Pressure-controlled Ventilation Mode Research Articles

Comparison of volume-controlled and pressure-controlled ventilation using a laryngeal mask airway during gynecological laparoscopy

BackgroundSeveral publications have reported the successful, safe use of Laryngeal Mask Airway (LMA)-Classic devices in patients undergoing laparoscopic surgery. However, there have been no studies that have examined the application of volume-controlled ventilation (VCV) or pressure-controlled ventilation (PCV) using a LMA during gynecological laparoscopy. The aim of this study is to compare how the VCV and PCV modes and using a LMA affect the pulmonary mechanics, the gas exchange and the cardiovascular responses in patients who are undergoing gynecological laparoscopy.MethodsSixty female patients were randomly allocated to one of two groups, (the VCV or PCV groups). In the VCV group, baseline ventilation of the lung was performed with volume-controlled ventilation and a tidal volume of 10 ml/kg ideal body weight (IBW). In the PCV group, baseline ventilation of the lung using pressure-controlled ventilation was initiated with a peak airway pressure that provided a tidal volume of 10 ml/kg IBW and an upper limit of 35 cmH2O. The end-tidal CO2, the peak airway pressures (Ppeak), the compliance, the airway resistance and the arterial oxygen saturation were recorded at T1: 5 minutes after insertion of the laryngeal airway, and at T2 and T3: 5 and 15 minutes, respectively, after CO2 insufflation.ResultsThe Ppeak at 5 minutes and 15 minutes after CO2 insufflation were significantly increased compared to the baseline values in both groups. Also, at 5 minutes and 15 minutes after CO2 insufflation, there were significant differences of the Ppeak between the two groups. The compliance decreased in both groups after creating the pneumopertoneim (P < 0.05).ConclusionsOur results demonstrate that PCV may be an effective method of ventilation during gynecological laparoscopy, and it ensures oxygenation while minimizing the increases of the peak airway pressure after CO2 insufflation.

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.

Postoperative Noninvasive Ventilation

Thesemodificationsoftherespiratoryfunctionoccur early after surgery and are more often transient andcould lead to ARF. The clinical result (severity of theARF) is the product of perioperative-related ventilatoryimpairment and severity of the preoperative pulmonarycondition. Maintenance of adequate oxygenation in thepostoperative period is of major importance, especiallywhen pulmonary complications such as ARF occur. Al-though invasive endotracheal mechanical ventilation hasremained the cornerstone of ventilatory strategy for manyyearsforsevereARF,severalstudieshaveshownthatmor-tality associated with pulmonary disease is largely relatedto complications of postoperative reintubation and me-chanicalventilation.Therefore,majorobjectivesforanes-thesiologists are first to prevent the occurrence of postop-erative complications and second to ensure oxygenadministration and carbon dioxide removal while avoid-ing intubation if ARF occurs. Noninvasive ventilation(NIV) does not require an artificial airway (endotrachealtube or tracheotomy), and its use is well established toprevent ARF occurrence (prophylactic treatment) or totreat ARF to avoid reintubation (curative treatment) (fig.1). Studies show that patient-related risk factors, such aschronic obstructive pulmonary disease, age older than 60yr, American Society of Anesthesiologists class of II orhigher, obesity, functional dependence, and congestiveheart failure, increase the risk for postoperative pulmo-nary complications.

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.

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.

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.

Positive End Expiratory Pressure Prevents Loss Of Respiratory Compliance During Low Tidal Volume Ventilation In Acute Lung Injury Patients

A total of 120 patients were enrolled in the present study over a period of 3 years from (2005 – 2008) . Pressure controlled ventilation (PCV) and volume controlled ventilation (VCV), with an average tidal Volume (VT) of 8.2 ± 0.4 ml/kg was applied at three levels of PEEP (5, 10, 15 cm H2O). Before each PCV & VCV period, lung volume history was standardized by manual hyperinflation maneuvers. The compliance was measured from the beginning at time 0 (start), 10, 20 & 30 (end) min of each PCV & VCV period. Three gas exchange and hemodynamic data were collected in the end. After statistical analysis results showed progressive decay in compliance with both PCV & VCV modes at 5 & 10 cm H2O. At PEEP 5 cm H2Ocompliance decrease was higher during PCV mode than VCV mode and at PEEP 15 cm H2O, compliance did not decay significantly. The values of PaO2 were significant but statistically insignificant in PCV mode at 15 cm H2O than VCV mode. Hemodynamic data did not differ between PCV & VCV mode.

