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PubMed1984

Role of collateral ventilation in ventilation-perfusion balance.

Species with collateral ventilation have an auxiliary respiratory mechanism that could protect them, under certain circumstances, from regional alveolar hypoxia. Species without collateral ventilation may have a greater potential for routinely experiencing regional hypoxia; to maintain ventilation-perfusion balance they would have to rely on pulmonary vasoconstriction. We tested these ideas by ventilating a sublobar region of pig lung (no collateral ventilation) with 13% O2 while the rest of the lung was ventilated with 30% O2. Blood flow, as measured by radioactive microsphere distribution to the sublobar region, was reduced 50% during hypoxia. The hypoxia-induced vasoconstriction effectively defended arterial PO2. When a vasodilator was infused, regional blood flow increased to control levels; shunt fraction rose, and arterial PO2 fell. In dogs (collateral ventilation present) the same experimental maneuvers had no significant effect on regional end-tidal gases or on microsphere distribution, indicating that collateral ventilation was able to maintain ventilation-perfusion balance. When regional hypoxia was created in dogs by overcoming collateral ventilation with slightly positive airway pressure in the sublobar region, the dog acted like the pig and used hypoxic vasoconstriction to shift approximately 30% of the blood flow away from the hypoxic alveoli.

Animals↗
PubMed1995

Independent lung ventilation with a single ventilator using a variable resistance valve.

Independent lung ventilation using two ventilators has been attempted in the treatment of acute respiratory failure due to unilateral lung disease. However, this method has been found to be cumbersome and difficult to use. We reasoned that a bifurcated endotracheal tube with a variable resistance valve may enable us to change the inspiratory airway pressures and, hence, the inspired tidal volume to one lung using a single ventilator. We tested this hypothesis in eight anesthetized sheep and created a bronchopleural fistula in one lung as a model of unilateral lung disease. A bifurcated endotracheal tube was placed to separate the ventilation to each lung and, through a "Y" connector, both right and left lungs were ventilated simultaneously with a single ventilator. A variable resistance valve was placed between the "Y" connector and the tube ventilating the experimental lung with bronchopleural fistula. With a ventilator-generated peak inspiratory pressure of 31 +/- 2 cm H2O, the airway pressure distal to the valve was randomly changed from 31 cm H2O to 23 +/- 2, 15 +/- 1, 8 +/- 1, and 0 cm H2O. This resulted in progressive diversion of tidal volume from the experimental lung to the control lung and an increase in exhaled tidal volume due to a decrease in air leak from the bronchopleural fistula. These data suggest that a variable resistance valve may be used for independent lung ventilation using a single ventilator.

Animals↗
PubMed1998

Extending ventilator circuit change interval beyond 2 days reduces the likelihood of ventilator-associated pneumonia.

OBJECTIVE: To determine the risk of acquiring ventilator-associated pneumonia (VAP) and the impact on costs when extending ventilator circuit change intervals beyond 2 days to 7 and 30 days. DESIGN: Prospective 4-year review of mechanically ventilated patients. SETTING: The respiratory and medical ICUs of an 800-bed tertiary teaching Veterans Affairs hospital. PATIENTS: All adult patients receiving mechanical ventilation from January 1991 through December 1994. INTERVENTIONS: Ventilator circuits with active heated water humidifiers were changed at 2-day intervals during a 2-year control period, followed by 7-day and 30-day intervals (for 1 year each). Heated wire circuits were adopted with the 30-day interval. The rate of VAP per 1,000 ventilator days was calculated for each circuit change interval group. Survival analysis was used to model VAP with ventilator circuit change to determine risk. RESULTS: During the study period, 637 patients received mechanical ventilation. During the 2 years with 2-day change intervals, the VAP per 1,000 ventilator days was 11.88 (n=343), compared with 3.34 (n=137) and 6.28 (n=157) for 7-day and 30-day change intervals, respectively. The risk of acquiring a VAP for those with a circuit change every 2 days was significantly greater (relative risk, 3.1; p=0.0004; 95% confidence interval, 1.662, 5.812) than those with the 7- and 30-day circuit changes. Extending circuit change intervals reduced supply and labor costs averaging $4,231/yr for each ventilator in use. CONCLUSIONS: Circuit change intervals of 7 and 30 days have lower risks for VAP than the 2-day intervals, yielding substantial reductions in morbidity as well labor and supply costs.

