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Kua J, Potter T, Wong DJN, Nurmi E, El-Boghdadly K, Cronin JN. UK-wide rates of videolaryngoscopy use and barriers to universal uptake: a retrospective analysis of a multicentre observational study. Anaesthesia 2024; 79:100-101. [PMID: 37712109 DOI: 10.1111/anae.16121] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/08/2023] [Indexed: 09/16/2023]
Affiliation(s)
- J Kua
- Guy's and St. Thomas' NHS Foundation Trust, London, UK
| | - T Potter
- Guy's and St. Thomas' NHS Foundation Trust, London, UK
| | - D J N Wong
- Guy's and St. Thomas' NHS Foundation Trust, London, UK
| | - E Nurmi
- Guy's and St. Thomas' NHS Foundation Trust, London, UK
| | | | - J N Cronin
- Guy's and St. Thomas' NHS Foundation Trust, London, UK
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2
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Cronin JN, Crockett DC, Perchiazzi G, Farmery AD, Camporota L, Formenti F. Intra-tidal PaO 2 oscillations associated with mechanical ventilation: a pilot study to identify discrete morphologies in a porcine model. Intensive Care Med Exp 2023; 11:60. [PMID: 37672140 PMCID: PMC10482813 DOI: 10.1186/s40635-023-00544-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Accepted: 08/28/2023] [Indexed: 09/07/2023] Open
Abstract
BACKGROUND Within-breath oscillations in arterial oxygen tension (PaO2) can be detected using fast responding intra-arterial oxygen sensors in animal models. These PaO2 signals, which rise in inspiration and fall in expiration, may represent cyclical recruitment/derecruitment and, therefore, a potential clinical monitor to allow titration of ventilator settings in lung injury. However, in hypovolaemia models, these oscillations have the potential to become inverted, such that they decline, rather than rise, in inspiration. This inversion suggests multiple aetiologies may underlie these oscillations. A correct interpretation of the various PaO2 oscillation morphologies is essential to translate this signal into a monitoring tool for clinical practice. We present a pilot study to demonstrate the feasibility of a new analysis method to identify these morphologies. METHODS Seven domestic pigs (average weight 31.1 kg) were studied under general anaesthesia with muscle relaxation and mechanical ventilation. Three underwent saline-lavage lung injury and four were uninjured. Variations in PEEP, tidal volume and presence/absence of lung injury were used to induce different morphologies of PaO2 oscillation. Functional principal component analysis and k-means clustering were employed to separate PaO2 oscillations into distinct morphologies, and the cardiorespiratory physiology associated with these PaO2 morphologies was compared. RESULTS PaO2 oscillations from 73 ventilatory conditions were included. Five functional principal components were sufficient to explain ≥ 95% of the variance of the recorded PaO2 signals. From these, five unique morphologies of PaO2 oscillation were identified, ranging from those which increased in inspiration and decreased in expiration, through to those which decreased in inspiration and increased in expiration. This progression was associated with the estimates of the first functional principal component (P < 0.001, R2 = 0.88). Intermediate morphologies demonstrated waveforms with two peaks and troughs per breath. The progression towards inverted oscillations was associated with increased pulse pressure variation (P = 0.03). CONCLUSIONS Functional principal component analysis and k-means clustering are appropriate to identify unique morphologies of PaO2 waveform associated with distinct cardiorespiratory physiology. We demonstrated novel intermediate morphologies of PaO2 waveform, which may represent a development of zone 2 physiologies within the lung. Future studies of PaO2 oscillations and modelling should aim to understand the aetiologies of these morphologies.
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Affiliation(s)
- John N Cronin
- Department of Anaesthesia and Perioperative Medicine, St. Thomas' Hospital, Guy's and St. Thomas' NHS Foundation Trust, Westminster Bridge Road, London, SE1 7EH, UK.
- Faculty of Life Sciences and Medicine, King's College London, London, UK.
| | - Douglas C Crockett
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - Gaetano Perchiazzi
- Hedenstierna Laboratory, Department of Surgical Sciences, University of Uppsala, Uppsala, Sweden
| | - Andrew D Farmery
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - Luigi Camporota
- Faculty of Life Sciences and Medicine, King's College London, London, UK
- Department of Intensive Care, Guy's and St. Thomas' NHS Foundation Trust, London, UK
| | - Federico Formenti
- Faculty of Life Sciences and Medicine, King's College London, London, UK
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
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Bridgen P, Malik S, Wilkinson T, Cronin JN, Bhagat T, Hart N, Corkell SM, Perkins J, Tibby S, Hanna S, Kirwan R, Pauly T, Weeks A, Charles-Edwards G, Padormo F, Stell D, El-Boghdadly K, Ourselin S, Giles SL, Edwards AD, Hajnal JV, Blaise BJ. Reliability and safety of anaesthetic equipment around an high-field 7-Tesla MRI scanner. Br J Anaesth 2023; 130:e490-e492. [PMID: 36997472 DOI: 10.1016/j.bja.2023.02.019] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2022] [Revised: 01/31/2023] [Accepted: 02/19/2023] [Indexed: 03/30/2023] Open
Affiliation(s)
- Philippa Bridgen
- Center for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, St. Thomas' Hospital, London, UK; Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, London, UK; London Collaborative Ultra High Field System (LoCUS), London, UK
| | - Shaihan Malik
- Center for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, St. Thomas' Hospital, London, UK; Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, London, UK; London Collaborative Ultra High Field System (LoCUS), London, UK
| | - Thomas Wilkinson
- Center for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, St. Thomas' Hospital, London, UK; Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, London, UK
| | - John N Cronin
- Department of Anaesthetics, St Thomas' Hospital, London, UK
| | | | - Nicholas Hart
- Lane Fox Clinical Respiratory Physiology Research Centre, London, UK; Lane Fox Respiratory Service, London, UK; Centre for Human and Applied Physiological Sciences, King's College London, London, UK
| | | | | | - Shane Tibby
- Department of Paediatric Intensive Care, London, UK
| | - Sara Hanna
- Department of Paediatric Intensive Care, London, UK
| | - Richard Kirwan
- Department of Anaesthetics, St Thomas' Hospital, London, UK; Department of Paediatric Anaesthetics, London, UK
| | | | | | - Geoff Charles-Edwards
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, London, UK; Department of Medical Physics, Guy's and St Thomas' NHS Foundation Trust, London, UK
| | - Francesco Padormo
- Department of Medical Physics, Guy's and St Thomas' NHS Foundation Trust, London, UK
| | - David Stell
- Department of Medical Physics, Guy's and St Thomas' NHS Foundation Trust, London, UK
| | | | | | - Sharon L Giles
- Center for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, St. Thomas' Hospital, London, UK; Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, London, UK
| | - Anthony D Edwards
- Center for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, St. Thomas' Hospital, London, UK; Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, London, UK; Department of Neonatology, Evelina London Children's Hospital, Guy's and St Thomas' NHS Foundation Trust, London, UK
| | - Joseph V Hajnal
- Center for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, St. Thomas' Hospital, London, UK; Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, London, UK
| | - Benjamin J Blaise
- Center for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, St. Thomas' Hospital, London, UK; Department of Paediatric Anaesthetics, London, UK.
