Pressure-limited ventilation of infants with low-compliance lungs: the efficacy of an adult circle system versus two free-standing intensive care unit ventilator systems using an in vitro model.

We compared the efficacy of a Drager Narkomed GS (North American Drager, Telford, PA) equipped with an adult circle system with two free-standing infant ventilator systems (Servo 300; Siemens Medical Systems, Danvers, MA and Babylog 8000; North American Drager) to deliver minute ventilation (VE) using pressure-limited ventilation to a test lung set to low compliance. To simulate a wide variety of potential patterns of ventilation, VE was measured at peak inspiratory pressures (PIP) of 20, 30, 40, and 50 cm H2O and at respiratory rates (RR) of 20, 30, 40, and 50 breaths/min. Each measurement was made three times; the average was used for data analysis using the multiple regression technique. Delivered V(E) was positively correlated with both PIP (P = 0.001) and RR (P = 0.001). Only minimal differences in VE were observed between the circle and the two free-standing systems. At lower RR and PIP, the Babylog 8000 system delivered slightly higher VE than the circle system, whereas at higher RR and PIP, the Babylog 8000 delivered slightly lower VE than the circle system; these differences in VE were not statistically significant (P = 0.45). The Servo 300 delivered slightly higher VE than the circle system in all test conditions, but these differences were not statistically significant (P = 0.09). None of the differences in delivered VE between the Servo 300 and the circle system are of clinical importance. IMPLICATIONS: Our laboratory investigation suggests that pressure-limited ventilation delivered by a standard adult circle system compares favorably with that of freestanding infant ventilators used in pressure-limited mode. Changing from an adult circle system to a free-standing pressure-limited ventilator may not substantially improve ventilation of a low-compliance infant lung; the efficacy of such a practice should be investigated.     

The effect of circuit compliance on delivered ventilation with use of an adult circle system for time cycled volume controlled ventilation using an infant lung model

This in vitro study examined the effect of circuit compliance on delivered ventilation (V_E) using a time-cycled, volume controlled circle system in an infant lung model. A Bio-Tek ventilator tester set to simulate normal and abnormal lung compliance measured V_E delivered by the Narkomed 2B system. Circle circuits of varied compliance (2.75, 1.22 and 0.73 μl·cm H₂O^?1) were tested. Tidal volume was adjusted to peak inflation pressures (PIP) of 20, 30, 40, and 50 cm H₂O with three circuits, two lung compliances, and four different size tracheal tubes (TT) (2.5, 3.5, 4, 4.5 mm ID). Data were analysed using the multiple regression technique. Delivered V_E was directly related to PIP and lung compliance. Delivered V_E was not affected by the choice of circuit. TT size had minimal effects on V_E when lung compliance was low; TT size was a more important factor when test lung compliance was normal. Extrapolating this data to the clinical setting, adequate ventilation of infants can be achieved with an adult circle system if an appropriate PIP is chosen, regardless of the compliance of the circuit used. Infants with poor lung compliance may require very high PIP for adequate ventilation.     

Pressure control ventilation: three anesthesia ventilators compared using an infant lung model

We compared three ventilators-Servo 900C (Siemens Medical Systems, Danvers, MA), Aestiva 3000 (Datex-Ohmeda, Madison, WI), and NAD 6000 (North American Dr?ger, Telford, PA)-set to deliver pressure control ventilation using an infant test lung model. Ventilator settings were selected to test "near-maximum" settings that would be used for a neonatal patient (peak inspiratory pressure [PIP] 30 cm H(2)O) or older child (PIP 60 cm H(2)O). When adjusted for set inspiratory pressure and compliance, the average tidal volume (V(t)) produced by the NAD 6000 was 5.8 mL less than the Servo 900C (P: = 0. 103), and the average V(t) produced by the Aestiva 3000 was 18.9 mL less than the Servo 900C (P: < 0.001). The Servo 900C generated increased peak pressures, tending to overshoot the set maximum inflating pressures, especially during rapid respiratory rates with decreased inspiratory times. The Aestiva 3000 did not achieve the set PIP during testing conditions of decreased inspiratory times, and the NAD 6000 was not greatly affected by changes in inspiratory time. All three ventilators measured expiratory V(t) to be larger than the actual V(t) delivered to the lung; however, the NAD 6000 was more accurate. Implications: There are differences in performance of ventilators when set to deliver pressure control ventilation to an infant test lung model.     

