Effective Pulmonary Blood Flow Research Articles

Collaterals in congenital heart disease: when and how to treat?

The development of collateral circulation is not that rare in patients with congenital heart defects. These collaterals can affect cardiovascular hemodynamics and cause systemic arterial desaturation, which arises the question whether these should be closed. To date, few if any reports have been published on the therapeutic management of collaterals in adult patients with congenital heart disease in heart failure (HF). The focus of this article is to provide a pragmatic approach in the assessment of collateral circulation of the patient with HF. By considering the underlying hemodynamics and overall effects of the collateral circulation, we aim to provide a practical tool useful in clinical decision making. The paper highlights mainly the systemic venous to systemic venous collaterals, systemic venous to pulmonary venous (or pulmonary venous atrium) collaterals, and pulmonary arterio-venous malformations. Systemic venous anomalies are frequent and reported in 20% to 40% of patients who underwent Glenn or Fontan procedure. A reduction in effective pulmonary blood flow, coupled with increasing oxygen demands with growth, as well as a pressure difference between the higher pressure caval venous system and lower pressure atria (so called decompressing collaterals) are potential causes of collateral formation. Whether angiogenesis de novo or reappearance of embryological venous channels is responsible for collateral formation remains to be elucidated.

Can Isolated Discordant Atrioventricular Connections Survive Without Interatrial or Interventricular Shunt?

Clinical presentation of isolated discordant atrioventricular connections is akin to transposition of the great arteries. In the absence of a significant intracardiac shunt, profound cyanosis is expected at birth. We report one such 5-month-old infant who had only mild cyanosis. The left-sided tricuspid valve straddled the interventricular septum with a closed interventricular communication, a type of "Double Outlet Left Atrium with three atrioventricular valves," which provided the necessary "left to right" shunt while severe regurgitation through the straddling part and a patent ductus arteriosus provided the effective pulmonary blood flow.

Capnodynamics - noninvasive cardiac output and mixed venous oxygen saturation monitoring in children.

Hemodynamic monitoring in children is challenging for many reasons. Technical limitations in combination with insufficient validation against reference methods, makes reliable monitoring systems difficult to establish. Since recent studies have highlighted perioperative cardiovascular stability as an important factor for patient outcome in pediatrics, the need for accurate hemodynamic monitoring methods in children is obvious. The development of mathematical processing of fast response mainstream capnography signals, has allowed for the development of capnodynamic hemodynamic monitoring. By inducing small changes in ventilation in intubated and mechanically ventilated patients, fluctuations in alveolar carbon dioxide are created. The subsequent changes in carbon dioxide elimination can be used to calculate the blood flow participating in gas exchange, i.e., effective pulmonary blood flow which equals the non-shunted pulmonary blood flow. Cardiac output can then be estimated and continuously monitored in a breath-by-breath fashion without the need for additional equipment, training, or calibration. In addition, the method allows for mixed venous oxygen saturation (SvO2) monitoring, without pulmonary artery catheterization. The current review will discuss the capnodyamic method and its application and limitation as well as future potential development and functions in pediatric patients.

Capnodynamic monitoring of lung volume and blood flow in response to increased positive end-expiratory pressure in moderate to severe COVID-19 pneumonia: an observational study

