Accidental dural puncture during epidural blood patch: a narrative review.

Whilst performing an epidural blood patch (EBP) to treat post dural-puncture headache following accidental or intentional dural puncture, the risk of a subsequent accidental dural puncture (ADP) is commonly quoted as 1%. However, a recent review reported only three documented cases. It seems likely that this complication is more common than is acknowledged, yet there is a paucity of literature and an absence of any guidance as to how to proceed in practice. This review addresses three unanswered questions regarding ADP during EBP: what is the incidence; what are the immediate clinical consequences; and what is the optimal clinical management? The incidence may reasonably be estimated to be 0.5-1%. Even on large units, this complication will not be experienced by every consultant anaesthetist during their career. It is likely to occur 20-30 times per year in the United Kingdom, and in greater numbers in those countries with higher epidural rates. Immediately re-attempting an EBP at a different level may be a reasonable management approach which has high efficacy, and is without clear evidence of significant harm. However, the limited evidence means that the risks are poorly characterised, and more data may lead to alternative conclusions. There is uncertainty amongst obstetric anaesthetists about how to manage ADP during EBP. More data and pragmatic guidance, which evolves with further evidence, will ensure optimal care for patients suffering this compound iatrogenic complication.

Diagnostic terminology in Placenta Accreta Spectrum: a scoping review.

BACKGROUND: Anaesthetic management strategies for Placenta Accreta Spectrum (PAS) remain diverse, and literature interpretation is complicated by a range of terminology. The International Federation for Gynaecology and Obstetrics (FIGO) published guidance in 2018 to improve PAS diagnosis and management by standardising definitions. We mapped the range, clarity and consistency of terminology in literature pertaining to both PAS and anaesthesia, and determined whether this changed followed FIGO guidance. METHODS: A literature search of four medical databases was performed. Papers included had PAS (or any 'synonym') in the title, and mode of anaesthesia in the title or abstract. Narrative reviews, and papers not containing original data, were excluded. Diagnostic terms, and evidence supporting their use, were described. RESULTS: Among 680 abstracts identified, 62 papers were included. Thirty distinct terms were used to describe PAS and subtypes. Terminology was clearly defined 46% of the time and used consistently within a paper 47% of the time. Nine papers (15%) provided no diagnostic evidence to support the terminology used. In 14 (23%) papers published after FIGO guidelines, 14 terms were used to describe PAS. Two papers (14%) specified the diagnostic criteria used. Six (43%) confirmed diagnoses using pathology. Four (29%) were consistent in use of terminology throughout the paper. CONCLUSIONS: Despite international consensus criteria for reporting PAS, the language pertaining to PAS and anaesthesia remains heterogeneous, inconsistent and variably defined. Reporting of PAS should adhere to FIGO criteria to allow unambiguous interpretation of work, and generation of evidence that is transferrable into clinical practice.

Towards a replicator dynamics model of age structured populations.

We present a new modelling framework combining replicator dynamics, the standard model of frequency dependent selection, with an age-structured population model. The new framework allows for the modelling of populations consisting of competing strategies carried by individuals who change across their life cycle. Firstly the discretization of the McKendrick von Foerster model is derived. We show that the Euler-Lotka equation is satisfied when the new model reaches a steady state (i.e. stable frequencies between the age classes). This discretization consists of unit age classes where the timescale is chosen so that only a fraction of individuals play a single game round. This implies a linear dynamics and individuals not killed during the round are moved to the next age class; linearity means that the system is equivalent to a large Bernadelli-Lewis-Leslie matrix. Then we use the methodology of multipopulation games to derive two, mutually equivalent systems of equations. The first contains equations describing the evolution of the strategy frequencies in the whole population, completed by subsystems of equations describing the evolution of the age structure for each strategy. The second contains equations describing the changes of the general population's age structure, completed with subsystems of equations describing the selection of the strategies within each age class. We then present the obtained system of replicator dynamics in the form of the mixed ODE-PDE system which is independent of the chosen timescale, and much simpler. The obtained results are illustrated by the example of the sex ratio model which shows that when different mortalities of the sexes are assumed, the sex ratio of 0.5 is obtained but that Fisher's mechanism, driven by the reproductive value of the different sexes, is not in equilibrium.

Interaction rates, vital rates, background fitness and replicator dynamics: how to embed evolutionary game structure into realistic population dynamics.