Multilevel Ventilation: Theory and Simplified Mathematical Model

Considering the issues of artificial ventilation (AV) in non-homogenous pathological lung processes (acute lung injury, acute respiratory distress syndrome, pneumonia, etc.), the authors created a mathematical model of multicompartment non-homogenous injured lungs that were ventilated by a new mode of AV, the so-called three-level ventilation. Multilevel ventilation was defined a type (modification) of ALV whose basic ventilation level was produced by the modes CMV, PCV or PS (ASB) and add-on level, and the so-called background ventilation was generated by the levels of PEEP and high PEEP (PEEPh) with varying frequency and duration. Multi-level ventilation on 3 pressure levels was realized by the mathematical model as a combination of pressure-controlled ventilation (PCV) and two levels of PEEP and PEEPh. The objective was to prove that in cases of considerably non-homogenous gas distribution in acute pathological disorders of lungs, gas entry into the so-called slow bronchoalveolar compartments could be improved by multilevel AV, without substabtially changing the volume of so-called fast compartments. Material and Method. Multi-level ventilation at 3 pressure levels was realized by the mathematical model as a combination of PCV and two levels of PEEP and PEEPh. Results. By comparing the single-level AV in the PCV mode with the so-called three-level ventilation defined as a combination of PCV+PEEPh/PEEP, the authors have discovered that the loading of slow compartments in the model was considerably improved by 50—60% as compared with the baseline values. In absolute terms, this difference was as many as 2—10 times of the volume. Conclusion. The mathematical model may demonstrate that the application of the so-called three-level AV causes considerable changes in gas distribution in the lung parenchyma disordered by a non-homogenous pathological process. The authors state that the proposed mathematical model requires clinical verification in order to evaluate the efficiency of this modification of AV. Key words: artificial ventilation, multilevel artificial ventilation, acute lung injury, acute respiratory distress syndrome.

Compliance and Dead Space Fraction Indicate an Optimal Level of Positive End-Expiratory Pressure After Recruitment in Anesthetized Patients

"Optimal" positive end-expiratory pressure (PEEP) can be defined as the PEEP that prevents recollapse after a recruitment maneuver, avoids over-distension, and, consequently, leads to optimal lung mechanics at minimal dead space ventilation. In this study, we analyzed the effects of PEEP and recruitment on functional residual capacity (FRC), compliance, arterial oxygen partial pressure (Pao2) and dead space fraction, and we determined the most suitable variables indicating optimal PEEP. We studied 20 anesthetized patients with healthy lungs undergoing faciomaxillary surgery. After a stepwise increase of PEEP/inspiratory pressures (0/10, 5/15, 10/20, 15/25 cm H2O, each level lasting for 20 min) using a pressure-controlled ventilation mode, a recruitment maneuver (at 20/45 cm H2O for a maximum of 20 min) was performed, followed by a stepwise pressure reduction (15/25, 10/20, 5/15, 0/10 cm H2O, with 20 min at each level). At each pressure level, FRC, compliance, Pao2, and dead space fraction were measured. When comparing the values before and after recruitment at identical PEEP levels, all variables showed significant changes at 10/20 cm H2O; compliance was also significantly higher at the pressure step 15/25 cm H2O. In addition, FRC values showed significant differences at 5/15 cm H2O and 15/25 cm H2O. All variables showed the positive effects of PEEP in conjunction with a recruitment maneuver. Optimal PEEP was 10 cm H2O because at this pressure level the highest compliance value in conjunction with the lowest dead space fraction indicated a maximum amount of effectively expanded alveoli. FRC and Pao2 were insensitive to alveolar over-distension.

