Intratracheal pulmonary ventilation at low airway pressures in a ventilator-induced model of acute respiratory failure improves lung function and survival.

STUDY OBJECTIVE: The pulmonary parenchyma in patients with acute respiratory failure (ARF) is commonly not involved in a homogenous disease process. Conventional mechanical ventilation (MV) at elevated positive end-expiratory pressure (PEEP) and peak inspiratory pressure (PIP) aims at recruiting collapsed or nonventilated lung units. Invariably, those pressures are also transmitted to the healthiest regions, with possible extension of the disease process (barotrauma). During intratracheal pulmonary ventilation (ITPV), a continuous flow of fresh gas is delivered directly at the carina, bypassing the dead space proximal to the catheter tip. In healthy sheep, it allows lowering tidal volume (VT) to as low as 1.0 mL/kg, at respiratory rates (RR) up to 120 breaths/min, while maintaining normocapnia. In a model of ventilator-induced lung injury, we wished to explore whether ITPV, applied at low VT and low PEEP and tailored to ventilate the healthiest regions of the lungs, could provide adequate oxygenation and alveolar ventilation, without any attempt to recruit lungs. DESIGN: Randomized study in sheep. SETTING: Animal research laboratory. PARTICIPANTS: We induced ARF in 12 sheep following 1 to 2 days of MV at a PIP of 50 cm H2O, except that 5 to 8% of lungs were kept on apneic oxygenation of 5 cm H2O, sparing those regions from the injury process. INTERVENTIONS: Sheep were randomized to volume-controlled MV (control group) (n = 6) with VT of 8 to 12 mL/kg, PEEP of 5 to 10 cm H2O, or to ITPV (n = 6) at PEEP of 3 to 5 cm H2O, VT of 2.5 to 4 mL/kg, PIP of <20 cm H2O, at RRs sufficient to sustain normocapnia. MEASUREMENTS AND RESULTS: Hemodynamic status in the ITPV group progressively improved, and all six sheep were weaned to room air within 83+/-54 h. Sheep in the control group had progressively deteriorating conditions and all animals died after a mean of 50+/-39 h. Barotrauma and postmortem histopathologic changes were more pronounced in the control group. CONCLUSION: In this model of ventilator-induced lung injury, low PEEP-low VT ventilation with ITPV sustained normocapnia and prevented further lung injury, allowing weaning to room air ventilation.

Design and development of ultrathin-walled, nonkinking endotracheal tubes of a new "no-pressure" laryngeal seal design. A preliminary report.

BACKGROUND: Endotracheal tubes (ETTs) of conventional design and manufacture greatly increase the air-flow resistance of the upper airways. This increase in upper-airway resistance can lead to a significant increase in the work of breathing and may necessitate the use of assisted mechanical ventilation. Current ETTs are relatively stiff and contribute greatly to patient discomfort. The inflatable cuffs now mounted onto the ETTs function well in short-term use but impart significant morbidity when used over longer periods. These issues were addressed by the designing of a low-resistance ETT. METHODS: Using new techniques, we developed ultrathin-walled, wire reinforced ETTs of conventional configuration and ETTs the oropharyngeal-section diameter of which was a few millimeters larger than the diameter of the tracheal section. The wall thickness was a constant 0.20 mm. The wire reinforcement was stainless steel flat wire or superelastic nickel-titanium alloy. The superelastic nickel-titanium alloy reinforcement made those ETTs crush-proof; after forceful manual compression, recovery was complete. To obtain a seal with the upper airways, we first shaped a short section of the oropharyngeal section of the ETT from round to oval (or egg-shaped) to conform better to the larynx. We then attached to this segment numerous soft, pliable, 0.025-0.075-mm-thick rings of polyurethane to occlude voids for potential air leaks from within the larynx. RESULTS: In vitro pressure-flow studies showed a decrease by as much as four- or fivefold in air-flow resistance in the adult ETT range, effectively increasing the internal diameter by 2.3-3.7 mm, compared with conventional ETTs of the same outside diameter. In vivo studies for 24 h in sheep showed no air leaks at airway pressures to 30 cmH2O and minimal leak at greater pressures. The gross appearance of the trachea was normal. CONCLUSIONS: Although the new tubes appear to offer advantages to those currently used, testing in humans is required to assess the clinical utility of the tube-cuff design.

Intratracheal pulmonary ventilation (ITPV): control of positive end-expiratory pressure at the level of the carina through the use of a novel ITPV catheter design.

A new mode of pulmonary ventilation called intratracheal pulmonary ventilation (ITPV) was studied. Briefly, a continuous flow of air/oxygen is introduced through a small catheter, the tip of which is positioned at the carina, with a diffuser mounted at its distal end. A timed expiration valve, when closed, provides for inspiration; when open, it provides for expiration. The system as first described had a potential for significant back pressure at the level of the carina, which was more at rapid gas flows and with smaller endotracheal tubes. We have now mounted a venturi on the tip of the catheter (reverse thrust catheter [RTC]) that avoids back pressure, and which facilitates expiration. At respiratory rates from 10 to 120/min, the ITPV system with the RTC maintained end-expiratory pressure at the level of the carina at, or near 0 cm H2O. Compared to conventional mechanical ventilation, at identical respiratory rates, this system reduced tidal volume by one half at the lowest respiratory rates, and by as much as two thirds at the highest respiratory rates, with a proportional decrease in peak inspiratory pressure. ITPV has the smallest minute volume ventilation of any conventional or nonconventional mode of pulmonary ventilation.

