Effects on Breathing Mechanics and Gas Exchange of Different Inspiratory Gas Flow Patterns During Anaesthesia

Ten patients without known cardiac or respiratory disease were investigated with breathing mechanics and gas exchange studies during anaesthesia and artifical ventilation. The effects of three different inspiratory gas flow patterns, namely, accelerating, constant and decelerating flows were studied. A decelerating flow resulted in an increase of total compliance when compared to an accelerating or a constant flow. However, at the same time, there was an increase in physiological dead space and a decrease in alveolar ventilation with a decelerating flow compared to an accelerating flow. These results seem to indicate an improved gas distribution in the greater airways with a decelerating flow pattern, but when the total effects of gas exchange were judged, the greatest benefits were with an accelerating flow.     

Differential Ventilation in Acute Bilateral Lung Disease. Influence on Gas Exchange and Central Haemodynamics

Eight patients with acute respiratory failure (ARF) due to diffuse and rather uniform lung disease were intubated with a double-lumen bronchial tube and ventilated in the lateral decubital position by two synchronized ventilators. Ventilation of each lung was individually adjusted to match the expected regional blood flow (differential ventilation). When ventilation with equal volumes (i.e. 50% of tidal volume to each lung) was performed, a 19% reduction of venous admixture (P less than 0.001) and a 22% increment in arterial oxygen tension (P less than 0.001) were seen. Comcomitantly, the cardiac output increased by 17% (P less than 0.001), to which a reduced pulmonary vascular resistance may have contributed. The net result was a 14% increment of the oxygen availability (P less than 0.001). An attempt to go further, giving 2/3 of the tidal ventilation to the dependent lung, was made on six of the patients. However, this ventilatory pattern did not further improve the gas exchange and also had detrimental effects on the haemodynamics. It is concluded that differential ventilation with equal tidal volumes in the lateral position can substantially improve gas exchange and central haemodynamics in patients with ARF due to diffuse lung disease.     

Open-lung Protective Ventilation with Pressure Control Ventilation, High-frequency Oscillation, and Intratracheal Pulmonary Ventilation Results in Similar Gas Exchange, Hemodynamics, and Lung Mechanics

Background: Pressure control ventilation (PCV), high-frequency oscillation (HFO), and intratracheal pulmonary ventilation (ITPV) may all be used to provide lung protective ventilation in acute respiratory distress syndrome, but the specific approach that is optimal remains controversial.

Methods: Saline lavage was used to produce acute respiratory distress syndrome in 21 sheep randomly assigned to receive PCV, HFO, or ITPV as follows: positive end-expiratory pressure (PCV and ITPV) and mean airway pressure (HFO) were set in a pressure-decreasing manner after lung recruitment that achieved a ratio of Pao2/Fio2 > 400 mmHg. Respiratory rates were 30 breaths/min, 120 breaths/min, and 8 Hz, respectively, for PCV, ITPV, and HFO. Eucapnia was targeted with peak carinal pressure of no more than 35 cm H2O. Animals were then ventilated for 4 h.

Results: There were no differences among groups in gas exchange, lung mechanics, or hemodynamics. Tidal volume (PCV, 8.9 +/- 2.1 ml/kg; ITPV, 2.7 +/- 0.8 ml/kg; HFO, approximately 2.0 ml/kg) and peak carinal pressure (PCV, 30.6 +/- 2.6 cm H2O; ITPV, 22.3 +/- 4.8 cm H2O; HFO, approximately 24.3 cm H2O) were higher in PCV. Pilot histologic data showed greater interstitial hemorrhage and alveolar septal expansion in PCV than in HFO or ITPV.     

Pressure-controlled Ventilation Does Not Improve Gas Exchange in Morbidly Obese Patients Undergoing Abdominal Surgery

Background

Morbid obesity results in marked respiratory pathophysiologic changes that may lead to impaired intraoperative gas exchange. The decelerating inspiratory flow and constant inspiratory airway pressure resulting from pressure-controlled ventilation (PCV) may be more adapted to these changes and improve gas exchanges compared with volume-controlled ventilation (VCV).