BackgroundThe optimal level of positive end-expiratory pressure (PEEP) during mechanical ventilation for COVID-19 pneumonia remains debated and should ideally be guided by responses in both lung volume and perfusion. Capnodynamic monitoring allows both end-expiratory lung volume ({text{EELV}}_{{{text{CO}}_{2} }}) and effective pulmonary blood flow (EPBF) to be determined at the bedside with ongoing ventilation.MethodsPatients with COVID-19-related moderate to severe respiratory failure underwent capnodynamic monitoring of {text{EELV}}_{{{text{CO}}_{2} }} and EPBF during a step increase in PEEP by 50% above the baseline (PEEPlow to PEEPhigh). The primary outcome was a > 20 mm Hg increase in arterial oxygen tension to inspired fraction of oxygen (P/F) ratio to define responders versus non-responders. Secondary outcomes included changes in physiological dead space and correlations with independently determined recruited lung volume and the recruitment-to-inflation ratio at an instantaneous, single breath decrease in PEEP. Mixed factor ANOVA for group mean differences and correlations by Pearson’s correlation coefficient are reported including their 95% confidence intervals.ResultsOf 27 patients studied, 15 responders increased the P/F ratio by 55 [24–86] mm Hg compared to 12 non-responders (p < 0.01) as PEEPlow (11 ± 2.7 cm H2O) was increased to PEEPhigh (18 ± 3.0 cm H2O). The {text{EELV}}_{{{text{CO}}_{2} }} was 461 [82–839] ml less in responders at PEEPlow (p = 0.02) but not statistically different between groups at PEEPhigh. Responders increased both {text{EELV}}_{{{text{CO}}_{2} }} and EPBF at PEEPhigh (r = 0.56 [0.18–0.83], p = 0.03). In contrast, non-responders demonstrated a negative correlation (r = − 0.65 [− 0.12 to − 0.89], p = 0.02) with increased lung volume associated with decreased pulmonary perfusion. Decreased (− 0.06 [− 0.02 to − 0.09] %, p < 0.01) dead space was observed in responders. The change in {text{EELV}}_{{{text{CO}}_{2} }} correlated with both the recruited lung volume (r = 0.85 [0.69–0.93], p < 0.01) and the recruitment-to-inflation ratio (r = 0.87 [0.74–0.94], p < 0.01).ConclusionsIn mechanically ventilated patients with moderate to severe COVID-19 respiratory failure, improved oxygenation in response to increased PEEP was associated with increased end-expiratory lung volume and pulmonary perfusion. The change in end-expiratory lung volume was positively correlated with the lung volume recruited and the recruitment-to-inflation ratio. This study demonstrates the feasibility of capnodynamic monitoring to assess physiological responses to PEEP at the bedside to facilitate an individualised setting of PEEP.Trial registration: NCT05082168 (18th October 2021).

Mechanical support for the failing single ventricle after Fontan

Mechanical support for the failing single ventricle after Fontan

Monitoring Expired CO2 Kinetics to Individualize Lung-Protective Ventilation in Patients With the Acute Respiratory Distress Syndrome.

Mechanical ventilation (MV) is a lifesaving supportive intervention in the management of acute respiratory distress syndrome (ARDS), buying time while the primary precipitating cause is being corrected. However, MV can contribute to a worsening of the primary lung injury, known as ventilation-induced lung injury (VILI), which could have an important impact on outcome. The ARDS lung is characterized by diffuse and heterogeneous lung damage and is particularly prone to suffer the consequences of an excessive mechanical stress imposed by higher airway pressures and volumes during MV. Of major concern is cyclic overdistension, affecting those lung segments receiving a proportionally higher tidal volume in an overall reduced lung volume. Theoretically, healthier lung regions are submitted to a larger stress and cyclic deformation and thus at high risk for developing VILI. Clinicians have difficulties in detecting VILI, particularly cyclic overdistension at the bedside, since routine monitoring of gas exchange and lung mechanics are relatively insensitive to this mechanism of VILI. Expired CO2 kinetics integrates relevant pathophysiological information of high interest for monitoring. CO2 is produced by cell metabolism in large daily quantities. After diffusing to tissue capillaries, CO2 is transported first by the venous and then by pulmonary circulation to the lung. Thereafter diffusing from capillaries to lung alveoli, it is finally convectively transported by lung ventilation for its elimination to the atmosphere. Modern readily clinically available sensor technology integrates information related to pulmonary ventilation, perfusion, and gas exchange from the single analysis of expired CO2 kinetics measured at the airway opening. Current volumetric capnography (VCap), the representation of the volume of expired CO2 in one single breath, informs about pulmonary perfusion, end-expiratory lung volume, dead space, and pulmonary ventilation inhomogeneities, all intimately related to cyclic overdistension during MV. Additionally, the recently described capnodynamic method provides the possibility to continuously measure the end-expiratory lung volume and effective pulmonary blood flow. All this information is accessed non-invasively and breath-by-breath helping clinicians to personalize ventilatory settings at the bedside and minimize overdistension and cyclic deformation of lung tissue.

