Nasal ventilation in acute exacerbations of chronic obstructive pulmonary disease: effect of ventilator mode on arterial blood gas tensions.

BACKGROUND--There are no controlled trials of the use of different modes of nasal intermittent positive pressure ventilation (NIPPV) in patients with exacerbations of chronic obstructive pulmonary disease (COPD). This study describes the effect on blood gas tensions of four different modes of nasal ventilation. METHODS--Twelve patients with acute exacerbations of COPD were studied (mean (SD) FEV1 0.59 (0.13) l, PaO2 (air) 5.10 (1.12) kPa, PaCO2 9.28 (1.97) kPa, pH 7.32 (0.03)). Each patient underwent four one-hour periods of nasal ventilation in randomised order: (a) inspiratory pressure support 18 cm H2O; (b) pressure support 18 cm H2O+positive end expiratory pressure (PEEP) 6 cm H2O (IPAP+EPAP); (c) continuous positive airway pressure (CPAP) 8 cm H2O; and (d) volume cycled NIPPV. Arterial blood samples were obtained before each period of ventilation and at one hour. RESULTS--Pressure support, CPAP, and volume cycled NIPPV all produced significant improvements in PaO2; there was no difference between these three modes. The change in PaO2 with IPAP+EPAP did not reach statistical significance. None of the modes produced significant changes in mean PaCO2; patients with higher baseline levels tended to show a rise in PaCO2 whereas those with lower baseline levels tended to show a fall. CONCLUSIONS--Although PaO2 improved in all patients there are differences in efficacy between the modes, while the changes in PaCO2 were variable. The addition of EPAP conferred no advantage in terms of blood gas tensions.     

Hemodynamic and respiratory response to varying gradients between end-expiratory pressure and end-inspiratory pressure in patients breathing on continuous positive airway pressure.

Nine patients on intermittent mandatory ventilation (IMV) and continuous positive airway pressure (CPAP) were allowed to breathe spontaneously at varying end expiratory pressure-end inspiratory pressure (EEP-EIP) gradients up to 10 cm H2O. There was no change in the mean cardiac output and oxygen delivery despite a lowered mean airway pressure (MAWP) when the gradient was increased. Three patients were uncomfortable at the higher gradients and another manifested evidence of fatigue of the muscles of respiration by raising her arterial PCO2 (PaCO2) and intrapulmonary shunt (Qs/Qt). In view of the difficulty experienced by some patients and lack of improvement in cardiac outputs (CO) during spontaneous inspiration when the EEP-EIP gradient is raised from zero to 5 and 10 cm H2O, it is recommended that the variation in airway pressure during spontaneous breaths while a patient is on CPAP be minimized.     

Effect of propofol anesthesia and continuous positive airway pressure on upper airway size and configuration in infants

BACKGROUND: Infants are prone to obstruction of the upper airway during general anesthesia. Continuous positive airway pressure (CPAP) is often used to prevent or treat anesthesia-induced airway obstruction. The authors studied the interaction of propofol anesthesia and CPAP on airway caliber in infants using magnetic resonance imaging. METHODS: Nine infants undergoing elective magnetic resonance imaging of the brain were studied. Head position was standardized. Spin echo magnetic resonance images of the airway were acquired at the level of the soft palate, base of the tongue, and tip of the epiglottis. Four sets of images were acquired in sequence: (1) during light propofol anesthesia at an infusion rate of 80 microg . kg(-1) . min(-1), (2) after increasing the depth of propofol anesthesia by administering a bolus dose (2.0 mg/kg) and increasing the infusion rate to 240 microg . kg(-1) . min(-1), (3) during continued infusion of 240 microg . kg(-1). min propofol and application of 10 cm H2O CPAP, and (4) after removal of CPAP and continued infusion of 240 microg . kg(-1). min propofol. RESULTS: Increasing depth of propofol anesthesia decreased airway caliber at each anatomical level, predominantly due to anteroposterior narrowing. Application of CPAP completely reversed the propofol-induced decrease in airway caliber, primarily by increasing the transverse dimension. CONCLUSIONS: Airway narrowing with increasing depth of propofol anesthesia results predominantly from a reduction in anteroposterior dimension, whereas CPAP acts primarily to increase the transverse dimension. Although airway caliber during deep propofol anesthesia and application of CPAP was similar to that during light propofol anesthesia, there were significant configurational differences.     

