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PubMedDate not supplied

Recent innovations in total liquid ventilation system and component design.

In addition to partial liquid ventilation (PLV), total liquid ventilation (TLV) is being explored as a potential therapy to mitigate ventilator-associated lung injury and acute lung failure. TLV is ventilation of the completely liquid-filled lung using tidal flow of oxygenated perfluorochemical (PFC) liquid delivered by a "liquid ventilator." Most TLV research to date has focused on "small" lung (animals < 20 kg; vast majority < 5 kg), with primary relevance to its use in children. Recent investigations regarding TLV in larger lungs have helped define new design challenges for liquid ventilator systems to succeed as clinical products. Adult TLV requires the delivery of significantly higher liquid tidal volumes, with proportionately greater O2 and CO2 exchange. Although a simple scale-up of liquid ventilator components such as pumps, tubing, fittings, and gas and heat exchangers might be considered the most straightforward way to compensate for the increased demand, there are a number of practical problems with this approach. These include requirements to: 1) minimize priming volume, 2) minimize PFC evaporative loss, 3) suppress flow-induced cavitation in fittings and components, 4) monitor and control ventilation based on pressure signals exhibiting noise, 5) maintain ability and accuracy of delivered breaths in a fluid mechanical environment having higher inertial forces and pressure losses than for small lung systems, 6) use disposable or sterilizable fluid-contacting components, and 7) maintain PFC materials compatibility. TLV system and component innovations implemented on a new large-animal liquid ventilator prototype are presented. The advantages of new pumps, gas exchangers, and temperature-control components are discussed.

Adult↗
PubMed2000

[Noninvasive ventilation for decompensation of chronic respiratory failure].

MASK DELIVERY: Noninvasive ventilation designates ventilation methods which do not use the endotracheal route. Noninvasive ventilation is generally delivered via a facial mask (generally for patients with acute respiratory failure) or a nasal mask (widely used for home-delivery systems). INDICATIONS: Following work conducted by Rideau in the eighties who made the first ventilation trials in patients with myopathy, Meduri then Brochard focused interest on noninvasive ventilation for the management of acute episodes in patients with chronic respiratory failure. Following a simple algorithm, first intention noninvasive ventilation can be used in case of acute decompensation of chronic respiratory failure when the degree of urgency and the patient's status do not require immediate endotracheal ventilation. A WEANING TOOL: In addition to this well recognized indication, recent trials have demonstrated the usefulness of noninvasive ventilation as a weaning tool for patients on conventional endotracheal ventilation.

Chronic Disease↗
PubMed2004

The critical airway, rescue ventilation, and the combitube: Part 1.

Emergency and unexpected difficult airway management can rapidly deteriorate into a critical airway event such as "cannot ventilate, cannot intubate" (CVCI). A critical airway event (i.e., inadequate mask ventilation, failed intubation, and CVCI) can be resolved by rescue ventilation, thus avoiding potential neurological disability or death. Recommended options include use of the larygeal mask airway, the esophageal-tracheal Combitube (ETC; Tyco-Healthcare-Nellcor, Pleasanton, Calif), transtracheal jet ventilation, or a surgical airway. This article reviews proper use of the ETC in combination with the self-inflating bulb (SIB) and/or portable carbon dioxide detector to resolve critical airway situations. The combined use of these 3 devices provides on ideal integrated system for airway control and ventilation. In addition, critical airway events and rescue ventilation options; ETC design, technical aspects, training, insertion, and ventilation; determining ETC location (i.e., esophagus vs trachea); and monitoring ETC lung ventilation are reviewed. The SIB primarily assesses ETC location within the esophagus or the trachea; the carbon dioxide detector also permits monitoring lung ventilation. Use of the ETC in prehospital, emergency medicine, and anesthesia settings, including ETC advantages, contraindications, and reported complications will be reviewed in Part 2. How to safely exchange the ETC for a definitive airway also will be reviewed.

Clinical Competence↗
PubMed1985

Ventilation during transport of postoperative patients: comparison of methods.

