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PubMed1997

Patient-initiated, pressure-regulated, volume-controlled ventilation compared with intermittent mandatory ventilation in neonates: a prospective, randomised study.

OBJECTIVE: To compare the effects of patient-initiated, pressure-regulated, volume-controlled ventilation (PRVC) with pressure-preset intermittent mandatory ventilation (IMV) in neonates with respiratory failure. DESIGN: Randomised, prospective study. SETTING: Intensive care unit (14 beds) in a 300-bed paediatric teaching hospital. PATIENTS: 60 neonates with respiratory distress syndrome (RDS) or congenital pneumonia, weighing < 2500 g and requiring mechanical ventilation. INTERVENTIONS: Ventilatory support until extubation via either IMV (n = 30) or PRVC (n = 27). In PRVC, the tidal volume (VT) was preset and pressure-controlled breaths delivered with peak inspiratory pressure values adapted to achieve the preset VT. MEASUREMENTS AND RESULTS: Main outcome measures were duration of ventilation and incidence of bronchopulmonary dysplasia (BPD). Pulmonary air leaks and intraventricular haemorrhage (IVH) were considered major adverse effects. Demographic data, ventilation parameters and arterial/alveolar oxygen tension ratio were similar at randomisation. Duration of ventilation and incidence of BPD were not decreased by the use of PRVC. Air leaks occurred in 3 neonates in the PRVC group and in 7 babies treated with IMV (NS). The incidence of IVH grade > II was lower in babies treated with PRVC (p < 0.05). In a subgroup of neonates weighing < 1000 g, the duration of ventilation and incidence of hypotension were reduced in the PRVC group (p < 0.05). CONCLUSION: Patient-initiated, pressure-regulated, volume-controlled ventilation can be safely used in neonates and may contribute to a lower incidence of complications.

Female↗
PubMed1991

Preliminary evaluation of a prototype tube-valve-mask ventilator for emergency artificial ventilation.

STUDY OBJECTIVE: The objective was to design a prototype tube-valve-mask ventilator that would permit relatively inexperienced operators to provide adequate emergency artificial ventilation, namely, adequate ventilatory volumes and a high oxygen and low carbon dioxide delivery. DESIGN: The tube-valve-mask ventilator is powered by the exhaled air of the operator and uses a tube to act as an oxygen reservoir (1,300 mL) that is filled between breaths. Mouth-to-mouth breathing was the standard against which the tube-valve-mask ventilator and the other accepted methods of mouth-to-mask and bag-valve-mask were assessed. SETTING: Comparison studies were conducted during simulated two-person CPR using a training mannikin equipped to measure ventilation volume and delivered oxygen and carbon dioxide concentrations. TYPE OF PARTICIPANTS: Seventeen volunteer first-year nursing students were used as operators. INTERVENTIONS: The order in which the pairs of operators performed each of the techniques was randomized. MEASUREMENTS AND MAIN RESULTS: The ventilation volume and the percentage of oxygen and carbon dioxide delivered by each technique were as follows (mean +/- SD): Mouth-to mouth (760 +/- 290 mL, 17 +/- 1% O2, 3.4 +/- 0.4% CO2), mouth-to-mask (910 +/- 350 mL, 41 +/- 8% O2, 2.5 +/- 0.4% CO2), bag-valve-(soft) mask (550 +/- 230 mL, 94 +/- 3% O2, 0.03 +/- 0.02% CO2), bag-valve-(rigid) mask (560 +/- 300 mL, 96 +/- 3% O2, 0.03 +/- 0.02% CO2), and tube-valve-mask (860 +/- 290 mL, 91 +/- 7% O2, 0.2 +/- 0.2% CO2). CONCLUSION: In the hands of relatively inexperienced operators, mouth-to-mouth, mouth-to-mask, and tube-valve-mask techniques provide adequate ventilation volumes to a mannikin. This was not the case with the bag-valve-mask systems (800 mL; P = .05 by t test). Of the systems that provide adequate ventilation volume, the tube-valve-mask appears, superior in that higher oxygen and lower carbon dioxide concentrations can also be obtained (P = .05 by paired t test).

Breath Tests↗
PubMed2004

Periodically changing ventilator circuits is not necessary to prevent ventilator-associated pneumonia when a heat and moisture exchanger is used.

