Control Ventilation Mode Research Articles

High-Level Pressure Support Ventilation Attenuates Ventilator-Induced Diaphragm Dysfunction in Rabbits

BackgroundThe effects of different modes of mechanical ventilation in the same ventilatory support level on ventilator-induced diaphragm dysfunction onset were assessed in healthy rabbits. MethodsTwenty New Zealand rabbits were randomly assigned to 4 groups (n = 5 in each group). Group 1: no mechanical ventilation; group 2: controlled mechanical ventilation (CMV) for 24 hours; group 3: assist/ control ventilation (A/C) mode for 24 hours; group 4: high-level pressure support ventilation (PSV) mode for 24 hours. Heart rate, mean arterial blood pressure, PH, partial pressure of arterial oxygen/fraction of inspired oxygen and partial pressure of arterial carbon dioxide were monitored and diaphragm electrical activity was analyzed in the 4 groups. Caspase-3 was evaluated by protein analysis and diaphragm ultra structure was assessed by electron microscopy. ResultsThe centroid frequency and the ratio of high frequency to low frequency were significantly reduced in the CMV, A/C and PSV groups (P < 0.001). The percent change in centroid frequency was significantly lower in the PSV group than in the CMV and A/C groups (P = 0.001 andP =0.028, respectively). Electromyography of diaphragm integral amplitude decreased by 90% ± 1.48%, 67.8% ± 3.13% and 70.2% ± 4.72% in the CMV, A/C and PSV groups, respectively (P< 0.001). Caspase-3 protein activation was attenuated in the PSV group compared with the CMV and A/C groups (P = 0.035 andP= 0.033, respectively). Irregular swelling of mitochondria along with fractured and fuzzy cristae was observed in the CMV group, whereas mitochondrial cristae were dense and rich in the PSV group. The mitochondrial injury scores (Flameng scores) in the PSV group were the lowest among the 3 ventilatory groups (0.93 ± 0.09 in PSV versus 2.69 ± 0.05 in the CMV [P < 0.01] and PSV versus A/C groups [2.02 ± 0.08,P <0.01]). ConclusionsThe diaphragm myoelectric activity was reduced in the PSV group, although excessive oxidative stress and ultrastructural changes of diaphragm were found. However, partial diaphragm electrical activity was retained and diaphragm injury was minimized using the PSV mode.

The effects of different modes of mechanical ventilation under general anesthesia on children undergoing removal of foreign body with bronchofiberscopy

Objective To explore the effects of different ventilation modes of tracheobronchial foreign body in children with fiberoptic operation under general anesthesia. Methods Sixty children (1ys≤age≤3ys) undergoing fiberoptic bronchoscopy tracheal foreign body removal according to the combinations of different ventilation modes during and after fiberoptic bronchoscopy (FOB) procedures were divided into group A [volume control ventilation (VCV) + VCV, n= 20], group B [pressure control ventilation (PCV) + VCV, n= 20] and group C (PCV + PCV, n= 20) randomly. The P mean, P max, and PetCO2 during and after fiberoptic bronchoscopy procedures were monitored. The SpO2, PaO2, and PaCO2 after mechanical ventilation 1.5 hours were recorded. Results Compared to group A, groups B and C had lower P max and P mean (P<0.05) during the FOB procedures. Compared to groups A and B, group C had a lower P max and P mean (P<0.01) after the FOB procedures. At the 1.5 hours after the procedure, all the children showed significant increase in SpO2 and PaO2 (P<0.05) and decrease in PaCO2 (P<0.05) in groups A, B, and C. Conclusions When fiberoptic bronchoscopy in tracheobronchial foreign body operation is applied in children undergoing general anesthesia, the pressure control ventilation (VCV) mode can decrease the pressure of airway (P aw) and PaCO2 than volume control mode during procedure. Key words: Anesthesia, general; Respiration, artificial; Bronchoscopy; Foreign bodies/SU; Tracheal diseases/SU

Effect of Tidal Volume and Nebulizer Type and Position on Albuterol Delivery in a Pediatric Model of Mechanical Ventilation.

