Positive Pressure Inflation Research Articles

Carbon dioxide monitoring during neonatal stabilisation at delivery (COSTA-Neo)-multi centre observational study

BackgroundThe data is evolving on exhaled carbon dioxide (ECO2) levels for preterm infants requiring stabilisation. ObjectivesTo establish the trends of ECO2 levels during the first 10 minutes of stabilisation in preterm infants at birth. MethodsWe conducted a multi-centre, prospective observational study. We included all preterm infants ≤ 32 weeks needing stabilisation. We recorded blinded ECO2 using Masimo Rad-97TM Pulse oximeter with Capnography. We used the first 10 minutes of ECO2, pulse rate (PR) and oxygen saturation (SpO2) data from pulse oximeter for our analysis. We collected stabilisation and clinical details. Ethics approval and informed consent was obtained. ResultsWe recruited 150 preterm infants, with data of 131 babies available for analysis. Median (and interquartile range) birth gestational age and birth weight were 28 (26.5–30) weeks and 1110 (800–1422.5) grams. All infants received positive end expiratory pressure (PEEP). In addition, 91 (69%) received positive pressure inflations, 34 (26%) received only PEEP and 34 (26%) were intubated within the first 10 minutes of life. Using bootstrapping, the 50% confidence interval for ECO2 at 5 minutes was estimated to range from 3.042 kPa††1Kpa is equivalent to 7.501 mmHg; so, 3.042Kpa=22.82 mmHg. to 3.328 kPa and has minimal change after 5 minutes. ECO2 appeared earlier than any valid PR and SpO2 data with median time difference of 16 (2–22) s) and 14 (0–20) s respectively. ConclusionsWe have provided trends of ECO2 in preterm infants needing stabilisation during the first 10 minutes of life. ECO2 appeared at least as early as any valid PR and earlier than SpO2.

Neonatal respiratory support strategies-short and long-term respiratory outcomes.

Mechanical ventilation (MV), although life-saving, is associated with chronic respiratory morbidity in both preterm and term born infants. New ventilation modes have been developed with the aim of minimising lung injury. These include invasive and non-invasive respiratory support strategies, techniques for less invasive surfactant administration (LISA) and closed-loop automated oxygen control (CLAC) systems. Increasingly, newborn infants with signs of respiratory distress are stabilised on continuous positive airway pressure (CPAP) and receive LISA. Early CPAP when compared to mechanical ventilation reduced the incidence of BPD and respiratory morbidity at 18 to 22 months corrected age. Nasal intermittent positive pressure ventilation reduced treatment failure rates compared to CPAP, but not bronchopulmonary dysplasia (BPD). LISA compared with intubation and surfactant delivery reduced BPD, but there is no evidence from randomised trials regarding long-term respiratory and neurodevelopmental outcomes. Synchronisation of positive pressure inflations with the infant's respiratory efforts used with volume targeting should be applied for infants requiring intubation as this strategy reduces BPD. A large RCT with long term follow up data demonstrated that prophylactic high frequency oscillatory ventilation (HFOV) improved respiratory and functional outcomes at school age, but those effects were not maintained after puberty. CLAC systems appear promising, but their effect on long term clinical outcomes has not yet been explored in randomised trials. Further studies are required to determine the role of newer ventilation modes such as neurally adjusted ventilator assist (NAVA). All such respiratory support strategies should be tested in randomised controlled trials powered to assess long-term outcomes.

Modeling the influence of gravity and the mechanical properties of elastin and collagen fibers on alveolar and lung pressure–volume curves

The relationship between pressure (P) and volume (V) in the human lung has been extensively studied. However, the combined effects of gravity and the mechanical properties of elastin and collagen on alveolar and lung P–V curves during breathing are not well understood. Here, we extended a previously established thick-walled spherical model of a single alveolus with wavy collagen fibers during positive pressure inflation. First, we updated the model for negative pressure-driven inflation that allowed incorporation of a gravity-induced pleural pressure gradient to predict how the static alveolar P–V relations vary spatially throughout an upright human lung. Second, by introducing dynamic surface tension and collagen viscoelasticity, we computed the hysteresis loop of the lung P–V curve. The model was tested by comparing its predicted regional ventilation to literature data, which offered insight into the effects of microgravity on ventilation. The model has also produced novel testable predictions for future experiments about the variation of mechanical stresses in the septal walls and the contribution of collagen and elastin fibers to the P–V curve and throughout the lung. The model may help us better understand how mechanical stresses arising from breathing and pleural pressure variations affect regional cellular mechanotransduction in the lung.

