Anaesthesia and Intensive Care

The aim of this study was to determine the incidence of true local anaesthetic allergy in patients with an alleged history of local anaesthetic allergy and whether subsequent exposure to local anaesthetics is safe.

Two hundred and eight patients with a history of allergy to local anaesthesia were referred over a twenty-year period to our Anaesthetic Allergy Clinic. In this open study, intradermal testing was performed in three patients and progressive challenge in 202 patients.

Four patients had immediate allergy and four patients delayed allergic reactions. One hundred and ninety-seven patients were not allergic to local anaesthetics. In 39 patients an adverse response to additives in local anaesthetic solutions could not be excluded. In all but one patient local anaesthesia has been given uneventfully subsequently.

A history of allergy to local anaesthesia is unlikely to be genuine and local anaesthetic allergy is rare. In most instances LA allergy can be excluded from the history and the safety of LA verified by progressive challenge.

Twenty-seven halothane-anaesthetized, mechanically ventilated adult mongrel dogs were randomly assigned to either respiratory acidosis group [pHa 7.22 (0.03, SD), PaCO₂ 9.6 (1.1) kPa, base excess –0.5 (1.4) mmol.l^–1, n=9], metabolic acidosis group [pHa 7.20 (0.05), PaCO₂ 5.5 (0.4) kPa, base excess –11.1 (2.1) mmol.l^–1, n=9], or non-acidosis group [pHa 7.37 (0.07), PaCO₂ 5.2 (0.4) kPa, base excess –1.1 (1.5) mmol.l^–1, n=9]. Respiratory acidosis and metabolic acidosis were induced by decreasing respiratory rate and continuous infusion of 2 mmol.l^–1 hydrochloric acid, respectively. Sodium bicarbonate solution 1 mmol.kg^–1 was injected into the right atrium over five seconds when haemodynamic stability was obtained.

In all three groups, acute administration of sodium bicarbonate produced transient decreases in mean arterial pressure and RV dP/dtmax, and transient increase in right atrial pressure 30 seconds after injections, but these variables returned to the pre-injection values by the end of the three minutes observation period. Although no significant differences were seen in haemodynamic variables among the three groups at 30 seconds, one and three minutes, maximum reductions in both RV dP/dtmax and PBF in the metabolic acidosis group (260 (143) mmHg.s^–1 and 0.38 (0.26) l.min^–1) were significantly greater than those in the non-acidosis group (127 (34) mmHg.s^–1 and 0.08 (0.09) l.min^–1; P<0.05).

The heart rate variability of 40 patients has been examined by spectral analysis following cardiac surgery. The heart rate variability was measured upon patient arrival in ICU in both a resting supine position, and following passive straight-leg raising. After 12 hours in ICU, the patients were classified as having been cardiovascularly stable or unstable according to a specially devised inventory. Their heart rale variability data was then examined to seek any predictor of instability.

Passive straight-leg raising induced a decrease in spectral power across all of the component frequency bands. The LF/HF ratio rose with passive straight-leg raising, but failed to reach significance. None of these changes were sustained. There was no significant difference in heart rate variability patterns between the stable and unstable groups, and so no predictor was identified. Initial clinical assessment was also studied, and it too provided no reliable prediction of short-term cardiovascular instability.

The cardiovascular effects of slow (over two minutes) intravenous infusions of thiopentone 750 mg in conscious instrumented sheep breathing 100% oxygen were examined for 30 minutes following the start of the infusion.

The maximum rate of rise of left ventricular pressure (an index of myocardial contractility) decreased significantly from 1 to 10 minutes, to a minimum of 45% of baseline. Heart rate increased by up to 33% above baseline from 0.5 min onwards. Both mean arterial pressure and cardiac output were decreased from between 1 and 7 min. Left ventricular minute work was transiently decreased, but left coronary blood flow and myocardial oxygen consumption showed little or no change from baseline.