Optimization of factors affecting aerosol delivery during mechanical ventilation in the pediatric population is important. We hypothesized that increasing the tidal volume (V(T)), using a vibrating mesh nebulizer, and placing the nebulizer at the ventilator would increase lung dose/delivery efficiency. Continuous-output jet and vibrating mesh nebulizers loaded with albuterol (2.5 mg/3 mL) were compared when placed before the Y-piece and at the ventilator. The model consisted of a ventilator operated in pressure-regulated volume control ventilation mode at a breathing frequency of 20 breaths/min, PEEP of 5 cm H2O, FIO2 of 0.4, inspiratory time of 0.75 s, and bias flow of 0.5 L/min with a humidifier (37 ± 1.5°C) and an adult heated-wired circuit. V(T) values of 100, 150, 200, and 300 mL were studied. The circuit was connected in series to a 5.5-mm inner diameter endotracheal tube with a filter (lung dose) interposed between them. Delivery efficiency was calculated as a percentage of the nominal dose captured on the filter. Albuterol content was analyzed by spectrophotometry (276 nm). No differences in lung dose/delivery efficiency were found at different V(T) values for the jet nebulizer (both positions) and the vibrating mesh nebulizer (ventilator). Lung dose/delivery efficiency was higher (P < .02) at a VT of 100 mL compared with the other volumes tested. The vibrating mesh nebulizer had higher lung dose/delivery efficiency compared with the jet nebulizer only when placed before the Y-piece. Moving the nebulizers from before the Y-piece to the ventilator increased lung dose/delivery efficiency for all conditions tested except the vibrating mesh nebulizer at a V(T) of 100 mL (P = .36). Optimization of inhaled drug delivery during pediatric mechanical ventilation should include careful selection of the type of delivery device and its placement in the ventilator circuit. Increasing V(T) during nebulization did not increase lung dose/delivery efficiency.

Impact of optimal respiratory system dynamic compliance strategy for titrating positive end- expiratory pressure on the prognosis of acute respiratory distress syndrome in infants

Objective To investigate the impact of optimal respiratory system dynamic compliance(Cdyn)strategy for titrating positive end-expiratory pressure(PEEP)on the prognosis of acute respiratory distress syndrome(ARDS)in infants. Methods A total of 30 patients with ARDS admitted in Pediatric Intensive Care Unit(PICU)of Guangxi Maternity and Child Health Hospital were divided into 2 groups randomly (n=15). PEEP was set in the control group according to PEEP/FiO2 in American ARDS collaboration while optimal Cdyn was for the treatment group.Pressure control ventilation(PCV)mode and small tidal volume(7 mL/kg)strategy were taken.Respiratory mechanics, hemodynamics and inflammatory cytokines were monitored in each group before and after experiment.The time of assisted ventilation, and the hospital stay in PICU and 28-day mortality were compared. Results (1)There was no significant differences in gender, age and severity of disease between the 2 groups (all P>0.05). (2)The optimal PEEP of the control group was significant lower than that of the treatment group[(6.4±1.4) cmH2O vs (9.9±1.6) cmH2O, P 0.05). (4)Interleukin-6 (IL-6)in two groups all decreased gradually, and the decrease in treatment group was more obvious than that of control group after the experiment at 24 h: (84.58±9.11) ng/L vs (93.18±9.27) ng/L, P 0.05). Conclusions Optimal Cdyn method for titrating PEEP improves respiratory mechanics of ARDS obviously, shortens the time of assisted ventilation, and has no serious adverse effect on hemodynamics. Key words: Infant; Positive end-expiratory pressure; Respiratory system dynamic compliance; Acute respi-ratory distress syndrome

The comparison of manual and LabVIEW-based fuzzy control on mechanical ventilation.

The aim of this article is to develop a knowledge-based therapy for management of rats with respiratory distress. A mechanical ventilator was designed to achieve this aim. The designed ventilator is called an intelligent mechanical ventilator since fuzzy logic was used to control the pneumatic equipment according to the rat's status. LabVIEW software was used to control all equipments in the ventilator prototype and to monitor respiratory variables in the experiment. The designed ventilator can be controlled both manually and by fuzzy logic. Eight female Wistar-Albino rats were used to test the designed ventilator and to show the effectiveness of fuzzy control over manual control on pressure control ventilation mode. The anesthetized rats were first ventilated for 20 min manually. After that time, they were ventilated for 20 min by fuzzy logic. Student's t-test for p < 0.05 was applied to the measured minimum, maximum and mean peak inspiration pressures to analyze the obtained results. The results show that there is no statistical difference in the rat's lung parameters before and after the experiments. It can be said that the designed ventilator and developed knowledge-based therapy support artificial respiration of living things successfully.

