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Slobod D, Damia A, Leali M, Spinelli E, Mauri T. Pathophysiology and Clinical Meaning of Ventilation-Perfusion Mismatch in the Acute Respiratory Distress Syndrome. BIOLOGY 2022; 12:biology12010067. [PMID: 36671759 PMCID: PMC9855693 DOI: 10.3390/biology12010067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/21/2022] [Revised: 12/20/2022] [Accepted: 12/27/2022] [Indexed: 01/03/2023]
Abstract
Acute respiratory distress syndrome (ARDS) remains an important clinical challenge with a mortality rate of 35-45%. It is being increasingly demonstrated that the improvement of outcomes requires a tailored, individualized approach to therapy, guided by a detailed understanding of each patient's pathophysiology. In patients with ARDS, disturbances in the physiological matching of alveolar ventilation (V) and pulmonary perfusion (Q) (V/Q mismatch) are a hallmark derangement. The perfusion of collapsed or consolidated lung units gives rise to intrapulmonary shunting and arterial hypoxemia, whereas the ventilation of non-perfused lung zones increases physiological dead-space, which potentially necessitates increased ventilation to avoid hypercapnia. Beyond its impact on gas exchange, V/Q mismatch is a predictor of adverse outcomes in patients with ARDS; more recently, its role in ventilation-induced lung injury and worsening lung edema has been described. Innovations in bedside imaging technologies such as electrical impedance tomography readily allow clinicians to determine the regional distributions of V and Q, as well as the adequacy of their matching, providing new insights into the phenotyping, prognostication, and clinical management of patients with ARDS. The purpose of this review is to discuss the pathophysiology, identification, consequences, and treatment of V/Q mismatch in the setting of ARDS, employing experimental data from clinical and preclinical studies as support.
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Affiliation(s)
- Douglas Slobod
- Department of Anesthesia, Critical Care and Emergency, Fondazione Istituto di Ricovero e Cura a Carattere Scientifico Ca’ Granda, Ospedale Maggiore Policlinico, 20122 Milan, Italy
- Department of Critical Care Medicine, McGill University, Montreal, QC H3A 3R1, Canada
| | - Anna Damia
- Department of Pathophysiology and Transplantation, University of Milan, 20122 Milan, Italy
| | - Marco Leali
- Department of Pathophysiology and Transplantation, University of Milan, 20122 Milan, Italy
| | - Elena Spinelli
- Department of Anesthesia, Critical Care and Emergency, Fondazione Istituto di Ricovero e Cura a Carattere Scientifico Ca’ Granda, Ospedale Maggiore Policlinico, 20122 Milan, Italy
| | - Tommaso Mauri
- Department of Anesthesia, Critical Care and Emergency, Fondazione Istituto di Ricovero e Cura a Carattere Scientifico Ca’ Granda, Ospedale Maggiore Policlinico, 20122 Milan, Italy
- Department of Pathophysiology and Transplantation, University of Milan, 20122 Milan, Italy
- Correspondence:
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Zuiki M, Kume R, Matsuura A, Mitsuno K, Kitamura K, Kanayama T, Komatsu H. Large difference between Enghoff and Bohr dead space in ventilated infants with hypoxemic respiratory failure. Pediatr Pulmonol 2021; 56:2102-2107. [PMID: 33866691 DOI: 10.1002/ppul.25403] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/09/2020] [Revised: 03/16/2021] [Accepted: 03/26/2021] [Indexed: 11/06/2022]
Abstract
BACKGROUND Ventilated neonates with hypoxemic respiratory failure (HRF) may show a ventilation-perfusion (V/Q) mismatch. OBJECTIVE To evaluate the difference between the Bohr (Vd, Bohr ) and Enghoff (Vd, Enghoff ) dead spaces in infants by using volumetric capnography based on ventilator graphics and capnograms. METHODS This study enrolled 46 ventilated infants (mean birth weight, 2239 ± 640 g; mean gestational age, 35.5 ± 3.3 weeks). We performed volumetric capnography and calculated Vd, Bohr and Vd, Enghoff when arterial blood sampling was necessary for treatment. According to the oxygenation index (OI) based on the Montreux definition of neonatal acute respiratory distress syndrome, each measurement was classified into the HRF (OI ≥ 4) or control (OI < 4) group. Then, a regression analysis was performed to evaluate the correlation between the OI and the difference between Vd, Enghoff and Vd, Bohr . RESULTS The median Vd, Enghoff /tidal volume (VT ) was significantly higher in the HRF group (0.55 [interquartile range, 0.47-0.68]) than in the control group (0.46 [0.37-0.57]). The HRF group showed a larger difference between Vd, Enghoff /VT and Vd, Bohr /VT than the control group (median, 0.22 [0.15-0.29] vs. 0.10 [0.06-0.14], respectively). Moreover, the regression analysis of the relationship between OI and Vd, Enghoff /VT - Vd, Bohr /VT showed a positive correlation (r = .60, p < .001). CONCLUSION Ventilated neonates with hypoxemic respiratory failure showed a large difference between Vd, Enghoff and Vd, Bohr , possibly reflecting a low V/Q mismatch and right-to-left shunting.