Changes in arterial blood gases as a result of transporting 28 stable postoperative cardiovascular surgical patients to the intensive care unit were studied. Three methods of ventilation during the 3-minute transport period were compared. All patients were ventilated with 100% oxygen prior to transport. Nine patients were ventilated with air by a self-inflating, non-rebreathing bag. Ten patients were not ventilated at all. Nine patients were ventilated with oxygen in a closed rebreathing circuit constructed from disposable portions of the anesthesia circuit. Oxygen tension on arrival in the intensive care unit was highest in the group ventilated with the closed rebreathing circuit and lowest in the group ventilated with room air. Carbon dixoide tension rose 6.2 mm Hg/min in unventilated patients, 3.2 mm Hg/min in patients ventilated with the closed rebreathing circuit, and did not change in the group ventilated with air. We conclude that stable patients can be safely transported while breathing air for 3 minutes. For longer periods of transport, the closed rebreathing circuit provides high oxygen tension with acceptable hypercarbia and provides a convenient alternative to the use of portable oxygen tanks.

Journal Article↗
PubMed2005

Cuirass ventilation: a review and update.

OBJECTIVE: This review highlights the development and application of modern chest wall cuirass ventilators. DATA SOURCES: Initial animal studies and subsequent publications of applications of various modes of noninvasive cuirass ventilation are recorded. SUMMARY OF REVIEW: Use of the modern cuirass ventilator in continuous negative, intermittent negative or biphasic (negative and positive) modes is described. Techniques of synchronisation of the cuirass ventilation to the patient's inspiratory and expiratory demands, or even to the patient's cardiac cycle are described. Use of noninvasive cuirass ventilation at normal physiological respiratory rates and at high frequency is highlighted in published studies and in the authors' clinical practice in intensive care. Case reports of patients with cardiac, respiratory and neurological diseases having been successfully managed are used in the review to highlight the desirability, versatility and safety of noninvasive cuirass ventilation for optimal patient care in selected cases. CONCLUSIONS: Cuirass ventilation is a valid and valuable method of ventilation in a subset of patients as illustrated by the case reports in this review. Future possibilities for the use of noninvasive cuirass ventilation including in emergency situations where expertise for endotracheal intubation is unavailable; or where physicians or paramedics are unlikely to be able to intubate unconscious/paralysed patients quickly enough to save their lives (e.g. in biological or chemical warfare situations).

Journal Article↗
PubMed2006

Early mobilization of LVAD recipients who require prolonged mechanical ventilation.

Early mobilization and aggressive physical therapy are essential in patients who receive left ventricular assist devices (LVADs) due to long-term, end-stage heart failure. Some of these patients remain ventilator dependent for quite some time after device implantation. We report our regimen of mobilization with the aid of a portable ventilator, in patients with cardiac cachexia and LVAD implantation. Further, we describe the specific physical therapy interventions used in an LVAD patient who required prolonged mechanical ventilation after device implantation. The patient was critically ill for 5 weeks before the surgery and was ventilator dependent for 48 days postoperatively. There were significant functional gains during the period of prolonged mechanical ventilation. The patient was able to walk up to 600 feet by the time he was weaned from the ventilator and transferred out of the intensive care unit. He underwent successful heart transplantation 6 weeks after being weaned from the ventilator We believe that improving the mobility of LVAD patients who require mechanical ventilation has the potential both to facilitate ventilator weaning and to improve the outcomes of transplantation.

Critical Illness↗
PubMed1989

[Lung inflation or mechanical ventilation in extracorporeal circulation?].

Extracorporeal circulation (ECC), with its shock-like pulmonary perfusion, leads to pathomorphologic and functional pulmonary changes, the postperfusion syndrome. This study investigated the effects of different types of ventilation during ECC on postoperative pulmonary function and the resulting pulmonary blood gas changes. METHOD. Thirty patients scheduled for aortocoronary bypass surgery were studied. Patients with pre-operative left ventricular end-diastolic pressures exceeding 15 mmHg or signs of right ventricular failure, pulmonary hypertension, or pre-existing pulmonary disease were excluded. The patients were randomly assigned to one of the following three groups: Group 1 (n = 10): static pulmonary inflation during ECC, PEEP 5-10 cm H2O, F1O2 1.0; Group 2 (n = 10): low-frequency ventilation during ECC, rate 10/min, PEEP 5 cm 5H2O, F1O2 1.0; Group 3 (n = 10): medium-frequency ventilation during ECC, rate 120/min, PEEP 5 cm 5H2O, F1O2 1.0. The measurements were made under relative steady-state conditions before the start of surgery and postoperatively after an equilibrium phase of at least 15 min. During ECC using a bubble oxygenator (Bentley BOS 10 S) in moderate hypothermia, blood was aspirated from the pulmonary artery during inflation of the wedge balloon and blood gases were analyzed. Postoperative changes in pulmonary function were evaluated by venous admixture (QVA/Qt); changes in pulmonary vascular resistance after ECC were determined using the pulmonary pressure-flow relationship. RESULTS. In group 1, QVA/Qt rose significantly from 9.6 +/- 2.9% preoperatively to 13.6 +/- 3.5% postoperatively (P less than 0.05, t-test for paired samples). In groups 2 and 3, postoperative QVA/Qt was significantly lower than preoperative QVA/Qt (P less than 0.05; group 2: preoperative 11.9 +/- 3.5%, postoperative 8.1 +/- 2.6%; group 3: preoperative 11.9 +/- 3.0%, postoperative 7.8 +/- 3.2%; Fig. 1). The postoperative pulmonary pressure-flow relationship changed similarly in all three groups (Fig. 2). During ECC, blood aspirated from the pulmonary artery during inflation of the wedge balloon was fully oxygenated with a hematocrit approximating that of arterial blood. In ventilated patients, pO2 during ECC was higher in pulmonary arterial blood than in arterial blood. Pulmonary ventilation during ECC did not lead to pulmonary arterial alkalosis. CONCLUSIONS. Pulmonary ventilation during ECC can prevent a post-operative increase in venous admixture. ECC-related pulmonary vascular changes were not affected by ventilation. Middle-frequency ventilation offers no advantage over low-frequency ventilation during ECC, except that the operating field is more quiet.

