SummaryThis article is a review of the peri-operative use of paracetamol. It reviews the pharmacology of paracetamol, highlighting new information about the mechanism of action, and examines its therapeutic use in the peri-operative period, focusing on efficacy, route of administration, and the use of a loading dose to improve early postoperative analgesia.

SummaryPeripheral pulse oximetry has become a core monitoring modality in most fields of medicine. Pulse oximeters are used ubiquitously in operating theatres, hospital wards, outpatient clinics and general practice surgeries. This study used a portable spectrometer (Lightman Ò , The Electrode Co. Ltd., Monmouthshire, UK) to measure the emission spectra of the two light emitting diodes within the pulse oximeter sensor and to determine the accuracy of 847 pulse oximeters currently in use in 29 NHS hospitals in the UK. The standard manufacturing claim of accuracy for pulse oximeters is ± 2-3% over the range of 70-100% S p O 2 . Eighty-nine sensors (10.5%) were found to have a functional error of their electrical circuitry that could cause inaccuracy of measurement. Of the remaining 758 sensors, 169 (22.3%) were found to have emission spectra different from the manufacturers' specification that would cause an inaccuracy in saturation estimation of > 4% in the range of 70-100% saturation. This study has demonstrated that a significant proportion of pulse oximeter sensors may be inaccurate. Pulse oximeters use two light emitting diodes (LEDs) of specific and differing wavelength (typically 660 and 940 nm) to measure the combined absorption by a mixture of oxyhaemoglobin and deoxyhaemoglobin of red and infrared light measured using a photodiode. The photodiode measures the variation in the intensity of light falling upon it, and converts this into an electrical voltage. The ratio of the absorption at these two wavelengths is called the R value, and is compared with R values that are calibrated against direct measurements of arterial oxyhaemoglobin saturation (S a O 2 ) and arterial partial pressure of oxygen (P a O 2 ) for an individual model of pulse oximeter, using a volunteer population sample. Volunteers breathe controlled hypoxic gas mixtures to create a range of S a O 2 values between 70% and 100% against which the S p O 2 of an individual pulse oximeter sensor may be calibrated.Once in use, there is little evidence that pulse oximeters are ever re-calibrated or have their accuracy assessed. A high reliance is placed upon the continuing reliability of the wavelength of the light emitted from the LEDs. Should the wavelength of the light emitted by one or both LEDs alter, the degree of absorption will alter and the R value will change. The mathematical algo-

BackgroundPeripheral venous cannulation is an everyday practice in hospitals, which many adults find painful. However, anaesthesia for cannulation is usually only offered to children. Inadequate pain relief is not only unpleasant for patients but may cause anxiety about further treatment and deter patients from seeking medical care in the future. The aim of this study is to discover the most effective local anaesthetic for adult peripheral venous cannulation and to find out how the pain of local anaesthetic application compares with that of unattenuated cannulation.MethodsThese aims are addressed through a systematic review, network meta-analysis and random-effects meta-analysis. Searching covered 12 databases including MEDLINE and EMBASE from 1990 to August 2015. The main included study design was RCTs. The primary outcome measure is self-reported pain, measured on a 100 mm visual analogue scale.ResultsThe systematic review found 37 includable studies, 27 of which were suitable for network meta-analysis and two for random-effects meta-analysis. The results of the network meta-analysis indicate that none of the 17 anaesthetic considered had a very high probability of being the most effective when compared to each other; 2 % lidocaine had the highest probability (44 %). When the anaesthetics were compared to no treatment, the network meta-analysis showed that again 2 % lidocaine was estimated to be the most effective (mean difference −25.42 (95 % CI −32.25, −18.57). Other members of the ‘caine’ family were also estimated to be more effective than no treatment as were Ametop®, EMLA® and Rapydan® patch. The meta-analysis compared the pain of anaesthetic application with the unattenuated pain of cannulation. This found that all applications of local anaesthetic were less painful than cannulation without local anaesthetic. In particular a 1 % lidocaine injection was estimated to be −12.97 (95 % CI −15.71, −10.24) points (100 mm VAS) less painful than unattenuated cannulation.ConclusionsThe pain of peripheral venous cannulation in adults can be successfully treated. The pain of application of any local anaesthetic is less than that of unattenuated cannulation. Local anaesthetic prior to cannulation should become normal practice and a marker of high quality care.Protocol registrationThe protocol for the larger study was registered with PROSPERO no. CRD42012002093.Electronic supplementary materialThe online version of this article (doi:10.1186/s12871-016-0252-8) contains supplementary material, which is available to authorized users.

A telephone survey of 20 English intensive care units (ICUs) confirmed that visual estimation of patient weight is often performed. Four experienced intensive care staff (three doctors and one nurse) estimated the weight and measured the height of 30 volunteers and the estimates were compared with accurate reference measurements. The estimates were shown to be significantly inaccurate for individual observers. We consider the degree of inaccuracy to be of clinical importance. However, pooling the individual estimates of weight as mean values improved accuracy. Recommendations are made concerning the performance of height and weight determination.

for this group of local anaesthetics. This study demonstrates that 1 mL of 1% sodium bicarbonate solution A number of methods exist by which the pH of local may be used to alkalinize this range of local anaesthetic solutions may be increased. Most comanaesthetics without the risk of precipitation. We also monly, these require the addition of differing amounts conclude that Ropivacaine (at concentration 0.75% of sodium bicarbonate solution according to the local and 1.0%), is unsuitable for alkalinization since it preanaesthetic drugs. Sodium bicarbonate (1%) was ticipitates at a pH of 6.0. trated against pH in six commonly used local anaesthetic solutions. Titration curves of pH and vol-Keywords: local anaesthetics, alkalinization, sodium bicarbonate. ume of sodium bicarbonate solution added are shown commercial local anaesthetic solutions is in the