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Affiliation(s)
- Masashi Zuiki
- Department of Pediatrics, National Hospital Organization Maizuru Medical Center, Maizuru, Kyoto, Japan.,Department of Pediatrics, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kamigyo-ku, Kyoto, Japan
| | - Rika Kume
- Department of Pediatrics, National Hospital Organization Maizuru Medical Center, Maizuru, Kyoto, Japan
| | - Amane Matsuura
- Department of Pediatrics, National Hospital Organization Maizuru Medical Center, Maizuru, Kyoto, Japan
| | - Kohei Mitsuno
- Department of Pediatrics, National Hospital Organization Maizuru Medical Center, Maizuru, Kyoto, Japan
| | - Kazumasa Kitamura
- Department of Pediatrics, National Hospital Organization Maizuru Medical Center, Maizuru, Kyoto, Japan
| | - Takuyo Kanayama
- Department of Pediatrics, National Hospital Organization Maizuru Medical Center, Maizuru, Kyoto, Japan
| | - Hiroshi Komatsu
- Department of Pediatrics, National Hospital Organization Maizuru Medical Center, Maizuru, Kyoto, Japan
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Zuiki M, Naito Y, Kitamura K, Tsurukawa S, Matsumura U, Kanayama T, Komatsu H. Reduction in minute alveolar ventilation causes hypercapnia in ventilated neonates with respiratory distress. Eur J Pediatr 2021; 180:241-246. [PMID: 32748016 PMCID: PMC7397965 DOI: 10.1007/s00431-020-03761-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Revised: 07/19/2020] [Accepted: 07/28/2020] [Indexed: 11/28/2022]
Abstract
Hypercapnia occurs in ventilated infants even if tidal volume (VT) and minute ventilation (VE) are maintained. We hypothesised that increased physiological dead space (Vd,phys) caused decreased minute alveolar ventilation (VA; alveolar ventilation (VA) × respiratory rate) in well-ventilated infants with hypercapnia. We investigated the relationship between dead space and partial pressure of carbon dioxide (PaCO2) and assessed VA. Intubated infants (n = 33; mean birth weight, 2257 ± 641 g; mean gestational age, 35.0 ± 3.3 weeks) were enrolled. We performed volumetric capnography (Vcap), and calculated Vd,phys and VA when arterial blood sampling was necessary. PaCO2 was positively correlated with alveolar dead space (Vd,alv) (r = 0.54, p < 0.001) and Vd,phys (r = 0.48, p < 0.001), but not Fowler dead space (r = 0.14, p = 0.12). Normocapnia (82 measurements; 35 mmHg ≤ PaCO2 < 45 mmHg) and hypercapnia groups (57 measurements; 45 mmHg ≤ PaCO2) were classified. The hypercapnia group had higher Vd,phys (median 0.57 (IQR, 0.44-0.67)) than the normocapnia group (median Vd,phys/VT = 0.46 (IQR, 0.37-0.58)], with no difference in VT. The hypercapnia group had lower VA (123 (IQR, 87-166) ml/kg/min) than the normocapnia group (151 (IQR, 115-180) ml/kg/min), with no difference in VE.Conclusion: Reduction of VA in well-ventilated neonates induces hypercapnia, caused by an increase in Vd,phys. What is Known: • Volumetric capnography based on ventilator graphics and capnograms is a useful tool in determining physiological dead space of ventilated infants and investigating the cause of hypercapnia. What is New: • This study adds evidence that reduction in minute alveolar ventilation causes hypercapnia in ventilated neonates.
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Affiliation(s)
- Masashi Zuiki
- Department of Pediatrics, National Hospital Organization Maizuru Medical Center, 2410 Yukinaga, Maizuru, Kyoto, 625-8502, Japan.
| | - Yuki Naito
- Department of Pediatrics, National Hospital Organization Maizuru Medical Center, 2410 Yukinaga, Maizuru, Kyoto, 625-8502 Japan
| | - Kazumasa Kitamura
- Department of Pediatrics, National Hospital Organization Maizuru Medical Center, 2410 Yukinaga, Maizuru, Kyoto, 625-8502 Japan
| | - Shinichiro Tsurukawa
- Department of Pediatrics, National Hospital Organization Maizuru Medical Center, 2410 Yukinaga, Maizuru, Kyoto, 625-8502 Japan
| | - Utsuki Matsumura
- Department of Pediatrics, National Hospital Organization Maizuru Medical Center, 2410 Yukinaga, Maizuru, Kyoto, 625-8502 Japan
| | - Takuyo Kanayama
- Department of Pediatrics, National Hospital Organization Maizuru Medical Center, 2410 Yukinaga, Maizuru, Kyoto, 625-8502 Japan
| | - Hiroshi Komatsu
- Department of Pediatrics, National Hospital Organization Maizuru Medical Center, 2410 Yukinaga, Maizuru, Kyoto, 625-8502 Japan
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Capnography as a Hemodynamic Indicator: Another Heart Lung Interaction. Pediatr Crit Care Med 2020; 21:403-404. [PMID: 32251192 DOI: 10.1097/pcc.0000000000002214] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Ghita M, Copot D, Ghita M, Derom E, Ionescu C. Low Frequency Forced Oscillation Lung Function Test Can Distinguish Dynamic Tissue Non-linearity in COPD Patients. Front Physiol 2019; 10:1390. [PMID: 31803060 PMCID: PMC6877497 DOI: 10.3389/fphys.2019.01390] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Accepted: 10/25/2019] [Indexed: 01/11/2023] Open
Abstract
This paper introduces the use of low frequencies forced oscillation technique (FOT) in the presence of breathing signal. The hypothesis tested is to evaluate the sensitivity of FOT to various degrees of obstruction in COPD patients. The measurements were performed in the frequency range 0–2 Hz. The use of FOT to evaluate respiratory impedance has been broadly recognized and its complementary use next to standardized method as spirometry and body plethysmography has been well-documented. Typical use of FOT uses frequencies between 4–32 Hz and above. However, interesting information at frequencies below 4 Hz is related to viscoelastic properties of parenchyma. Structural changes in COPD affect viscoelastic properties and we propose to investigate the use of FOT at low frequencies with a fourth generation fan-based FOT device. The generator non-linearity introduced by the device is separated from the linear approximation of the impedance before evaluating the results on patients. Three groups of COPD obstruction, GOLD II, III, and IV are evaluated. We found significant differences in mechanical parameters (tissue damping, tissue elasticity, hysteresivity) and increased degrees of non-linear dynamic contributions in the impedance data with increasing degree of obstruction (p < 0.01). The results obtained suggest that the non-linear index correlates better with degrees of heterogeneity linked to COPD GOLD stages, than the currently used hysteresivity index. The protocol and method may prove useful to improve current diagnosis percentages for various COPD phenotypes.