Mechanical ventilation in an anesthetic circle system using the lowest tidal volume--studies of 3 anesthesia ventilators in a lung model and an animal experiment]

No anesthesia ventilator attached to a circle system is manufactured for use in neonates. However, a small bellows can be supplied for the following anesthesia ventilators: Spiromat NS 656 (NS), Ventilog 2 (V2) and AV1 (Draeger Co.) We investigated the minimal tidal volume delivered by each of the three ventilators. In addition, we tested the performance of the AV1 in neonatal piglets for manual and controlled ventilation, and in decreased lung compliance. MATERIALS AND METHODS. All circuits were equipped with one CO2 canister (750 ml) and the low-compliance tubes of the "Ulmer Kinder Set" (Ruesch Co.) The circuits were connected to a lung model consisting of a glass cylinder filled with copper wool with a compliance of 3.0 ml/mbar. By using calibrated glass syringes we created a pressure-volume correlation for the entire system, i.e., the lung model, the anesthesia circuit and the ventilator, which was linear for each of the three ventilators. The pressure was measured in the test lung. The pressure increase caused by the tidal volume therefore reflected the actual tidal volume delivered, which was calculated using the pressure-volume correlation. Tidal volumes were determined for varying the fresh gas flow (FGF), the respiratory rate (RR), which was varied between 20 and 60/min and the I:E ratio (IE), which was varied between 1:1 and 1:2. Six newborn piglets aged 2-12 h and with body weight 1000-1300 g were anesthetized, tracheotomized and ventilated with an oxygen-nitrous oxide mixture (FIO2 0.25). The manual ventilation lasted 30 min (period 1) and was followed by mechanical ventilation for 60 min (period 2). Thereafter, a left pneumothorax with constant pressure of 20 mbar and then 40 mbar for 15 min each was created (period 3). A fall in blood pressure was treated with 10 ml colloids in five of the six animals. During the experiment arterial blood pressure in the carotid artery, mean airway pressure at the distal end of the tracheal tube and end-tidal CO2 were continuously recorded. Arterial blood gases were analyzed at the end of each period. RESULTS. The tidal volumes delivered with an identical position of the bellows varied in ventilators NS and V2 with changes in FGF, RR and IE. Decrease in FGF, higher RR and longer expiration resulted in a decrease in the tidal volume. The "smallest" tidal volume delivered by NS varied from 50 ml (FGF 2 l/min, RR 60, IE 1:2) to 188 ml (FGF 4 l/min, RR 20, IE 1:1) and from 11 ml (FGF 2 l/min, RR 60, IE 1:2) to 110 (FGF 4 l/min, RR 20, IE 1:1) in the V2. The AV1 showed a minimal tidal volume of about 5 ml, and no changes in tidal volume attributable to alterations in FGF, RR or IE could be observed. No problems occurred during manual or mechanical ventilation in the piglets. With the experimental decrease in lung compliance no increase in airway pressure was noted, but an increase in arterial pCO2 by 8 mmHg (mean) reflects hypoventilation that was not corrected by the ventilator. DISCUSSION. We believe that the changes in tidal volume in ventilators NS and V2 are caused by adding FGF to the volume delivered by the below during inspiration. Because of the unpredictability of the tidal volumes, these ventilators are not suitable for the use in neonates. The AV1 has a very low systemic compliance which makes it suitable for use in neonatal anesthesia. However, a decrease in lung compliance is not compensated by an increase in airway pressure and leads to hypoventilation. When small tidal volumes are used in patients with low lung compliance, it does not act as expected of a volume-cycled ventilator.     

