Synchronized gas and partial liquid ventilation in lung-injured animals: improved gas exchange with decreased effort

We hypothesized that partial liquid ventilation (PLV) with perflubron in spontaneously breathing lung-injured animals would increase respiratory workload compared to animals treated with gas ventilation (GV), and that a fully synchronized mode, assist-control ventilation (AC), would reduce the piglets' effort when compared to intermittent mandatory ventilation (IMV) or synchronized IMV (SIMV) during both GV and PLV. Newborn piglets with saline lavage-induced lung injury were randomized to sequential 30-min periods of IMV --> SIMV --> AC (n = 5), or AC --> SIMV --> IMV (n = 5) during GV followed by PLV. Pulmonary mechanics measurements and an esophageal patient effort index (PEI, defined as the product of the area below baseline of the esophageal pressure-time curve and respiratory rate [RR]) were determined to estimate the patient's nonmechanical work of breathing, using a computer-assisted lung mechanics analyzer. GV to PLV comparisons showed no change in PEI (IMV, 57.8 vs. 49.7; SIMV, 52.3 vs. 46.8; AC, 15.7 vs. 13.7 cm H2O x s/min); intermode comparisons showed significantly decreased PEI in AC vs. IMV and SIMV during GV, and in AC vs. SIMV (AC vs. IMV, P = 0.06) during PLV. AC consistently resulted in the highest minute ventilation, lowest total respiratory rate, most physiologic pH, and least tidal volume variability. These observations suggest that synchronization with AC during GV and PLV may have substantial physiologic benefits.     

Influence of different methods of synchronized mechanical ventilation on ventilation,gas exchange,patient effort,and blood pressure fluctuations in premature neonates

We studied the effects of two methods of synchronized mechanical ventilation [synchronized intermittent mandatory ventilation (SIMV) and assist/control (A/C)] on ventilation, gas exchange, patient effort, and arterial blood pressure (ABP) fluctuations. SIMV and A/C were applied in random order in 12 preterm neonates (gestational age, 29.7 ± 2.3 weeks; birth weight, 1,217 ± 402 g). We measured total (Ve_tot) and mechanical (Ve_mech) minute ventilation, spontaneous (Vt_spont) and ventilator supported (Vt_mech) tidal volume, transcutaneous oxygen saturation (Sp_O2), transculaneous P_O2 (TcP_O2), and PC_O2, (TcP_CO2), mean airway pressure (Paw), phasic esophageal pressure deflections (Pe) as an estimate of inspiratory effort, mean arterial blood pressure (ABP), and beat-to-beat ABP fluctuations. The measurements obtained during conventional intermittent mandatory ventilation (IMV) were compared with the recordings during SIMV and A/C. To make the measurement conditions comparable and to prevent hyperventilation, peak inspiratory pressure was reduced during the A/C mode so that Ve_tot remained in the same range as during the IMV mode. Whereas Ve_tot was similar in all three conditions by study design, Ve_mech was larger during SIMV and A/C than during IMV. Vt_mech increased during SIMV and by study design was smaller during A/C than during IMV. Pe decreased during SIMV and A/C compared with IMV, and Paw was higher during A/C than during IMV or SIMV. Beat-to-beat ABP fluctuations were reduced during SIMV and A/C compared with IMV and showed a close positive correlation with Pe changes. We conclude that SIMV increases Ve_mech and reduces Pe compared with IMV, resulting in smaller intrathoracic and ABP fluctuations. During A/C, a substantial portion of the spontaneous respiratory effort is shifted to the ventilator, resulting in a further decrease in Pe and ABP fluctuations Pediatr Pulmonol. 1996; 22:305–313. © 1996 Wiley-Liss, Inc.     