OBJECTIVE: To analyze the efficacy of periodically changing ventilator circuits for decreasing the rate of ventilator-associated pneumonia when a heat and moisture exchanger (HME) is used for humidification. The Centers for Disease Control and Prevention recommended not changing the circuits periodically. DESIGN: Randomized, controlled trial conducted between April 2001 and August 2002. SETTING: A 24-bed, medical-surgical intensive care unit in a 650-bed, tertiary-care hospital. PATIENTS: All patients requiring mechanical ventilation during more than 72 hours from April 2001 to August 2002. INTERVENTIONS: Patients were randomized into two groups: (1) ventilation with change of ventilator circuits every 48 hours and (2) ventilation with no change of circuits. Throat swabs were taken on admission and twice weekly until discharge to classify pneumonia as endogenous or exogenous. RESULTS: Three hundred four patients (143 from group 1 and 161 from group 2) with similar characteristics (age, gender, Acute Physiology and Chronic Health Evaluation II score, diagnostic group, and mortality) were analyzed. There was no significant difference in the rate of pneumonia between the groups (23.1% vs 23.0% and 15.5 vs 14.8 per 1,000 ventilator-days). There was no significant difference in the incidence of exogenous pneumonia per 1,000 days of mechanical ventilation (1.71 vs 1.25). There was no difference in the distribution of microorganisms causing pneumonia. CONCLUSIONS: Circuit change using an HME for humidification does not decrease pneumonia and represents an unnecessary cost.

Costs and Cost Analysis↗
PubMed1998

The laryngeal mask airway reliably provides rescue ventilation in cases of unanticipated difficult tracheal intubation along with difficult mask ventilation.

UNLABELLED: In 1995, our department of anesthesiology established an airway team to assist in treating unanticipated difficult endotracheal intubations and an airway quality improvement (QI) form to document the use of emergency airway techniques in airway crises (laryngeal mask airway [LMA], flexible fiberoptic bronchoscopy, retrograde intubation [RI], transtracheal jet ventilation [TTJV], and cricothyrotomy). Over a 2-yr period, team members and staff anesthesiologists completed airway QI forms to document the smallest peripheral SpO2 during an airway crisis, the number of direct laryngoscopies (DL) performed before using an emergency airway technique, and the emergency airway technique that succeeded in rescue ventilation. Team members agreed to use the LMA as the first emergency airway technique to treat the difficult ventilation/difficult intubation scenario. A SpO2 value < or =90% during mask ventilation defined difficult ventilation. Inability to perform tracheal intubation by DL defined difficult intubation. An increase in the SpO2 value >90% defined rescue ventilation. Review of airway QI forms from October 1, 1995 until October 1, 1997 revealed 25 cases of difficult ventilation/difficult intubation. Before airway rescue, the median SpO2 was 80% (range 50%-90%), and there were four median attempts at DL (range one to nine). The LMA had a success rate of 94% (95% confidence interval [CI] 77-100). Flexible fiberoptic bronchoscopy, TTJV, RI, and surgical cricothyrotomy had success rates of 50% (95% CI 0-100), 33% (95% CI 0-100), 100% (95% CI 37-100), and 100% (95% CI 37-100), respectively. LMA insertion as the first alternative airway technique was useful in dealing with unanticipated instances of simultaneous difficulty with mask ventilation and tracheal intubation. IMPLICATIONS: Twenty-five cases of simultaneous difficulty with mask ventilation and tracheal intubation occurred after the induction of general anesthesia during the study period. The laryngeal mask was used in 17 cases, and it provided rescue ventilation without complication in 94% of these cases (95% confidence interval 77-100).

Anesthesia↗
PubMed1999

An adult system versus a Bain system: comparative ability to deliver minute ventilation to an infant lung model with pressure-limited ventilation.

