Anaesthesia and Intensive Care

Pethidine is the only member of the opioid family that has clinically important local anaesthetic activity in the dose range normally used for analgesia. Pethidine is unique as the only opioid in current use that is effective as the sole agent for spinal anaesthesia. In lower doses, intrathecal pethidine is also an effective analgesic for treating pain in labour. This paper reviews the pharmacology of intrathecal pethidine and clinical experience reported to date. Articles reviewed include those identified by a Medline search using keywords “intrathecal” or “spinal anaesthesia/ anesthesia” and “pethidine” or “meperidine”. Reference lists from identified papers were scrutinized to identify further relevant articles.

The use of subcutaneous tunnelling to prevent movement of epidural catheters was examined in a prospective controlled trial. There were 113 patients in the standard group and 100 in the tunnelled group. The groups were similar with respect to age, sex and weight. There were 176 thoracic catheters, and 37 lumbar catheters. Mean duration of catheterization in the tunnelled group was 3.5±1.3 days and in the standard group, 3.1±1.5 days. In total, 60 catheters moved significantly from their initial position: 17 (28%) moved inwards and 43 (72%) moved outwards. 159 catheters were still functioning at the time of their removal, 76 standard and 83 tunnelled. This represents 67 and 83% of the two groups respectively.

Subcutaneous tunnelling was shown to prevent clinically significant inwards (P=0.043) and outwards (P=0.0005) movement of epidural catheters and is more likely to result in a functional epidural blockade at the time of catheter removal (P=0.0084).

Postoperative nausea and vomiting (PONV) is still an important and common problem. Despite the introduction of new antiemetic drugs, the management of PONV remains difficult. In this article we describe the development and evaluation of a management protocol for PONV, which consists of a treatment algorithm accompanied by a nursing education program. Implementation of this management protocol has been well-accepted by staff, appears to have reduced delay in patient treatment and improved patient care, and has significantly reduced staff workload.

It is planned to use continuous quality improvement techniques to further refine the algorithm and continue assessment of its efficacy and of patient satisfaction.

Epidemics of bacteraemia and wound infection have been associated with the infusion of bacterially contaminated propofol administered during anaesthesia. We conducted an observational study to determine the incidence and clinical significance of administration of potentially contaminated propofol to patients in an ICU setting. One hundred patients received a total of 302 infusions of propofol. Eighteen episodes of possible contamination of propofol syringes were identified, but in all cases contamination was by a low-grade virulence pathogen. There were no episodes of clinical infection or colonization which could be attributed to the administration of contaminated propofol. During the routine use of propofol to provide sedation in ICU patients the risk of nosocomial infection secondary to contamination of propofol is extremely low.

A prospective survey of one thousand and sixty-two patients receiving epidural analgesia in surgical wards was undertaken over a two-year period. The duration of infusion ranged from one to fourteen days, with a mode of three days. There were 1131 episodes where a local anaesthetic and opioid mixture was used and 160 where opioids were used alone. Local anaesthetic was not used without opioids. 23% of catheters were removed prematurely because of catheter related problems including accidental dislodgement (13%) and skin site inflammation (5.3%). No epidural abscess or haematoma was identified. In 14% of the total number of episodes there was either no demonstrable block or complications occurred requiring a change of solution: 30% of this group were salvaged following intervention by the Acute Pain Service (APS). The incidence of respiratory depression was 0.24%. There was no case of delayed respiratory depression. Epidural analgesia can be used safely in surgical wards provided that regular review of the patients is undertaken. It must be anticipated however, that up to 20% of patients will not receive adequate analgesia for the first 48 hours postoperatively. The failure rate could be halved if accidental dislodgement of epidural catheters could be eliminated.

The study consisted of two parts:

1. The standard system in use at our hospital for gas delivery under the drapes during eye surgery under local anaesthesia was compared with one incorporating a venturi.

2. The oxygen concentration at the operation site was measured with three methods of draping using the two systems.

Twenty-three patients and thirty-one volunteers from the operating room staff were subjected to operating conditions and gas concentrations and certain vital signs measured using both systems. The subjective response of the volunteers, none of whom had blocks or premedication, was noted.