Dynamics of spontaneous breathing during patient-triggered partial liquid ventilation

This study evaluates different ventilator strategies during gas (GV) and partial liquid ventilation (PLV) in spontaneously breathing animals. We hypothesized that during PLV, spontaneously breathing animals would self-regulate respiratory parameters by increasing respiratory rate (RR) and minute ventilation (V′_E) when compared to animals mechanically ventilated with gas, and further that full synchronization of each animal's effort to the ventilator cycle would decrease RR at stable tidal volumes (V_T). We studied 12 newborn piglets (1.54 ± 0.24 kg) undergoing GV and PLV in 3 different modes: intermittent mandatory ventilation (IMV), synchronized IMV (SIMV), and assist control ventilation (AC). Modes occurred sequentially in random order during GV first, with the same order then repeated during PLV. Animals initially received continuous positive airway pressure (CPAP) and returned to CPAP during PLV at the end of the experiment. Pressure-limited, volume-targeted ventilation was used with a tidal volume goal of 13 cc/kg. Rate was set at 10/min during IMV and SIMV, with a back-up rate of 10/min during AC. RR, V′_E, mechanical (V_T) and spontaneous tidal volumes (sV_T) were measured breath-to-breath using a computer-assisted lung mechanics analyzer; mean values were determined over 30-min periods. Data analysis used paired t-tests with Bonferroni correction as needed (P < 0.05). Blood gases were stable in all modes during GV and PLV. RR (min⁻¹) and V′_E (L·min⁻¹/kg) increased in all modes from GV to PLV (RR: CPAP 71 vs. 128; IMV 69 vs. 112; SIMV 65 vs. 107; AC 33 vs. 47. V′_E: CPAP 0.47 vs. 0.72; IMV 0.46 vs. 0.61; SIMV 0.45 vs. 0.61; AC 0.38 vs. 0.53; P < 0.05). Intermode comparisons during PLV showed a lower RR with AC (P < 0.02), and a higher V′_E with CPAP (P < 0.05). V_T and dynamic respiratory system compliance decreased from GV to PLV (V_T P < 0.05; C_rs,dyn P < 0.01 ); sV_T remained unchanged. V_T and sV_T did not differ in intermode comparisons. We conclude that during PLV, spontaneously breathing piglets with normal lungs maintain physiologic blood gases by increasing V′_E through increased RR. AC produced the most efficient respiratory pattern during PLV, with increased V′_E achieved by a modest increase in RR. Pediatr Pulmonol. 1998; 26:319–325. © 1998 Wiley-Liss, Inc.     

Increased incidence of sighs (augmented inspiratory efforts) during synchronized intermittent mandatory ventilation (SIMV) in preterm neonates

A reflex resulting in a deep, sigh-like inspiratory effort (augmented breath) is frequently triggered during synchronized mechanical ventilation in preterm infants. We studied the incidence of augmented inspiratory efforts and their effect on ventilation and lung compliance during conventional IMV and synchronized IMV (SIMV) in 15 preterm neonates (GA 26.7 ± 1.5 wks (mean ± SD), BW 925 ± 222 g, age 1–8 days). Augmentation of spontaneous inspiratory effort was defined as an esophageal pressure deflection occurring coincident with a synchronized mechanical breath and exceeding the previous unassisted spontaneous effort by more than 50%. The incidence of augmented breaths was higher during SIMV (11.1 ± 7.7%; P < 0.01) than during conventional IMV (5.1 ± 6.1%). However, when the synchronized breaths were triggered late (200–300 msec) after the onset of inspiration, augmented breaths occurred no more frequently than during conventional IMV (6.0 ± 4.7%). The incidence of augmented breaths correlated inversely with dynamic lung compliance (P = 0.014), but was not significantly influenced by a change in PEEP. Although inspiratory effort increased nearly three times during the augmented breaths, tidal volume increased only 12%. The change in tidal volume was limited because the augmented effort reached its maximal negativity only approximately 500 ms after the beginning of the synchronized, mechanical breath and at a time when the mechanical breath had already ended. For this reason the augmented effort did not contribute significantly to minute ventilation, but only prolonged inspiration. Dynamic lung compliance did not change significantly after an augmented breath. The results indicate that augmented inspiratory efforts are more common in preterm neonates ventilated with SIMV than with conventional IMV, but do not contribute significantly to ventilation. Pediatr. Pulmonol. 1997; 24:195–203. © 1997 Wiley-Liss, Inc.     

