Perioperative Continuous Noninvasive Cardiac Output Monitoring in Cardiac Surgery Patients by a Novel Capnodynamic Method.

OBJECTIVES: To test the clinical performance of a novel continuous noninvasive cardiac output (CO) monitoring based on expired carbon dioxide kinetics in cardiac surgery patients. DESIGN: A prospective feasibility pragmatic clinical study. SETTING: A single-center, large community hospital. PARTICIPANTS: Thirty-two patients undergoing cardiac surgery were studied during the intraoperative (before cardiopulmonary bypass) and postoperative (in the intensive care unit before extubation) periods. INTERVENTIONS: CO was measured simultaneously by the continuous capnodynamic method and by transpulmonary thermodilution during changes in the patient's hemodynamic and/or respiratory conditions. MEASUREMENTS AND MAIN RESULTS: The current recommended comparative statistics for CO measurement methods were analyzed, including bias, precision, and percentage error obtained from Bland-Altman analysis, and concordance between methods obtained from the four-quadrant plot analysis to evaluate the trending ability. Bias ± limits of agreement and percentage error were -0.6 (-1.9 to +0.8; 95% CI of 3.73-5.25) L/min and 31% (n = 147 measurements) for the intraoperative period, -0.8 (-2.4 to +0.9; 95% CI of 3.03-5.21) L/min and 41% (n = 66) for the postoperative period, and -0.6 (-2.1 to +0.8; 95% CI of 3.74-5.00) L/min and 34% (n = 213) for the pooled data. The trending analysis obtained a concordance of 82% (n = 65) for the intraoperative and 71% (n = 24) for the early postoperative periods. Aggregation of both data sets gave a concordance of 79% (n = 89). CONCLUSIONS: The continuous capnodynamic method was reliable and in good agreement with the reference method, and had an accuracy and trending ability good enough to make it a possible future alternative for hemodynamic monitoring in the studied population of elective adult cardiac surgery patients.

Sequential lateral positioning as a new lung recruitment maneuver: an exploratory study in early mechanically ventilated Covid-19 ARDS patients.

BACKGROUND: A sequential change in body position from supine-to-both lateral positions under constant ventilatory settings could be used as a postural recruitment maneuver in case of acute respiratory distress syndrome (ARDS), provided that sufficient positive end-expiratory pressure (PEEP) prevents derecruitment. This study aims to evaluate the feasibility and physiological effects of a sequential postural recruitment maneuver in early mechanically ventilated COVID-19 ARDS patients. METHODS: A cohort of 15 patients receiving lung-protective mechanical ventilation in volume-controlled with PEEP based on recruitability were prospectively enrolled and evaluated in five sequentially applied positions for 30 min each: Supine-baseline; Lateral-1st side; 2nd Supine; Lateral-2nd side; Supine-final. PEEP level was selected using the recruitment-to-inflation ratio (R/I ratio) based on which patients received PEEP 12 cmH2O for R/I ratio ≤ 0.5 or PEEP 15 cmH2O for R/I ratio > 0.5. At the end of each period, we measured respiratory mechanics, arterial blood gases, lung ultrasound aeration, end-expiratory lung impedance (EELI), and regional distribution of ventilation and perfusion using electric impedance tomography (EIT). RESULTS: Comparing supine baseline and final, respiratory compliance (29 ± 9 vs 32 ± 8 mL/cmH2O; p < 0.01) and PaO2/FIO2 ratio (138 ± 36 vs 164 ± 46 mmHg; p < 0.01) increased, while driving pressure (13 ± 2 vs 11 ± 2 cmH2O; p < 0.01) and lung ultrasound consolidation score decreased [5 (4-5) vs 2 (1-4); p < 0.01]. EELI decreased ventrally (218 ± 205 mL; p < 0.01) and increased dorsally (192 ± 475 mL; p = 0.02), while regional compliance increased in both ventral (11.5 ± 0.7 vs 12.9 ± 0.8 mL/cmH2O; p < 0.01) and dorsal regions (17.1 ± 1.8 vs 18.8 ± 1.8 mL/cmH2O; p < 0.01). Dorsal distribution of perfusion increased (64.8 ± 7.3% vs 66.3 ± 7.2%; p = 0.01). CONCLUSIONS: Without increasing airway pressure, a sequential postural recruitment maneuver improves global and regional respiratory mechanics and gas exchange along with a redistribution of EELI from ventral to dorsal lung areas and less consolidation. Trial registration ClinicalTrials.gov, NCT04475068. Registered 17 July 2020, https://clinicaltrials.gov/ct2/show/NCT04475068.