The burden of rebreathing seen with a significant proportion of cases using 6 l/min of fresh gas flow was not seen when the venturi system was used. The safety from fire hazard using 26% oxygen and diathermy was demonstrated with occlusive and free draping.

We compared the effects of humidity delivered by the circle system at low fresh gas flows (FGF) with a conventional two-limb and coaxial circuit on the structure and function of the tracheobronchial epithelium in dogs. Animals were anaesthetized and mechanically ventilated using an anaesthesia ventilator to maintain normocarbia. Group I (control) animals received a FGF equal to the required minute ventilation mimicking an open circuit technique. Group II and III animals had FGF set at 20% of the required minute ventilation. Group II used a two-limb circuit and Group III used a coaxial circuit. Relative humidity and temperature of inspired gases were measured at baseline and hourly afterwards. In the first experiment, biopsies of the tracheobronchial tree were obtained bronchoscopically at baseline and then hourly for six hours. Microscopic examination of these samples allowed calculation of mean ciliary length. In the second experiment, tracheal mucus flow velocity (TMFV) was measured at baseline and hourly afterward, using a cinebroncho-fibrescopic method.

Delivered absolute humidity was greatest with low FGF and the coaxial circuit, followed by low FGF and a conventional circuit, and high FGF (15±1.4 vs 9±0.8 vs 5±0.4 mg H₂O, P<0.01) after two hours. Mean cilia length (μm) and TMFV (mm/min) fell during the first hour in all three groups. At hour two TMFV returned to baseline in Group III and was significantly greater than Groups I and II (0.8±0.4 vs 8.6±1.1 vs 15.4±2.1, P<0.001). Mean ciliary length demonstrated a similar pattern with reductions from baseline in all three groups for the first two hours. Groups II and III had an increase in cilia length beginning at hour three and were both significantly greater than Group I at hours 3 through 6 (1.3±0.5 vs 3.2±1.1 vs 4.2±0.8, P <0.001).

Alterations in tracheobronchial structure and function result from exposure to dry gases and are amplified by the duration of exposure. Our findings suggest a minimum of 12 to 15 mg H₂O/l is necessary to prevent these alterations. In this study, the combination of low FGF and a coaxial anaesthesia circuit reached this minimum threshold more quickly than a conventional two-limb circuit.

In critically ill patients, serial measurements of blood lactate may indicate adequacy of therapy and predict development of multi-organ failure. We studied the accuracy, precision, and repeatability of the newly developed 800 Series Lactate Sensor (Ciba Corning Diagnostic Corp., Medfield, U.S.A.). Lactate levels determined with the sensor were compared with the standard laboratory method (Abbott TDX) in 75 paired arterial blood samples from 20 patients. Agreement between methods was determined and the mean coefficient of variation calculated for repeated measurements. The bias of the sensor was -0.38 mmol/l (CI -0.23 to -0.53), and the precision ±0.67. The coefficient of variation for repeated measurements was 1.95% with the sensor, and 11.5% with the TDX (P=0.007). The new sensor offers a more reproducible, rapid method of measuring lactate, vital for serial measurements. The relatively wide limits of agreement between the methods reflect the greater variability of the TDX assay.

A resuscitation trolley has been designed to meet the following requirements.

Continuous oxygen supply from the trolley for the duration of the emergency; medical suction of similar strength to that of an ICU treatment bay and provision of equipment and drugs in a modular form, which is uniform across the institution, and which allows immediate replacement from stock.

These requirements have been fulfilled whilst maintaining a total trolley weight and manoeuvrability similar to that of commercially manufactured trolleys available in Australia.

Inotrope-dependent patients may become haemodynamically unstable during treatment in the hyperbaric chamber. One possible cause is altered performance of infusion devices. We tested six Atom 235 syringe infusion pumps under hyperbaric conditions of 2.8 atmospheres absolute in a multiplace chamber using a gravimetric method. There was a small but significant reduction in infused volume during a thirty-minute period including compression time. We concluded that altered inotrope delivery may explain at least some of the haemodynamic instability sometimes seen, although a physiologic effect of hyperbaric treatment cannot be excluded.

Although the preoperative use of alpha-receptor antagonist drugs is generally accepted for patients with phaeo-chromocytoma, evidence on the most appropriate treatment and its timing is scarce.