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Affiliation(s)
- Maria Ghita
- Dynamical Systems and Control Research Group, Ghent University, Ghent, Belgium.,EEDT Core Lab on Decision and Control, Flanders Make Consortium, Ghent, Belgium
| | - Dana Copot
- Dynamical Systems and Control Research Group, Ghent University, Ghent, Belgium.,EEDT Core Lab on Decision and Control, Flanders Make Consortium, Ghent, Belgium
| | - Mihaela Ghita
- Dynamical Systems and Control Research Group, Ghent University, Ghent, Belgium.,EEDT Core Lab on Decision and Control, Flanders Make Consortium, Ghent, Belgium
| | - Eric Derom
- Department of Respiratory Diseases, Ghent University Hospital, Ghent, Belgium
| | - Clara Ionescu
- Dynamical Systems and Control Research Group, Ghent University, Ghent, Belgium.,EEDT Core Lab on Decision and Control, Flanders Make Consortium, Ghent, Belgium.,Department of Automation, Technical University of Cluj-Napoca, Cluj-Napoca, Romania
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Lyons C, Callaghan M. Uses and mechanisms of apnoeic oxygenation: a narrative review. Anaesthesia 2019; 74:497-507. [DOI: 10.1111/anae.14565] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/02/2018] [Indexed: 12/31/2022]
Affiliation(s)
- C. Lyons
- Department of Anaesthesia; Mater Misericordiae University Hospital; Dublin Ireland
| | - M. Callaghan
- Department of Anaesthesia; Galway University Hospitals; Galway Ireland
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Abstract
OBJECTIVES 1) Determine the correlation between pulmonary dead space fraction and extubation success in postoperative pediatric cardiac patients; and 2) document the natural history of pulmonary dead space fractions, dynamic compliance, and airway resistance during the first 72 hours postoperatively in postoperative pediatric cardiac patients. DESIGN A retrospective chart review. SETTING Cardiac ICU in a quaternary care free-standing children's hospital. PATIENTS Twenty-nine with balanced single ventricle physiology, 61 with two ventricle physiology. INTERVENTIONS None. MEASUREMENTS AND MAIN RESULTS We collected data for all pediatric patients undergoing congenital cardiac surgery over a 14-month period during the first 72 hours postoperatively as well as prior to extubation. Overall, patients with successful extubations had lower preextubation dead space fractions and shorter lengths of stay. Single ventricle patients had higher initial postoperative and preextubation dead space fractions. Two-ventricle physiology patients had higher extubation failure rates if the preextubation dead space fraction was greater than 0.5, whereas single ventricle patients had similar extubation failure rates whether preextubation dead space fractions were less than or equal to 0.5 or greater than 0.5. Additionally, increasing initial dead space fraction values predicted prolonged mechanical ventilation times. Airway resistance and dynamic compliance were similar between those with successful extubations and those who failed. CONCLUSIONS Initial postoperative dead space fraction correlates with the length of mechanical ventilation in two ventricle patients but not in single ventricle patients. Lower preextubation dead space fractions are a strong predictor of successful extubation in two ventricle patients after cardiac surgery, but may not be as useful in single ventricle patients.
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Dassios T, Dixon P, Hickey A, Fouzas S, Greenough A. Physiological and anatomical dead space in mechanically ventilated newborn infants. Pediatr Pulmonol 2018; 53:57-63. [PMID: 29152912 DOI: 10.1002/ppul.23918] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Accepted: 11/01/2017] [Indexed: 11/08/2022]
Abstract
OBJECTIVES To compare the anatomical (VD-Ana ) and alveolar dead space (VD-Alv ) in term and prematurely born infants and identify the clinical determinants of those indices. WORKING HYPOTHESIS VD-Ana and VD-Alv will be higher in prematurely born compared to term born infants. STUDY DESIGN Retrospective analysis of data collected at King's College Hospital NHS Foundation Trust, London, UK. PATIENT SELECTION Fifty-six infants (11 term, 45 preterm) were studied at a median age of 8 (IQR 2-33) days. METHODOLOGY VD-Ana was determined using Fowler's method of volumetric capnography. VD-Alv was determined by subtracting VD-Ana from the physiological dead space which was determined by the Bohr-Enghoff equation. VD-Ana and VD-Alv were related to body weight at the time of study. RESULTS The median VD-Ana /kg was higher in prematurely born infants [3.7 (IQR: 3.0-4.5) mL/kg] compared to term infants [2.4 (IQR: 1.9-2.9) mL/kg, adjusted P = 0.001]. The median VD-Alv /kg was not higher in prematurely born infants [0.3 (IQR: 0.1-0.5)] compared to term infants [0.1 (IQR: 0.0-0.2) mL/kg] after adjusting for differences in respiratory rate and days of ventilation (P = 0.482). VD-Ana /kg was related to postmenstrual age (r = -0.388, P < 0.001), birth weight (r = -0.397, P < 0.001), and weight at measurement (r = -0.476, P < 0.001). VD-Alv /kg was related to postmenstrual age (r = -0.254, P < 0.001), birth weight (r = -0.291, P = 0.002), and weight at measurement (r = -0.281, P = 0.003) and related to days of ventilation (r = 0.194, P = 0.044). CONCLUSIONS VD-Ana /kg and VD-Alv /kg increased with decreasing weight and gestation. VD-Alv was higher in infants that have undergone prolonged mechanical ventilation.
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Affiliation(s)
- Theodore Dassios
- Neonatal Intensive Care Centre, King's College Hospital NHS Foundation Trust, London, United Kingdom
| | - Paul Dixon
- Individual Consultant, London, United Kingdom
| | - Ann Hickey
- Neonatal Intensive Care Centre, King's College Hospital NHS Foundation Trust, London, United Kingdom
| | - Sotirios Fouzas
- Paediatric Respiratory Unit, University Hospital of Patras, Patras, Greece
| | - Anne Greenough
- Division of Asthma, Allergy and Lung Biology, MRC & Asthma UK Centre in Allergic Mechanisms of Asthma, King's College London, London, United Kingdom.,NIHR Biomedical Centre at Guy's and St Thomas NHS Foundation Trust and King's College London, United Kingdom
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Phan PA, Hahn CEW, Farmery AD. A modification of the Bohr method to determine airways deadspace for non-uniform inspired gas tensions. Physiol Meas 2017; 38:N107-N117. [PMID: 28467322 DOI: 10.1088/1361-6579/aa70c0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
BACKGROUND The Bohr method is a technique to determine airways deadspace using a tracer gas such as carbon dioxide or nitrogen. It is based on the assumption that the inspired concentration of the tracer gas is constant throughout inspiration. However, in some lung function measurement techniques where inspired concentration of the tracer gas may be required to vary, or where rapid injection of the tracer gas is made in real time, uniform inspired concentration is difficult or impossible to achieve, which leads to inaccurate estimation of deadspace using the Bohr equation. One such lung function measurement technique is the inspired sinewave technique. OBJECTIVE In this paper, we proposed a modification of the Bohr method, relaxing the requirement of absolute uniformity of tracer concentration in the inspired breath. METHOD The new method used integration of flow and concentration. A computer algorithm sought an appropriate value of deadspace to satisfy the mass balance equation for each breath. A modern gas mixing apparatus with rapid mass flow controllers was used to verify the procedure. RESULT Experiments on a tidally ventilated bench lung showed that the new method estimated dead space within 10% of the actual values whereas the traditional Bohr deadspace gave more than 50% error. CONCLUSION The new method improved the accuracy of deadspace estimation when the inspired concentration is not uniform. This improvement would lead to more accurate diagnosis and more accurate estimations of other lung parameters such as functional residual capacity and pulmonary blood flow.
