Cardiorespiratory Alterations Following Acute Normovolemic Hemodilution in a Pediatric and an Adult Porcine Model: A Prospective Interventional Study

BACKGROUND: Acute normovolemic hemodilution (ANH) is considered as a blood-sparing intervention during the perioperative management. We aimed at comparing the cardiopulmonary consequences of ANH between adult pigs and weaned piglets to establish the effects of lowering hematocrit in these age groups, and thereby testing the hypothesis that difference in the age-related physiological behavior will be reflected in the cardiorespiratory changes following ANH. METHODS: ANH was achieved in anesthetized, mechanically ventilated adult minipigs and 5-week-old weaned piglets by stepwise blood withdrawal (10 mL/kg) with crystalloids replacement. Cardiorespiratory assessments consisted of measuring airway resistance, respiratory tissue elastance, effective lung volume, extravascular lung water, mean arterial pressure, pulmonary blood flow, and cardiac output. Respiratory and hemodynamic measurements were made at control conditions and following each ANH condition obtained with 5 to 7 steps. RESULTS: ANH induced immediate and progressive increases in airway resistance and tissue elastance in both groups, with more pronounced worsening in adults despite the similar decreases in hematocrit. The increases in extravascular lung water were significantly greater in the adult population with the differences in mean (DM) of 25.1% (95% confidence interval [CI], 5.3%-44.9%). Progressive ANH led to significant decreases in the DM of pulmonary blood flow (45.3%; 95% CI, 19.8%-70.8%) and mean arterial pressure (36.3%; 95% CI, 18.7%-53.9%) only in adults, whereas cardiac output increased significantly only in the piglets (DM, 51.6; 95% CI, 14.2%-89.0%). CONCLUSIONS: While ANH led to mild detrimental cardiorespiratory changes in weaned piglets, gradual developments of bronchoconstriction, lung tissue extravasation and stiffening, and deteriorations in systemic and pulmonary hemodynamics were observed in adults. ANH may exert age-dependent cardiorespiratory effect

Flow-controlled ventilation maintains gas exchange and lung aeration in a pediatric model of healthy and injured lungs: A randomized cross-over experimental study

Flow-controlled ventilation (FCV) is characterized by a constant flow to generate active inspiration and expiration. While the benefit of FCV on gas exchange has been demonstrated in preclinical and clinical studies with adults, the value of this modality for a pediatric population remains unknown. Thus, we aimed at observing the effects of FCV as compared to pressure-regulated volume control (PRVC) ventilation on lung mechanics, gas exchange and lung aeration before and after surfactant depletion in a pediatric model. Ten anesthetized piglets (10.4 ± 0.2 kg) were randomly assigned to start 1-h ventilation with FCV or PRVC before switching the ventilation modes for another hour. This sequence was repeated after inducing lung injury by bronchoalveolar lavage and injurious ventilation. The primary outcome was respiratory tissue elastance. Secondary outcomes included oxygenation index (PaO2/FiO2), PaCO2, intrapulmonary shunt (Qs/Qt), airway resistance, respiratory tissue damping, end-expiratory lung volume, lung clearance index and lung aeration by chest electrical impedance tomography. Measurements were performed at the end of each protocol stage. Ventilation modality had no effect on any respiratory mechanical parameter. Adequate gas exchange was provided by FCV, similar to PRVC, with sufficient CO2 elimination both in healthy and surfactant-depleted lungs (39.46 ± 7.2 mmHg and 46.2 ± 11.4 mmHg for FCV; 36.0 ± 4.1 and 39.5 ± 4.9 mmHg, for PRVC, respectively). Somewhat lower PaO2/FiO2 and higher Qs/Qt were observed in healthy and surfactant depleted lungs during FCV compared to PRVC (p < 0.05, for all). Compared to PRVC, lung aeration was significantly elevated, particularly in the ventral dependent zones during FCV (p < 0.05), but this difference was not evidenced in injured lungs. Somewhat lower oxygenation and higher shunt ratio was observed during FCV, nevertheless lung aeration improved and adequate gas exchange was ensured. Therefore, in the absence of major differences in respiratory mechanics and lung volumes, FCV may be considered as an alternative in ventilation therapy of pediatric patients with healthy and injured lungs