The long Bain breathing system: an investigation into the implications of remote ventilation

A long version of the Bain breathing system is commonly used when remote anaesthesia is required, such as during magnetic resonance imaging or radiotherapy. We compared the static compliance and distal pressures over a range of flows in a 1.6 and 9.6 m Bain system. We examined the effect on ventilation of increasing the length of the Bain system in lung models for 10, 20 and 70 kg patients. We found that static compliance was increased in the long Bain system. We found that with matched peak inspiratory ventilator pressures there was a reduction in peak inspiratory pressures at the patient end with the longer system (p < 0.001). A reduction in tidal volume was found with the 9.6 m Bain (p < 0.001), and positive end-expiratory pressure was increased (p = 0.01). Although the effect on tidal volume was proportionally small in the 70 kg simulation (660 and 617 ml in 1.6 and 9.6 m systems, respectively) it increases in significance in children, with a 23% reduction in tidal volume in the 10 kg mock lung (95 and 73 ml in 1.6 and 9.6 m systems, respectively). Anaesthetists should be aware of the reduction in tidal volume and increased positive end-expiratory pressure. During remote anaesthesia with a long Bain system, the ventilator should be adjusted to compensate.     

Wasted ventilation measured in vitro with eight anesthetic circuits with and without inline humidification

Compression of gases (Boyle's law) and circuit compliance are major determinants of anesthesia circuit function. The materials of which circuits are constructed and the use of heated humidifiers may result in clinically important variations in delivered minute ventilation (VE) secondary to variations in compression volume. We examined eight anesthetic circuits both with and without a heated humidifier in an in vitro setting. Compression volume was determined with a large calibrated syringe. Circuit efficiency was determined by measuring VE at multiple peak inflation pressures (PIP) while using a pediatric ventilator with fixed VE, respiratory rate, fresh gas flow, and I/E ratio. As expected, both compression volume and delivered VE highly correlated with the type of circuit and the pressure at which it was examined (P less than 0.001). Mapleson D circuits had the lowest compression volume and were the most efficient circuits (P less than 0.0001). Pediatric circle systems were intermediate and adult circle systems had the largest compression volume and were the least efficient. Humidifiers uniformly increased compression volume. The following conclusions were drawn: 1) the anesthetic circuit, its material, and the pressure at which it operates are important determinants of circuit function; 2) humidifiers increase compression volume; 3) Mapleson D circuits had the lowest compression volume and therefore were the most efficient; 4) highly compliant adult circuits may result in compression volume losses that exceed the tidal volume of a pediatric ventilator; 5) humidifiers with low volume and rigid tubing should have the least effect on minute ventilation; and 6) highly compliant adult circuits when used in the care of infants and small children must be used with caution.     

甲型H11感危重症患者机械通气治疗后发生气压伤的相关危险因素分析

目的：分析甲型H1N1流感危重症患者在机械通气时发生气压伤的危险因素.方法：对2009年11月-2010年2月山东省胸科医院ICU收治的15例行机械通气的甲型H1N1流感危重症患者按有无发生气压伤分成两组,对患者性别、年龄、28 d在院病死率、急性生理学和慢性健康状况评分、肺损伤评分、氧合指数及呼吸支持时肺部静态顺应性、呼吸频率、呼气末正压、最大吸气压力、潮气量和氧浓度指标进行回顾分析.结果：气压伤组患者的肺损伤评分、吸入氧浓度明显高于无气压伤组患者（P=0.001,P=0.008）,肺部静态顺应性（Cstat）要明显低于未出现气压伤的患者（P=0.024）,两组之间差异具有统计学意义.两组患者的年龄、性别、APACHEⅡ评分、呼气末正压、最大吸气压力、潮气量和呼吸频率之间差异无统计学意义（P均〉0.05）.结论：甲型H1N1流感病毒对肺组织的严重损害及其导致的肺静态顺应性下降可能是导致危重症患者机械通气时发生气压伤的重要因素.     