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Affiliation(s)
- Phi Anh Phan
- Nuffield Division of Anaesthetics, University of Oxford, John Radcliffe Hospital, Oxford, OX3 9DU, United Kingdom
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10
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Dassios T, Kaltsogianni O, Greenough A. Determinants of pulmonary dead space in ventilated newborn infants. Early Hum Dev 2017; 108:29-32. [PMID: 28371672 DOI: 10.1016/j.earlhumdev.2017.03.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Revised: 03/17/2017] [Accepted: 03/19/2017] [Indexed: 12/15/2022]
Abstract
BACKGROUND Pulmonary dead space (VD) is an index of ventilation inhomogeneity and one of the determinants of the magnitude of tidal volume to maintain optimal blood gases. AIMS To identify the determinants of VD in ventilated newborns and to investigate differences in VD between prematurely born and term infants and those prematurely born infants who did or did not develop bronchopulmonary dysplasia (BPD). METHODS Sixty-one mechanically ventilated infants (15 term, 46 preterm) were studied at a median age of 8 (IQR 2-31) days; 32 of the preterm infants developed BPD. VD was determined from the difference between arterial and end tidal carbon dioxide (CO2) using a low dead space CO2 detector using the Bohr/Enghoff equation and was related to body weight (VD/kg) at the time of study. The time to peak tidal expiratory flow/expiratory time (TPTEF/TE) was measured during spontaneous breathing using a fixed orifice pneumotachograph. RESULTS VD/kg was related to gestational age (r=-0.285, p=0.001), birth weight (r=-0.356, p<0.001), weight (r=-0.316, p<0.001) and postmenstrual age (r=-0.205, p=0.020) at measurement, days of ventilation (r=0.322, p<0.001) and TPTEF/TE (r=-0.397, p=0.003). The median VD/kg was higher in prematurely born infants [2.3 (IQR: 1.7-3.0) ml/kg] compared to term infants [1.5 (1.3-2.1) ml/kg, (p=0.003)] and in premature infants that developed BPD [2.6 (IQR 1.8-3.4) ml/kg] compared to those who did not [1.7 (IQR 1.1-1.9) ml/kg], (p<0.001). CONCLUSIONS Numerous factors influence pulmonary dead space and thus an optimum tidal volume will differ according to the underlying demographics and respiratory status.
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Affiliation(s)
- Theodore Dassios
- Neonatal Intensive Care Centre, King's College Hospital NHS Foundation Trust, London, UK.
| | - Ourania Kaltsogianni
- Neonatal Intensive Care Centre, King's College Hospital NHS Foundation Trust, London, UK
| | - Anne Greenough
- Division of Asthma, Allergy and Lung Biology, MRC-Asthma UK Centre in Allergic Mechanisms of Asthma, King's College London, UK; National Institute for Health Research (NIHR), Biomedical Research Centre, Guy's and St Thomas' NHS Foundation Trust, King's College London, UK
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Ghodrati M, Pournajafian A, Khatibi A, Niakan M, Hemadi MH, Zamani MM. Comparing the Effect of Adaptive Support Ventilation (ASV) and Synchronized Intermittent Mandatory Ventilation (SIMV) on Respiratory Parameters in Neurosurgical ICU Patients. Anesth Pain Med 2016; 6:e40368. [PMID: 28975076 PMCID: PMC5560625 DOI: 10.5812/aapm.40368] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2016] [Revised: 08/24/2016] [Accepted: 09/21/2016] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND Various modes of mechanical ventilation have different effects on respiratory variables. Lack of patients' neuro-ventilatory coordination and increasing the work of breathing are major disadvantages in mechanically ventilated patients. OBJECTIVES This study is conducted to compare the respiratory parameters differences in Adaptive support ventilation (ASV) and synchronized intermittent mandatory ventilation (SIMV) modes in neurosurgical ICU patients. METHODS In a crossover study, patients under mechanical ventilation in neurosurgical ICU were enrolled. The patients alternatively experienced two types of ventilations for 30 minutes (adaptive support ventilation and synchronized intermittent mandatory ventilation). The respiratory parameters (tidal volume, respiratory rate, airway pressure, lung compliance, end-tidal carbon dioxide, peripheral oxygenation and respiratory dead space), hemodynamic variables, every 10 minutes and arterial blood gas analysis at the end of each 30 minutes were recorded. Results were compared and analyzed with SPSS v.19. RESULTS Sixty patients were involved in this study. In ASV mode, values including peak airway pressure (P-peak), end-tidal carbon dioxide (EtCO2), tidal volume and respiratory dead space were significantly lower than SIMV mode. Although the mean value for dynamic compliance had no significant difference in the two types of ventilation, it was better in ASV mode. CONCLUSIONS ASV mode compared with SIMV mode can lead to improve lung compliance and respiratory dead space.
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Affiliation(s)
- Mohammadreza Ghodrati
- Anesthesia Department, Firoozgar Hospital, Iran University of Medical Sciences, Tehran, Iran
| | - Alireza Pournajafian
- Anesthesia Department, Firoozgar Hospital, Iran University of Medical Sciences, Tehran, Iran
| | - Ali Khatibi
- Anesthesia Department, Firoozgar Hospital, Iran University of Medical Sciences, Tehran, Iran
| | - Mohammad Niakan
- Anesthesia Department, Rasoul Akram Hospital, Iran University of Medical Sciences, Tehran, Iran
| | - Mohammad Hosein Hemadi
- Anesthesia Department, Firoozgar Hospital, Iran University of Medical Sciences, Tehran, Iran
| | - Mohammad Mahdi Zamani
- Anesthesia Department, Firoozgar Hospital, Iran University of Medical Sciences, Tehran, Iran
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Tonelli AR, Alkukhun L, Cikach F, Ahmed M, Dweik RA. Are transcutaneous oxygen and carbon dioxide determinations of value in pulmonary arterial hypertension? Microcirculation 2016; 22:249-56. [PMID: 25641509 DOI: 10.1111/micc.12191] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2014] [Accepted: 01/26/2015] [Indexed: 11/29/2022]
Abstract
BACKGROUND We hypothesized that transcutaneous gas determinations of O2 and CO2 (TcPO2 and TcPCO2 ) are associated with the severity of PAH. METHODS In this cross-sectional study, we included consecutive patients with PAH (group 1 PH; n = 34). Transcutaneous gas determinations were compared to those of age- and gender-matched healthy controls (n = 14), nongroup 1 PH (n = 19) or patients with high estimated RVSP on echocardiography but without hemodynamic evidence of PH (n = 12). RESULTS In patients with PAH, TcPO2 , and TcPCO2 were significantly associated with PaO2 (R = 0.44, p = 0.03) and PaCO2 (R = 0.77, p < 0.001), respectively. TcPO2 /FiO2 (mean difference: -65.0 [95% CI: -121.3, -8.7]) and TcPCO2 (mean difference: -7.4 [95% CI: -11.6, -3.1]) were significantly lower in patients with PAH than healthy controls. TcPCO2 was useful in discriminating PAH patients from other individuals (AUC: 0.74 [95% CI: 0.62, 0.83]). TcPO2 /FiO2 ratio was significantly associated with mean PAP, TPG, PVR, CI, SVI, DLCO, six-minute walk distance and components of the CAMPHOR questionnaire. CONCLUSIONS Transcutaneous pressure of CO2 was lower in patients with PAH. Transcutaneous pressure of O2 over inspired fraction of O2 ratio was inversely associated with severity of disease in patients with PAH.