UNLABELLED: We compared the efficacy of an adult circle system versus a Bain system to deliver minute ventilation (V(E)) to an infant test lung model using pressure-limited ventilation. To simulate a wide variety of potential infant clinical states, V(E) was measured with two compliances: at peak inspiratory pressures (PIP) of 20, 30, 40, and 50 cm H2O and at respiratory rates (RR) of 20, 30, 40, and 50 breaths/min. Each measurement was made three times, and their average was used for analysis. Data were analyzed using the multiple regression technique. In both normal and low-compliance lung models, V(E) was nearly identical between adult circle and Bain systems (P = 0.67 for normal compliance model, P = 0.89 for low-compliance model). V(E) positively correlated with RR (P < 0.001), PIP (P < 0.001), and lung compliance (P < 0.001). Very high PIP or RR were required to deliver V(E) to the low-compliance lung model. The adult circle system is equivalent to the Bain system in its ability to ventilate an infant test lung over a wide range of RR, PIP, and two compliances during pressure-limited ventilation. V(E) is dependent of PIP, RR, and lung compliance. With low-compliance lungs, both systems require a high PIP. We conclude that both anesthetic systems deliver ventilation over a wide range of respiratory variables during pressure-limited ventilation in infants. IMPLICATIONS: We obtained results from this infant test lung study that indicate that either an adult circle breathing system or the Bain system can reliably deliver ventilation over a wide range of respiratory variables during pressure-limited ventilation in infants.

Adult↗
PubMed1999

Pressure-limited ventilation of infants with low-compliance lungs: the efficacy of an adult circle system versus two free-standing intensive care unit ventilator systems using an in vitro model.

UNLABELLED: We compared the efficacy of a Drager Narkomed GS (North American Drager, Telford, PA) equipped with an adult circle system with two free-standing infant ventilator systems (Servo 300; Siemens Medical Systems, Danvers, MA and Babylog 8000; North American Drager) to deliver minute ventilation (VE) using pressure-limited ventilation to a test lung set to low compliance. To simulate a wide variety of potential patterns of ventilation, VE was measured at peak inspiratory pressures (PIP) of 20, 30, 40, and 50 cm H2O and at respiratory rates (RR) of 20, 30, 40, and 50 breaths/min. Each measurement was made three times; the average was used for data analysis using the multiple regression technique. Delivered V(E) was positively correlated with both PIP (P = 0.001) and RR (P = 0.001). Only minimal differences in VE were observed between the circle and the two free-standing systems. At lower RR and PIP, the Babylog 8000 system delivered slightly higher VE than the circle system, whereas at higher RR and PIP, the Babylog 8000 delivered slightly lower VE than the circle system; these differences in VE were not statistically significant (P = 0.45). The Servo 300 delivered slightly higher VE than the circle system in all test conditions, but these differences were not statistically significant (P = 0.09). None of the differences in delivered VE between the Servo 300 and the circle system are of clinical importance. IMPLICATIONS: Our laboratory investigation suggests that pressure-limited ventilation delivered by a standard adult circle system compares favorably with that of freestanding infant ventilators used in pressure-limited mode. Changing from an adult circle system to a free-standing pressure-limited ventilator may not substantially improve ventilation of a low-compliance infant lung; the efficacy of such a practice should be investigated.

Adult↗
PubMed2006

Biologically variable ventilation improves oxygenation and respiratory mechanics during one-lung ventilation.

BACKGROUND: Hypoxemia is common during one-lung ventilation (OLV). Atelectasis contributes to the problem. Biologically variable ventilation (BVV), using microprocessors to reinstitute physiologic variability to respiratory rate and tidal volume, has been shown to be advantageous over conventional monotonous control mode ventilation (CMV) in improving oxygenation during the period of lung reinflation after OLV in an experimental model. Here, using a porcine model, the authors compared BVV with CMV during OLV to assess gas exchange and respiratory mechanics. METHODS: Eight pigs (25-30 kg) were studied in each of two groups. After induction of anesthesia-tidal volume 12 ml/kg with CMV and surgical intervention-tidal volume was reduced to 9 ml/kg. OLV was initiated with an endobronchial blocker, and the animals were randomly allocated to either continue CMV or switch to BVV for 90 min. After OLV, a recruitment maneuver was undertaken, and both lungs were ventilated for a further 60 min. At predetermined intervals, hemodynamics, respiratory gases (arterial, venous, and end-tidal samples) and mechanics (airway pressures, static and dynamic compliances) were measured. Derived indices (pulmonary vascular resistance, shunt fraction, and dead space ventilation) were calculated. RESULTS: By 15 min of OLV, arterial oxygen tension was greater in the BVV group (group x time interaction, P = 0.003), and shunt fraction was lower with BVV from 30 to 90 min (group effect, P = 0.0004). From 60 to 90 min, arterial carbon dioxide tension was lower with BVV (group x time interaction, P = 0.0001) and dead space ventilation was less from 60 to 90 min (group x time interaction, P = 0.0001). Static compliance was greater by 60 min of BVV and remained greater during return to ventilation of both lungs (group effect, P = 0.0001). CONCLUSIONS: In this model of OLV, BVV resulted in superior gas exchange and respiratory mechanics when compared with CMV. Improved static compliance persisted with restoration of two-lung ventilation.

