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PubMed2002

Automatic tube compensation-assisted respiratory rate to tidal volume ratio improves the prediction of weaning outcome.

OBJECTIVE: To assess whether the respiratory rate to tidal volume ratio (RVR) measured while receiving automatic tube compensation (ATC) [RVRATC] would have a better predictive value as a weaning measure than unassisted RVR. DESIGN: Prospective cohort study. SETTING: General ICU of a tertiary-care university hospital. PATIENTS: Forty-three patients who received mechanical ventilation for > 24 h and were considered ready for weaning. INTERVENTIONS: All patients underwent a 60-min spontaneous breathing trial (SBT) [positive end-expiratory pressure of 5 cm H(2)O; ATC, 100%]. Patients tolerating the trial (n = 35) were extubated immediately. The following parameters were measured at the onset and end of the SBT: RVR, RVRATC, peak airway pressure (Paw), airway occlusion pressure, and minute ventilation. The outcome measure was successful extubation (ability to maintain spontaneous breathing for > 48 h). MEASUREMENTS AND RESULTS: Median age was 55 years (range, 25 to 88 years), median APACHE (acute physiology and chronic health evaluation) II score was 15.5 (range, 3 to 29), and median duration of mechanical ventilation prior to the SBT was 7 days (range, 1 to 40 days). Extubation was successful in 25 patients (72%). There were no significant differences in baseline characteristics between patients successfully extubated (group 1) and those requiring reintubation. On multivariate analysis, RVRATC measured at 60 min (RVR(60)ATC) was most predictive of successful extubation (p = 0.03). The area under the receiver operator characteristic curve was also highest for RVR(60)ATC (0.81 +/- 0.03) as compared to RVR (0.77 +/- 0.03), RVRATC (0.75 +/- 0.04), and RVR measured at 60 min (0.69 +/- 0.05). The ratio of RVR(60)ATC to Paw was the best predictor (0.84 +/- 0.02). CONCLUSIONS: RVRATC measured at the end of the SBT was the best predictor of successful extubation. A new ratio (ratio of RVRATC to Paw) was most predictive and deserves further study.

Adult↗
PubMed1986

Effect of tidal volume and anesthetic agent on airway responsiveness to histamine.

Dose-response relationships for bronchoconstriction in response to aerosal histamine were assessed before and after vagotomy in 11 dogs anesthetized with barbiturates and in 9 dogs anesthetized with alpha-chloralose-urethan. The dose-response relationships following vagotomy were assessed during spontaneous ventilation and during muscular paralysis and mechanical ventilation with tidal volume (VT) similar to each animal's VT prior to vagotomy. After vagotomy the spontaneous VT of both groups increased but the VT of the alpha-chloralose-urethan group was significantly less than that of the barbiturate group. The histamine responsiveness of the animals anesthetized with barbiturates was significantly greater during mechanical ventilation when VT was reduced to prevagotomy levels compared with during spontaneous ventilation. In contrast, the histamine responsiveness of the alpha-chloralose-urethan group was not significantly changed by reducing VT to prevagotomy levels. In six other dogs anesthetized with pentobarbital sodium and studied after vagotomy, responsiveness to histamine aerosol during controlled ventilation with breaths of prevagotomy VT was greater than responsiveness during mechanical ventilation with large volume breaths given immediately afterward. Thus the magnitude of VT of dogs after vagotomy may influence airway responsiveness, and the influence of anesthetic agents on airway responsiveness after vagotomy may in part be due to their effects on VT. Furthermore, bronchodilation accompanying large volume ventilation persists after vagotomy, suggesting that it is not exclusively mediated by changes in parasympathetic activity.

Airway Resistance↗
PubMed1985

Lung mechanical profiles in acute respiratory failure: diagnostic and prognostic value of compliance at different tidal volumes.

The mean airway pressure difference within a respiratory cycle at end-inspiration was measured at different tidal volumes (VT) in 59 patients treated with mechanical ventilation, and plotted in a pressure-volume (P-V) diagram. Regression analysis revealed three types of regression lines which were clearly correlated with clinical pulmonary condition and outcome. The slope of such regression lines may be a more realistic representation of lung elasticity than conventional total static compliance, which is measured at only one VT, and the intercept of these lines may be a more appropriate reflection of operating lung volume than functional residual capacity. Ventilator settings should put the patient's lungs on the steepest part of the P-V curve with the smallest intercept, while maintaining acceptable arterial blood gas tensions.

Adult↗
PubMed2005

Large tidal volume mechanical ventilation induces vascular dysfunction in rats.