Adult↗
PubMed1998

Pulmonary epithelial permeability and gas exchange: a comparison of inverse ratio ventilation and conventional mechanical ventilation in oleic acid-induced lung injury in rabbits.

STUDY OBJECTIVE: (1) To explore the interaction between mechanical ventilation and oleic acid (OA)-induced lung injury on indexes of pulmonary gas exchange and epithelial permeability, and (2) to compare this interaction using two different modes of ventilation: pressure-controlled inverse ratio ventilation (PCIRV) and volume-controlled ventilation with positive end-expiratory pressure (VCV PEEP). DESIGN: Randomized animal study. SETTING: Experimental laboratory investigation at Södersjukhuset, Stockholm, Sweden. ANIMALS: Twenty-four New Zealand white rabbits. INTERVENTIONS: (1) Ventilation with PCIRV (n=6) or VCV PEEP (n=6) for 6 h at equal end-expiratory alveolar pressure levels of 5 cm H2O followed by induction of lung injury (IV injection of OA 0.15 mL/kg). (2) Induction of lung injury followed by 6 h of ventilation with either PCIRV (n=6) or VCV PEEP (n=6) as described above. MEASUREMENTS AND RESULTS: Lung mechanics, heart rate, BP, and gas exchange results were equal at baseline. In group A, after 1 h of ventilation, mean airway pressure was 11.9+/-4.4 with PCIRV and 8.3+/-1.0 cm H2O with VCV PEEP (p<0.05). Forty minutes after OA injection, PaO2/fraction of inspired oxygen (FIO2) was 24+/-10 kPa with PCIRV and 44+/-15 kPa with VCV PEEP (p<0.05). Mean airway pressure was higher and peak airway pressure was lower with PCIRV. In group B, after 6 h of ventilation, PaO2/FIO2 was 17+/-5 kPa with PCIRV and 43+/-8 kPa with VCV PEEP (p<0.01). Systemic BP was lower with PCIRV and mean airway pressure was higher. Technetium-99m diethylene triamine penta-acetic acid lung clearance: In group A, curves were monoexponential with both PCIRV (half-life time [T 1/2], 21+/-8 min and VCV PEEP (T 1/2, 126+/-59 min, p<0.005) until injection of OA. In the VCV PEEP-treated animals, a marked increase in clearance rate was observed within 60 s of OA injection (T 1/2, 13+/-9 min, p<0.001). Fifteen minutes after OA injections, T 1/2 had decreased to 38+/-17 min with VCV PEEP. In the animals treated with PCIRV, OA injection did not lead to a significant change in clearance rate, although the elimination pattern was observed to change from single-compartment to multicompartment type. In group B, clearance curves were monoexponential with both ventilatory modes. There was no significant difference in clearance rate between PCIRV (T 1/2, 25+/-9 min) and VCV PEEP (T 1/2, 36+/-16 min, not significant). CONCLUSIONS: The observation that PaO2 was lower in the PCIRV-treated groups must be interpreted with caution in this animal study with relatively few observations. The finding may reflect differences in the effect of OA injection in the two ventilatory modes. It is also possible that externally applied PEEP is more effective than PCIRV in increasing oxygen tension, either because of a less inhomogenous distribution of ventilation and perfusion or for other reasons. The clearance results imply that PCIRV causes an alteration in lung epithelial or membrane function in comparison to VCV PEEP. This functional difference is most likely caused by the large time-weighted lung volume produced by pressure control in combination with a prolonged inspiration. Induction of high permeability lung injury with OA eliminates the difference between PCIRV and VCV PEEP. It remains to be established whether these findings are relevant with regard to ventilator-associated structural lung injury in man.

Acute Disease↗
PubMed2003

Regional ventilation by electrical impedance tomography: a comparison with ventilation scintigraphy in pigs.

