Continuous Tracheal Gas Insufflation Research Articles

Instrumental dead space: A glass ceiling for extremely low birth weight preterm infants? A dead space washout bench study.

When ventilating extremely low birth weight infants, clinicians face the problem of instrumental dead space, which is often larger than tidal volume. Hence, aggressive ventilation is necessary to achieve CO2 removal. Continuous tracheal gas insufflation can wash out CO2 from dead space and might also have an impact on O2 and water vapor transport. The objective of this bench study is to test the impact of instrumental dead space on the transport of CO2 , O2 , and water vapor and the ability of continuous tracheal gas insufflation to remedy this problem during small tidal volume ventilation. A test-lung located in an incubator at 37°C was ventilated with pressure levels needed to reach different tidal volumes from 1.5to 5 mL. End-tidal CO2 at the test-lung exit, O2 concentration, and relative humidity in the test-lung were measured for each tidal volume with and without a 0.2 L/min continuous tracheal gas insufflation flow. CO2 clearance was improved by continuous tracheal gas insufflation allowing a 28%-44% of tidal volume reduction. With continuous tracheal gas insufflation, time to reach desired O2 concentration was reduced from 20% to 80% and relative humidity was restored. These results are inversely related to tidal volume and are particularly critical below 3 mL. For the smallest tidal volumes, reduction of instrumental dead space seems mandatory for CO2 , O2 , and water vapor transfer. Continuous tracheal gas insufflation improved CO2 clearance, time to reach desired O2 concentration and humidification of airways and, thus, may be an option to protect lung development.

Tracheal gas insufflation with partial liquid ventilation to treat LPS‐induced acute lung injury in juvenile piglets

Partial liquid ventilation (PLV) with perfluorocarbons (PFC) seems not superior to conventional ventilation clinically. We hypothesized that a combination of continuous tracheal gas insufflation (TGI) with protective strategy of PLV (low dose of PFC, low inflation pressure, moderate inhalation of oxygen and moderate anesthesia) would improve cardiopulmonary function in acute lung injury. Twenty-four healthy juvenile piglets were anesthetized and mechanically ventilated at PEEP of 2 cmH(2)O with a peak inspiratory pressure of 10 cmH(2)O and FIO(2) of 0.4. The piglets were challenged with lipopolysaccharide and randomly assigned to four groups (n = 6 each): (1) mechanical ventilation alone (MV); (2) PLV with perfluorodecalin (10 ml/kg); (3) TGI with continuous airway flow 2 L/min; and (4) combination of PLV and TGI. The outcome was assessed functionally and histologically. All treatments except MV improved pH, PaO(2)/FIO(2), PaCO(2), ventilation efficacy index (VEI) and tidal volume. Both PLV-associated treatments also improved heart rate, respiratory rate, pulse contour cardiac output, systemic vascular resistance, dynamic lung compliance, mean airway resistance and mean airway pressure. The combination group resulted in higher PaO(2)/FIO(2), VEI and a better lung histology score than any other treatments. The new protective strategy may provide a better treatment for sepsis-induced acute lung injury.

A randomized trial of delayed extubation for the reduction of reintubation in extremely preterm infants

To compare immediate extubation versus delayed extubation after 36 hr in extremely low-birth weight infants receiving gentle mechanical ventilation and perinatal lung protective interventions. Our hypothesis was that a delayed extubation in this setting would decrease the rate of reintubation. STUDY DESIGN/METHODOLOGY: A prospective, unmasked, randomized, controlled trial to compare immediate extubation and delayed extubation after 36 hr. Optimized ventilation in both groups included continuous tracheal gas insufflation (CTGI), prophylactic surfactant administration, low oxygen saturation target and moderate permissive hypercapnia. Successful extubation for at least 7 days was the primary criterion and ventilatory support requirements until 36 weeks gestational age the main secondary criteria. Eighty-six infants under 28 weeks gestational age in a single neonatal intensive tertiary care unit. Delayed extubation (1.9 +/- 0.8 days vs. 0.5 +/- 0.7 days) did not improve the rate of successful extubation but had no long-term adverse effects. CTGI and the lung protective strategy we describe resulted in a very gentle ventilation. The rate of survival without bronchopulmonary dysplasia (BPD, defined as any respiratory support at 36 weeks gestational age) was similar in the two groups and remarkably high for the global population (78%) and for the subgroup of infants <1,000 g at birth (75%). Adding 36 hr of optimized mechanical ventilation before first extubation does not improve the rate of successful extubation but has no adverse effects.