Acid-Base Equilibrium↗
PubMed1988

Discontinuation of mechanical ventilation.

The vast majority of patients who undergo mechanical ventilation are able to discontinue ventilatory assistance within a few days. Typically, patients who require only short-term mechanical ventilation do not have severe underlying lung disease, and the problem for which they require ventilatory support is most commonly rapidly reversible. In these patients on short-term ventilatory support, parameters of spontaneous ventilatory requirements and respiratory muscle strength, including minute ventilation, maximal voluntary ventilation, vital capacity, and maximal inspiratory pressure, are useful in predicting the success of discontinuation of mechanical ventilation. Ventilatory support can generally be discontinued by a variety of techniques in these patients without the need for weaning from the ventilator per se. The smaller group of patients in whom it is not possible to discontinue mechanical ventilation within less than 7 days comprises individuals who frequently have severe acute or chronic lung disease, multisystem extrapulmonary disease, or neuromuscular disease. After a period of prolonged mechanical ventilatory support, these complicated patients require a process of progressive weaning in which they gradually become able to support spontaneous ventilation. Spontaneous ventilatory parameters do not correlate well with weaning ability in patients on long-term ventilatory support. A systematic and comprehensive approach in which attention is focused on optimizing pulmonary and nonpulmonary factors that affect the weaning process provides the best chance for successful withdrawal of ventilatory support after long-term mechanical ventilation. Inadequate ventilatory drive, respiratory muscle weakness and fatigue, increased work of breathing, excessive CO2 production, and cardiac failure are potential mechanisms that may play a role in inhibiting successful weaning. Adverse factors relevant to each of these mechanisms must be addressed and corrected to whatever extent possible. Studies have not demonstrated the superiority of either classic T-piece weaning or IMV weaning methods in difficult-to-wean patients on long-term ventilatory support. Both techniques may be used successfully as long as all patient variables that may adversely affect weaning ability are corrected or optimized and close care and attention to the details of the weaning process itself are provided.(ABSTRACT TRUNCATED AT 400 WORDS)

Heart Failure↗
PubMed1988

Conventional mechanical ventilation.

Mechanical ventilation has become a very common and well-accepted practice in modern intensive care units. The use of the mechanical ventilator has progressed from being a support system during surgery and for acutely ill patients to being used in both moderate and long-term life support in patients with inadequate ventilation. The sophistication of modern ventilators and the ability of trained respiratory therapists and nursing personnel have permitted this technology to explode. This is occurring at a time when there are still many controversies about the relative benefits and modes of action of conventional ventilation. As newer techniques are developed, it is mandatory that the application of these techniques be tempered with controlled clinical trials, documenting their effectiveness. The beneficial effects of new modalities must be documented as mechanical ventilation expands from use in the intensive care unit to use in standard medical wards and the patient's home. In these latter two settings, the vigilance of an intensive care unit is absent and the simplest method will be preferable. The requirement to demonstrate efficacy of new techniques with adequate studies is especially necessary now as the economics of health delivery have come under increasing scrutiny. Even more important than new technologies may be the efficacy of prolonged mechanical ventilation. A recent study by Spicher and White evaluated the outcome in 250 patients ventilated for 10 days or more at the Hershey Medical Center (Pennsylvania State University). The mortality, morbidity, and disability in patients in this study population requiring prolonged ventilation were extremely high. As these studies have pointed out, further evaluations of predictors of meaningful survival are necessary to avoid unnecessary human suffering and to best use limited resources.