双相正压通气与持续正压通气对急性呼吸窘迫综合征患者肺复张效果的比较

目的 比较双相正压通气(BIPAP)与持续正压通气(CPAP)对急性呼吸窘迫综合征(ARDS)患者肺复张的效果.方法 选择ARDS患者44例,ASA Ⅲ或Ⅳ级,性别不限,年龄35～63岁,体重52～74 kg,肺复张前基础通气模式为同步间歇指令通气联合压力支持通气,随机分为2组(n=22):CPAP组和BIPAP组.CPAP组10 s内逐渐上升呼气末正压(PEEP)至30 cm H2O,持续30 s,然后在5～10 8内恢复肺复张前通气模式.BIPAP组高水平和低水平压力分别为40、20 cm H2O,持续90 s,然后在5～10 s内恢复肺复张前通气模式.记录肺复张通气前即刻(T1),肺复张通气结束后即刻(T2)、2 min(T3)、5 min(T4)、15 min(T5)、30 min(T6)时HR、MAP、CVP、SpO2和肺动态顺应性(Cdyn).分别于T1、T5、肺复张通气结束后1 h(T7)、2 h(T8)、4 h(T9)时采集桡动脉血样,测定pH值、PaO2和PaCO2,计算PaO2/FiO2比值.结果 与CPAP组比较,BIPAP组SpO2、Cdyn、PaO2和PaO2/FiO2升高,CVP降低(P<0.05),HR和MAP比较差异无统计学意义(P>0.05).与T1时比较,CPAP组T3时MAP升高,T2时CVP升高,Cdyn降低,T3～6时SpO2和Cdyn升高,T7,8时PaO2升高,T5,7,8时PaO2/FiO2升高,BIPAP组T2～6时SpO2升高,T3～6时Cdyn升高,T5,7,8时PaO2和PaO2/FiO2升高(P<0.05).结论 与CPAP比较,BIPAP对ARDS患者行肺复张通气时血液动力学影响小,可进一步提高氧合和肺顺应性,是一种安全有效的肺复张方法 .     

Effect of Propofol Anesthesia and Continuous Positive Airway Pressure on Upper Airway Size and Configuration in Infants

Background: Infants are prone to obstruction of the upper airway during general anesthesia. Continuous positive airway pressure (CPAP) is often used to prevent or treat anesthesia-induced airway obstruction. The authors studied the interaction of propofol anesthesia and CPAP on airway caliber in infants using magnetic resonance imaging.

Methods: Nine infants undergoing elective magnetic resonance imaging of the brain were studied. Head position was standardized. Spin echo magnetic resonance images of the airway were acquired at the level of the soft palate, base of the tongue, and tip of the epiglottis. Four sets of images were acquired in sequence: (1) during light propofol anesthesia at an infusion rate of 80 [mu]g [middle dot] kg-1 [middle dot] min-1, (2) after increasing the depth of propofol anesthesia by administering a bolus dose (2.0 mg/kg) and increasing the infusion rate to 240 [mu]g [middle dot] kg-1 [middle dot] min-1, (3) during continued infusion of 240 [mu]g [middle dot] kg-1 [middle dot] min-1 propofol and application of 10 cm H2O CPAP, and (4) after removal of CPAP and continued infusion of 240 [mu]g [middle dot] kg-1 [middle dot] min-1 propofol.

Results: Increasing depth of propofol anesthesia decreased airway caliber at each anatomical level, predominantly due to anteroposterior narrowing. Application of CPAP completely reversed the propofol-induced decrease in airway caliber, primarily by increasing the transverse dimension.     

