The effects of oxygen induced pulmonary vasoconstriction on bedside measurement of pulmonary gas exchange (original) (raw)
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Journal of Cardiothoracic Surgery, 2011
Background Measurement of vital capacity (VC) by spirometry is the most widely used technique for lung function evaluation, however, this form of assessment is costly and further investigation of other reliable methods at lower cost is necessary. Objective: To analyze the correlation between direct vital capacity measured with ventilometer and with incentive inspirometer in patients in pre and post cardiac surgery. Methodology Cross-sectional comparative study with patients undergoing cardiac surgery. Respiratory parameters were evaluated through the measurement of VC performed by ventilometer and inspirometer. To analyze data normality the Kolmogorov-Smirnov test was applied, for correlation the Pearson correlation coefficient was used and for comparison of variables in pre and post operative period Student's t test was adopted. We established a level of ignificance of 5%. Data was presented as an average, standard deviation and relative frequency when needed. The significance ...
European Journal of Anaesthesiology, 2014
Editor's key points † The clinical gold standard technique for cardiac output (CO) monitoring involves thermodilution via a pulmonary artery catheter. † This and other less invasive techniques suffer from several disadvantages. † The authors have developed a capnodynamic method of non-invasive estimation of CO. † They now compare the performance of their technique with that of ultrasonic and thermodilution techniques in 10 pigs.
Journal of Evolution of Medical and Dental Sciences, 2016
BACKGROUND One Lung Anaesthesia (OLA) is used in thoracic surgery for prevention of spillage of blood and pus into the healthy lung to facilitate surgical exposure. During OLA since the collapsed lung continues to be perfused, there will be large right to left shunt which leads to hypoxaemia. Objective-To find out the potential factors that reduce arterial oxygenation (PaO2) during OLA and to find out the possibility of predicting the PaO2 during OLA based on these potential factors. MATERIALS AND METHODS A cross-sectional study was conducted among 34 patients who came for lung or non-lung surgery in the CMC Vellore during a period of 2 years. All the ASA grade I and II patients who needed OLA were included. Preoperative PaO2, TLV PaO2, PaO2 at 10 mins. and 25 mins. after starting OLA were assessed. Alteration in PaO2 related to side, smoking and gender was measured by mean±SD and multiple linear regression was done to assess the independent contribution of each of 9 predictors with OLA PaO2 at 25 min. RESULTS Three factors were of significance in predicting the PaO2 which were gender, side of surgery and smoking. Women had significantly (p=0.04) higher PaO2 as compared to men. Similarly, left side had significantly (p = 0.01) higher PaO2 as compared to right side and non-smokers had significantly lower PaO2 compared to smokers (p = 0.03). A predictive equation was constructed for PaO2 on OLV at 25 mins. by using the significant predictors in this study. CONCLUSION Our study was an attempt to show that it is possible to predict preoperatively the patient who is likely to suffer from hypoxaemia during OLA. The ability to predict the subsequent arterial oxygenation allows the anaesthetists/surgeons to assess and rationalise risk/benefits regarding the use of OLA during thoracic surgery and permits more controlled intraoperative management of oxygenation.
Use of noninvasive gas exchange to track pulmonary vascular responses to exercise in heart failure
Clinical medicine insights. Circulatory, respiratory and pulmonary medicine, 2013
We determined whether a non-invasive gas exchange based estimate of pulmonary vascular (PV) capacitance [PVCAP = stroke volume (SV) × pulmonary arterial pressure (Ppa)] (GXCAP) tracked the PV response to exercise in heart-failure (HF) patients. Pulmonary wedge pressure (Ppw), Ppa, PV resistance (PVR), and gas exchange were measured simultaneously during cycle exercise in 42 HF patients undergoing right-heart catheterization. During exercise, PETCO2 and VE/VCO2 were related to each other (r = -0.93, P < 0.01) and similarly related to mean Ppa (mPpa) (r = -0.39 and 0.36; P < 0.05); PETCO2 was subsequently used as a metric of mPpa. Oxygen pulse (O2 pulse) tracked the SV response to exercise (r = 0.91, P < 0.01). Thus, GXCAP was calculated as O2 pulse × PETCO2. During exercise, invasively determined PVCAP and non-invasive GXCAP were related (r = 0.86, P < 0.01), and GXCAP correlated with mPpa and PVR (r = -0.46 and -0.54; P < 0.01). In conclusion, noninvasive gas exchange...
