Anaesthesia and Intensive Care

The use of patient-controlled analgesia is described for forty children who had undergone major orthopaedic or general surgery. Ages ranged from 6 to 18 years (mean 11.4 years) and PCA was used for an average of 46.2 hours postoperatively. Morphine requirements overall averaged 40.5 μg/kg/hr (SD 22.6). Requirements for the first six hours were not significantly different to a similar period 24 hours later. There was a large individual variation for patients undergoing similar procedures.

Patients undergoing scoliosis surgery required significantly more morphine than any other group of patients. Problems with patient-controlled analgesia have been of a minor nature. We conclude that patient-controlled analgesia is a suitable and safe method of pain relief for paediatric patients and that the lower age limit is that at which a child can understand the concept after suitable explanation. In this study children as young as six years were able to successfully use the method.

Pethidine requirements and verbal pain scores were recorded in 36 patients after cholecystectomy via subcostal incision. All patients also received 20 ml 0.5% bupivacaine with adrenaline 1/200,000. Group 1 (12 patients) received unilateral intercostal nerve blocks. Interpleural catheters were inserted through the 8th intercostal space in the remaining patients; 12 received local anaesthetic via the catheter immediately after surgery (Group 2) and 12 were given local anaesthetic at three hours (Group 3). Small asymptomatic pneumothoraces were noted on chest X-ray in six of the 24 patients with interpleural catheters. Both types of local anaesthesia produced lower pain scores than pethidine alone (P < 0.05) with 25% of intercostal nerve blocks and 63% of interpleural catheters requiring no pethidine in the following three hours. The provision of catheter ‘top-ups’ between six and 18 hours after surgery also resulted in lower pain scores and a reduction in pethidine requirements (P < 0.05).

Seventy-seven patients presenting for outpatient cystoscopy participated in a trial to assess postoperative recovery when either alfentanil, halothane, or enflurane were used in combination with nitrous oxide/oxygen anaesthesia. Anaesthesia was uneventful in all cases. Apnoea occurred once with alfentanil, but naloxone was not required. Vomiting occurred once with alfentanil and once with enflurane. Anti-emetics were not required. Blood pressure and pulse rate variations from preoperative levels occurred with similar frequency in all groups. Times to open eyes, show left thumb, and give correct date of birth were significantly less with alfentanil than with the other agents tested. Trieger testing failed to demonstrate an advantage of alfentanil, although two patients in each of the halothane and enflurane groups were insufficiently recovered to complete the tests. As tested, alfentanil represents a useful alternative to halothane or enflurane as postoperative recovery of mental function is significantly more rapid than with the inhalational agents.

The pharmacodynamic properties of repeated injections of atracurium were studied in twenty-two patients. A control group received narcotic-based anaesthesia while another group received the same narcotic-based anaesthesia subsequently modified by the addition of 0.5% isoflurane. The twitch response of the adductor pollicis muscle was recorded after train-of-four (TOF) stimulation of the ulnar nerve at the wrist. Duration of effect and recovery time were measured. A bolus dose of atracurium (0.5 mg/kg b.w.) was given for tracheal intubation and maintenance doses of 0.2 mg/kg b.w. were given during anaesthesia at a TOF ratio of 0.25.

Mean duration of anaesthesia was 7.5 hours (range 3–19). In the control group mean duration of effect and mean recovery time remained unchanged (six doses studied). A noteworthy inter-individual variation was found. In the isoflurane group mean duration of effect increased from 36.1 (SD 6.3) minutes to 42.2 (SD 8.1) minutes (P<0.05) following the addition of isoflurane. Corresponding recovery times remained unchanged.

We conclude that during repeated administration of atracurium during narcotic-based anaesthesia, each patient shows a constant interval between requirements for maintenance doses of atracurium of 0.2 mg/kg b.w. Addition of 0.5% isoflurane causes a moderate prolongation of the duration of effect, but recovery time remains unchanged.