Methods

Forty morbidly obese patients scheduled for gastric bypass were included in this study. Total intravenous anesthesia was given using the target-controlled infusion technique. During the first intraoperative hour, VCV was used and the tidal volume was adjusted to keep end-tidal PCO₂ around 35 mmHg. After 1 h, patients were randomly allocated to 30-min VCV followed by 30-min PCV or the opposite sequence using a Siemens® Servo 300. FiO₂ was 0.6. During PCV, airway pressure was adjusted to provide the same tidal volume as during VCV. Arterial blood was sampled for gas analysis every 15 min. Ventilatory parameters were also recorded.

Results

Peak inspiratory airway pressures were significantly lower during PCV than during VCV (P? <?0.0001). The other ventilatory parameters were similar during the two periods of ventilation. PaO₂ and PaCO₂ were not significantly different during PCV and VCV.

Conclusion

PCV does not improve gas exchange in morbidly obese patients undergoing gastric bypass compared to VCV.

     

Effects of Ventilation on Hemodynamics and Myocardial Blood Flow during Active Compression-Decompression Resuscitation in Pigs

Background: Active compression-decompression (ACD) improves hemodynamics and vital organ blood flow during cardiopulmonary resuscitation. The effects of intermittent positive pressure ventilation (IPPV) on ACD have not been studied. This study was designed to compare the effects of ACD with and without IPPV on gas exchange, hemodynamics, and myocardial blood flow.

Methods: After 30 s ventricular fibrillation, 14 tracheally intubated pigs were allocated to receive either ACD combined with IPPV (ACD-IPPV) or ACD alone. In animals treated with ACD-IPPV, the lungs were ventilated using a servo ventilator. Animals treated with ACD received 100% oxygen by a reservoir but ventilation was not assisted.

Results: Minute ventilation (median) was 6.5 and 6.1 l/min after 1 and 7 min of ACD-IPPV, and was 4.2 and 1.6 l/min after 1 and 7 min of ACD. In contrast to ACD-IPPV, PaO2 was less and PaCO2 was greater with ACD. Mean arterial (53 and 40 mmHg; P < 0.05) and mean central venous pressure (25 and 14 mmHg; P < 0.01) were greater during ACD-IPPV as compared with ACD. After administration of epinephrine 0.2 mg/kg, myocardial blood flow increased only in ACD-IPPV treated animals, and 5 min after epinephrine administration, myocardial blood flow was greater during ACD-IPPV (33 ml *symbol* min sup -1 *symbol* 100 g sup -1) as compared with ACD (15 ml *symbol* min sup -1 *symbol* 100 g sup -1; P < 0.05). Restoration of spontaneous circulation could be achieved only in animals subjected to ACD-IPPV.     

Continuous Flow Apneic Ventilation

A study was designed to evaluate the adequacy of gas exchange during continuous flow apneic ventilation (CFAV) in dogs. Seventeen dogs (average weight 22.9 kg) were divided into three experimental groups. Group I (n = 7) was anesthetized, paralyzed and ventilated with air using intermittent positive pressure ventilation (IPPV) through a tracheal tube. The tube was removed and each main stem bronchus was cannulated with a 2.5 mm i.d., 4 mm o.d. polyethylene catheter using a fiberoptic bronchoscope. The tracheal tube was replaced to hold the catheters in place. Heated, humidified air was continuously delivered equally to each catheter. Total flows ranged from 8 to 28 1/min (0.4—1.4 1 + kg^-1 min-^-1). Airway pressure (P_aw) in the trachea did not exceed 2 mmHg (0.27 kPa). Adequate gas exchange in terms of arterial oxygen and arterial carbon dioxide tension (Pao₂ and Paco₂) was found after 30 min at flows greater than 16 l · min_-1. Group II (n = 7) was managed similarly to the first group, insufflating endobronchial air using the optimal flow of 1.0 1 · kg ¹ · min^-1 obtained from Group I. CFAV continued for 5 h in all animals. Blood gas samples and measurements of systemic blood pressure, heart rate (HR), pulmonary artery blood pressure, pulmonary artery wedge pressure, cardiac output (Qt), and temperature were taken every 30 min. Group III (n = 3) was anesthetized similarly to the other groups. Pulmonary gas distribution was evaluated in relation to catheter placement using Xe¹³³. Results showed significant differences between Paoj values during CFAV and IPPV; however, all animals were adequately oxygenated. During 5 h of CFAV, adequate CO₂ elimination was achieved in all animals. There was no difference in PaO₂, Paco₂ and shunt fraction (Qs/C}t) with CFAV at 30 min and 5 h. Differences in HR, Qt, and systemic vascular resistance at 30 min and 5 h were related to the hypothermia during the developing course of experimentation. With the catheters above the carina, gas distribution studies demonstrated gas limited to the large airways with no peripheral distribution, resulting in low Pao₂ levels and elevated Paco₂ levels. Endobronchial catheters permitted gas distribution to the peripheral airways, and oxygenation and ventilation were normal.     