BACKGROUND: Experimental studies have shown that mechanical ventilation using high tidal volumes (V(T)) damages the lungs, causing pulmonary edema. We tested the hypothesis that high V(T) ventilation in rats induces major vascular dysfunction. METHODS: Healthy Sprague-Dawley rats, weighing (mean +/- SD) 340 +/- 15 g, were ventilated with either V(T) = 9 mL/kg and positive end-expiratory pressure (PEEP) = 8 (n = 8) or V(T) = 35 mL/kg and PEEP = 0 (n = 8). The high V(T) used in the injurious ventilation group is in the V(T) range used in other studies to induce lung damage in a short period of time in rats. Lungs were removed for examination under light microscopy and vascular rings from the thoracic aorta were studied for isometric tension recording. RESULTS: Relaxations to acetylcholine (p < 0.001) and sodium nitroprusside (p < 0.05) and contractions to norepinephrine were markedly decreased (p < 0.001) in the high V(T) group, as compared with the low V(T) group. CONCLUSION: Injurious mechanical ventilation in normal rats is associated with vascular dysfunction characterized by decreased relaxation to an endothelium-dependent vasodilator and to a nitrous oxide donor and by decreased response to norepinephrine.

Analysis of Variance↗
PubMed2005

Effect of tidal volume and respiratory rate on the power of breathing calculation.

BACKGROUND: The power of breathing (PoB) is used to estimate the mechanical workload of the respiratory system. Aim of this study was to investigate the effect of different tidal volume-respiratory rate combinations on the PoB when the elastic load is constant. In order to assure strict control of the experimental conditions, the PoB was calculated on an airway pressure-volume curve in mechanically ventilated patients. METHODS: Ten patients received three different tidal volume-respiratory rate combinations while minute ventilation was constant. Respiratory mechanics, PoB and its elastic and resistive components were calculated. Alternative methods to estimate the elastic workload were assessed: elastic work of breathing per litre per minute, elastic workload index (the square root of elastic work of breathing multiplied by respiratory rate) and elastic double product of the respiratory system (the elastic pressure multiplied by respiratory rate). RESULTS: Despite constant elastance and minute ventilation, the elastic PoB showed an increment greater than 200% from the lower to the greater tidal volume, accounting for approximately 80% of the whole PoB increment. On the contrary, elastic work of breathing per litre per minute, elastic workload index and elastic double product did not change. CONCLUSION: Changes in breathing pattern markedly affect the PoB despite constant mechanical load. Other indexes could assess the elastic workload without tidal volume dependence. Power of breathing use should be avoided to compare different mechanical loads or efficiencies of the respiratory muscles when tidal volume is variable.

Aged↗
PubMed1999

Lung recruitment during small tidal volume ventilation allows minimal positive end-expiratory pressure without augmenting lung injury.

OBJECTIVES: Ventilation with positive end-expiratory pressure (PEEP) above the inflection point (P(inf)) has been shown to reduce lung injury by recruiting previously closed alveolar regions; however, it carries the risk of hyperinflating the lungs. The present study examined the hypothesis that a new strategy of recruiting the lung with a sustained inflation (SI), followed by ventilation with small tidal volumes, would allow the maintenance of low PEEP levels ( P(inf). MEASUREMENTS AND MAIN RESULTS: In groups 2 and 4, static compliance decreased after ventilation (p < .01). Histologically, group 2 (PEEP < P(inf) without SI) showed significantly greater injury of small airways, but not of terminal respiratory units, compared with group 1. Group 3 (PEEP < P(inf) after a SI), but not group 4, showed significantly less injury of small airways and terminal respiratory units compared with group 2. CONCLUSIONS: We conclude that small tidal volume ventilation after a recruitment maneuver allows ventilation on the deflation limb of the pressure/volume curve of the lungs at a PEEP < P(inf). This strategy a) minimizes lung injury as well as, or better than, use of PEEP > P(inf), and b) ensures a lower PEEP, which may minimize the detrimental consequences of high lung volume ventilation.

Analysis of Variance↗
PubMed2000

Tidal volumes for ventilated infants should be determined with a pneumotachometer placed at the endotracheal tube.