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Kua J, Nurmi E, Wong DJN, Potter T, Cronin JN, El-Boghdadly K. Clinical evidence needed for risks of PPE. Anaesthesia 2023; 78:393-394. [PMID: 36261154 DOI: 10.1111/anae.15895] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/04/2022] [Indexed: 11/30/2022]
Affiliation(s)
- J Kua
- University College London, London, UK
| | - E Nurmi
- University College London Hospitals NHS Foundation Trust, London, UK
| | - D J N Wong
- Guy's and St Thomas' NHS Foundation Trust, London, UK
| | - T Potter
- Guy's and St Thomas' NHS Foundation Trust, London, UK
| | - J N Cronin
- Guy's and St Thomas' NHS Foundation Trust, London, UK
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5
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Cronin JN, Formenti F. Experimental asynchrony to study self-inflicted lung injury. Br J Anaesth 2023; 130:e44-e46. [PMID: 34903360 DOI: 10.1016/j.bja.2021.11.020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2021] [Revised: 11/05/2021] [Accepted: 11/07/2021] [Indexed: 01/06/2023] Open
Abstract
Patient self-inflicted lung injury may be associated with worse clinical outcomes and higher mortality. Patient-ventilator asynchrony is associated with increased ventilator days and mortality, and it has been hypothesised as one of the important mechanisms leading to patient self-inflicted lung injury. However, given the observational nature of the key studies in the field so far, the hypothesis that patient-ventilator asynchrony causes patient self-inflicted lung injury has not been supported by evidence yet. Wittenstein and colleagues present a novel approach that enables controlling patient-ventilator asynchrony in a pig model of acute lung injury, to investigate the patient-ventilator asynchrony and patient self-inflicted lung injury causality. Their results suggest that increased patient-ventilator asynchrony associated with poor clinical outcomes reported in observational trials could be a marker, rather than a cause of patient self-inflicted lung injury. These findings on their own are not sufficient to justify a greater tolerance of patient-ventilator asynchrony amongst clinicians, a change for which further experimental work and clinical evidence is needed.
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Affiliation(s)
- John N Cronin
- Centre for Human and Applied Physiological Sciences, School of Basic and Medical Biosciences, King's College London, London, UK; Department of Anaesthesia, Guy's and St Thomas' NHS Foundation Trust, London, UK
| | - Federico Formenti
- Centre for Human and Applied Physiological Sciences, School of Basic and Medical Biosciences, King's College London, London, UK; Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK; Department of Biomechanics, University of Nebraska Omaha, Omaha, NE, USA.
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6
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Potter T, Cronin JN, Kua J, Nurmi E, Wong DJN, Ahmad I, Cook TM, El-Boghdadly K. Aerosol precautions and airway complications: a national prospective multicentre cohort study. Anaesthesia 2023; 78:23-35. [PMID: 36070622 PMCID: PMC10087829 DOI: 10.1111/anae.15851] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/26/2022] [Indexed: 12/13/2022]
Abstract
The perceived risk of transmission of aerosolised viral particles from patients to airway practitioners during the COVID-19 pandemic led to the widespread use of aerosol precautions, including personal protective equipment and modifications to anaesthetic technique. The risk of these aerosol precautions on peri-operative airway complications has not been assessed outside of simulation studies. This prospective, national, multicentre cohort study aimed to quantify this risk. Adult patients undergoing general anaesthesia for elective or emergency procedures over a 96-hour period were included. Data collected included use of aerosol precautions by the airway practitioner, airway complications and potential confounding variables. Mixed-effects logistic regression was used to assess the risk of individual aerosol precautions on overall and specific airway complications. Data from 5905 patients from 70 hospital sites were included. The rate of airway complications was 10.0% (95%CI 9.2-10.8%). Use of filtering facepiece class 2 or class 3 respirators was associated with an increased risk of airway complications (odds ratio 1.38, 95%CI 1.04-1.83), predominantly due to an association with difficult facemask ventilation (odds ratio 1.68, 95%CI 1.09-2.61) and desaturation on pulse oximetry (odds ratio 2.39, 95%CI 1.26-4.54). Use of goggles, powered air-purifying respirators, long-sleeved gowns, double gloves and videolaryngoscopy were not associated with any alteration in the risk of airway complications. Overall, the use of filtering facepiece class 2 or class 3 respirators was associated with an increased risk of airway complications, but most aerosol precautions used during the COVID-19 pandemic were not.
