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PubMed2006

Performance of mechanical ventilators at the patient's home: a multicentre quality control study.

BACKGROUND: Quality control procedures vary considerably among the providers of equipment for home mechanical ventilation (HMV). METHODS: A multicentre quality control survey of HMV was performed at the home of 300 patients included in the HMV programmes of four hospitals in Barcelona. It consisted of three steps: (1) the prescribed ventilation settings, the actual settings in the ventilator control panel, and the actual performance of the ventilator measured at home were compared; (2) the different ventilator alarms were tested; and (3) the effect of differences between the prescribed settings and the actual performance of the ventilator on non-programmed readmissions of the patient was determined. RESULTS: Considerable differences were found between actual, set, and prescribed values of ventilator variables; these differences were similar in volume and pressure preset ventilators. The percentage of patients with a discrepancy between the prescribed and actual measured main ventilator variable (minute ventilation or inspiratory pressure) of more than 20% and 30% was 13% and 4%, respectively. The number of ventilators with built in alarms for power off, disconnection, or obstruction was 225, 280 and 157, respectively. These alarms did not work in two (0.9%), 52 (18.6%) and eight (5.1%) ventilators, respectively. The number of non-programmed hospital readmissions in the year before the study did not correlate with the index of ventilator error. CONCLUSIONS: This study illustrates the current limitations of the quality control of HMV and suggests that improvements should be made to ensure adequate ventilator settings and correct ventilator performance and ventilator alarm operation.

Analysis of Variance↗
PubMed1994

Modes of mechanical ventilation and weaning. A national survey of Spanish hospitals. The Spanish Lung Failure Collaborative Group.

Little information exists regarding the proportion of patients treated with mechanical ventilation in intensive care units (ICUs), their underlying disease states, the modes of ventilation used, duration of ventilator support, methods and time required for weaning, and mortality in these patients. We carried out a cross-sectional multicenter study in 47 medical-surgical ICUs in Spain to investigate these issues in 290 patients who required mechanical ventilation for at least 24 hs. Relative frequency of different modes was as follows: assist-control ventilation (AC), 55%; synchronized intermittent mandatory ventilation (SIMV), 26%; pressure support ventilation (PSV), 8%; SIMV plus PSV, 8%; pressure-controlled ventilation (PCV), 1%; and continuous positive airway pressure (CPAP), 2%. Overall duration of mechanical ventilation was 27.1 +/- 1.1 (SE). A variety of techniques were used for weaning: T-tube trials, 24%; SIMV, 18%; PSV, 15%; SIMV plus PSV, 9%; and some combination of two or more methods in succession in 33% of the patients. Time required for weaning using a combination of SIMV and PSV was longer (17.8 days) than with other techniques (about 5 days, p < 0.01). Time between initiation of weaning and removal of mechanical ventilation accounted for 41% of total ventilator time and was particularly high (59%) in patients with chronic obstructive pulmonary disease. Overall mortality rate was 34%, and it was higher in patients who were ventilated for 1 to 10 days than in those ventilated for a longer time. Despite the availability of several new modes of ventilator support, older modes such as AC and SIMV were more commonly used. Weaning constitutes a large portion of total ventilator time, and thus, measures that expedite the weaning process should markedly decrease the duration of mechanical ventilation.

APACHE↗
PubMed1996

[Nitric oxide delivery through ventilator and its toxic oxidative product nitrogen dioxide].

OBJECTIVE: To observe nitric oxide(NO) delivery through mechanically ventilator. NO is rapidly converted to nitrogen dioxide(NO2)in oxygen(O2) environments. METHODS: NO(800 ppm)was blended with compressed air, delivered to the high-pressure air inlet of a Siemens Servo 900C or VIP BIRD ventilator, and used to ventilator as a test lung. The ventilator settings were varied, minute ventilation (VE)from 2 to 6 L/min, inspired O2 fraction(FiO2)from 0.25 to 0.65, and NO concentration from 10 to 80 ppm. The inspiratory gas mixture was sampled just at the outlet port of ventilator. NO and NO2 were measured both by hemiluminescence and electro-chemical fuel cell technique. RESULTS: No NO was detected during any trial with VE 5 or 6 L/min., with FiO2 0.35 or 0.25, with NO 20 or 10 ppm. Low VE and low NO, NO2 values were greater with Servo 900C ventilator than with VIP BIRD ventilator at similar settings High VE and low NO or low VE and high NO, NO2 values were similar with both ventilators. High VE and high NO, NO2 values were greater with VIP BIRD ventilator than with Servo 900C ventilator. At same VE, NO2 values increased with increased FiO2 and NO. (NO2) = 0.0607 (NO)- 0.6604 VE + 7.004 FiO2, R2 = 0.7649 with Servo 900C ventilator,(NO2) = 0.0929(NO)- 0.1296 VE + 7.9360 FiO2, R2 = 0.8687 with VIP BIRD ventilator. CONCLUSIONS: NO(800 ppm) was blended with compressed air, delivered to the high-pressure air inlet of a Siemens Servo 900C or VIP BIRD ventilator is a portable, accurate, and adaptable system to deliver NO. During NO inhalation, VIP BIRD ventilator is more adaptable while low VE. Servo 900C ventilator is more adaptable while high VE.

