A simple method to estimate flow restriction for dual ventilation of dissimilar patients: The BathRC model.

BACKGROUND: With large numbers of COVID-19 patients requiring mechanical ventilation and ventilators possibly being in short supply, in extremis two patients may have to share one ventilator. Careful matching of patient ventilation requirements is necessary. However, good matching is difficult to achieve as lung characteristics can have a wide range and may vary over time. Adding flow restriction to the flow path between ventilator and patient gives the opportunity to control the airway pressure and hence flow and volume individually for each patient. This study aimed to create and validate a simple model for calculating required flow restriction. METHODS AND FINDINGS: We created a simple linear resistance-compliance model, termed the BathRC model, of the ventilator tubing system and lung allowing direct calculation of the relationships between pressures, volumes, and required flow restriction. Experimental measurements were made for parameter determination and validation using a clinical ventilator connected to two test lungs. For validation, differing amounts of restriction were introduced into the ventilator circuit. The BathRC model was able to predict tidal lung volumes with a mean error of 4% (min:1.2%, max:9.3%). CONCLUSION: We present a simple model validated model that can be used to estimate required flow restriction for dual patient ventilation. The BathRC model is freely available; this tool is provided to demonstrate that flow restriction can be readily estimated. Models and data are available at DOI 10.15125/BATH-00816.

Does hyperglycaemia precede the clinical onset of myocardial ischaemia?

Stress hyperglycaemia has been observed previously in a large proportion of patients with acute myocardial infarction. We report a patient who presented to our intensive care unit (ICU) on two occasions with acute hyperglycaemia preceding new onset myocardial ischaemia by several hours.

Therapeutic hypothermia after cardiac arrest in a 66-year-old man.

Hypoxic-ischaemic brain injury is an important cause of morbidity and mortality following both in- and out-of-hospital cardiac arrest. Despite significant advances in critical care the only intervention proven to increase survival rates after cardiac arrest is mild hypothermia. The authors present a case describing the use of therapeutic hypothermia after ventricular fibrillation cardiac arrest, including its indications and contra-indications, and the techniques that can be used to induce it.

How to weigh the current evidence for clinical practice.

This article presents a template for judging trials of tight glucose control in critically ill patients. It reviews threats to both internal validity and generalisability using examples from the current literature. When judging internal validity, it is important to consider factors specific to trials of glucose control (particularly the methods of glucose control, measurement and reporting) in addition to factors common to all randomised controlled trials (such as treatment allocation, losses to follow-up and protocol violations). Judging generalisability requires the identification of differences between the trial population and the population for whom the intervention is being considered. These may relate to the setting, the patients or the practical delivery of tight glucose control or other interventions. Once identified, a judgement must be made for each difference of whether it is likely to modify the effect of tight glucose control.

Introducing intensive insulin therapy: the nursing perspective.

Intensive insulin therapy (IIT) for the management of high blood glucose can reduce mortality and morbidity in the critically ill. However, there is little published literature on how to implement it successfully. The aim of this study is to chronicle the development and difficulties encountered in implementing an IIT protocol in a critical care unit in a district general hospital. A nurse-led protocol was developed. Qualitative audit was undertaken during development and implementation to identify potential problems with using the Bath Insulin Protocol. Regular feedback sessions were introduced to encourage change and further identify problem issues. Qualitative audit led to changes in practice for individual nurses and changes to other unit protocols. The main change for individual nurses was to measure blood glucose hourly using a bedside glucometer. The unit's feeding and drug dilution policies were identified as a potential cause of glucose instability and were modified. To implement IIT successfully, it is necessary to consider changing working practices and to identify other unit protocols which can cause glucose instability. The additional nursing workload must be considered and appropriate means of supporting staff identified.

Epidemiology of severe sepsis occurring in the first 24 hrs in intensive care units in England, Wales, and Northern Ireland.

OBJECTIVE: To investigate the numbers, clinical characteristics, resource use, and outcomes of admissions who met precise clinical and physiologic criteria for severe sepsis (as defined in the PROWESS trial) in the first 24 hrs in the intensive care unit. DESIGN: Observational cohort study, with retrospective analysis of prospectively collected data. SETTING: Ninety-one adult general intensive care units in England, Wales, and Northern Ireland between 1995 and 2000. PATIENTS: Patients were 56,673 adult admissions. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: We found that 27.1% of adult intensive care unit admissions met severe sepsis criteria in the first 24 hrs in the intensive care unit. Most were nonsurgical (67%), and the most common organ system dysfunctions were seen in the cardiovascular (88%) and respiratory (81%) systems. Modeling the data for England and Wales for 1997 suggested that 51 (95% confidence interval, 46-58) per 100,000 population per year were admitted to intensive care units and met severe sepsis criteria in the first 24 hrs.Of the intensive care unit admissions who met severe sepsis criteria in the first 24 hrs, 35% died before intensive care unit discharge and 47% died during their hospital stay. Hospital mortality rate ranged from 17% in the 16-19 age group to 64% in those >85 yrs. In England and Wales in 1997, an estimated 24 (95% confidence interval, 21-28) per 100,000 population per year died after intensive care unit admissions with severe sepsis in the first 24 hrs. For intensive care unit admissions who met severe sepsis criteria in the first 24 hrs, median intensive care unit length of stay was 3.56 days (interquartile range, 1.50-9.32) and median hospital length of stay was 18 days (interquartile range, 8-36 days). These admissions used 45% of the intensive care unit and 33% of the hospital bed days used by all intensive care unit admissions. CONCLUSIONS: Severe sepsis is common and presents a major challenge for clinicians, managers, and healthcare policymakers. Intensive care unit admissions meeting severe sepsis criteria have a high mortality rate and high resource use.