Positive end-expiratory pressure individualization guided by continuous end-expiratory lung volume monitoring during laparoscopic surgery.

To determine whether end-expiratory lung volume measured with volumetric capnography (EELVCO2) can individualize positive end-expiratory pressure (PEEP) setting during laparoscopic surgery. We studied patients undergoing laparoscopic surgery subjected to Fowler (F-group; n = 20) or Trendelenburg (T-group; n = 20) positions. EELVCO2 was measured at 0° supine (baseline), during capnoperitoneum (CP) at 0° supine, during CP with Fowler (head up + 20°) or Trendelenburg (head down - 30°) positions and after CP back to 0° supine. PEEP was adjusted to preserve baseline EELVCO2 during and after CP. Baseline EELVCO2 was statistically similar to predicted FRC in both groups. At supine and CP, EELVCO2 decreased from baseline values in F-group [median and IQR 2079 (768) to 1545 (725) mL; p = 0.0001] and in T-group [2164 (789) to 1870 (940) mL; p = 0.0001]. Change in body position maintained EELVCO2 unchanged in both groups. PEEP adjustments from 5.6 (1.1) to 10.0 (2.5) cmH2O in the F-group (p = 0.0001) and from 5.6 (0.9) to 10.0 (2.6) cmH2O in T-group (p = 0.0001) were necessary to reach baseline EELVCO2 values. EELVCO2 increased close to baseline with PEEP in the F-group [1984 (600) mL; p = 0.073] and in the T-group [2175 (703) mL; p = 0.167]. After capnoperitoneum and back to 0° supine, PEEP needed to maintain EELVCO2 was similar to baseline PEEP in F-group [5.9 (1.8) cmH2O; p = 0.179] but slightly higher in the T-group [6.5 (2.2) cmH2O; p = 0.006]. Those new PEEP values gave EELVCO2 similar to baseline in the F-group [2039 (980) mL; p = 0.370] and in the T-group [2150 (715) mL; p = 0.881]. Breath-by-breath noninvasive EELVCO2 detected changes in lung volume induced by capnoperitoneum and body position and was useful to individualize the level of PEEP during laparoscopy.Trial registry: Clinicaltrials.gov NCT03693352. Protocol started 1st October 2018.

Multimodal non-invasive monitoring to apply an open lung approach strategy in morbidly obese patients during bariatric surgery.

To evaluate the use of non-invasive variables for monitoring an open-lung approach (OLA) strategy in bariatric surgery. Twelve morbidly obese patients undergoing bariatric surgery received a baseline protective ventilation with 8 cmH2O of positive-end expiratory pressure (PEEP). Then, the OLA strategy was applied consisting in lung recruitment followed by a decremental PEEP trial, from 20 to 8 cmH2O, in steps of 2 cmH2O to find the lung's closing pressure. Baseline ventilation was then resumed setting open lung PEEP (OL-PEEP) at 2 cmH2O above this pressure. The multimodal non-invasive variables used for monitoring OLA consisted in pulse oximetry (SpO2), respiratory compliance (Crs), end-expiratory lung volume measured by a capnodynamic method (EELVCO2), and esophageal manometry. OL-PEEP was detected at 15.9 ± 1.7 cmH2O corresponding to a positive end-expiratory transpulmonary pressure (PL,ee) of 0.9 ± 1.1 cmH2O. ROC analysis showed that SpO2 was more accurate (AUC 0.92, IC95% 0.87-0.97) than Crs (AUC 0.76, IC95% 0.87-0.97) and EELVCO2 (AUC 0.73, IC95% 0.64-0.82) to detect the lung's closing pressure according to the change of PL,ee from positive to negative values. Compared to baseline ventilation with 8 cmH2O of PEEP, OLA increased EELVCO2 (1309 ± 517 vs. 2177 ± 679 mL) and decreased driving pressure (18.3 ± 2.2 vs. 10.1 ± 1.7 cmH2O), estimated shunt (17.7 ± 3.4 vs. 4.2 ± 1.4%), lung strain (0.39 ± 0.07 vs. 0.22 ± 0.06) and lung elastance (28.4 ± 5.8 vs. 15.3 ± 4.3 cmH2O/L), respectively; all p < 0.0001. The OLA strategy can be monitored using noninvasive variables during bariatric surgery. This strategy decreased lung strain, elastance and driving pressure compared with standard protective ventilatory settings.Clinical trial number NTC03694665.