Humans↗
PubMed2000

Nocturnal mechanical ventilation for chronic hypoventilation in patients with neuromuscular and chest wall disorders.

BACKGROUND: Chronic alveolar hypoventilation is a common complication of many neuromuscular and chest wall disorders. Long term nocturnal mechanical ventilation is used to treat an increasing number of patients. OBJECTIVES: To examine the efficacy of nocturnal mechanical ventilation in relieving hypoventilation related symptoms in patients with neuromuscular or chest wall disorders. SEARCH STRATEGY: Search of the Cochrane Neuromuscular Disease Group register for randomized trials and enquiry from authors of trials and other experts in the field. SELECTION CRITERIA: Types of studies: quasi-randomized or randomized controlled trials TYPES OF PARTICIPANTS: patients with neuromuscular or chest wall disorder-related stable chronic hypoventilation of all ages and all degrees of severity. Types of interventions: any type and any mode of nocturnal mechanical ventilation. Types of outcome measures: Primary: short term and long term reversal of hypoventilation related clinical symptoms Secondary: unplanned hospital admission rate, one year mortality, short term and long term reversal of day time hypercapnia, improvement of lung function and improvement of sleep breathing disorders. DATA COLLECTION AND ANALYSIS: We identified four randomized trials. One author extracted the data and another checked them. Individual data were available from the authors of the largest study. MAIN RESULTS: The four eligible trials included a total of 51 patients. The risk difference (proportion of patients) of no improvement of hypoventilation related clinical symptoms in the short term following nocturnal mechanical ventilation was significant and favoured treatment, -0.417 (95% CI -0.639 to -0.194). However, there was significant heterogeneity across the studies (p<0.001). Similarly, the risk difference of no reversal of day time hypercapnia in the short term following nocturnal ventilation was significant and favoured treatment, -0.635 (95% CI -0.874 to -0.396). The weighted mean difference of nocturnal mean oxygen saturation percent was 5.5 (95% CI 1.5 to 9.4) more improvement in patients treated with nocturnal mechanical ventilation. For the primary and most of the secondary outcome measures there was no significant difference between nocturnal mechanical ventilation and no ventilation in the long term, except for one-year mortality. Indeed, the risk difference of death one year following implementation of nocturnal mechanical ventilation was significant and favoured treatment, -0.259 (95% CI -0.478 to -0. 041). However, there was significant heterogeneity across the studies (p<0.001). Most of the secondary outcomes were not assessed in the eligible trials. No data could be summarised for the comparisons between invasive and non-invasive mechanical ventilation, between intermittent positive pressure and negative pressure ventilation, and between volume-cycled and pressure-cycled ventilation. REVIEWER'S CONCLUSIONS: Current evidence about the therapeutic benefit of mechanical ventilation is weak, but consistent, suggesting alleviation of the symptoms of chronic hypoventilation in the short term, and in two small studies survival was prolonged. Mechanical ventilation should be offered as a therapeutic option to patients with chronic hypoventilation due to neuromuscular diseases. Further larger randomized trials are needed to confirm long term beneficial effects of nocturnal mechanical ventilation on quality of life, morbidity and mortality, to assess its cost-benefit ratio, and to compare the different types and modes of ventilation.

Chronic Disease↗
PubMed1996

Reassessing the need for ventilation during CPR.

In the United States debate continues about the necessity of ventilation during CPR because of fear of contracting infectious diseases. Three questions will be considered in this article. First, is ventilation necessary for the treatment of cardiac arrest? Second, is mouth-to-mouth ventilation any better than no ventilation at all? Third, are other techniques of ventilation as effective or more effective than mouth-to-mouth ventilation during basic life support CPR? Although research is still inconclusive with regard to the need for ventilation during CPR, recent findings have clarified the effect of ventilation during low blood flow states and how ventilation influences resuscitation. Ventilation affects oxygenation, carbon dioxide elimination, and pH during times of low rates of blood flow. Ventilation may be unnecessary during the first few minutes of CPR. Under conditions of prolonged, untreated cardiac arrest, ventilation during CPR affects return of spontaneous circulation. Isolated hypoxemia and hypercarbia independently have adverse effects on survival of cardiac arrest. Because ventilation with exhaled gas contains as much as 4% CO2 and less oxygen than air, it may have adverse effects during CPR. Spontaneous gasping may provide sufficient ventilation during CPR. Chest compression alone provides some pulmonary ventilation and gas exchange. Active chest compression-decompression may improve gas exchange better than does standard chest compression. Other forms of manual ventilation may also have a role in CPR.

Animals↗
PubMed2004

Pressure-controlled ventilation in children with severe status asthmaticus.