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Affiliation(s)
- Adriano R Tonelli
- Department of Pulmonary, Allergy and Critical Care Medicine, Respiratory Institute, Cleveland Clinic, Cleveland, Ohio, USA
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ETORPHINE-KETAMINE-MEDETOMIDINE TOTAL INTRAVENOUS ANESTHESIA IN WILD IMPALA (AEPYCEROS MELAMPUS) OF 120-MINUTE DURATION. J Zoo Wildl Med 2015; 46:755-66. [PMID: 26667531 DOI: 10.1638/2015-0052.1] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
There is a growing necessity to perform long-term anesthesia in wildlife, especially antelope. The costs and logistics of transporting wildlife to veterinary practices make surgical intervention a high-stakes operation. Thus there is a need for a field-ready total intravenous anesthesia (TIVA) infusion to maintain anesthesia in antelope. This study explored the feasibility of an etorphine-ketamine-medetomidine TIVA for field anesthesia. Ten wild-caught, adult impala ( Aepyceros melampus ) were enrolled in the study. Impala were immobilized with a standardized combination of etorphine (2 mg) and medetomidine (2.2 mg), which equated to a median (interquartile range [IQR]) etorphine and medetomidine dose of 50.1 (46.2-50.3) and 55.1 (50.8-55.4) μg/kg, respectively. Recumbency was attained in a median (IQR) time of 13.9 (12.0-16.5) min. Respiratory gas tensions, spirometry, and arterial blood gas were analyzed over a 120-min infusion. Once instrumented, the TIVA was infused as follows: etorphine at a variable rate initiated at 40 μg/kg per hour (adjusted according to intermittent deep-pain testing); ketamine and medetomidine at a fixed rate of 1.5 mg/kg per hour and 5 μg/kg per hour, respectively. The etorphine had an erratic titration to clinical effect in four impala. Arterial blood pressure and respiratory and heart rates were all within normal physiological ranges. However, arterial blood gas analysis revealed severe hypoxemia, hypercapnia, and acidosis. Oxygenation and ventilation indices were calculated and highlighted possible co-etiologies to the suspected etorphine-induced respiratory depression as the cause of the blood gas derangements. Impala recovered in the boma post atipamezole (13 mg) and naltrexone (42 mg) antagonism of medetomidine and etorphine, respectively. The etorphine-ketamine-medetomidine TIVA protocol for impala may be sufficient for field procedures of up to 120-min duration. However, hypoxemia and hypercapnia are of paramount concern and thus oxygen supplementation should be considered mandatory. Other TIVA combinations may be superior and warrant further investigation.
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Pfurtscheller K, Ring S, Beran E, Sorantin E, Zobel J, Ganster D, Avian A, Zobel G. Effect of body position on ventilation distribution during PEEP titration in a porcine model of acute lung injury using advanced respiratory monitoring and electrical impedance tomography. Intensive Care Med Exp 2015. [PMID: 26215805 PMCID: PMC4513029 DOI: 10.1186/s40635-014-0038-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
Background Lung failure after acute lung injury remains a challenge in different clinical settings. Various interventions for restoration of gas exchange have been investigated. Recruitment of collapsed alveoli by positive end expiratory pressure (PEEP) titration and optimization of ventilation-perfusion ratio by prone positioning have been extensively described in animal and clinical trials. This animal study was conducted to investigate the effects of PEEP and positioning by means of advanced respiratory monitoring including gas exchange, respiratory mechanics, volumetric capnography and electrical impedance tomography. Methods After induction of acute lung injury by oleic acid and lung lavage, 12 domestic pigs were studied in randomly assigned supine or prone position during a PEEP titration trial with maximal PEEP of 30 mbar. Results Induction of lung injury resulted in significant deterioration of oxygenation [partial pressure of arterial oxygen/inspiratory fraction of oxygen (PaO2/FiO2): p = 0.002] and ventilation [partial pressure of arterial carbon dioxide (PaCO2): p = 0.002] and elevated alveolar dead-space ratios (Valv/Vte: p = 0.003) in both groups. Differences in the prone and the supine group were significant for PaCO2 at incremental PEEP 10 and 20 and at decremental PEEP 20 (20d) and 10 (10d), for PaO2/FiO2 at PEEP 10 and 10d and for alveolar dead space at PEEP 10d. Electrical impedance tomography revealed homogenous ventilation distribution in prone position during PEEP 20, 30 and 20d. Conclusions Prone position leads to improved oxygenation and ventilation parameters in a lung injury model. Respiratory monitoring with measurement of alveolar dead space and electrical impedance tomography may visualize optimized ventilation in a PEEP titration trial.