Evaluation of Optimization of Pulmonary and Systemic Blood Flow in Children after Bidirectional Cavapulmonary Anastomosis

In patients after bidirectional cavapulmonary anastomosis, blood flow through the superior vena cava (SVC), providing effective pulmonary blood flow, is the most important factor influencing blood oxygen saturation. Blood flow through the inferior vena cava recirculates into the systemic bloodstream. The study of the ratio of these flows will provide better understanding of the physiology of blood circulation after anastomosis and determine systemic oxygen saturation of blood and optimal time to perform surgery.&#x0D; &#x0D; The aim. To determine volumetric blood flow in the SVC, calculate pulmonary to systemic blood flow ratio in children after bidirectional cavapulmonary anastomosis, and evaluate its contribution to cardiac output and oxygen saturation in systemic blood flow.&#x0D; Materials and methods. In the period from January 2010 to June 2021, 51 patients with congenital heart defects with depleted pulmonary blood flow underwent hemodynamic correction at the National Amosov Institute of Cardiovascular Surgery of the National Academy of Medical Sciences of Ukraine. There were 29 male patients (57%) and 22 female patients (43%). The mean age of the patients at the time of the surgery was 34 ± 18.2 months (2 to 120 months), the mean age of patients at the time of examination was 43.5 ± 28.4 months (12 to 134 months). The main method of diagnosis in determining the defect and assessing the immediate and long-term results was echocardiographic examination and probing of the heart cavities. To evaluate the optimization of pulmonary/systemic blood flow we used equations obtained using the Fick method. Pulmonary to systemic blood flow ratio was calculated separately for 35 patients. Among the examined 35 patients, 18 children were older than 2.5 years, so all the examined patients were conveniently divided into 2 age groups: I group (n = 17) up to 2.5 years, II group (n = 18) older than 2.5 years to assess the contribution of SVC to the systemic circulation depending on age.&#x0D; Results. Pulmonary to systemic blood flow ratio was calculated for 35 patients Qp/Qs = (82% – 66%) / (97% – 66%) = 0.52. The calculated cardiac index according to echocardiography was 4.0 ± 0.85 L/min/m2 which corresponds to the SVC saturation (r = 0.60, p = &lt;0.001). The flow in the superior vena cava = 2.08 L/min/m2. There was a very interesting trend towards decrease in the average rate of systemic saturation in patients after bidirectional cavapulmonary anastomosis depending on age and duration of surgery. Thus, in 17 patients of group I, the calculated Qp/Qs was (84% – 67%) / (97% – 67%) = 0.57. In patients of group II, the average systemic oxygen saturation was 78 ± 2% (from 65% to 81%). Calculated Qp/Qs for 18 patients of group II = (78% – 66%) / (97% – 66%) = 0.39, which indicates a decrease in pulmonary to systemic ratio with the growth of the child.&#x0D; Decreased systemic saturation after bidirectional cavapulmonary anastomosis in patients with increasing age and body surface area is associated with a decrease in the proportional flow from the superior vena cava. Therefore, in our clinical material, we confirmed the phenomenon of change in pulmonary to systemic ratio depending on age, which was described by Salim et al. according to a study conducted on healthy babies.&#x0D; Conclusions. The contribution of SVC flow to total cardiac output after bidirectional cavapulmonary anastomosis is directly associated with the patient’s age and gradually decreases in older patients, as indicated by a decrease in systemic saturation, so the clinical effect of bidirectional cavapulmonary anastomosis may be significantly better when performing surgery in early childhood.

Pediatric Extracorporeal Cardiopulmonary Resuscitation ELSO Guidelines.

Pediatric Extracorporeal Cardiopulmonary Resuscitation ELSO Guidelines.

A Continuous Noninvasive Method to Assess Mixed Venous Oxygen Saturation: A Proof-of-Concept Study in Pigs.