Effects of continuous tracheal gas insufflation during pressure limited ventilation on pulmonary surfactant in rabbits with acute lung injury

Pulmonary surfactant dysfunction may contribute to the development of ventilator induced lung injury (VILI). Tracheal gas insufflation (TGI) is a technique in which fresh gas is introduced into the trachea and augment ventilation by reducing the dead space of ventilatory system, reducing ventilatory pressures and tidal volume (V(T)) while maintaining constant partial arterial CO2 pressure (PaCO(2)). We hypothesised that TGI limited peak inspiratory pressure (PIP) and V(T) and would minimize conventional mechanical ventilation (CMV) induced pulmonary surfactant dysfunction and thereby attenuate VILI in rabbits with acute lung injury (ALI). ALI was induced by intratracheal administration of lipopolysaccharide in anaesthetized, ventilated healthy adult rabbits randomly assigned to continuous TGI at 0.5 L/min (TGI group) or CMV group (n = 8 for each group), and subsequently ventilated with limited PIP and V(T) to maintain PaCO(2) within 35 to 45 mmHg for 4 hours. Physiological dead space to V(T) ratio (V(D)/V(T)), dynamic respiratory compliance (Cdyn) and partial arterial O(2) pressure (PaO(2)) were monitored. After ventilation, lungs were analysed for total phospholipids (TPL), total proteins (TP), pulmonary surfactant small to large aggregates ratio (SA/LA) in bronchoalveolar lavage fluid (BALF) and for determination of alveolar volume density (V(V)), myeloperoxidase and interleukin (IL)-8. TGI resulted in significant (P < 0.05 or P < 0.01) decrease in PIP [(22.4 +/- 1.8) cmH2O vs (29.5 +/- 1.1) cmH2O], V(T) [(6.9 +/- 1.3) ml/kg vs (9.8 +/- 1.11) ml/kg], V(D)/V(T) [(32 +/- 5)% vs (46 +/- 2)%], TP [(109 +/- 22) mg/kg vs (187 +/- 25) mg/kg], SA/LA (2.5 +/- 0.4 vs 5.4 +/- 0.7), myeloperoxidase [(6.2 +/- 0.5) U/g tissue vs (12.3 +/- 0.8) U/g tissue] and IL-8 [(987 +/- 106) ng/g tissue vs (24 +/- 3) mN/m] of BALF, and significant (P < 0.05) increase in Cdyn [(0.47 +/- 0.02) ml.cmH2O(-1).kg(-1) vs (0.31 +/- 0.02) ml.cmH2O(-1).kg(-1)], PaO(2) [(175 +/- 24) mmHg vs (135 +/- 26) mmHg], TPL/TP (52 +/- 8 vs 33 +/- 11) and Vv (0.65 +/- 0.05 vs 0.44 +/- 0.07) as compared with CMV. In this animal model of ALI, TGI decreased ventilatory requirements (PIP, V(T) and V(D)/V(T)), resulted in more favourable alveolar pulmonary surfactant composition and function and less severity of lung injury than CMV. TGI in combination with pressure limited ventilation may be a lung protective strategy for ALI.

Tracheal gas insufflation as a lung-protective strategy: Physiologic, histologic, and biochemical markers