Many ventilators measure expired tidal volume (VT) without compensation either for the compliance of the ventilator circuit or for variations in the circuit setup. We hypothesized that the exhaled VT measured with a conventional ventilator at the expiratory valve would differ significantly from the exhaled VT measured with a pneumotachometer placed at the endotracheal tube. To investigate this we studied 98 infants and children requiring conventional ventilation. We used linear regression analysis to compare the VT obtained with the pneumotachometer with the ventilator-measured volume. An additional comparison was made between the pneumotachometer volume and a calculated effective VT. For infant circuits (n = 70), our analysis revealed a poor correlation between the expiratory VT measured with the pneumotachometer and the ventilator-measured volume (r(2) = 0.54). Similarly, the expiratory VT measured with the pneumotachometer did not correlate with the calculated effective volume (r(2) = 0.58). For pediatric circuits (n = 28), there was improved correlation between the expiratory VT measured with the pneumotachometer and both the ventilator-measured volume and the calculated effective VT (r(2) = 0.84 and r(2) = 0.85, respectively). The data demonstrate a significant discrepancy between expiratory VT measured at a ventilator and that measured with a pneumotachometer placed at the endotracheal tube in infants. Correcting for the compliance of the ventilator circuit by calculating the effective VT did not alter this discrepancy. In conventionally ventilated infants, exhaled VT should be determined with a pneumotachometer placed at the airway.

Analysis of Variance↗
PubMed1989

High tidal volume ventilation produces increased lung water in oleic acid-injured rabbit lungs.

Repeated lung inflation with very high tidal volumes (VT) is associated with the production of permeability pulmonary edema in animal models using previously normal lungs. We studied the effect of mechanical ventilation, at VT values approaching those used clinically, on lung weight gain (lung water) in salt-perfused rabbit lungs diffusely injured by the administration of oleic acid. Lungs ventilated at a VT of 18 ml/kg gained significantly more weight at 30 through 90 min than did lungs ventilated at 6 ml/kg. These differences in weight gain were not associated with differences in the evolution of thromboxane B2 in the perfusate. The impact of VT on lung water and outcome in patients with lung injury deserves further study.

Animals↗
PubMed2001

Lung collapse during low tidal volume ventilation in acute respiratory distress syndrome.

BACKGROUND: Current ventilator management for acute respiratory distress syndrome (ARDS) incorporates low tidal volume (V(T)) ventilation in order to limit ventilator-induced lung injury. Low V(T) ventilation in supine patients, without the use of intermittent hyperinflations, may cause small airway closure, progressive atelectasis, and secretion retention. Use of high positive end-expiratory pressure (PEEP) levels with low V(T) ventilation may not counter this effect, because regional differences in intra-abdominal hydrostatic pressure may diminish the volume-stabilizing effects of PEEP. CASE SUMMARY: A 35-year-old man with abdominal compartment syndrome (intra-abdominal pressure > 48 cm H2O developed ARDS and was treated with V(T) of 4.5 mL/kg and PEEP of 20 cm H2O. Despite aggressive fluid therapy, appropriate airway humidification and tracheal suctioning, the patient developed complete bronchial obstruction, involving the entire right lung and left upper lobe. After bronchoscopy the patient was placed on a higher V(T) (7.0 mL/kg). Intermittent PEEP was instituted at 30 cm H2O for 2 breaths every 3 minutes. This intermittently raised the end-inspiratory plateau pressure from 38 cm H2O to 50 cm H2O. With the same airway humidity and tracheal suctioning practices bronchial obstruction did not reoccur. CONCLUSION: Low V(T) ventilation in ARDS may increase the risk of small airway closure and retained secretions. This adverse effect highlights the importance of pulmonary hygiene measures in ARDS during lung-protective ventilation.

Adult↗
PubMed2006

An audible indication of exhalation increases delivered tidal volume during bag valve mask ventilation of a patient simulator.

Self-inflating manual resuscitators (SIMRs) can mislead caregivers because the bag, unlike a Mapleson-type device, reinflates even without patient exhalation. We added a whistle as an audible indicator to the exhalation port of a SIMR. In randomized order, each participant provided two sets of breaths via mask ventilation with a SIMR, one with and one without audible feedback, to a Human Patient Simulator modified to log lung volume changes. The last three breaths in each set were used to compare average tidal volume (Vt) under both conditions. Eighty-seven advanced cardiac life support trainees (54 males, 33 females) with clinical experience averaging 6.4 +/- 9.4 yr were recruited. Average Vt delivered with the standard SIMR was 486 +/- 166 mL and 624 +/- 96 mL with the modified SIMR. Average Vt delivered by a modified SIMR was significantly larger by 40% when it followed standard SIMR use and 19% when using the modified SIMR first. Use of a SIMR with an audible indicator of exhalation significantly (P < 0.001) increased mask ventilation of a patient simulator, suggesting that mask ventilation of a patient with a SIMR may also be increased by objective, real-time feedback of exhaled Vt.