Mixed venous oxygen saturation (Svo2) is important when evaluating the balance between oxygen delivery and whole-body oxygen consumption. Monitoring Svo2 has so far required blood samples from a pulmonary artery catheter. By combining volumetric capnography, for measurement of effective pulmonary blood flow, with the Fick principle for oxygen consumption, we have developed a continuous noninvasive method, capnodynamic Svo2, for assessment of Svo2. The objective of this study was to validate this new technique against the gold standard cardiac output (CO)-oximetry Svo2 measurement of blood samples obtained from a pulmonary artery catheter and to assess the potential influence of intrapulmonary shunting. Eight anesthetized mechanically ventilated domestic-breed piglets of both sexes (median weight 23.9 kg) were exposed to a series of interventions intended to reduce as well as increase Svo2. Simultaneous recordings of capnodynamic and CO-oximetry Svo2 as well as shunt fraction, using the Berggren formula, were performed throughout the protocol. Agreement of absolute values for capnodynamic and CO-oximetry Svo2 and the ability for capnodynamic Svo2 to detect change were assessed using Bland-Altman plot and concordance analysis. Overall bias for capnodynamic versus CO-oximetry Svo2 was -1 percentage point (limits of agreement -13 to +11 percentage points), a mean percentage error of 22%, and a concordance rate of 100%. Shunt fraction varied between 13% at baseline and 22% at the end of the study and was associated with only minor alterations in agreement between the tested methods. In the current experimental setting, capnodynamic assessment of Svo2 generates absolute values very close to the reference method CO-oximetry and is associated with 100% trending ability.

Superior Cavopulmonary Connection: Its Physiology, Limitations, and Anesthetic Implications.

The superior cavopulmonary connection (SCPC) or "bidirectional Glenn" is an integral, intermediate stage in palliation of single ventricle patients to the Fontan procedure. The procedure, normally performed at 3 to 6 months of life, increases effective pulmonary blood flow and reduces the ventricular volume load in patients with single ventricle (parallel circulation) physiology. While the SCPC, with or without additional sources of pulmonary blood flow, cannot be considered a long-term palliation strategy, there are a subset of patients who require SCPC palliation for a longer interval than the typical patient. In this article, we will review the physiology of SCPC, the consequences of prolonged SCPC palliation, and modes of failure. We will also discuss strategies to augment pulmonary blood flow in the presence of an SCPC. The anesthetic considerations in SCPC patients will also be discussed, as these patients may present for noncardiac surgery from infancy to adulthood.

Performance of a capnodynamic method estimating cardiac output during respiratory failure - before and after lung recruitment

Respiratory failure may cause hemodynamic instability with strain on the right ventricle. The capnodynamic method continuously calculates cardiac output (CO) based on effective pulmonary blood flow (COEPBF) and could provide CO monitoring complementary to mechanical ventilation during surgery and intensive care. The aim of the current study was to evaluate the ability of a revised capnodynamic method, based on short expiratory holds (COEPBFexp), to estimate CO during acute respiratory failure (LI) with high shunt fractions before and after compliance-based lung recruitment. Ten pigs were submitted to lung lavage and subsequent ventilator-induced lung injury. COEPBFexp, without any shunt correction, was compared to a reference method for CO, an ultrasonic flow probe placed around the pulmonary artery trunk (COTS) at (1) baseline in healthy lungs with PEEP 5 cmH2O (HLP5), (2) LI with PEEP 5 cmH2O (LIP5) and (3) LI after lung recruitment and PEEP adjustment (LIPadj). CO changes were enforced during LIP5 and LIPadj to estimate trending. LI resulted in changes in shunt fraction from 0.1 (0.03) to 0.36 (0.1) and restored to 0.09 (0.04) after recruitment manoeuvre. Bias (levels of agreement) and percentage error between COEPBFexp and COTS changed from 0.5 (− 0.5 to 1.5) L/min and 30% at HLP5 to − 0.6 (− 2.3 to 1.1) L/min and 39% during LIP5 and finally 1.1 (− 0.3 to 2.5) L/min and 38% at LIPadj. Concordance during CO changes improved from 87 to 100% after lung recruitment and PEEP adjustment. COEPBFexp could possibly be used for continuous CO monitoring and trending in hemodynamically unstable patients with increased shunt and after recruitment manoeuvre.