Cardiopulmonary effects of pressure support ventilation

Pressure support ventilation (PSV) is a newer mode of ventilatory support that augments the patient's spontaneous inspirations to a preselected peak inspiratory pressure. We studied the effects of adding low levels of PSV (5 to 10 cm H2O) in conjunction with intermittent mandatory ventilation (IMV) on 15 patients who required mechanical ventilation for flail chest and pulmonary contusion. Patients were selected for the study if, during weaning from IMV, the following criteria were met: (1) a PaCO2 level greater than 45 mm Hg, (2) a spontaneous respiratory rate (RR) greater than 30 breaths per minute, (3) a minute ventilation (VE) greater than 9.0 L/min, and (4) spontaneous tidal volumes (VT) of less than 2 mL/kg. The PSV was added to the IMV at a level that augmented spontaneous VT to greater than 4 mL/kg. An average of 9 +/- 3 cm H2O of pressure support resulted in a fall in the level of PaCO2 (50 +/- 4 to 43 +/- 5 mm Hg), spontaneous RR (36 +/- 5 to 16 +/- 3 breaths per minute), VE (12 +/- 2 to 8.4 +/- 1.5 L/min), and dead space-tidal volume ratio from (0.68 +/- 0.1 to 0.47 +/- 0.05). Mean airway pressure and PaO2 both increased, but these changes were not statistically significant. Oxygen consumption was also unchanged. These results suggest that in patients who are difficult to wean due to respiratory muscle fatigue (characterized by increasing RR and decreasing VT), PSV normalizes lung volumes, improves ventilation, and may expedite the weaning process.     

Collapsibility of the upper airway at different concentrations of propofol anesthesia

BACKGROUND: This study investigated the effect of varying concentrations of propofol on upper airway collapsibility and the mechanisms responsible for it. METHODS: Upper airway collapsibility was determined from pressure-flow relations at three concentrations of propofol anesthesia (effect site concentration = 2.5, 4.0, and 6.0 mug/ml) in 12 subjects spontaneously breathing on continuous positive airway pressure. At each level of anesthesia, mask pressure was transiently reduced from a pressure sufficient to abolish inspiratory flow limitation (maintenance pressure = 12 +/- 1 cm H2O) to pressures resulting in variable degrees of flow limitation. The relation between mask pressure and maximal inspiratory flow was determined, and the critical pressure at which the airway occluded was recorded. Electromyographic activity of the genioglossus muscle (EMGgg) was obtained via intramuscular electrodes in 8 subjects. RESULTS: With increasing depth of anesthesia, (1) critical closing pressure progressively increased (-0.3 +/- 3.5, 0.5 +/- 3.7, and 1.4 +/- 3.5 cm H2O at propofol concentrations of 2.5, 4.0, and 6.0 microg/ml respectively; P < 0.05 between each level), indicating a more collapsible upper airway; (2) inspiratory flow at the maintenance pressure significantly decreased; and (3) respiration-related phasic changes in EMGgg at the maintenance pressure decreased from 7.3 +/- 9.9% of maximum at 2.5 microg/ml to 0.8 +/- 0.5% of maximum at 6.0 microg/ml, whereas tonic EMGgg was unchanged. Relative to the levels of phasic and tonic EMGgg at the maintenance pressure immediately before a decrease in mask pressure, tonic activity tended to increase over the course of five flow-limited breaths at a propofol concentration of 2.5 microg/ml but not at propofol concentrations of 4.0 and 6.0 microg/ml, whereas phasic EMGgg was unchanged. CONCLUSIONS: Increasing depth of propofol anesthesia is associated with increased collapsibility of the upper airway. This was associated with profound inhibition of genioglossus muscle activity. This dose-related inhibition seems to be the combined result of depression of central respiratory output to upper airway dilator muscles and of upper airway reflexes.     

Continuous positive airway pressure. The use of low levels in adult patients with artificial airways

Twelve adult surgical patients recovering from acute respiratory failure (ARF) had a catheter inserted for measurement of pulmonary capillary wedge pressure, pulmonary artery pressure, and cardiac output; and for calculation of arterial-mixed venous oxygen content difference, physiologic shunt, and systemic and pulmonary vascular resistances. Measurements were made with 5 cm H2O continuous positive airway pressure (CPAP), during spontaneous respiration at ambient airway pressure, and then again with 5 cm H2O CPAP. During breathing without CPAP, the total physiologic shunt increased, and the PaO2/fraction of inspired oxygen concentration (FiO2) ratio decreased significantly from control values. After CPAP therapy was again introduced, the physiologic shunt decreased and the PaO2/FiO2 ratio increased significantly. This improvement in oxygenation took place without any significant change in cardiovascular status. Thus, low levels of CPAP are helpful in maintaining the pulmonary status in intubated adult patients recovering from ARF.     