Beatmungsstrategien bei chronisch obstruktiver Lungenerkrankung

Chronic obstructive pulmonary disease (COPD) is considered to be one of the most frequent pulmonary diseases in industrialized countries. Non-invasive ventilation (NIV) is the first choice therapy in acute exacerbations of chronic hypercapnic respiratory failure (AE-COPD). Effective delivery of NIV requires a specialized interdisciplinary team with sufficient monitoring. NIV is delivered as assisted positive pressure ventilation where high inspiratory flow and peak pressure are required. The external positive end expiratory pressure (PEEP) should be adjusted to the intrinsic PEEP. Criteria of success are improvement in the clinical, especially neurological condition as well as improvement of pH and PaCO(2). Patients with a pH between 7.25 and 7.35 have demonstrated most benefit from NIV. In cases of patients not responding to NIV endotracheal intubation should be initiated in a timely manner. Assisted ventilation modes are preferred over controlled ventilation modes in intubated COPD patients. Settings of respirators have to be aimed at a reduction of intrinsic PEEP and dynamic hyperinflation. This includes sufficient external PEEP, long expiration times and low respiratory frequencies even allowing for permissive hypercapnia.

Effects of controlled and pressure support mechanical ventilation on rat diaphragm muscle

The objective of this study was to analyze the effects of Pressure Controlled Ventilation mode (PCV-C) and PSV mode in diaphragm muscle of rats. Wistar rats (n=18) were randomly assigned to the control group or to receive 6 hours of PCV and PSV. After this period, animals were euthanized and their diaphragms were excised, frozen in liquid nitrogen and stored in at -80º C for further histomorphometric analysis. Results showed a 15% decrease in cross-sectional area of muscle fibers on the PCV-C group when compared to the control group (p<0.001) and by 10% when compared to the PSV group (p<0.05). Minor diameter was decreased in PCV-C group by 9% when compared with the control group (p<0.001) and by 6% when compared to the PSV group (p<0.05). When myonuclear area was analyzed, a 16% decrease was observed in the PCV-C group when compared to the PSV group (p<0.05). No significant difference between the groups was observed in myonuclear perimeter (p>0.05). Short-term controlled mechanical ventilation seems to lead to muscular atrophy in diaphragm fibers. The PSV mode may attenuate the effects of VIDD.

Failure to Ventilate with the Dräger Apollo® Anesthesia Workstation

Failure to Ventilate with the Dräger Apollo® Anesthesia Workstation

A survey of the use of ventilator hyperinflation in Australian tertiary intensive care units

Objective: To ascertain the prevalence of use of ventilator hyperinflation (VHI) by physiotherapists practising in tertiary Australian intensive care units in the management of artificially ventilated patients, and whether standard protocols are in place in these facilities.Design, setting and participants: A prospective, multicentre prevalence survey of 64 Australian hospitals with tertiary ICU facilities and physiotherapists. The cohort was compiled from details provided by the Australian and New Zealand Intensive Care Society Centre for Outcome and Resource Evaluation. Senior physiotherapists at participating sites completed a telephone questionnaire regarding the implementation of VHI at their facility.Results: The response rate was 100%. Twenty-five facilities reported using VHI. There was broad agreement on the indications and contraindications for the technique and little difference in the dosage of VHI for the purpose of either sputum clearance or respiratory recruitment manoeuvre. The most common position used for treatment (71% of patients) was side lying with the affected side uppermost.Conclusions: Our survey provides information on the nature and the extent of VHI utilisation by physiotherapists in Australian tertiary ICUs. These data can now be pooled to develop standardised evidence-based VHI protocols for both spontaneous and controlled ventilation modes.