婴儿麻醉中紧闭循环通气与Jackson-Rees回路通气呼吸动力学的比较

目的 评价Ｏｈｍｅｄａ Ｅｘｃｅｌ２１０麻醉机＋７９００呼吸机紧闭循环通气用于婴儿麻醉的可行性。方法 选择１０ｋｇ以下婴儿唇裂或腭裂手术病例３０例。以同组病例前后比较紧闭循环通气与Ｊａｃｋｓｏｎ－Ｒｅｅｓ婴儿回路通气的各项呼吸动力学指标。以呼吸频率（ＲＲ）＝２２次／ｍｉｎ,Ｉ：Ｅ＝１：１．５及ＰＥＴＣＯ２＝４０ｍｍＨｇ为控制值,相应调节潮气量。观测紧闭循环通气与Ｊａｃｋｓｏｎ－Ｒｅｅｓ婴儿回路通气     

Biologically variable ventilation improves oxygenation and respiratory mechanics during one-lung ventilation

BACKGROUND: Hypoxemia is common during one-lung ventilation (OLV). Atelectasis contributes to the problem. Biologically variable ventilation (BVV), using microprocessors to reinstitute physiologic variability to respiratory rate and tidal volume, has been shown to be advantageous over conventional monotonous control mode ventilation (CMV) in improving oxygenation during the period of lung reinflation after OLV in an experimental model. Here, using a porcine model, the authors compared BVV with CMV during OLV to assess gas exchange and respiratory mechanics. METHODS: Eight pigs (25-30 kg) were studied in each of two groups. After induction of anesthesia-tidal volume 12 ml/kg with CMV and surgical intervention-tidal volume was reduced to 9 ml/kg. OLV was initiated with an endobronchial blocker, and the animals were randomly allocated to either continue CMV or switch to BVV for 90 min. After OLV, a recruitment maneuver was undertaken, and both lungs were ventilated for a further 60 min. At predetermined intervals, hemodynamics, respiratory gases (arterial, venous, and end-tidal samples) and mechanics (airway pressures, static and dynamic compliances) were measured. Derived indices (pulmonary vascular resistance, shunt fraction, and dead space ventilation) were calculated. RESULTS: By 15 min of OLV, arterial oxygen tension was greater in the BVV group (group x time interaction, P = 0.003), and shunt fraction was lower with BVV from 30 to 90 min (group effect, P = 0.0004). From 60 to 90 min, arterial carbon dioxide tension was lower with BVV (group x time interaction, P = 0.0001) and dead space ventilation was less from 60 to 90 min (group x time interaction, P = 0.0001). Static compliance was greater by 60 min of BVV and remained greater during return to ventilation of both lungs (group effect, P = 0.0001). CONCLUSIONS: In this model of OLV, BVV resulted in superior gas exchange and respiratory mechanics when compared with CMV. Improved static compliance persisted with restoration of two-lung ventilation.     

Effect of rate and inspiratory flow on ventilator-induced lung injury

BACKGROUND: We examined the effects of decreasing respiratory rate (RR) at variable inspiratory times (It) and reducing inspiratory flow on the development of ventilator-induced lung injury. METHODS: Forty sheep weighing 24.6+/-3.2 kg were ventilated for 6 hours with one of five strategies (FIO2 = 1.0, positive end-expiratory pressure = 5 cm H2O): (1) pressure-controlled ventilation (PCV), RR = 15 breaths/min, peak inspiratory pressure (PIP) = 25 cm H2O, n = 8; (2) PCV, RR = 15 breaths/min, PIP = 50 cm H2O, n = 8; (3) PCV, RR = 5 breaths/min, PIP = 50 cm H2O, It = 6 seconds, n = 8; (4) PCV, RR = 5 breaths/min, PIP = 50 cm H2O, It = 2 seconds, n = 8; and (5) limited inspiratory flow volume-controlled ventilation, RR = 5 breaths/min, pressure-limit = 50 cm H2O, flow = 15 L/min, n = 8. RESULTS: Decreasing RR at conventional flows did not reduce injury. However, limiting inspiratory flow rate (LIFR) maintained compliance and resulted in lower Qs/Qt (HiPIP = 38+/-18%, LIFR = 19+/-6%, p < 0.001), reduced histologic injury (HiPIP = 14+/-0.9, LIFR = 2.2+/-0.9, p < 0.05), decreased intra-alveolar neutrophils (HiPIP = 90+/-49, LIFR = 7.6+/-3.8,p = 0.001), and reduced wet-dry lung weight (HiPIP = 87.3+/-8.5%, LIFR = 40.8+/-17.4%,p < 0.001). CONCLUSIONS: High-pressure ventilation for 6 hours using conventional flow patterns produces severe lung injury, irrespective of RR or It. Reduction of inspiratory flow at similar PIP provides pulmonary protection.     