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Affiliation(s)
- Klaus Pfurtscheller
- Pediatric Intensive Care Unit, University Children's Hospital and Medical University Graz, Auenbruggerplatz 34, 8036, Graz, Austria,
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An integrated physiology model to study regional lung damage effects and the physiologic response. Theor Biol Med Model 2014; 11:32. [PMID: 25044032 PMCID: PMC4164122 DOI: 10.1186/1742-4682-11-32] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Accepted: 07/14/2014] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND This work expands upon a previously developed exercise dynamic physiology model (DPM) with the addition of an anatomic pulmonary system in order to quantify the impact of lung damage on oxygen transport and physical performance decrement. METHODS A pulmonary model is derived with an anatomic structure based on morphometric measurements, accounting for heterogeneous ventilation and perfusion observed experimentally. The model is incorporated into an existing exercise physiology model; the combined system is validated using human exercise data. Pulmonary damage from blast, blunt trauma, and chemical injury is quantified in the model based on lung fluid infiltration (edema) which reduces oxygen delivery to the blood. The pulmonary damage component is derived and calibrated based on published animal experiments; scaling laws are used to predict the human response to lung injury in terms of physical performance decrement. RESULTS The augmented dynamic physiology model (DPM) accurately predicted the human response to hypoxia, altitude, and exercise observed experimentally. The pulmonary damage parameters (shunt and diffusing capacity reduction) were fit to experimental animal data obtained in blast, blunt trauma, and chemical damage studies which link lung damage to lung weight change; the model is able to predict the reduced oxygen delivery in damage conditions. The model accurately estimates physical performance reduction with pulmonary damage. CONCLUSIONS We have developed a physiologically-based mathematical model to predict performance decrement endpoints in the presence of thoracic damage; simulations can be extended to estimate human performance and escape in extreme situations.
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Lack of functional information explains the poor performance of ‘clot load scores’ at predicting outcome in acute pulmonary embolism. Respir Physiol Neurobiol 2014; 190:1-13. [DOI: 10.1016/j.resp.2013.09.005] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2013] [Revised: 09/01/2013] [Accepted: 09/10/2013] [Indexed: 11/20/2022]
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Corrections of Enghoff's dead space formula for shunt effects still overestimate Bohr's dead space. Respir Physiol Neurobiol 2013; 189:99-105. [PMID: 23827851 DOI: 10.1016/j.resp.2013.06.020] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2013] [Revised: 05/19/2013] [Accepted: 06/24/2013] [Indexed: 12/28/2022]
Abstract
Dead space ratio is determined using Enghoff's modification (VD(B-E)/VT) of Bohr's formula (VD(Bohr)/VT) in which arterial is used as a surrogate of alveolar PCO₂. In presence of intrapulmonary shunt Enghoff's approach overestimates dead space. In 40 lung-lavaged pigs we evaluated the Kuwabara's and Niklason's algorithms to correct for shunt effects and hypothesized that corrected VD(B-E)/VT should provide similar values as VD(Bohr)/VT. We analyzed 396 volumetric capnograms and arterial and mixed-venous blood samples to calculate VD(Bohr)/VT and VD(B-E)/VT. Thereafter, we corrected the latter for shunt effects using Kuwabara's (K) VD(B-E)/VT and Niklason's (N) VD(B-E)/VT algorithms. Uncorrected VD(B-E)/VT (mean ± SD of 0.70 ± 0.10) overestimated VD(Bohr)/VT (0.59 ± 0.12) (p < 0.05), over the entire range of shunts. Mean (K) VD(B-E)/VT was significantly higher than VD(Bohr)/VT (0.67 ± 0.08, bias -0.085, limits of agreement -0.232 to 0.085; p < 0.05) whereas (N)VD(B-E)/VT showed a better correction for shunt effects (0.64 ± 0.09, bias 0.048, limits of agreement -0.168 to 0.072; p < 0.05). Neither Kuwabara's nor Niklason's algorithms were able to correct Enghoff's dead space formula for shunt effects.
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Yamauchi H, Ito S, Sasano H, Azami T, Fisher J, Sobue K. Dependence of the gradient between arterial and end-tidal P(CO(2)) on the fraction of inspired oxygen. Br J Anaesth 2011; 107:631-5. [PMID: 21700613 DOI: 10.1093/bja/aer171] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
BACKGROUND End-tidal P(CO(2)) (Pe'(CO(2))) is routinely used in the clinical assessment of the adequacy of ventilation because it provides an estimate of Pa(CO(2)). How well Pe'(CO(2)) reflects Pa(CO(2)) depends on the gradient between them, expressed as ΔPa-e'(CO(2)). The major determinant of ΔPa-e'(CO(2)) is alveolar dead space (Vd(alv)). The fraction of inspired O(2) (Fi(O(2))) is not thought to substantially affect ΔPa-e'(CO(2)) in anaesthetized patients. We hypothesized that a high Fi(O(2)) may indeed increase ΔPa-e'(CO(2)) by preferentially vasodilating well-perfused alveoli, resulting in the redistribution of blood flow to these alveoli from poorly perfused alveoli and an increase in Vd(alv). We therefore investigated the effects of changes in Fi(O(2)) on ΔPa-e'(CO(2)) and Vd(alv). METHODS With Institutional Review Board approval and informed consent, we studied 20 ASA I-II supine patients undergoing elective lower abdominal surgery under combined general and epidural anaesthesia. At constant levels of ventilation, Fi(O(2)) levels of 0.21, 0.33, 0.5, 0.75, and 0.97 were applied in a random order and ΔPa-e'(CO(2)) and Vd(alv) were calculated. RESULTS The ΔPa-e'(CO(2)) values were, in order of ascending Fi(O(2)), {mean [standard error of the mean (SEM)]} 0.13 (0.04), 0.28 (0.08), 0.29 (0.09), 0.44 (0.11), and 0.53 (0.09) kPa. The corresponding values of Vd(alv) were 25.5, 33.8, 35.8, 48.9, and 47.4 ml. Each successive hyperoxic level showed a significant increase in ΔPa-e'(CO(2)) except between the 0.33-0.5 and 0.75-0.97 Fi(O(2)) levels. CONCLUSIONS These data demonstrate that ΔPa-e'(CO(2)), in anaesthetized patients depends on Fi(O(2)).
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Affiliation(s)
- H Yamauchi
- TOYOTA-KAI Medical Corporation KARIYA TOYOTA General Hospital, Kariya, Aichi, Japan.