In this paper we are concerned with how aggregated outcomes of individual behaviours, during interactions with other individuals (games) or with environmental factors, determine the vital rates constituting the growth rate of the population. This approach needs additional elements, namely the rates of event occurrence (interaction rates). Interaction rates describe the distribution of the interaction events in time, which seriously affects the population dynamics, as is shown in this paper. This leads to the model of a population of individuals playing different games, where focal game affected by the considered trait can be extracted from the general model, and the impact on the dynamics of other events (which is not neutral) can be described by an average background fertility and mortality. This leads to a distinction between two types of background fitness, strategically neutral elements of the focal games (correlated with the focal game events) and the aggregated outcomes of other interactions (independent of the focal game). The new approach is useful for clarification of the biological meaning of concepts such as weak selection. Results are illustrated by a Hawk-Dove example.

A safety and feasibility study of the use of 670 nm red light in premature neonates.

OBJECTIVE: Retinopathy of prematurity (ROP) is a vasoproliferative disorder of the retina affecting extremely preterm or low birth weight infants The aim of this study was to assess the feasibility and safety of 670 nm red light use in a neonatal intensive care unit. STUDY DESIGN: Neonates <30 weeks gestation and <1150 g were enrolled within 48 h of birth. Data collected included cause of preterm delivery, Apgar scores and birthweight. 670 nm red light was administered for 15 min per day from a distance of 25 cm, delivering 9 J cm(-)(2), from the time of inclusion in the study until 34 weeks postmenstrual age. Infants were assessed daily for the presence of any skin burns or other adverse signs. RESULT: Twenty-eight neonates were enrolled, seven 24 to 26 weeks and twenty-one 27 to 29 weeks gestation. The most common cause for preterm delivery was preterm labor (14/28) with five of these having evidence of chorioamnionitis. There were no skin burns or other documented adverse events. Entry into the study was readily achieved and treatment was well accepted by parents and nursing staff. CONCLUSION: 670 nm red light appears to be a safe and feasible treatment for further research in respect to ROP.

Distractions during critical phases of anaesthesia for caesarean section: an observational study.

Aviation's 'sterile cockpit' rule holds that distractions on the flight deck should be kept at a minimum during critical phases of flight. To assess current practice at comparable points during obstetric regional anaesthesia, we measured ambient noise and distracting events during 30 caesarean sections in three phases: during establishment of regional anaesthesia; during testing of regional blockade; and after delivery of the fetal head. Mean (SD) noise levels were 62.5 (3.9) dB during establishment of blockade, 63.9 (4.1) dB during testing and 66.8 (5.0) dB after delivery (p < 0.001). The median rates of sudden, loud (> 70 dB) noises, non-clinical conversations and numbers of staff present in the operating theatre increased during each of the three phases. Conversely, entrances into, and exits from, theatre per minute were highest during establishment of regional anaesthesia and decreased over the subsequent two time periods (p < 0.001).

The nest site lottery: how selectively neutral density dependent growth suppression induces frequency dependent selection.

Modern developments in population dynamics emphasize the role of the turnover of individuals. In the new approaches stable population size is a dynamic equilibrium between different mortality and fecundity factors instead of an arbitrary fixed carrying capacity. The latest replicator dynamics models assume that regulation of the population size acts through feedback driven by density dependent juvenile mortality. Here, we consider a simplified model to extract the properties of this approach. We show that at the stable population size, the structure of the frequency dependent evolutionary game emerges. Turnover of individuals induces a lottery mechanism where for each nest site released by a dead adult individual a single newborn is drawn from the pool of newborn candidates. This frequency dependent selection leads towards the strategy maximizing the number of newborns per adult death. However, multiple strategies can maximize this value. Among them, the strategy with the greatest mortality (which implies the greatest instantaneous growth rate) is selected. This result is important for the discussion about universal fitness measures and which parameters are maximized by natural selection. This is related to the fitness measures R0 and r, because the number of newborns per single dead individual equals the lifetime production of newborn R0 in models without aging. We thus have a two-stage procedure, instead of a single fitness measure, which is a combination of R0 and r. According to the nest site lottery mechanism, at stable population size, selection favors strategies with the greatest r, i.e. those with the highest turnover, from those with the greatest R0.

On the evolutionary stability of zero-cost pooled-equilibrium signals.