Using pressure-limited mechanical ventilation in caring for organ donors

Pressure-limited (controlled) ventilation is commonly employed to provide mechanical ventilation in the intensive care unit when lung compliance is poor or when airway resistance is irreversibly high. Modification of the inspiratory-expiratory ratio to include inspiratory-expiratory ratio reversal and permissive hypercapnia can also be used when lung disease or injury is severe. Because other donor organs often can be saved for transplantation even when the lungs have been badly damaged, the organ procurement coordinator should adopt pressure-limited ventilation as well as inspiratory-expiratory ratio reversal and permissive hypercapnia as potentially helpful methods while providing mechanical ventilation to selected donors.     

Respiratory and haemodynamic effects of conventional volume controlled PEEP ventilation, pressure regulated volume controlled ventilation and low frequency positive pressure ventilation with extracorporeal carbon dioxide removal in pigs with acute ARDS

The purpose of this study was to evaluate whether any benefit of low frequency positive pressure ventilation with extracorporeal carbon dioxide removal (LFPPV–ECCO₂R) existed over either volume controlled ventilation (VCV) with measured best–PEEP or pressure regulated volume controlled ventilation (PRVCV) with an inspiration/expiration (I/E) ratio of 4:1, with respect to arterial oxygenation, lung mechanics and haemodynamics, in acute respiratory failure.
Fifteen adult pigs were used for the study. Respiratory failure was induced by surfactant depletion by repeated lung lavage. The different therapeutic approaches were applied randomly to each pig for 1 h. Measurements of gas exchange, airway pressures and haemodynamics were performed during ventilatory and haemodynamic steady state. Paco₂ was kept constant in all modes.
At almost similar total–PEEP, Pao₂ values were significantly higher with LFPPV–ECCO₂R comared to VCV with best–PEEP. Peak inspiratory pressure (PIP) and intrapulmonary pressure amplitude defined as the difference between PIP and total–PEEP were significantly lower with PRVCV and LFPPV–ECCO₂R compared to VCV with best–PEEP. There was no significant difference between the modes concerning cardiocircu–latory parameters.
PRVCV with I/E ratio of 4:1 and LFPPV–ECCO₂R proved to be better modes to achieve better gas exchange and lower PIP at lower intrapulmonary pressure amplitudes. It is concluded that PRVCV is an adequate form of treatment under these experimental conditions imitating acute respiratory failure, without necessitating other invasive measures.     

Preliminary experience with airway pressure release ventilation in a trauma/surgical intensive care unit