STUDY OBJECTIVE: The validation of electrical impedance tomography (EIT) for measuring regional ventilation distribution by comparing it with single photon emission CT (SPECT) scanning. DESIGN: Randomized, prospective animal study. SETTINGS: Animal laboratories and nuclear medicine laboratories at a university hospital. PARTICIPANTS: Twelve anesthetized and mechanically ventilated pigs. INTERVENTIONS: Lung injury was induced by central venous injection of oleic acid. Then pigs were randomized to pressure-controlled mechanical ventilation, airway pressure-release ventilation, or spontaneous breathing. MEASUREMENTS AND RESULTS: Ventilation distribution was assessed by EIT using cross-sectional electrotomographic measurements of the thorax, and simultaneously by single SPECT scanning with the inhalation of (99m)Tc-labeled carbon particles. For both methods, the evaluation of ventilation distribution was performed in the same transverse slice that was approximately 4 cm in thickness. The transverse slice then was divided into 20 coronal segments (going from the sternum to the spine). We compared the percentage of ventilation in each segment, normalized to the entire ventilation in the observed slice. Our data showed an excellent linear correlation between the ventilation distribution measured by SPECT scanning and EIT according to the following equation: y = 0.82x + 0.7 (R(2) = 0.92; range, 0.86 to 0.97). CONCLUSION: Based on these data, EIT seems to allow, at least in comparable states of lung injury, real-time monitoring of regional ventilation distribution at the bedside.

Animals↗
PubMed1984

Early prediction of outcome of respiratory failure. Comparison of high-frequency jet ventilation and volume-cycled ventilation.

Data from a prospective randomized investigation comparing volume-cycled ventilation and high-frequency jet ventilation were reexamined to determine whether improvement of respiratory and hemodynamic function, as well as ultimate outcome (death or survival), could be predicted early in the course of the disease. End points were selected for the ratio of the arterial oxygen pressure over the fractional concentration of oxygen in the inspired gas (PaO2/FIO2), the arterial oxygen saturation (SaO2), the arterial carbon dioxide tension (PaCO2), and the cardiac index. Patients were assigned to "success" or "failure" groups, according to the values recorded for those end points 24 hours after institution of mechanical ventilation. Values obtained from initiation of mechanical ventilation to 16 hours later were divided into four time groups. Differences between patients who "succeeded" and "failed" were compared at each time interval. Ultimate outcome was also compared. The PaCO2 and cardiac index were poor predictors of survival. Early values did not foretell the progression of these variables. The PaO2/FIO2 and SaO2 effectively discriminated, at all time intervals, between patients who succeeded and failed on volume-cycled ventilation. On high-frequency jet ventilation, significant differences were evident only after eight hours of support. With both types of ventilator, patients who reached the end point of oxygenation at 24 hours survived in far greater numbers than those who did not. On the basis of this investigation, it appears justified to attempt high-frequency jet ventilation in patients who do not rapidly improve on volume-cycled ventilation. Institution of high-frequency jet ventilation as the initial support method may not be advisable, since failure does not become apparent for many hours.

Cardiac Output↗
PubMed2001

Prospective randomized multicenter comparison of high-frequency oscillatory ventilation and conventional ventilation in preterm infants of less than 30 weeks with respiratory distress syndrome.