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Affiliation(s)
- T Potter
- Department of Anaesthesia and Peri-operative Medicine, Guy's and St. Thomas' NHS Foundation Trust, London, UK
| | - J N Cronin
- Department of Anaesthesia and Peri-operative Medicine, Guy's and St. Thomas' NHS Foundation Trust, London, UK
| | - J Kua
- Surgical Outcomes Research Centre, University College London, UK
| | - E Nurmi
- Department of Anaesthesia and Peri-operative Medicine, Guy's and St. Thomas' NHS Foundation Trust, London, UK
| | - D J N Wong
- Department of Anaesthesia and Peri-operative Medicine, Guy's and St. Thomas' NHS Foundation Trust, London, UK
| | - I Ahmad
- Department of Anaesthesia and Peri-operative Medicine, Guy's and St. Thomas' NHS Foundation Trust, London, UK.,King's College London, UK
| | - T M Cook
- Department of Anaesthesia, Royal United Hospitals Bath NHS Foundation Trust, Bath, UK.,School of Medicine, University of Bristol, UK
| | - K El-Boghdadly
- Department of Anaesthesia and Peri-operative Medicine, Guy's and St. Thomas' NHS Foundation Trust, London, UK.,King's College London, UK
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Abstract
PURPOSE OF REVIEW More than 230 million people have tested positive for severe acute respiratory syndrome-coronavirus-2 infection globally by September 2021. The infection affects primarily the function of the respiratory system, where ∼20% of infected individuals develop coronavirus-19 disease (COVID-19) pneumonia. This review provides an update on the pathophysiology of the COVID-19 acute lung injury. RECENT FINDINGS In patients with COVID-19 pneumonia admitted to the intensive care unit, the PaO2/FiO2 ratio is typically <26.7 kPa (200 mmHg), whereas lung volume appears relatively unchanged. This hypoxaemia is likely determined by a heterogeneous mismatch of pulmonary ventilation and perfusion, mainly associated with immunothrombosis, endothelialitis and neovascularisation. During the disease, lung weight, elastance and dead space can increase, affecting respiratory drive, effort and dyspnoea. In some severe cases, COVID-19 pneumonia may lead to irreversible pulmonary fibrosis. SUMMARY This review summarises the fundamental pathophysiological features of COVID-19 in the context of the respiratory system. It provides an overview of the key clinical manifestations of COVID-19 pneumonia, including gas exchange impairment, altered pulmonary mechanics and implications of abnormal chemical and mechanical stimuli. It also critically discusses the clinical implications for mechanical ventilation therapy.
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Affiliation(s)
- Luigi Camporota
- Centre for Human and Applied Physiological Sciences, School of Basic and Medical Biosciences, King's College London
- Intensive Care Unit, Guy's and St Thomas' NHS Foundation Trust
| | - John N Cronin
- Centre for Human and Applied Physiological Sciences, School of Basic and Medical Biosciences, King's College London
- Department of Anaesthetics, Royal Brompton and Harefield, part of Guy's and St. Thomas' NHS Foundation Trust, London, UK
| | - Mattia Busana
- Department of Anesthesiology, University Medical Center of Göttingen, Göttingen, Germany
| | - Luciano Gattinoni
- Department of Anesthesiology, University Medical Center of Göttingen, Göttingen, Germany
| | - Federico Formenti
- Centre for Human and Applied Physiological Sciences, School of Basic and Medical Biosciences, King's College London
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK
- Department of Biomechanics, University of Nebraska Omaha, Omaha, Nebraska, USA
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Beale R, Rosendo JB, Bergeles C, Beverly A, Camporota L, Castrejón-Pita AA, Crockett DC, Cronin JN, Denison T, East S, Edwardes C, Farmery AD, Fele F, Fisk J, Fuenteslópez CV, Garstka M, Goulart P, Heaysman C, Hussain A, Jha P, Kempf I, Kumar AS, Möslein A, Orr ACJ, Ourselin S, Salisbury D, Seneci C, Staruch R, Steel H, Thompson M, Tran MC, Vitiello V, Xochicale M, Zhou F, Formenti F, Kirk T. OxVent: Design and evaluation of a rapidly-manufactured Covid-19 ventilator. EBioMedicine 2022; 76:103868. [PMID: 35172957 PMCID: PMC8842095 DOI: 10.1016/j.ebiom.2022.103868] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2021] [Revised: 12/08/2021] [Accepted: 01/21/2022] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND The manufacturing of any standard mechanical ventilator cannot rapidly be upscaled to several thousand units per week, largely due to supply chain limitations. The aim of this study was to design, verify and perform a pre-clinical evaluation of a mechanical ventilator based on components not required for standard ventilators, and that met the specifications provided by the Medicines and Healthcare Products Regulatory Agency (MHRA) for rapidly-manufactured ventilator systems (RMVS). METHODS The design utilises closed-loop negative feedback control, with real-time monitoring and alarms. Using a standard test lung, we determined the difference between delivered and target tidal volume (VT) at respiratory rates between 20 and 29 breaths per minute, and the ventilator's ability to deliver consistent VT during continuous operation for >14 days (RMVS specification). Additionally, four anaesthetised domestic pigs (3 male-1 female) were studied before and after lung injury to provide evidence of the ventilator's functionality, and ability to support spontaneous breathing. FINDINGS Continuous operation lasted 23 days, when the greatest difference between delivered and target VT was 10% at inspiratory flow rates >825 mL/s. In the pre-clinical evaluation, the VT difference was -1 (-90 to 88) mL [mean (LoA)], and positive end-expiratory pressure (PEEP) difference was -2 (-8 to 4) cmH2O. VT delivery being triggered by pressures below PEEP demonstrated spontaneous ventilation support. INTERPRETATION The mechanical ventilator presented meets the MHRA therapy standards for RMVS and, being based on largely available components, can be manufactured at scale. FUNDING Work supported by Wellcome/EPSRC Centre for Medical Engineering,King's Together Fund and Oxford University.