Acoustic Stimulation↗
PubMed1990

Are low tidal volumes safe?

High airway pressure may be injurious to lung parenchyma, but lowering airway pressure using conventional mechanical ventilation necessitates lowering tidal volume (VT). Intubated patients in the surgical intensive care unit (SICU) were randomly assigned to group 1 (VT = 12 ml/kg, n = 56) or group 2 (VT = 6 ml/kg, n = 47). Variables recorded included acute physiology and chronic health evaluation (APACHE II) score, mean peak airway pressure (MPAP), mean PaO2/FIO2, incidence of pulmonary infectious complications (PIC), duration of intubation (DOI), and duration of SICU stay (DOS). Results in the table are means +/- SE. (table; see text) The incidence of pulmonary infection tended to be lower and DOI and DOS tended to be shorter for nonneurosurgical and noncardiac surgical patients randomized to low VT, suggesting that morbidity may be decreased. The use of low VT was associated with a statistically significant but clinically irrelevant decrease in oxygenation. The routine use of low VT appeared to be safe in a selected population of patients in the SICU.

Female↗
PubMed2005

Effects of tidal volume and respiratory frequency on lung lymph flow.

Ventilation (V) increases lung lymph flow (Ql), but the separate effects of tidal volume (Vt) and frequency (f) and the role of V-induced changes in edema formation are poorly understood. An isolated, in situ sheep lung preparation was used to examine these effects. In eight sheep with f = 10 min(-1), results obtained during 30-min periods with Vt = 5 or 20 ml/kg were compared with values obtained during bracketed 30-min control periods (Vt = 12.5 ml/kg). Eight other sheep with constant Vt (12.5 ml/kg) were studied at f = 5 or 20 min(-1) and compared with f = 10 min(-1). Three additional groups of six sheep were perfused for 100 min with control V (10 ml/kg, 10 min(-1)). Vt was then kept constant or changed to 20 or 3 ml/kg during a second 100-min period. Increases in Vt or f increased Ql and vice versa, without corresponding effects on the rate of edema formation. For the same change in V, changing Vt had a greater effect on Ql than changing f. The change in Ql caused by an increase in Vt was significantly greater after the accumulation of interstitial edema. The change in Ql caused by a sustained increase in Vt was transient and did not correlate with the rate of edema formation, suggesting that V altered Ql through direct mechanical effects on edema-filled compartments and lymphatic vessels rather than through V-induced changes in fluid filtration.

Animals↗
PubMed2005

[Effects of recruitment maneuvers with low tidal volume ventilation in patients with acute respiratory distress syndrome].

OBJECTIVE: To assess the effects of recruitment maneuvers (RMs) with low tidal volume (V(T)) ventilation on gas oxygenation and reduction of ventilation-associated lung injury (VALI) in patients suffering from acute respiratory distress syndrome (ARDS), to assess the effects of RMs on blood pressure, heart rate and occurrence of barotrauma. METHODS: Patients in intensive care unit (ICU) of Beijing Fuxing Hospital were randomized into two groups: low V(T)+RM group and low V(T) without RM group (non-RM group). Twenty-eight patients with early ARDS admitted from January 2003 to March 2004 were enrolled in the study. All patients received protective ventilation: V(T) was set at 6 ml/kg with plateau pressure limited at 30 cm H(2)O (1 cm H(2)O=0.098 kPa) or lower, positive end-expiratory pressure (PEEP) and fraction of inspired oxygen (FiO(2)) were set to obtain an partial pressure of arterial oxygen (PaO(2)) between 60 to 80 mm Hg (1 mm Hg=0.133 kPa). RMs were conducted by regulating FiO(2) to 1.00, applying 40 cm H(2)O of continuous positive airway pressure (CPAP) for 40 seconds, and then resumed the previous ventilator settings (mode, PEEP, and FiO(2)). This modality was repeated once every 8 hours for a total of 5 days. Measurements of PaO(2)/FiO(2), serum interleukin-6 (IL-6) concentration, respiratory and radiographic data, and ventilatory parameters were obtained at baseline and for the first 5 days. Mean arterial pressure and heart rate and pulse oxygen saturation (SpO(2)) were measured before and after the RM. The primary outcome was mortality at 28 days. RESULTS: (1) After RM, PaO(2)/FiO(2) and PaO(2) in RM group and non-RM group increased, but the values were higher in RM group, and the difference between two groups was significant (all P<0.05). (2) IL-6 concentrations decreased in both groups but lower in RM group with significant difference (P<0.05). (3) Barotrauma did not occur in both groups. (4) No significant changes in blood pressure and heart rate were found during RMs. HR and MAP remained unchanged after RM. CONCLUSION: RM could recruit the collapsed alveoli in ARDS. It could significantly improve oxygenation and decrease VALI. A superimposed RM is safe, and repeated RM could also decrease barotrauma.