OBJECTIVE: The optimum strategy for mechanical ventilation in a child with status asthmaticus is not established. Volume-controlled ventilation continues to be the traditional approach in such children. Pressure-controlled ventilation may be theoretically more advantageous in allowing for more uniform ventilation. We describe our experience with pressure-controlled ventilation in children with severe respiratory failure from status asthmaticus. DESIGN: Retrospective review. SETTING: Pediatric intensive care unit in a university-affiliated children's hospital. PATIENTS: All patients who received mechanical ventilation for status asthmaticus. INTERVENTIONS: Pressure-controlled ventilation was used as the initial ventilatory strategy. The optimum pressure control, rate, and inspiratory and expiratory time were determined based on blood gas values, flow waveform, and exhaled tidal volume. MEASUREMENT AND MAIN RESULTS: Forty patients were admitted for 51 episodes of severe status asthmaticus requiring mechanical ventilation. Before the institution of pressure-controlled ventilation, median pH and Pco(2) were 7.21 (range, 6.65-7.39) and 65 torr (29-264 torr), respectively. Four hours after pressure-controlled ventilation, median pH increased to 7.31 (6.98-7.45, p <.005), and Pco(2) decreased to 41 torr (21-118 torr, p <.005). For patients with respiratory acidosis (Pco(2) >45 torr) within 1 hr of starting pressure-controlled ventilation, the median length of time until Pco(2) decreased to <45 torr was 5 hrs (1-51 hrs). Oxygen saturation was maintained >95% in all patients. Two patients had pneumomediastinum before pressure-controlled ventilation. One patient each developed pneumothorax and subcutaneous emphysema after initiation of pressure-controlled ventilation. All patients survived without any neurologic morbidity. Median duration of mechanical ventilation was 29 hrs (4-107 hrs), intensive care stay was 56 hrs (17-183 hrs), and hospitalization was 5 days (2-20 days). CONCLUSIONS: Based on this retrospective study, we suggest that pressure-controlled ventilation is an effective ventilatory strategy in severe status asthmaticus in children. Pressure-controlled ventilation represents a therapeutic option in the management of such children.

Acidosis, Respiratory↗
PubMed2000

Long term non-invasive ventilation in the community for patients with musculoskeletal disorders: 46 year experience and review.

BACKGROUND: A study was undertaken to assess the long term physiological and clinical outcome in 79 patients with musculoskeletal disorders (73 neuromuscular, six of the chest wall) who received non-invasive ventilation for chronic respiratory failure over a period of 46 years. METHODS: Vital capacity (VC) and carbon dioxide tension (PCO(2)) before and after initiation of ventilation, type and duration of ventilatory assistance, the need for tracheostomy, and mortality were retrospectively studied in 48 patients who were managed with mouth/nasal intermittent positive pressure ventilation (M/NIPPV) and 31 who received body ventilation. The two largest groups analysed were 45 patients with poliomyelitis and 15 with Duchenne's muscular dystrophy. Twenty five patients with poliomyelitis received body ventilation (for a mean of 290 months) and 20 were supported by M/NIPPV (mean 38 months). All 15 patients with Duchenne's muscular dystrophy were ventilated by NIPPV (mean 22 months). RESULTS: Fourteen patients with poliomyelitis on body ventilation (56%) but only one on M/NIPPV, and 10 of 15 patients (67%) with Duchenne's muscular dystrophy eventually received tracheostomies for ventilatory support. Five patients with other neuromuscular disorders required tracheostomies. Twenty of 29 tracheostomies (69%) were provided because of progressive disease and hypercarbia which could not be controlled by non-invasive ventilation; the remaining nine were placed because of bulbar dysfunction and aspiration related complications. Nine of 10 deaths occurred in patients on body ventilation (six with poliomyelitis), although the causes of death were varied and not necessarily related to respiratory complications. A proportionately greater number of patients on M/NIPPV (67%) reported positive outcomes (improved sense of wellbeing and independence) than did those on body ventilation (29%, p<0.01). However, other than tracheostomies and deaths, negative outcomes in the form of machine/interface discomfort and self-discontinuation of ventilation also occurred at a rate 2.3 times higher than in the group who received body ventilation. None of the six patients with chest wall disorders (all on M/NIPPV) required tracheostomy or died. Hospital admission rates increased nearly eightfold in patients receiving body ventilation (all poliomyelitis patients) compared with before ventilation (p<0.01) while in those supported by M/NIPPV they were reduced by 36%. CONCLUSIONS: Non-invasive ventilation (NIV) in the community over prolonged periods is a feasible although variably tolerated form of management in patients with neuromuscular disorders. While patients who received body ventilation were followed the longest (mean 24 years), the need for tracheostomy and deaths occurred more often in this group (most commonly in the poliomyelitis patients). Despite a number of discomforts associated with M/NIPPV, a larger proportion of patients experienced improved wellbeing, independence, and ability to perform daily activities.

Adolescent↗
PubMed1994

Hemodynamic effects of different modes of mechanical ventilation in acute cardiac and pulmonary failure: an experimental study.