Animals↗
PubMed1997

Intratracheal pressure monitoring during synchronized intermittent mandatory ventilation and pressure controlled-inverse ratio ventilation.

OBJECTIVES: To directly measure airway pressures proximal and distal to endotracheal tubes during conventional synchronized intermittent mandatory ventilation (SIMV) and pressure controlled-inverse ratio ventilation (PC-IRV), and to compare them with these values measured by the ventilator. DESIGN: Prospective, nonrandomized study. SETTING: Surgical intensive care unit at a trauma center. PATIENTS: Group 1: Eight intubated adult patients connected to mechanical ventilators in the SIMV mode were studied. All patients required mechanical ventilation following traumatic injuries. Group 2: Five intubated adult patients with adult respiratory distress syndrome connected to mechanical ventilators were studied. INTERVENTIONS: A small polyethylene catheter was threaded through each endotracheal tube such that it could be positioned to measure pressures proximal and distal to the tubes. MEASUREMENTS AND MAIN RESULTS: During SIMV, a significant pressure gradient exists across endotracheal tubes. In addition, although initiation of PC-IRV did lead to a lower peak airway pressure measured proximally, intratracheal peak airway pressure was unchanged. CONCLUSIONS: A pressure gradient exists during inspiration from the ventilator to the trachea in mechanically ventilated patients. Tracheal pressures cannot be predicted from proximal airway pressure monitors because of marked variation in endotracheal tube resistance in vivo. Initiation of PC-IRV does not result in a decrease in peak airway pressure when measured intratracheally.

Adult↗
PubMed1994

Differential lung ventilation as an alternative to one-lung ventilation during thoracotomy. Report of three cases.

Investigation was carried out on three elderly patients undergoing thoracotomy. During one-lung ventilation using a Robertshaw double-lumen tube, the PaO2 decreased below 11.7 kPa despite ventilation of the dependent lung with 100% oxygen. Differential lung ventilation was then initiated by partial occlusion of the adapter limb to the nondependent lung, whilst maintaining unrestricted ventilation of the dependent lung. In the three patients, differential lung ventilation increased the PaO2 to 15-37.2 kPa. The increased PaO2 may be attributed to diffusion oxygenation via the partially inflated, nondependent lung. Differential lung ventilation can be used during thoracotomy whenever one-lung ventilation is followed by hypoxaemia, despite adequate ventilation of the dependent lung with 100% oxygen.

Adult↗
PubMed1987

Regional ventilation during spontaneous breathing and mechanical ventilation in dogs.

We evaluated the effects of the different patterns of chest wall deformation that occur with different body positions and modes of breathing on regional lung deformation and ventilation. Using the parenchymal marker technique, we determined regional lung behavior during mechanical ventilation and spontaneous breathing in five anesthetized recumbent dogs. Regional lung behavior was related to the patterns of diaphragm motion estimated from X-ray projection images obtained at functional residual capacity (FRC) and end inspiration. Our results indicate that 1) in the prone and supine positions, FRC was larger during mechanical ventilation than during spontaneous breathing; 2) there were significant differences in the patterns of diaphragm motion and regional ventilation between mechanical ventilation and spontaneous breathing in both body positions; 3) in the supine position only, there was a vertical gradient in lung volume at FRC; 4) in both positions and for both modes of breathing, regional ventilation was nonlinearly related to changes in lobar and overall lung volumes; and 5) different patterns of diaphragm motion caused different sliding motions and differential rotations of upper and lower lobes. Our results are inconsistent with the classic model of regional ventilation, and we conclude that the distribution of ventilation is determined by a complex interaction of lung and chest wall shapes and by the motion of the lobes relative to each other, all of which help to minimize distortion of the lung parenchyma.