Volume targeted ventilation (volume guarantee) in the weaning phase of premature newborn infants

OBJECTIVE: Several options are currently available in neonatal mechanical ventilation: complete breathing synchronization (patient triggered ventilation, synchronized intermittent positive pressure ventilation--SIPPV); positive pressure flow-cycled ventilation (pressure support ventilation, PSV); and volume targeted positive pressure ventilation (volume guarantee, VG). The software algorithm for the guarantee volume attempts to deliver a tidal volume (Vt) as close as possible to what has been selected by the clinician as the target volume. Main objectives of the present study were to compare patient-ventilator interactions and Vt variability in premature infants recovering from respiratory distress syndrome (RDS) who were weaned by various ventilator modes (SIMV/PSV + VG/SIPPV + VG and SIMV + VG). METHODS: This was a short-term crossover trial in which each infant served as his/her own control. Ten premature infants born before the 32nd week of gestation in the recovery phase of RDS were enrolled in the study. All recruited infants started ventilation with SIPPV and in the weaning phase were switched to synchronized intermittent mandatory ventilation (SIMV). Baseline data were collected during an initial 20-min period of monitoring with the infant receiving SIMV alone, then they were switched to SIPPV + VG for a 20-min period and then switched back to SIMV for 15 min. Next, they were switched to PSV + VG for the study period and switched back to SIMV for a further 15 min. Finally, they were switched to SIMV + VG and, at the end of monitoring, they were again switched back to SIMV alone. RESULTS: Each mode combined with VG discharged comparable Vts, which were very close to the target volume. Among the VG-combined modes, mean variability of Vt from preset Vt was significantly different. Variability from the target value was significantly lower in SIPPV and PSV modes than in SIMV (P < 0.0001 and P < 0.04 respectively). SIPPV + VG showed greater stability of Vt, fewer large breaths, lower respiratory rate, and allowed for lower peak inspiratory pressure than what was delivered by the ventilator during other modes. No significant changes in blood gases were observed after each of the study periods. CONCLUSIONS: With regards to the weaning phase, among combined modes, both of the ones in which every breath is supported (SIPPV/PSV) are likely to be the most effective in the delivery of stable Vt using a low working pressure, thus, at least in the short term, likely more gentle for the neonatal lung. In summary, we can suggest that the VG option, when combined with traditional, patient triggered ventilation, adheres very closely to the proposed theoretical algorithm, achieving highly effective ventilation.     

Patient-ventilator interactions in new modes of patient-triggered ventilation.

Recently, synchronized modes of conventional mechanical ventilation became available for neonatal ventilatory support, but there has been little information regarding details of patient-ventilator interactions during pressure support, volume support, or any other volume-targeted modes of synchronized ventilation in newborn infants. Our objective was to obtain comparative data on patient-ventilator interactions and stability of delivered tidal volume (V(T)) for the different modes of synchronized mechanical ventilation in stable ventilated newborn infants. We examined the effects of pressure support ventilation (PSV) and volume guarantee (VG) modes of a prototype Dr?ger Babylog ventilator on peak and mean airway pressures (PIP and Paw), inspiratory time (t(in)), and V(T) in 23 ventilated newborn infants. Twelve infants were studied while on assist/control (AC) and 11 on synchronized intermittent mandatory ventilation (SIMV). Mean birth weight was 1,650 +/- 1,180 g, gestational age 31 +/- 6 weeks, and age at time of study was 19 +/- 26 days. Data for 400-600 breaths from each infant were downloaded directly from the ventilator pressure and volume-monitoring module, and analyzed using ANOVA for repeated measures. Mean values and breath-to-breath variability were compared for 20-min periods of AC or SIMV followed by PSV, PSV+VG, and back to baseline AC or SIMV. PSV and PSV+VG led to shorter t(in) and thus to lower Paw, compared to AC. Mean PIP was similar across all AC modes but more variable during VG, reflecting the servocontrol of PIP. V(T) did not differ between AC modes, but was significantly less variable with VG added. PSV and PSV+VG led to lower and less variable PIP and Paw, compared to SIMV, because t(in) was shorter and every breath was supported in PSV and PSV+VG. V(T) was similar in SIMV, PSV, and PSV+VG, but less variable with PSV+VG. Arterial blood gas tensions were similar across all ventilation modes. We conclude that the ventilator prototype functioned as intended. Breath-to-breath tidal volume variability was significantly reduced in VG modes, although not completely eliminated.     