In a randomised, double-blind study, a transdermal patch containing either hyoscine or placebo was applied post-auricularly in 190 adult patients under 65 years old, seven to twelve hours prior to their undergoing minor orthopaedic or plastic surgery under thiopentone/nitrous oxide/halothane general anaesthesia. In the first 24 hours after surgery 34% of patients vomited. The incidence of nausea (31% vs 54%; P< 0.01) and the number of episodes of vomiting (66 vs 125; P< 0.05) during the first 24 hours were significantly less with hyoscine than with placebo. The hyoscine group required fewer doses of antiemetic than the placebo group (12 vs 27; P < 0.05). Side-effects were mild, the only difference between the two groups being the frequency of dry mouth immediately preoperatively. No differences were seen in the second 24 hours after surgery. We conclude that transdermal hyoscine is moderately effective in reducing the occurrence of postoperative nausea and vomiting following minor surgery.

The ability of flumazenil to reverse the effects of midazolam sedation was examined in a randomised, crossover, placebo controlled study in six male volunteers. Subjects received intravenous injections of either (a) midazolam 10 mg followed 10 minutes later by flumazenil 1.0 mg or (b) midazolam 10 mg followed after 10 minutes by flumazenil 4 mg or (c) placebo followed after 10 minutes by placebo. Post reversal drug effects were examined using a psychomotor battery (critical flicker fusion, digit symbol substitution, tapping test, ball-bearing test, number recall, reflex time) and linear analogue mood scales.

It was found that a residual psychomotor deficit was present following flumazenil and that this persisted for up to 125 minutes after the 1.0 mg dose and 65 minutes following 4 mg. A small deterioration in performance was apparent after initial reversal with 1.0 mg, the peak deterioration occurring at 35 minutes.

A processed electroencephalogram (EEG) produced by the Lifescan monitor (Neurometrics), was compared to awake neurological assessment for detecting cerebral ischaemia in seventy patients undergoing carotid endarterectomy under cervical plexus block. Of the six patients demonstrating neurological signs on cross-clamping the carotid, five displayed simultaneous EEG changes, four being detected during surgery, and one being detected after reviewing the EEG postoperatively. Another four patients displayed EEG changes indicative of ischaemia but unassociated with neurological signs. A further patient displayed contralateral intraoperative EEG changes. Hypotension resulted in one EEG change and two cases were associated with technical difficulties with the monitor. The presence of false negatives, possible false positives, technical errors and subjective interpretation associated with the processed EEG make it less reliable than awake neurological assessment for the detection of cerebral ischaemia.

Following recent evidence that brachial and femoral artery pressures are more reliable than radial artery pressures after cardiopulmonary bypass, thirty-one adults had simultaneous pre and post-bypass measurements of brachial, femoral, and ascending aortic pressures. Two minutes after cardiopulmonary bypass, brachial artery systolic pressure and mean arterial pressure fell significantly below corresponding pressures in the femoral artery and aorta. Five minutes after cardiopulmonary bypass, only brachial artery systolic pressure was still less than femoral and aortic systolic pressures. By ten minutes after bypass, all significant pressure differences had resolved except between brachial and femoral artery systolic pressures. Clinically significant (≥ 5 mmHg) aortic-to-brachial reductions in mean arterial pressures occurred in six (19%) patients at two minutes and in three (10%) patients at five and ten minutes after bypass. Equivalent aortic-to-femoral mean pressure diminution occurred in two (6%) patients at two minutes and one (3%) patient at five and ten minutes after bypass. Neither systemic vascular resistance nor body temperatures contributed significantly to post-bypass central-to-peripheral pressure reductions. Immediately following bypass, femoral artery pressures reproduce central aortic pressures more reliably than do radial or brachial artery pressures.

Information has come forward recently from several sources which provides new insights into the mechanisms that underlie the haemodynamic responses to acute blood loss. In unanaesthetised animals and human volunteers there are two distinct phases to these responses. At first, the engagement of baroreflexes results in a progressive rise in sympathetic vasoconstrictor drive and peripheral resistance, and the maintenance of arterial blood pressure at a near-normal level. When about one-third of blood volume has been lost, reflex sympathetic drive is switched off, and peripheral resistance and blood pressure fall abruptly to low levels despite a burst of vasopressin release.

