Recipes for obstetric spinal hypotension: The clinical context counts

Hypotension following obstetric spinal anaesthesia remains a common and important problem. While recent research advances have brought us closer to the perfect recipe for the obstetric spinal anaesthetic, these advances have not been translated into practical guidelines able to reduce the unacceptable number of fatalities that occur in environments where resources are limited. In South Africa, more than half of anaesthetic deaths are still related to spinal hypotension. A gap exists between the ‘perfect recipe’, developed from a clinical context rooted in resource-rich research environments, and its application and performance in real-world resource-poor environments – conditions experienced by more than 75% of the world’s population. This review attempts to define this knowledge gap and proposes a research agenda to address the deficiencies

The development of spray-coated perovskite solar cells

Over the past six years, researchers have investigated the use of spray coating to fabricate perovskite solar cells (PSCs), with the aim of demonstrating its viability as an industrial manufacturing process. This spotlight on applications outlines the key benefits of this coating technology and summarizes progress made to date, with attention focused on varied efforts to control the crystallization and uniformity of the perovskite layer. The emerging understanding of processes required to create smooth, dense spray-cast perovskite films has recently led to the demonstration of fully spray-cast PSCs with a power conversion efficiency of 19.4%

Hypotension during spinal anaesthesia for Caesarean section in a resourcelimited setting: towards a consensus definition

Background: Intraoperative hypotension following spinal anaesthesia for Caesarean section is associated with maternal morbidity and mortality. Because of inconsistent definitions the reported incidence of hypotension varies between 7% and 74%, making it almost impossible to set standard targets. Developing and adopting a clinically significant threshold for intraoperative hypotension will allow for benchmarking, comparison between studies, and consistency in guidelines and recommendations.Methods: Common definitions for spinal hypotension were first identified from a recent systematic review of the literature and a consensus statement on spinal hypotension. These definitions were applied to haemodynamic data taken from a prospective interventional obstetric spinal hypotension study conducted at Edendale Hospital, to determine the incidence of hypotension when applying these different thresholds. Finally, a definition was proposed based on these incidences and a review of the relevant literature.Results: Fifteen different definitions were identified. These were then applied to the study population with a resultant incidence of hypotension ranging from 15.8% to 91.4%. Based on a literature review of obstetric and other relevant perioperative and critical care medicine, targeting a mean arterial pressure > 70 mmHg and systolic blood pressure > 100 mmHg is recommended, and it is proposed that the lowest absolute values at which vasopressor therapy should be initiated are a mean arterial blood pressure < 65 mmHg or systolic blood pressure < 90 mmHg. Optimally, practitioners should maintain systolic blood pressure at greater than 90% of the baseline pre-spinal anaesthesia value.Conclusion: This study confirmed a wide variation in the incidence of obstetric spinal hypotension in a South African setting, depending on the definition used. An absolute threshold for intervention with vasopressor and an optimal target relative to baseline blood pressure are suggested. Further work is required to establish the effect of the adherence to these recommendations on important maternal and foetal outcomes.Keywords: Caesarean section, hypotension, incidence, neuraxial anaesthesia, regional anaesthesia, spinal anaesthesi

Obstetric spinal hypotension: Preoperative risk factors and the development of a preliminary risk score – the PRAM score

Background. Obstetric spinal hypotension is a common and important problem during caesarean delivery. Identifying patients at risk for hypotension may guide clinical decision-making and allow timeous referral.Objective. Using preoperative risk factors, to develop a simple scoring system to predict systolic hypotension.Methods. This prospective, single-centre, observational study of patients undergoing elective or urgent caesarean delivery assessed body mass index, baseline heart rate, baseline mean arterial pressure (MAP), maternal age, urgency of surgery (elective v. non-elective) and preoperative haemoglobin concentration as predictors of spinal hypotension (systolic blood pressure <90 mmHg). We used empirical cut-point estimations in a logistic regression model to develop a scoring system for prediction of hypotension.Results. From 504 eligible patients, preoperative heart rate (odds ratio (OR) 1.02, 95% confidence interval (CI) 1.00 - 1.03; p=0.012), preoperative MAP (OR 0.97, 95% CI 0.95 - 0.98; p<0.001) and maternal age (OR 1.05, 95% CI 1.02 - 1.08; p=0.002) were found to be predictors of hypotension. We derived a preliminary scoring system (pulse rate >90 bpm, age >25 years, MAP <90 mmHg – the PRAM score) for the prediction of systolic hypotension following obstetric spinal anaesthesia. Patients with three factors had a 53% chance of developing hypotension, compared with the overall incidence of 30%. The PRAM score showed good discrimination, with a c-statistic of 0.626 (95% CI 0.576 - 0.676) and good calibration.Conclusions. Preoperative heart rate, preoperative MAP and maternal age were predictive of hypotension in elective and emergency caesarean delivery. The PRAM score shows promise as a simple, practical means to identify these patients preoperatively, but requires prospective validation