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Affiliation(s)
- Richard Beale
- Centre for Human and Applied Physiological Sciences, King's College London, UK; Intensive Care Unit, Guy's and St Thomas' NHS Foundation Trust, London, UK
| | | | - Christos Bergeles
- School of Biomedical Engineering and Imaging Sciences, King's College London, UK
| | - Anair Beverly
- Department of Engineering Science, University of Oxford, UK
| | - Luigi Camporota
- Centre for Human and Applied Physiological Sciences, King's College London, UK; Intensive Care Unit, Guy's and St Thomas' NHS Foundation Trust, London, UK
| | | | - Douglas C Crockett
- Nuffield Department of Clinical Neurosciences, University of Oxford, UK; Milton Keynes University Hospital NHS Foundation Trust, Milton Keynes, UK
| | - John N Cronin
- Centre for Human and Applied Physiological Sciences, King's College London, UK; Department of Anaesthesia, Guy's and St Thomas' NHS Foundation Trust, London, UK
| | - Timothy Denison
- Department of Engineering Science, Institute of Biomedical Engineering, University of Oxford, UK
| | - Sebastian East
- Department of Engineering Science, University of Oxford, UK
| | | | - Andrew D Farmery
- Nuffield Department of Clinical Neurosciences, University of Oxford, UK
| | - Filiberto Fele
- Department of Engineering Science, University of Oxford, UK
| | - James Fisk
- Department of Engineering Science, Institute of Biomedical Engineering, University of Oxford, UK
| | - Carla V Fuenteslópez
- Department of Engineering Science, Institute of Biomedical Engineering, University of Oxford, UK
| | | | - Paul Goulart
- Department of Engineering Science, University of Oxford, UK
| | - Clare Heaysman
- School of Biomedical Engineering and Imaging Sciences, King's College London, UK
| | | | - Prashant Jha
- School of Biomedical Engineering and Imaging Sciences, King's College London, UK
| | - Idris Kempf
- Department of Engineering Science, University of Oxford, UK
| | | | - Annika Möslein
- Department of Engineering Science, University of Oxford, UK
| | - Andrew C J Orr
- Department of Engineering Science, University of Oxford, UK
| | - Sebastien Ourselin
- School of Biomedical Engineering and Imaging Sciences, King's College London, UK
| | - David Salisbury
- Department of Engineering Science, Institute of Biomedical Engineering, University of Oxford, UK
| | - Carlo Seneci
- School of Biomedical Engineering and Imaging Sciences, King's College London, UK
| | - Robert Staruch
- Department of Engineering Science, Institute of Biomedical Engineering, University of Oxford, UK; Nuffield Department of Orthopaedic, Rheumatology and Musculoskeletal Sciences, University of Oxford, UK; The Academic Department of Military Surgery and Trauma, Birmingham, UK
| | - Harrison Steel
- Department of Engineering Science, University of Oxford, UK
| | - Mark Thompson
- Department of Engineering Science, Institute of Biomedical Engineering, University of Oxford, UK
| | - Minh C Tran
- Department of Engineering Science, University of Oxford, UK; Nuffield Department of Clinical Neurosciences, University of Oxford, UK
| | - Valentina Vitiello
- School of Biomedical Engineering and Imaging Sciences, King's College London, UK
| | - Miguel Xochicale
- School of Biomedical Engineering and Imaging Sciences, King's College London, UK
| | - Feibiao Zhou
- Department of Engineering Science, University of Oxford, UK
| | - Federico Formenti
- Centre for Human and Applied Physiological Sciences, King's College London, UK; Nuffield Department of Clinical Neurosciences, University of Oxford, UK; Department of Biomechanics, University of Nebraska Omaha, Omaha, NE, USA.
| | - Thomas Kirk
- Nuffield Department of Clinical Neurosciences, University of Oxford, UK; Department of Engineering Science, Institute of Biomedical Engineering, University of Oxford, UK.