A key question in the development of understanding of animal communication has been what maintains the honesty of signals, stopping dishonesty (cheating) from spreading. The dominant theory used to address this question is a refinement of Zahavi's handicap principle. The vital thing about handicap signals is that their honesty requires that those signals are costly to the sender over and above the minimum costs associated with transmission; these costs are generally called strategic costs. An alternative "pooled equilibria" has been proposed. If signalling is constrained to two levels, then it can be demonstrated that even if there is no cost associated with giving a signal, there can be a signalling evolutionarily stable strategy (ESS) where signallers are arranged into pools according to their state: those below a threshold give one signal, those above this threshold always give the other. Further, this can be generalized to any finite number of discrete signals. Here we explore the consequence of generalizing to a continuously varying signal form. We show that unless there is some physical impediment to the diversity of signals possible, then pooled-equilibrium signalling strategies are not stable. Such a strategy would be invaded by a more complex signal, where some individuals within a "pool" benefit from signalling their difference from other individuals within the pool. We suggest that such impediments to variation in signal form will be uncommon in nature, and thus so will pooled equilibria.

Ecological theatre and the evolutionary game: how environmental and demographic factors determine payoffs in evolutionary games.

In the standard approach to evolutionary games and replicator dynamics, differences in fitness can be interpreted as an excess from the mean Malthusian growth rate in the population. In the underlying reasoning, related to an analysis of "costs" and "benefits", there is a silent assumption that fitness can be described in some type of units. However, in most cases these units of measure are not explicitly specified. Then the question arises: are these theories testable? How can we measure "benefit" or "cost"? A natural language, useful for describing and justifying comparisons of strategic "cost" versus "benefits", is the terminology of demography, because the basic events that shape the outcome of natural selection are births and deaths. In this paper, we present the consequences of an explicit analysis of births and deaths in an evolutionary game theoretic framework. We will investigate different types of mortality pressures, their combinations and the possibility of trade-offs between mortality and fertility. We will show that within this new approach it is possible to model how strictly ecological factors such as density dependence and additive background fitness, which seem neutral in classical theory, can affect the outcomes of the game. We consider the example of the Hawk-Dove game, and show that when reformulated in terms of our new approach new details and new biological predictions are produced.

Evolutionarily stable sexual allocation by both stressed and unstressed potentially simultaneous hermaphrodites within the same population.

Factors influencing allocation of resources to male and female offspring continue to be of great interest to evolutionary biologists. A simultaneous hermaphrodite is capable of functioning in both male and female mode at the same time, and such a life-history strategy is adopted by most flowering plants and by many sessile aquatic animals. In this paper, we focus on hermaphrodites that nourish post-zygotic stages, e.g. flowering plants and internally fertilising invertebrates, and consider how their sex allocation should respond to an environmental stress that reduces prospects of survival but does not affect all individuals equally, rather acting only on a subset of the population. Whereas dissemination of pollen and sperm can begin at sexual maturation, release of seeds and larvae is delayed by embryonic development. We find that the evolutionarily stable strategy for allocation between male and female functions will be critically dependent on the effect of stress on the trade-off between the costs of male and female reproduction, (i.e. of sperm and embryos). Thus, we identify evaluation of this factor as an important challenge to empiricists interested in the effects of stress on sex allocation. When only a small fraction of the population is stressed, we predict that stressed individuals will allocate their resources entirely to male function and unstressed individuals will increase their allocation to female function. Conversely, when the fraction of stress-affected individuals is high, stressed individuals should respond to this stressor by increasing investment in sperm and unstressed individuals should invest solely in embryos. A further prediction of the model is that we would not expect to find populations in the natural world where both stressed and unstressed individuals are both hermaphrodite.

Methods of weaning preterm babies <30 weeks gestation off CPAP: a multicentre randomised controlled trial.