Capnodynamic determination of cardiac output in hypoxia-induced pulmonary hypertension in pigs

Effective pulmonary blood flow (COEPBF) has recently been validated for its ability to measure cardiac output (CO) in children and animals. This study compared COEPBF with the Fick method (COFick) and CO measurements using an invasive pulmonary artery flow probe (COTS). The aim of the study was to validate COEPBF against these reference methods in a porcine model of hypoxia-induced selective pulmonary hypertension. Ten anaesthetised mechanically ventilated piglets (median weight 23.9 kg) were exposed to a hypoxic gas mixture inducing selective pulmonary hypertension. Pulmonary hypertension was subsequently reversed with inhaled nitric oxide. Simultaneous recordings of COEPBF, COFick, and COTS were performed throughout the protocol and examined for agreement and trending ability. Overall bias (Bland-Altman) between COEPBF and COTS was 0.2 L min-1 (limits of agreement-0.5 and+0.9 L min-1) with a mean percentage error of 25%. Overall bias between COEPBF and COFick was-0.1 L min-1 (limits of agreement-0.9 and+0.6 L min-1) and a mean percentage error of 25%. The concordance rate was 86% for COEPBF when compared with COTS using a 10% exclusion zone. Estimation of CO with COEPBF results in values very close to the gold standard reference methods COFick and COTS. COEPBF appears to be an accurate tool for monitoring absolute values and changes in CO during hypoxia-induced pulmonary hypertension and inhaled nitric oxide treatment.

Validation of capnodynamic determination of cardiac output by measuring effective pulmonary blood flow: a study in anaesthetised children and piglets

BackgroundEffective pulmonary blood flow (COEPBF) has recently been validated as a technique for determining cardiac output (CO) in animals of varying sizes. The primary aim of our study was to investigate this new technique in paediatric surgical patients, compared with suprasternal two-dimensional Doppler (COSSD). MethodsA total of 15 children undergoing cleft lip/palate surgery were investigated. Before the start of surgery, manoeuvres that were anticipated to reduce (increase in PEEP from 3 to 10 cm H2O) and increase (atropine) CO were undertaken. A study in mechanically ventilated piglets was also undertaken under general anaesthesia, measuring COEPBF and pulmonary artery (COTS) flow by ultrasonic probe as the comparator. Bias (Bland−Altman plots) and limits of agreement were assessed for effective pulmonary blood flow and COSSD or COTS. ResultsIn paediatric patients (median age 8.5 months), overall bias was −8.1 (limits of agreement −82 to +66) ml kg−1 min−1, with a mean percentage error of 48% and a concordance rate of 64%. In the piglet model, overall bias was −1 (−36 to +38) ml kg−1 min−1, with a mean percentage error of 31% and a concordance rate of 95%. ConclusionsUnder controlled experimental conditions, COEPBF is associated with excellent agreement and good trending ability when compared with the gold standard COTS. In the paediatric clinical setting, COEPBF performs well; by contrast, COSSD, an operator- and anatomy-dependent technology, appears less reliable than COEPBF.

Performance of a capnodynamic method estimating effective pulmonary blood flow during transient and sustained hypercapnia

The capnodynamic method is a minimally invasive method continuously calculating effective pulmonary blood flow (COEPBF), equivalent to cardiac output when intra pulmonary shunt flow is low. The capnodynamic equation joined with a ventilator pattern containing cyclic reoccurring expiratory holds, provides breath to breath hemodynamic monitoring in the anesthetized patient. Its performance however, might be affected by changes in the mixed venous content of carbon dioxide (CvCO2). The aim of the current study was to evaluate COEPBF during rapid measurable changes in mixed venous carbon dioxide partial pressure (PvCO2) following ischemia–reperfusion and during sustained hypercapnia in a porcine model. Sixteen pigs were submitted to either ischemia–reperfusion (n = 8) after the release of an aortic balloon inflated during 30 min or to prolonged hypercapnia (n = 8) induced by adding an instrumental dead space. Reference cardiac output (CO) was measured by an ultrasonic flow probe placed around the pulmonary artery trunk (COTS). Hemodynamic measurements were obtained at baseline, end of ischemia and during the first 5 min of reperfusion as well as during prolonged hypercapnia at high and low CO states. Ischemia–reperfusion resulted in large changes in PvCO2, hemodynamics and lactate. Bias (limits of agreement) was 0.7 (−0.4 to 1.8) L/min with a mean error of 28% at baseline. COEPBF was impaired during reperfusion but agreement was restored within 5 min. During prolonged hypercapnia, agreement remained good during changes in CO. The mean polar angle was −4.19° (−8.8° to 0.42°). Capnodynamic COEPBF is affected but recovers rapidly after transient large changes in PvCO2 and preserves good agreement and trending ability during states of prolonged hypercapnia at different levels of CO.