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Hummer EV, Soares JHN, Crockett DC, Aguiar AJA, Tran MC, Cronin JN, Brosnan RJ, Braun C, Formenti F. Continuous measurement of arterial oxygenation in mechanically ventilated horses. Equine Vet J 2021; 54:1144-1152. [PMID: 34797580 DOI: 10.1111/evj.13542] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Revised: 11/01/2021] [Accepted: 11/11/2021] [Indexed: 11/29/2022]
Abstract
BACKGROUND The possibility of accurately and continuously measuring arterial oxygen partial pressure (PaO2 ) in horses may facilitate the management of hypoxaemia during general anaesthesia. OBJECTIVES The aim of this study was to evaluate the ability of a novel fibreoptic sensor to measure PaO2 (PaO2Sensor ) continuously and in real time in horses undergoing ventilatory manoeuvres during general anaesthesia. STUDY DESIGN In vivo experimental study. METHODS Six adult healthy horses were anaesthetised and mechanically ventilated in dorsal recumbency. A fibreoptic sensor was placed in one of the facial arteries through a catheter to continuously measure and record PaO2Sensor . After an alveolar recruitment manoeuvre, a decremental positive end-expiratory pressure (PEEP) titration using 20-minute steps of 5 cm H2 O from 20 to 0 cm H2 O was performed. An arterial blood sample was collected at 15 minutes of ventilation at each PEEP level for PaO2 measurement using an automated blood gas machine (PaO2Ref ). The agreement between PaO2Sensor and PaO2Ref was assessed by Pearson's correlation, Bland-Altman plot and four-quadrant plot analysis. In the last minute of ventilation at each PEEP level, a slow tidal inflation/deflation manoeuvre was performed. RESULTS The mean relative bias between PaO2Sensor and PaO2Ref was 4% with limits of agreement between -17% and 29%. The correlation coefficient between PaO2Sensor and PaO2Ref was 0.98 (P < .001). The PaO2Sensor and PaO2Ref concordance rate for changes was 95%. Measurements of PaO2Sensor during the slow inflation/deflation manoeuvre at PEEP 15 and 10 cm H2 O were not possible because of significant noise on the PaO2 signal generated by a small blood clot. MAIN LIMITATIONS Small sample size. CONCLUSION The tested fibreoptic probe was able to accurately and continuously measure PaO2Sensor in anaesthetised horses undergoing ventilatory manoeuvres. A heparinised system in the catheter used by the fibreoptic sensor should be used to avoid blood clots and artefacts in the PaO2 measurements.
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Affiliation(s)
- Emma V Hummer
- William Pritchard Veterinary Medical Teaching Hospital, University of California Davis, Davis, California, USA
| | - Joao H N Soares
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California Davis, Davis, California, USA
| | | | - Antonio J A Aguiar
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California Davis, Davis, California, USA.,Departamento de Cirurgia e Anestesiologia Veterinária, Faculdade de Medicina Veterinária e Zootecnia, UNESP - Univ. Estadual Paulista, Botucatu, São Paulo, Brazil
| | - Minh C Tran
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK.,Department of Engineering Science, University of Oxford, Oxford, UK
| | - John N Cronin
- Centre for Human and Applied Physiological Sciences, King's College London, London, UK.,Department of Anaesthetics, Guy's and St Thomas' NHS Foundation Trust, London, UK
| | - Robert J Brosnan
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California Davis, Davis, California, USA
| | - Christina Braun
- Anaesthesiology and Perioperative Intensive Care, Vetmeduni Vienna, Vienna, Austria
| | - Federico Formenti
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK.,Centre for Human and Applied Physiological Sciences, King's College London, London, UK
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Abstract
New Findings What is the topic of this review? This review presents the fundamental concepts of respiratory physiology and pathophysiology, with particular reference to lung mechanics and the pulmonary phenotype associated with severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection and subsequent coronavirus disease 2019 (COVID‐19) pneumonia. What advances does it highlight? The review provides a critical summary of the main physiological aspects to be considered for safe and effective mechanical ventilation in patients with severe COVID‐19 in the intensive care unit.
Abstract Severe respiratory failure from coronavirus disease 2019 (COVID‐19) pneumonia not responding to non‐invasive respiratory support requires mechanical ventilation. Although ventilation can be a life‐saving therapy, it can cause further lung injury if airway pressure and flow and their timing are not tailored to the respiratory system mechanics of the individual patient. The pathophysiology of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection can lead to a pattern of lung injury in patients with severe COVID‐19 pneumonia typically associated with two distinct phenotypes, along a temporal and pathophysiological continuum, characterized by different levels of elastance, ventilation‐to‐perfusion ratio, right‐to‐left shunt, lung weight and recruitability. Understanding the underlying pathophysiology, duration of symptoms, radiological characteristics and lung mechanics at the individual patient level is crucial for the appropriate choice of mechanical ventilation settings to optimize gas exchange and prevent further lung injury. By critical analysis of the literature, we propose fundamental physiological and mechanical criteria for the selection of ventilation settings for COVID‐19 patients in intensive care units. In particular, the choice of tidal volume should be based on obtaining a driving pressure < 14 cmH2O, ensuring the avoidance of hypoventilation in patients with preserved compliance and of excessive strain in patients with smaller lung volumes and lower lung compliance. The level of positive end‐expiratory pressure (PEEP) should be informed by the measurement of the potential for lung recruitability, where patients with greater recruitability potential may benefit from higher PEEP levels. Prone positioning is often beneficial and should be considered early. The rationale for the proposed mechanical ventilation settings criteria is presented and discussed.
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Affiliation(s)
- John N Cronin
- Centre for Human and Applied Physiological Sciences, School of Basic and Medical Biosciences, King's College London, London, UK.,Department of Anaesthetics, Royal Brompton and Harefield, part of Guy's and St. Thomas' NHS Foundation Trust, London, UK
| | - Luigi Camporota
- Centre for Human and Applied Physiological Sciences, School of Basic and Medical Biosciences, King's College London, London, UK.,Intensive Care Unit, Guy's and St Thomas' NHS Foundation Trust, London, UK
| | - Federico Formenti
- Centre for Human and Applied Physiological Sciences, School of Basic and Medical Biosciences, King's College London, London, UK.,Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK.,Department of Biomechanics, University of Nebraska Omaha, Omaha, Nebraska, USA
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Gallifant J, Cronin JN, Formenti F. Quantification of lobar gas exchange: a proof-of-concept study in pigs. Br J Anaesth 2021; 127:e55-e58. [PMID: 34116804 DOI: 10.1016/j.bja.2021.04.022] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Revised: 04/13/2021] [Accepted: 04/16/2021] [Indexed: 11/17/2022] Open
Affiliation(s)
- Jack Gallifant
- Centre for Human and Applied Physiological Sciences, School of Basic and Medical Biosciences, King's College London, London, UK
| | - John N Cronin
- Centre for Human and Applied Physiological Sciences, School of Basic and Medical Biosciences, King's College London, London, UK; Department of Anaesthesia, Guy's and St Thomas' NHS Foundation Trust, London, UK.