BACKGROUND: Airway pressure-release ventilation (APRV) is a pressure-limited, time-cycled mode of mechanical ventilation. The purpose of this study was to evaluate our initial experience with the use of APRV in acutely injured, ventilated patients. METHODS: Since March 2003, APRV has been used selectively in adult trauma patients with or at risk for acute lung injury/acute respiratory distress syndrome. Data were obtained before and during the 72 hours after switching to APRV. A retrospective analysis of these data was then performed. RESULTS: Complete data were available on 46 of 60 patients (77%) for the first 72 hours of APRV. Before APRV, the average Pao2/Fio2 ratio was 243 and the average peak airway pressure was 28 cm H2O. Peak airway pressure decreased 19% (p = 0.001), Pao2/Fio2 improved by 23% (p = 0.017) and release tidal volumes improved by 13% (p = 0.020) over the course of the analysis. CONCLUSION: APRV significantly improved oxygenation by alveolar recruitment and allowed for a reduction in peak airway pressures. This relatively new modality had favorable results and appears to be an effective alternative for lung recruitment in traumatically injured patients at risk for acute lung injury/acute respiratory distress syndrome.     

腹腔镜手术患儿压力控制通气和容量控制通气效果的比较

目的 比较腹腔镜手术患儿压力控制通气和容量控制通气的效果.方法 择期行腹腔镜手术患儿30例,性别不限,年龄12～36月,ASA分级Ⅰ或Ⅱ级,体重9～15 kg,采用随机数字表法,将其随机分为2组(n=15):压力控制通气组(P组)和容量控制通气组(V组).麻醉诱导后气管插管行机械通气,P组调节麻醉机最大吸气压力使潮气量达到12 ml/kg,V组设置潮气量12 ml/kg,维持PETCO235～45mmHg.于气管插管后即刻(T0)、切皮前即刻(T1)、气腹30 min(T2)和气腹结束后15 min (T3)时,记录MAP、HR、PETCO2、分钟通气量和气道峰压,并采集动脉血样,进行血气分析,计算肺动态顺应性和生理死腔量/潮气量.结果 与V组比较,P组T1,2时PaCO2和PETCO2降低,肺动态顺应性升高,T0～3时分钟通气量和气道峰压降低(P<0.01),MAP、HR和生理死腔量/潮气量差异无统计学意义(P>0.05).结论 与容量控制通气相比,压力控制通气可更好地改善腹腔镜手术患儿肺通气效果,有利于气体交换,减少气腹对呼吸功能的影响.

Abstract：

Objective To compare the efficacy of pressure-controlled ventilation and volume-controlled ventilation in children undergoing laparoscopic surgery. Methods Thirty ASA Ⅰ or Ⅱ children of both sexes,aged 12-36 months, weighing 9-15 kg, scheduled for laparoscopic surgery, were randomly divided into 2 groups (n = 15 each): pressure-controlled ventilation group (group P) and volume-controlled ventilation group (group V) . Anesthesia was induced with propofol 2-4 mg/kg, vecuronium 0.1 mg/kg and fentanyl 2 μg/kg. The children were tracheal intubated and mechanically ventilated. The maximum inspiratory pressure was adjusted to make the tidal volume (VT ) achieve 12 ml/kg in group P and the VT was set at 12 ml/kg in group V. PETCO2 was maintained at 35-45 mm Hg. MAP, HR, PETCO2 , minute ventilation and peak airway pressure were recorded immediately after intubation (T0 ) , immediately before skin incision (T1 ) , 30 min of pneumoperitoneum (T2 ) and 15 min after the end of pneumoperitoneum (T3 ) . Arterial blood samples were taken at the same time points mentioned above for blood gas analysis. Dynamic lung compliance and physiological dead space to tidal volume ratio were calculated.Results Compared with group V, PaCO2 and PETCO2 were significantly decreased and dynamic lung compliance was significantly increased at T1,2 , and minute ventilation and peak airway pressure were significantly decreased at T0-3 in group P ( P < 0.01) . There was no significant difference in MAP, HR and physiological dead space to tidal volume ratio between the two groups ( P > 0.05) . Conclusion Compared with volume-controlled ventilation, pressure-controlled ventilation can better improve the ventilatory efficacy, is more beneficial to gas exchange and reduces the influence of pneumoperitoneum on respiratory function in children undergoing laparoscopic surgery.     