Animals↗
PubMed1988

Gas exchange and intrapulmonary distribution of ventilation during continuous-flow ventilation.

In 12 anesthetized paralyzed dogs, pulmonary gas exchange and intrapulmonary inspired gas distribution were compared between continuous-flow ventilation (CFV) and conventional mechanical ventilation (CMV). Nine dogs were studied while they were lying supine, and three dogs were studied while they were lying prone. A single-lumen catheter for tracheal insufflation and a double-lumen catheter for bilateral endobronchial insufflation [inspired O2 fraction = 0.4; inspired minute ventilation = 1.7 +/- 0.3 (SD) 1.kg-1.min-1] were evaluated. Intrapulmonary gas distribution was assessed from regional 133Xe clearances. In dogs lying supine, CO2 elimination was more efficient with endobronchial insufflation than with tracheal insufflation, but the alveolar-arterial O2 partial pressure difference was larger during CFV than during CMV, regardless of the type of insufflation. By contrast, endobronchial insufflation maintained both arterial PCO2 and alveolar-arterial O2 partial pressure difference at significantly lower levels in dogs lying prone than in dogs lying supine. In dogs lying supine, the dependent lung was preferentially ventilated during CMV but not during CFV. In dogs lying prone, gas distribution was uniform with both modes of ventilation. The alveolar-arterial O2 partial pressure difference during CFV in dogs lying supine was negatively correlated with the reduced ventilation of the dependent lung, which suggests that increased ventilation-perfusion mismatching was responsible for the increase in alveolar-arterial O2 partial pressure difference. The more efficient oxygenation during CFV in dogs lying prone suggests a more efficient matching of ventilation to perfusion, presumably because the distribution of blood flow is also nearly uniform.

Animals↗
PubMed1995

Intratracheal pulmonary ventilation versus conventional mechanical ventilation in a rabbit model of surfactant deficiency.

Intratracheal pulmonary ventilation (ITPV) enhances the clearance of CO2 from dead space and lungs by a bias flow of gas administered in the distal trachea. ITPV flow is continuously administered through a separate catheter placed within an endotracheal tube (ETT). After exiting from catheter's tip in the distal trachea, the flow of gas is redirected outward away from the lungs. We hypothesized that, compared with conventional mechanical ventilation (CMV), ITPV may increase minute CO2 clearance (VCO2), reduce the partial pressure of CO2 dioxide in arterial gas (PaCO2), and reduce distal tracheal peak inspiratory pressure (dPIP). We induced surfactant deficiency in 15 adult rabbits by lung lavage with 10 mL/kg normal saline. Animals were ventilated through a double-lumen 4.0 ETT, inserted through a tracheotomy incision. dPIP, distal positive end expiratory pressure, and distal mean airway pressure were monitored, and the mean exhaled CO2 concentration was measured. For ventilator rates (respiratory rate) of 30, 45, and 70 breaths/min, the study included two phases: phase I compared CO2 clearance and PaCO2 between ITPV and CMV using similar ventilatory pressures; phase II evaluated the effectiveness of ITPV in reducing dPIP and tidal volume (Vt), compared with CMV, while maintaining eucapnea. When comparing ITPV and CMV, the following results (mean +/- SD) were achieved at respiratory rate of 30, 45, and 70 breaths/min, respectively. Phase I ITPV resulted in mean percent reduction of PaCO2 by 31.4 +/- 10%, 37.1 +/- 9.7% and 38.3 +/- 9%; mean percent increase in VCO2 by 61.3 +/- 29%, 56 +/- 23, and 98 +/- 40%, compared with CMV. Phase II ITPV resulted in mean percent reduction of dPIP by 35.5 +/- 14%, 38 +/- 10.8%, and 37.2 +/- 13.7%, and mean percent reduction in Vt by 34.7 +/- 12.9%, 36.4 +/- 15%, and 52.7 +/- 10.7%, compared with CMV. The changes in PaCO2, VCO2 (phase I), and dPIP and Vt (phase II) were all significantly more than 25% (p < 0.05). Oxygenation and pH were not significantly different between ITPV and CMV. We conclude that, in a surfactant deficiency rabbit model, ITPV is an efficient mode of assisted ventilation that increases CO2 clearance and reduces ventilator pressures required for adequate ventilation. We speculate that ITPV can minimize lung barotrauma associated with mechanical ventilation.