Cardiorespiratory effects of spontaneous breathing in two different models of experimental lung injury: a randomized controlled trial

IntroductionAcute lung injury (ALI) can result from various insults to the pulmonary tissue. Experimental and clinical data suggest that spontaneous breathing (SB) during pressure-controlled ventilation (PCV) in ALI results in better lung aeration and improved oxygenation. Our objective was to evaluate whether the addition of SB has different effects in two different models of ALI.MethodsForty-four pigs were randomly assigned to ALI resulting either from hydrochloric acid aspiration (HCl-ALI) or from increased intra-abdominal pressure plus intravenous oleic acid injections (OA-ALI) and were ventilated in PCV mode either with SB (PCV + SB) or without SB (PCV – SB). Cardiorespiratory variables were measured at baseline after induction of ALI and after 4 hours of treatment (PCV + SB or PCV – SB). Finally, density distributions and end-expiratory lung volume (EELV) were assessed by thoracic spiral computed tomography.ResultsPCV + SB improved arterial partial pressure of oxygen/inspiratory fraction of oxygen (PaO2/FiO2) by a reduction in intrapulmonary shunt fraction in HCl-ALI from 27% ± 6% to 23% ± 13% and in OA-ALI from 33% ± 19% to 26% ± 18%, whereas during PCV – SB PaO2/FiO2 deteriorated and shunt fraction increased in the HCl group from 28% ± 8% to 37% ± 17% and in the OA group from 32% ± 12% to 47% ± 17% (P < 0.05 for interaction time and treatment, but not ALI type). PCV + SB also resulted in higher EELV (HCl-ALI: 606 ± 171 mL, OA-ALI: 439 ± 90 mL) as compared with PCV – SB (HCl-ALI: 372 ± 130 mL, OA-ALI: 192 ± 51 mL, with P < 0.05 for interaction of time, treatment, and ALI type).ConclusionsSB improves oxygenation, reduces shunt fraction, and increases EELV in both models of ALI.

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.

Carbon Dioxide Clearance in Rabbits During Expiratory Phase Intratracheal Pulmonary Ventilation

The purpose of this study was to compare the efficacy of CO2 removal during conventional mechanical ventilation (CMV) with and without expiratory phase intratracheal pulmonary ventilation (expiratory ITPV or Exp-ITPV); and to compare CO2 clearance during Exp-ITPV, in pressure-controlled ventilation (PCV) and in volume-controlled ventilation (VCV) modes. Seven anesthetized rabbits were tracheotomized and intubated using a 4 mm endotracheal tube. Venous and arterial lines were established. The rabbits were paralyzed, mechanically ventilated, and ventilation parameters were adjusted to achieve baseline arterial hypercapnia. Animals were then ventilated during 30-minute trials of CMV and Exp-ITPV, in both PCV and VCV modes. A custom-built, microprocessor-controlled solenoid valve was used to limit ITPV gas flow to the expiratory phase. Proximal and carinal airway pressures and hemodynamic variables were continuously recorded, and arterial blood gases were analyzed at the end of each trial. Exp-ITPV, as compared with CMV, reduced arterial PCO2 by 12% and 21% in PCV and VCV modes, respectively (p < 0.02 and p < 0.001; one-sided paired t test), without significant changes in other cardiorespiratory variables. In conclusion, Exp-ITPV is more effective than CMV in clearing CO2 through a small endotracheal tube. Exp-ITPV is also more effective in VCV mode than PCV mode.