Dead space analysis at different levels of positive end-expiratory pressure in acute respiratory distress syndrome patients.

PURPOSE: To analyze the effects of positive end-expiratory pressure (PEEP) on Bohr's dead space (VDBohr/VT) in patients with acute respiratory distress syndrome (ARDS). MATERIAL AND METHODS: Fourteen ARDS patients under lung protective ventilation settings were submitted to 4 different levels of PEEP (0, 6, 10, 16 cmH2O). Respiratory mechanics, hemodynamics and volumetric capnography were recorded at each protocol step. RESULTS: Two groups of patients responded differently to PEEP when comparing baseline with 16-PEEP: those in which driving pressure increased > 15% (∆P˃15%, n = 7, p = .016) and those in which the change was ≤15% (∆P≤15%, n = 7, p = .700). VDBohr/VT was higher in ∆P≤15% than in ∆P≤15% patients at baseline ventilation [0.58 (0.49-0.60) vs 0.46 (0.43-0.46) p = .018], at 0-PEEP [0.50 (0.47-0.54) vs 0.41 (0.40-0.43) p = .012], at 6-PEEP [0.55 (0.49-0.57) vs 0.44 (0.42-0.45) p = .008], at 10-PEEP [0.59 (0.51-0.59) vs 0.45 (0.44-0.46) p = .006] and at 16-PEEP [0.61 (0.56-0.65) vs 0.47 (0.45-0.48) p = .001]. We found a good correlation between ∆P and VDBohr/VT only in the ∆P˃15% group (r = 0.74, p < .001). CONCLUSIONS: Increases in PEEP result in higher VDBohr/VT only when associated with an increase in driving pressure.

Doppler images of intra-pulmonary shunt within atelectasis in anesthetized children.

BACKGROUND: Doppler images of pulmonary vessels in pulmonary diseases associated with subpleural consolidations have been described. Color Doppler easily identifies such vessels within consolidations while spectral Doppler analysis allows the differentiation between pulmonary and bronchial arteries. Thus, Doppler helps in diagnosing the nature of consolidations. To our knowledge, Doppler analysis of pulmonary vessels within anesthesia-induced atelectasis has never been described before. The aim of this case series is to demonstrate the ability of lung ultrasound to detect the shunting of blood within atelectatic lung areas in anesthetized children. FINDINGS: Three anesthetized and mechanically ventilated children were scanned in the supine position using a high-resolution linear probe of 6-12 MHz. Once subpleural consolidations were detected in the most dependent posterior lung regions, the probe was rotated such that its long axis followed the intercostal space. In this oblique position, color Doppler mapping was performed to detect blood flow within the consolidation. Thereafter, pulsed waved spectral Doppler was applied in the previously identified vessels during a short expiratory pause, which prevented interferences from respiratory motion. Different flow patterns were identified which corresponded to both, pulmonary and bronchial vessels. Finally, a lung recruitment maneuver was performed which leads to the complete resolution of the aforementioned consolidation thereby confirming the pathophysiological entity of anesthesia-induced atelectasis. CONCLUSIONS: Lung ultrasound is a non-invasive imaging tool that not only enables the diagnosis of anesthesia-induced atelectasis in pediatric patients but also analysis of shunting blood within this consolidation.

Feasibility of (68)Ga-labeled Siglec-9 peptide for the imaging of acute lung inflammation: a pilot study in a porcine model of acute respiratory distress syndrome.

There is an unmet need for noninvasive, specific and quantitative imaging of inherent inflammatory activity. Vascular adhesion protein-1 (VAP-1) translocates to the luminal surface of endothelial cells upon inflammatory challenge. We hypothesized that in a porcine model of acute respiratory distress syndrome (ARDS), positron emission tomography (PET) with sialic acid-binding immunoglobulin-like lectin 9 (Siglec-9) based imaging agent targeting VAP-1 would allow quantification of regional pulmonary inflammation. ARDS was induced by lung lavages and injurious mechanical ventilation. Hemodynamics, respiratory system compliance (Crs) and blood gases were monitored. Dynamic examination using [(15)O]water PET-CT (10 min) was followed by dynamic (90 min) and whole-body examination using VAP-1 targeting (68)Ga-labeled 1,4,7,10-tetraaza cyclododecane-1,4,7-tris-acetic acid-10-ethylene glycol-conjugated Siglec-9 motif peptide ([(68)Ga]Ga-DOTA-Siglec-9). The animals received an anti-VAP-1 antibody for post-mortem immunohistochemistry assay of VAP-1 receptors. Tissue samples were collected post-mortem for the radioactivity uptake, histology and immunohistochemistry assessment. Marked reduction of oxygenation and Crs, and higher degree of inflammation were observed in ARDS animals. [(68)Ga]Ga-DOTA-Siglec-9 PET showed significant uptake in lungs, kidneys and urinary bladder. Normalization of the net uptake rate (Ki) for the tissue perfusion resulted in 4-fold higher uptake rate of [(68)Ga]Ga-DOTA-Siglec-9 in the ARDS lungs. Immunohistochemistry showed positive VAP-1 signal in the injured lungs. Detection of pulmonary inflammation associated with a porcine model of ARDS was possible with [(68)Ga]Ga-DOTA-Siglec-9 PET when using kinetic modeling and normalization for tissue perfusion.