Bedside monitoring of lung volume available for gas exchange
Intensive Care Medicine Experimental, 2021
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.
End-tidal to arterial PCO2 ratio: a bedside meter of the overall gas exchanger performance
Intensive Care Medicine Experimental, 2021
Background The physiological dead space is a strong indicator of severity and outcome of acute respiratory distress syndrome (ARDS). The “ideal” alveolar PCO 2 , in equilibrium with pulmonary capillary PCO 2 , is a central concept in the physiological dead space measurement. As it cannot be measured, it is surrogated by arterial PCO 2 which, unfortunately, may be far higher than ideal alveolar PCO 2 , when the right-to-left venous admixture is present. The “ideal” alveolar PCO 2 equals the end-tidal PCO 2 (P ET CO 2 ) only in absence of alveolar dead space. Therefore, in the perfect gas exchanger (alveolar dead space = 0, venous admixture = 0), the P ET CO 2 /PaCO 2 is 1, as P ET CO 2 , P A CO 2 and PaCO 2 are equal. Our aim is to investigate if and at which extent the P ET CO 2 /PaCO 2 , a comprehensive meter of the “gas exchanger” performance, is related to the anatomo physiological characteristics in ARDS. Results We retrospectively studied 200 patients with ARDS. The source was ...
Hypoxic pulmonary vasoconstriction and pulmonary gas exchange in normal man
Respiration Physiology, 1987
Blood gases, hemodynamics and ventilation were measured in 7 healthy volunteers at baseline while breathing room air (FIo2 0.21), during hypoxia (Fio2 0.125, 15 min) and after nifedipine 20 mg sublingually at FIo2 0.21 (45 min) and at Fro2 0.125 (15 min). Distributions of ventilation-perfusion ratios (VA/t)) were determined, using the multiple inert gas elimination technique, at baseline, during hypoxia, and again during hypoxia after nifedipine intake. Hypoxia was associated with an average increase in pulmonary vascular resistances by 1049/o,which was partially inhibited by nifedipine. The inert gas data showed a mild deterioration in the distribution of ~rA/(~ ratios during hypoxia. However, when blood flow and ventilation were constrained to the baseline normoxic values in the distributions recovered during hypoxia ('normalization procedure') a slight improvement in ~rA/(~ matching could be evidenced, which was blunted during hypoxia after nifedipine. This was interpreted as the functional effect of hypoxic pulmonary vasoconstriction (HPV). Using the 'normalized' distributions, we computed the relationship between the decrease in compartmental blood flow that occurred during hypoxia and the corresponding alveolar Po2, and calculated the gain due to HPV feedback using equations of the control theory. The contribution of HPV to the stability of compartmental VA/t~ was greatest for alveolar Po2 values around 60 mm Hg, but at best the feedback had only a moderate efficiency.
Critical care (London, England), 2006
It is possible that taking a static pressure-volume (PV) measurement could durably affect oxygenation and thus interfere with early evaluation of a therapeutic intervention delivered just after that measurement. The aim of the present study was to investigate the effects over time of a single static PV measurement on gas exchange and haemodynamics; the PV measurements were taken using a super syringe and by using the constant flow method in patients with acute respiratory distress syndrome. We conducted a prospective, randomized and controlled interventional study in an intensive care unit. The study was conducted in 17 patients with early acute respiratory distress syndrome ventilated with a tidal volume of 6.9 +/- 1.0 ml/kg, a plateau pressure of 27 +/- 7 cmH2O and a positive end-expiratory pressure [PEEP] of 10 cmH2O. They were all evaluated for 1 hour after each of the following two measurements was taken and during a control period (in a randomized order): generation of a PV cu...