We conclude that in vivo, thiopentone administered at a relatively slow rate caused large reductions in myocardial contractility, and therefore cardiac reserve, in the absence of significant changes in myocardial blood flow or oxygen consumption.

Pulmonary hypertensive crises (PHC) are a recognized cause of sudden clinical deterioration and death after the surgical correction of congenital heart disease. In this study, pulmonary artery pressure was monitored in 84 children (at high risk to develop PHC) aged nine days to five years (mean 1.4 years) using monitoring lines inserted percutaneously through the right internal jugular vein (IJV). Success rate of placement of the catheter tip in the pulmonary artery (PA) in the pre-incision period was not high (7%) but all catheter-tips were successfully placed in the PA by the surgeon before right atrial closure prior to separation from cardiopulmonary bypass. Complications related to the technique were transient ventricular/atrial arrhythmias (78.5%) during insertion and slipping or coiling (20%) of the catheter in the right ventricle. Complications relating to the IJV puncture included carotid arterial puncture¹ and pneumothorax¹. No other complications were encountered. Monitoring lines inserted percutaneously and guided into the pulmonary artery during surgery provide a safe and practical way of monitoring pulmonary artery in infants and children at risk of postoperative pulmonary hypertensive crises.

We report a survey of 196 consecutive central venous catheters (CVCs) placed in 151 patients in the Intensive Care Unit (ICU) over a ten-month period. Over this time the use of a new antiseptic-impregnated triple lumen CVC (Arrowgard Blue, Arrow International Inc., Pennsylvania, U.S.A.) was alternated on a bimonthly basis with the standard triple-lumen CVC (Arrow International Inc., Pennsylvania, U.S.A.).

The overall rate of CVC tip infection was lower in the impregnated CVC group (15.6% vs 30.9%, P<0.05). The impregnated CVC group had a much lower cumulative infection rate when the dwell time in patients was five days or less (3.3% vs 26.9%, P<0.05). However, the difference between the cumulative infection rate was not statistically significant (P>0.05) for dwell times of 6, 7 or 8 days respectively. There was no difference in the CVC related bacteraemia rates between the two groups (3.9% vs 3.7%, P>0.05).

The potential for commonly infused drug solutions to support or inhibit microbial growth was explored in this study. Drugs examined were midazolam HCl, morphine sulphate, fentanyl citrate, pethidine HCl, bupivacaine HCl, atracurium besylate, vecuronium bromide, adrenaline, dopamine, dobutamine, noradrenaline, isoprenaline, glyceryl trinitrate, sodium nitroprusside and propofol. All drugs were studied in both diluted and undiluted forms. Of the 15 medications investigated, all except propofol were found to be bactericidal and to reduce fungal growth.

A phase III, open label, randomized study was conducted in 50 patients comparing halothane and sevoflurane for paediatric day case surgery. A graded inhalational induction resulted in only slightly more rapid induction with sevoflurane (3.34±0.92 versus 3.85±1.02 minutes; P>0.05). In children receiving sevoflurane, systolic blood pressure decreased to a lesser extent during induction (14.3±19.2 versus 26.9±10.9 percent decrease from resting values; P<0.01) and heart rate was maintained. Respiratory events (coughing, breath-holding, bronchospasm, laryngospasm) were more common during induction with halothane, and excitement more common in children receiving sevoflurane. Emergence times were significantly more rapid in children who had received sevoflurane (21.4±10.9 versus 33.1 ±13.7 minutes; P<0.01). Objective pain/discomfort scores were higher in patients receiving sevoflurane at 10, 20, 30 and 40 minutes after arrival in the recovery room, and the incidence of excitement during emergence was higher in this group. It is concluded that sevoflurane is well tolerated for inhalational induction and has an improved cardiovascular profile compared to halothane. Emergence was significantly more rapid following sevoflurane.

We aimed to determine the usefulness of intrathecal pethidine as the sole anaesthetic for transurethral resection of prostate (TURP) while comparing the incidence of hypotension with intrathecal bupivacaine.