Conventional mechanical ventilation in acute lung failure potentiates lung injury, which can be assessed by physiologic, histologic, and biochemical markers. Thus, new ventilation strategies are directed at reducing lung injury. Tracheal gas insufflation has been shown to reduce endotracheal tube prosthetic deadspace and peak inspiratory pressure during conventional mechanical ventilation. Our objective was to use physiologic, histologic, and biochemical markers to test the hypothesis that tracheal gas insufflation in acute lung injury is lung protective. Animal experiment. University setting. Juvenile rabbits (n = 12; 1.95 +/- 0.1 SE kg). Rabbits were anesthetized, instrumented, paralyzed, and ventilated with Fio(2) = 1.0. Lung injury was induced with repeated saline lavage (10 mL/kg per lavage until Pao(2) </=150 mm Hg and compliance </=0.50 mL/cm H(2)O/kg for 30 mins). Animals were randomized to conventional mechanical ventilation with and without 0.5 lpm of continuous tracheal gas insufflation (Vygon endotracheal tube) for 4 hrs to maintain Paco(2) at 45-55 mm Hg by adjusting the peak inspiratory pressure; other conventional mechanical ventilation settings remained constant. Gas exchange and pulmonary mechanics were measured every 30 mins; plasma and pulmonary tissue were taken for cytokine and histologic evaluation after 4 hrs. Peak inspiratory pressure, tidal volume, and physiologic deadspace were significantly less (p < .05) in the tracheal gas insufflation animals when compared with conventional mechanical ventilation animals. Pao(2), positive end-expiratory pressure, mean airway pressure, vital signs, Paco(2), and respiratory resistance and compliance were not statistically different between the two groups. There was a difference (p < .05) in interleukin-8 tissue (pg/mug protein; dependent = 52.4 +/- 7.6 vs. nondependent = 32.8 +/- 4.2) and plasma levels (pg/mL; preinjury = 7.2 +/- 2.3 vs. postinjury = 118 +/- 58). Histology showed a trend toward protection of alveolar structures for tracheal gas insufflation. Tracheal gas insufflation resulted in lower ventilatory requirements (peak inspiratory pressure, tidal volume, and deadspace) and a more favorable histologic trend than conventional mechanical ventilation. Tracheal gas insufflation offers potential as a lung-protective strategy for acute lung injury in the developing rabbit lung and may be a useful clinical adjunct to neonatal respiratory management.

Continuous tracheal gas insufflation during partial liquid ventilation in juvenile rabbits with acute lung injury

To examine the hypothesis that combined treatment with tracheal gas insufflation (TGI) and partial liquid ventilation (PLV) may improve pulmonary outcome relative to either treatment alone in acute lung injury (ALI), saline lavage lung injury was induced in 24 anesthetized, ventilated juvenile rabbits that were then randomly assigned to receive (n = 6/group) 1) conventional mechanical ventilation (CMV) alone, 2) continuous TGI at 0.5 l/min, 3) PLV with perfluorochemical liquid, and 4) combined TGI and PLV (TGI + PLV), and subsequently ventilated with minimized pressures and tidal volume (Vt) to keep arterial Po(2) (Pa(O(2))) >100 Torr and arterial Pco(2) (Pa(CO(2))) at 45-60 Torr for 4 h. Gas exchange, lung mechanics, myeloperoxidase, IL-8, and histomorphometry [including expansion index (EI)] were assessed. The CMV group showed no improvement in lung mechanics and gas exchange; all treated groups had significant increases in compliance, Pa(O(2)), ventilation efficacy index (VEI), and EI, and decreases in PaCO(2), oxygenation index, physiological dead space-to-Vt ratio (Vd/Vt), myeloperoxidase, and IL-8, relative to the CMV group. TGI resulted in lower peak inspiratory pressure, Vt, Vd/Vt, and greater VEI vs. PLV group; PLV resulted in greater compliance, Pa(O(2)), and EI vs. TGI. TGI + PLV resulted in decreased peak inspiratory pressure, Vt, Vd/Vt, and increased VEI compared with TGI, improved compliance and EI compared with PLV, and a further increase in Pa(O(2)) and oxygenation index and a decrease in PaCO(2) vs. either treatment alone. These results indicate that combined treatment of TGI and PLV results in improved pulmonary outcome than either treatment alone in this animal model of ALI.

Instrumental dead space in neonatology, and its elimination by continuous tracheal gas insufflation during conventional ventilation

Instrumental dead space (iDS) is a major part of total dead space in newborns, and thus significantly determines effective alveolar ventilation. Continuous tracheal gas insufflation (CTGI) is a method for reducing the role of iDS, allowing a reduction in respiratory support and secondary lung injury. The literature and authors' experience with the method are reviewed. Major attention is paid to the risks in providing CTGI, optimal equipment and optimal management of CTGI.

Instrumental dead space in neonatology, and its elimination by continuous tracheal gas insufflation during conventional ventilation.

Instrumental dead space (iDS) is a major part of total dead space in newborns, and thus significantly determines effective alveolar ventilation. Continuous tracheal gas insufflation (CTGI) is a method for reducing the role of iDS, allowing a reduction in respiratory support and secondary lung injury. The literature and authors' experience with the method are reviewed. Major attention is paid to the risks in providing CTGI, optimal equipment and optimal management of CTGI.