OBJECTIVE: To determine the hemodynamic effects of four different modes of mechanical ventilation in an animal model of acute cardiac and pulmonary failure. DESIGN: Prospective, randomized, crossover design. SETTING: University research laboratory. SUBJECTS: Twelve piglets weighing 10 to 16 kg. INTERVENTIONS: The experimental protocol consisted of three stable 30-min periods: when ventricular and pulmonary functions were normal (control), after the induction of acute cardiac failure by the administration of a beta-adrenergic receptor blocker, and after pulmonary failure induced by repeated lung lavage. Modes of mechanical ventilation included controlled mechanical ventilation, high-frequency oscillation, synchronized high-frequency jet ventilation, and external negative pressure oscillation combined with pressure support ventilation. Each mode of respiratory support was randomly and sequentially applied to each animal with the assessment of cardiopulmonary function at the end of each period. MEASUREMENTS AND MAIN RESULTS: Continuous monitoring included electrocardiogram, right atrial, left ventricular end-diastolic, pulmonary arterial, intrathoracic aortic, arterial, esophageal, and transpulmonary pressures and arterial and mixed venous oxygen saturation measurements. In addition, cardiac output using the thermodilution technique was measured intermittently. Whereas in the control period cardiac index was significantly (p < .05) higher during synchronized high-frequency jet ventilation (193 +/- 19.3 mL/kg/min) than during controlled mechanical ventilation (151 +/- 12.1 mL/kg/min) and high-frequency oscillation (151 +/- 18.1 mL/kg/min), there was no significant hemodynamic difference between the four modes of mechanical ventilation in the cardiac and pulmonary failure periods. In the pulmonary failure period, transpulmonary pressure was significantly higher during high-frequency oscillation (7.1 +/- 1.6 mm Hg) than during controlled mechanical ventilation (5.6 +/- 0.6 mm Hg), high-frequency ventilation (4.1 +/- 0.4 mm Hg), and external negative pressure oscillation combined with pressure support ventilation (5.3 +/- 0.5 mm Hg). CONCLUSIONS: Synchronized high-frequency ventilation improves cardiac performance in control conditions. No hemodynamic difference is present between the four modes of mechanical ventilation in the cardiac and pulmonary failure periods. External negative pressure oscillation combined with pressure support ventilation has moderate hemodynamic advantages over controlled mechanical ventilation and high-frequency oscillation in different clinical settings, but it also results in a deterioration of pulmonary gas exchange during the pulmonary failure period.

Animals↗
PubMed1994

Influence of pressure- and flow-triggered synchronous intermittent mandatory ventilation on inspiratory muscle work.

OBJECTIVE: To determine the effect of pressure- and flow-triggered synchronous intermittent mandatory ventilation on inspiratory muscle work. DESIGN: Consecutive clinical, prospective, randomized trial. SETTING: Medical intensive care unit (ICU) of a U.S. Veterans Affairs Medical Center. PATIENTS: Eight patients recovering from acute respiratory failure of various etiologies. INTERVENTIONS: Assist control, followed by randomized application of pressure- and flow-triggered synchronous intermittent mandatory ventilation at 60%, 40%, 20% of the assist-control rate, and flow-triggered continuous positive airway pressure. A total of eight settings were maintained for 10 mins each. MEASUREMENTS AND MAIN RESULTS: Total work rate (joules/min), inspiratory muscle work (joules/L), and pressure time-product per breath (cm H2O-sec) were measured. During pressure- or flow-triggered synchronous intermittent mandatory ventilation, total work rate increased as the mandatory rate was decreased. The method of ventilator triggering had a significant effect on the total work rate. With pressure-triggered synchronous intermittent mandatory ventilation, the total work rate at 60% of the assist-control rate was similar to that with assist-control; whereas with flow-triggered synchronous intermittent mandatory ventilation, this result was achieved at 40% of the assist-control rate. At a machine support level of 20%, total work rate with pressure-triggered synchronous intermittent mandatory ventilation was significantly greater than with flow-triggered synchronous intermittent mandatory ventilation. The method of ventilator triggering had no significant effect on the inspiratory muscle work of the mandatory breaths. This finding was in contrast to the effect on inspiratory muscle work of spontaneous breaths. With pressure-triggered synchronous intermittent mandatory ventilation, inspiratory muscle work of the spontaneous breaths was greater than with the flow-triggered at machine support of 40% and 20%. With either pressure- or flow-triggered synchronous intermittent mandatory ventilation, inspiratory muscle work of the mandatory breaths was not significantly different from that of the corresponding spontaneous breaths, except at the lower machine support levels with the pressure-triggered synchronous intermittent mandatory ventilation. Pressure-time product followed a trend similar to that of inspiratory muscle work. CONCLUSIONS: During synchronous intermittent mandatory ventilation, the method of ventilator triggering has a significant effect on the total work rate and inspiratory muscle work of the spontaneous breaths, particularly at lower machine support levels. Conversely, the method of ventilator triggering has no significant effect on inspiratory muscle work of the mandatory breaths.

Acute Disease↗
PubMed2006

Effect of non-invasive positive pressure ventilation (NIPPV) on mortality in patients with acute cardiogenic pulmonary oedema: a meta-analysis.