Real-time images of tidal recruitment using lung ultrasound.

BACKGROUND: Ventilator-induced lung injury is a form of mechanical damage leading to a pulmonary inflammatory response related to the use of mechanical ventilation enhanced by the presence of atelectasis. One proposed mechanism of this injury is the repetitive opening and closing of collapsed alveoli and small airways within these atelectatic areas-a phenomenon called tidal recruitment. The presence of tidal recruitment is difficult to detect, even with high-resolution images of the lungs like CT scan. The purpose of this article is to give evidence of tidal recruitment by lung ultrasound. FINDINGS: A standard lung ultrasound inspection detected lung zones of atelectasis in mechanically ventilated patients. With a linear probe placed in the intercostal oblique position. We observed tidal recruitment within atelectasis as an improvement in aeration at the end of inspiration followed by the re-collapse at the end of expiration. This mechanism disappeared after the performance of a lung recruitment maneuver. CONCLUSIONS: Lung ultrasound was helpful in detecting the presence of atelectasis and tidal recruitment and in confirming their resolution after a lung recruitment maneuver.

Volumetric capnography: the time has come.

PURPOSE OF REVIEW: Volumetric capnography (VCap) measures the kinetics of carbon dioxide (CO2) elimination on a breath-by-breath basis. A volumetric capnogram contains extensive physiological information about metabolic production, circulatory transport and CO2 elimination within the lungs. VCap is also the best clinical tool to measure dead spaces allowing a detailed analysis of the functional components of each tidal volume, thereby providing clinically useful hints about the lung's efficiency of gas exchange. Difficulties in its bedside measurement, oversimplifications of its interpretation along with prevailing misconceptions regarding dead space analysis have, however, limited its adoption as a routine tool for monitoring mechanically ventilated patients. RECENT FINDINGS: Improvements in CO2 measuring technologies and more advanced algorithms for faster and more accurate analysis of volumetric capnograms have increased our physiological understanding and thus the clinical usefulness of VCap. The recently validated VCap-based method for estimating alveolar partial pressure of CO2 provided a breakthrough for a fully noninvasive breath-by-breath measurement of physiological dead space. SUMMARY: Recent advances in VCap and our improved understanding of its clinical implications may help in overcoming the known limitations and reluctances to include expired CO2 kinetics and dead space analysis in routine bedside monitoring. It is about time to start using this powerful monitoring tool to support decision making in the intensive care environment.

Reference values for volumetric capnography-derived non-invasive parameters in healthy individuals.

The aim of this study was to determine typical values for non-invasive volumetric capnography (VCap) parameters for healthy volunteers and anesthetized individuals. VCap was obtained by a capnograph connected to the airway opening. We prospectively studied 33 healthy volunteers 32 ± 6 years of age weighing 70 ± 13 kg at a height of 171 ± 11 cm in the supine position. Data from these volunteers were compared with a cohort of similar healthy anesthetized patients ventilated with the following settings: tidal volume (VT) of 6-8 mL/kg, respiratory rate 10-15 bpm, PEEP of 5-6 cmH2O and FiO2 of 0.5. Volunteers showed better clearance of CO2 compared to anesthetized patients as indicated by (median and interquartile range): (1) an increased elimination of CO2 per mL of VT of 0.028 (0.005) in volunteers versus 0.023 (0.003) in anesthetized patients, p < 0.05; (2) a lower normalized slope of phase III of 0.26 (0.17) in volunteers versus 0.39 (0.38) in anesthetized patients, p < 0.05; and (3) a lower Bohr dead space ratio of 0.23 (0.05) in volunteers versus 0.28 (0.05) in anesthetized patients, p < 0.05. This study presents reference values for non-invasive volumetric capnography-derived parameters in healthy individuals. Mechanical ventilation and anesthesia altered these values significantly.