| | - Federico Formenti
- Centre for Human and Applied Physiological Sciences, School of Basic and Medical Biosciences, King's College London, London, UK; Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK; Department of Biomechanics, University of Nebraska Omaha, Omaha, NE, USA.
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Tran MC, Crockett DC, Cronin JN, Borges JB, Hedenstierna G, Larsson A, Farmery AD, Formenti F. Bedside monitoring of lung volume available for gas exchange. Intensive Care Med Exp 2021; 9:3. [PMID: 33496887 PMCID: PMC7835652 DOI: 10.1186/s40635-020-00364-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2020] [Accepted: 12/02/2020] [Indexed: 02/08/2023] Open
Abstract
BACKGROUND Bedside measurement of lung volume may provide guidance in the personalised setting of respiratory support, especially in patients with the acute respiratory distress syndrome at risk of ventilator-induced lung injury. We propose here a novel operator-independent technique, enabled by a fibre optic oxygen sensor, to quantify the lung volume available for gas exchange. We hypothesised that the continuous measurement of arterial partial pressure of oxygen (PaO2) decline during a breath-holding manoeuvre could be used to estimate lung volume in a single-compartment physiological model of the respiratory system. METHODS Thirteen pigs with a saline lavage lung injury model and six control pigs were studied under general anaesthesia during mechanical ventilation. Lung volumes were measured by simultaneous PaO2 rate of decline (VPaO2) and whole-lung computed tomography scan (VCT) during apnoea at different positive end-expiratory and end-inspiratory pressures. RESULTS A total of 146 volume measurements was completed (range 134 to 1869 mL). A linear correlation between VCT and VPaO2 was found both in control (slope = 0.9, R2 = 0.88) and in saline-lavaged pigs (slope = 0.64, R2 = 0.70). The bias from Bland-Altman analysis for the agreement between the VCT and VPaO2 was - 84 mL (limits of agreement ± 301 mL) in control and + 2 mL (LoA ± 406 mL) in saline-lavaged pigs. The concordance for changes in lung volume, quantified with polar plot analysis, was - 4º (LoA ± 19°) in control and - 9° (LoA ± 33°) in saline-lavaged pigs. CONCLUSION Bedside measurement of PaO2 rate of decline during apnoea is a potential approach for estimation of lung volume changes associated with different levels of airway pressure.
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Affiliation(s)
- Minh C Tran
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK.
- Department of Engineering Science, University of Oxford, Oxford, UK.
| | | | - John N Cronin
- Centre for Human and Applied Physiological Sciences, King's College London, London, UK
- Department of Anaesthetics, Guy's and St. Thomas' NHS Foundation Trust, London, UK
| | - João Batista Borges
- Centre for Human and Applied Physiological Sciences, King's College London, London, UK
| | - Göran Hedenstierna
- Hedenstierna Laboratory, Department of Medical Sciences, Uppsala University, Uppsala, Sweden
| | - Anders Larsson
- Hedenstierna Laboratory, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden
| | - Andrew D Farmery
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK
| | - Federico Formenti
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK.
- Centre for Human and Applied Physiological Sciences, King's College London, London, UK.
- Department of Biomechanics, University of Nebraska, Omaha, NE, USA.
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Borges JB, Cronin JN, Crockett DC, Hedenstierna G, Larsson A, Formenti F. Real-time effects of PEEP and tidal volume on regional ventilation and perfusion in experimental lung injury. Intensive Care Med Exp 2020; 8:10. [PMID: 32086632 PMCID: PMC7035410 DOI: 10.1186/s40635-020-0298-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2019] [Accepted: 01/30/2020] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Real-time bedside information on regional ventilation and perfusion during mechanical ventilation (MV) may help to elucidate the physiological and pathophysiological effects of MV settings in healthy and injured lungs. We aimed to study the effects of positive end-expiratory pressure (PEEP) and tidal volume (VT) on the distributions of regional ventilation and perfusion by electrical impedance tomography (EIT) in healthy and injured lungs. METHODS One-hit acute lung injury model was established in 6 piglets by repeated lung lavages (injured group). Four ventilated piglets served as the control group. A randomized sequence of any possible combination of three VT (7, 10, and 15 ml/kg) and four levels of PEEP (5, 8, 10, and 12 cmH2O) was performed in all animals. Ventilation and perfusion distributions were computed by EIT within three regions-of-interest (ROIs): nondependent, middle, dependent. A mixed design with one between-subjects factor (group: intervention or control), and two within-subjects factors (PEEP and VT) was used, with a three-way mixed analysis of variance (ANOVA). RESULTS Two-way interactions between PEEP and group, and VT and group, were observed for the dependent ROI (p = 0.035 and 0.012, respectively), indicating that the increase in the dependent ROI ventilation was greater at higher PEEP and VT in the injured group than in the control group. A two-way interaction between PEEP and VT was observed for perfusion distribution in each ROI: nondependent (p = 0.030), middle (p = 0.006), and dependent (p = 0.001); no interaction was observed between injured and control groups. CONCLUSIONS Large PEEP and VT levels were associated with greater pulmonary ventilation of the dependent lung region in experimental lung injury, whereas they affected pulmonary perfusion of all lung regions both in the control and in the experimental lung injury groups.