Performance Characteristics of a Novel 3D-Printed Bubble Intermittent Mandatory Ventilator (B-IMV) for Adult Pulmonary Support.

The COVID-19 pandemic has brought attention to the need for developing effective respiratory support that can be rapidly implemented during critical surge capacity scenarios in healthcare settings. Lung support with bubble continuous positive airway pressure (B-CPAP) is a well-established therapeutic approach for supporting neonatal patients. However, the effectiveness of B-CPAP in larger pediatric and adult patients has not been addressed. Using similar principles of B-CPAP pressure generation, application of intermittent positive pressure inflations above CPAP could support gas exchange and high work of breathing levels in larger patients experiencing more severe forms of respiratory failure. This report describes the design and performance characteristics of the BubbleVent, a novel 3D-printed valve system that combined with commonly found tubes, hoses, and connectors can provide intermittent mandatory ventilation (IMV) suitable for adult mechanical ventilation without direct electrification. Testing of the BubbleVent was performed on a passive adult test lung model and compared with a critical care ventilator commonly used in tertiary care centers. The BubbleVent was shown to deliver stable PIP and PEEP levels, as well as timing control of breath delivery that was comparable with a critical care ventilator.

Alternative Methods of Surfactant Administration in Preterm Infants with Respiratory Distress Syndrome: State of the Art.

For preterm infants with respiratory distress syndrome, delivery of surfactant via brief intubation (INtubate, SURfactant, Extubate; InSurE) has been the standard technique of surfactant administration. However, this method requires intubation and positive pressure ventilation. It is thought that even the short exposure to positive pressure inflations may be enough to initiate the cascade of events that lead to lung injury in the smallest neonates. In an effort to avoid tracheal intubation and positive pressure ventilation, several alternative and less invasive techniques of exogenous surfactant administration have been developed over the years. These have been investigated in clinical studies, including randomized clinical trials, and have demonstrated advantages such as a decrease in the need for mechanical ventilation and incidence of bronchopulmonary dysplasia. These newer techniques of surfactant delivery also have the benefit of being easier to perform. Surfactant delivery via pharyngeal instillation, laryngeal mask, aerosolization, and placement of a thin catheter are being actively pursued in research. We present a contemporary review of surfactant administration for respiratory distress syndrome via these alternative methods in the hope of guiding physicians in their choices for surfactant application in the neonatal intensive care unit.

Autonomic modulation for the management of patients with chronic heart failure.

Dysregulation of the autonomic nervous system in heart failure (HF) has received considerable attention during the past 3 decades, largely because of the well-recognized association between increased sympathetic activity and the elaboration of biologically active molecules, collectively referred to as neurohormones, that help to maintain cardiovascular homeostasis through increased volume expansion, peripheral arterial vasoconstriction, and increased myocardial contractility. However, high and sustained levels of these biologically active molecules (eg, norepinephrine, angiotensin II, aldosterone) are overtly toxic to the heart and circulation.1 These and other insights have led to the clinical use of neurohormonal antagonists, such as angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, aldosterone antagonists, and β-blockers to treat patients with HF with a reduced left ventricular ejection fraction (LVEF).1 The effectiveness of these pharmacological agents is predominantly because of their ability to directly antagonize the deleterious effects of excessive sympathetic and renin–angiotensin activation. However, the current guideline-directed medical therapy (GDMT) in patients with HF fails to completely restore normal autonomic balance disrupted as a part of HF pathophysiology. During the last decade, a novel approach has generated widespread interest: modulation of the autonomic nervous system as a result of either a one-time intervention (eg, denervation) or of ongoing active therapy (eg, electric stimulation) as a means of further diminishing the sympathovagal imbalance that develops in HF.2,3 Of note, therapeutic neuromodulation with device-based therapies, either with spinal cord stimulation (SCS) or vagal stimulation (VS), has been used safely in patients with chronic pain, epilepsy, and depression, since the 1980s. As noted above, HF with a reduced LVEF is associated with sustained activation of the sympathetic nervous system that is accompanied by a withdrawal of parasympathetic tone. Impaired arterial baroreflexes have been proposed as an important mechanism that contributes to the sympathovagal imbalance present in HF4 …

Transpulmonary pressure and lung elastance can be estimated by a PEEP-step manoeuvre.

