Browsing by Author "Argent, Andrew C"

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    Open Access
    Airflow limitation in croup
    (1999) Jaroslawski, ML; Capper, Wayne; Argent, Andrew C
    This thesis investigates a mechanism for air flow limitation in children with croup. Croup is a common condition affecting many young children. Infection (usually viral) causes swelling of the mucosa in the subglottic region of the airway with consequent narrowing of the airway. Although researchers have investigated croup for the past sixty years, there is still very little information available on how croup affects air flow dynamics. The current theory assumes that the stenosis formed by croup in the subglottis of infants leads to a dynamic collapse of the extrathoracic trachea (Chernick, 1990). According to this literature, the dynamic collapse of the extrathoracic trachea will limit the inspiratory flow. It was believed that in severe cases of croup, the dynamic collapse may even temporarily block the airways. In order to investigate the mechanism for air flow limitation in croup the author used the intrathoracic pressure - flow traces from twenty patients with croup, four patients who had been intubated for croup and five normal subjects. Laryngeal X-rays from another twenty patients with croup were analysed as well as five videos, made during laryngoscopy, of the subglottic cross-sectional area of an additional five patients with croup requiring intubation. All data used in this project was collected by an experienced paediatrician from the Red Cross War Memorial Children's Hospital who is also the supervisor of this thesis. Both the video and the X-ray data showed that the dynamic collapse of the trachea contributes much less to airflow obstruction than the subglottic swelling itself. The hypothesis investigated in this thesis is that air flow becomes restricted due to wave speed limitation. According to the theory of wave speed limitation, an increase in driving pressure (the intrathoracic pressure) does not increase the flow if the speed of the air particles exceeds the wave speed. In our case the wave speed is the speed of sound within the lumen of the compliant, narrowed airway. In order to test that theory, it was necessary to obtain the flow, the driving pressure in the subglottis and the cross-sectional area of the subglottis of patients with croup. Unfortunately, the measurement of subglottal cross-sectional areas from videos made during laryngoscopies, proved to be impossible due to both ethical and practical constraints. The measurement of the subglottal cross-sectional areas from X-rays was also difficult in practice. Therefore, the cross-sectional area is calculated. The general orifice equation is modified m order to calculate the subglottal cross-sectional areas in patients with croup. Two methods are used to test the hypothesis of wave speed limitation: i) The wave speed limitation formula. The wave speed limitation formula directly calculates the maximum flow from the pressure - flow data. Hereafter the calculated maximum flow is compared with the measured flow. ii) A lumped component model. A nonlinear, lumped component model has been used to calculate the flow from the driving pressure (intrathoracic pressure). Flow is not limited in this model and an increase in driving pressure will result in a corresponding increase in flow. The flow which is calculated using this model has also been compared to the measured flow. It was found that, in children with croup, there is a good correlation (r=0.82) between calculated and measured values of maximum flow using the wave speed limitation model. The slope of the linear fit using a least square's approximation is 0.98 and this linear relationship is valid for a 0.05 level of significance for Conover's nonparametric test (Daniel and Terrell, 1989). The lumped component model was able to fit the inspiratory flow data with a small sum of square error in the case of both normal ((7.56 ± 0.86) · 10⁻⁹ (ml/s)²) and intubated patients ((3.2 ± 0.75)·10⁻⁹ (ml/s)²). However, the error rose dramatically in patients with croup ((2.04 ± 0.5) -10⁻⁸ (ml/s)²) thus indicating that the lumped component model is no longer valid in these patients. It is concluded that the measured flow velocities in patients with croup approach the calculated velocity of sound in the region of the subglottic swelling, and that the wave speed theory accurately describes the flow limitation. Further support of this is the fact that the lumped component model, which does not incorporate a flow limiting mechanism, breaks down in patients with croup.