BACKGROUND: Non-invasive positive pressure ventilation (NIPPV), using continuous positive airway pressure (CPAP) or bilevel ventilation, has been shown to reduce the need for invasive mechanical ventilation in patients with acute cardiogenic pulmonary oedema. We assessed additional benefits of NIPPV in a meta-analysis. METHODS: Meta-analysis comparison in acute cardiogenic pulmonary oedema was undertaken to compare (1) CPAP with standard therapy (oxygen by face-mask, diuretics, nitrates, and other supportive care), (2) bilevel ventilation with standard therapy, and (3) bilevel ventilation with CPAP, incorporating randomised controlled trials identified by electronic and hand search (1966-May, 2005). In 23 trials that fulfilled inclusion criteria, we assessed the effect of NIPPV on hospital mortality and mechanical ventilation, estimated as relative risks. FINDINGS: CPAP was associated with a significantly lower mortality rate than standard therapy (relative risk 0.59, 95% CI 0.38-0.90, p=0.015). A non-significant trend towards reduced mortality was seen in the comparison between bilevel ventilation and standard therapy (0.63, 0.37-1.10, p=0.11). We recorded no substantial difference in mortality risk between bilevel ventilation and CPAP (p=0.38). The need for mechanical ventilation was reduced with CPAP (0.44, 0.29-0.66, p=0.0003) and with bilevel ventilation (0.50, 0.27-0.90, p=0.02), compared with standard therapy; but no significant difference was seen between CPAP and bilevel ventilation (p=0.86). Weak evidence of an increase in the incidence of new myocardial infarction with bilevel ventilation versus CPAP was recorded (1.49, 0.92-2.42, p=0.11). Heterogeneity of treatment effects was not evident for mortality or mechanical ventilation across patients' groups. INTERPRETATION: In patients with acute cardiogenic pulmonary oedema, CPAP and bilevel ventilation reduces the need for subsequent mechanical ventilation. Compared with standard therapy, CPAP reduces mortality; our results also suggest a trend towards reduced mortality after bilevel NIPPV.

Continuous Positive Airway Pressure↗
PubMed1998

Effect of a protective-ventilation strategy on mortality in the acute respiratory distress syndrome.

BACKGROUND: In patients with the acute respiratory distress syndrome, massive alveolar collapse and cyclic lung reopening and overdistention during mechanical ventilation may perpetuate alveolar injury. We determined whether a ventilatory strategy designed to minimize such lung injuries could reduce not only pulmonary complications but also mortality at 28 days in patients with the acute respiratory distress syndrome. METHODS: We randomly assigned 53 patients with early acute respiratory distress syndrome (including 28 described previously), all of whom were receiving identical hemodynamic and general support, to conventional or protective mechanical ventilation. Conventional ventilation was based on the strategy of maintaining the lowest positive end-expiratory pressure (PEEP) for acceptable oxygenation, with a tidal volume of 12 ml per kilogram of body weight and normal arterial carbon dioxide levels (35 to 38 mm Hg). Protective ventilation involved end-expiratory pressures above the lower inflection point on the static pressure-volume curve, a tidal volume of less than 6 ml per kilogram, driving pressures of less than 20 cm of water above the PEEP value, permissive hypercapnia, and preferential use of pressure-limited ventilatory modes. RESULTS: After 28 days, 11 of 29 patients (38 percent) in the protective-ventilation group had died, as compared with 17 of 24 (71 percent) in the conventional-ventilation group (P<0.001). The rates of weaning from mechanical ventilation were 66 percent in the protective-ventilation group and 29 percent in the conventional-ventilation group (P=0.005): the rates of clinical barotrauma were 7 percent and 42 percent, respectively (P=0.02), despite the use of higher PEEP and mean airway pressures in the protective-ventilation group. The difference in survival to hospital discharge was not significant; 13 of 29 patients (45 percent) in the protective-ventilation group died in the hospital, as compared with 17 of 24 in the conventional-ventilation group (71 percent, P=0.37). CONCLUSIONS: As compared with conventional ventilation, the protective strategy was associated with improved survival at 28 days, a higher rate of weaning from mechanical ventilation, and a lower rate of barotrauma in patients with the acute respiratory distress syndrome. Protective ventilation was not associated with a higher rate of survival to hospital discharge.

Adult↗
PubMed1996

Effect of jet ventilation on heart failure: decreased afterload but negative response in left ventricular end-systolic pressure-volume function.