High-frequency oscillation versus conventional ventilation following surfactant administration and partial liquid ventilation

Surfactant followed by partial liquid ventilation (PLV) with perfluorocarbon (PFC; LiquiVent®) improves oxygenation, lung compliance, and lung pathology in lung-injured animals receiving conventional ventilation (CV). In this study, we hypothesize that high-frequency oscillation (HFO) and CV will provide equivalent oxygenation in lung-injured animals following surfactant repletion and PLV, once lung volume is optimized. After saline-lavage lung injury during CV, newborn piglets were randomized to either HFO (n = 10) or CV (n = 9). HFO animals were stabilized over 15 min without optimization of lung volume; CV animals continued treatment with time-cycled, pressure-limited, volume-targeted ventilation. All animals then received 100 mg/kg of surfactant (Survanta®). Thirty minutes later, all received intratracheal PFC to approximate functional residual capacity. Thirty minutes after PLV began, mean airway pressure (MAP) in both groups was increased to improve oxygenation. MAP was directly adjusted during HFO; PEEP and PIP were adjusted during IMV, maintaining a pressure sufficient to deliver 15 mL/kg tidal volume. Animals were treated for 4 h. The CV group showed improved oxygenation following surfactant administration (OI: 26.79 ± 1.98 vs. 8.59 ± 6.29, P < 0.0004), with little further improvement following PFC administration or adjustments in MAP. Oxygenation in HFO-treated animals did not improve following surfactant, but did improve following PFC (OI: 27.78 ± 6.84 vs. 15.86 ± 5.53, P < 0.005) and adjustments in MAP (OI: 15.86 ± 5.53 vs. 8.96 ± 2.18, P < 0.03). After MAP adjustments, there were no significant intergroup differences in oxygenation. Animals in the CV group required lower MAP than animals in the HFO group to maintain similar oxygenation. We conclude that surfactant repletion followed by PLV improves oxygenation during both CV and HFO. The initial response to administration of surfactant and PFC was different for the conventional and high-frequency oscillation groups, likely reflecting the ventilation strategy used; animals in the CV group responded most to surfactant, whereas animals in the HFO group responded most after PFC instillation. The ultimately similar oxygenation of the two groups once lung volume had been optimized suggests that HFO may be used effectively during administration of, and treatment with, surfactant and perfluorocarbon. Pediatr Pulmonol. 1998;26:21–29. © 1998 Wiley-Liss, Inc.     

Efficacy of early piston-type high-frequency oscillatory ventilation in infants with respiratory distress syndrome

We investigated whether the combination of surfactant replacement therapy and early application of high-frequency oscillatory ventilation (HFOV) was more effective in patients with respiratory distress syndrome (RDS) than late application of HFOV and conventional mechanical ventilation (CMV). To determine this, we retrospectively reviewed the cases of 126 neonates with RDS who received surfactant replacement therapy within 4 hr after birth. Patients were grouped into those who received HFOV immediately after birth (HFOV group), those who initially were ventilated by CMV and subsequently received HFOV (CMV/HFOV group), and those who did not receive HFOV (CMV group). Changes in respiratory system compliance (Crs), arterial-alveolar oxygen gradient (a/ApO(2)), and mean airway pressure (MAP) were compared. Infants who received HFOV were less mature than those who received CMV. The a/ApO(2) measured immediately after birth before surfactant replacement therapy was significantly lower in the HFOV and CMV/HFOV group than in the CMV group. After 72 hr, the Crs in the HFOV group was higher than in any other group and was significantly higher than the CMV/HFOV group at 48 and 120 hr. These results suggest that initiating HFOV in combination with surfactant replacement therapy immediately after birth provides effective ventilatory support for infants with RDS.     