A new ultrathin-walled, non-kinking, low-resistance endotracheal tube for neonatal use: preliminary studies of a new no-pressure cuff.

Using a new technology, the authors fabricated a series of ultrathin-walled, non-kinking, wire-reinforced polyurethane endotracheal (ET) tubes for use in the newborn, with a wall thickness of 0.2 mm from the smallest to the largest ET tubes (one-stage tubes), as well as two-stage ET tubes, with the tracheal section of smaller diameter than the oropharyngeal section. The wire reinforcement consisted of 0.1-mm x 0.5-mm stainless steel 304 flat wire; to impart crush-proof features, some ET tubes were reinforced with Nitinol (nickel-titanium shape-memory alloy) wire. Circular layers of highly pliable polyurethane film ("gills"), 0.025 mm thick, in series, were then incorporated onto the distal sections of the ET tubes to reduce potential air leakage (no-pressure cuff). In-vitro pressure-flow measurements showed a sixfold-to-ninefold decrease in airflow resistance for the two-stage ET tubes, compared with standard tubes. For example, a two-stage ET tube of the new design with the outside diameter of a standard 2.5-mm ET tube has the airflow resistance of a hypothetical conventional 4.2-mm ET tube, while a straight ET tube with a similar thin wall and the same outside diameter throughout (one-stage ET tube) has the resistance of an imputed 3.2-mm standard ET tube, or a twofold-to-threefold decrease in air flow resistance. When tested in a 4-kg rabbit, the air leak of the 2.5-mm two-stage ET tube with "gills" and the outside diameter of a standard 2.5-mm ET tube was much less than that of a standard 2.5-mm ET tube, and was similar to the air leak found with a 4.0-mm ET tube of conventional design (without cuff). The authors conclude that the new ET tubes have a greatly reduced air flow resistance compared with conventional ET tubes; they provide enhanced sealing from possible air leaks; they are non-kinking and crush-resistant; and they are crush-proof when used with Nitinol wire reinforcement.

How to ventilate lungs as small as 12.5% of normal: the new technique of intratracheal pulmonary ventilation.

We wished to determine in a laboratory animal model how much residual lung was needed to sustain total gas exchange. In a series of young, healthy lambs weighing approximately 10 kg that were sedated and paralyzed, we progressively excluded from gas exchange all the left lung (a total of 43%), plus the right lower and cardiac lobes (81%), plus the right middle lobe (87.5%). In some studies, the respective lobes were surgically removed; in others, the bronchi and the pulmonary arteries to the respective lobes were ligated. We provided pulmonary ventilation using the pressure control mode (Servo 900 C) at a tidal volume of 20 mL/kg multiplied by the fraction of the remaining lungs, a respiratory rate up to 120/min, a peak inspiratory pressure of 12-15 cm H2O, and a positive end-expiratory pressure of 3 cm H2O. Those lambs with at least both the right upper lobe (RUL) and right middle lobe remaining (19% of total lungs) were weaned to room air on mechanical ventilation within 48 h. Ventilating RUL (12.5% of remaining lung) with the same ventilator required a substantially higher tidal volume and peak inspiratory pressure to result in adequate alveolar ventilation but led to respiratory failure and death within 8 h. We then applied a newly developed system of intratracheal pulmonary ventilation to ventilate the RUL (12.5% of remaining lung) alone. A continuous flow of humidified mixture of air and oxygen was directly passed into the trachea at the level of the carina through a diffuser at a tidal volume of 2.5 mL/kg. A single valve controlled expiration and respiratory rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Respiratory mechanics and bronchodilator responsiveness in patients with the adult respiratory distress syndrome.

OBJECTIVE: To study the effects of salbutamol (a selective beta 2-adrenergic receptor agonist) on respiratory mechanics in patients with the adult respiratory distress syndrome (ARDS). DESIGN: Prospective study. SETTING: ICU in a university hospital. PATIENTS: Seven mechanically ventilated, paralyzed ARDS patients. MAIN OUTCOME MEASUREMENTS: Measurements of respiratory system compliance, maximum, and minimum inspiratory resistance (by the end-inspiratory occlusion method during constant flow inflation) were performed at 0, 5, 10 cm H2O positive end-expiratory pressure, both before and at least 30 mins after the start of a continuous iv infusion of salbutamol (15 micrograms/min). Minimum inspiratory resistance represents the ohmic air flow resistance, while maximum inspiratory resistance includes minimum inspiratory resistance plus the effective additional resistance due to stress adaptation and to time constant inhomogeneities. Air flow was measured at the airway connector and tracheal pressure near the central end of the artificial airway. RESULTS: Maximum inspiratory resistance, minimum inspiratory resistance, and additional resistance were higher than the values reported for normal anesthetized subjects. On average, salbutamol caused a decrease in maximum and minimum inspiratory resistances (from 6.48 +/- 2.56 to 4.67 +/- 1.74 and from 4.06 +/- 2.12 to 2.07 +/- 0.95 cm H2O/L/sec, respectively). Positive end-expiratory pressure increased additional resistance, whereas it decreased minimum inspiratory resistance. No interaction was found between positive end-expiratory pressure and salbutamol. Respiratory system compliance was not significantly affected by salbutamol nor by positive end-expiratory pressure. CONCLUSIONS: In ARDS patients, salbutamol decreases the abnormally high airway resistance, by reducing minimum resistance, but has no effect on the effective additional resistance.