OBJECTIVE: To examine the mechanism of cardiac assist with systolic jet ventilation, specifically effects on loading conditions and left ventricular pressure-volume function. Both systolic and diastolic jet ventilation were compared in the absence and presence of heart failure. DESIGN: Prospective, two-factor, repeated-measures study. SETTING: Animal laboratory. SUBJECTS: Ten anesthetized, closed-chest dogs. INTERVENTIONS: The measurement protocol consisted of two phases: a) apnea, randomized jet ventilation (systole- and diastole-synchronized); b) postjet ventilation apnea, before and after heart failure, induced with a propranolol-imipramine-plasma expansion treatment. MEASUREMENT AND MAIN RESULTS: Systolic and diastolic jet ventilation was associated with mean airway pressures of approximately 7 mm Hg and intrapleural pressures of approximately 3 mm Hg in both heart conditions. In normal hearts, jet ventilation (either mode) decreased transmural left ventricular end-diastolic pressure by 40% to 60% (p < .05), left ventricular end-diastolic volume 25 +/- 8%, and stroke volume by 28% to 30%. Heart failure was associated with decreases (41 +/- 6%) in end-systolic pressure-volume function (i.e., pressure change/volume change or elastance), transmural left ventricular end-systolic pressure (22 +/- 3%), and stroke volume (16 +/- 4%), and increased transmural left ventricular end-diastolic pressure (139 +/- 6%). Application of jet ventilation (either mode) during heart failure did not affect stroke volume but significantly (p < .05) attenuated transmural left ventricular end-diastolic pressure by 30% to 40%, left ventricular end-diastolic volumes by 33 +/- 9%, and transmural left ventricular end-systolic pressure by 11% to 19% (p < .05). After jet ventilation, left ventricular elastance was decreased 36 +/- 8% in normal hearts and 35 +/- 11% in failing hearts. Stroke volume, however, returned to baseline levels because of increases in transmural left ventricular end-diastolic pressure in both heart conditions, and also in failing hearts, because transmural left ventricular end-systolic pressure remained decreased approximately 30% (p < .05). CONCLUSIONS: Jet ventilation did not decrease stroke volume in failing hearts because of the afterload-reducing benefit (decreased transmural left ventricular end-systolic pressure) of increased intrapleural pressure in dilated ventricles. Moreover, jet ventilation did not have positive effects on myocardial function and had negative effects on left ventricular elastance in the postjet ventilation period in both normal and failing hearts. Cardiac assist by jet ventilation was not cycle specific, suggesting no selective benefit of jet ventilation over conventional positive-pressure ventilation during heart failure. These studies demonstrate a negative inotropy associated with jet ventilation that, during heart failure, may compromise the general benefit of positive-pressure-mediated increases in intrapleural pressure.

Adrenergic Uptake Inhibitors↗
PubMed2005

Combining high-frequency oscillatory ventilation and recruitment maneuvers in adults with early acute respiratory distress syndrome: the Treatment with Oscillation and an Open Lung Strategy (TOOLS) Trial pilot study.

OBJECTIVE: To determine the safety, feasibility, and lung-recruitment efficacy of an explicit ventilation protocol combining high-frequency oscillatory ventilation and recruitment maneuvers. DESIGN: Prospective, multiple-center, single-intervention pilot study. SETTING: Four university-affiliated intensive care units. PATIENTS: Twenty-five patients with early acute respiratory distress syndrome and severe oxygenation failure. INTERVENTIONS: Patients were transitioned from standardized conventional ventilation to high-frequency oscillatory ventilation beginning with an initial cycle of up to three sustained inflation recruitment maneuvers (40 cm H2O x 40 secs), followed by a decremental titration of Fio2 and then mean airway pressure. Recruitment maneuvers were repeated for hypoxemia and routinely at least twice daily if the Fio2 was >0.4. A specific protocol was used for weaning high-frequency oscillatory ventilation, for transitioning to conventional ventilation, and for judging intolerance of conventional ventilation whereby patients should be put back on high-frequency oscillatory ventilation. MEASUREMENTS AND MAIN RESULTS: Patients (median [interquartile range] Acute Physiology and Chronic Health Evaluation II, 24 [19-32]; age, 50 [41-64]) were enrolled after 13 (range, 6-51) hrs of conventional ventilation. Following the initial cycle of recruitment, the mean (+/-sd) Pao2/Fio2 increased significantly compared with standardized conventional ventilation (200 +/- 117 vs. 92 +/- 36 mm Hg, p < .001). After a mean of 12 hrs of high-frequency oscillatory ventilation, the mean Fio2 was significantly reduced compared with prestudy levels (0.5 +/- 0.2 vs. 0.9 +/- 0.1, p < .001). A median of seven (four to 11) recruitment maneuvers was performed per patient over the study period, with only eight of 244 (3.3%) being aborted. Six of 19 patients transitioned to conventional ventilation (32%) were deemed intolerant and were switched back to high-frequency oscillatory ventilation. Protocol adherence was excellent with documented rates >90%. CONCLUSIONS: The combination of high-frequency oscillatory ventilation and recruitment maneuvers resulted in rapid and sustained improvement in oxygenation, likely through lung recruitment. This explicit high-frequency oscillatory ventilation protocol appears well tolerated, feasible, and physiologically sound.

Adult↗
PubMed2000

How is mechanical ventilation employed in the intensive care unit? An international utilization review.

A 1-d point-prevalence study was performed with the aim of describing the characteristics of conventional mechanical ventilation in intensive care units ICUs from North America, South America, Spain, and Portugal. The study involved 412 medical-surgical ICUs and 1,638 patients receiving mechanical ventilation at the moment of the study. The main outcome measures were characterization of the indications for initiation of mechanical ventilation, the artificial airways used to deliver mechanical ventilation, the ventilator modes and settings, and the methods of weaning. The median age of the study patients was 61 yr, and the median duration of mechanical ventilation at the time of the study was 7 d. Common indications for the initiation of mechanical ventilation included acute respiratory failure (66%), acute exacerbation of chronic obstructive pulmonary disease (13%), coma (10%), and neuromuscular disorders (10%). Mechanical ventilation was delivered via an endotracheal tube in 75% of patients, a tracheostomy in 24%, and a facial mask in 1%. Ventilator modes consisted of assist/control ventilation in 47% of patients and 46% were ventilated with synchronized intermittent mandatory ventilation, pressure support, or the combination of both. The median tidal volume setting was 9 ml/kg in patients receiving assist/control and the median setting of pressure support was 18 cm H(2)O. Positive end-expiratory pressure was not employed in 31% of patients. Method of weaning varied considerably from country to country, and even within a country several methods were in use. We conclude that the primary indications for mechanical ventilation and the ventilator settings were remarkably similar across countries, but the selection of modes of mechanical ventilation and methods of weaning varied considerably from country to country.