Auto-positive end-expiratory pressure during tracheal gas insufflation: testing a hypothetical model.

The major benefit of tracheal gas insufflation (TGI) is an increase in CO2 elimination efficiency by removal of CO2 from the anatomical deadspace. In conjunction with mechanical ventilation, TGI may also alter variables that affect CO2 elimination, such as minute ventilation and peak airway pressure (peak Paw) and cause the development of auto-positive end-expiratory pressure (auto-PEEP). We tested the hypothesis that TGI-induced auto-PEEP alters ventilatory variables. We predicted that TGI-induced auto-PEEP offsets the beneficial effects of TGI on CO2 elimination and that keeping total PEEP (ventilator PEEP + auto-PEEP) constant enhances the CO2 elimination efficiency afforded by TGI. Prospective study of two series of patients with acute respiratory distress syndrome receiving mechanical ventilation. Intensive care units at a university medical center. Each series consisted of eight sequential hypercapnic patients. In series 1, we examined the effect of continuous TGI at 0 and 10 L/min on PaCO2, without compensating for the development of auto-PEEP. In series 2, we examined this same effect of continuous TGI while reducing ventilator PEEP to keep total PEEP constant. TGI-induced auto-PEEP was calculated based on dynamic compliance measurements during zero TGI flow conditions (deltaV/deltaP) after averaging the two baseline values for peak Paw and tidal volume and assuming compliance did not change between the zero TGI and TGI flow conditions (deltaVTGI/deltaPTGI). In series 1, total PEEP increased from 13.2 +/- 3.2 cm H2O to 17.8 +/- 3.5 cm H2O without compensation for auto-PEEP (p = .01). PaCO2 decreased (p = .03) from 56.2 +/- 10.6 mm Hg (zero TGI) to 52.9 +/- 9.3 mm Hg (TGI at 10 L/min), a 6% decrement. In series 2, total PEEP was unchanged (p = NS). PaCO2 decreased (p = .03) from 59.5 +/- 10.4 mm Hg (zero TGI) to 52.2 +/- 8.3 mm Hg (TGI at 10 L/min), a 12% decrement. There was no significant change in PaO2; there were no untoward hemodynamic effects in either series. These data are consistent with the hypothesis that mechanical ventilation + TGI causes an increase in auto-PEEP that can blunt CO2 elimination. In addition to the ventilator modifications necessary to keep ventilatory variables constant when TGI is used, it is also necessary to reduce ventilator PEEP to keep total PEEP constant and further enhance CO2 elimination efficiency.

Tracheal gas insufflation. Limits of efficacy in adults with acute respiratory distress syndrome.

In mechanically ventilated adults with acute respiratory distress syndrome (ARDS), peak airway pressures (Paw(peak)) above 35 cm H(2)O may increase the risk of barotrauma or volutrauma. Tracheal gas insufflation (TGI), an adjunctive ventilatory technique, may facilitate a reduction in set inspiratory pressure in these patients, and thereby in the tidal volume (VT) and Paw(peak) used in their ventilation, without a consequent increase in arterial carbon dioxide tension (PaCO(2)). The purpose of this study was to: (1) assess the limits of efficacy of continuous TGI at two levels of decreased mechanical ventilatory support; and (2) determine an appropriate time interval after initiation of TGI at which to evaluate response. We prospectively studied eight adults with ARDS and increased airway pressures (40.2 +/- 2.7 cm H(2)O) who were managed with pressure-control ventilation (PCV). After obtaining baseline ventilatory and hemodynamic measures, we initiated TGI at 10 L/min, adjusting ventilator positive-end expiratory pressure (PEEP) to maintain baseline VT, and decreased the set inspiratory pressure by 5 cm H(2)O. Data were obtained after 30 and 60 min. Set inspiratory pressure was then decreased by an additional 5 cm H(2)O (total: 10 cm H(2)O), and data were again obtained after 30 min. Baseline (zero TGI) measures were then again recorded. Thirty minutes after decreasing the set inspiratory pressure by 5 cm H(2)O with TGI at 10 L/min, there was a 15% decrease in Paw(peak) and a 16% decrease in VT as compared with their baseline values. However, Pa(CO(2)) remained constant (59 +/- 10 mm Hg versus 57 +/- 6 mm Hg) (p = NS). There was no change in Pa(O(2)) or in hemodynamic variables, and no differences between variables, at 30 min versus 60 min in seven subjects. The remaining subject did not tolerate the reduction in set inspiratory pressure for 60 min. Thirty minutes after the set inspiratory pressure was decreased by 10 cm H(2)O with TGI at 10 L/min, there was a 26% decrease in Paw(peak) and a 26% decrease in VT. However, Pa(CO(2)) increased by 19% and Pa(O(2)) decreased by 13%. Six subjects completed this phase of the protocol for 30 min, and one subject completed it for 60 min. TGI can be used to rapidly facilitate a 5 cm H(2)O reduction in set inspiratory pressure without an increase in Pa(CO(2)). The ability to achieve a 5 cm H(2)O reduction in set inspiratory pressure without adverse physiologic effects was evident within 30 min. Attempts to further reduce set inspiratory pressure were not successful.