Animals↗
PubMed1999

A comparison of the hemodynamic and respiratory effects of surfactant instillation during interrupted ventilation versus noninterrupted ventilation in rabbits with severe respiratory failure.

The purpose of this study was to evaluate whether avoiding interruption of ventilation during surfactant instillation improves the effects on lung function and surfactant distribution and whether it prevents the adverse effects on blood pressure and cerebral blood flow. The study was performed using rabbits with severe respiratory failure induced by lung lavages. These rabbits were randomized to 99mTc-Nanocoll labeled surfactant instillation through a side lumen of the endotracheal tube without interrupting ventilation or instillation during a short interruption of ventilation. After surfactant instillation with interruption of ventilation, PaO2 rose from 8.7+/-1.3 to 24.9+/-6.4 kPa (mean+/-SEM). Without interruption, PaO2 rose from 8.4+/-0.8 to 32.4+/-4.3 kPa. PaCO2 decreased with interruption from 4.69+/-0.51 to 3.61+/-0.26 kPa and without interruption from 5.06+/-0.41 to 4.13+/-0.23 kPa. Dynamic and static compliance indices were not statistically different after both procedures. Surfactant distribution tended to be less nonuniform after instillation without interrupting ventilation. In contrast, avoidance of interruption of ventilation resulted in less uniform lobar distribution and less peripheral deposition of surfactant. By instillation with interruption, blood pressure increased quickly (28+/-6.6%), followed by a 22+/-5.3% decrease. Blood pressure increased quickly (16+/-4.2%), followed by a 40+/-10% decrease by surfactant instillation without interruption. Cerebral blood flow, measured by an ultrasonic transit time flow probe on the carotid artery, increased quickly (45+/-14%), followed by a 64+/-11% decrease with interruption, whereas it increased 15+/-4.9% (p = 0.06 versus with interruption) and decreased 61+/-13% without interruption of ventilation. Therefore, avoiding interruption of ventilation during surfactant instillation tends to prevent the potential adverse effects of a rapid rise in cerebral blood flow, and furthermore, tends to improve uniformity of surfactant distribution, whereas having no detrimental effect on respiratory function.

Animals↗
PubMed1999

[Non-invasive ventilation in acute or chronic respiratory failure: a comparison of volumetric ventilation].

BACKGROUND: Although experience acquired with non-invasive ventilation is recent, it is often proposed in selected patients with acute respiratory failure occurring in a background of chronic airflow obstruction. Barometric or volumetric techniques can be used. PATIENTS AND METHODS: We compared tolerance and efficacy of inspiration assist (IA) using a preset pressure and volume-controlled ventilation (VC). Twelve patients with chronic airflow obstruction were randomized to IA (n = 7) or VC (n = 9) mode and ventilated with the appropriate mask. RESULTS: Tolerance was equivalent for the two groups although hypercapnia fell more in the IA group, particularly after 24 h ventilation (p < 0.03), after three days (p < 0.05), and at complete weaning (p < 0.03). Correction of pH was significantly more rapid in the IA group than in the VC group (p < 0.05 at 24 h). There was no difference in the number of days of ventilation, total ventilation time, or length of hospital stay. Success of non-invasive ventilation, defined as the control of acute respiratory failure without recourse to endotracheal ventilation, was similar in the two groups (86% in group IA and 60% in group VC). Two of the 5 patients in the VC group and one of the 7 in the IA group required intubation.

Aged↗
PubMed1999

[Ventilation at high-frequency oscillation: towards diminished barotrauma in the ventilated newborn?].