A modified breathing pattern improves the performance of a continuous capnodynamic method for estimation of effective pulmonary blood flow.

In a previous study a new capnodynamic method for estimation of effective pulmonary blood flow (COEPBF) presented a good trending ability but a poor agreement with a reference cardiac output (CO) measurement at high levels of PEEP. In this study we aimed at evaluating the agreement and trending ability of a modified COEPBF algorithm that uses expiratory instead of inspiratory holds during CO and ventilatory manipulations. COEPBF was evaluated in a porcine model at different PEEP levels, tidal volumes and CO manipulations (N=8). An ultrasonic flow probe placed around the pulmonary trunk was used for CO measurement. We tested the COEPBF algorithm using a modified breathing pattern that introduces cyclic end-expiratory time pauses. The subsequent changes in mean alveolar fraction of carbon dioxide were integrated into a capnodynamic equation and effective pulmonary blood flow, i.e. non-shunted CO, was calculated continuously breath by breath. The overall agreement between COEPBF and the reference method during all interventions was good with bias (limits of agreement) 0.05 (-1.1 to 1.2) L/min and percentage error of 36%. The overall trending ability as assessed by the four-quadrant and the polar plot methodology was high with a concordance rate of 93 and 94% respectively. The mean polar angle was 0.4 (95% CI -3.7 to 4.5)°. A ventilatory pattern recurrently introducing end-expiratory pauses maintains a good agreement between COEPBF and the reference CO method while preserving its trending ability during CO and ventilatory alterations.

A new approach to detect early lung functional impairment in very light smokers

PurposeThe aim of our study is to investigate if lung carbon monoxide diffusing capacity (DLCO) measured during effort is able to detect early respiratory functional impairment. MethodsWe enrolled 25 very light smokers and 20 healthy non smokers. Subjects underwent plethysmography, DLCO (single breath technique) and calculated effective pulmonary blood flow (Qc) by rebreathing method. During exercise by cycle ergometer (duration 10±2min; recovery 11±3min) DLCO and Qc were calculated at 25% and 50% of theoretical maximum workload. ResultsAt baseline lung function and Qc did not differ between groups. DLCO and DLCO/Qc measured during exercise were significantly greater in non smokers (p<0.001); Qc was not statistically different. In very light smokers, DLCO, DLCO/Qc measured during exercise significantly correlated with the number of pack years (r=−0.60 p<0.001; r=−0.58 p<0.05; r=−0.55 p<0.05, respectively). ConclusionsIn very light smokers there is lung function impairment and our data show that DLCO during exercise may reveal this underlying early damage.

Airway and alveolar nitric oxide production, lung function, and pulmonary blood flow in sickle cell disease.

Children with sickle cell disease (SCD) often have obstructive lung function abnormalities which could be due to asthma or increased pulmonary blood volume; it is important to determine the underlying mechanism to direct appropriate treatment. In asthmatics, exhaled nitric oxide (FeNO) is elevated. FeNO, however, can also be raised due to increased alveolar production. Our aim, therefore, was to determine if airway or alveolar NO production differed between SCD children and ethnic and age-matched controls. Lung function, airway NO flux and alveolar NO production, and effective pulmonary blood flow were assessed in 18 SCD children and 18 ethnic and age-matched controls. The SCD children compared to the controls had a higher respiratory system resistance (P = 0.0008), alveolar NO production (P = 0.0224), and pulmonary blood flow (P < 0.0001), but not airway NO flux. There was no significant correlation between FeNO and respiratory system resistance in either group, but in the SCD children, there were correlations between alveolar NO production (P = 0.0006) and concentration (P < 0.0001) and pulmonary blood flow. Airway NO flux was not elevated in the SCD children nor correlated with airways obstruction, suggesting that airways obstruction, at least in some SCD children, is not due to asthma.

Capnodynamic assessment of effective lung volume during cardiac output manipulations in a porcine model.