Gas exchange during mechanical ventilation and spontaneous breathing. Intermittent mandatory ventilation after open heart surgery

Pulmonary gas exchange rates in eight patients after open heart surgery were studied during weaning from the ventilator. We investigated continuous positive pressure ventilation (CPPV), intermittent mandatory ventilation (IMV) and spontaneous breathing with continuous positive airway pressure (CPAP). During each mode of ventilation we measured: CO2 production (VCO2), O2 consumption (VO2), cardiac output (CO), PaO2, Qs/QT and functional residual capacity (FRC). In addition, we analyzed in each single breath: tidal volume (VT), series dead space volume (Vds), alveolar ventilation, alveolar efficiency for CO2 elimination (alv eff CO2) and end-tidal CO2 concentration (FCO2et). We compared the results of CPPV, IMV and CPAP and the mandatory breaths (MB) with the spontaneous breaths (SB) measured during IMV. CO was low during CPPV, when the patient still deeply sedated; it was increased in IMV and remained constant in the following CPAP period. VCO2 and VO2 did not differ significantly when switching from IMV to CPAP; therefore, work due to breathing seemed not to be reduced by the mandatory breath during IMV. Oxygenation (PaO2, Qs/QT) did not change significantly when switching from one mode to the other. FRC was constant when changing from CPPV to IMV, did not alter within the IMV-cycle and was reduced significantly when switching from IMV to CPAP. Dead space ventilation was reduced in SB (compared to MB). The latter result is discussed on the basis of two mechanisms: Vds was reduced and alv eff CO2 was increased. We conclude that compared to CPPV, IMV decreases mean alveolar pressure and reduces dead space ventilation at constant FRC and with constant oxygenation. This may explain why, in the weaning process, IMV makes it possible to start spontaneous breathing very early.     

Acute effects of PEEP on tidal volume and respiratory center output during synchronized ventilation in preterm infants

BACKGROUND: Positive end expiratory pressure (PEEP) is routinely used in mechanically ventilated preterm infants to maintain lung volume. An acute increase in PEEP can affect lung mechanics and tidal volume, but it is unknown if these effects elicit compensatory changes in respiratory center output. OBJECTIVES: To investigate the acute effects of changes in PEEP on tidal volume (V(T)), lung compliance (C(L)), and respiratory center output (RCO) during synchronized intermittent mandatory ventilation (SIMV) in preterm infants at different levels of basal respiratory drive. METHODS: Preterm infants were studied during SIMV at three levels of PEEP (2, 4, and 6 cm H(2)O for 2-3 min each) and at two levels of inspired CO(2). Peak inspiratory pressure (PIP) was adjusted to maintain the same delta pressure at the airway. RCO was assessed by measuring total diaphragmatic electrical activity. The level of inspired CO(2) was adjusted by modifying the instrumental dead space. RESULTS: Sixteen preterm infants GA: 25 +/- 2 weeks, BW: 786 +/- 242 g, age: 18 +/- 15 days, SIMV: rate 14 +/- 3 b/min, Ti: 0.35 +/- 0.01 s, PIP: 16 +/- 1 cm H(2)O, and FiO(2): 0.31 +/- 0.06 were studied. At both levels of inspired CO(2), C(L), V(T), and V'(E) from spontaneous and mechanical breaths decreased significantly with higher PEEP. RCO did not change, but at lower respiratory drive, there was a trend towards an increase in RCO with higher PEEP. CONCLUSION: Higher PEEP levels can have acute negative effects on lung mechanics and ventilation in preterm infants without a sufficient compensatory increase in RCO.     