BACKGROUND: Early use of high-frequency ventilation and exogenous surfactant is proposed as the optimal mode of ventilatory support in infants with respiratory distress syndrome. In very premature infants, we tested the hypothesis that high-frequency versus conventional ventilation could decrease exogenous surfactant requirements and improve pulmonary outcome, without altering the complication rate, including that of severe intraventricular hemorrhage. METHODS: Preterm infants with a postmenstrual age of 24 to 29 weeks, presenting with respiratory distress syndrome were randomly assigned to high-frequency oscillatory ventilation (lung volume recruitment strategy) or conventional ventilation. RESULTS: Two hundred seventy-three infants were enrolled. One hundred fifty-three had a postmenstrual age of 24 to 27 weeks, and 143 had a birth weight </=1000 g. One hundred thirty-four infants were randomized at 142 minutes of life (median) to receive conventional ventilation (mean postmenstrual age at birth: 27. 6 +/- 1.5 weeks; mean birth weight: 997 +/- 245 g); and 139 infants were randomized at 145 minutes of life to receive high-frequency ventilation (mean postmenstrual age at birth: 27.5 +/- 1.4 weeks; mean birth weight: 976 +/- 219 g). High-frequency ventilation, compared with conventional ventilation, was associated with a twofold reduction in the requirement for >/=2 instillations of exogenous surfactant (30% vs 62%; odds ratio:.27; 95% confidence interval:.16-.44) and no difference in pulmonary outcome. The incidence of severe intraventricular hemorrhage was 24% in the high-frequency group and 14% in the conventional ventilation group (adjusted odds ratio: 1.50; 95% confidence interval:.68-3.30). CONCLUSION: Early use of high-frequency oscillatory ventilation in very premature infants decreases exogenous surfactant requirements, does not improve the pulmonary outcome, and may be associated with an increased incidence of severe intraventricular hemorrhage.

Bronchopulmonary Dysplasia↗
PubMed2005

Using ventilator graphics to identify patient-ventilator asynchrony.

Patient-ventilator interaction can be described as the relationship between 2 respiratory pumps: (1) the patient's pulmonary system, which is controlled by the neuromuscular system and influenced by the mechanical characteristics of the lungs and thorax, and (2) the ventilator, which is controlled by the ventilator settings and the function of the flow valve. When the 2 pumps function in synchrony, every phase of the breath is perfectly matched. Anything that upsets the harmony between the 2 pumps results in asynchrony and causes patient discomfort and unnecessarily increases work of breathing. This article discusses asynchrony relative to the 4 phases of a breath and illustrates how asynchrony can be identified with the 3 standard ventilator waveforms: pressure, flow, and volume. The 4 phases of a breath are: (1) The trigger mechanism (ie, initiation of the inspiration), which is influenced by the trigger-sensitivity setting, patient effort, and valve responsiveness. (2) The inspiratory-flow phase. During both volume-controlled and pressure-controlled ventilation the patient's flow demand should be carefully evaluated, using the pressure and flow waveforms. (3) Breath termination (ie, the end of the inspiration). Ideally, the ventilator terminates inspiratory flow in synchrony with the patient's neural timing, but frequently the ventilator terminates inspiration either early or late, relative to the patient's neural timing. During volume-controlled ventilation we can adjust variables that affect inspiratory time (eg, peak flow, tidal volume). During pressure-controlled or pressure-support ventilation we can adjust variables that affect when the inspiration terminates (eg, inspiratory time, expiratory sensitivity). (4) Expiratory phase. Patients with obstructive lung disease are particularly prone to developing intrinsic positive end-expiratory pressure (auto-PEEP) and therefore have difficulty triggering the ventilator. Bedside evaluation for the presence of auto-PEEP should be routinely performed and corrective adjustments made when appropriate.

Data Display↗
PubMed1991

Pulmonary mechanics in preterm neonates with respiratory failure treated with high-frequency oscillatory ventilation compared with conventional mechanical ventilation.

Pulmonary mechanics were measured in 43 preterm neonates (mean +/- SD values of birth weight 1.2 +/- 0.3 kg, gestational age 30 +/- 2 weeks) with respiratory failure who were concurrently randomly assigned to receive conventional mechanical ventilation (n = 22) or high-frequency ventilation (n = 21). The incidence of bronchopulmonary dysplasia was comparable in the two groups (high-frequency ventilation 57%, conventional ventilation 50%). Pulmonary functions were determined at 0.5, 1.0, 2.0, and 4.0 weeks postnatal ages. Data were collected while subjects were in a nonsedated state during spontaneous breathing. These sequential data show similar patterns of change in pulmonary mechanics during high-frequency ventilation and conventional mechanical ventilation irrespective of gestational age, birth weight stratification, or bronchopulmonary dysplasia. There was no significant difference in the pulmonary functions with either mode of ventilation during the acute phase (less than or equal to 4 weeks) of respiratory disease. When evaluated by the clinical diagnosis of bronchopulmonary dysplasia, the pulmonary data suggested a less severe dysfunction in the high-frequency oscillatory ventilation-treated bronchopulmonary dysplasia group compared with the conventional mechanical ventilation-treated group. These results indicate that high-frequency oscillatory ventilation in preterm neonates does not reduce the risk of acute lung injury; however, the magnitude of the pulmonary dysfunction in the first 2 weeks of life merits a reevaluation.