Data Collection↗
PubMed2004

Positive pressure versus pressure support ventilation at different levels of PEEP using the ProSeal laryngeal mask airway.

We compared positive pressure ventilation with pressure support ventilation at different levels of positive end expiratory pressure (PEEP) using the ProSeal laryngeal mask airway (PLMA). Forty-two anaesthetized adults (ASA 1-2, aged 19 to 63 years) underwent positive pressure ventilation and then pressure support ventilation each with PEEP set at 0, 5 and 10 cmH2O in random order. Pressure support ventilation was with the inspired tidal volume (VTInsp) set at 7 ml/kg and the respiratory rate adjusted to maintain the end-tidal CO2 (ETCO2) at 40 mmHg. Pressure support ventilation was with pressure support set at 5 cmH2O above PEEP and initiated when inspiration produced a 2 cmH2O reduction in airway pressure. Tidal volumes were similar during positive pressure and pressure support ventilation with PEEP, but were higher for the former without PEEP Respiratory rate and peak inspiratory flow rate were higher during pressure support than positive pressure ventilation (all P < 0.001). Peak airway pressure (Ppaw), mean airway pressure (Mpaw), peak expiratory flow rate, and expired airway resistance were lower during pressure support than positive pressure ventilation (all P < 0.001). With PEEP set at 10 cmH2O, ETCO2 was lower for pressure support than positive pressure ventilation. During positive pressure ventilation, there was an increase in Ppaw, Mpaw and dynamic compliance (Cdyn) with increasing levels of PEEP (all P < 0.01). During pressure support ventilation, there was an increase in inspired and expired tidal volume, Ppaw, peak inspiratory and expiratory flow rates and Cdyn, and a reduction in ETCO2, work of breathing, and expired airway resistance with increasing levels of PEEP (all P < 0.01). There were no differences in SpO2, non-invasive mean arterial pressure, heart rate or leak fraction. We conclude that pressure support ventilation provides equally effective gas exchange as positive pressure ventilation during PLMA anaesthesia with or without PEEP at the tested settings. During pressure support, PEEP increases ventilation and reduces work on breathing without increasing leak fraction.

Adult↗
PubMed2006

A single ventilator for multiple simulated patients to meet disaster surge.

OBJECTIVES: To determine if a ventilator available in an emergency department could quickly be modified to provide ventilation for four adults simultaneously. METHODS: Using lung simulators, readily available plastic tubing, and ventilators (840 Series Ventilator; Puritan-Bennett), human lung simulators were added in parallel until the ventilator was ventilating the equivalent of four adults. Data collected included peak pressure, positive end-expiratory pressure, total tidal volume, and total minute ventilation. Any obvious asymmetry in the delivery of gas to the lung simulators was also documented. The ventilator was run for almost 12 consecutive hours (5.5 hours of pressure control and more than six hours of volume control). RESULTS: Using readily available plastic tubing set up to minimize dead space volume, the four lung simulators were easily ventilated for 12 hours using one ventilator. In pressure control (set at 25 mm H2O), the mean tidal volume was 1,884 mL (approximately 471 mL/lung simulator) with an average minute ventilation of 30.2 L/min (or 7.5 L/min/lung simulator). In volume control (set at 2 L), the mean peak pressure was 28 cm H2O and the minute ventilation was 32.5 L/min total (8.1 L/min/lung simulator). CONCLUSIONS: A single ventilator may be quickly modified to ventilate four simulated adults for a limited time. The volumes delivered in this simulation should be able to sustain four 70-kg individuals. While further study is necessary, this pilot study suggests significant potential for the expanded use of a single ventilator during cases of disaster surge involving multiple casualties with respiratory failure.

Adult↗
PubMed1993

Measurements of ventilation in freely ranging subjects.