A capnodynamic calculation of effective pulmonary blood flow includes a lung volume factor (ELV) that has to be estimated to solve the mathematical equation. In previous studies ELV correlated to reference methods for functional residual capacity (FRC). The aim was to evaluate the stability of ELV during significant manipulations of cardiac output (CO) and assess the agreement for absolute values and trending capacity during PEEP changes at different lung conditions. Ten pigs were included. Alterations of alveolar carbon dioxide were induced by cyclic reoccurring inspiratory holds. The Sulphur hexafluoride technique for FRC measurements was used as reference. Cardiac output was altered by preload reduction and inotropic stimulation at PEEP 5 and 12cmH2O both in normal lung conditions and after repeated lung lavages. ELV at baseline PEEP 5 was [mean (SD)], 810 (163)mL and decreased to 400 (42)mL after lavage. ELV was not significantly affected by CO alterations within the same PEEP level. In relation to FRC the overall bias (limits of agreement) was -35 (-271 to 201)mL, and percentage error 36%. A small difference between ELV and FRC was seen at PEEP 5cmH2O before lavage and at PEEP 12cmH2O after lavage. ELV trending capability between PEEP steps, showed a concordance rate of 100%. ELV was closely related to FRC and remained stable during significant changes in CO. The trending capability was excellent both before and after surfactant depletion.

A novel continuous capnodynamic method for cardiac output assessment in a porcine model of lung lavage.

We have evaluated a new method for continuous monitoring of effective pulmonary blood flow (COEPBF ), i.e. cardiac output (CO) minus intra-pulmonary shunt, during mechanical ventilation. The method has shown good trending ability during severe hemodynamic challenges in a porcine model with intact lungs. In this study, we further evaluate the COEPBF method in a model of lung lavage. COEPBF was compared to a reference method for CO during hemodynamic and PEEP alterations, 5 and 12cmH2 O, before and after repeated lung lavages in 10 anaesthetised pigs. Bland-Altman, four-quadrant and polar plot methodologies were used to determine agreement and trending ability. After lung lavage at PEEP 5cmH2 O, the ratio of arterial oxygen partial pressure related to inspired fraction of oxygen significantly decreased. The mean difference (limits of agreement) between methods changed from 0.2 (-1.1 to 1.5) to -0.9 (-3.6 to 1.9)l/min and percentage error increased from 34% to 70%. Trending ability remained good according to the four-quadrant plot (concordance rate 94%), whereas mean angular bias increased from 4° to -16° when using the polar plot methodology. Both agreement and precision of COEPBF were impaired in relation to CO when the shunt fraction was increased after lavage at PEEP 5cmH2 O. However, trending ability remained good as assessed by the four-quadrant plot, whereas the mean polar angle, calculated by the polar plot, was wide.

Novel continuous capnodynamic method for cardiac output assessment during mechanical ventilation

It is important to be able to accurately monitor cardiac output (CO) during high-risk surgery and in critically ill patients. The invasiveness of the pulmonary artery catheter (PAC) limits its use, and therefore, new minimally invasive methods for CO monitoring are needed. A potential method is estimation of CO from endogenous carbon dioxide measurements, using a differentiated Fick's principle to determine effective pulmonary blood flow (EPBF). In this study, we aimed to validate a novel capnodynamic method (COEPBF) in a wide range of clinically relevant haemodynamic conditions. COEPBF was studied in 10 pigs during changes in preload, afterload, CO increase, and bleeding. An ultrasonic flow probe around the pulmonary artery was used as reference method of CO determination. CO was also measured using a PAC thermodilution technique (COPAC). CO and other haemodynamic data were recorded before and during each intervention. Accuracy and precision and also the ability to track changes in CO were determined using Bland-Altman, four-quadrant plot and polar plot analysis. COEPBF and COPAC showed equally good agreement, with a tendency to overestimate CO (bias 0.2 and 0.3 litre min(-1), respectively). The overall percentage error was 47% for COEPBF and 49% for COPAC. The concordance for tracking CO changes was 97 and 95% for COEPBF and COPAC, respectively, with an exclusion zone of 15% and radial limits of ±30°. COEPBF showed reliable trending abilities, equivalent to COPAC. COEPBF and COPAC also showed low bias but high percentage errors. Further studies in animal models of lung injury and in high-risk surgery patients are warranted.