Effects of Vaporized Perfluorocarbon on Pulmonary Blood Flow and Ventilation/Perfusion Distribution in a Model of Acute Respiratory Distress Syndrome

Background : Perfluorocarbon (PFC) liquids are known to improve gas exchange and pulmonary function in various models of acute respiratory failure . Vaporization has been recently reported as a new method of delivering PFC to the lung. Our aim was to study the effect of PFC vapor on the ventilation/perfusion ( A/ ) matching and relative pulmonary blood flow ( rel) distribution.

Methods : In nine sheep, lung injury was induced using oleic acid. Four sheep were treated with vaporized perfluorohexane (PFX) for 30 min, whereas the remaining sheep served as control animals. Vaporization was achieved using a modified isoflurane vaporizer. The animals were studied for 90 min after vaporization. A/ distributions were estimated using the multiple inert gas elimination technique. Change in rel distribution was assessed using fluorescent-labeled microspheres.

Results : Treatment with PFX vapor improved oxygenation significantly and led to significantly lower shunt values (P < 0.05, repeated-measures analysis of covariance). Analysis of the multiple inert gas elimination technique data showed that animals treated with PFX vapor demonstrated a higher A/ he-terogeneity than the control animals (P < 0.05, repeated-measures analysis of covariance). Microsphere data showed a redistribution of rel attributable to oleic acid injury. rel shifted from areas that were initially high-flow to areas that were initially low-flow, with no difference in redistribution between the groups. After established injury, rel was redistributed to the nondependent lung areas in control animals, whereas rel distribution did not change in treatment animals.     

Effects on Breathing Mechanics and Gas Exchange of Different Inspiratory Gas Flow Patterns in Patients Undergoing Respirator Treatment

In order to investigate the importance of different inspiratory gas flow patterns in respirator treatment, eight intensive care patients were studied with breathing mechanics and five patients also with gas exchange studies. Three different inspiratory gas flow patterns were tested in randomized sequences namely, accelerating, constant and decelerating flow. All three flow patterns were generated by the same respirator. No end-inspiratory pause was used. The results point to a favourable effect on breathing mechanics of a decelerating and a constant flow when compared with an accelerating flow type. However, when the total effects on gas distribution and lung perfusion were evaluated in the gas exchange studies, no significant differences were seen between the three flow patterns.     

Changes in Pulmonary Blood Flow during Gaseous and Partial Liquid Ventilation in Experimental Acute Lung Injury

Background: It has been proposed that partial liquid ventilation (PLV) causes a compression of the pulmonary vasculature by the dense perfluorocarbons and a subsequent redistribution of pulmonary blood flow from dorsal to better-ventilated middle and ventral lung regions, thereby improving arterial oxygenation in situations of acute lung injury.

Methods: After induction of acute lung injury by repeated lung lavage with saline, 20 pigs were randomly assigned to partial liquid ventilation with two sequential doses of 15 ml/kg perfluorocarbon (PLV group, n = 10) or to continued gaseous ventilation (GV group, n = 10). Single-photon emission computed tomography was used to study regional pulmonary blood flow. Gas exchange, hemodynamics, and pulmonary blood flow were determined in both groups before and after the induction of acute lung injury and at corresponding time points 1 and 2 h after each instillation of perfluorocarbon in the PLV group.