Research in conscious animals has now shown that the onset of this decompensatory phase is triggered by a signal from the heart, which activates an endogenous opioid mechanism in the brain. Activation of this mechanism can be prevented by administering a selective δ-receptor antagonist, or selective μ-receptor agonists (including alfentanil). It has not yet been established that this endogenous opioid mechanism is responsible for the decompensatory phase of acute blood loss in man, nor that it can be prevented or reversed by selective opioid agonists or antagonists.

A review of the anaesthetic management of children with congenital myotonic dystrophy anaesthetised at the Royal Children's Hospital over the past ten years is presented. Seven children underwent a total of fourteen anaesthetics. Anaesthetic considerations must include the degree of muscle weakness and hypotonia altering muscle relaxant requirements, aspiration risk due to palatopharyngeal dysfunction, and cardiomyopathy. Succinylcholine caused muscle contracture in a patient without clinical myotonia. This drug should be avoided. Although a low threshold to institute postoperative respiratory support must exist when treating neonates and infants, the older children did not clinically exhibit increased sensitivity to respiratory depressant drugs.

The Christiansen-Douglas-Haldane effect, in short the Haldane effect, describes the dependence of the CO₂ binding of blood on the degree of oxygenation of haemoglobin. Under the physiological conditions of an ‘open’ system between blood and alveoli the partial pressure of arterial C0₂ (P_aCO₂), must be less than that of mixed venous blood (P _{V ¯} CO₂).

During the unphysiological conditions of a ‘closed’ system, e.g. hyperoxic apnoea, i.e. continuous oxygen uptake without CO₂ delivery by the lungs, the P_aco₂ will not only approximate the P _{V ¯} CO₂ but will even exceed it. Without the Haldane effect, rapid adjustment of P_aco₂ to P _{V ¯} CO₂ would be expected during apnoea due to the lack of CO₂ excretion. If however, as undertaken in this study, ongoing oxygenation (high alveolar Po₂ (P_ACO₂) with concomitant lack of C0₂ delivery (apnoea, i. e. the C0₂ concentration remains constant) lead to a continuing sufficient oxygenation of blood during its passage through the lung capillaries, then this leads to a rightwards shift of the CO₂ binding curve — the Haldane effect.

The resulting increase in Pco₂ as shown here actually leads to an arterial-mixed venous CO₂ partial pressure difference (a V ¯ DPco₂) of 2.8±1.8 mmHg. The results described substantiate for the first time the existence of the Haldane effect under clinical conditions.

In order to introduce the technique of epidural narcotics for pain relief in Papua New Guinea, fifty patients were given low doses of epidural morphine and thereupon the quality of analgesia and morbidity evaluated. The lowest effective epidural morphine dose was determined by considering the patient's characteristics and height of surgical incision. Pain relief was provided for three postoperative days in the surgical or gynaecological wards. The quality of analgesia thus provided was excellent in all the patients with no incidence of clinically significant respiratory depression or hypotension. Minor complications such as nausea, vomiting, pruritis and retention of urine were also relatively uncommon.

Combined tibial and common peroneal nerve anaesthesia was used for foot and ankle surgery in fifty-six adults. Where necessary, the saphenous nerve was also blocked. A calibrated constant current nerve stimulator was used to localise the nerves in the popliteal fossa. Using lignocaine 1%, an opioid premedication, but no other sedation or top-up injection, 60% of the blocks were successful. If a patient felt pain at incision or during surgery, the block was recorded as a failure.

The New South Wales Anaesthetics Continuing Education Committee conducted their 23rd meeting in Sydney on April 7–8, 1989. This was titled ‘Local Anaesthesia and Acute Pain’ and dedicated to the honour of Brian Dwyer who will retire from an illustrious clinical career early in 1990. We record the foreword to the proceedings of the meeting and addresses given at the associated dinner for the benefit of those whose lives and practice have been touched, whether they are aware of it or not, by a great anaesthetist and a great man.