Novel ventilation techniques in children

Extraordinary progress has been made during the past few decades in the development of anesthesia machines and ventilation techniques. With unprecedented precision and performance, modern machines for pediatric anesthesia can deliver appropriate mechanical ventilation for children and infants of all sizes and with ongoing respiratory diseases, ensuring very small volume delivery and compensating for circuit compliance. Along with highly accurate monitoring of the delivered ventilation, modern ventilators for pediatric anesthesia also have a broad choice of ventilation modalities, including synchronized and assisted ventilation modes, which were initially conceived for ventilation weaning in the intensive care setting. Despite these technical advances, there is still room for improvement in pediatric mechanical ventilation. There is a growing effort to minimize the harm of intraoperative mechanical ventilation of children by adopting the protective ventilation strategies that were previously employed only for prolonged mechanical ventilation. More than ever, the pediatric anesthesiologist should now recognize that positive-pressure ventilation is potentially a harmful procedure, even in healthy children, as it can contribute to both ventilator-induced lung injury and ventilator-induced diaphragmatic dysfunction. Therefore, careful choice of the ventilation modality and its parameters is of paramount importance to optimize gas exchange and to protect the lungs from injury during general anesthesia. The present report reviews the novel ventilation techniques used for children, discussing the advantages and pitfalls of the ventilation modalities available in modern anesthesia machines, as well as innovative ventilation modes currently under development or research. Several innovative strategies and devices are discussed. These novel modalities are likely to become part of the armamentarium of the pediatric anesthesiologist in the near future and are particularly relevant for challenging ventilation scenarios

Negative impact of the noseclip on high-frequency respiratory impedance measurements

The noseclip is conventionally used in lung function testing to prevent leakage via the nasal compartments. However, some subjects exhibit a velum-opening reflex which may affect results. We performed forced oscillation measurements at frequencies (8–256 Hz) that include the first antiresonance, comparing the noseclip with a cotton wool nose plug to eliminate upper airway contribution. Three sets of measurements were made in 18 adults: with and without noseclip, and with cotton wool. Velum opening during noseclip measurements was monitored using a nasal pressure transducer. A significantly greater proportion of subjects produced a characteristic distortion to the first antiresonance with the noseclip than with either no noseclip or with cotton wool. Distortion of the spectrum coincided with the transmission of oscillations into the nasal cavity. Thus, the noseclip cannot be used in high-frequency forced oscillation measurements because of the velum reflex. The cotton wool plug offers a simple alternative. This effect has unknown impact in other lung function tests

Prevention of airway hyperresponsiveness induced by left ventricular dysfunction in rats