Assisted ventilation modes reduce the expression of lung inflammatory and fibrogenic mediators in a model of mild acute lung injury

The goal of the study was to compare the effects of different assisted ventilation modes with pressure controlled ventilation (PCV) on lung histology, arterial blood gases, inflammatory and fibrogenic mediators in experimental acute lung injury (ALI). Paraquat-induced ALI rats were studied. At 24 h, animals were anaesthetised and further randomized as follows (n = 6/group): (1) pressure controlled ventilation mode (PCV) with tidal volume (V (T)) = 6 ml/kg and inspiratory to expiratory ratio (I:E) = 1:2; (2) three assisted ventilation modes: (a) assist-pressure controlled ventilation (APCV1:2) with I:E = 1:2, (b) APCV1:1 with I:E = 1:1; and (c) biphasic positive airway pressure and pressure support ventilation (BiVent + PSV), and (3) spontaneous breathing without PEEP in air. PCV, APCV1:1, and APCV1:2 were set with P (insp) = 10 cmH(2)O and PEEP = 5 cmH(2)O. BiVent + PSV was set with two levels of CPAP [inspiratory pressure (P (High) = 10 cmH(2)O) and positive end-expiratory pressure (P (Low) = 5 cmH(2)O)] and inspiratory/expiratory times: T (High) = 0.3 s and T (Low) = 0.3 s. PSV was set as follows: 2 cmH(2)O above P (High) and 7 cmH(2)O above P (Low). All rats were mechanically ventilated in air and PEEP = 5 cmH(2)O for 1 h. Assisted ventilation modes led to better functional improvement and less lung injury compared to PCV. APCV1:1 and BiVent + PSV presented similar oxygenation levels, which were higher than in APCV1:2. Bivent + PSV led to less alveolar epithelium injury and lower expression of tumour necrosis factor-alpha, interleukin-6, and type III procollagen. In this experimental ALI model, assisted ventilation modes presented greater beneficial effects on respiratory function and a reduction in lung injury compared to PCV. Among assisted ventilation modes, Bi-Vent + PSV demonstrated better functional results with less lung damage and expression of inflammatory mediators.

Influence of pulse indicator continuous cardiac output in monitoring on the volume parameters of different tidal volume under pressure control ventilation mode and volume-controlled ventilation mode in sheep

To compare the influence of pulse indicator continuous cardiac output (PiCCO) in monitoring tidal volume (V(T)) under pressure control ventilation mode and volume-controlled ventilation mode in sheep. After anesthesia and tracheotomy, 5 sheep, which were apneic and receiving mechanical ventilation. Twenty minutes later, central venous pressure (CVP) and cardiac function were monitored with different selected V(T) levels of 6, 10, 15, 20 ml/kg under bi-level positive airway pressure (BiPAP) mode by changing the pressure of inspiration, or under the synchronized intermittent mandatory ventilation (SIMV) mode with the same ventilation conditions. In both modes, the increase in V(T) led to an decrease of cardiac index (CI) and intrathoracic blood volume index (ITBVI), reaching a statistically significant difference at 15 ml/kg [SIMV mode: CI (3.94 + or - 1.03) L x min(-1) x m(-2), ITBVI (707 + or - 105) ml/m(2); BiPAP mode: CI (4.11 + or - 1.11) L x mi(-1) x m(-2), ITBVI (715 + or - 122) ml/m(2)] and 20 ml/kg [SIMV mode: CI (3.87 + or - 1.04) L x min(-1) x m(-2), ITBVI (705 + or - 116) ml/m(2); BiPAP mode: CI (3.64 + or - 0.96) L x min(-1) x m(-2), ITBVI (694 + or - 114) ml/m(2)] compared with 6 ml/kg [SIMV mode: CI (4.96 + or - 1.58) L x min(-1) x m(-2),ITBVI(811 + or - 169) ml/m(2); BiPAP mode:CI(5.67 + or - 1.96) L x min(-1) x m(-2), ITBVI (823 + or - 182) ml/m(2), all P<0.05]; an increase in systemic vascular resistance index (SVRI) and mean airway pressure (Pmean) at 15 ml/kg [SIMV mode: SVRI (237.6 + or - 56.2) kPaxs(-1) x L(-1), Pmean (14.0 + or - 3.2) cm H(2)O (1 cm H(2)O=0.098 kPa); BiPAP mode: SVRI (230.8 + or - 32.9) kPaxs(-1) x L(-1), Pmean (13.0 + or - 2.2) cm H(2)O] and 20 ml/kg [SIMV mode: SVRI (253.1 + or - 76.7) kPaxs(-1) x L(-1), Pmean (18.2 + or - 4.8) cm H(2)O ; BiPAP mode: SVRI (246.7 + or - 48.8) kPaxs(-1) x L(-1), Pmean (16.8 + or - 3.3) cm H(2)O] compared with 6 ml/kg [SIMV mode: SVRI (184.8 + or - 47.5) kPaxs(-1) x L(-1); Pmean (8.8 + or - 1.6) cm H(2)O; BiPAP mode: SVRI (184.5 + or - 51.5) kPaxs(-1) x L(-1), Pmean (8.6 + or - 0.5) cm H(2)O, all P<0.05]; but there was no significant effects on CVP, heart rate (HR), mean blood pressure (MBP). There was no significant difference of CI, ITBVI, SVRI and Pmean between the two ventilation modes with various V(T) levels. When the cardiac function was normal, the increase in V(T) led to a decrease of CI and ITBVI, but it had no significant effects on CVP. There was no significant difference of CI and ITBVI in the two ventilation modes, both were decreased. So a relatively constant V(T) should be maintained in determining ITBVI.