Episodes of hypoxemia during synchronized intermittent mandatory ventilation in ventilator-dependent very low birth weight infants

Distinct patterns of asynchrony, and episodes of hypoxemia, may occur in a spontaneously breathing preterm infant during conventional intermittent mandatory ventilation (IMV) on traditional time-cycled, pressure-limited ventilators. Synchronized IMV (SIMV) and assist/control ventilation are frequent modes of patient-triggered ventilation used with infant ventilators. The objective of this study was to use computerized pulse oximetry to quantify the occurrence of episodes of hypoxemia (oxygen desaturation) during SIMV vs. IMV, in preterm infants < or = 1,250 g who required mechanical ventilation at > or = 14 days of age. We performed a randomized, crossover study with each infant being randomized to IMV or SIMV (Infant Star ventilator) for initial testing for a 1-hr period. Patients were subsequently tested on the alternate modality after a stabilization period of 10 min at the same ventilator and fractional inspired oxygen concentration (FiO2) settings. Pulse oximetry data were obtained with a Nellcor N-200 monitor, a microcomputer, and a software program (SatMaster). An investigator blinded to the randomized assignment evaluated all measurements. Eighteen very low birth weight (VLBW) infants with a birth weight of 777 +/- 39 g (mean +/- SEM) and gestational age 25.1 +/- 0.3 weeks were studied. The average pulse oximeter oxygen saturation (SaO2) was higher on SIMV than IMV (P < 0.01). During SIMV, these infants had significantly fewer episodes of hypoxemia (duration of episodes of oxygen desaturation as a percentage of scorable recording time) to 86-90% SaO2 (P < 0.01), 81-85% SaO2 (P < 0.01), and 76-80% SaO2 (P < 0.05) when compared to IMV. There was also a significant decrease in percentage of time of desaturation to SaO2 < 90% (P = 0.002), < 85% SaO2 (P = 0.003), and < 80% SaO2 (P = 0.02) during SIMV vs. IMV. Our preliminary findings indicate that the use of SIMV in a population of VLBW ventilator-dependent infants (> or = 14 days of age) results in better oxygenation and decreased episodes of hypoxemia as compared to IMV.     

适应性支持通气在AECOPDⅡ型呼吸衰竭中的应用

目的 探讨适应性支持通气(ASV)在慢性阻塞性肺疾病急性加重期(acute chronic obstruc-tive pumonary disease,AECOPD)Ⅱ型呼吸衰竭患者中的临床意义.方法 选择AECOPDⅡ型呼吸衰竭机械通气患者58例,将其随机分为两组,观察组(ASV组)29例,对照组同步间竭指令通气+压力支持通气+呼气末正压(SIMV+ PSV+ PEEP组)29例,两组同时进行机械通气治疗直至撤机,比较两种模式下的各项呼吸力学及血流动力学参数、血气分析、舒适程度、通气时间和撤机成功率.结果 全部患者均成功脱机,ASV组呼吸频率明显下降,潮气量(VT)明显升高(P＜0.05),气道峰压(Ppeak)和吸气阻力(R)下降显著(P＜0.05),静态顺应性(Cstat)逐渐增加(P＜0.05),附加附加功(WOBimp)吸气压力时间乘积(PTP)均低于SIMV+ PSV+ PEEP组(P＜0.01).上机时间明显缩短(P＜0.05).结论 ASV可根据患者的呼吸力学状况自动调整吸气压力支持水平,提高潮气量,降低呼吸频率,呼吸肌做功减少,改善人机协调性,并能缩短上机时间,明显优于常规通气,而且操作简单,值得推广应用.     