States of low pulmonary blood flow can be detected non-invasively at the bedside measuring alveolar dead space.

We tested whether the ratio of alveolar dead space to alveolar tidal volume (VD(alv)/VT(alv)) can detect states of low pulmonary blood flow (PBF) in a non-invasive way. Fifteen patients undergoing cardiovascular surgeries with cardiopulmonary bypass (CPB) were studied. CPB is a technique that excludes the lungs from the general circulation. The weaning of CPB is a model that manipulates PBF in vivo because each time blood flow through the CPB decreases, expected PBF (ePBF) increases. Patients were liberated from CPB in steps of 20 % every 2' starting from 100 % CPB (very low ePBF) to 0 % CPB (100 % ePBF). During constant ventilation, volumetric capnograms were recorded and Bohr's dead space ratio (VD(Bohr)/VT), VD(alv)/VT(alv) and the ratio of airway dead space to tidal volume (VD(aw)/VT) were calculated. Before CPB, VD(Bohr)/VT was 0.36 ± 0.05, VD(aw)/VT 0.21 ± 0.04 and VD(alv)/VT(alv) 0.18 ± 0.06 (mean ± SD). During weaning from CPB, VD(aw)/VT remained unchanged while VD(Bohr)/VT and VD(alv)/VT(alv) decreased with increasing ePBF. At CPB of 80, 60, 40 and 20 % VD(Bohr)/VT was 0.64 ± 0.06, 0.55 ± 0.06, 0.47 ± 0.05 and 0.40 ± 0.04, respectively; p < 0.001 and VD(alv)/VT(alv) 0.53 ± 0.07, 0.40 ± 0.07, 0.29 ± 0.06 and 0.25 ± 0.04, respectively; p < 0.001). After CPB, VD(Bohr)/VT and VD(alv)/VT(alv) reached values similar to baseline (0.37 ± 0.04 and 0.19 ± 0.06, respectively). At constant ventilation the alveolar component of VD(Bohr)/VT increased in proportion to the deficit in lung perfusion.

Lung recruitment and positive end-expiratory pressure have different effects on CO2 elimination in healthy and sick lungs.

BACKGROUND: We studied the effects that the lung recruitment maneuver (RM) and positive end-expiratory pressure (PEEP) have on the elimination of CO(2) per breath (Vtco(2,br)). METHODS: In 7 healthy and 7 lung-lavaged pigs at constant ventilation, PEEP was increased from 0 to 18 cm H(2)O and then decreased to 0 in steps of 6 cm H(2)O every 10 minutes. Cycling RMs with plateau pressure/PEEP of 40/20 (healthy) and 50/25 (lavaged) cm H(2)O were applied for 2 minutes between 18-PEEP steps. Volumetric capnography, respiratory mechanics, blood gas, and hemodynamic data were recorded. RESULTS: In healthy lungs before the RM, Vtco(2,br) was inversely proportional to PEEP decreasing from 4.0 (3.6-4.4) mL (median and interquartile range) at 0-PEEP to 3.1 (2.8-3.4) mL at 18-PEEP (P < 0.05). After the RM, Vtco(2,br) increased from 3.3 (3-3.6) mL at 18-PEEP to 4.0 (3.5-4.5) mL at 0-PEEP (P < 0.05). In lavaged lungs before the RM, Vtco(2,br) increased initially from 2.0 (1.7-2.3) mL at 0-PEEP to 2.6 (2.2-3) mL at 12-PEEP (P < 0.05) but then decreased to 2.4 (2-2.8) mL when PEEP was increased further to 18 cm H(2)O (P < 0.05). After the RM, the highest Vtco(2,br) of 2.9 (2.1-3.7) mL was observed at 12-PEEP and then decreased to 2.5 (1.9-3.1) mL at 0-PEEP (P < 0.05). Vtco(2,br) was directly related to changes in lung perfusion, the area of gas exchange, and alveolar ventilation but inversely related to changes in dead space. CONCLUSIONS: CO(2) elimination by the lungs was dependent on PEEP and recruitment and showed major differences between healthy and lavaged lungs.

Model fitting of volumetric capnograms improves calculations of airway dead space and slope of phase III.