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Affiliation(s)
- João Batista Borges
- Centre for Human and Applied Physiological Sciences, King's College London, London, UK.
| | - John N Cronin
- Centre for Human and Applied Physiological Sciences, King's College London, London, UK
| | | | - Göran Hedenstierna
- Hedenstierna Laboratory, Department of Medical Sciences, Uppsala University, Uppsala, Sweden
| | - Anders Larsson
- Hedenstierna Laboratory, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden
| | - Federico Formenti
- Centre for Human and Applied Physiological Sciences, King's College London, London, UK. .,Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK.
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14
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Cronin JN, Borges JB, Crockett DC, Farmery AD, Hedenstierna G, Larsson A, Tran MC, Camporota L, Formenti F. Dynamic single-slice CT estimates whole-lung dual-energy CT variables in pigs with and without experimental lung injury. Intensive Care Med Exp 2019; 7:59. [PMID: 31676929 PMCID: PMC6825104 DOI: 10.1186/s40635-019-0273-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Accepted: 10/01/2019] [Indexed: 11/23/2022] Open
Abstract
Background Dynamic single-slice CT (dCT) is increasingly used to examine the intra-tidal, physiological variation in aeration and lung density in experimental lung injury. The ability of dCT to predict whole-lung values is unclear, especially for dual-energy CT (DECT) variables. Additionally, the effect of inspiration-related lung movement on CT variables has not yet been quantified. Methods Eight domestic pigs were studied under general anaesthesia, including four following saline-lavage surfactant depletion (lung injury model). DECT, dCT and whole-lung images were collected at 12 ventilatory settings. Whole-lung single energy scans images were collected during expiratory and inspiratory apnoeas at positive end-expiratory pressures from 0 to 20 cmH2O. Means and distributions of CT variables were calculated for both dCT and whole-lung images. The cranio-caudal displacement of the anatomical slice was measured from whole-lung images. Results Mean CT density and volume fractions of soft tissue, gas, iodinated blood, atelectasis, poor aeration, normal aeration and overdistension correlated between dCT and the whole lung (r2 0.75–0.94) with agreement between CT density distributions (r 0.89–0.97). Inspiration increased the matching between dCT and whole-lung values and was associated with a movement of 32% (SD 15%) of the imaged slice out of the scanner field-of-view. This effect introduced an artefactual increase in dCT mean CT density during inspiration, opposite to that caused by the underlying physiology. Conclusions Overall, dCT closely approximates whole-lung aeration and density. This approximation is improved by inspiration where a decrease in CT density and atelectasis can be interpreted as physiological rather than artefactual.
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Affiliation(s)
- John N Cronin
- Centre for Human and Applied Physiological Sciences, King's College London, London, UK
| | - João Batista Borges
- Centre for Human and Applied Physiological Sciences, King's College London, London, UK
| | | | - Andrew D Farmery
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK
| | - Göran Hedenstierna
- Hedenstierna Laboratory, Department of Medical Sciences, Uppsala University, Uppsala, Sweden
| | - Anders Larsson
- Hedenstierna Laboratory, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden
| | - Minh C Tran
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK
| | - Luigi Camporota
- Centre for Human and Applied Physiological Sciences, King's College London, London, UK.,Department of Adult Critical Care, St. Thomas' Hospital, Guy's and St. Thomas' NHS Foundation Trust, King's Health Partners, London, UK
| | - Federico Formenti
- Centre for Human and Applied Physiological Sciences, King's College London, London, UK. .,Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK.
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Crockett DC, Cronin JN, Bommakanti N, Chen R, Hahn CEW, Hedenstierna G, Larsson A, Farmery AD, Formenti F. Tidal changes in PaO 2 and their relationship to cyclical lung recruitment/derecruitment in a porcine lung injury model. Br J Anaesth 2018; 122:277-285. [PMID: 30686314 PMCID: PMC6354046 DOI: 10.1016/j.bja.2018.09.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2018] [Revised: 08/21/2018] [Accepted: 09/10/2018] [Indexed: 01/03/2023] Open
Abstract
BACKGROUND Tidal recruitment/derecruitment (R/D) of collapsed regions in lung injury has been presumed to cause respiratory oscillations in the partial pressure of arterial oxygen (PaO2). These phenomena have not yet been studied simultaneously. We examined the relationship between R/D and PaO2 oscillations by contemporaneous measurement of lung-density changes and PaO2. METHODS Five anaesthetised pigs were studied after surfactant depletion via a saline-lavage model of R/D. The animals were ventilated with a mean fraction of inspired O2 (FiO2) of 0.7 and a tidal volume of 10 ml kg-1. Protocolised changes in pressure- and volume-controlled modes, inspiratory:expiratory ratio (I:E), and three types of breath-hold manoeuvres were undertaken. Lung collapse and PaO2 were recorded using dynamic computed tomography (dCT) and a rapid PaO2 sensor. RESULTS During tidal ventilation, the expiratory lung collapse increased when I:E <1 [mean (standard deviation) lung collapse=15.7 (8.7)%; P<0.05], but the amplitude of respiratory PaO2 oscillations [2.2 (0.8) kPa] did not change during the respiratory cycle. The expected relationship between respiratory PaO2 oscillation amplitude and R/D was therefore not clear. Lung collapse increased during breath-hold manoeuvres at end-expiration and end-inspiration (14% vs 0.9-2.1%; P<0.0001). The mean change in PaO2 from beginning to end of breath-hold manoeuvres was significantly different with each type of breath-hold manoeuvre (P<0.0001). CONCLUSIONS This study in a porcine model of collapse-prone lungs did not demonstrate the expected association between PaO2 oscillation amplitude and the degree of recruitment/derecruitment. The results suggest that changes in pulmonary ventilation are not the sole determinant of changes in PaO2 during mechanical ventilation in lung injury.