Biopsy↗
PubMed1985

Halothane and isoflurane do not decrease PaO2 during one-lung ventilation in intravenously anesthetized patients.

We examined the effect of the inhalational anesthetics halothane (H) and isoflurane (IF) on arterial oxygenation during one-lung ventilation. Twenty consenting patients who required thoracotomy and one-lung ventilation were initially anesthetized only with the intravenous agents, diazepam, fentanyl, pancuronium, metocurine, and infusions of either ketamine or methohexital. A double lumen endotracheal tube was inserted, and each patient's lungs were mechanically ventilated (two-lung ventilation, step 1) with 100% O2 while the patient was in the lateral decubitus position. After the pleura was opened, the nondependent lung was collapsed while the dependent lung continued to be ventilated with 100% O2. After serial PaO2 measurements indicated achievement of stable one-lung ventilation conditions (step 2), intravenous anesthetic agents were discontinued, and either H (n = 10) or IF (n = 10) was administered (step 3) so that PETH = 7.70 +/- 0.61 mm Hg and PETIF = 9.89 +/- 1.08 mm Hg for more than 15 min; at the end of step 3, PaH/PETH = 0.82 (n = 5), PaIF/PETIF = 0.75 (n = 5), PvH/PETH = 0.64 (n = 3), and PvIF/PETIF = 0.68 (n = 3). The inhalational anesthetics were then discontinued, and intravenous agents were reinstituted, allowing PETH and PETIF to decrease below 0.50 mm Hg (step 4). Two-lung ventilation was resumed at the end of the surgical procedure (step 5). PaO2 decreased from 441 +/- 64 to 252 +/- 70 mm Hg when one-lung ventilation was achieved (steps 1-2), and PaO2 increased from 258 +/- 72 to 395 +/- 65 mm Hg when two-lung ventilation was resumed (steps 4-5).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Differential artificial ventilation in anesthetized horses positioned in lateral recumbency.

Effects of differential ventilation on gas exchange were studied in 7 isoflurane-anesthetized, laterally recumbent horses, and were compared with effects of conventional ventilation, using similar minute volume. A tracheal tube-in-tube intubation technique allowed each lung to be connected separately to an anesthetic circle system with a ventilator. Two distribution patterns of tidal volume were investigated; half the tidal volume was distributed to each lung and two-thirds the tidal volume was distributed to the dependent lung. Effects of the combination of these patterns with positive end-expiratory pressure (PEEP) of 10 and 20 cm of H2O to the dependent lung were investigated. Differential ventilation maintained PaCO2, but significantly increased PaO2 from 180 to 270 mm of Hg (+44%) and decreased shunt perfusion from 22 to 19% (-15%), regardless of the distribution pattern used. Mean airway pressure was lower than the value detected during conventional ventilation. The combination of differential ventilation with selective PEEP was followed by a decrease in PaCO2 and further increase of PaO2 and decrease of shunt, which were similar for both distribution patterns. Effects of PEEP of 20 cm of H2O were more pronounced than those of PEEP of 10 cm of H2O. Owing to the combined effects of differential ventilation and selective PEEP, PaO2 increased to 399 mm of Hg and shunt decreased to 15%. This represents increase of 112% and decrease of 33% respectively, compared with values for conventional ventilation. Mean airway pressure increased maximally to 23 cm of H2O, which was 11 cm of H2O greater than the value for conventional ventilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, General↗
PubMed1996

Histology and microbiology of ventilator-associated pneumonias.