Effects of pressure support ventilation plus volume guarantee vs. high-frequency oscillatory ventilation on lung inflammation in preterm infants

The aim of the present study was to evaluate if high-frequency oscillatory ventilation (HFOV) might reduce lung inflammation in preterm infants with infant respiratory distress syndrome (RDS) in comparison with the early application of another potentially lung-protective ventilation strategy, such as pressure support ventilation plus volume guarantee (PSV + VG). Infants at less than 30 weeks of gestation with RDS were enrolled consecutively in the study if they required mechanical ventilation, and were randomly allocated to receive HFOV or PSV + VG. Bronchial aspirate samples for the measurement of interleukin (IL)-1beta, IL-8, and IL-10 were obtained before surfactant treatment (T1), after 6-18 hr of ventilation (T2), after 24-48 hr of ventilation (T3), and before extubation (T4). Thirteen patients were enrolled in the HFOV group, and 12 in the PSV + VG group. The mean values of IL-1beta, IL-8, and IL-10 at T4 were lower in the HFOV group than in the PSV + VG group. The present study demonstrates that early treatment with HFOV is associated with a reduction of lung inflammation in comparison with PSV + VG in preterm infants with RDS.     

Vascular endothelial growth factor in preterm infants with respiratory distress syndrome

Respiratory distress syndrome (RDS) secondary to surfactant deficiency is a common cause of morbidity and mortality in premature infants. Increasing evidence suggests that vascular endothelial growth factor (VEGF) may contribute to surfactant secretion and pulmonary maturation. However, differences in cord blood VEGF concentrations in infants with and without respiratory distress syndrome have not been reported. We hypothesized that premature infants with higher VEGF levels in cord blood had a lower risk of developing RDS. Cord blood samples were obtained from preterm infants born at 32 weeks of gestation or earlier. Infants were excluded if there was evidence of prenatal maternal infection or any infection within the first 3 days of life. Cord blood VEGF levels were measured using an enzyme-linked immunosorbent assay (ELISA). We found that neonates with clinically diagnosed RDS had a lower gestational age (GA), lower birth weight (BW), higher incidence of mechanical ventilation requirements, longer duration of mechanical ventilation, and lower Apgar scores at 1 and 5 min. Infants with RDS had significantly lower cord blood VEGF levels. GA, BW, premature rupture of membranes (PROM), and antenatal steroid treatment were not associated with changes in cord blood VEGF levels. The specificity of cord blood VEGF above 34 pg/ml for predicting the absence of RDS was 86%, the sensitivity was 53%, the positive predictive value was 84%, and the negative predictive value was 56%. Our data demonstrated that cord blood VEGF elevation was significantly correlated with an absence of RDS.     

Clinicians' approaches to mechanical ventilation in acute lung injury and ARDS.

STUDY OBJECTIVES: To examine clinicians' approaches to mechanical ventilation in patients with acute lung injury (ALI; PaO(2)/fraction of inspired oxygen [FIO(2)] 35 cm H(2)O in 26% of patients. Seventy-eight percent of patients with ARDS received 相似文献   

High-frequency oscillatory ventilation in pediatric patients

HFOV is a mode of ventilation that can achieve oxygenation and ventilation while maintaining maximal lung recruitment on the deflation limb of its pressure-volume curve. The primary theoretical advantages of HFOV over CMV in the management of acute lung injury are that HFOV allows adequate alveolar ventilation with minimal peak-trough pressure changes, provides lung recruitment, and avoids end-inspiratory overdistension of the relatively compliant nondependent lung. Taken together, the results of studies in animals, preterm and term neonates, and older pediatric patients reveal that an "open-lung" strategy, with the goal of a high end-expiratory lung volume, is safe and superior to CMV in both the short-term (rapidly improved oxygenation and/or ventilation) and longer-term (lower incidence of chronic lung disease). The improved longer-term clinical outcomes on HFOV are presumably because of less ventilator-induced lung injury. As experience with HFOV in older patients grows, ventilator technology matures, and understanding of the pathophysiology of acute respiratory distress syndrome (RDS) deepens, it is likely that HFOV will find widespread use for the management of respiratory failure caused by acute lung injury in patients from preterm neonates to adults.     