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    An audit of transfers into the PICU at the Red Cross War Memorial Children's Hospital: a follow up study
    (2016) Dimitriades, Konstantinos; Argent, Andrew C; Morrow, Brenda M
    Background: Children are transferred from various facilities into the paediatric intensive care unit (PICU) at the Red Cross War Memorial Children's Hospital for critical care, without a specialised paediatric transfer service. A previous audit in 2003 reported a high incidence of technical, clinical and critical adverse events during transfers. Objective: To conduct a follow -up audit on interfacility transfers into PICU to determine practice and outcome changes. Methodology: Prospective observational study of all patients transferred into PICU between 1 Dec ember 2013 and 30 November 2014 and compared to the 2003 audit by Hatherill et al. Results: Analysis was performed on 204 transfers (median (IQR) age 1.8 (0.2 – 12.6) months and compared to results reported by Hatherill et al (2003). The proportion of medical transfers decreased (49% to 34.3% p=0.003) as well as the referrals from metropolitan hospitals (34.7% to 17.6%, p = 0.0001), whilst the number of referrals from academic hospitals increased from 35.1% to 44.6% (p = 0.05). Staff accompanying transfers and transfer times remained unchanged. The proportion of fixed wing transfers increased from 14.4% to 25.5% (p=0.006) whilst Helicopter transfers decreased from 9.9% to 1% (p <0.0001). 58.4% of patients were in tubated for transfer in 2003 compared to 69.1% in 2014 (p = 0.02). The rate of technical (35.6% to 39.7%, p = 0.4), clinical (26.7% to 31.9%, p = 0.25), and critical (8.9% to 8.8%, p = 0.97) adverse events remained unchanged. PICU Mortality decreased from 16.8% to 9.45% (p=0.03) with a decrease in Standardized Mortality Rate from 1.11 to 0.68. Three children died on arrival to PICU. The communication tool was used in 45.1% of transfers and its use was noted to be associated with significantly less critical adverse events (4.3% vs. 12.5%, p = 0.048). Technical adverse events were positively correlated with the clinical adverse events (Spearman's R = 0.3; p=0.000008) and critical adverse events (Spearman's R = 0.1; p = 0.03). In turn the total number of clinical adverse events were positively correlated with the total number of critical adverse events (Spearman's R = 0.5; p < 0.000001). The multiple regression analysis for PICU mortality found the total number of clinical adverse events to be independently associated with ICU mortality (adjusted OR 95% CI 2.8 (1.7 -4.7); p = 0.0001) Conclusion: The rate and staffing structure of interfacility transfers into PICU have remained unchanged, and associated adverse event rates remain high. Changes are noted in the profile of transferred patients as well as adverse events. Efforts to formalize the paediatric transfer service must be strengthened whilst using interim measures to improve the current standard through education, improved skills and PICU support.
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    Caregivers' experiences of pathways to care for seriously ill children in Cape Town, South Africa: A qualitative investigation
    (Public Library of Science, 2016) Jones, Caroline H D; Ward, Alison; Hodkinson, Peter W; Reid, Stephen J; Wallis, Lee A; Harrison, Sian; Argent, Andrew C
    Purpose Understanding caregivers' experiences of care can identify barriers to timely and good quality care, and support the improvement of services. We aimed to explore caregivers' experiences and perceptions of pathways to care, from first access through various levels of health service, for seriously ill and injured children in Cape Town, South Africa, in order to identify areas for improvement. METHODS: Semi-structured, qualitative interviews were conducted with primary caregivers of children who were admitted to paediatric intensive care or died in the health system prior to intensive care admission. Interviews explored caregivers' experiences from when their child first became ill, through each level of health care to paediatric intensive care or death. A maximum variation sample of transcripts was purposively sampled from a larger cohort study based on demographic characteristics, child diagnosis, and outcome at 30 days; and analysed using the method of constant comparison. RESULTS: Of the 282 caregivers who were interviewed in the larger cohort study, 45 interviews were included in this qualitative analysis. Some caregivers employed 'tactics' to gain quicker access to care, including bypassing lower levels of care, and negotiating or demanding to see a healthcare professional ahead of other patients. It was sometimes unclear how to access emergency care within facilities; and non-medical personnel informally judged illness severity and helped or hindered quicker access. Caregivers commonly misconceived ambulances to be slow to arrive, and were concerned when ambulance transfers were seemingly not prioritised by illness severity. Communication was often good, but some caregivers experienced language difficulties and/or criticism. CONCLUSIONS: Interventions to improve child health care could be based on: reorganising the reception of seriously ill children and making the emergency route within healthcare facilities clear; promoting caregivers' use of ambulances and prioritising transfers according to illness severity; addressing language barriers, and emphasising the importance of effective communication to healthcare providers.
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    Informed consent in paediatric critical care research – a South African perspective
    (BioMed Central, 2015-09-09) Morrow, Brenda M; Argent, Andrew C; Kling, Sharon
    Background: Medical care of critically ill and injured infants and children globally should be based on best research evidence to ensure safe, efficacious treatment. In South Africa and other low and middle-income countries, research is needed to optimise care and ensure rational, equitable allocation of scare paediatric critical care resources. Ethical oversight is essential for safe, appropriate research conduct. Informed consent by the parent or legal guardian is usually required for child research participation, but obtaining consent may be challenging in paediatric critical care research. Local regulations may also impede important research if overly restrictive. By narratively synthesising and contextualising the results of a comprehensive literature review, this paper describes ethical principles and regulations; potential barriers to obtaining prospective informed consent; and consent options in the context of paediatric critical care research in South Africa. Discussion: Voluntary prospective informed consent from a parent or legal guardian is a statutory requirement for child research participation in South Africa. However, parents of critically ill or injured children might be incapable of or unwilling to provide the level of consent required to uphold the ethical principle of autonomy. In emergency care research it may not be practical to obtain consent when urgent action is required. Therapeutic misconceptions and sociocultural and language issues are also barriers to obtaining valid consent. Alternative consent options for paediatric critical care research include a waiver or deferred consent for minimal risk and/or emergency research, whilst prospective informed consent is appropriate for randomised trials of novel therapies or devices. Summary: We propose that parents or legal guardians of critically ill or injured children should only be approached to consent for their child’s participation in clinical research when it is ethically justifiable and in the best interests of both child participant and parent. Where appropriate, alternatives to prospective informed consent should be considered to ensure that important paediatric critical care research can be undertaken in South Africa, whilst being cognisant of research risk. This document could provide a basis for debate on consent options in paediatric critical care research and contribute to efforts to advocate for South African law reform.
