Rosemary Macdonald

Epidural catheter migration during labour

A study was undertaken to determine the incidence, magnitude and direction of catheter migration in 100 patients who had epidural analgesia for pain relief in labour. Over 50% of catheters migrated from the original position at siting. The relevance of this migration and the usefulness of its measurement are discussed.

An evaluation of a 30-gauge needle for spinal anaesthesia for caesarean section.

A 30‐gauge spinal needle was evaluated for Caesarean section, using a combined epidural/spinal technique, in 50 mothers. Spinal anaesthesia failed in six mothers and was inadequate in another six. General anaesthesia was required on one occasion. A 25% overall failure rate suggests that a 30‐gauge needle is not a practical proposition for routine clinical practice.

Red cell 2,3‐diphosphoglycerate and oxygen affinity

The ease with which haemoglobin releases oxygen to the tissues is controlled by erythrocytic 2,3-diphosphoglycerate (2,3-DPG) such that an increase in the concentration of 2,3-DPG decreases oxygen affinity and vice versa. This review article describes the synthesis and breakdown of 2,3-DPG in the Embden-Meyerof pathway in red cells and briefly explains the molecular basis for its effect on oxygen affinity. Interaction of the effects of pH, Pco2, temperature and 2,3-DPG on the oxyhaemoglobin dissociation curve are discussed. The role of 2,3-DPG in the intraerythrocytic adaptation to various types of hypoxaemia is described. The increased oxygen affinity of blood stored in acid-citrate-dextrose (ACD) solution has been shown to be due to the decrease in the concentration of 2,3-DPG which occurs during storage. Methods of maintaining the concentration of 2,3-DPG in stored blood are described. The clinical implication of transfusion of elderly people, anaemic or pregnant patients with ACD stored blood to anaesthetically and surgically acceptable haemoglobin concentrations are discussed. Hypophosphataemia in association with parenteral feeding reduces 2,3-DPG concentration and so increases oxygen affinity. Since post-operative use of intravenous fluids such as dextrose or dextrose/saline also lead to hypophosphataemia, the addition of inorganic phosphorus to routine post-operative intravenous fluid may be advisable. Disorders of acid-base balance effect oxygen affinity not only by the direct effect of pH on the oxyhaemoglobin dissociation curve but by its control of 2,3-DPG metabolism. Management of acid-base disorders and pre-operative aklalinization of patients with sickle cell disease whould take account of this. It is known that anaesthesia alters the position of the oxyhaemoglobin dissociation curve, but it is thought that this is independent of any effects which anaesthetic agents may have on 2,3-DPG concentration. In vitro manipulation of 2,3-DPG concentration with steroids has already been carried out. Elucidation of the role of 2,3-DPG in the control of oxygen affinity may ultimately lead to iatrogenic manipulation of oxygen affinity in vivo.

Diclofenac for analgesia after Caesarean section

The analgesic efficacy of a single intramuscular dose of 75 mg diclofenac given after elective Caesarean section was studied in 50 women in a double‐blind randomised manner using a patient‐controlled analgesia system. The mean 18 h papavaretum consumption of the placebo group was significantly greater (91.4 mg compared to 61.4 mg). Subjective experience of pain and observed sedation were significantly greater in the control group up to 6 h after operation.

Laryngeal oedema and pre-eclampsia

A case of laryngeal obstruction secondary to laryngeal oedema and a superimposed upper respiratory tract infection in a pre‐eclamptic patient is reported. The management of the case is described and the possible effects of drug therapy on the uterus are discussed. Other reports of asymptomatic laryngeal oedema in pregnancy are reviewed.

Suxamethonium apnoea associated with plasmaphoresis

A patient is reported who developed suxamethonium apnoea as a result of reduction in serum cholinesterase activity secondary to both pregnancy and plasmaphoresis. Had the enzyme studies been carried out before operation, regional rather than general, anaesthesia would have been used. In order to avoid the problems associated with prolonged paralysis we recommend the measurement of cholinesterase activity in all patients who have undergone plasmaphoresis and in whom anaesthesia involving the use of suxamethonium is contemplated.

Dr Doughty's technique for the location of the epidural space

I have read the article by Dr Holmboe and Dr Kongsrud with great interest (Anaesthesia 1982; 37: 60-2). I would like to report the occurrence of a cerebral convulsion which occurred in a clinically healthy female patient after epidural analgesia with 0.75% bupivacaine which we attributed to possible intravascular injection and to the high concentration of local analgesic. There appears to be no significant correlation between speed of injection or the injection pressure and the rate of spread of the analgesia’ but more concentrated solutions have a greater potential to cause toxic reactions if they are injected intravascularly. Increased toxicity after epidural injection with bupivacaine 0.75% has not so far been observed up to a maximum of 128 mg2 and this is less than the dose of bupivacaine to which minor systemic reactions have been attributed in the adult. Toxic reactions usually occur in two phases-an excitatory central nervous system (CNS) phase followed by depression of the CNS and the cardiovascular system (CVS). If the drug is injected intravascularly the phase of excitation may not occur and there is primary depression of the CNS and CVS.J-5 Absorbtion of the bupivacaine solution may be slow. We have observed the development of hypotension 90 to I 0 0 minutes after the epidural injection of 0.75% bupivacaine despite adequate intravenous loading with crystalloid solutions. Patients who have received 0.75% bupivacaine epidurally need very close supervision. We believe that the 0.75% concentration should be reserved for intraabdominal surgery in which more rapid onset, longer action and better muscular relaxation are an advantage.

Spinal anaesthesia with hyperbaric lignocaine for elective Caesarean section

This study was carried out in 30 patients undergoing elective Caesarean section to assess the predictability and reliability of spinal anaesthesia with 5% hyperbaric lignocaine, with a view to incorporating the technique in our failed intubation drill. The spinal was performed with a 25‐gauge needle in either the sitting (15 patients) or left lateral position (15 patients). The speed of onset of anaesthesia to T6 was significantly faster (p < 0.01) in the lateral group. but the duration of action was similar in both groups. Twelve patients had hypotension and four developed severe postspinal headaches. The block progressed to the C2 dermatome in four patients and was associated with dysphagia. This was totally unpredictable and may be due to altered cerebrospinal fluid dynamics in late pregnancy. Therefore, the use of spinal anaesthesia with heavy lignocaine may be inadvisable in obstetric patients, especially following failed intubation.

Plasma phosphate and red cell 2,3‐diphosphoglycerate following abdominal surgery

Changes in plasma phosphate have been serially examined in 20 patients undergoing uncomplicated abdominal surgery. These studies confirm previous reports that a fall in plasma phosphate occurs in the postoperative period, but this does not appear to be metabolically deleterious to the patient since it is not accompanied by a significant concomitant fall in red cell 2,3‐DPG. These investigations form a basis for studies in complicated patients and serve to refute the suggestion that phosphate supplements should be added to all routine postoperative infusions.

Obstetric anaesthetic workload in a teaching unit

The distribution of obstetric anaesthetic work through the day was examined. Workload audit and prediction are discussed with their relevance to service and training.