Transpulmonary pressure is a key factor for protective ventilation. This requires measurements of oesophageal pressure that is rarely used clinically. A simple method may be found, if it could be shown that tidal and positive end-expiratory pressure (PEEP) inflation of the lungs with the same volume increases transpulmonary pressure equally. The aim of the present study was to compare tidal and PEEP inflation of the respiratory system. A total of 12 patients with acute respiratory failure were subjected to PEEP trials of 0-4-8-12-16 cmH2O. Changes in end-expiratory lung volume (ΔEELV) following a PEEP step were determined from cumulative differences in inspiratory-expiratory tidal volumes. Oesophageal pressure was measured with a balloon catheter. Following a PEEP increase from 0 to 16 cmH2O end-expiratory oesophageal pressure did not increase (0.5 ± 4.0 cmH2O). Average increase in EELV following a PEEP step of 4 cmH2O was 230 ± 132 ml. The increase in EELV was related to the change in PEEP divided by lung elastance (El) derived from oesophageal pressure as ΔPEEP/El. There was a good correlation between transpulmonary pressure by oesophageal pressure and transpulmonary pressure based on El determined as ΔPEEP/ΔEELV, r(2) = 0.80, y = 0.96x, mean bias -0.4 ± 3.0 cmH2 O with limits of agreement from 5.4 to -6.2 cmH2O (2 standard deviations). PEEP inflation of the respiratory system is extremely slow, and allows the chest wall complex, especially the abdomen, to yield and adapt to intrusion of the diaphragm. As a consequence a change in transpulmonary pressure is equal to the change in PEEP and transpulmonary pressure can be determined without oesophageal pressure measurements.

Lung Ultrasonography May Provide an Indirect Estimation of Lung Porosity and Airspace Geometry

Background: Echographic vertical artifacts (B-lines) in chest ultrasonography have often been associated with pathological patterns. A scientifically sound explanation of these artifacts has not yet been proposed. Objectives: The ‘spongy' nature of the lung in its liquid and solid components and the changes that take place in peripheral airspace (PAS) geometry might be the key point to understanding these phenomena. Methods: Six excised right rabbit lungs were obtained. Each lung underwent direct ultrasound evaluation in two different conditions: at complete tissue elastic recoil volume and at pulmonary expansion volume achieved by applying a constant positive pressure of 12 cm H₂O. Lung volumes and densities were reported in both conditions. Histological examination was performed on three naturally collapsed lungs and on three lungs under positive pressure inflation after having been fixed in formalin solution. Results: Mean volumes of naturally collapsed lungs and fixed expanded lungs were 11.2 ± 0.36 and 44.83 ± 3.03 ml, respectively. Mean densities were 0.622 ± 0.016 and 0.155 ± 0.007 g/ml, respectively. Ultrasound evaluation of collapsed lungs showed dense vertical artifacts and a ‘white lung' pattern, while the evaluation of expanded lungs showed hyperechoic line and horizontal artifacts of reflection. Histological evaluation showed a different PAS geometry in collapsed lungs caused by alveolar size reduction and shape changes with unfolded and closed units modifying the peripheral porosity of the frothy nature of the lung. Conclusions: Airspace geometry, frothy nature and porosity are the determinants of the different behavior of ultrasound interacting with the subpleural lung parenchyma. Chest ultrasound may thus be interpreted as an indirect ‘estimator' of lung porosity.

Randomised trial comparing assist control and pressure support ventilation during weaning

AimAssist control ventilation (ACV) compared to pressure limited, time cycled ventilation is associated with shorter duration of weaning. During both ACV and pressure support ventilation (PSV), all the infant's breaths...

S107 Comparison of high-stretch versus atelectasis in the pathophysiology of ventilator-induced lung injury using the mouse isolated perfused lung

IntroductionMechanical ventilation promotes pulmonary inflammation and oedema formation, a process known as ventilator-induced lung injury (VILI). Various aspects of ventilation have been proposed as injurious, including over distension of alveoli...

Preliminary evaluation of a new technique of minimally invasive surfactant therapy

ObjectiveTo investigate a method of minimally invasive surfactant therapy (MIST) to be used in spontaneously breathing preterm infants on continuous positive airway pressure (CPAP), evaluating the feasibility of the technique...