Bronchopulmonary Dysplasia↗
PubMed1990

[Postoperative ventilation in non-intubated patients with iron lung versus conventional ventilation].

Postoperative ventilation using a steel lung is an alternative to conventional ventilation through an endotracheal cannula. Both methods were compared in two groups of patients undergoing major abdominal surgery. Group A was ventilated using a Servo Ventilator 900C, whereas group B was ventilated using a newly designed steel lung. The duration of ventilation using the steel lung and that of postoperative intubation were significantly shorter than those used in group A, in spite of a higher anesthesiological and surgical risk in patients in group B. pO2 was significantly increased during ventilation with the steel lung in comparison to conventional ventilation. An automatic classification of EEG activity was used to estimate depth of anesthesia. This showed a close correlation between clinical signs and anesthesiological levels. The spectroanalytical evaluation of ventilation curves allowed the early recognition of spontaneous breathing and determined tidal volumes using steel lung ventilation.

Aged↗
PubMed2000

Inhaled beta-agonists for asthma in mechanically ventilated patients.

BACKGROUND: A small number of patients with acute severe asthma require intubation and positive pressure ventilation. The beneficial effects of inhaled bronchodilators on acute asthma in spontaneously breathing subjects are well established, but there remain important questions regarding inhaled beta2-agonists, for patients who are intubated and receiving ventilation. OBJECTIVES: To determine the effects of inhaled beta-agonists on asthmatic patients who require intubation and mechanical ventilation. SEARCH STRATEGY: Randomised controlled trials were sought from the Cochrane Airways Group Asthma Register. Primary authors and content experts were contacted to identify eligible studies and bibliographies from known reviews and texts were searched. SELECTION CRITERIA: Randomised, controlled clinical trials involving adult patients with acute asthma, who were intubated and supported with positive pressure ventilation. Studies were to be included if patients were treated with beta2-adrenergic agonist agents and there was a comparator group treated with either placebo, no medication, or 'standard' treatment. DATA COLLECTION AND ANALYSIS: Two reviewers independently examined all identified articles. The full text of any potentially relevant article was reviewed independently by two reviewers. MAIN RESULTS: The search yielded 152 abstracts. Of these, four articles were identified as potential trials. None of the four trials met the inclusion criteria for the review. REVIEWER'S CONCLUSIONS: There are no data from randomised controlled trials to provide evidence for or against current practices regarding the use of inhaled beta2-agonists in asthmatic subjects who are intubated and ventilated.

Acute Disease↗
PubMed1996

The automatic selection of ventilation parameters during the initial phase of mechanical ventilation.

OBJECTIVE: To test a method that allows automatic set-up of the ventilator controls at the onset of ventilation. DESIGN: Prospective randomized crossover study. SETTING: ICUs in one adult and one children's hospital in Switzerland. PATIENTS: Thirty intubated stable, critically ill patients (20 adults and 10 children). INTERVENTIONS: The patients were ventilated during two 20-min periods using a modified Hamilton AMADEUS ventilator. During the control period the ventilator settings were chosen immediately prior to the study. During the other period individual settings were automatically determined by the ventilatior (AutoInit). MEASUREMENTS AND RESULTS: Pressure, flow, and instantaneous CO2 concentration were measured at the airway opening. From these measurements, series dead space (V(DS)), expiratory time constant (RC), tidal volume (VT, total respiratory frequency (f(tot), minute ventilation (MV), and maximal and mean airway pressure (Paw, max and Paw, mean) were calculated. Arterial blood gases were analyzed at the end of each period. Paw, max was significantly less with the AutoInit ventilator settings while f(tot) was significantly greater (P < 0.05). The other values were not statistically significant. CONCLUSIONS: The AutoInit ventilator settings, which were automatically derived, were acceptable for all patients for a period of 20 min and were not found to be inferior to the control ventilator settings. This makes the AutoInit method potentially useful as an automatic start-up procedure for mechanical ventilation.