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Sinha P, Flower O, Soni N. Deadspace ventilation: a waste of breath! Intensive Care Med 2011; 37:735-46. [DOI: 10.1007/s00134-011-2194-4] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2010] [Accepted: 02/06/2011] [Indexed: 10/18/2022]
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Wang A, Mahfouf M, Mills GH, Panoutsos G, Linkens DA, Goode K, Kwok HF, Denaï M. Intelligent model-based advisory system for the management of ventilated intensive care patients: Hybrid blood gas patient model. COMPUTER METHODS AND PROGRAMS IN BIOMEDICINE 2010; 99:195-207. [PMID: 19864039 DOI: 10.1016/j.cmpb.2009.09.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2009] [Revised: 08/04/2009] [Accepted: 09/18/2009] [Indexed: 05/28/2023]
Abstract
Arterial blood gas (ABG) analyses are essential for assessing the acid-base status and guiding the adjustment of mechanical ventilation in critically ill patients. Conventional ABG sampling requires repeated arterial punctures or the insertion of an arterial catheter causing pain, haemorrhage and thrombosis to the patients. Less invasive and non-invasive blood gas analysers, with a technology still in transition, have offered some promise in the recent years. SOPAVent (Simulation of Patients under Artificial Ventilation) is a five compartment blood gas model which captures the basic features of respiratory physiology and gas exchange in the human lungs. It uses ventilator settings and routinely monitored physiological parameters as inputs to produce steady-state estimates of the patient's ABG. This paper overviews the original SOPAVent model and presents an improved data-driven hybrid model that is patient-specific and gives continuous and totally non-invasive ABG predictions. The model has been comprehensively tested in simulations and validated using recorded measurements of ABG and ventilator parameters from ICU patients.
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Affiliation(s)
- A Wang
- Process Automation, ABB Limited, Eaton Socon, Cambridgeshire, UK.
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van der Plas MN, Reesink HJ, Roos CM, van Steenwijk RP, Kloek JJ, Bresser P. Pulmonary Endarterectomy Improves Dyspnea by the Relief of Dead Space Ventilation. Ann Thorac Surg 2010; 89:347-52. [DOI: 10.1016/j.athoracsur.2009.08.001] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/29/2009] [Revised: 07/31/2009] [Accepted: 08/03/2009] [Indexed: 10/19/2022]
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Predicting dead space ventilation in critically ill patients using clinically available data. Crit Care Med 2010; 38:288-91. [PMID: 19789453 DOI: 10.1097/ccm.0b013e3181b42e13] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVE To develop and validate an equation to predict dead space to tidal volume ratio (Vd/Vt) from clinically available data in critically ill mechanically ventilated patients. DESIGN Prospective, observational study using a convenience sample of patients whose arterial blood gas and respiratory gas exchange had been measured with indirect calorimetry. SETTING Medical and surgical critical care units of a university medical center. PATIENTS Adult, mechanically ventilated patients at rest with Fio2 < or =0.60 and no air leaks who had recent arterial blood gas recordings and end-tidal carbon dioxide concentration monitoring. INTERVENTIONS Observational only. MEASUREMENTS AND MAIN RESULTS Indirect calorimetry was used to determine carbon dioxide production and expired minute ventilation in 135 patients. Tidal volume and respiratory rate were recorded from the ventilator. End tidal carbon dioxide concentration, body temperature, arterial carbon dioxide partial pressure (Paco2), and other clinical data were recorded. Vd/Vt was calculated using the Enghoff modification of the Bohr equation (Paco2 - PECO2/Paco2). Regression analysis was then used to construct a predictive equation for Vd/Vt using the clinical data: Vd/Vt = 0.32 + 0.0106 (Paco2 - ETCO2) + 0.003 (RR) + 0.0015 (age) (R = 0.67). A second group of 50 patients was measured using the same protocol and their data were used to validate the equations developed from the original 135 patients. The equation was found to be unbiased and precise. CONCLUSIONS Vd/Vt is predictable from clinically available data. Whether this predicted quantity is valuable clinically must still be determined.
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Enekvist BJ, Luttropp HH, Johansson A. The effect of increased apparatus dead space and tidal volumes on carbon dioxide elimination and oxygen saturations in a low-flow anesthesia system. J Clin Anesth 2008; 20:170-4. [DOI: 10.1016/j.jclinane.2007.09.013] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2006] [Revised: 09/04/2007] [Accepted: 09/21/2007] [Indexed: 10/22/2022]
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Tang Y, Turner MJ, Baker AB. Systematic errors and susceptibility to noise of four methods for calculating anatomical dead space from the CO 2 expirogram. Br J Anaesth 2007; 98:828-34. [PMID: 17470845 DOI: 10.1093/bja/aem090] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND Anatomical dead space is usually measured using the Fowler equal area method. Alternative methods include the Hatch, Cumming, and Bowes methods, in which first, second, and third order polynomials, respectively, fitted to an expired CO2 volume vs expired volume curve, intercept the x-axis at the anatomical dead space. This study assessed systematic errors and susceptibility to noise of the Fowler, Hatch, Cumming, and Bowes dead spaces calculated over 40-80% of the CO2 expirogram. METHODS Simulated CO2 expirograms with 220 ml anatomical dead space and varying alveolar plateau slopes were generated digitally and zero-mean Gaussian noise added. CO2 expirograms were recorded in 10 anaesthetized human subjects. Anatomical dead space was calculated by the Fowler, Hatch, Cumming, and Bowes methods. RESULTS The Fowler, Hatch, Cumming, and Bowes methods displayed systematic biases of -1.8%, 13.2%, 2.4%, and -1.3%, respectively, at a normalized simulated alveolar plateau slope of 1.6 litre(-1). At a noise level of 0.0066 vol/vol, the standard deviations of recovered simulated dead spaces were 70.6, 1.8, 2.4, and 3.7 ml, respectively. The Hatch, Cumming, and Bowes methods applied to human expirograms differed significantly from that of Fowler by 13, -4, and -11 ml, respectively. In the human study, the Hatch and Cumming methods yielded the lowest intra-individual dead space variability. CONCLUSIONS The Fowler method shows greatest susceptibility to measurement noise and the Hatch method exhibits the largest systematic error. The Cumming method, which exhibits both low bias and low noise susceptibility, is preferred for estimating anatomical dead space from CO2 expirograms.
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Affiliation(s)
- Y Tang
- Department of Anaesthetics, Royal Prince Alfred Hospital, University of Sydney, NSW 2050, Sydney, Australia.