Enhanced airway dilation by positive-pressure inflation of the lungs compared with active deep inspiration in patients with asthma

Deep inspiration temporarily reduces induced airways obstruction in healthy subjects. This bronchodilatory effect of deep inspiration is impaired in asthma. Passive machine-assisted lung inflation may augment bronchodilation compared with an active deep inspiration in patients with asthma by either opening closed airways or by reducing fluid flux across the airway wall during deep inspiration, and thereby increasing the tethering forces on the airway wall. We recruited 24 patients with asthma [18-46 yr old, forced expiratory volume in 1 s (FEV(1)) > 70% predicted; provocative concentration of methacholine inducing a 20% fall in FEV(1) (PC(20)) < 8 mg/ml], with either an impaired (n = 12) or an intact (n = 12) bronchodilatory response to deep inspiration. Two methacholine challenges were performed on separate days. At a 50% increase in respiratory resistance (forced oscillation technique at 8 Hz), the change in resistance by a positive-pressure inflation (computer-driven syringe) or an active deep inspiration was measured in randomized order. The reduction in resistance by positive-pressure inflation was significantly greater than by active deep inspiration in the impaired deep inspiration response group (mean change +/- SE: -0.6 +/- 0.1 vs. -0.03 +/- 0.2 cmH(2)O.l(-1).s, P = 0.002). No significant difference was found between positive-pressure inflation and active deep inspiration in the intact deep inspiration response group (-0.6 +/- 0.2 vs. -1.0 +/- 0.3 cmH(2)O.l(-1).s, P = 0.18). Positive-pressure inflation of the lungs can significantly enhance deep inspiration-induced bronchodilation in patients with asthma.

Selective Death of Lens Epithelial Cells Using Demineralized Water and Triton X-100 With PerfectCapsule Sealed Capsule Irrigation

Sealed irrigation of the capsular bag after removal of the cataractous lens isolates the interior of the capsular bag from the anterior segment, permitting isolated targeting of lens epithelial cells (LECs) in vivo using pharmacologic agents while minimizing the risk of damage to other intraocular structures. To assess the ability to deliver a nonspecific, extremely toxic agent (Triton X-100) directly to the LECs after crystalline lens removal, and to assess the eyes histologically for evidence of collateral damage. Twelve eyes from 6 New Zealand White rabbits were divided into 3 groups of 4 eyes that underwent phacoaspiration of the crystalline lens. Group 1 was a control. In group 2, the anterior segment was irrigated with Triton X-100 and demineralized water for injection for 5 minutes. In group 3, the lens capsule was isolated from the anterior segment using sealed capsule irrigation (SCI) with PerfectCapsule (Milvella Pty Ltd, Sydney, Australia). After surgery, the rabbits were humanely euthanized. The enucleated eyes were immediately fixed in 10% neutral buffered formalin, histological analysis was performed to assess the corneal endothelium, iris, and retina, and the capsular bag and residual equatorial LECs were assessed. The capsular bag was sealed and inflated under SCI in all treated eyes in group 3. Histological evaluation revealed no evidence of collateral damage in group 1 and group 3. Significant histological damage to the cornea, iris, and peripheral retina was noted in group 2. Histological evaluation of each capsular bag suggests presence of LECs in group 1 and group 2. In the presence of SCI, Triton X-100 caused almost complete destruction of LECs in the capsular bag. Results suggest that SCI allows selective delivery of toxic agents directly into the capsular bag, preventing collateral damage to surrounding intraocular structures. The PerfectCapsule device kept the capsular bag well inflated intraoperatively, which may allow the isolated, safe delivery of pharmacologic agents into the capsular bag during cataract surgery. Clinical Relevance Postoperative proliferation of LECs in the capsular bag remains the most frequent complication of cataract surgery. Unprotected intraocular infusion of cytotoxic drugs, antimetabolites, or hypo-osmotic agents during cataract surgery has the potential risk of causing toxic effects in corneal endothelium and adjacent intraocular tissues. Selective delivery of pharmacologic/hypo-osmotic agents into the capsular bag requires positive pressure inflation of the bag and is now possible using an SCI device. This device allows the surgeon to reseal the capsular bag intraoperatively, achieve positive pressure inflation of the capsular bag, and direct selective targeting of LECs.