Spray-cast multilayer perovskite solar cells with an active-area of 1.5 cm(2)

We utilise spray-coating under ambient conditions to sequentially deposit compact-TiO2, mesoporous-TiO2, CH3NH3PbI(3-x)Clx perovskite and doped spiro-OMeTAD layers, creating a mesoporous standard architecture perovskite solar cell (PSC). The devices created had an average power conversion efficiency (PCE) of 9.2% and a peak PCE of 10.2%; values that compare favourably with control-devices fabricated by spin-casting that had an average efficiency of 11.4%. We show that our process can be used to create devices having an active-area of 1.5 cm(2) having an independently verified efficiency of 6.6%. This work demonstrates the versatility of spray-coating as well as its potential as a method of manufacturing low-cost, large-area, efficient perovskite devices

Advances in Spray-Cast Perovskite Solar Cells

Spray-coating is a deposition technique that is widely used in industry and could in principle be used to fabricate perovskite photovoltaic (PV) devices at low cost and high volume. As with any deposition technique, the fabrication of thin films requires optimization of a range of parameter space in order to control film uniformity and homogeneity. This is particularly important in PV fabrication as the quality of the thin film has an important effect on device efficiency. This Perspective summarizes the developments in spray-cast perovskite solar cells made over the past few years, with particular attention paid to strategies employed to control the crystallization of the perovskite. Steady progress has now been made with spray-cast perovskite PV devices recently demonstrated having a power conversion efficiency of 18.3%. We highlight trends within the research field and discuss challenges that will be necessary to drive such techniques toward practical application

Renormalization of Hamiltonian Field Theory; a non-perturbative and non-unitarity approach

Renormalization of Hamiltonian field theory is usually a rather painful algebraic or numerical exercise. By combining a method based on the coupled cluster method, analysed in detail by Suzuki and Okamoto, with a Wilsonian approach to renormalization, we show that a powerful and elegant method exist to solve such problems. The method is in principle non-perturbative, and is not necessarily unitary.Comment: 16 pages, version shortened and improved, references added. To appear in JHE

Efficient perovskite photovoltaic devices using chemically doped PCDTBT as a hole-transport material

It is shown that by chemically doping the carbazole-based conjugated polymer PCDTBT using the molecular materials TBP, LiTFSI and FK209, its conductivity can be increased by a factor of 105 times. Such doped PCDTBT films are used as a hole transport material (HTM) for standard architecture (CH(NH2)2PbI3)0.85(CH3NH3PbBr3)0.15 perovskite solar cells (PSCs). We show that devices with optimised PCDTBT thickness and doping level achieve a peak power conversion efficiency (PCE) of 15.9%. We expect a number of related doped conjugated polymers to also be capable of acting as efficient HTMs for PSCs

Rapid scalable processing of tin oxide transport layers for perovskite solar cells

The development of scalable deposition methods for perovskite solar cell materials is critical to enable the commercialization of this nascent technology. Herein, we investigate the use and processing of nanoparticle SnO2 films as electron transport layers in perovskite solar cells and develop deposition methods for ultrasonic spray coating and slot-die coating, leading to photovoltaic device efficiencies over 19%. The effects of postprocessing treatments (thermal annealing, UV ozone, and O2 plasma) are then probed using structural and spectroscopic techniques to characterize the nature of the np-SnO2/perovskite interface. We show that a brief “hot air flow” method can be used to replace extended thermal annealing, confirming that this approach is compatible with high-throughput processing. Our results highlight the importance of interface management to minimize nonradiative losses and provide a deeper understanding of the processing requirements for large-area deposition of nanoparticle metal oxides

High-efficiency spray-coated perovskite solar cells utilizing vacuum-assisted solution processing

We use ultrasonic spray-coating to fabricate cesium-containing triple-cation perovskite solar cells with a power-conversion efficiency of up to 17.8%. Our fabrication route involves a brief exposure of the partially wet spray-cast films to a low vacuum, a process that is used to control film crystallization. We show that films that are not vacuum-exposed are relatively rough and inhomogeneous, while vacuum-exposed films are smooth and consist of small and densely packed perovskite crystals. The process techniques developed here represent a step toward a scalable and industrially compatible manufacturing process capable of creating stable and high-performance perovskite solar cells