive heart failure may take priority and allow time to plan the elective procedures of embolization and surgical excision of the AVM. Operative intervention is hazardous and peroperative complications can be expected in more than 50% of patients. The morbidity and mortality associated with cerebral AVM are high, especially in infants who present in the neonatal period with congestive cardiac failure. The overall mortality in this series was 20%. Children presenting with intracranial arteriovenous malformations require a multidisciplinary approach. The successful management of anaesthesia either for embolization or surgical resection necessitates an understanding of the disciplines of paediatric and neuroanaesthesia. Special care and specific attention to detail may contribute to reduce the high morbidity and mortality encountered in these compromised children.

Changing Mallampati score during labour

Abstract: We present the case of a changing Mallampati score during the course of labour in a healthy primigravida. On admission to hospital, the airway was assessed as Mallampati class I–II. At 5 cm cervical dilation, the woman began to bear down strenuously and continued this despite being advised of the inherent hazard. At 8 cm dilation, Caesarean delivery was contemplated because of fetal heart rate decelerations. Repeat airway evaluation revealed marked oedema of the lower pharynx giving rise to a Mallampati score of III–IV. Improvement of the fetal heart rate tracing permitted vaginal delivery under local infiltration. Postpartum, the Mallampati score was still III–IV However, 12 hr later it had returned to the admission classification of I–II. We recommend that, in addition to the usual airway evaluation on admission, the assessment be repeated in the obstetric patient before induction of general anaesthesia.

Parental upset associated with participation in induction of anaesthesia in children.

Abstract: To evaluate the magnitude of parental upset associated with (1) the features of induction most upsetting to parents; (2) the characteristics of parents most likely to become upset; and (3) the accuracy of the anaesthetist's perception of the magnitude of parental upset. The parents (101 mothers and 43 fathers) of 103 children scheduled for elective outpatient surgery requiring general anaesthesia with induction by mask were asked on admission to participate in this study. Parents and children were educated about anaesthesia and surgery according to unit protocols. Immediately after induction of anaesthesia, the parents were asked to complete a demographic information sheet and the Parental Reactions to Anesthesia Induction Questionnaire. Responses were analyzed using descriptive statistics and content analysis. The most upsetting factors for both mothers and fathers in order of significance were: (1) separation from the child after induction of anaesthesia; (2) watching/feeling the child go limp during induction; and (3) seeing the child upset before induction. Characteristics of parents most likely to become upset revealed positive correlations between the amount of upset between mothers and fathers, mothers of an only child, and mothers or fathers who were health care workers (P < 0.05). The anaesthetist's perception of upset correlated with maternal (P < 0.05), but not parental, self-assessment of upset. We conclude that selected factors of parental participation are upsetting for the parents and that recognizing the factors associated with parental upset may enable operating room personnel to minimize these negative consequences.

Preliminary investigations of the clinical pharmacology of three short-acting non-depolarizing neuromuscular blocking agents, Org 9453, Org 9489 and Org 9487.

Abstract: Three muscle relaxants, Org 9453, Org 9489 and Org 9487, short-acting in animals, were investigated to establish their profiles in humans. Potency, time course of action, and pharmacokinetic behaviour were studied in 90 healthy patients during fentanyl/halothane/N2O anaesthesia. Neuromuscular function was monitored mechanomyographically. Plasma and urine concentrations (three patients per compound) were measured by HPLC, and these data were analyzed by iterative linear least square regression analysis. The ED90 values for Org 9453, Org 9489 and Org 9487 were 1.4, 0.45 and 1.15 mg.kg-1 respectively. The onset times of Org 9453 (1.5 mg.kg-1, 1.1 X ED90), Org 9489 (0.9 mg.kg-1, 2 X ED90) and Org 9487 (1.5 mg.kg-1, 1.3 X ED90) were 1.2, 1.6 and 1.5 min, and the durations until 25% twitch recovery were 8.6, 22.0 and 8.9 min, respectively. Clearances of these doses were 6.9, 5.8, and 11.1 ml.kg-1.min-1, and mean residence times 26, 79, and 41 min, respectively. Mean renal excretion (parent compound and metabolites) within 24 hr amounted to 5, 11.3 and 12.2% respectively. No side effects other than a moderate short-lasting decrease of blood pressure and a concomittant increase in heart rate were noted. It is concluded that Org 9453 and Org 9487 are short-acting muscle relaxants in humans.