<p>Abstract</p> <p>Background</p> <p>The effectiveness of strategies for treatment of the altered static lung volume and against the development of bronchial hyperreactivity (BHR) following a left ventricular dysfunction (LVD) induced by myocardial ischaemia was investigated in a rat model of sustained postcapillary pulmonary hypertension.</p> <p>Methods</p> <p>Airway resistance (Raw) was identified from the respiratory system input impedance (Zrs) in four groups of rats. End-expiratory lung volume (EELV) was determined plethysmographically, and Zrs was measured under baseline conditions and following iv infusions of 2, 6 or 18 μg/kg/min methacholine. Sham surgery was performed in the rats in Group C, while the left interventricular coronary artery was ligated and Zrs and its changes following identical methacholine challenges were reassessed in the same rats 8 weeks later, during which no treatment was applied (Group I), or the animals were treated daily with a combination of an angiotensin enzyme converter inhibitor and a diuretic (enalapril and furosemide, Group IE), or a calcium channel blocker (diltiazem, Group ID). The equivalent dose of methacholine causing a 100% increase in Raw (ED₅₀) was determined in each group. Diastolic pulmonary arterial pressure (Pap_D) was assessed by introducing a catheter into the pulmonary artery.</p> <p>Results</p> <p>The sustained presence of a LVD increased Pap_D in all groups of rats, with variable but significant elevations in Groups I (p = 0.004), ID (p = 0.013) and IE (p = 0.006). A LVD for 8 weeks induced no changes in baseline Raw but elevated the EELV independently of the treatments. In Group I, BHR consistently developed following the LVD, with a significant decrease in ED₅₀ from 10.0 ± 2.5 to 6.9 ± 2.5 μg/kg/min (p = 0.006). The BHR was completely abolished in both Groups ID and IE, with no changes in ED₅₀ (9.5 ± 3.6 vs. 10.7 ± 4.7, p = 0.33 and 10.6 ± 2.1 vs. 9.8 ± 3.5 μg/kg/min p = 0.56, respectively).</p> <p>Conclusions</p> <p>These findings suggest that a LVD following coronary ischaemia consistently induces BHR. The more consistent efficacy of both treatment strategies in preventing BHR than in treating the adverse pulmonary vascular consequences suggests the benefit of both calcium channel blockade and ACE inhibition to counteract the airway susceptibility following a LVD.</p

The contribution of the pulmonary microvascular pressure in the maintenance of an open lung during mechanical ventilation

Changes in pulmonary hemodynamics modify the mechanical properties of the lungs. The effects of alterations in pulmonary capillary pressure (Pc) were investigated on the airway and lung tissue mechanics during positive-pressure ventilation and following lung recruitment maneuvers. Isolated, mechanically normoventilated (PEEP 2.5 cmH(2)O) rat lungs were perfused with Pc set to 0 (unperfused), 5, 10 or 15 mmHg, in random sequence. The pulmonary input impedance (ZL) was measured at end-expiration before and after a 10-min long ventilation. After inflation of the lung to 30 cmH(2)O during P-V curve recordings, another set of ZL was measured to evaluate the degree of recruitment. The PEEP was then decreased to 0.5 cmH(2)O and the sequence was repeated. Airway resistance and parenchymal damping and elastance (H) were estimated from ZL by model fitting. From the P-V curves, elastance (E) and hysteresis indices were determined. Mechanical ventilation at both PEEP levels resulted primarily in elevations in the tissue parameters, with the greatest increases at the 0 Pc level (H changes of 27.8+/-4.2 and 61.3+/-3.7% at 2.5 and 0.5 cmH(2)O PEEP, respectively). The maintenance of physiological Pc (10 mmHg) led to a significantly lower elevation in H (11.6+/-1.5% versus 31.4+/-3.6%). The changes in the oscillatory mechanics were also reflected in E and the hysteresis of the P-V curves. These findings indicate that pulmonary hypoperfusion during mechanical ventilation forecasts a parenchymal mechanical deterioration. Physiological pressure in the pulmonary capillaries is therefore an important mechanical factor promoting maintenance of the stability of the alveolar architecture during positive-pressure mechanical ventilation

Variable Ventilation Is Equally Effective as Conventional Pressure Control Ventilation for Optimizing Lung Function in a Rabbit Model of ARDS

Introducing mathematically derived variability (MVV) into the otherwise monotonous conventional mechanical ventilation has been suggested to improve lung recruitment and gas exchange. Although the application of a ventilation pattern based on variations in physiological breathing (PVV) is beneficial for healthy lungs, its value in the presence of acute respiratory distress syndrome (ARDS) has not been characterized. We therefore aimed at comparing conventional pressure-controlled ventilation with (PCS) or without regular sighs (PCV) to MVV and PVV at two levels of positive end-expiratory pressure (PEEP) in a model of severe ARDS

Comparison between neurally-assisted, controlled, and physiologically variable ventilation in healthy rabbits

Background: Various ventilation strategies have been proposed to reduce ventilation-induced lung injury that occurs even in individuals with healthy lungs. We compared new modalities based on an individualised physiological variable ventilation model to a conventional pressure-controlled mode