A good knowledge of histological and bacteriological characteristics of experimental and human ventilator-associated bronchopneumonias (BPN) is of critical importance for the intensivist. BPN can be experimentally produced by intratracheal inoculation of microorganisms in high concentrations and ventilator-associated BPN by ventilating baboons with oleic-acid lung injury. Experimental ventilator-associated BPN is frequently polymicrobial, and bacterial lung burden increases with the severity of lung infection. In human ventilator-associated BPN, gross examination is of poor value for diagnosing lung infection. Four histologic categories of increasing severity have been described: bronchiolitis, focal bronchopneumonia, confluent bronchopneumonia, and lung abscess. Nonspecific inflammatory lesions are always associated with histologic lung infection: primary lung infection causes secondary inflammatory lung damage, whereas non-specific alveolar injury is rapidly superinfected when the lungs are mechanically ventilated. Infectious pulmonary lesions are disseminated within all pulmonary segments but preferentially found in the dependent segments. This fact suggests that ventilator-associated BPN has a bronchogenic origin and that gravity plays an important role in the dissemination of microorganisms within lung parenchyma. Ventilator-associated BPN is a nosocomial infection with a predominance of gram-negative bacteria, staphylococci species, and yeasts. It is frequently polymicrobial, and the lung bacterial burden depends on the histologic grade, the administration of topical and intravenous antibiotics, and the host's local antibacterial defenses. The bacterial complexity of human lung infection does not support the concept of a threshold for the diagnosis of nosocomial BPN. Intensivists should always keep in mind that human ventilator-associated BPN is a complex and rapidly changing entity.

Animals↗
PubMed1996

Negative-pressure ventilation improves cardiac output after right heart surgery.

BACKGROUND: A low cardiac output state can complicate the postoperative course of patients undergoing Fontan-type operations and tetralogy of Fallot repair. METHODS AND RESULTS: We investigated the effect of negative-pressure ventilation on cardiac output in 11 children in the early postoperative period after right heart surgery. All patients were initially ventilated with volume-cycled intermittent positive-pressure ventilation, and negative-pressure ventilation was delivered with the Hayek external high-frequency oscillator. Cardiac output was calculated by the direct Fick method, oxygen consumption being measured by respiratory mass spectrometry. Cardiac output was measured during intermittent positive-pressure ventilation and after 15 minutes of negative-pressure ventilation. Negative-pressure ventilation improved the cardiac output by a mean of 46% (P = .005). Heart rate did not change, and stroke volume increased by a mean of 48.5% (P = .005). Mixed venous saturation increased by 4.6% (P < .02), and consequently arteriovenous oxygen content difference fell significantly (P = .01). The systemic and pulmonary vascular resistances were reduced significantly during negative-pressure ventilation (P < .05 and P < .03, respectively). CONCLUSIONS: Negative-pressure ventilation improves cardiac output in children after total cavopulmonary connection and tetralogy of Fallot repair and may prove to be an important therapeutic option in children with the low cardiac output state.

Adolescent↗
PubMed1997

Morphometrics of normal and hypoplastic lungs in preterm lambs with gas and partial liquid ventilation

To test the hypothesis that perfluorochemical (PFC) instillation may reduce the pulmonary trauma commonly associated with conventional gas ventilation, we studied 12 lambs with normal lungs and 10 with pulmonary hypoplasia secondary to congenital diaphragmatic hernia (CDH). We used mechanical ventilation for up to 3.5 h, with and without tracheal instillation of LiquiVent PFC liquid. At the end of experimentation lungs were fixed for morphometrical analysis of their components and pulmonary trauma was evaluated by measurement of the perivascular compression index (PCI = % perivascular emphysema/% vessels). In normal lungs good gas exchange and respiratory mechanics were obtained with all modes of ventilation, with no statistical difference in the index of pulmonary trauma with or without instillation of LiquiVent (P >0.05). In the hypoplastic lungs, tracheal instillation of PFC liquid after 30 min of conventional gas ventilation significantly improved PaCO2 (from 107+/-8 to 55+/-6 mmHg, P <0.05), pH (from 7.00+/-0.03 to 7.29+/-0.04, P <0.05), compliance (from 0.08+/-0.01 to 0.25+/-0.03 ml/cmH2O . kg, P <0.05), and ventilatory index (from 1,445+/-148 to 794+/-139, P <0.05). Survival was 6/6 animals with PFC ventilation compared to 1/4 with conventional gas ventilation with no more pulmonary trauma (mean PCI 12.6+/-1.8 vs. 11.4+/-4.0%, P >0.05) for a longer mean ventilatory period in the PFC group. We conclude that the PFC liquid technique of ventilation can improve respiratory physiology when conventional gas ventilation alone is proving inefficient. There was no significant difference in pulmonary trauma at morphometrics between gas and partial liquid ventilation.

Journal Article↗
PubMed1997

Morphometrics of normal and hypoplastic lungs in preterm lambs with gas and partial liquid ventilation.