Comparison between pressure adjusting volume ventilation mode and volume control ventilation mode in whole lung lavage

目的 探讨压力调节容量控制(pressure regulated volume control,PRVC、)通气与容量控制(volume control,VC)通气在大容量全肺灌洗术(WLL)中的应用.方法 随机选取87例各期尘肺患者,采用规范的WLL进行治疗.每例患者第1侧肺灌洗后予VC模式通气25 min,记录灌洗侧肺单肺通气时的吸气峰压(PPEAK)、动态肺顺应性(Cdyn)、平均气道压(PMEAN)、呼吸肌做功(WOBM)及灌洗肺单肺通气3 min后血气分析各参数;第2侧肺灌洗后(第1侧灌洗肺完全恢复)予PRVC通气25 min,呼吸机设置参数保持不变,记录PPEAK、Cdyn、PMEAN、WOBM以及第2灌洗侧肺单通3 min后血气分析各参数.结果 PRVC模式下PPEAK为(30.35±6.50)cm H2O、Cdyn为(23.47±6.12)ml/cm H2O,WOBM为(2.86±0.66)J;VC模式下各参数分别为(39.98±6.91)cm H2O、(26.86±6.49)ml/cm H2O,(3.22±0.75)J,两者比较,差异有统计学意义(P＜0.01).两种模式下PMEAN和PO2、PCO2的差异无统计学意义(P＞0.05).结论 在WLL术中PRVC通气更能降低PPEAK,减少WOBM,减少呼吸肌相关的肺损伤。

Incidence of tracheal aspiration in tracheotomized patients in use of mechanical ventilation

Many patients in use of mechanical ventilation show clinical complications due to tracheal aspiration. Assessment and early methods are necessary, so that preventive and safety measures apply to this patients. To study the incidence of tracheal aspiration of saliva in tracheotomized patients treated in intensive care unit using two modes of mechanical ventilation and with different sedation levels. Prospective study with 14 tracheotomized non-neurological patients using mechanical ventilation. The sample was divided into two groups based on ventilation mode: pressure support ventilation and pressure controlled ventilation. Those two groups were subdivided into two others according to sedation level. The speech pathology evaluation was completed via the blue dye test in order to analyze the incidence of tracheal aspiration of saliva. Sedation levels and mechanical ventilation time related to tracheal aspiration were not statistically significant in this study. On the other hand, ventilation mode and tracheal aspiration showed statistical significance, and there was a higher incidence of tracheal aspiration in the pressure controlled ventilation mode. It was possible to observe a significant relationship between tracheal aspiration incidence and pressure controlled ventilation mode, which means the inclusion of those patients in the risk group for oropharyngeal dysphagia and their insertion in prevention protocols. The relationship between tracheal aspiration and sedation level, as well as tracheal aspiration and mechanical ventilation, were not statistically significant in this sample, needing further research.