Collapsibility of the Upper Airway at Different Concentrations of Propofol Anesthesia

Background: This study investigated the effect of varying concentrations of propofol on upper airway collapsibility and the mechanisms responsible for it.

Methods: Upper airway collapsibility was determined from pressure-flow relations at three concentrations of propofol anesthesia (effect site concentration = 2.5, 4.0, and 6.0 [mu]g/ml) in 12 subjects spontaneously breathing on continuous positive airway pressure. At each level of anesthesia, mask pressure was transiently reduced from a pressure sufficient to abolish inspiratory flow limitation (maintenance pressure = 12 +/- 1 cm H2O) to pressures resulting in variable degrees of flow limitation. The relation between mask pressure and maximal inspiratory flow was determined, and the critical pressure at which the airway occluded was recorded. Electromyographic activity of the genioglossus muscle (EMGgg) was obtained via intramuscular electrodes in 8 subjects.

Results: With increasing depth of anesthesia, (1) critical closing pressure progressively increased (-0.3 +/- 3.5, 0.5 +/- 3.7, and 1.4 +/- 3.5 cm H2O at propofol concentrations of 2.5, 4.0, and 6.0 [mu]g/ml respectively; P < 0.05 between each level), indicating a more collapsible upper airway; (2) inspiratory flow at the maintenance pressure significantly decreased; and (3) respiration-related phasic changes in EMGgg at the maintenance pressure decreased from 7.3 +/- 9.9% of maximum at 2.5 [mu]g/ml to 0.8 +/- 0.5% of maximum at 6.0 [mu]g/ml, whereas tonic EMGgg was unchanged. Relative to the levels of phasic and tonic EMGgg at the maintenance pressure immediately before a decrease in mask pressure, tonic activity tended to increase over the course of five flow-limited breaths at a propofol concentration of 2.5 [mu]g/ml but not at propofol concentrations of 4.0 and 6.0 [mu]g/ml, whereas phasic EMGgg was unchanged.     

Effects of Recruitment Maneuver on Atelectasis in Anesthetized Children

Background: General anesthesia is known to promote atelectasis formation. High inspiratory pressures are required to reexpand healthy but collapsed alveoli. However, in the absence of positive end-expiratory pressure (PEEP), reexpanded alveoli collapse again. Using magnetic resonance imaging, the impact of an alveolar recruitment strategy on the amount and distribution of atelectasis was tested.

Methods: The authors prospectively randomized 24 children who met American Society of Anesthesiologists physical status I or II criteria, were aged 6 months-6 yr, and were undergoing cranial magnetic resonance imaging into three groups. After anesthesia induction, in the alveolar recruitment strategy (ARS) group, an alveolar recruitment maneuver was performed by manually ventilating the lungs with a peak airway pressure of 40 cm H2O and a PEEP of 15 cm H2O for 10 breaths. PEEP was then reduced to and kept at 5 cm H2O. The continuous positive airway pressure (CPAP) group received 5 cm H2O of continuous positive airway pressure without recruitment. The zero end-expiratory pressure (ZEEP) group received neither PEEP nor the recruitment maneuver. All patients breathed spontaneously during the procedure. After cranial magnetic resonance imaging, thoracic magnetic resonance imaging was performed.

Results: The atelectatic volume (median, first and third standard quartiles) detected in the ZEEP group was 1.25 (0.75-4.56) cm3 in the right lung and 4.25 (3.2-13.9) cm3 in the left lung. The CPAP group had 9.5 (3.1-23.7) cm3 of collapsed lung tissue in the right lung and 8.8 (5.3-28.5) cm3 in the left lung. Only one patient in the ARS group presented an atelectasis of less than 2 cm3. An uneven distribution of the atelectasis was observed within each lung and between the right and left lungs, with a clear predominance of the left basal paradiaphragmatic regions.     