长期机械通气致肺不张行持续性膨肺对呼吸力学的影响

目的：探讨持续性膨肺对长期机械通气致肺不张病人呼吸力学的影响。方法：对长期机械通气已发生肺不张的9例ICU病人行持续性膨肺，监测其呼吸力学的改变。结果：与膨肺前比较，膨肺后30min气道峰压（PIP）、平台压（Pplat）、阻力（R）、呼吸机作功（WOBv）均有所降低（均P＜0．05），差异有显著性意义；顺应性改善最为明显（P＜0．01）。120min PIP、Pplat、R、WOBv与膨肺前比较,差异均无显著性意义 （P＞0．05）。结论：持续性膨肺可以明显改善呼吸力学特征，增加肺容积，从而改善氧合功能，由于持续性膨肺对呼吸和血流动力学有一定影响，需严密观察病人的血压、心率及血氧饱和度情况，加强护理。     

A coaxial circle circuit: Comparison with conventional circle and bain circuit

A coaxial system to be used for gas delivery to patients in a closed or low fresh gas flow anaesthetic system is described. The resistance to gas flow, humidity of inspired gases, and static compliance of the circuit are provided and compared with the circle tubing customarily employed or the coaxial Mapleson D (“Bain”) circuit, The resistance to gas flow is highest in the coaxial circle and “Bain” circuits; the resistance of the conventional circle is approximately 40 per cent less. Static compliance of this coaxial circle is 50 per cent greater than the conventional circle. During artificial ventilation humidity of inspired gases is maintained at levels recommended in the literature for all circuits, but during spontaneous breathing only the conventional rubber circle maintains appropriate levels. Advantages of this coaxial circle over the conventional circle include light weight and small size. Advantages of this coaxial circle over the “Bain” circuit include lower fresh gas flows and improved humidity during spontaneous breathing. These advantages make this coaxial circle useful for routine use.     

Gas flow distribution in distal high frequency jet ventilation and lung thorax compliance

To investigate the influence of changes in thorax and lung compliance on ventilation during distal High Frequency Jet Ventilation (HFJV), similar ventilator settings were compared before and after changing the compliance in two groups of anaesthetized mongrel dogs. Each period of distal HFJV was preceded by adequate Intermittent Positive Pressure Ventilation (IPPV) to assure a start with baseline values. In Group 1 (n = 7), thorax compliance was changed by chest strapping, while in Group 2 (n = 7) lung compliance was changed by inducing acute lung injury by injection of oleic acid into the right atrium. Gas flow distribution in the ventilatory circuit during distal HFJV was determined before and after the changes in compliance were induced. Comparing similar ventilator settings during distal HFJV in the same dog, a decrease in lung or thorax compliance led to changes in gas flow distribution in the ventilatory circuit. Entrainment was decreased and bypass increased with a negative effect on the gas volume entering the lungs and on gas exchange. The results indicate that distal HFJV should be regarded as pressure-limited ventilation.     

Estimating respiratory system compliance during mechanical ventilation using artificial neural networks

In this study we evaluated whether a technology based on artificial neural networks (ANN) could estimate the static compliance (C(RS)) of the respiratory system, even in the absence of an end-inspiratory pause, during continuous mechanical ventilation. A porcine model of acute lung injury was used to provide recordings of different respiratory mechanics conditions. Each recording consisted of 10 or more consecutive breaths in volume-controlled mechanical ventilation, followed by a breath having an end-inspiratory pause used to calculate C(RS) according to the interrupter technique (IT). The volume-pressure loop of the breath immediately preceding the one with pause was given to the ANN for the training, together with the C(RS) separately calculated by the IT. The prospective phase consisted of giving only the loops to the trained ANN and comparing the results yielded by it to the compliance separately calculated by the investigators. Determination of measurement agreement between ANN and IT methods showed an error of -0.67 +/- 1.52 mL/cm H(2)O (bias +/- SD). We could conclude that ANN, during volume-controlled mechanical ventilation, can extract C(RS) without needing to stop inspiratory flow. IMPLICATIONS: We studied the application of artificial neural networks (ANN) to the estimation of respiratory compliance during mechanical ventilation. The study was performed on an animal model of acute lung injury, testing the performance of ANN in both healthy and diseased conditions of the lung.     