Trauma cranioencefálico e síndrome do desconforto respiratório agudo: como ventilar? Avaliação da prática clínica

The traumatic brain injury (TBI) is a healthy-world problem, some of his patients develop respiratory failure, requiring intubation and mechanical ventilation, and the most common complications are the acute respiratory distress syndrome (ARDS). In this way, this study has the objective describe the daily clinical practice of respiratory care in this patients submit mechanical ventilation. The methods and ventilatories parameters used to ventilate the patients with TBI and ARDS has been evaluated by a sample of physiotherapists from the city of Salvador, BA, from a descriptive study. The data were collected by face-to-face interviews in the period of October 2005 to March 2006. For in such way a half structuralized questionnaire was elaborated contends changeable social-demographic, about the hospital profile and the applied ventilatory strategy in patients with TBI that come to develop ARDS. The sample was composed by 70 physiotherapists, 41 (58.6%) was female, with mean of age of 31.2 ± 6.4 (24-49) years-old and graduated time 7.7 ± 6.4 (1-27) years, which 37 (52.9%) works on public hospital; 67 (95.7%) has any specialization. Sixty four physiotherapists affirm the usage of the pressure controlled ventilation mode. The peak pressure and the plateau pressure wanted to ventilate the patients with TBI and ARDS were in mean 35.6 ± 5,3 (25-50) and 28,4 ± 5,8 (15-35) cmH2O respectively. Forty eighty (68.6%) of the interviewed wants a PaCO2 in 30-35 mmHg. Thirty one (44.3%) of the interviewed finds the ideal PEEP through the best SpO2 with minor FiO2. It's incontestable that the ventilatory strategy of a patient with severe TBI that become to develop ALI or ARDS is an authentic challenge; a predilection for PCV mode is observed due to the already known protective ventilation strategy.

Effects of body temperature on ventilator-induced lung injury

Purpose To evaluate the effects of body temperature on ventilator-induced lung injury. Material and Methods Thirty-four male Sprague-Dawley rats were randomized into 6 groups based on their body temperature (normothermia, 37 ± 1°C; hypothermia, 31 ± 1°C; hyperthermia, 41 ± 1°C). Ventilator-induced lung injury was achieved by ventilating for 1 hour with pressure-controlled ventilation mode set at peak inspiratory pressure (PIP) of 30 cmH 2O (high pressure, or HP) and positive end-expiratory pressure (PEEP) of 0 cmH 2O. In control subjects, PIP was set at 14 cmH 2O (low pressure, or LP) and PEEP set at 0 cmH 2O. Systemic chemokine and cytokine (tumor necrosis factor α, interleukin 1 β, interleukin 6, and monocyte chemoatractant protein 1) levels were measured. The lungs were assessed for histological changes. Results Serum chemokines and cytokines were significantly elevated in the hyperthermia HP group compared with all 3 groups, LP (control), normothermia HP, and hypothermia HP. Oxygenation was better but not statistically significant in hypothermia HP compared with other HP groups. Cumulative mean histology scores were higher in hyperthermia HP and normothermia HP groups compared with control and normothermia HP groups. Conclusions Concomitant hyperthermia increased systemic inflammatory response during HP ventilation. Although hypothermia decreased local inflammation in the lung, it did not completely attenuate systemic inflammatory response associated with HP ventilation.

Post-suction recruitment manoeuvre restores lung function in healthy, anaesthetized pigs.