To test the hypothesis that perfluorochemical (PFC) instillation may reduce the pulmonary trauma commonly associated with conventional gas ventilation, we studied 12 lambs with normal lungs and 10 with pulmonary hypoplasia secondary to congenital diaphragmatic hernia (CDH). We used mechanical ventilation for up to 3.5 h, with and without tracheal instillation of LiquiVent PFC liquid. At the end of experimentation lungs were fixed for morphometrical analysis of their components and pulmonary trauma was evaluated by measurement of the perivascular compression index (PCI = % perivascular emphysema/% vessels). In normal lungs good gas exchange and respiratory mechanics were obtained with all modes of ventilation, with no statistical difference in the index of pulmonary trauma with or without instillation of LiquiVent (P >0.05). In the hypoplastic lungs, tracheal instillation of PFC liquid after 30 min of conventional gas ventilation significantly improved PaCO2 (from 107+/-8 to 55+/-6 mmHg, P <0.05), pH (from 7.00+/-0.03 to 7.29+/-0. 04, P <0.05), compliance (from 0.08+/-0.01 to 0.25+/-0.03 ml/cmH2O . kg, P <0.05), and ventilatory index (from 1,445+/-148 to 794+/-139, P <0.05). Survival was 6/6 animals with PFC ventilation compared to 1/4 with conventional gas ventilation with no more pulmonary trauma (mean PCI 12.6+/-1.8 vs. 11.4+/-4.0%, P >0.05) for a longer mean ventilatory period in the PFC group. We conclude that the PFC liquid technique of ventilation can improve respiratory physiology when conventional gas ventilation alone is proving inefficient. There was no significant difference in pulmonary trauma at morphometrics between gas and partial liquid ventilation.

Animals↗
PubMed1998

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 x 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.

Animals↗
PubMedDate not supplied

Measurement of respiratory mechanics using the Siemens Servo Ventilator 900C.

The interrupter technique involves measuring the pressure changes at the airway opening during sudden cessation of flow and has been advocated for monitoring respiratory mechanics in artificially ventilated patients. The Siemens Servo Ventilator 900C has the ability to make airway occlusions without interrupting the patient's respiratory support. This study was performed to determine the suitability of the end-inspiratory occlusion facility of the ventilator for interrupter measurements of respiratory resistance and compliance. Measurements were made in a physical model of the respiratory system consisting of two parallel compartments, whose individual resistances and elastances were independently determined. The accuracy of the resistance measurements made using the ventilator were found to be dependent on the inspiratory flow. With an inspiratory flow of 100 ml/s, the resistance of the system could be measured to within 18% of the true value, and the static compliance could be measured to within 26% of the true value. Much of the error in these determinations was due to the finite closure time of the valve in the ventilator, and to the compliance of the gas in the tubing connecting the ventilator with the model. We conclude that the Siemens Servo Ventilator 900C can be used to conveniently obtain estimates of resistance and compliance in ventilated patients.

Airway Resistance↗
PubMed2001

Effects of patient-triggered automatic switching between mandatory and supported ventilation in the postoperative weaning period.

OBJECTIVE: To compare two ventilator settings in the postoperative weaning period. Patient-triggered automatic switching between controlled ventilation and supported spontaneous breathing (Automode, AM) was compared to synchronised intermittent mandatory ventilation (SIMV) with stepwise manual adjustment of mandatory frequency according to the breathing activity. DESIGN: Prospective clinical investigation. SETTING: Eighteen-bed intensive care unit in a university hospital. PATIENTS: Forty postoperative patients with healthy lungs who had undergone brain tumour surgery. INTERVENTIONS: Randomisation either to the AM or SIMV weaning procedure after entering the ICU. MEASUREMENTS AND RESULTS: Total weaning time and number of manipulations on the ventilator were observed. Cardiocirculatory and respiratory parameters were measured consecutively at five points during the weaning period. No significant differences were seen for cardiocirculatory parameters, airway pressures and oxygenation between the two groups. There was a trend to shorter weaning times with AM (136 +/- 46 min vs 169 +/- 68 min, n.s.), the average number of manipulations on the ventilator was lower (0.55 +/- 0.69 vs 5.05 +/- 1.19,p < 0.001) and arterial partial pressure of carbon dioxide (PaCO2) levels showed fewer variations in the late phase of the weaning period (39.5 +/- 3.1 vs 38.3 +/- 7.2, p < 0.001 for differences in variance). CONCLUSIONS: Automatic, patient-triggered switching between controlled and supported mode of ventilation can be used for postoperative weaning of neurosurgical patients with healthy lungs. Compared to a SIMV weaning procedure, fewer manipulations on the ventilator are necessary and individual adaptation of ventilation seems to be more accurate.

Adult↗