Continuous Positive Airway Pressure and Lung Inflation in Sleep Apnea Patients

Background: It was shown in normals that an important decrease in upper airway resistance can be obtained with continuous positive airway pressure (CPAP). It was suggested that lung inflation in patients with sleep apnea syndrome (SAS) could also be a mechanism of action of CPAP. Objective: In the present study we wanted to evaluate the effects of nocturnal CPAP on the daytime lung function pattern in patients with SAS. Methods: We measured arterial blood gases and possible changes in static lung volumes in 57 SAS patients (37 with normal lung function, 10 with COPD and 10 with restrictive lung disease) after at least one month of CPAP therapy. Results: A significant increase in PaO₂ (from 79 to 84 mm Hg, p = 0.01) and a decrease in AaDO₂ (from 23 ± 1 to 16 ± 1, p < 0.01) was only observed in SAS patients with normal lung function. This improved gas exchange was parallelled by a small but non significant change in the FRC (from 96.5 ± 3.2 to 105.4 ± 3.7%pred, p = 0.07) and TLC (from 101.3 ± 1.7 to 104.1 ± 1.4%pred, p = 0.15). Similar changes in TLC and FRC were also observed in SAS patients with obstructive and restrictive lung disease. Conclusions: Chronic nocturnal CPAP therapy can improve daytime gas exchange and may influence lung inflation during the daytime. The small changes seem to be a functional effect but of no clinical relevance.

Protein kinase C stimulates swelling-induced chloride current in canine atrial cells.

The whole-cell patch-clamp technique was used to study the effect of protein kinase C (PKC) stimulation and alpha-adrenergic agonists on the swelling-induced chloride current (ICl,swell) in canine atrial cells. ICl,swell was activated by positive-pressure inflation. 4beta-Phorbol 12, 13-dibutyrate (PDBu) concentration-dependently stimulated ICl,swell. PDBu (500 nM) increased the current density of ICl,swell from 9.1+/-1.3 to 24.2+/-4.8 pA/pF at +20 mV (n=4). This effect developed slowly, reaching a steady-state after more than 5 min of exposure. 4alpha-Phorbol 12, 13-dibutyrate (4alpha-PDBu, 500 nM), an inactive analogue of PDBu, did not affect ICl,swell. The effect of PDBu was inhibited by bisindolylmaleimide I. After down regulation of PKC by phorbol 12-myristate 13-acetate (PMA, 1.6 microM, 24 h), ICl,swell no longer responded to PDBu (n=4). Neither the basal whole-cell current (prior to cell inflation) nor inflation-induced ICl,swell were affected by PKC down regulation. Phenylephrine did not affect ICl,swell. We conclude that PKC activity stimulates and does not prevent the activation of dog atrial ICl,swell. These results contrast with reports of PKC-dependent inhibition of rabbit atrial ICl,swell and currents conducted by ClC-3, a putative clone for ICl,swell. The data suggest species-dependent variations in the modulation of cardiac ICl,swell by PKC.

The Hering-Breuer reflex in ventilated children

The authors tested the hypothesis that, in the paediatric population, the Hering-Breuer reflex would be provoked by the positive pressure inflation of mechanical ventilation (IPPV), and that the strength of the reflex would relate to the child's age and compliance of the respiratory system (CRS). During IPPV, changes in air flow, volume and airway pressure were recorded simultaneously. From the traces, expiratory times and CRS were calculated. The mean expiratory time (Te 1) prior to each inflation and the mean expiratory time (Te 2) immediately following an inflation were determined. The presence of the reflex was indicated by Te 2 being longer than Te 1, and the strength of the reflex was calculated as the difference between Te 2 and Te 1 expressed as a percentage of Te 1. Twenty children were studied who had a mean age of 0·7 years (range 0·1–9·8 years). The reflex was provoked in 19 of the 20 patients and was not seen in the oldest patient. The strength of the reflex varied from 22 to 144% and was inversely related to postnatal age significantly ( r = −0·73) but not CRS or inflation volume. It is concluded that the Hering-Breuer reflex is provoked during IPPV in young children; whether, as in neonates, this influences the efficacy of ventilation deserves investigation.

Volume delivery during positive pressure inflation--relationship to spontaneous tidal volume of neonates.