Adult↗
PubMed2006

Patient-ventilator asynchrony during assisted mechanical ventilation.

OBJECTIVE: The incidence, pathophysiology, and consequences of patient-ventilator asynchrony are poorly known. We assessed the incidence of patient-ventilator asynchrony during assisted mechanical ventilation and we identified associated factors. METHODS: Sixty-two consecutive patients requiring mechanical ventilation for more than 24 h were included prospectively as soon as they triggered all ventilator breaths: assist-control ventilation (ACV) in 11 and pressure-support ventilation (PSV) in 51. MEASUREMENTS: Gross asynchrony detected visually on 30-min recordings of flow and airway pressure was quantified using an asynchrony index. RESULTS: Fifteen patients (24%) had an asynchrony index greater than 10% of respiratory efforts. Ineffective triggering and double-triggering were the two main asynchrony patterns. Asynchrony existed during both ACV and PSV, with a median number of episodes per patient of 72 (range 13-215) vs. 16 (4-47) in 30 min, respectively (p=0.04). Double-triggering was more common during ACV than during PSV, but no difference was found for ineffective triggering. Ineffective triggering was associated with a less sensitive inspiratory trigger, higher level of pressure support (15 cmH(2)O, IQR 12-16, vs. 17.5, IQR 16-20), higher tidal volume, and higher pH. A high incidence of asynchrony was also associated with a longer duration of mechanical ventilation (7.5 days, IQR 3-20, vs. 25.5, IQR 9.5-42.5). CONCLUSIONS: One-fourth of patients exhibit a high incidence of asynchrony during assisted ventilation. Such a high incidence is associated with a prolonged duration of mechanical ventilation. Patients with frequent ineffective triggering may receive excessive levels of ventilatory support.

Aged↗
PubMed2001

The development of ventilator-associated pneumonia does not change aspects of mechanical ventilation.

OBJECTIVE: To evaluate whether the development of ventilator-associated pneumonia (VAP) is associated with changes in ventilation parameters. DESIGN: Matched case-control study. SETTING: Mixed intensive care unit of a university hospital. PATIENTS: From a large database we selected 33 patients with VAP, diagnosed with quantitative cultures of bronchoscopically obtained specimens. In addition, 33 other mechanically ventilated patients who did not develop VAP were selected (controls). Patients with VAP and controls were matched on seven variables representing severity of illness: duration of ventilation until matching, diagnosis on admission, renal function, liver function, preceding infection, preceding surgery and immunosuppressive therapy. Each patient with VAP was matched to a single control. Variables regarding type and mode of ventilation and interpretation of chest radiographs were not included in the matching procedure. MEASUREMENTS AND RESULTS: Characteristics of mechanical ventilation (mode of ventilation, tidal volume, expired minute ventilation, peak airway pressures, mean airway pressures, level of positive end-expiratory pressure, arterial oxygen tension(PaO2)/fractional inspired oxygen (FIO2) ratio), were compared on the day of diagnosis of VAP (or matching for controls) and 2 and 4 days before. Although there was a significant difference in PaO2/FIO2 ratios between cases and controls on the day of diagnosis of VAP, the change in PaO2/FIO2 ratios during the days of study were not statistically different between patients developing VAP and controls. No significant differences were found for any of the other variables of ventilation at any of the three time points studied, nor were there significant differences in changes of these parameters within individual patients. CONCLUSIONS: Characteristics and parameters of mechanical ventilation are not influenced by the development of VAP. It is, therefore, unlikely that these variables are useful in the diagnostic work-up of VAP.

Case-Control Studies↗
PubMed1994

Chronic otitis media requiring ventilation tubes in tracheotomized ventilator dependent children.