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    An investigation into regional ventilation in infants and children; its distribution and determinants
    (2017) Lupton-Smith, Alison Rosalie; Morrow, Brenda M; Argent, Andrew C
    Changing body position is commonly used in the management of individuals with respiratory diseases and those receiving mechanical ventilation, in order to optimise ventilation and oxygenation. In acute respiratory distress syndrome (ARDS), prone positioning is reported to improve oxygenation by recruiting collapsed dorsal lung regions, although this has not been confirmed in children. Ventilation distribution is well established in adults as being gravity dependent. Clinical practice in the paediatric population has been guided by the notion that all children, irrespective of the presence or absence of disease and age, consistently demonstrate the opposite ventilation distribution pattern to adults and this pattern is said to occur until the second decade of life. Studies in the paediatric population are limited to a few reported from the 1980's, on very heterogeneous populations. With advances in technology, new methods of examining regional ventilation, such as electrical impedance tomography (EIT), have become available. Recent neonatal studies using EIT have reported a dissimilar ventilation distribution to the conventional paediatric pattern. Despite a growing number of studies examining the effects of various interventions on ventilation distribution, very few exist in infants and children older than 6 months of age. Furthermore, differing methodologies and the manner in which ventilation distribution is described and analysed makes pooling the available data in the paediatric population extremely difficult. An understanding of how ventilation is distributed under normal conditions is imperative when examining the effects of different interventions and medical conditions on ventilation distribution. This thesis aimed to describe the effects of body position, head position, age, and respiratory muscle activity on ventilation distribution in children between six months and nine years of age under normal conditions, with respiratory disease, neuromuscular disease, and during mechanical ventilation. Furthermore, the effect on ventilation distribution of prone positioning in children with ARDS was evaluated. Regional ventilation distribution was measured using thoracic EIT and respiratory muscle activity was measured using surface electromyography (sEMG) using standardised methodology. Results of a series of sub-studies indicate that ventilation distribution is more complex and variable than previously thought, with no standard "paediatric pattern" of ventilation. Overall, greater ventilation occurred in the right and dorsal lungs, respectively, in different positons. Head position did not affect regional ventilation in the children studied. Age had a variable effect on ventilation distribution, with healthy children under 12 months of age more likely to follow the paediatric pattern, particularly in side lying positions; however the response was not uniform. The presence of mechanical ventilation, disease state and respiratory muscle activity did not affect ventilation distribution with these children also showing variable patterns of regional ventilation distribution. Data suggests that turning children with ARDS into the prone position does not result in recruitment of the dorsal lung regions, but rather more homogenous ventilation throughout the lungs. Furthermore, results suggest that children with greater ventilation inhomogeneity at baseline are more likely to respond positively (improvement in oxygenation index) to prone positioning. This research provides novel insights into ventilation distribution and respiratory muscle activity in infants and children older than six months of age under a number of different conditions. These results contribute to a better understanding of the factors influencing the distribution of regional ventilation and the mechanisms by which prone positioning in ARDS may improve oxygenation in this population. These findings have potentially important clinical implications, as well as providing baseline data for future clinical studies. Given the variability observed, these studies highlight the potential clinical utility of EIT to monitor different interventions and outcomes. An important strength of the studies presented in this thesis, is that they were performed in a standardised manner, using relatively homogenous individual populations and validated measures of describing ventilation distribution. This methodology could provide a template for future studies in the paediatric population, to allow for comparison between studies.
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    Outcomes of Human Immunodeficiency Virus infected children admitted to a paediatric intensive care unit in Cape Town, South Africa
    (2015) Salie, Mogamat Shamiel; Argent, Andrew C
    During the mid to late 1990's, nearly all HIV infected children admitted to South African paediatric intensive care units died. This was in the context of an increasing HIV epidemic in Sub-Saharan Africa, a limited number of intensive care beds in public hospitals and the South African government refusing to supply antiretroviral medication to public sector patients. HIV infected children all die without ARV medication, and it resulted in an increase in the South African under-5 mortality rate. In this context critically ill HIV infected children were often denied PICU admission. Developed countries introduced ARV medication in the early 1990's and the South African government only started supplying ARV medication in late 2003. When ARV medication became available in South Africa, it was started on the basis of the individual child's clinical and immunological status and there was not much published data on initiation of ARV therapy in critical ill children in intensive care units. Many HIV infected children had recurrent hospital admissions and many children died before initiating ARV medication. HIV infected children are not only susceptible to the normal bacteria and viruses, but at increased risk of opportunistic and mycobacterial infections. CMV has increasingly been recognized as a common co-infection with PCP, but has been difficult to diagnose and treat effectively. We retrospectively reviewed all HIV exposed and infected children admitted to our PICU in 2009. In addition to our standard treatment, we initiated ARV medication as soon as logistically possible and children with suspected CMV infections were empirically treated with gancyclovir.