Volume delivery by positive pressure inflation was determined in 20 premature infants and 10 infants born at term on days 1 and 2. The spontaneous tidal volume, respiratory rate and inspiratory to expiratory (I:E) ratio were measured daily in the first week of life in an additional group of 20 infants born prematurely. Measurements were made using a pneumotachograph only when the infants were stable and had acceptable blood gases for at least 2 h. There was variability between individuals but the median delivered volume by positive pressure ventilation ranged between 4.9 and 6.1 ml/kg on days 1 and 2 and within the groups of different maturity. There was no significant difference in the results of infants born prematurely or at term or when studied on days 1 or 2. The median spontaneous tidal volume during the first week of life varied between 5.4 and 6.7 ml/kg; respiratory rate between 72 and 80 breaths/min and I:E ratio from 0.67 to 0.77. Postnatal age had no significant effect on the results. These results suggest volume delivery by positive pressure inflation during a stable period of ventilation is similar to the spontaneous tidal volume.

276 INFLUENCE OF LUNG FUNCTION AND REFLEX ACTIVITY ON THE SUCCESS OF PATIENT TRIGGERED VENTILATION

During patient triggered ventilation (PTV) each of the infant's respiratory efforts will trigger a positive pressure inflation, providing that the respiratory effort is of sufficient magnitude to exceed the critical trigger level. It is likely therefore that the nature of the infant's lung function and respiratory reflex activity will influence the success of PTV. The aim of this study was to test that hypothesis. 20 premature infants (median gestational age 29 weeks) in the recovery stage of respiratory distress were studied at a median postnatal age of 2.5 days. Lung function was assessed by measurement of compliance using a single breath technique. Reflex activity was assessed by measurement of the strength of the Hering Breuer reflex, indicated by the degree of prolongation of expiration following end inspiratory occlusion. PTV was considered to have failed if the infant became apnoeic or required an increased level of respiratory support. PTV failed ultimately in 6 infants, compliance of the respiratory system of those 6 infants did not differ significantly from the rest of the cohon, but the Hering Breuer reflex was significantly weaker (p<0.01). Although the infants in whom PTV failed compared to those in whom it succeeded were significantly more immature and of lower birthweight (p < 0.01), multiple regression analysis demonstrated that reflex activity was independently associated with PTV failure after accounting for gestational age. birthweight and compliance. We conclude that failure of PTV is more likely in immature infants who have a weak Hering Breuer reflex.

HPV and Cervical Cancer

<h3>Objective</h3> To investigate a method of minimally invasive surfactant therapy (MIST) to be used in spontaneously breathing preterm infants on continuous positive airway pressure (CPAP), evaluating the feasibility of the technique and the therapeutic benefit after MIST. <h3>Design</h3> Non-randomised feasibility study. <h3>Setting</h3> Tertiary neonatal intensive care unit. <h3>Patients and interventions</h3> Study subjects were preterm infants with respiratory distress supported with CPAP, with early enrolment of 25–28-week infants (n=11) at any CPAP pressure and fractional inspired O₂ concentration (FiO₂), and enrolment of 29–34-week infants (n=14) at CPAP pressure ≥7 cm H₂O and FiO₂ ≥0.35. Without premedication, a 16 gauge vascular catheter was inserted through the vocal cords under direct vision. Porcine surfactant (∼100 mg/kg) was then instilled, followed by reinstitution of CPAP. <h3>Measurements and results</h3> Respiratory indices were documented for 4 h following MIST, and neonatal outcomes ascertained. In all cases, surfactant was successfully administered and CPAP re-established. Coughing (32%) and bradycardia (44%) were transiently noted, and 44% received positive pressure inflations. There was a clear surfactant effect, with lower FiO₂ after MIST (pre-MIST: 0.39±0.092 (mean±SD); 4 h: 0.26±0.093; p&lt;0.01), and a modest reduction in CPAP pressure. Adverse outcomes were few: intubation within 72 h (n=3), pneumothorax (n=1), chronic lung disease (n=3) and death (n=1), all in the 25–28-week group. Outcome was otherwise favourable in both gestation groups, with a trend towards reduction in intubation in the first 72 h in the 25–28-week infants compared with historical controls. <h3>Conclusions</h3> Surfactant can be effectively delivered via a vascular catheter, and this method of MIST deserves further investigation.

Do infants always breathe synchronously with positive pressure inflation during patient triggered ventilation (PTV) : M. Hird and A. Greenough, Dept. of Child Health, King's College Hospital, London SE5 9RS, U.K.

Do infants always breathe synchronously with positive pressure inflation during patient triggered ventilation (PTV) : M. Hird and A. Greenough, Dept. of Child Health, King's College Hospital, London SE5 9RS, U.K.