BACKGROUND: Controversy exists whether different continuous positive airway pressure (CPAP) weaning methods influence time to wean off CPAP, CPAP duration, oxygen duration, Bronchopulmonary Dysplasia (BPD) or length of admission. AIMS: In a multicentre randomised controlled trial, the authors have primarily compared CPAP weaning methods impact on time to wean off CPAP and CPAP duration and secondarily their effect on oxygen duration, BPD and time of admission. METHODS: Between April 2006 and October 2009, 177 infants <30 weeks gestational age (GA) who fulfilled stability criteria on CPAP were randomised to one of the three CPAP weaning methods (M). M1: Taken 'OFF' CPAP with the view to stay 'OFF'. M2: Cycled on and off CPAP with incremental time 'OFF'. M3: As with m(2), cycled on and off CPAP but during 'OFF' periods were supported by 2 mm nasal cannula at a flow of 0.5 l/min. RESULTS: Based on intention to treat analysis, there was no significant difference in mean GA or birthweight between the groups (27.1 ± 1.4, 26.9 ± 1.6 and 27.3 ± 1.5 (weeks ± 1SD) and 988 ± 247, 987 ± 249 and 1015 ± 257 (grams ± 1SD), respectively). Primary outcomes showed M1 produced a significantly shorter time to wean from CPAP (11.3 ± 0.8, 16.8 ± 1.0, 19.4 ± 1.3 (days ± 1SE) p<0.0001, respectively) and CPAP duration (24.4 ± 0.1, 38.6 ± 0.1, 30.5 ± 0.1 (days ± 1SE) p<0.0001, respectively). All the secondary outcomes were significantly shorter with M1, (oxygen duration: 24.1 ± 1.5, 45.8 ± 2.2, 34.1 ± 2.0 (days ± 1SE) p<0.0001, BPD: 7/56 (12.5%), 29/69 (42%), 10/52 (19%) p=0.011 and length of admission: 58.5 ± 0.1, 73.8 ± 0.1 69.5 ± 0.1 (days ± 1SE) p<0.0001, respectively). CONCLUSION: Method 1 significantly shortens CPAP weaning time, CPAP duration, oxygen duration, BPD and admission time.

Critical phase distractions in anaesthesia and the sterile cockpit concept.

In aviation, the sterile cockpit rule prohibits non-essential activities during critical phases of flight, takeoff and landing, phases analogous to induction of, and emergence from, anaesthesia. We studied distraction during 30 anaesthetic inductions, maintenances and emergences. Mean (SD) noise during emergence (58.3 (6.2) dB) was higher than during induction (46.4 (4.3) dB) and maintenance (52 (4.5) dB; p<0.001). Sudden loud noises, greater than 70 dB, occurred more frequently at emergence (occurring 34 times) than at induction (occurring nine times) or maintenance (occurring 13 times). The median (IQR [range]) of staff entrances or exits were 0 (0-2 [0-7]), 6 (3-10 [1-18]) and 10 (5-12 [1-20]) for induction, maintenance and emergence, respectively (p<0.001). Conversations unrelated to the procedure occurred in 28/30 (93%) emergences. These data demonstrate increased distraction during emergence compared with other phases of anaesthesia. Recognising and minimising distraction should improve patient safety. Applying aviation's sterile cockpit rule may be a useful addition to our clinical practice.

Kleptoparasitic melees--modelling food stealing featuring contests with multiple individuals.

Kleptoparasitism is the stealing of food by one animal from another. This has been modelled in various ways before, but all previous models have only allowed contests between two individuals. We investigate a model of kleptoparasitism where individuals are allowed to fight in groups of more than two, as often occurs in real populations. We find the equilibrium distribution of the population amongst various behavioural states, conditional upon the strategies played and environmental parameters, and then find evolutionarily stable challenging strategies. We find that there is always at least one ESS, but sometimes there are two or more, and discuss the circumstances when particular ESSs occur, and when there are likely to be multiple ESSs.

A game-theoretic model of interspecific brood parasitism with sequential decisions.

The interaction between hosts and parasites in bird populations has been studied extensively. This paper uses game-theoretic methods to model this interaction. This has been done in previous papers but has not been studied taking into account the detailed sequential nature of this game. We introduce a model allowing the host and parasite to make a number of decisions which will depend on various natural factors. The sequence of events begins with the host forming a nest and laying a number of eggs, followed by the possibility that a parasite bird will arrive at the nest; if it does it can choose to destroy some of the host eggs and lay one of its own. A sequence of events follows, which is broken down into two key stages; firstly the interaction between the host and the parasite adult, and secondly that between the host and the parasite chick. The final decision involves the host choosing whether to raise or abandon the chicks that are in the nest. There are certain natural parameters and probabilities which are central to these various decisions; in particular the host is generally uncertain whether parasitism has taken place, but can assess the likelihood of parasitism based upon certain cues (e.g. how many eggs remain in its nest). We then use this methodology to model two real-world interactions, that of the Reed Warbler with the Common Cuckoo and also the Yellow Warbler with the Brown-headed Cowbird. These parasites have different methods in the way they parasitize the nests of their hosts, and the hosts can in turn have different reactions to these parasites. Our model predictions generally match the real results well, and the model also makes predictions of the effect of changes in various key parameters on the type of parasitic interactions that should occur.