A Slightly Different Tune: The Multipart Harmony of Noisy Life Support

University of Manitoba, Winnipeg, Manitoba, Canada. amutch@cc.umanitoba.caI would like to bring to the attention of readers of Anesthesiology some inaccuracies in the Editorial View “Noisy Mechanical Ventilation: Listen to the Melody” by Drs. Shimabukuro and Gropper.1This article provided an overview of the research published in the journal by Spieth et al., 2“Effects of different levels of pressure support variability in experimental lung injury.” As stated by the editorialists, “Using variability in breathing patterns is not a completely new concept. It was probably first elucidated by Suki et al. 3in Nature in 1998.” In fact such an approach, subsequently called biologically variable ventilation, was first elucidated in 1996 in work done in my laboratory by Lefevre et al .4Careful reading of the article in Nature indicates that stochastic resonance was advanced as an explanation for the improvement in compliance and oxygenation with a noisy end-inspiratory pressure based on analysis of data from our publication. We have since extended these observations to more generally indicate where noisy ventilation will be efficacious and where it may be detrimental.5This analysis is based on Jensen’s inequality–a mathematical proof stating that a variable input will enhance an output when a smoothly continuous curvilinear function is convex.6In contrast, if the function describing a relationship is concave, the addition of noise can diminish output and potentially be detrimental. Noisy ventilation is especially advantageous with tidal volume protocols according to the Acute Respiratory Distress Syndrome Network trial because the volume-pressure curve is convex curvilinear in the range of low tidal volumes.7The lone negative animal study examining noisy ventilation in an acute respiratory distress syndrome model may be a consequence of large tidal volumes administered over the concave region of the sigmoidal volume-pressure curve—the portion of the static compliance curve where it may be deleterious to provide positive pressure ventilation based on modeling using Jensen’s inequality.8The editorial further raises the question of the use of noisy ventilation in normal lungs. My laboratory has examined the use of noisy ventilation in the experimental setting of baseline anesthesia without lung injury9and during ventilation of the dependent lung during one-lung anesthesia (an article published in Anesthesiology).10Colleagues published, again in Anesthesiology, the first clinical trial examining the application of variable ventilation during abdominal aneurysmectomy.11In each of these studies better gas exchange and respiratory mechanics were seen with noisy ventilation, as compared with conventional monotonous control mode ventilation, similar to the findings by Spieth et al. I do concur with the editorialists that “The importance of variability, whether referring to the respiratory system or DNA, in biologic systems should not be underestimated.” Based on the nonlinear amplification of output in convex curvilinear systems as outlined above, we have shown that noisy perfusion can improve cerebral oxygenation,12diminish renal injury,13and enhance delivery of cardioplegia14during cardiopulmonary bypass. These improvements are likely a consequence of better flow with noisy perfusion pressure over the convex curvilinear flow-pressure curve manifest by the microvasculature. An overview of some of these issues is discussed in a short review.15I also concur that “the time is here to translate these studies to the bedside.” The article by Spieth et al. reinforces prior work by this European group, the group in Boston, and the group in Canada, all demonstrating the advantage of adding noise to life support systems.University of Manitoba, Winnipeg, Manitoba, Canada. amutch@cc.umanitoba.ca

Risk factors for the deterioration of oxygenation ratio in ventilated intensive care unit patients: A retrospective cohort study

Purpose The aim of the study is to determine which factors are associated with the deterioration of Pa o 2/fraction of inspired oxygen (F io 2) ratio in patients with normal oxygenation at admission and ventilated according to a lung protective ventilation strategy. Materials and Methods Retrospective cohort study of ventilated (≥3 days) intensive care unit patients with an admission Pa o 2/F io 2 ratio of 300 mm Hg or higher (n = 105). Patients who developed lung injury (Pa o 2/F io 2 ratio, <300 mm Hg) on day 7 (n = 37) were compared to those who did not (n = 68), with regard to ventilator settings, gas exchange variables, and lung injury risk factors. Results Mean ± SD of administered tidal volume was 7.9 ± 1.3 mL/kg. Patients who developed lung injury were older ( P = .019), had lower Pa o 2 ( P = .009), higher Pa co 2 ( P = .045), and lower Pa o 2/F io 2 ratio ( P = .002) at admission. Postoperative state (Hazard risk [HR], 5.1) and controlled ventilation mode (HR, 4.3) were identified as independent risk factors. Lung injury-free time was shorter in patients with low initial Pa o 2/F io 2 ratio (odds ratio, 1.7; P = .039). This effect was not only caused by the baseline difference, as the decrease in Pa o 2/F io 2 ratio was more pronounced in patients who developed lung injury compared to those who did not ( P = .008). Conclusions Lung injury exacerbates during mechanical ventilation. In patients treated with a mean tidal volume of 7.9 mL/kg, controlled ventilation is a major risk factor.