Results: During partial liquid ventilation, there were no changes in pulmonary blood flow distribution when compared with values obtained after induction of acute lung injury in the PLV group or to the animals submitted to gaseous ventilation. Arterial oxygenation improved significantly in the PLV group after instillation of the second dose of perfluorocarbon.     

High Frequency Ventilation and Gas Diffusion

The efficiency of CO2 removal was studied using a simple lung model with a high frequency positive pressure device (up to 100 b.p.m.) with and without an anatomical deadspace. At a constant minute ventilation without an anatomical dead space, the efficiency of CO2 elimination increased with increasing frequency. However, when a dead space was introduced, the efficiency of CO2 elimination decreased with increasing frequency. Using a high frequency oscillation technique (360 to 900 b.p.m.), it was not possible to maintain a reasonable CO2 elimination with tidal volumes less than the anatomical dead space. In this model there was no evidence that accelerated diffusion was a factor in CO2 removal during high frequency ventilation or oscillation.     

Hemodilution during Venous Gas Embolization Improves Gas Exchange, without Altering V̇A/Q̇ or Pulmonary Blood Flow Distributions

Background: Isovolemic anemia results in improved gas exchange in rabbits with normal lungs but in relatively poorer gas exchange in rabbits with whole-lung atelectasis. In the current study, the authors characterized the effects of hemodilution on gas exchange in a distinct model of diffuse lung injury: venous gas embolization.

Methods: Twelve anesthetized rabbits were mechanically ventilated at a fixed rate and volume. Gas embolization was induced by continuous infusion of nitrogen via an internal jugular venous catheter. Serial hemodilution was performed in six rabbits by simultaneous withdrawal of blood and infusion of an equal volume of 6% hetastarch; six rabbits were followed as controls over time. Measurements included hemodynamic parameters and blood gases, ventilation-perfusion ( A/ ) distribution (multiple inert gas elimination technique), pulmonary blood flow distribution (fluorescent microspheres), and expired nitric oxide (NO; chemoluminescence).

Results: Venous gas embolization resulted in a decrease in partial pressure of arterial oxygen (PaO2) and an increase in partial pressure of arterial carbon dioxide (PaCO2), with markedly abnormal overall A/ distribution and a predominance of high A/ areas. Pulmonary blood flow distribution was markedly left-skewed, with low-flow areas predominating. Hematocrit decreased from 30 +/- 1% to 11 +/- 1% (mean +/- SE) with hemodilution. The alveolar-arterial PO2 (A-aPO2) difference decreased from 375 +/- 61 mmHg at 30% hematocrit to 218 +/- 12.8 mmHg at 15% hematocrit, but increased again (301 +/- 33 mmHg) at 11% hematocrit. In contrast, the A-aPO2 difference increased over time in the control group (P< 0.05 between groups over time). Changes in PaO2 in both groups could be explained in large part by variations in intrapulmonary shunt and mixed venous oxygen saturation (SvO2); however, the improvement in gas exchange with hemodilution was not fully explained by significant changes in A/ or pulmonary blood flow distributions, as quantitated by the coefficient of variation (CV), fractal dimension, and spatial correlation of blood flow. Expired NO increased with with gas embolization but did not change significantly with time or hemodilution.     

Sigh Improves Gas Exchange and Lung Volume in Patients with Acute Respiratory Distress Syndrome Undergoing Pressure Support Ventilation

Background: The aim of our study was to assess the effect of periodic hyperinflations (sighs) during pressure support ventilation (PSV) on lung volume, gas exchange, and respiratory pattern in patients with early acute respiratory distress syndrome (ARDS).

Methods: Thirteen patients undergoing PSV were enrolled. The study comprised 3 steps: baseline 1, sigh, and baseline 2, of 1 h each. During baseline 1 and baseline 2, patients underwent PSV. Sighs were administered once per minute by adding to baseline PSV a 3- to 5-s continuous positive airway pressure (CPAP) period, set at a level 20% higher than the peak airway pressure of the PSV breaths or at least 35 cm H2O. Mean airway pressure was kept constant by reducing the positive end-expiratory pressure (PEEP) during the sigh period as required. At the end of each study period, arterial blood gas tensions, air flow and pressures traces, end-expiratory lung volume (EELV), compliance of respiratory system (Crs), and ventilatory parameters were recorded.