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Soro M, García-Pérez ML, Belda FJ, Ferrandis R, Aguilar G, Tusman G, Gramuntell F. Effects of prone position on alveolar dead space and gas exchange during general anaesthesia in surgery of long duration. Eur J Anaesthesiol 2007; 24:431-7. [PMID: 17156508 DOI: 10.1017/s0265021506001888] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
BACKGROUND AND OBJECTIVE We investigated the effects of prone position on respiratory dead space and gas exchange in 14 anaesthetized healthy patients undergoing elective posterior spinal surgery of more than 3 h of duration. METHODS The patients received a total intravenous anaesthetic with propofol/remifentanil/cisatracurium. They were ventilated at a tidal volume of 8-10 mL kg(-1), zero positive end-expiratory pressure and an inspired oxygen fraction of 0.4. Physiological, airway and alveolar dead spaces were calculated by analysis of the volumetric capnography waveform. Measurements were made in supine position (20 min after the beginning of mechanical ventilation) and 30, 120 and 180 min after turning to prone position. RESULTS We found that the alveolar dead space/tidal volume ratio did not change. PaO(2)/F(i)O(2) increased, although not statistically significantly. Dynamic compliance was reduced due to a reduction in tidal volume and an increase in plateau pressure. CONCLUSIONS Patients undergoing surgery in prone position for a duration of 3 h under general anaesthesia including muscle relaxation and mechanical ventilation without positive end-expiratory pressure have stable haemodynamics and no significant changes in the alveolar dead space to tidal volume ratio. Oxygenation tended to improve.
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Affiliation(s)
- M Soro
- Hospital Clínico Universitario, Department of Anaesthesia and Critical Care, Valencia, Spain
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Yem JS, Turner MJ, Baker AB, Young IH, Crawford ABH. A tidally breathing model of ventilation, perfusion and volume in normal and diseased lungs †. Br J Anaesth 2006; 97:718-31. [PMID: 16926169 DOI: 10.1093/bja/ael216] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND To simulate the short-term dynamics of soluble gas exchange (e.g. CO2 rebreathing), model structure, ventilation-perfusion (VA/Q) and ventilation-volume (VA/VA) parameters must be selected correctly. Some diseases affect mainly the VA/Q distribution while others affect both VA/Q and VA/VA distributions. Results from the multiple inert gas elimination technique (MIGET) and multiple breath nitrogen washout (MBNW) can be used to select VA/Q and VA/VA parameters, but no method exists for combining VA/Q and VA/VA parameters in a multicompartment lung model. METHODS We define a tidally breathing lung model containing shunt and up to eight alveolar compartments. Quantitative and qualitative understanding of the diseases is used to reduce the number of model compartments to achieve a unique solution. The reduced model is fitted simultaneously to inert gas retentions calculated from published VA/Q distributions and normalized MBNWs obtained from similar subjects. Normal lungs and representative cases of emphysema and embolism are studied. RESULTS The normal, emphysematous and embolism models simplify to one, three and two alveolar compartments, respectively. CONCLUSIONS The models reproduce their respective MIGET and MBNW patient results well, and predict disease-specific steady-state and dynamic soluble and insoluble gas responses.
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Affiliation(s)
- J S Yem
- Department of Anaesthetics, The University of Sydney, Royal Prince Alfred Hospital Missenden Road, Camperdown, NSW 2050, Australia
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Yem JS, Turner MJ, Baker AB. Sources of error in partial rebreathing pulmonary blood flow measurements in lungs with emphysema and pulmonary embolism. Br J Anaesth 2006; 97:732-41. [PMID: 16926170 DOI: 10.1093/bja/ael214] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
BACKGROUND Studies of the accuracy of partial rebreathing measurements of pulmonary blood flow (PBF) in patients with abnormal lungs have not fully explained the sources of error. METHODS We used computer models of emphysema and pulmonary embolism incorporating both ventilation-perfusion (V/Q) and ventilation-volume (V/V) heterogeneity to investigate systematic errors in partial rebreathing PBF measurements. We studied (i) errors produced under usual conditions, (ii) effects of recirculation, (iii) effects of alveolar-proximal airway and alveolar-capillary PCO2 and VCO2 differences, (iv) effects of alveolar V/Q inhomogeneity and (v) effects of rebreathing time. RESULTS In the pulmonary embolism model the systematic error is only acceptable (<10%) when the simulated PBF is low (2-3 litre min(-1)). In the emphysema model PBF is underestimated by more than 20% at all cardiac outputs studied. Four sources of systematic errors were found. (i) Alveolar-proximal airway PCO2 gradients and flux differences between the proximal airway and alveolar compartments contribute most to the systematic error. (ii) V/Q inhomogeneity causes PCO2 gradients between the alveolar compartments and pulmonary capillary blood, and between pulmonary capillary compartments. (iii) Rebreathing times are inadequate in the presence of V/V mismatch. (iv) The apparent effect of venous blood recirculation is small in emphysema but significant in pulmonary embolism. CONCLUSIONS We conclude that PBF cannot be measured accurately by partial rebreathing in lungs with emphysema or embolism. Systematic errors are caused mainly by errors in end-tidal PCO2 values.
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Affiliation(s)
- J S Yem
- Department of Anaesthetics, The University of Sydney, Royal Prince Alfred Hospital Missenden Road, Camperdown, NSW 2050, Australia
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Tang Y, Turner MJ, Baker AB. Effects of lung time constant, gas analyser delay and rise time on measurements of respiratory dead-space. Physiol Meas 2005; 26:1103-14. [PMID: 16311457 DOI: 10.1088/0967-3334/26/6/019] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
This study evaluated effects of mechanical time constants (tau(m)) of the respiratory system, delays between flow and CO(2) partial pressure (P(CO)(2)) signals and rise time of the CO(2) analyser on dead-space measurements. A computer model simulated low alveolar dead-space, high alveolar dead-space, 0.2 <or= tau(m) <or= 3.6 s and varying ventilation-perfusion ratios (V/Q). CO(2) expirograms were recorded from the model under each condition and from 22 anaesthetized intubated patients. P(CO)(2) signals were shifted with respect to flow to produce varying time delays and anatomic and physiological dead-spaces were calculated. The CO(2) analyser was simulated as a critically damped second-order system with 10-90% rise times of 25-400 ms. The error in measured dead-space increases approximately 2.5% per 10 ms signal delay for normal lungs (tau(m) = 1 s), but has low sensitivity (0.58% per 10 ms) to the rise time of the CO(2) analyser. Sensitivity of physiological dead-space, but not anatomic dead-space to delay is decreased in high alveolar dead-space and abnormal V/Q distribution. Shorter tau(m) increase the error sensitivity of both physiological and anatomic dead-spaces to both delay and rise time. P(CO)(2) and flow should be well synchronized, particularly when tau(m) are short, to avoid dead-space errors.
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Affiliation(s)
- Yongquan Tang
- Department of Anaesthetics, University of Sydney, Royal Prince Alfred Hospital, NSW 2050, Sydney, Australia.
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