The Effects of Flexible Bronchoscopy on Mechanical Ventilation in a Pediatric Lung Model

Flexible bronchoscopy performed through endotracheal tubes (ETTs) in children receiving mechanical ventilation can significantly impact ventilation, but the magnitude of this impact has not been established. We used a lung model to simulate mechanical ventilation in a range of child sizes in order to determine how the insertion of pediatric flexible bronchoscopes into ETTs alters ventilatory parameters, especially tidal volume (Vt) and peak inspiratory pressure (PIP), in both healthy and diseased lungs. We simulated five child sizes based on weight, and evaluated 22 bronchoscope/ETT combinations, first in pressure control (PC) ventilation mode and then in volume control (VC) ventilation mode. The combinations ranged from the 2.2-mm (bronchoscope outer diameter)/3.0-mm (ETT inner diameter) to 5.0-mm bronchoscope/8.0-mm ETT. The primary outcome measures were decrease in Vt after bronchoscope insertion during PC ventilation and increase in PIP during VC ventilation. In the PC ventilator mode, Vt decreased by > 50% with nine of the combinations, while during VC ventilation, PIP increased by >or= 20 cm H(2)O with seven combinations. The 2.2-mm bronchoscope/3.0-mm ETT, 2.8-mm bronchoscope/5.0-mm ETT, and 3.6-mm bronchoscope/5.0-mm ETT combinations severely impaired ventilation, while the 3.6-mm bronchoscope/4.5-mm ETT, 5.0-mm bronchoscope/6.5-mm ETT, and 5.0-mm bronchoscope/7.0-mm ETT combinations were incompatible with adequate ventilation. The insertion of bronchoscopes into ETTs can lead to clinically relevant decreases in Vt when in the PC ventilator mode and large increases in PIP during VC ventilation. The minimum bronchoscope/ETT diameter difference required to maintain adequate ventilation increases with child size.

Multicenter Prospective Observational Study about the Usage Patterns of Sedatives, Analgesics and Neuromuscular Blocking Agents in the Patients Requiring More Than 72 Hours Mechanical Ventilation in Intensive Care Units of Korea

Background: To investigate the usage patterns of sedatives, analgesics and neuromuscular blocking agents (NMBAs) in patients requiring mechanical ventilation more than 72 hours in intensive care units (ICUs) of Korea. Methods: A total of 536 patients continuing mechanical ventilation more than 72 hours had been enrolled among the twenty-one ICUs of Korea from May 2003 to July 2003. Data about mechanical ventilation, the use of sedatives, analgesics, and NMBAs were prospectively collected for f our weeks. We analyzed the patterns of using these drugs and effects on outcomes. Results: More than half of the patients (50.4%) received sedative drug alone. Most commonly used sedatives and analgesics were midazolam and morphine. NMBAs were administered in 41% of the patients. Volume controlled ventilation mode was associated with more frequent use of NMBAs. There were no significant differences in outcome variables among the usage patterns of sedatives, analgesics and NMBAs. Conclusions: Our investigation shows that analgesics were much less frequently used in the intensive care units of Korea compared with the use of sedatives. And the use of NMB As were quite a common.

Two Distinct Controllers for Pressure Regulation in Total Liquid Ventilation

Total liquid ventilation is an experimental method of mechanical assisted ventilation in which lungs are totally filled and then ventilated with a tidal volume of perfluorochemical liquid by using a liquid ventilator. However to apply this approach to humans, liquid ventilators must reach the same level of reliability as conventional mechanical gas ventilators. In control terms, the problem is to design a controller to perform pressure regulated ventilation in spite of large uncertainties on physiological parameters, and nonlinear behavior of the lungs. The presented pressure controlled ventilation mode is similar to those used in conventional gas ventilator excepted that the airway pressure and the positive end-expiratory pressure require two distinct controllers. Simulations, in-vitro experiments and in-vivo results with 5 healthy term newborn lambs have validated the presented controllers.