Results: Pao2 improved (P < 0.001) from baseline 1 (91.4 +/- 27.4 mmHg) to sigh (133 +/- 42.5 mmHg), without changes of Paco2. EELV increased (P < 0.01) from baseline 1 (1,242 +/- 507 ml) to sigh (1,377 +/- 484 ml). Crs improved (P < 0.01) from baseline 1 (40.2 +/- 12.5 ml/cm H2O) to sigh (45.1 +/- 15.3 ml/cm H2O). Tidal volume of pressure-supported breaths and the airway occlusion pressure (P0.1) decreased (P < 0.01) during the sigh period. There were no significant differences between baselines 1 and 2 for all parameters.     

Effect of Inverse I: E Ratio Ventilation on Pulmonary Gas Exchange in Acute Respiratory Distress Syndrome

Background: It is not known whether inverse I:E ratio ventilation (IRV) offers any real benefit over conventional mechanical ventilation with positive end-expiratory pressure (CMV-PEEP) at similar levels of end-expiratory pressure.

Methods: The effects of volume-controlled and pressure-controlled IRV (VC-IRV and PC-IRV, respectively) on V with dotA /Q with dot inequality were compared with those of CMV-PEEP at a similar level of end-expiratory pressure and with CMV without PEEP (CMV) in eight patients in the early stages of acute respiratory distress syndrome (ARDS). Respiratory blood gases, inert gases, lung mechanics, and hemodynamics were measured 30 min after the onset of each ventilatory mode.

Results: Recruitment of nonventilated, poorly ventilated (or both) but well-perfused alveoli increased the partial pressure of oxygen (PaO sub 2) during CMV-PEEP (+13 mmHg) and IRV-VC (+10 mmHg; P < 0.05) compared with CMV. In contrast, PC-IRV did not affect PaO2 but caused a decrease in PaCO2 (-7 mmHg; P < 0.05). The latter was due to a concomitant decrease in dead space (P < 0.01) and shift to the right of V with dotA /Q with dot distributions. During PC-IRV, the increase in the mean of blood flow distribution (mean Q; P < 0.01) without a change in the dispersion (log SD Q) did not result in an increase in PaO2, probably because it reflected redistribution of blood flow within well-ventilated areas.     

双水平正压通气对急性肺损伤患者血气及血流动力学指标的影响

目的探讨应用脉搏指数连续心排血量（PiCCO）容量监测仪技术研究双水平正压通气模式对急性肺损伤（ALI）患者血气及血流动力学的影响,探讨这种新型呼吸模式应用于ALI患者的临床疗效,对循环系统的影响程度,以提高ALI的治愈率。方法42例ALI患者,男27例,女15例;年龄15～75岁。按患者的入院先后顺序将40例患者（2例未完成研究）分为两组,每组20例。双水平正压通气组：入院的第1～20例患者,给予双水平正压通气呼吸支持,采用支持/时间（S/T）模式,吸气末压初始设为8～10cmH2O,逐渐增加至14～20cmH2O,以患者舒适为宜;呼气末压初设为3～5cmH2O,逐渐增加至8～12cmH2O,吸入氧浓度（FiO2）保持不变。对照组：入院的第21～40例患者,采用辅助/控制（A/C）通气模式,并依次按5cmH2O,10cmH2O,15cmH2O,20cmH2O增加呼气末正压（PEEP）,每种压力持续30min,通气支持过程中FiO2保持不变。观察两组患者的心排血量（CO）、体循环血管阻力（SVR）等血流动力学和血气指标改变。结果两组死亡13例,其中双水平正压通气组死亡5例,对照组死亡8例。死于多器官功能衰竭7例,感染性休克3例,循环衰竭3例。双水平正压通气组气管内插管时间（2.9±0.8dvs.4.2±0.9d,t=7.737,P=0.006）和住院时间（17.2±4.5dvs.18.5±3.6d,t=2.558,P=0.039）明显短于对照组。对照组：当PEEP在5～15cmH2O范围内,患者动脉血氧分压（PaO2）、氧合指数（PaO2/FiO2）随着PEEP的增高而逐渐增加（P〈0.05）;当PEEP增加至20cmH2O时CO降低,SVR、肺循环阻力（PVR）和气道峰值压（PIP）较5～15cmH2O范围时增加（P〈0.05）。双水平正压通气组：PaO2、PaO2/FiO2随着EPAP的增高而逐渐增加,当EPAP增加至10cmH2O时PaO2、PaO2/FiO2达最大值（P〈0.05）;与对照组比较PIP明显降低（t=7.831,P=0.000）。结论对ALI/急性呼吸窘迫综合征（ARDS）患者给予双水平正压通气治疗可减少对呼吸和血     