Effects of recruitment maneuver on atelectasis in anesthetized children

BACKGROUND: General anesthesia is known to promote atelectasis formation. High inspiratory pressures are required to reexpand healthy but collapsed alveoli. However, in the absence of positive end-expiratory pressure (PEEP), reexpanded alveoli collapse again. Using magnetic resonance imaging, the impact of an alveolar recruitment strategy on the amount and distribution of atelectasis was tested. METHODS: The authors prospectively randomized 24 children who met American Society of Anesthesiologists physical status I or II criteria, were aged 6 months-6 yr, and were undergoing cranial magnetic resonance imaging into three groups. After anesthesia induction, in the alveolar recruitment strategy (ARS) group, an alveolar recruitment maneuver was performed by manually ventilating the lungs with a peak airway pressure of 40 cm H2O and a PEEP of 15 cm H2O for 10 breaths. PEEP was then reduced to and kept at 5 cm H2O. The continuous positive airway pressure (CPAP) group received 5 cm H2O of continuous positive airway pressure without recruitment. The zero end-expiratory pressure (ZEEP) group received neither PEEP nor the recruitment maneuver. All patients breathed spontaneously during the procedure. After cranial magnetic resonance imaging, thoracic magnetic resonance imaging was performed. RESULTS: The atelectatic volume (median, first and third standard quartiles) detected in the ZEEP group was 1.25 (0.75-4.56) cm3 in the right lung and 4.25 (3.2-13.9) cm3 in the left lung. The CPAP group had 9.5 (3.1-23.7) cm3 of collapsed lung tissue in the right lung and 8.8 (5.3-28.5) cm3 in the left lung. Only one patient in the ARS group presented an atelectasis of less than 2 cm3. An uneven distribution of the atelectasis was observed within each lung and between the right and left lungs, with a clear predominance of the left basal paradiaphragmatic regions. CONCLUSION: Frequency of atelectasis was much less following the alveolar recruitment strategy, compared with children who did not have the maneuver performed. The mere application of 5 cm H2O of CPAP without a prior recruitment did not show the same treatment effect and showed no difference compared to the control group without PEEP.     

Optimal positive end-expiratory pressure during pumpless extracorporeal lung membrane support

The aim of this study was to determine the optimal positive end-expiratory pressure (PEEP) required during extracorporeal lung membrane support (interventional lung assist [iLA]; Novalung GmbH, Hechingen, Germany). Twenty healthy pigs were initially (4 h) mechanically ventilated with a tidal volume (V(T)) of 10 mL/Kg, respiratory rate (RR) of 20 breaths/min, PEEP of 5 cm H(2)O, and fraction of inspired O(2) (FiO(2)) of 1.0. Thereafter, the iLAs were placed arteriovenously transfemorally and settings reduced to reach near static ventilation (V(T) < or = 2 mL/Kg, RR 4 breaths/min, PEEP of 5, FiO(2) 1.0). Then, animals were assigned to four study groups evaluating 5 cm H(2)O increasing levels of PEEP for 8 h. Gas exchanges with PEEP < or = 10 cm H(2)O were significantly worse than those with PEEP > 12 cm H(2)O, and this without hemodynamical imbalance. This study suggests that the iLA may provide adequate gas exchange during static ventilation only with PEEP levels > 10 cm H(2)O, and this without pulmonary or systemic hemodynamic imbalance.     

Continuous positive airway pressure versus positive end-expiratory pressure in respiratory distress syndrome.

The hemodynamic and respiratory effects of spontaneous ventilation with continuous positive airway pressure (CPAP) and mechanical ventilation with positive end-expiratory pressure (PEEP) were compared in nine patients who had adult respiratory distress syndrome. These patients were capable of maintaining spontaneous ventilation (tidal volume above 300 ml. and PaCO2 below 45 torr). Arterial and mixed venous blood gases, cardiac output, oxygen delivery and consumption, pulmonary artery pressure, and pulmonary wedge pressure were measured in 11 instances, with each patient on 5 or 10 cm. H2O CPAP or PEEP, and in nine instances, with each patient on the ventilator but without PEEP (O PEEP). During CPAP, when compared to PEEP at the same level of end-expiratory pressure, mean PaO2 increased significantly (p less than 0.05) and mean physiological shunt decreased (p less than 0.05). In nine of 11 instances, cardiac output was higher on CPAP than on a corresponding level of PEEP. Thus CPAP was more effective than the same amount of PEEP in improving arterial oxygenation by the lung without adversely affecting cardiac output.     