A double-binded randomized prospective trial was conducted involving 40 patients for TURP. The patients were divided equally into two groups; group A received 2 ml 0.5% bupivacaine intrathecally and group B received 40 mg pethidine intrathecally. Changes in blood pressure and heart rate were measured over the first 30 minutes. The highest sensory block and the time to reach it were documented. The degree of motor blockade was also recorded.

There was no significant difference in the incidence of hypotension. The pethidine group had significantly greater reduction in heart rate, a lower degree of motor block, shorter period before requests for postoperative analgesia but a higher incidence of sedation, nausea and vomiting.

Intrathecal pethidine did not offer any advantage over intrathecal bupivacaine for TURP.

A method for objective evaluation of the difficulty of endotracheal intubation is described. Our data indicate that the angle formed by the light-beam axis of the laryngoscope blade and the laryngotracheal axis, which we call “angle ϕ”, is analogous to the degree of difficulty of endotracheal intubation. Using this method, we compared the effectiveness of a standard Macintosh and a modified bevelled Macintosh blade in 27 tracheostomized Intensive Care Unit patients under general anaesthesia. Statistical analysis of our results indicate that the bevelled blade significantly facilitates endotracheal intubation.

Few authors have addressed the topic of graphic data presentation. The purpose of our study was to combine several guidelines in order to evaluate three anaesthesiology journals listed in Index Medicus (Australian, American and Italian) in terms of the appropriateness and the quality of presentation of graphs.

Our analysis was based on concepts expressed by Cox and Tufte. We calculated the optimization of the amount of information in each graph using two parameters: Data Density Index (DDI) and Data Ink Ratio (DIR). The correctness and clearness of each component of the graph (scale, title, axes, legends and abbreviations) was evaluated on the basis of a binary score.

We analysed 300 exploratory plots, quantitative graphs and summaries of statistical analysis. About 50% of papers had more than three graphs. Mean scores were 3.22 for the Italian journal, 3.47 for the American journal and 3.82 for the Australian journal. Tufte parameters were calculated on 42 scatterplots: DDI was 5.4±13.9 and DIR was 0.7±0.1.

The criteria applied in our study appear sufficiently sensitive to differentiate the quality of graphs.

The provision of good analgesia can be influenced by ethnic differences in how pain is expressed, the attitudes of patients and health professionals towards pain management and pharmacological differences in the responses to opioids. It is difficult to generalize results so that they are applicable to any ethnic group as a whole. There is also the question of how best to categorize ethnic Asians who have been in Australasia for several generations. Much of the pharmacogenetic work has focused on the metabolism of codeine, morphine and pethidine, and there are some differences between Chinese and Caucasians. Asians may receive less analgesia because they are more likely to experience, or are less tolerant of the adverse effects of opioids.

Despite this, ethnic factors are probably only a small contributor to the inter-individual variation in opioid requirements. Unlike earlier studies, recent larger studies using patient-controlled analgesia have shown similar opioid usage between Asians and Caucasians in the postoperative period. An individualized pain management program is essential for any patient, whatever his or her ethnic origin. The use of patient-controlled analgesia will minimize some of the problems that may occur because of poor communication between the patient and the healthcare staff. Nevertheless, in a multicultural society like Australia's, health professionals should be conscious of the many factors that may influence the effects of prescribed treatment to manage pain in different ethnic groups.

Auckland anaesthetists were surveyed. Of these, 68% obtain written informed consent, 67% are familiar with the New Zealand Medical Council's statement on informed consent, and 57% believe that they conform with this statement in their practice. 4% of anaesthetists always warn their patients of the possibility of death, 9% never do. 87% warn of minor complications such as vomiting, 28% warn of possible awareness, 27% of possible paralysis with spinal or epidural. 83% felt that some form of risk-disclosing anaesthetic information leaflet would be of value for elective patients. After perusing a proposed information leaflet, 40% answered “yes” they would be happy for it to be combined with the non-risk-specific anaesthetic information currently given to patients, 23% answered “yes, with reservations”, 18% answered “yes, if modified first”, 13% “no, only if the patient asks to know more about risks”, and 5% “no, not to any patient”.