In this retrospective study, the effectiveness of the preoperative preparation of fourteen patients who required surgical excision of a phaeochromocytoma was examined in the light of their operative stability. A simple score was developed of blood pressure stability by scoring the need for additional antihypertensive agents intraoperatively before, and blood pressure support after, tumour removal. A higher score indicated greater instability.

Twelve patients received phenoxybenzamine and their stability was superior to the two patients treated with labetalol and with prazosin. There was no correlation between the duration of treatment with phenoxybenzamine and the operative stability (r=0.18 P=0.55 Spearman). The five patients who were treated with phenoxybenzamine for longer than 10 days did not have better perioperative blood pressure stability than the five patients who had treatment for less than a week.

Predictive factors for intra-operative blood pressure stability were also sought. The degree of postural hypotension after treatment with phenoxybenzamine did not predict operative stability (r=-0.31, P=0.33 Spearman). However, the peak total catecholamine level found during surgery correlated quite well with more operative instability (r=0.65, P=0.031, Spearman), suggesting that patients with phaeochromocytomas with high production of catecholamines are more likely to show cardiovascular instability.

Undergraduate teaching of anaesthesia occurs in about two-thirds of Australian departments of anaesthesia: however, student contact hours are limited compared with those of other disciplines.

Seventy-five directors of anaesthesia were surveyed by written questionnaire concerning the time devoted in their department to undergraduate study and teaching of practice/skills to undergraduate students (40 responded).

One hundred and sixty final year students were surveyed regarding career choice, anaesthesia skills taught them and role models identified during their training (101 responded).

Most final year students had been taught and had learnt the basic skills of life support such as bag and mask ventilation, cardiopulmonary resuscitation and intravenous cannulation. However, fewer were taught more specialized skills such as induction of anaesthesia and spinal anaesthesia. Positive role models in teaching anaesthetists were identified by 66% of students, more commonly if they were taught advanced skills, and were significantly associated with satisfaction with theoretical and practical training. For those students intending a career in anaesthesia (18%), 94% identified a positive role model compared to 65% who did not (P=0.03).

Ropivacaine, a new local anaesthetic agent, has been demonstrated to have less potential than bupivacaine for central nervous system toxicity on the basis of human and animal studies. We report a case of a convulsion secondary to presumed inadvertent intravascular injection of 20 mg of ropivacaine in a 44 kg patient during an epidural for chronic pain. There were minimal signs of cardiovascular toxicity.

Midogas ^® (CIG Australia) nitrous oxide/oxygen blenders are commonly used in delivery wards in Australia. In this case report we describe an incident where a small hole in the diaphragm of the oxygen failure alarm in a Midogas nitrous oxide/oxygen blender led to retrograde flow of oxygen contaminating the nitrous oxide pipeline supply to the operating theatres and the delivery ward. This caused a reduced level of nitrous oxide to the patient in theatre, but there was no adverse outcome. However, if the oxygen pipeline pressure had been lower than the nitrous oxide pipeline pressure, the contamination would have been reversed, potentially resulting in a hypoxic mixture being delivered to many patients. Suggestions are made as to a method of prevention of this problem.

We report a case of trans-sternal thymectomy for myasthenia gravis using a non relaxant, total intravenous technique with propofol and remifentanil. This afforded excellent control of heart rate and pressor responses during surgery while allowing early return of spontaneous ventilation and extubation within nine minutes of termination of anaesthesia. Advantages and disadvantages of this approach versus relaxant and volatile techniques are discussed with particular reference to preservation of neuromuscular function.

An unusual and potentially life-threatening complication arising from a relatively common event—bleeding due to traumatic laryngeal mask insertion—is presented. It demonstrates that the laryngeal mask airway (LMA) cannot always be relied upon to protect the lower airway from upper airway bleeding.

Functional disorders of the vocal cords can present with acute, dramatic upper airway obstruction, with features mimicking asthma or functional dysphonia. We report the case of an eighteen-year-old female with acute airway obstruction initially misdiagnosed as asthma. Laryngoscopy, bronchoscopy and psychiatric assessment confirmed a diagnosis of functional disorder of the vocal cords. Although a diagnosis of exclusion, it must be borne in mind in order to reduce unnecessary medical therapy and surgical intervention. It is only with the correct diagnosis that patients can receive appropriate therapy.