Continuous Tracheal Gas Insufflation Enables a Significant Reduction of Tidal Volume without Modification of Oxygenation: A Randomized Study

Continuous Tracheal Gas Insufflation Enables a Significant Reduction of Tidal Volume without Modification of Oxygenation: A Randomized Study

Continuous tracheal gas insufflation enables a volume reduction strategy in hyaline membrane disease: technical aspects and clinical results.

Instrumental dead space wash-out can be used to improve carbon dioxide clearance. The aim of this study was to define, using a bench test, an optimal protocol for long-term use, and to assess the efficacy of this technique in neonates. A bench test with an artificial lung model, and an observational prospective study. Dead space wash-out was performed by continuous tracheal gas insufflation (CTGI), via six capillaries molded in the wall of a specially designed endotracheal tube, in 30 preterm neonates with hyaline membrane disease. Neonatal intensive care unit of a regional hospital. The bench test study showed that a CTGI flow of 0.5 l/ min had the optimal efficacy-to-side-effect ratio, resulting in a maximal or submaximal efficacy (93 to 100%) without a marked increase in tracheal and CTGI circuit pressures. In the 30 newborns, 15 min of CTGI induced a significant fall in arterial carbon dioxide tension (PaCO2), from 45 +/- 7 to 35 +/- 5 mmHg (p = 0.0001), and in 14 patients allowed a reduction in the gradient between Peack inspirating pressure and positive end-expiratory pressure from 20.8 +/- 4.6 to 14.4 +/- 3.7 cmH2O (p < 0.0001) while keeping the transcutaneous partial pressure of carbon dioxide constant. As predicted by the bench test, the decrease in PaCO2 induced by CTGI correlated well with PaCO2 values before CTGI (r = 0.58, p < 0.002) and with instrumental dead space-to-tidal volume ratio (r = 0.54, p < 0.005). CTGI may be a useful adjunct to conventional ventilation in preterm neonates with respiratory disease, enabling an increase in CO2 clearance or a reduction in ventilatory pressure.