The occurrence of sinusitis and middle ear effusions has frequently been attributed to the obstruction of the sinus ostia and/or eustachian tube. In the intensive care unit setting, edema caused by the irritation from nasogastric, nasotracheal and orotracheal tubes has been associated with this pathology and has been responsible for occult sepsis in this population. Our investigation was performed to determine the risk of chronic otitis media with effusion necessitating myringotomy with tympanostomy tubes among tracheotomized, ventilator dependent children in a consecutive series of children admitted to our recently created stable ventilator unit. We retrospectively reviewed the medical records of all tracheotomized, chronically ventilator dependent children < 48 months of age who had been hospitalized in this unit from the initial opening in September 1990 to January 1993. Data collected consisted of patient demographics, gestational age, cognitive abilities, age at onset of mechanical ventilation, age at tracheostomy, age at myringotomy, presence of nasogastric and gastroenterostomy tubes and evidence of gastric-esophageal reflux. All children underwent a tracheostomy procedure subsequent to the onset of mechanical ventilation. Of these patients, 9/12 (75%) later required myringotomy with tympanostomy tube placement following the occurrence of chronic otitis media with effusion. Ventilation tubes for chronic otitis media with effusion were not required in 3 patients. Using a case control study design, we examined the need of myringotomy tubes for children requiring continuous mechanical ventilation versus those requiring night-time only ventilation. The risk of myringotomy tubes in the continuously ventilated group (9/9) was significantly greater than the risk in the intermittently ventilated group (0/3) P < 0.01.(ABSTRACT TRUNCATED AT 250 WORDS)

Case-Control Studies↗
PubMed1994

Ventilation caused by external chest compression is unable to sustain effective gas exchange during CPR: a comparison with mechanical ventilation.

OBJECTIVE: To compare the tidal volume, minute ventilation, and gas exchange caused by mechanical chest compression with and without mechanical ventilatory support during cardiopulmonary resuscitation (CPR) in a laboratory model of cardiac arrest. DESIGN: A laboratory swine model of CPR was used. Eight animals with and eight animals without mechanical ventilation received chest compression (100/min) for 10 min. Coronary perfusion pressure, tidal volume, and minute ventilation were recorded continuously. INTERVENTIONS: Ventricular fibrillation for 6 min without CPR, then mechanical chest compression for 10 min. RESULTS: During the first minute of chest compression, mean (+/- S.D.) minute ventilation was 11.2 +/- 5.9 l/min in the mechanically ventilated group and 4.5 +/- 2.8 l/min in the group without mechanical ventilation (P = 0.01). Minute ventilation gradually declined to 5.8 +/- 1.4 l/min and 1.7 +/- 1.6 l/min, respectively, during the last minute of chest compression (P < 0.0001). After 10 min of chest compression, mean arterial pH was significantly more acidemic in the group without mechanical ventilation (7.16 +/- 0.13 compared with 7.30 +/- 0.07 units) and PCO2 was higher (62 +/- 19 compared with 35 +/- 9 mmHg). Mixed venous PCO2 was also higher (76 +/- 15 compared with 61 +/- 8 mmHg). CONCLUSION: Standard chest compression alone produced measurable tidal volume and minute ventilation. However, after 10 min of chest compression following 6 min of untreated ventricular fibrillation, it failed to sustain pulmonary gas exchange as indicated by significantly greater arterial and mixed venous hypercarbic acidosis when compared with a group receiving mechanical ventilation.

Acid-Base Equilibrium↗
PubMed1991

Measurement of alveolar ventilation and changes in deadspace by indirect calorimetry during mechanical ventilation: a laboratory and clinical validation.