Operative lung constant positive airway pressure with the Univent bronchial blocker tube.

Constant positive airway pressure (CPAP) to the operative lung during one-lung ventilation (1-LV) with a double-lumen tube increases PaO2; there have been no reports of application of CPAP to the operative lung during 1-LV with the Univent bronchial blocker (BB) tube. This study determined the method of administration and the effect on PaO2 of 10 cm H2O of CPAP to the operative lung during 1-LV (1-LV + 10 CPAP) produced by the Univent BB system. We designed our CPAP system for the Univent BB using an in vitro lung model so that low O2 flow rates (2-4 L/min) yielded clinically relevant levels of CPAP (5-20 cm H2O) over a wide range of lung compliance. The CPAP system simply consisted of placing a resistance to a variable oxygen flow distal to the operative lung. Seven consenting patients who required thoracotomy and 1-LV were anesthetized and their tracheas were intubated with the Univent BB tube; the BB was inserted into the appropriate mainstem bronchus until the proximal surface of the BB cuff was just distal to the tracheal carina. PaO2 was measured in the seven patients during 12 sequences of two-lung ventilation (2-LV), one-lung ventilation (1-LV), and 1-LV with 10 cm H2O CPAP (1-LV + 10 CPAP). 1-LV + 10 CPAP was always instituted on the deflation phase of a previous single tidal inhalation. We found in our patients with a lung compliance of 32 +/- 4 mL/cm H2O that 2.4 +/- 0.2 L/min of oxygen flow produced 1-LV + 10 CPAP.(ABSTRACT TRUNCATED AT 250 WORDS)     

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. CONCLUSIONS: The addition of 1 sigh per minute during PSV in patients with early ARDS improved gas exchange and lung volume and decreased the respiratory drive.     

Supraglottic combined frequency jet ventilation versus subglottic monofrequent jet ventilation in patients undergoing microlaryngeal surgery

We compared the efficacy of gas exchange during supraglottic combined-frequency jet ventilation via a jet ventilation laryngoscope and during monofrequent jet ventilation via the Mon-Jet catheter (Xomed, Jacksonville, FL). Twenty-three anesthetized (propofol, fentanyl, vecuronium) patients undergoing microlaryngeal surgery were prospectively studied and randomly assigned to one of two groups. The patients' lungs were ventilated with combined-frequency jet ventilation (10 min, 15 and 600 breaths/min, inspiration/expiration time ratio = 1, driving pressure 750-1500 mm Hg), monofrequent (low-frequency group: 15 breaths/min; high-frequency group: 600 breaths/min) jet ventilation (20 min), and again combined-frequency jet ventilation (15 min). PaO(2), PaCO(2), and the inspiratory oxygen fraction (FIO(2)) were measured. Wilcoxon's signed rank test was applied. During monofrequent jet ventilation, PaCO(2) increased and the PaO(2)/FIO(2) decreased significantly (P < 0.05) as compared with combined-frequency jet ventilation (low-frequency group: PaCO(2) from 39.4 +/- 3.3 to 50. 8 +/- 8.0 mm Hg, PaO(2)/FIO(2) from 306 +/- 100 to 225 +/- 94 mm Hg; high-frequency group: PaCO(2) from 36.7 +/- 7.2 to 60.3 +/- 6.1 mm Hg, PaO(2)/FIO(2) from 429 +/- 87 to 190 +/- 51 mm Hg; mean +/- SD). After switching back to combined-frequency jet ventilation, PaCO(2) decreased and PaO(2)/FIO(2) increased to baseline levels. We conclude that gas exchange during microlaryngeal surgery can be more easily maintained with supraglottic combined-frequency jet ventilation than with subglottic monofrequent jet ventilation via the Mon-Jet catheter. IMPLICATIONS: This study demonstrates that the combination of high- and low-frequency supraglottic jet ventilation via a jet ventilation laryngoscope provides a better pulmonary gas exchange and allows more accurate airway pressure monitoring during microlaryngeal surgery than subglottic monofrequent jet ventilation via an endotracheal catheter.     