BACKGROUND: This study assessed the performance of a Functional Approximation based on a Levenberg-Marquardt Algorithm (FA-LMA) to calculate airway dead space (VD(aw)) and the slope of phase III (S(III)) from capnograms. METHODS: We performed mathematical simulations to test the effect of noises on the calculation of VD(aw) and S(III). Data from ten mechanically ventilated patients at 0, 5 and 10 cmH(2)O of PEEP were also studied. FA-LMA was compared with the traditional Fowler's method (FM). RESULTS: Simulations showed that: (1) The FM determined VD(aw) with accuracy only if the capnogram approximated a symmetrical curve (S(III) = 0). When capnograms became asymmetrical (S(III) > 0), the FM underestimated VD(aw) (-3.1% to -0.9%). (2) When adding noises on 800 capnograms, VD(aw) was underestimated whenever the FM was used thereby creating a bias between -5.54 and -1.28 ml at standard deviations (SD) of 0.1-1.8 ml (P < 0.0001). FA-LMA calculations of VD(aw) were close to the simulated values with the bias ranging from -0.21 to 0.16 ml at SD from 0.1 to 0.4 ml. The FM overestimated S(III) and showed more bias (0.0041-0.0078 mmHg/ml, P < 0.0001) than the FA-LMA (0.0002-0.0030 mmHg/ml). When calculating VD(aw) from patients, variability was less with the FA-LMA leading to mean variation coefficients of 0.0102, 0.0111 and 0.0123 compared to the FM (0.0243, 0.0247 and 0.0262, P < 0.001) for 0, 5 and 10 cmH(2)O of PEEP, respectively. The FA-LMA also showed less variability in S(III) with mean variation coefficients of 0.0739, 0.0662 and 0.0730 compared to the FM (0.1379, 0.1208 and 0.1246, P < 0.001) for 0, 5 and 10 cmH(2)O of PEEP, respectively. CONCLUSIONS: The Functional Approximation based on a Levenberg-Marquardt Algorithm showed less bias and dispersion compared to the traditional Fowler's method when calculating VD(aw) and S(III).

Pulmonary blood flow generates cardiogenic oscillations.

Cardiogenic oscillations are small waves produced by heartbeats, which are superimposed on the pressure and flow signals at the airway opening. The aim of this study was to investigate the role of the two main factors believed to generate these oscillations: (1) contact between heart and lungs and (2) pulmonary blood flow. We studied 15 heart surgery patients on cardiopulmonary bypass so both factors could be manipulated independently. At minimal heart-lung contact pressure and flow oscillations were larger than during maximal contact (1.20+/-0.17 cmH(2)O and 2.36+/-0.08 L min(-1) vs 0.92+/-0.15 cmH(2)O and 1.78+/-0.26 L min(-1), mean+/-SD, p<0.05). Cardiogenic oscillations for pressure and flow were smaller at 50% compared to 100% pulmonary blood flow (0.80+/-0.12 cmH(2)O and 1.56+/-0.34 L min(-1) vs 1.19+/-0.14 cmH(2)O and 2.38+/-0.19 L min(-1)). We conclude that the amount of pulmonary blood flow and not the contact between heart and lungs is the main factor determining the amplitude of cardiogenic oscillations.

Bedside estimation of recruitable alveolar collapse and hyperdistension by electrical impedance tomography.

OBJECTIVE: To present a novel algorithm for estimating recruitable alveolar collapse and hyperdistension based on electrical impedance tomography (EIT) during a decremental positive end-expiratory pressure (PEEP) titration. DESIGN: Technical note with illustrative case reports. SETTING: Respiratory intensive care unit. PATIENT: Patients with acute respiratory distress syndrome. INTERVENTIONS: Lung recruitment and PEEP titration maneuver. MEASUREMENTS AND RESULTS: Simultaneous acquisition of EIT and X-ray computerized tomography (CT) data. We found good agreement (in terms of amount and spatial location) between the collapse estimated by EIT and CT for all levels of PEEP. The optimal PEEP values detected by EIT for patients 1 and 2 (keeping lung collapse <10%) were 19 and 17 cmH(2)O, respectively. Although pointing to the same non-dependent lung regions, EIT estimates of hyperdistension represent the functional deterioration of lung units, instead of their anatomical changes, and could not be compared directly with static CT estimates for hyperinflation. CONCLUSIONS: We described an EIT-based method for estimating recruitable alveolar collapse at the bedside, pointing out its regional distribution. Additionally, we proposed a measure of lung hyperdistension based on regional lung mechanics.