Reply

Chef du Service de Reanimation, Polyvalente Hopital des Diaconesses, Paris, France (Kalfon).Professor of Anesthesia and Critical Care, Chef de l'Unite de Reanimation Chirurgicale, Hopital de la Pitie-Salpetriere, Universite Paris VI, Paris, France (Rouby).jjrouby.pitie@invivo.edu.In Reply:-The letters from Oppenheim and Pizov and from Findlay et al. indicate an important potential drawback of expiratory washout: auto-PEEP resulting in an increase in inspiratory plateau airway pressure, which may reintroduce a risk of lung barotrauma.Different solutions exist to overcome EWO-induced auto-PEEP. As suggested by Findlay et al., one is to deliver EWO during pressure-controlled ventilation. [1]In such circumstances, because EWO-induced increase in airway pressure automatically results in a decrease in the tidal volume, the lack of EWO-induced auto-PEEP is associated with a reduction in the efficiency of EWO on CO2elimination. In Findlay's study, a 6 l/min EWO flow delivered during pressure-controlled ventilation was associated with a modest reduction in PaCO2(-14%). [1]As a consequence, this technique for counteracting EWO-induced auto-PEEP appears to have serious limitations. It is more simple and efficient to reduce the PEEP level. In a recent study, [2]we could demonstrate in a series of patients with ARDS that inspiratory plateau airway pressure, mean airway pressure, and consequently arterial oxygenation and pulmonary shunt could be maintained constant when the PEEP level was reduced of an amount equal to EWO-induced auto-PEEP. In this study wherein a 15 l/min EWO flow was used, PaCO2could be reduced by 26% if compared with control values without EWO. [22]As emphasized by Findlay et al., it is technically possible to measure EWO-induced auto-PEEP by synchronizing suppression of EWO and occlusion of the expiratory valve. [1]This technical option, already present in prototypes, should be available on any medical device providing EWO and should be considered as a critical element of safety. Findlay et al. have outlined an important limitation of our study, although the indication for EWO was unquestionnable-severe ARDS with lung hyperdensities involving 50% of the lung parenchyma, low respiratory compliance, and profound hypercarbia with acid-base compromise resulting in increased pulmonary artery pressure [3]-the technical conditions of EWO administration were not optimized. EWO-induced auto-PEEP should have been counterbalanced by a concomittant reduction in PEEP, a technique that does not compromise CO2elimination and arterial oxygenation. [2]We agree with Findlay et al. that our study should not bias intensivists against the use of EWO in patients with severe ARDS.Another solution proposed by Oppenheim and Pizov to limit the auto-PEEP resulting from tracheal gas insufflation is to replace oxygen by helium. In an interesting study, [4]these authors have demonstrated that helium is more effective than oxygen for improving CO sub 2 elimination and limiting auto-PEEP. However, helium does not totally avoid the increase in peak inspiratory airway pressure and therefore appears less effective than decreasing PEEP. In addition, its high cost and the risk of decreasing FIO2and worsening arterial oxygenation in patients with ARDS render problematic its routine use in clinical practice.Although we agree that EWO is a peculiar mode of tracheal gas insufflation, we think that it should be clearly individualized from a semantic point of view. The administration of an intratracheal gas flow during inspiration-inspiratory bypass-increases tidal volume and therefore cannot be considered as a new mode of CO2elimination. In contrast, EWO that removes the carbon dioxide-laden gas occupying the instrumental dead space without inducing major changes in tidal volume appears as an original technique for enhancing CO2clearance in patients treated by permissive hypercapnia. In our opinion, EWO rather than inspiratory bypass or continuous tracheal gas insufflation could be clinically used in the near future if technical problems related to the measurement of auto-PEEP are solved by manufacturers of ICU ventilators.Pierre Kalfon, M.D.Chef du Service de Reanimation; Polyvalente Hopital des Diaconesses; Paris, FranceJean-Jacques Rouby, M.D., Ph.D.Professor of Anesthesia and Critical Care; Chef de l'Unite de Reanimation Chirurgicale; Hopital de la Pitie-Salpetriere; Universite Paris VI; Paris, Francejjrouby.pitie@invivo.edu(Accepted for publication November 18, 1997.)

Functional residual capacity measurement during tracheal gas insufflation.

Tracheal gas insufflation (TGI) is considered an adjunctive method to enhance carbon dioxide elimination during permissive hypercapnia in patients with acute respiratory distress syndrome. Due to increasing tidal volume and/or expiratory resistance, TGI may cause intrinsic PEEP (PEEPi), and may lessen the advantages of permissive hypercapnia. There is no reliable method to measure PEEPi during TGI. Using an argon washout method to evaluate dynamic hyperinflation, we developed a method to measure FRC with TGI flow. We measured FRC during TGI by washing out both the ventilator and TGI circuit with 100% oxygen (O2) previously equilibrated with 10% argon and 90% O2. To test the accuracy of our system, we measured the volume in a model lung composed of two flasks. The FRC of the model lung was changed by varying its volume of water, to active 500, 1000, and 1500 mL. The change of FRC (deltaFRC) of the model lung was measured at a flow of 0, 4, 8, and 12 L/min. Then the FRC of a bellows-type model lung was measured at the same TGI flow. PEEPi of the model lung was also recorded as the pressure inside the bellows at end-expiration. Our FRC measurements were accurate within 10% except for that of 500 mL without TGI (12.7%+/-1.1%). As inspiratory time (TI) and/or TGI flow increased, the FRC of the bellows-type model lung increased. PEEPi and deltaFRC showed a positive correlation (r = 0.843, p < 0.001). The higher the TGI flow, the greater was the deltaFRC with both continuous and expiratory-phase TGI. FRC during continuous TGI was higher than during expiratory-phase TGI especially during long TI and high TGI flow. The system developed in this study can be used as a method to detect air-trapping during TGI.