鼻罩压力支持通气对肺部气体交换的影响

４０例硬膜外阻滞下行上腹部手术的患者，用ＢｉＰＡＰ呼吸器行鼻罩法吸气压力支持通气（ＰＳＶ），在吸浓度不变的情况下，均明显提高了患者术和动脉血氧分压（ＰａＯ２）平均升高，１．６ｋＰａ氧饱和度（ＳａＯ２）平均升高３％，而动脉二氧化碳分压（ＰａＣＯ２）改变不明显，与ＰａＯ２升高不成比例，８例从ＰＳＶ改变间歇正压通气（ＩＰＰＶ）后，６例ＳａＯ２明显降低２％～１０％。提示鼻罩ＰＳＶ改善上腹部手术中气体交换并     

Gas Exchange Efficiency of a Membrane Oxygenator with Use of a Vibrating Flow Pump

Abstract: We have developed a newly designed blood pump, named the vibrating flow pump (VFP), which can generate high frequency oscillated flow. The driving frequency is 10–50 Hz, and flow volume is linearly controlled electric power (current and voltage). The VFP was applied as the pump for extracorporeal circulation (ECC) in acute animal experiments. The gas exchange efficiency of the membrane oxygenator with the VFP and a roller pump (RP) was evaluated. Under general anesthesia with halothane, 7 adult goats underwent ECC; an inflow can-nula was inserted into the right atrium, an outflow cannula was sutured to the descending thoratic aorta, and total ECC was performed with a flow of about 80 ml/min/ kg. The ECC system with the VFP showed excellent gas exchange efficiency compared with that of the RP. The hemodynamics of ECC using the VFP were easily maintained within normal limits. These results suggest that the VFP is very useful as a pump for ECC; thus, a compact-sized ECC system may be achieved.     

Pulmonary Blood Flow Distribution in Sheep: Effects of Anesthesia, Mechanical Ventilation, and Change in Posture

Background: Recent studies providing high-resolution images of pulmonary perfusion have questioned the classical zone model of pulmonary perfusion. Hence the present work was undertaken to provide detailed maps of regional pulmonary perfusion to examine the influence of anesthesia, mechanical ventilation, and posture.

Methods: Pulmonary perfusion was analyzed with intravenous fluorescent microspheres (15 micro meter) in six sheep studied in four conditions: prone and awake, prone with pentobarbital-anesthesia and breathing spontaneously, prone with anesthesia and mechanical ventilation, and supine with anesthesia and mechanical ventilation. Lungs were air dried at total lung capacity and sectioned into approximately 1,100 pieces (about 2 cm3) per animal. The pieces were weighed and assigned spatial coordinates. Fluorescence was read on a spectrophotometer, and signals were corrected for piece weight and normalized to mean flow. Pulmonary blood flow heterogeneity was assessed using the coefficient of variation of flow data.

Results: Pentobarbital anesthesia and mechanical ventilation did not influence perfusion heterogeneity, but heterogeneity increased when the animals were in the supine posture (P < 0.01). Gravitational flow gradients were absent in the prone position but present in the supine (P < 0.001 compared with zero). Pulmonary perfusion was distributed with a hilar-to-peripheral gradient in breathing spontaneously (P < 0.05).