Monitoring dead space during recruitment and PEEP titration in an experimental model.

OBJECTIVE: To test the usefulness of dead space for determining open-lung PEEP, the lowest PEEP that prevents lung collapse after a lung recruitment maneuver. DESIGN: Prospective animal study. SETTING: Department of Clinical Physiology, University of Uppsala, Sweden. SUBJECTS: Eight lung-lavaged pigs. INTERVENTIONS: Animals were ventilated using constant flow mode with VT of 6ml/kg, respiratory rate of 30bpm, inspiratory-to-expiratory ratio of 1:2, and FiO(2) of 1. Baseline measurements were performed at 6cmH(2)O of PEEP. PEEP was increased in steps of 6cmH(2)O from 6 to 24cmH(2)O. Recruitment maneuver was achieved within 2min at pressure levels of 60/30cmH(2)O for Peak/PEEP. PEEP was decreased from 24 to 6cmH(2)O in steps of 2cmH(2)O and then to 0cmH(2)O. Each PEEP step was maintained for 10min. MEASUREMENTS AND RESULTS: Alveolar dead space (VD(alv)), the ratio of alveolar dead space to alveolar tidal volume (VD(alv)/VT(alv)), and the arterial to end-tidal PCO(2) difference (Pa-ET: CO(2)) showed a good correlation with PaO(2), normally aerated areas, and non-aerated CT areas in all animals (minimum-maximum r(2)=0.83-0.99; p<0.01). Lung collapse (non-aerated tissue>5%) started at 12[Symbol: see text]cmH(2)O PEEP; hence, open-lung PEEP was established at 14cmH(2)O. The receiver operating characteristics curve demonstrated a high specificity and sensitivity of VD(alv) (0.89 and 0.90), VD(alv)/VT(alv) (0.82 and 1.00), and Pa-ET: CO(2) (0.93 and 0.95) for detecting lung collapse. CONCLUSIONS: Monitoring of dead space was useful for detecting lung collapse and for establishing open-lung PEEP after a recruitment maneuver.

Alveolar recruitment improves ventilatory efficiency of the lungs during anesthesia.

PURPOSE: The goal of this study was to analyze the effect of positive end-expiratory pressure (PEEP), with and without a lung recruitment maneuver, on dead space. METHODS: 16 anesthetized patients were sequentially studied in three steps: 1) without PEEP (ZEEP), 2) with 5 cm H(2)O of PEEP and 3) with 5 cm H(2)O of PEEP after an alveolar recruitment strategy (ARS). Ventilation was maintained constant. The single breath test of CO(2) (SBT-CO(2)), arterial oxygenation, end-expiratory lung volume (EELV) and respiratory compliance were recorded every 30 min. RESULTS: Physiological dead space to tidal volume decreased after ARS (0.45 +/- 0.01) compared with ZEEP (0.50 +/- 0.07, P < 0.05) and PEEP (0.51 +/- 0.06, P < 0.05). The elimination of CO(2) per breath increased during PEEP (25 +/- 3.3 mL.min(-1)) and ARS (27 +/- 3.2 mL.min(-1)) compared to ZEEP (23 +/- 2.6 mL.min(-1), P < 0.05), although ARS showed larger values than PEEP (P < 0.05). Pa-etCO(2) difference was lower after recruitment (0.9 +/- 0.5 kPa, P < 0.05) compared to ZEEP (1.1 +/- 0.5 kPa) and PEEP (1.2 +/- 0.5 kPa). Slope II increased after ARS (63 +/- 11%/L, P < 0.05) compared with ZEEP (46 +/- 7.7%/L) and PEEP (56 +/- 10%/L). Slope III decreased significantly after recruitment (0.13 +/- 0.07 1/L) compared with ZEEP (0.21 +/- 0.11 1/L) and PEEP (0.18 +/- 0.10 1/L). The angle between slope II and III decreased only after ARS. After lung recruitment, PaO(2), EELV, and compliance increased significantly compared with ZEEP and PEEP. CONCLUSION: Lung recruitment improved the efficiency of ventilation in anesthetized patients.