Twenty anaesthetists were asked what equipment they would use to ventilate a patient after having performed an emergency cricothyroid puncture. Six systems were described and these were assessed for efficiency in delivery of oxygen through a 14 gauge cannula. Delivery of oxygen depended on the pressure achieved within the system. Apparatus utilizing a Bain circuit achieved volumes of around 200 ml for each double-handed squeeze of the reservoir bag. Use of a system taught on the Advanced Trauma and Life Support (ATLS) course resulted in higher system pressures and consequently greater volumes of oxygen delivered. Use of the oxygen flush with this system provides the highest flow rate and system pressure which results in 628 ml being delivered for a one second compression.

The term “evidence-based medicine” first appeared in the medical literature in 1992 and is in widespread use today. It is timely to examine the concept's relevance to anaesthetic practice as well as the validity of the premises on which it rests. An important difference between anaesthesia and the specialties which treat disease is that in anaesthesia there is very little research done with real outcomes as its end-point. Surrogate or intermediate outcomes predominate as the end-points of anaesthetic research, which is a weakness when the results serve as the evidence on which to base clinical decisions. Furthermore, in interventions which require personal skill, dexterity or decision-making, caution must be exercised in assuming that equally good outcomes are achievable by all. Key members of the Cochrane Collaboration, among the most prominent advocates of evidence-based medicine, promote the belief that much valid scientific evidence is to be found in sources outside the peer-reviewed published literature. This assertion must be treated with caution. Furthermore, some techniques central to the search for the evidence on which to base practice, including meta-analysis and multicentre trials, are prone to errors through incorrect application. Evidence-based medicine appears to have less to offer anaesthesia than it does to the “treating” specialties.

Anaesthetists, like most in the medical profession, often deny that they may be suffering from work-related stress. This article explores the sources and effects of occupational stress with suggestions for dealing with the stresses of our specialty.

An anaesthetic case report of children undergoing stereotactic radiosurgery is presented, with a review of the inherent unique anaesthetic challenges. Twelve stereotactic radiosurgery procedures performed at The Prince of Wales Hospital, Sydney, were retrospectively reviewed. Despite differences in approach by individual anaesthetists to managing these children, an overall safe sequence may be evolved.

The use of stereotactic radiosurgery for paediatric neuropathology is reviewed. The potential anaesthetic problems related to the paediatric patient and the peculiarities of the procedure are discussed and related to our series.

A case of hypoglossal nerve neuropraxia following elective drainage of bilateral chronic subdural haematomas is described. We postulate that the cause of neuropraxia was inadvertent extubation of the trachea with the cuff inflated, leading to compression and stretch of the nerve against the greater horn of the hyoid bone. The literature on cranial nerve palsies following endotracheal intubation is reviewed.

A case is described where systemic levels of prostacyclin metabolite were measured during inhaled aerosolized prostacyclin (IAP) therapy for severe hypoxaemia in a patient with the acute respiratory distress syndrome. Comparable levels of prostacyclin metabolite have been associated with a marked platelet aggregation defect in vitro. A platelet aggregation defect was also demonstrated in vivo in this patient. Haemodynamic and gas exchange data during the IAP therapy are described.

Sevoflurane is a newly available volatile anaesthetic agent which is suitable for inhalational induction of anaesthesia. Due to concerns about obstructing the upper airway as anaesthesia deepens, its use has until now been avoided in patients with upper airway obstruction. We used its smooth induction and recovery properties however to anaesthetize a patient with central airway obstruction and coexistent ischaemic heart disease. Sevoflurane proved to be a very satisfactory agent in this situation.

A case of self-ingestion of brodifacoum that resulted in spontaneous intra-abdominal haemorrhage, circulatory shock, rhabdomyolysis and acute renal failure is reported. Current knowledge and management of superwarfarin poisoning are discussed.