Mechanical ventilation is one of the fundamentals of intensive care assuring the correction of blood gas anomalies in patients with respiratory distress. However, positive pressure ventilation is extremely deleterious for the lung due to barotrauma. Among avenues of research over the last twenty years is a technique which has been successfully developed in neonatal intensive care: ventilation by high frequency oscillation (VOHF). Experimental studies have shown a net benefit in terms of oxygenation and diminution of barotrauma. A unique feature of this mechanical ventilation technique is that the clinical studies comparing VOHF to conventional ventilation have shown that for certain individuals there is decreased morbidity, notably in the incidence of bronchopulmonary dysplasia. In a paradoxical manner VOHF assures adequate gas exchange by using tidal volumes which are lower than the anatomical dead space. The usual model for alveolar ventilation is unable to explain how gas exchange is possible with this mode of ventilation. The explanations are still incomplete but this new type of artificial ventilation is in line with current studies by physiologists whose research may explain this totally new type of pulmonary physiology. However, it should be used cautiously and reserved to those practitioners experienced in the technique.

Barotrauma↗
PubMed1987

Traumatic respiratory insufficiency: comparison of conventional mechanical ventilation to high-frequency positive pressure with low-rate ventilation.

Eleven patients suffering severe traumatic respiratory insufficiency were mechanically ventilated using a new system which combined high-frequency positive-pressure ventilation (HFPPV) with low-rate conventional mechanical ventilation (LRCMV). Ten similar patients were ventilated by conventional mechanical ventilation (CMV) with PEEP. HFPPV patients were fully conscious and cooperative during ventilation and did not need sedatives or muscle relaxants. Arterial oxygenation was significantly (p less than .005) better in HFPPV than CMV patients (89.91 +/- 10.24 vs. 78.43 +/- 11.13 torr, respectively), and pulmonary shunt was also better in the HFPPV group (13.1 +/- 4.7% vs. 20.4 +/- 6.4%, p less than .01). Moreover, inspired oxygen concentrations were lower (PaO2/FIO2 197.8 +/- 51.3 in the HFPPV group vs. 130 +/- 46.6 in the CMV group, p less than .005) and the time required for mechanical ventilation was shorter (4.2 +/- 0.91 vs. 6.1 +/- 0.8 days, p less than .1). All HFPPV patients immediately began breathing spontaneously when they were disconnected from the ventilator. We suggest this method as a better ventilatory mode for patients suffering traumatic respiratory insufficiency.

Adult↗
PubMed1993

[Cardiopulmonary effects of CPPV (continuous positive pressure ventilation) and IRV (inverse ratio ventilation) in experimental myocardial ischemia].