Influence of pneumoperitoneum and patient positioning on respiratory system compliance

STUDY OBJECTIVE: To investigate the influence of pneumoperitoneum (PP) and posture on respiratory compliance and ventilation pressures. DESIGN: Prospective, single blind trial. PATIENTS: 10 female ASA physical status I and II patients scheduled for elective gynecologic laparoscopy. SETTING: University medical center. INTERVENTIONS: Anesthesia was performed as total IV anesthesia (TIVA) with propofol, alfentanil, and atracurium. After induction of anesthesia and orotracheal intubation, the lungs were ventilated to maintain partial pressure of CO(2) (P(ET)CO(2)) of 30 +/- 3 mmHg. Ventilation was kept constant. As gas mixture oxygen and air 1:1 was used without positive end-expiratory pressure (PEEP). MEASUREMENTS: Measurements were taken before and after creation of pneumoperitoneum with an intraabdominal pressure (IAP) of 10 mmHg, of 15 mmHg in 20 degrees head-down tilt, then in 20 degrees head-up tilt, and after deflation of PP. We determined peak inspiratory pressure (PIP), mean airway pressure (mPaw), P(ET)CO(2), expiratory minute volume (V(E)), heart rate (HR), and systolic (SBP), diastolic (DBP), and mean arterial pressure (MAP). Respiratory system compliance (C(eff rs)) was calculated as quotient of tidal volume (V(T)) and PIP. MAIN RESULTS: After creation of PP (IAP 10 mmHg), there was a significant increase of median PIP (3 cmH(2)O), mPaw (1 cm H(2)O) and arterial pressure (BP), (MAP by 7 mmHg), C(eff rs) decreased by 6 mL. cm H(2)O(-1). Increase of IAP to 15 mmHg led to a further increase of PIP (2 cm H(2)O) and mPaw (1 cm H(2)O), and a further decrease of C(eff rs) by 5 mL cm H(2)O(-1); BP decreased (MAP by 5.5 mmHg). Head-up or head down positions showed no significant hemodynamic or pulmonary changes. P(ET)CO(2)increased from 29.5 to 36 mmHg at an IAP of 15 mmHg, but then no further changes were noticed. Five minutes after deflation of pneumoperitoneum all values returned to baseline levels. CONCLUSIONS: Creation of PP at an IAP of 15 mmHg reduced respiratory system compliance, and increased peak inspiratory and mean airway pressures, which quickly returned to normal values after deflation. Head-down or head-up position did not further alter those parameters.     

急性呼吸窘迫综合征患者适应性支持通气的效果

目的 评价适应性支持通气（ASV）模式与间歇正压通气（IPPV）模式在急性呼吸窘迫综合征（ARDS）患者中的效果。方法 ARDS患者30例，年龄19—46岁，男18例，女12例，ASAⅢ或Ⅳ级。先应用IPPV模式，吸入氧浓度60％，PEEP为0，潮气量（VT）10ml／kg，吸呼比（I：E）1：2，维持8h后随机选择换用ASV或继续IPPV通气模式，通气时依次按0、5、10cm H2O增加PEEP，每一PEEP水平的通气时间为60min，在同样的分钟通气量的设置下，4h后更换另一种通气模式，仍按0,5、10cm H2O增加PEEP，每一PEEP水平的通气时间为60min。每个PEEP水平通气50min时，用Swan-Ganz导管、心电监测仪、呼吸机监测记录血液动力学、呼吸力学和氧代谢数据。结果 与IPPV模式比较，ASV模式下气道峰值压降低，肺动态顺应性（Cdyn）、动脉氧分压（PaO2）和氧供（DO2）增加（P〈0．05）。两种通气模式的血液动力学参数比较差异无统计学意义（P〉0．05）。结论 ASV模式比IPPV模式更有利于ARDS患者的通气治疗。