Efecto del reclutamiento pulmonar sobre la capnografía volumétrica después de la circulación extracorpórea / Effect of pulmonary recruitment on volumetric capnography after extracorporeal circulation

Antecedentes: El reclutamiento pulmonar modifica la morfología de la curva de capnografía volumétrica en pacientes anestesiados con pulmones sanos. Objetivo: La meta de esta presentación es evaluar este fenómeno en un modelo pulmonar con injuria pulmonar aguda (IPA). Lugar de aplicación: Hospital de Comunidad. Diseño: Estudio prospectivo, controlado, con pacientes distribuídos de manera aleatoria en dos grupos. Población: 22 pacientes sometidos a cirugía de revascularización coronaria bajo circulación extracorpórea distribuídos en un grupo control (n = 11) y un grupo con reclutamiento pulmonar (n = 11). Métodos: Se estudió la oxigenación y la capnografía volumétrica luego de la circulación extracorpórea, antes y después del cierre esternal. Los dos grupos recibieron la misma ventilación y nivel de PEEP (10 cmH2O). Al grupo con reclutamiento se le realizó una estrategia de reclutamiento alveolar con 45 cmH20 de presión pico y 20 cmH20 de PEEP durante 10 ciclos respiratorios, retornando a la ventilación basal luego del mismo. Resultados: La Pa02, un marcador del efecto del reclutamiento pulmonar, fue superior luego del reclutamiento pulmonar comparado con el grupo de pacientes sin reclutamiento (224 ± 34 mmHg vs 101 ± 22 mmHg, p < 0,001). La pendiente de fase II (PII) fue mayor después del reclutamiento (56 ± 8,6 por ciento/l) comparado con el grupo control (47,3 ± 7,1 por ciento/l, P < 0,05). La pendiente de fase III normalizada (PnIII) mostró un efecto opuesto a la PII, siendo menor después del reclutamiento (0,39 ± 0,029 1/l) comparado con el grupo control (0,77 ± 0,035 1/l, P < 0,05). Otras variables de la capnografía volumétrica relacionadas con la eficiencia ventilatoria como el área bajo la curva, Vol III/VT y Pa-etCO2 sólo mejoraron en el grupo tratado. Conclusión: La modificación en la morfología de la curva de la capnografía volumétrica con el reclutamiento pulmonar se relaciona con una ventilación alveolar e intercambio gaseoso más eficaz. (AU)

Efecto del reclutamiento pulmonar sobre la capnografía volumétrica después de la circulación extracorpórea / Effect of pulmonary recruitment on volumetric capnography after extracorporeal circulation

Antecedentes: El reclutamiento pulmonar modifica la morfología de la curva de capnografía volumétrica en pacientes anestesiados con pulmones sanos. Objetivo: La meta de esta presentación es evaluar este fenómeno en un modelo pulmonar con injuria pulmonar aguda (IPA). Lugar de aplicación: Hospital de Comunidad. Diseño: Estudio prospectivo, controlado, con pacientes distribuídos de manera aleatoria en dos grupos. Población: 22 pacientes sometidos a cirugía de revascularización coronaria bajo circulación extracorpórea distribuídos en un grupo control (n = 11) y un grupo con reclutamiento pulmonar (n = 11). Métodos: Se estudió la oxigenación y la capnografía volumétrica luego de la circulación extracorpórea, antes y después del cierre esternal. Los dos grupos recibieron la misma ventilación y nivel de PEEP (10 cmH2O). Al grupo con reclutamiento se le realizó una estrategia de reclutamiento alveolar con 45 cmH20 de presión pico y 20 cmH20 de PEEP durante 10 ciclos respiratorios, retornando a la ventilación basal luego del mismo. Resultados: La Pa02, un marcador del efecto del reclutamiento pulmonar, fue superior luego del reclutamiento pulmonar comparado con el grupo de pacientes sin reclutamiento (224 ± 34 mmHg vs 101 ± 22 mmHg, p < 0,001). La pendiente de fase II (PII) fue mayor después del reclutamiento (56 ± 8,6 por ciento/l) comparado con el grupo control (47,3 ± 7,1 por ciento/l, P < 0,05). La pendiente de fase III normalizada (PnIII) mostró un efecto opuesto a la PII, siendo menor después del reclutamiento (0,39 ± 0,029 1/l) comparado con el grupo control (0,77 ± 0,035 1/l, P < 0,05). Otras variables de la capnografía volumétrica relacionadas con la eficiencia ventilatoria como el área bajo la curva, Vol III/VT y Pa-etCO2 sólo mejoraron en el grupo tratado. Conclusión: La modificación en la morfología de la curva de la capnografía volumétrica con el reclutamiento pulmonar se relaciona con una ventilación alveolar e intercambio gaseoso más eficaz.