Pregnancy causes anatomical and physiological changes that have implications for the anaesthetist not only for intrapartum management but also when surgery is required incidentally to pregnancy. These adaptations primarily occur, so that the metabolic demands of the growing fetus may be met.

General anaesthesia for obstetric surgery has distinct characteristics that may contribute towards a higher risk of accidental awareness during general anaesthesia. The primary aim of this study was to investigate the incidence, experience and psychological implications of unintended conscious awareness during general anaesthesia in obstetric patients. From May 2017 to August 2018, 3115 consenting patients receiving general anaesthesia for obstetric surgery in 72 hospitals in England were recruited to the study. Patients received three repetitions of standardised questioning over 30 days, with responses indicating memories during general anaesthesia that were verified using interviews and record interrogation. A total of 12 patients had certain/ probable or possible awareness, an incidence of 1 in 256 (95%CI 149-500) for all obstetric surgery. The incidence was 1 in 212 (95%CI 122-417) for caesarean section surgery. Distressing experiences were reported by seven (58.3%) patients, paralysis by five (41.7%) and paralysis with pain by two (16.7%). Accidental awareness occurred during induction and emergence in nine (75%) of the patients who reported awareness. Factors associated with accidental awareness during general anaesthesia were: high BMI (25-30 kg.m -2 ); low BMI (<18.5 kg.m -2 ); out-of-hours surgery; and use of ketamine or thiopental for induction. Standardised psychological impact scores at 30 days were significantly higher in awareness patients (median (IQR [range]) 15 (2.7-52.0 [2-56]) than in patients without awareness 3 (1-9 [0-64]), p = 0.010. Four patients had a provisional diagnosis of post-traumatic stress disorder. We conclude that direct postoperative questioning reveals high rates of accidental awareness during general anaesthesia for obstetric surgery, which has implications for anaesthetic practice, consent and follow-up.

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Letters to the editor Central venous line securement technique O ver the years there have been numerous suggested methods and devices that have been marketed in an attempt to try to improve the securement of the central venous catheter to the skin. The 'no needle' technique such as the Arrow Staple device obviates the need for using sharps by reducing the exposure of clinicians to needlestick injury. 1 Some reports have suggested that these devices may decrease the time for securement, but they have also shown that their ability to reduce central catheter line migration is less than that by the conventional suture technique. 2 Which suture material is best to use has also been the subject of debate. On the one hand, there is an argument for using sutures made of silk, which for many years has been the material of choice. Silk offers the security of being non-absorbable, giving excellent non-slip knot formation and has a low memory which makes it easy to handle. However, with its advantages come disadvantages. It has been known for many years that silk can cause significant tissue inflammation 3 (and hence dehiscence), and increased risk of catheter infection due to its porous configuration. According to the literature, 1-13% of central venous catheters cause catheter-related blood stream infections. 4 The degree of infection elicited by different sutures depends on their physical and chemical properties. Silk is braided and as such, bacteria tends to adhere to it more avidly than to other materials such as nylon. 5 As a result, many practitioners have turned to the properties which may be offered by nylon sutures such as prolene or ethilon. These are synthetic, monofilament, non-absorbable and non-porous materials. They offer unique advantages such as having high tensile strength and eliciting less tissue reaction compared to silk. 6 Many institutions now use these synthetic materials but unfortunately they are difficult to handle and difficult to tie. This is primarily due to the tendency to return to its packaged shape. This is known as 'memory'. As the knot can unravel or slip it is important to place tight knots to the skin followed by sequential tight knot ties. 7 This may give a secure knot and therefore decrease catheter migration but may also cause problems to the patient and the practitioner, such as significant necrosis and scarring to the skin and difficult removal of tight sutures. An alternative approach may be to do the following: once the catheter has been inserted and the suture passed through the skin ± the hole in the catheter hub (depending on personal preference), the dilator from the central line pack which has been used to dilate the skin over the Seldinger wire can be placed over the skin and the untied suture. The first knot may then be tied over the dilator tightly, followed by sequential surgical ties (Figure 1A). Once this is done, the dilator may then Anna Riccoboni ST6 Anaesthetic Registrar, Anaesthetic