OBJECTIVE: To validate the assessment of changes in alveolar ventilation and deadspace by indirect calorimetry. DESIGN: An open comparison of two methods using a criterion standard. METHODS: Simultaneous measurement of minute ventilation with a metabolic monitor and a pneumotachometer during controlled and synchronized intermittent mandatory ventilation in intensive care patients (n = 14). Measurement of a change in alveolar ventilation with three different tidal volume values in a single-compartment lung model using an added external deadspace. Alveolar ventilation and deadspace/tidal volume were calculated from Bohr's equation using end-tidal PCO2 for the alveolar PCO2 value. RESULTS: The mean differences between minute ventilation measured by a metabolic monitor and minute ventilation measured by a pneumotachometer during controlled and synchronized intermittent mandatory ventilation were -0.04 +/- 0.61 (SD) L and 0.01 +/- 0.85 L, respectively. No significant difference was observed between measurements at the endotracheal tube and the expiratory port of the ventilator. In studies using the lung model, the external deadspace represented 6% to 19% of the three tidal volume measurements. The mean difference between the actual and measured deadspace was 3 +/- 9 mL (8.2 +/- 4.7%), with a slightly, but not significantly, lower precision at the high tidal volume. CONCLUSIONS: Changes in alveolar ventilation and deadspace can be accurately measured by combined use of indirect calorimetry and end-tidal CO2 analysis.

Calorimetry, Indirect↗
PubMed1996

Effects of heat and moisture exchangers on minute ventilation, ventilatory drive, and work of breathing during pressure-support ventilation in acute respiratory failure.

OBJECTIVES: To evaluate the effect of two commonly used heat and moisture exchangers on respiratory function and gas exchange in patients with acute respiratory failure during pressure-support ventilation. DESIGN: Prospective, randomized trial. SETTING: Intensive care unit of a university hospital. PATIENTS: Fourteen patients with moderate acute respiratory failure, receiving pressure-support ventilation. INTERVENTIONS: Patients were assigned randomly to two treatment groups, in which two different heat and moisture exchangers were used: Hygroster (DAR S.p.A., Mirandola, Italy) with higher deadspace and lower resistance (group 1, n = 7), and Hygrobac-S (DAR S.p.A.) with lower deadspace and higher resistance (group 2, n = 7). Patients were assessed at three pressure-support levels: a) baseline (10.3 +/- 2.4 cm H2O for group 1, 9.3 +/- 1.3 cm H2O for group 2); b) 5 cm H2O above baseline; and c) 5 cm H2O below baseline. Measurements obtained with the heat and moisture exchangers were compared with those values obtained using the standard heated hot water humidifier. MEASUREMENTS AND MAIN RESULTS: At baseline pressure-support ventilation, the insertion of both heat and moisture exchangers induced in all patients a significant increase in the following parameters: minute ventilation (12.4 +/- 3.2 to 15.0 +/- 2.6 L/min for group 1, and 11.8 +/- 3.6 to 14.2 +/- 3.5 L/min for group 2); static intrinsic positive end-expiratory pressure (2.9 +/- 2.0 to 5.1 +/- 3.2 cm H2O for group 1, and 2.9 +/- 1.7 to 5.5 +/- 3.0 cm H2O for group 2); ventilatory drive, expressed as P41 (2.7 +/- 2.0 to 5.2 +/- 4.0 cm H2O for group 1, and 3.3 +/- 2.0 to 5.3 +/- 3.0 cm H2O for group 2); and work of breathing, expressed as either power (8.8 +/- 9.4 to 14.5 +/- 10.3 joule/ min for group 1, and 10.5 +/- 7.4 to 16.6 +/- 11.0 joule/min for group 2) or work per liter of ventilation (0.6 +/- 0.6 to 1.0 +/- 0.7 joule/L for group 1, and 0.8 +/- 0.4 to 1.1 +/- 0.5 joule/L. for group 2). These increases also occurred when pressure-support ventilation was both above and below the baseline level, although at high pressure support the increase in work of breathing with heat and moisture exchangers was less evident. Gas exchange was unaffected by heat and moisture exchangers, as minute ventilation increased to compensate for the higher deadspace produced in the circuit by the insertion of heat and moisture exchangers. CONCLUSIONS: The tested heat and moisture exchangers should be used carefully in patients with acute respiratory failure during pressure-support ventilation, since these devices substantially increase minute ventilation, ventilatory drive, and work of breathing. However, an increase in pressure-support ventilation (5 to 10 cm H2O) may compensate for the increased work of breathing.

Acute Disease↗