Both the level of ventilation and breathing pattern (breathing frequency, inspiratory time, and tidal volume) have an important influence on particle deposition and gas uptake in the lungs. Accordingly, a description of these measures is needed to assess better the dose of particulate deposit and gas uptake in the lungs during varied activities. The long-term objectives of this study were to develop a means of measuring minute ventilation in the field by using body surface displacements, and to evaluate the utility of heart rate as an index of minute ventilation. By using respiratory inductance plethysmographic belts and magnetometers placed on the rib cage and abdomen, ventilation and breathing pattern can be noninvasively measured in mobile individuals. Our specific aims were (1) to validate measurements of ventilation using body surface displacement; (2) to describe breathing patterns in subjects performing a variety of daily activities in the laboratory; (3) to analyze relationships between minute ventilation and heart rate; and (4) to measure ventilation in the field with one technique utilizing body surface displacements and another based upon heart rate. We found that values of tidal volume, inspiratory time, and breathing frequency derived from body surface displacement measurements correlated well with those determined spirometrically during a variety of activities. The coefficient of determination for tidal volume was 0.97 +/- 0.2 for cycling, 0.93 +/- 0.07 for arm cranking, 0.91 +/- 0.05 for pulling, and 0.84 +/- 0.12 for lifting. Our experiments showed that the breathing pattern was altered by the use of a mouthpiece and varied according to the type of activity. The use of a mouthpiece increased tidal volume by 34%, decreased the breathing frequency by 10%, and increased minute ventilation by 16%. There was more variability of these parameters during lifting and pulling activities than during cycling. The ventilation-heart rate relationship varied from subject to subject and was altered by the use of a mouthpiece. We found that ventilation measured in the field from body surface displacement correlated well with ventilation measured using the pneumotachograph (R2 = 0.89). However, measurements of ventilation derived from heart rate were not as accurate as those derived from body surface displacements. We concluded that minute ventilation can be measured accurately using body surface displacements in the laboratory and in the field. Heart rate can also be utilized, but factors affecting the minute ventilation-heart rate relationship, such as the use of a mouthpiece and range of heart rate, must be addressed to obtain more accurate estimates of minute ventilation.

Adolescent↗
PubMed1994

[The effect of different types of anesthetic respirators on oxygenation and ventilation in infants during short-term anesthesia. A study using transcutaneous PO2 and PCO2 monitoring].

Monitoring of ventilation in infants is difficult and often not very reliable. In this study, transcutaneous measurement of blood gas tensions was used to investigate the influence of four different modes of ventilation on oxygenation and ventilation in anaesthetized infants. METHODS. In a randomised study, transcutaneously measured PO2 (tc-PO2) and PCO2 (tcPCO2) tensions were continuously registered in 42 ASA class I and II infants between 3 and 24 weeks of age undergoing minor surgical procedures (inguinal hernia repair). Two breathing systems combined with different modes of ventilation were evaluated: manual ventilation with Kuhn's T-piece system and face mask (group A; n = 11) or endotracheal tube (group B; n = 10); manual ventilation with paediatric circuit system and face mask (group C; n = 11); and mechanical ventilation with paediatric circle system, endotracheal tube, and positive end-expiratory pressure (PEEP) 3 cm H2O (group D; n = 10). Transcutaneous values were measured by a combined tcPO2/PCO2 electrode (E 5277, Radiometer). Anaesthesia was maintained by controlled ventilation with N2O/O2 (67%/33%) and halothane 0.5-1.5 vol.%. Surgical and anaesthetic techniques were standardized and the anaesthetist was blinded to the measured values. RESULTS. Preoperative mean tcPO2 values while spontaneously breathing air ranged between 69 and 75 mmHg in all patients. During anaesthesia and controlled ventilation (FiO2 = 0.33), there was a significant increase in tcPO2 (P < 0.01) in 3 groups: in groups A and D mean tcPO2 increased to 90-100 mmHg and in group C to 110-120 mmHg. In contrast, tcPO2 in group B reached only 75-80 mmHg, which was not considered significant. Postoperatively, tcPO2 immediately reached baseline values in all patients (Fig. 2). Compared to preoperative values, the alveolar-tcPO2 difference (AtcDO2) significantly increased during anaesthesia in all groups (Fig. 3). The tcPCO2 measurements revealed marked alveolar dysventilation, with hyperventilation supervening in groups A, B, and D; in group C, however, most (7 of 11) infants were normoventilated (Fig. 4). CONCLUSIONS. Adverse effects of anaesthesia on pulmonary function in infants are caused by loss of the PEEP effect induced by the physiological subglottic stenosis. Endotracheal intubation and the increase in chest wall compliance during anaesthesia lead to a decrease in functional residual capacity (FRC) associated with premature airway closure and ventilation/perfusion mismatch. These pathophysiological disturbances result in a marked increase in AaDO2 and low arterial PO2 values despite high FiO2, as could be observed when intubated infants had been ventilated with a high-flow T-piece system (group B). Mechanical ventilation with a paediatric circuit system and endotracheal tube allows the use of low PEEP levels (group D), which may replace the lost subglottic function and partially restore the FRC. Ventilation by mask does not disturb the functional subglottic stenosis, and the impairment of pulmonary function will depend solely on the decrease in FRC caused by increased chest wall compliance (group A). If mask ventilation is combined with a paediatric circuit system (group C), the pressure relief valve produces a low PEEP of 2 to 3 cm H2O, which may partially counteract the decrease in FRC. With regard to oxygenation, the paediatric circle system proved to be superior to the high-flow T-piece system independent of whether children were ventilated via a face mask or an endotracheal tube. The group-specific differences in degree of dysventilation with manual ventilation show that the type of breathing system is important with regard to the size of the tidal volume delivered. Thus, tidal volumes will be unintentionally increased by the high fresh gas flow needed when a T-piece system is used. The lower flow and preadjusted pressure limit may prevent the delivery of excessive tidal volumes with the paediatric circuit system...

Anesthesia↗