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Affiliation(s)
- D C Crockett
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK.
| | - J N Cronin
- Centre for Human and Applied Physiological Sciences, King's College, London, UK
| | - N Bommakanti
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK; Vagelos College of Physicians and Surgeons, Columbia University, New York, NY, USA
| | - R Chen
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK
| | - C E W Hahn
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK
| | - G Hedenstierna
- Hedenstierna Laboratory, Department of Medical Sciences, Uppsala University, Uppsala, Sweden
| | - A Larsson
- Hedenstierna Laboratory, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden
| | - A D Farmery
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK
| | - F Formenti
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, UK; Centre for Human and Applied Physiological Sciences, King's College, London, UK; Department of Biomechanics, University of Nebraska Omaha, Omaha, NE, USA.
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Formenti F, Bommakanti N, Chen R, Cronin JN, McPeak H, Holopherne-Doran D, Hedenstierna G, Hahn CEW, Larsson A, Farmery AD. Respiratory oscillations in alveolar oxygen tension measured in arterial blood. Sci Rep 2017; 7:7499. [PMID: 28878215 PMCID: PMC5587703 DOI: 10.1038/s41598-017-06975-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2017] [Accepted: 06/20/2017] [Indexed: 01/02/2023] Open
Abstract
Arterial oxygen partial pressure can increase during inspiration and decrease during expiration in the presence of a variable shunt fraction, such as with cyclical atelectasis, but it is generally presumed to remain constant within a respiratory cycle in the healthy lung. We measured arterial oxygen partial pressure continuously with a fast intra-vascular sensor in the carotid artery of anaesthetized, mechanically ventilated pigs, without lung injury. Here we demonstrate that arterial oxygen partial pressure shows respiratory oscillations in the uninjured pig lung, in the absence of cyclical atelectasis (as determined with dynamic computed tomography), with oscillation amplitudes that exceeded 50 mmHg, depending on the conditions of mechanical ventilation. These arterial oxygen partial pressure respiratory oscillations can be modelled from a single alveolar compartment and a constant oxygen uptake, without the requirement for an increased shunt fraction during expiration. Our results are likely to contribute to the interpretation of arterial oxygen respiratory oscillations observed during mechanical ventilation in the acute respiratory distress syndrome.
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Affiliation(s)
- Federico Formenti
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, United Kingdom. .,Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom.
| | - Nikhil Bommakanti
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, United Kingdom
| | - Rongsheng Chen
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, United Kingdom
| | - John N Cronin
- Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom
| | - Hanne McPeak
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, United Kingdom
| | | | | | - Clive E W Hahn
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, United Kingdom
| | - Anders Larsson
- Department of Surgical Sciences, University of Uppsala, Uppsala, Sweden
| | - Andrew D Farmery
- Nuffield Division of Anaesthetics, University of Oxford, Oxford, United Kingdom
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Cronin JN, Bradbury EJ, Lidierth M. Laminar distribution of GABAA- and glycine-receptor mediated tonic inhibition in the dorsal horn of the rat lumbar spinal cord: effects of picrotoxin and strychnine on expression of Fos-like immunoreactivity. Pain 2004; 112:156-63. [PMID: 15494196 DOI: 10.1016/j.pain.2004.08.010] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2004] [Revised: 07/14/2004] [Accepted: 08/03/2004] [Indexed: 10/26/2022]
Abstract
Inhibitory mechanisms are essential in suppressing the development of allodynia and hyperalgesia in the normal animal and there is evidence that loss of inhibition can lead to the development of neuropathic pain. We used Fos expression to map the distribution of tonically inhibited cells in the healthy rat lumbar spinal cord. In a control group, Fos-like immunoreactive (Fos-LI) cells were rare, averaging 7.5+/-2.2 cells (mean+/-SEM; N=13 sections) per 20 microm thick section of dorsal horn. This rose to 103+/-11 (mean+/-SEM; N=20) in picrotoxin-treated rats and to 88+/-11 (mean+/-SEM; N=18) in strychnine-treated rats. These changes were significant (ANOVA; P<0.001). There were marked regional variations in the distribution of Fos-LI cells between picrotoxin- and strychnine-treated animals. Picrotoxin induced a significant increase in the number of Fos-LI cells throughout the dorsal horn (lamina I-VI) while strychnine significantly elevated Fos-like immunoreactivity only in deep laminae (III-VI). For both picrotoxin and strychnine, the increase in Fos-like immunoreactivity peaked in lamina V (at 3579+/-319 and 3649+/-375% of control, respectively; mean+/-SEM) but for picrotoxin an additional peak was observed in the outer part of lamina II (1959+/-196%). Intrathecal administration of both GABAA and glycine receptor antagonists has been shown elsewhere to induce tactile allodynia. The present data suggest that this allodynia could arise due to blockade of tonic GABAA and glycine-receptor mediated inhibition in the deep dorsal horn. GABAA antagonists also induce hypersensitivity to noxious inputs. The blockade of tonic inhibition in the superficial dorsal horn shown here may underlie this hyperalgesia.
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Affiliation(s)
- John N Cronin
- Department of Physiology, Hodgkin Building, King's College London, London SE1 1UL, UK
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