Endotracheal suction can cause partial lung collapse and hypoxia and alter lung mechanics. We investigated the effects of adding a recruitment manoeuvre directly after endotracheal suction to restore lung volume in volume-controlled ventilation and pressure-controlled ventilation modes. Five anaesthetized pigs were investigated. The effects of endotracheal suction with or without a recruitment manoeuvre were compared in random order. In volume-controlled ventilation, compliance decreased after suction from 33 +/- 5 to 26 +/- 6 ml x cmH2O(-1) (P<0.05), and 30 minutes later it remained decreased at 25 +/- 6 ml x cmH2O(-1). Venous admixture increased after suction from 5 +/- 2 to 8 +/- 4% (P<0.05), but had recovered at 30 minutes. In pressure-controlled ventilation, compliance decreased after suction from 34 +/- 3 to 25 +/- 7 ml x cmH2O(-1) (P<0.05), and 30 minutes later it remained decreased at 25 +/- 7 ml x cmH2O(-1). Venous admixture increased after suction from 5 +/- 2 to 13 +/- 7% (P<0.05), and had not recovered after 30 minutes, 10 +/- 4%. When a recruitment manoeuvre was applied directly after suction, no negative side-effects were registered in volume-controlled ventilation or pressure-controlled ventilation. We conclude that the impairment of lung mechanics and gas exchange induced by endotracheal suction can be prevented by a simple post-suction recruitment manoeuvre. Further studies are needed to identify a suitable suction recruitment manoeuvre in patients with diseased lungs.

The effect of mode, inspiratory time, and positive end-expiratory pressure on partial liquid ventilation.

Partial liquid ventilation (PLV) has been shown to be an effective means of improving oxygenation in the injured lung. However, little is known about how approach to ventilation during PLV affects gas exchange and pulmonary mechanics. We hypothesized that gas exchange and pulmonary mechanics would be best with positive end-expiratory pressure (PEEP) set above the lower inflection point (LIP) of the pressure-volume (P-V) curve regardless of mode of ventilation or inspiratory to expiratory time (I:E) ratio and that the efficiency of ventilation would be greatest with volume-controlled ventilation (VCV) compared with pressure-controlled ventilation (PCV) and with long inspiratory time as compared with short inspiratory time. Lung injury was induced in 14 sheep by lavage, 10 of which were studied. Sheep were then assigned to high-PEEP (Group H, n = 5) and low-PEEP (Group L, n = 5) groups. In Group H applied PEEP was set at the LIP and in Group L applied PEEP was set at 5 cm H2O after the lung was filled with perflubron (PFB). We randomly compared VCV and PCV with I:E ratios of 1:2, 1:1, and 2:1. Peak inspiratory pressure and VT were adjusted to maintain a constant end-inspiratory plateau pressure (Pplat) of about 25 cm H2O in both groups and a constant total PEEP of about 5 cm H2O in Group L and about 12 cm H2O in Group H. There were no differences in oxygenation among modes in Group H. In Group L VCV 2:1 and all of the PCV modes in Group L had a lower PaO2 than VCV 1:1 (p < 0.05). PaCO2 and VD/VT were significantly different (p < 0.05) among modes. VD/VT was highest during PCV 1:2 with PEEP of 5 cm H2O (p < 0.05). Quasi-static compliance in Group H was higher than in Group L (p < 0.05). We conclude that during low PEEP gas exchange deteriorated in VCV with long inspiratory time and in PCV. Oxygenation was enhanced during VCV 1:1 when compared with VCV at longer I:E ratios or PCV at any I:E ratio. With PEEP set at the LIP, adequate gas exchange and improved lung mechanics could be obtained in all modes assessed.

Adaptive lung ventilation (ALV) during anesthesia for pulmonary surgery: automatic response to transitions to and from one-lung ventilation.