Continuous positive pressure ventilation (CPPV) is an established therapy for treatment of acute respiratory failure (ARF). However, cardiac performance may be severely disturbed due to elevated intrathoracic pressure, inducing a decrease in cardiac output (CO) and oxygen delivery (DO2). Alternatively, mechanical ventilation with prolonged inspiratory to expiratory duration ratio (inversed ratio ventilation IRV) has been successfully used in ARF. No data are available about IRV in acute haemodynamic oedema. Thus, the cardiopulmonary effects of CPPV (positive end-expiratory pressure [PEEP] = 10 cm H2O) and IRV (inspiration to expiration duration ratio [I:E] = 3.0) were studied in nine dogs (body weight 29.9 +/- 4.3 kg) before and after induction of myocardial ischaemia. METHODS. Continuous intravenous anaesthesia and muscle paralysis were provided by 1.2 mg.kg-1 x h-1 piritramide and 0.08 mg.kg-1 x h-1 pancuronium, and the animals were ventilated with intermittent positive pressure ventilation (IPPV) as reference method. Cardiocirculatory performance was determined by means of heart rate (HR), mean arterial pressure (MAP), mean pulmonary arterial pressure (MPAP), central venous pressure (CVP), pulmonary artery occlusion pressure (PAOP) and left ventricular end-diastolic pressure (LVEDP). Cardiac output (CO) was determined by thermodilution method. Systemic vascular resistance (SVR) was calculated. Pulmonary function was assessed by arterial and mixed venous blood gas tension for oxygen (PaO2, PvO2) and carbon dioxide (PaCO2). Functional residual lung capacity (FRC) was measured by means of the foreign gas wash-in method using helium as inert gas, and determination of extravascular lung water (EVLW) using the thermal-dye indicator technique. CPPV and IRV were studied in random sequence in the control phase and 60 min after induction of acute left ventricular ischaemia, which was achieved by occlusion of the ramus interventricularis anterior. RESULTS. During the control phase CPPV induced an increase in MPAP (P < 0.05), CVP (P < 0.05) and PAOP (P < 0.05). HR and MAP remained unchanged, whereas CO decreased by 16% (P < 0.05). FRC was elevated by 25 ml.kg-1 (P < 0.01), but not EVLW (9.1 +/- 3.5 ml.kg-1). There was no improvement in oxygenation; instead, oxygen delivery (DO2) decreased (P < 0.05). During inversed ratio ventilation MPAP, CVP, PAOP increased, but less than during CPPV. FRC was elevated mu 7.0 ml.kg-1 (P < 0.05), which was significantly less than during CPPV (P < 0.05). EVLW revealed no differences. During IPPV in the ischaemia phase cardiopulmonary performance deteriorated significantly. CO decreased by 19% (P < 0.05), whereas HR, MPAP, CVP and PAOP increased (P < 0.05). PaO2 was lower (P < 0.05) and alveolo-arterial PO2 gradient (PAaO2) increased (P < 0.05). All animals revealed moderate pulmonary oedema (EVLW = 15.1 +/- 8.4 ml.kg-1) (P < 0.01) and a lower FRC. Mechanical ventilation with PEEP significantly improved oxygenation and FRC; however, DO2 was slightly lower than during IPPV (not significant). IRV elevated PaO2, FRC and DO2, since CO was not depressed when compared with IPPV. CONCLUSIONS. CPPV and IRV may induce a recruitment of collapsed or hypoventilated lung areas, which is more pronounced during CPPV. During both modes of ventilation, oxygenation was improved without apparent changes in EVLW. Haemodynamic performance was more impaired during CPPV, and no improvement of left ventricular function secondary to an elevated intrathoracic pressure was observed. Occlusion of the RIVA coronary artery typically induces an infarction of 35% of left ventricular muscle mass; however, non-ischaemic myocardium reveals an unchanged or increased contractility. Thus, a reduction of left ventricular preload secondary to CPPV mainly contributes to haemodynamic depression, which is less pronounced during IRV due to a lower peak inspiratory airway pressure and mean airway pressure. IRV may be useful for mechanical ventCntCo

Animals↗
PubMed2001

Work of breathing associated with pressure support ventilation in two different ventilators.

The purpose of this study was to compare the work of breathing during pressure support ventilation (PSV) with positive end expiratory pressure (PEEP) utilizing the Siemens SV300 (SV300) and Dräger Evita 4 (EV4) ventilators. Our hypothesis was that patients' work of breathing (WOB(P)) would be unchanged in PSV utilizing flow triggering (FT) in both the SV300 and EV4. We compared two ventilators using six healthy, intubated, sedated, spontaneously breathing pigs weighing approximately 10 kg each. WOB(P) (j/L) and ventilator work of breathing (WOB(V)) (j/L) were measured using a portable monitor which utilizes an esophageal balloon and flow transducer. Each breath was further analyzed for duration of inspiratory effort and negative deflection of pressure needed to trigger PSV. Animals were studied with the SV300 and EV4 on a pressure support of 5 cmH(2)O and PEEP settings of 0 and 5 cmH(2)O. Data were analyzed using the Wilcoxon signed rank test with significance set at P <or= 0.05 WOB(P) was 90% (PS 5, PEEP 0) and 52% (PS 5, PEEP 5) lower on the SV300 compared to the EV4. WOB(V) was 94% (PS 5, PEEP 0) and 39% (PS 5, PEEP 5) higher on the SV300 when compared to the EV4. The change in airway pressure (delta p) from baseline and most negative deflection of pressure were greater with the EV4 as compared to the SV300, although delta pressure was not found to be statistically significant on PS of 5 cmH(2)O and PEEP of 5 cmH(2)O. The SV300 also had shorter duration of inspiratory effort from initiation of breath to most negative deflection of pressure and to maximum flow than the EV4. In conclusion, these results suggest there are significant differences in WOB(P) between the SV300 and EV4 ventilators. Response time of the ventilators may explain the differences in duration of inspiratory effort and the patient's work of breathing and thus may have an impact on weaning time for ventilated patients.

Animals↗