Tracheal gas insufflation improves ventilatory efficiency during methacholine-induced bronchospasm

Introduction: Barotrauma and cardiovascular insufficiency are frequently encountered problems in patients with acute bronchospastic disease who require mechanical ventilation. Permissive hypercapnia is a recognized strategy for minimizing these adverse effects; however, it has potential risks. Tracheal gas insufflation (TGI) has been shown to increase carbon dioxide elimination efficiency and thus could permit mechanical ventilation at lower peak airway pressures without inducing hypercapnia. However, caution exists as to the impact of TO on lung volumes, given that expiratory flow limitation is a hallmark of broncho-spastic disease. Purpose: To examine these issues, we studied ventilatory and hemodynamic effects of continuous TGI as an adjunct to mechanical ventilation before and after methacholine-induced bronchospasm. Materials and Methods: Ten anesthetized, paralyzed dogs were ventilated on volume-controlled mechanical ventilation during administration of continuous TGI (0, 2, 6, and 10 L/min) while total inspired minute ventilation (ventilator-derived minute ventilation plus TGI) was kept constant. In an additional step, with TGI flow of 10 L/min, total inspired minute ventilation was decreased by 30%. Results: Paco 2 decreased (44 ± 7 mm Hg at zero flow to 34 ± 7 mm Hg at 6 L/min and 31 ± 6 mm Hg at 10 L/min, respectively, P < .05), as did the dead space to tidal volume ratio at TGI of 6 and 10 L/min compared with zero flow. There were no significant changes in end-expiratory transpulmonary pressure, mean arterial pressure, or cardiac output. During the highest TGI flow (10 L/min), with a 30% reduction of total inspired minute ventilation, both Paco 2 and peak airway pressure remained less than during zero flow conditions. Conclusion: We conclude that TO increases carbon dioxide elimination efficiency during constant and decreased minute ventilation conditions without any evidence of hyperinflation or hemodynamic instability during methacholine-induced bronchospasm.

Tracheal gas insufflation during pressure-control ventilation: effect of using a pressure relief valve.

Pressure-control ventilation minimizes alveolar overdistention by limiting peak airway pressure, but a consequence of this pressure limitation may be a reduction in tidal volume with subsequent hypercarbia. Tracheal gas insufflation (TGI) can be used in combination with pressure-control ventilation to augment CO2 elimination. During pressure-control ventilation with continuous TGI, we observed that peak airway pressure increased above the set inspiratory pressure. Based on this observation, we investigated the ability of the pressure-control ventilator circuit to compensate for continuous TGI and the effect of insertion of a pressure relief valve to eliminate over-pressurization. University research laboratory. Using an artificial lung model, we studied the effects of continuous TGI with varying catheter flows (0, 2, 6, and 10 L/ min); ventilator frequencies (10 and 20 breaths/min); inspiratory duty cycles (0.33, 0.50, and 0.67); lung compliance (0.01, 0.02, and 0.04 L/cm H2O); and airway resistance (5, 20, and 50 cm H2O/L/sec) on: a) peak airway pressure; b) total inspiratory tidal volume; c) ventilator-derived tidal volume; and d) intrapulmonary pressure at end-exhalation (auto-PEEP). Tests were performed with and without a pressure relief valve whose threshold "pop-off" pressure was adjusted to match the set inspiratory pressure (35 cm H2O) for a total of 432 experimental conditions. Our data demonstrate that pressure-control ventilation augmented with continuous TGI can increase peak airway pressure above set inspiratory pressure due to delivery of a higher than intended tidal volume. Predisposing conditions include catheter flow rates of 6 and 10 L/min, long inspiratory time, low compliance, and low resistance. With the pressure relief valve, peak airway pressure was maintained at the set inspiratory pressure and total inspiratory tidal volume remained constant. A pressure relief valve is a necessary adjunct to maintain peak airway pressure at set inspiratory pressure and keep total inspiratory tidal volume constant when continuous TGI is administered in conjunction with pressure-control ventilation.