Adaptive lung ventilation is a novel closed-loop-controlled ventilation system. Based upon instantaneous breath-to-breath analyses, the ALV controller adjusts ventilation patterns automatically to momentary respiratory mechanics. Its goal is to provide a preset alveolar ventilation (V'A) and, at the same time, minimize the work of breathing. Aims of our study were (1) to investigate changes in respiratory mechanics during transition to and from one-lung ventilation (OLV), (2) to describe the automated adaptation of the ventilatory pattern. With institutional approval and informed consent, 9 patients (33-72 y, 66-88 kg) underwent ALV during total intravenous anesthesia for pulmonary surgery. The ALV controller uses a pressure controlled ventilation mode. V'A is preset by the anesthesiologist. Flow, pressure, and CO2 are continuously measured at the DLT connector. The signals were read into a IBM compatible PC and processed using a linear one-compartment model of the lung to calculate breath-by-breath resistance (R), compliance (C), respiratory time constant (TC), serial dead space (VdS) and V'A. Based upon the results, the controller optimizes respiratory rate (RR) and tidal volume (VT) such as to achieve the preset V'A with the minimum work of breathing. In addition to V'A, only PEEP and FIO2 settings are at the anesthesiologist's discretion. All patients were ventilated using FIO2 = 1,0 and PEEP = 3 cm H2O. Parameters of respiratory mechanics, ventilation, and ABG were recorded during three 5-min periods: 10 min prior to OLV (1), 20 min after onset of OLV (II), and after chest closure (III). Data analyses used nonparametric comparisons of paired samples (Wilcoxon, Friedman) with Bonferroni's correction. Significance was assumed at p < 0.05. Values are given as medians (range). 20 min after onset of OLV (II), resistance had approximately doubled compared with (1), compliance had decreased from 54 (36-81) to 50 (25-70) ml/cm H2O. TC remained stable at 1.4 (0.8-2.4) vs. 1.2 (0.9)-1.6) s. Institution of OLV was followed by a reproducible response of the ALV controller. The sudden changes in respiratory mechanics caused a transient reduction in VT by 42 (8-59)%, with RR unaffected. In order to reestablish the preset V'A, the controller increased inspiratory pressure in a stepwise fashion from 18 (14-23) to 27 (19-39) cm H2O, thereby increasing VT close to baseline (7.5 (6.6-9.0) ml/kg BW vs. 7.9 (5.4-11.7) ml/kg BW). The controller was, thus, effective in maintaining V'A. The minimum PaO2 during phase II was 101 mmHg. After chest closure, respiratory mechanics had returned to baseline. Respiratory mechanics during transition to and from OLV are characterized by marked changes in R and C into opposite directions, leaving TC unaffected. The ALV controller manages these transitions successfully, and maintains V'A reliably without intervention by the anesthesiologist. VT during OLV was found to be consistently lower than recommended in the literature.

Inaccuracies of nitric oxide delivery systems during adult mechanical ventilation.

Various systems to administer inhaled nitric oxide (NO) have been used in patients and experimental animals. We used a lung model to evaluate five NO delivery systems during mechanical ventilation with various ventilatory patterns. An adult mechanical ventilator was attached to a test lung configured to separate inspired and expired gases. Four injection systems were evaluated with NO injected either into the inspiratory circuit 90 cm proximal to the Y piece or directly at the Y piece and delivered either continuously or only during the inspiratory phase. Alternatively, NO was mixed with air using a blender and delivered to the high-pressure air inlet of the ventilator. Nitric oxide concentration was measured from the inspiratory limb of the ventilator circuit and the tracheal level using rapid- and slow-response chemiluminescence analyzers. The ventilator was set for constant-flow volume control ventilation, pressure control ventilation, pressure support ventilation, or synchronized intermittent mandatory ventilation. Tidal volumes of 0.5 l and 1 l were evaluated with inspiratory times of 1 s and 2 s. The system that premixed NO proximal to the ventilator was the only one that maintained constant NO delivery regardless of ventilatory pattern. The other systems delivered variable NO concentration during pressure control ventilation and spontaneous breathing modes. Systems that injected a continuous flow of NO delivered peak NO concentrations greater than the calculated dose. These variations were not apparent when a slow-response chemiluminescence analyzer was used. NO delivery systems that inject NO at a constant rate, either continuously or during inspiration only, into the inspiratory limb of the ventilator circuit produce highly variable and unpredictable NO delivery when inspiratory flow is not constant. Such systems may deliver a very high NO concentration to the lungs, which is not accurately reflected by measurements performed with slow-response analyzers.

The Evaluation of Home Ventilation with PCV (Pressure Control Ventilation) Mode Using Bear-33

The Evaluation of Home Ventilation with PCV (Pressure Control Ventilation) Mode Using Bear-33