A study of laryngeal mask inflation. Pressures exerted on the pharynx.

Laryngeal mask airway cuff inflation pressures were measured when inflated with the same volume of gas firstly in free space and then in position in the pharynx. A large difference in these pressures was observed and this was related to pharyngeal mucosal perfusion pressure. This study shows that it may be easy to produce pressures on the pharyngeal mucosa in excess of the critical perfusion pressure and thus potentiate mucosal trauma. Furthermore, laryngeal mask cuff pressures were measured at intervals during anaesthesia and were found to rise by a significant amount if room air was used as the cuff inflating gas. This effect could, however, be reversed if inspired gas was used to inflate the mask cuff. We conclude that care must be taken when inflating the laryngeal mask cuff if postoperative morbidity is to be avoided and also that it may not be necessary to use as high a volume of inflating gas as has been recommended during spontaneous respiration.

Bleeding time: is it a useful clinical tool?

The bleeding times of five volunteers were assessed individually by each of 12 observers. The reliability of the measurements obtained was examined by comparing statistically the variability between subjects and between observers. This variability was found to be similar for both groups. Consequently, we suggest that the bleeding time estimation is an unreliable test and should not be used in isolation without reference to the salient features of a history and examination, when determining if an individual patient is at risk of haematoma formation as a complication of regional anaesthetic techniques.

Identification of epidural space by drip method.

In 100 pregnant women, identification of the epidural space was performed by a modified drip method. A saline infusion was prepared, leaving the distal 40 cm of infusion tubing full of air, and then attached to the hub of a Tuohy needle. Accurate identification of the epidural space was accomplished in less than one minute in 95% of cases. There were no unintentional dural punctures. This technique has advantages over the hanging drop and the manual loss of resistance techniques.

The effect of micropore filters on the aspiration test in epidural analgesia.

Continuous epidural analgesia may be complicated by intravascular or subarachnoid injection of local analgesic, with disastrous consequences. One of the techniques described to prevent these complications is the aspiration test. It is the current standard of practice to employ a micropore bacterial filter for epidural infusions. We present an in vitro study of nine commercially available bacterial filters to determine whether or not the aspiration test could be reliably performed through them. Eight of the nine filters (except the Perifix, Braun) were found to be unreliable if air and liquid were both present in the system (air lock). The role of the aspiration test and the use of micropore filters in epidural analgesia are discussed, as are the implications and possible solutions in practice of this cause of failure of the test.

Anaesthetic management of caesarean section for a mother with pre-eclampsia, the Klippel-Feil syndrome and congenital hydrocephalus.

A mother with the Klippel-Feil syndrome, congenital hydrocephalus and increased intracranial pressure presented for delivery by Caesarean section at 33 weeks because of pre-eclampsia. Anaesthetic management comprised awake intubation using the fibreoptic bronchoscope, followed by induction and maintenance of general anaesthesia for the delivery of a live male infant. This case report describes the problems arising under these circumstances and the relative merits of different anaesthetic techniques.

Maternal inspired oxygen concentration and neonatal status for caesarean section under general anaesthesia. Comparison of effects of 33% or 50% oxygen in nitrous oxide.

The relationship between maternal FIO2 and umbilical venous PO2, PCO2, pH and neonatal Apgar and TSR (time to sustained respiration) scores was studied in 35 patients undergoing Caesarean section under general anaesthesia. Patients were allocated randomly to breathe an FIO2 of either 0.5 or 0.33. Umbilical venous blood was collected at the time of delivery, and TSR and 1- and 5-min Apgar scores recorded. Mean values for umbilical venous blood were: PO2 3.9 kPa and 3.7 kPa; PCO2 6.2 kPa and 6.2 kPa; pH 7.30 and 7.31 (50% and 33% groups, respectively (P greater than 0.05]. No differences were found between groups for 1- or 5-min Apgar scores or TSR values. It is concluded that no difference in fetal outcome or acid-base status can be detected when maternal FIO2 is decreased from 0.5 to 0.33, and that the use of 33% oxygen in 66% nitrous oxide appears to be safe for neonates who have not suffered fetal distress before delivery.

Fentanyl-droperidol supplementation of rapid sequence induction in the presence of severe pregnancy-induced and pregnancy-aggravated hypertension.

Twenty-six patients manifesting severe pregnancy-induced (PIH) or pregnancy-aggravated (PAH) hypertension who presented for emergency Caesarean section under general anaesthesia were studied. All patients came from a previously identified high risk group--namely greater than 25 yr, multiparous and with diastolic arterial pressures sustained at greater than 120 mm Hg. Our standard accelerated induction technique for the management of severely hypertensive mothers was modified to include the use of fentanyl and droperidol before induction. This modification of the induction sequence produced a clinically significant amelioration of the reflex sympathetic hypertensive response to laryngoscopy and intubation in most mothers receiving antihypertensive therapy, without apparent deleterious effect in the immediate postoperative period to those neonates unaffected by intrauterine asphyxia.

Comparison of midazolam and thiopental for rapid sequence anesthetic induction for elective cesarean section.

Sixty healthy mothers undergoing elective cesarean section received at random either midazolam 0.2 mg/kg or thiopental 3.5 mg/kg with succinylcholine 1 mg/kg for rapid sequence intravenous anesthetic induction. Maintenance of anesthesia was identical in all patients: 50:50 N2O in oxygen, halothane 0.5% and pancuronium 0.05 mg/kg. Hemodynamic responses were similar, as were the biochemical status of mothers and infants, and maternal to fetal blood gas/acid base gradients. Correlation between maternal arterial and fetal (umbilical venous/arterial) pH, PCO2 and base excess values were statistically better with midazolam. However, 1-min Apgar minus color (A-C) scores less than 5/8 (representing "severe" neonatal depression) were recorded in five infants after midazolam, three of whom required tracheal intubation, and one whose mother was given thiopental. This difference reached statistical significance (P less than 0.05). It is concluded that midazolam is less suitable than thiopental for anesthetic induction in patients undergoing cesarean section.

Inflation pressure, gastric insufflation and rapid sequence induction.

An investigation was carried out into the relationship between the inflation pressures of normally compliant lungs and the airways pressure necessary to produce the insufflation of gas to the stomach. This relationship was examined during manual ventilation with a mask, using a rapid sequence induction technique. In the absence of cricoid pressure the lungs of all the patients could be ventilated "gently" satisfactorily by hand without gas entering the stomach. In only half of the patients could gas be redirected to the stomach when maximal inflation pressures were generated. It was not possible to cause gas to enter the stomach in any patient with a patent airway when cricoid pressure was applied.

Fresh gas flow requirements using the ADE anaesthetic system during late pregnancy.

Thirty-two pregnant patients at term undergoing elective Caesarean section were ventilated with a non-co-axial ADE anaesthetic system (E mode) supplied with fresh gas flows (FGF) of either 70 or 100 ml kg-1 min-1, on a random basis. Ventilation with an FGF of 70 ml kg-1 min-1 produced mean PaCO2 and PE' CO2 values of 6.48 +/- 1.15 kPa and 6.41 +/- 0.76 kPa, respectively. Patients were thus hypercapnic, which contrasts with the normocapnia achieved using an FGF of 100 ml kg-1 min-1 via the ADE system (E mode) (PaCO2 5.07 +/- 0.7 kPa; PE' CO2 4.83 +/- 0.46 kPa) (mean values +/- SD). The latter FGF is therefore recommended for the pregnant patient at term when using a Mapleson E system such as the Humphrey ADE apparatus.