Tracheal gas insufflation is a useful adjunct in permissive hypercapnic management of acute respiratory distress syndrome1

Despite numerous advances in critical care, the mortality of postinjury acute respiratory distress syndrome (ARDS) remains high. Recently, permissive hypercapnia (PHC) has been shown to be a viable alternative to traditional ventilator management in patients with ARDS. However, lowering tidal volume, as employed in PHC, below 5 cc/kg impinges upon anatomic dead space and precipitates a significant rise in PaCO2 The purpose of this study was to determine if continuous tracheal gas insufflation (cTGI) is a useful adjunct to PHC by lowering PaCO2, thus allowing adequate reduction in minute ventilation to achieve alveolar protection. Over a 5-year period, 68 trauma patients with ARDS were placed on permissive hypercapnia. Nine of these patients additionally received cTGI at 7 L/min. Arterial blood gas determinations and ventilatory parameters were examined immediately prior to the implementation of cTGI and after 6h. The cTGI produced significant improvement in pH (7.25 +/- 0.03 to 7.33 +/- 0.03), PaCO2 (72 +/- 5 to 59 +/- 5 torr), tidal volume (7.9 +/- 0.6 to 7.2 +/- 0.6 cc/kg), and minute ventilation (13 +/- 1 to 11 +/- 1 L/min; P < 0.05). Continuous TGI is a useful adjunct to permissive hypercapnia, allowing maintenance of an acceptable pH and PaCO2 while allowing further reduction in tidal volume and minute ventilation.

Effect of Tracheal Gas Insufflation on Demand Valve Triggering and Total Work During Continuous Positive Airway Pressure Ventilation

Tracheal gas insufflation (TGI) improves CO2 clearance and may reduce work of breathing by lowering the required minute ventilation (VE). However, TGI might also impair the ability to trigger the ventilator, because to lower external circuit pressures, inspiratory effort must outstrip catheter flow rate (Vc) and overcome the dynamic hyperinflation caused by TGI. We studied these effects using a two-chamber lung model of the respiratory muscles (RM) and lungs (L). The RM-chamber was ventilated using a sinusoidal flow pattern with a tidal volume (VT) of 0.5 L at various peak inspiratory flow rates (Vpk) to simulate differences in effort intensity. The L-chamber was connected to a 60-L/min continuous flow circuit with a 10 cm H2O positive end-expiratory pressure valve and to 3 different ventilatory demand valve circuits, each set at continuous positive airway pressure (CPAP) of 10 cm H2O. We used continuous TGI at 0, 2.5, 5, 10, and 15 L/min. The work of triggering (W-trig) increased with increasing Vc and decreased with increasing Vpk. The L-ventilator failed to trigger when Vc was 15 L/min and Vpk was 20 L/min. At a fixed VE, the effect of TGI on total mechanical inspiratory work (W-tot) was relatively small and varied among the different CPAP systems used. We conclude that weak patients may fail to open the demand valve of the CPAP system during TGI at high catheter flow rates. The net effect of TGI on the effort made by ventilated patients would depend not only on the interactions between TGI and the ventilator, but also on the efficiency of TGI in decreasing dead-space and lowering the VE requirement.

Effect of catheter flow direction on CO2 removal during tracheal gas insufflation in dogs

Tracheal gas insufflation (TGI) improves the efficiency of CO2 elimination by replacing CO2 in the anatomic dead space proximal to the catheter tip with fresh gas during expiration. Turbulence generated by gas exiting the catheter tip may also contribute to alveolar ventilation. To separate distal (turbulence-related) and proximal (washout of dead space) effects of TGI, we compared the efficacy of a straight and an inverted catheter during continuous and expiratory TGI in six mechanically ventilated dogs. We reasoned that the inverted catheter cannot improve CO2 elimination from more distal conducting airways. During continuous TGI with the straight catheter, arterial PCO2 (PaCO2) decreased significantly from baseline (without TGI) of 56 +/- 10 Torr to 38 +/- 8, 36 +/- 8, and 35 +/- 8 Torr at catheter flow rates (Vcath) of 5, 10, and 15 l/min, respectively. For the same conditions, PaCO2 was always higher (P < 0.001) with the inverted catheter (42 +/- 10, 41 +/- 10, and 41 +/- 10 Torr). PaCO2 was lower with the straight (40 +/- 9 Torr) than with the inverted catheter (44 +/- 10 Torr, P < 0.001) during TGI delivered only during expiration at a Vcath of 10 l/min. End-expiratory lung volume relative to baseline increased during continuous, but not during expiratory, TGI and was significantly greater with the straight than with the inverted catheter (P < 0.0001). Our data confirm that the primary mechanism of TGI is expiratory washout of the proximal anatomic dead space but also suggest a minor contribution of turbulence beyond the tip of the straight catheter.