Physiological noise versus white noise to drive a variable ventilator in a porcine model of lung injury

Variable ventilation is superior to control mode ventilation in a number of circumstances. The nature of the breathing file used to deliver the variable rate and tidal volume has not been formally examined. We compared two different noise files in a randomized prospective trial of variable ventilation. Pigs were anesthetized, intubated, and mechanically ventilated. Oleic acid was infused to introduce lung injury. The animals were ventilated at a tidal volume of 7 mL x kg(-1), in variable mode, with either physiologically-derived noise (variability file - 1,587 breath intervals-obtained from a spontaneously breathing volunteer; n = 10) or a variability file of identical length derived from computer- generated white noise (n = 10). The physiologically-derived noise had a power law alpha-exponent of -0.27 and a Hölder exponent of -0.38, indicative of auto-correlated noise. The computer-generated noise had an alpha-exponent of -0.52 and a Hölder exponent of -0.49, indicative of white noise. Both files showed multifractal characteristics. There were no differences between groups, at any time period, for PaO2, PaCO2, and static or dynamic respiratory system compliance. No differences were observed between groups for wet:dry lung weight ratios or for interleukin-8 in bronchoalveolar lavage fluid. This study demonstrates that the nature of the variability files, chosen to drive the variable ventilator, had no effect on indices of gas exchange or respiratory mechanics in this model. A considerable overlap of the multifractal files existed. The potential to drive a variable ventilator using algorithm-derived files with multifractal characteristics, thereby eliminating the requirement to use physiologically-derived signals, is discussed.

The effects of different ventilatory modes and spontaneous breathing after recruitment maneuver in acute respiratory distress syndrome. Experiment with dogs

To investigate the role of different ventilatory modes and spontaneous breathing (SB) in prevention of derecruitment in acute respiratory distress syndrome (ARDS). Eighteen dog ARDS models were established by injection of oleic acid into the central vein and ventilated with volume controlled ventilation (VCV,) with the positive end expiratory pressure (PEEP) of 16 cm H(2)O, tidal volume (V(T)) of 10 ml/kg, and respiratory rate (RR) of 30 bpm, and the steady state in this mode was defined as baseline (0 min). After the baseline state was reached, all dogs accepted recruitment maneuver (RM) in pressure controlled ventilation (PCV) mode at the level of 15 cm H(2)O and PEEP of 35 cm H(2)O for 1 min, and then assigned into three groups and ventilated for 4 hs: VCV group (VCV with V(T) of 15 ml/kg), PCV group in which the peak inspiratory airway pressure was adjusted for keeping 15 ml/kg of V(T), and SB grouping which PCV with SB activity and inspiratory airway pressure were adjusted for keeping 15 ml/kg of V(T). PEEP of 10 cm H(2)O, RR of 20 bpm, and inspiratory/expiratory ratio of 1/2 were kept for all animals. Four hours later the dogs were killed and their lungs were taken out. (1) The lower inflection points were identified as 16.1 +/- 1.9, 17.4 +/- 1.5, and 17.1 +/- 1.6 cm H(2)O for the VCV, PCV, and SB group respectively. (2) After RM, the PaO(2) levels of the PCV and SB groups were kept higher than baseline, but the PaO(2) level was as same as that in the baseline state in the VCV group. Compared with the VCV group, higher PaO(2) the PaO(2) level 30 min after RM in the SB group was found (P < 0.05). The intrapulmonary shunt 5 min, 30 min and 1 hr after RM in the SB group were all lower than those in the VCP group, however, not significantly (P = 0.077, 0.058, 0.076). (3) Compared with baseline levels, the plateau pressure and mean airway pressure in all animals were decreased significantly after RM. The plateau pressure in the SB group was significantly lower than that in the VCV group (P < 0.05). PCV with spontaneous breathing activity can offset the effect of antiderecruitment for lower PEEP; it would be more safe and effective than VCV.