Female↗
PubMed1980

Barometric measurement of tidal volume: effects of pattern and nasal temperature.

The accuracy of the formula derived by Drorbaugh and Fenn (Pediatrics 16: 81-86, 1955) for calculating tidal volume (VT) from the phasic pressure change measured when an animal breathes in a closed chamber has recently been challenged. Epstein and Epstein (Respir. Physiol. 32: 105-120, 1978) argue that the formula may underestimate VT by up to 30% and predict that the error increases as the ratio of inspiratory duration (TI) to total breath duration (Ttot) increases, and as the expired temperature at the nares (TN) increases. To test their theory, I measured VT in anesthetized rats by the barometric technique and by conventional pneumotachography simultaneously. TN was varied from ambient to body temperature by passing a variable current through the pneumotachograph heater; TI/Ttot was varied by changing FICO2 and by selecting different rats. The predictions were confirmed. A factor is derived for retrospectively correcting VT estimated by the Drorbaugh-Fenn formula. It requires knowledge of TN and TI/Ttot and reduces the error between experiments to under 20% and within each experiment to about 5%. To facilitate its use, TN was measured in rat, rabbit, cat, man, and infant pigtail monkey.

Animals↗
PubMed1999

Smaller tidal volumes during cardiopulmonary resuscitation: comparison of adult and paediatric self-inflatable bags with three different ventilatory devices.

Gastric inflation and subsequent regurgitation of stomach contents is a major hazard of bag-valve-face mask ventilation during the basic life support phase of cardiopulmonary resuscitation (CPR). Recent investigations suggested that use of a paediatric self-inflating bag may reduce stomach inflation while ensuring sufficient lung ventilation. The purpose of our study was to examine whether use of a paediatric self-inflating bag in association with laryngeal mask airway, combitube, and bag-valve-face mask may provide adequate lung ventilation, while reducing the risk of gastric inflation in a bench model simulating the initial phase of CPR. Sixteen intensive care unit registered nurses volunteered for our study. Use of a paediatric versus adult self-inflating bag resulted in a significantly (P < 0.01) lower mean (+/- S.D.) tidal lung volume with both the laryngeal mask airway and combitube (laryngeal mask airway 349 +/- 149 ml versus 725 +/- 266 ml, combitube 389 +/- 113 ml versus 1061 +/- 451 ml). Lung tidal volumes were below the European Resuscitation Council recommendation with both self-inflatable bags in the bag-valve-face mask group (paediatric versus adult self-inflatable bag 256 +/- 77 ml versus 334 +/- 125 ml). Esophageal tidal volumes were significantly (P < 0.05) lower using the paediatric self-inflatable bag in the bag-valve-face mask group; almost no gastric inflation occurred with the laryngeal mask airway, and none with the combitube. In conclusion, use of the paediatric self-inflating bag may reduce gastric inflation, but measured lung tidal volumes are below the European Resuscitation Council recommendation when used with either, the laryngeal mask airway, combitube, or bag-valve-face mask.

Adult↗
PubMedDate not supplied

Aerosol inhalation and depth of deposition in the human lung. The effect of airway obstruction and tidal volume inhaled.

Ten patients with chronic bronchitis, whose FEV1.0 varied between 0.48 and 3.00 1, inhaled uniform 5-micronm particles tagged with technetium-99 in tidal volumes (VT) varying between 750 and 1830 ml. Their chests were scanned after inhalation to ascertain depth of deposition of the particles, and clearance from the lungs was monitored for 5 hr by serial whole-lung gamma counting. A significant inverse relationship (P less than .05) was found between depth of deposition after inhalation (D), measured horizontally across the lung as percentage per inch, and rate of clearance of the particles (5-hr retention [%] = 100- % cleared at 5 hr=69.12-3.02D). This confirmed previous findings. The depth of deposition depended directly on the FEV1.0 and VT (5-hr retention [%] = 0.026VT + 12.67FEV1.0-4.13); this resulted in a 14%-75% range for 5-hr retention. Regression slopes for VT and FEV1.0 were independently significant (P less than .05). The findings suggest that, as commonly administered at present, the therapeutic efficiency of most drugs given be aerosol will be reduced in proportion to the degree of airway obstruction as measured by the FEV1.0. The efficiency can be enhanced by increasing the depth of inspiration of the aerosol.

Aerosols↗