Effect on respiratory function of pressure support ventilation versus synchronised intermittent mandatory ventilation in preterm infants

Our objective was to compare the effects of pressure support ventilation and synchronized intermittent mandatory ventilation on respiratory function in preterm babies. Twenty preterm infants (mean gestational age, 29 weeks; mean weight at study, 1,354 g) were evaluated. Patients received two repeated cycles of synchronized intermittent mandatory ventilation, alternated with pressure support ventilation, for a total of four alternated phases, each phase lasting 4 hr. Spontaneous respiratory rate, tidal volume, minute volume, and mean airway pressure were recorded hourly. The tidal volume released by the ventilator was limited to 6 ml/kg. During the two pressure support ventilation phases, a statistically significant reduction of respiratory rate and a significant increase of tidal and minute volume were noted, as compared to the two synchronized intermittent mandatory ventilation periods. Mean airway pressure significantly increased only after the first shift from synchronized intermittent mandatory ventilation to pressure support ventilation. The changes of minute volume and respiratory rate observed during pressure support ventilation did not persist after the return to synchronized intermittent mandatory ventilation. In conclusion, pressure support ventilation, as compared to synchronized intermittent mandatory ventilation, seemed to improve respiratory function in preterm infants.     

Respiratory function during pressure support ventilation

Pressure support ventilation (PSV) is a pressure assist form of mechanical ventilatory support that augments the patient's spontaneous inspiratory efforts with a clinician selected level of positive airway pressure. To understand the effects of PSV on respiratory function, experiments were performed on 15 stable patients requiring synchronized intermittent mandatory ventilation (SIMV), as well as on a mechanical model simulating these patients' ventilatory systems. In the clinical study, gas exchange, airway pressures, blood pressure and heart rate were measured while SIMV was replaced by enough PSV to approximate the baseline SIMV tidal volume (VT). Measurements were repeated while this PSV level was then reduced in three 5 cm H2O steps every 10 to 15 minutes. It was found that PSV was a reasonable form of mechanical ventilatory support in patients with spontaneous ventilatory drives. It improves patient comfort, reduces the patient's ventilatory work, and provides a more balanced pressure and volume change form of muscle work to the patient. The clinical significance of these properties during the weaning process remain to be determined.     

Use of volume-targeted non-invasive bilevel positive airway pressure ventilation in a patient with amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease in which most patients die of respiratory failure. Although volume-targeted non-invasive bilevel positive airway pressure (BPAP) ventilation has been studied in patients with chronic respiratory failure of various etiologies, its use in ALS has not been reported. We present the case of a 66-year-old woman with ALS and respiratory failure treated with volume-targeted BPAP ventilation for 15 weeks. Weekly data downloads showed that disease progression was associated with increased respiratory muscle weakness, decreased spontaneous breathing, and increased use of non-invasive positive pressure ventilation, whereas tidal volume and minute ventilation remained relatively constant.     

Effect of intermittent mandatory ventilation on respiratory drive and timing

Seven patients receiving chronic ventilatory support were studied to better define the effects of intermittent mandatory ventilation (IMV) on the control and timing of spontaneous breathing between mandatory breaths. Each of these patients could sustain adequate spontaneous ventilation, as reflected by stable end-tidal carbon dioxide concentration (FETCO2), and arterial oxygen saturation (SO2) during periods of unassisted ventilation of sufficient duration to allow study. Inspiratory time (TI), respiratory cycle duration (Ttot), tidal volume (VT), and tracheal occlusion pressure (P0.1) were measured as IMV rate was progressively reduced. Respiratory timing was unaltered by decreasing IMV frequency; however, VT increased progressively. The P0.1 and mean inspiratory flow rate (VT/TI) also increased with each decrease in IMV rate, whereas FETCO2 and arterial SO2 remained constant. Thus, in these stable but ventilator-dependent patients, IMV did not alter respiratory timing or chemical stimuli, but it did alter respiratory drive as measured by VT/TI and P0.1.