单肺通气期间连续气道正压通气对胸腔镜房间隔缺损修补术患者肺功能的影响

目的 探讨单肺通气期间连续气道正压通气(CPAP)对胸腔镜房间隔缺损修补术患者肺功能的影响.方法 拟行房间隔缺损修补术的患者20例,年龄16～30岁,体重41～64 kg,性别不限,ASA分级Ⅱ级,随机分为2组(n=10):对照组和CPAP组.两组单肺通气时VT 8 ml/kg,呼吸频率12～16次/min,吸呼比1:2,维持PET CO2 35～40 mm Hg.CPAP组单肺通气期间,非通气侧肺采用CPAP,压力为6 cm H2O.术中监测氧合指数、肺顺应性和气道压,记录拔管时间、单肺通气期间心血管事件和低氧血症的发生情况.结果 与对照组比较,CPAP组氧合指数和肺顺应性升高,拔管时间缩短,低氧血症发生率低(P＜0.01),两组患者气道压力在正常范围且未发生心血管事件.结论 单肺通气期间行CPAP(6 cm H2O)可改善胸腔镜房间隔缺损修补术患者的肺功能.     

不同压力持续气道正压对单肺通气氧化应激反应的影响

目的比较不同压力持续气道正压(CPAP)对单肺通气氧化应激反应的影响。方法择期行食管癌根治术患者48例,随机均分为双肺通气组(A组)、单肺通气组(B组)、单肺通气非通气肺给予2cmH2OCPAP组(C组)及5cmH2OCPAP组(D组)。分别于开胸前(T0)、单肺通气后(A组于开胸后)30min(T1)、90min(T2)、150min(T3)、手术结束(T4)时测定血清超氧化物歧化酶(SOD)活性、丙二醛(MDA)、NO浓度。结果 T1～T4时B、C组及T2～T4时D组的SOD活性明显低于A组,T1～T4时B、C、D组MDA及NO浓度高于A组(P0.05)。T1～T4时C、D组MDA及NO浓度均显著低于B组(P0.05),T3时C、D组SOD活性显著高于B组(P0.05);T3时D组MDA及NO浓度高于C组(P0.05)。结论 CPAP能减轻单肺通气氧化应激反应,且2cmH2OCPAP优于5cmH2OCPAP。     

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.     

Magnetic Resonance Imaging of the Upper Airway: Effects of Propofol Anesthesia and Nasal Continuous Positive Airway Pressure in Humans

Background: Anesthetic agents inhibit the respiratory activity of upper airway muscles more than the diaphragm, creating a potential for narrowing or complete closure of the pharyngeal airway during anesthesia. Because the underlying mechanisms leading to airway obstruction in sleep apnea and during anesthesia are similar, it was hypothesized that anesthesia-induced pharyngeal narrowing could be counteracted by applying nasal continuous positive airway pressure (CPAP).

Methods: Anesthesia was induced in ten healthy volunteers (aged 25-34 yr) by intravenous administration of propofol in 50-mg increments every 30-s to a maximum of 300 mg. Magnetic resonance images of the upper airway (slice thickness of 5 mm or less) were obtained in the awake state, during propofol anesthesia, and during administration of propofol plus 10 cm nasal CPAP.

Results: Minimum anteroposterior diameter of the pharynx at the level of the soft palate decreased from 6.6+/-2.2 mm (SD) in the awake state to 2.7+/-1.5 mm (P < 0.05) during propofol anesthesia and increased to 8.43+/-2.5 mm (P < 0.05) after nasal CPAP application. Anteroposterior diameter of the pharynx at the level of the dorsum of the tongue increased from 7.9+/-3.5 mm during propofol anesthesia to 12.9+/-3.6 mm (P < 0.05) after nasal CPAP. Pharyngeal volume (from the tip of the epiglottis to the tip of the soft palate, assuming this space to be a truncated cone) significantly increased from 2,437+/-1,008 mm3 during propofol anesthesia to 5,847+/-2,827 mm3 (P < 0.05) after nasal CPAP application.