David G. Tingay

Monitoring of end tidal carbon dioxide and transcutaneous carbon dioxide during neonatal transport

Objective: To assess the accuracy of measurements of end tidal carbon dioxide (CO2) during neonatal transport compared with arterial and transcutaneous measurements. Design: Paired end tidal and transcutaneous CO2 recordings were taken frequently during road transport of 21 ventilated neonates. The first paired CO2 values were compared with an arterial blood gas. The differences between arterial CO2 (Paco2), transcutaneous CO2 (TcPco2), and end tidal CO2 (Petco2) were analysed. The Bland-Altman method was used to assess bias and repeatability. Results: Petco2 correlated strongly with Paco2 and TcPco2. However, Petco2 underestimated Paco2 at a clinically unacceptable level (mean (SD) 1.1 (0.70) kPa) and did not trend reliably over time within individual subjects. The Petco2 bias was independent of Paco2 and severity of lung disease. Conclusions: Petco2 had an unacceptable under-recording bias. TcPco2 should currently be considered the preferred method of non-invasive CO2 monitoring for neonatal transport.

Chest electrical impedance tomography examination, data analysis, terminology, clinical use and recommendations: consensus statement of the TRanslational EIT developmeNt stuDy group

Electrical impedance tomography (EIT) has undergone 30 years of development. Functional chest examinations with this technology are considered clinically relevant, especially for monitoring regional lung ventilation in mechanically ventilated patients and for regional pulmonary function testing in patients with chronic lung diseases. As EIT becomes an established medical technology, it requires consensus examination, nomenclature, data analysis and interpretation schemes. Such consensus is needed to compare, understand and reproduce study findings from and among different research groups, to enable large clinical trials and, ultimately, routine clinical use. Recommendations of how EIT findings can be applied to generate diagnoses and impact clinical decision-making and therapy planning are required. This consensus paper was prepared by an international working group, collaborating on the clinical promotion of EIT called TRanslational EIT developmeNt stuDy group. It addresses the stated needs by providing (1) a new classification of core processes involved in chest EIT examinations and data analysis, (2) focus on clinical applications with structured reviews and outlooks (separately for adult and neonatal/paediatric patients), (3) a structured framework to categorise and understand the relationships among analysis approaches and their clinical roles, (4) consensus, unified terminology with clinical user-friendly definitions and explanations, (5) a review of all major work in thoracic EIT and (6) recommendations for future development (193 pages of online supplements systematically linked with the chief sections of the main document). We expect this information to be useful for clinicians and researchers working with EIT, as well as for industry producers of this technology.

Randomized controlled trial of lung lavage with dilute surfactant for meconium aspiration syndrome.

OBJECTIVE To evaluate whether lung lavage with surfactant changes the duration of mechanical respiratory support or other outcomes in meconium aspiration syndrome (MAS). STUDY DESIGN We conducted a randomized controlled trial that enrolled ventilated infants with MAS. Infants randomized to lavage received two 15-mL/kg aliquots of dilute bovine surfactant instilled into, and recovered from, the lung. Control subjects received standard care, which in both groups included high frequency ventilation, nitric oxide, and, where available, extracorporeal membrane oxygenation (ECMO). RESULTS Sixty-six infants were randomized, with one ineligible infant excluded from analysis. Median duration of respiratory support was similar in infants who underwent lavage and control subjects (5.5 versus 6.0 days, P = .77). Requirement for high frequency ventilation and nitric oxide did not differ between the groups. Fewer infants who underwent lavage died or required ECMO: 10% (3/30) compared with 31% (11/35) in the control group (odds ratio, 0.24; 95% confidence interval, 0.060-0.97). Lavage transiently reduced oxygen saturation without substantial heart rate or blood pressure alterations. Mean airway pressure was more rapidly weaned in the lavage group after randomization. CONCLUSION Lung lavage with dilute surfactant does not alter duration of respiratory support, but may reduce mortality, especially in units not offering ECMO.

Lung volume and cardiorespiratory changes during open and closed endotracheal suction in ventilated newborn infants.

Objectives: To compare change in lung volume (ΔVL), using respiratory inductive plethysmography, time to recover pre-suction lung volume (trec) and the cardiorespiratory disturbances associated with open suction (OS) and closed suction (CS) in ventilated infants. Design: Randomised blinded crossover trial. Setting: Neonatal intensive care unit. Patients: Thirty neonates, 20 receiving synchronised intermittent mandatory ventilation (SIMV) and 10 high-frequency oscillatory ventilation (HFOV, four receiving muscle relaxant). Interventions: OS and CS were performed, in random order, on each infant using a 6FG catheter at −19 kPa for 6 seconds and repeated after 1 minute. Outcome measures: ΔVL, oxygen saturation (Spo2) and heart rate were continuously recorded from 2 minutes before until 5 minutes after suction. Lowest values were identified during the 60 seconds after suction. Results: Variations in all measures were seen during CS and OS. During SIMV no differences were found between OS and CS for maximum ΔVL or trec; mean (95% CI) difference of 3.5 ml/kg (−2.8 to 9.7) and 4 seconds (−5 to 13), respectively. During HFOV trec was longer during OS by 13 seconds (0 to 27) but there was no difference in the maximum ΔVL of 0.1 mV (−0.02 to 0.22). A small reduction in SpO2 with CS in the SIMV group mean difference 6% (2.1 to 9.8) was the only significant difference in physiological measurements. Conclusions: Both OS and CS produced transient variable reductions in heart rate and Spo2. During SIMV there was no difference between OS and CS in ΔVL or trec. During HFOV there was no difference in ΔVL but a slightly longer trec after OS.

Effect of sustained inflation vs. stepwise PEEP strategy at birth on gas exchange and lung mechanics in preterm lambs.

Background:Sustained inflation (SI) at birth facilitates establishment of functional residual capacity (FRC) in the preterm lung, but the ideal lung recruitment strategy is unclear. We have compared the effect of SI and a stepwise positive end-expiratory pressure (PEEP; SEP) strategy in a preterm model.Methods:127 d gestation lambs received either 20-s SI (n = 9) or 2 cmH2O stepwise PEEP increases to 20 cmH2O every 10 inflations, and then decreases to 6 cmH2O (n = 10). Ventilation continued for 70 min, with surfactant administered at 10 min. Alveolar–arterial oxygen gradient (AaDO2), compliance (Cdyn), end-expiratory thoracic volume (EEVRIP; respiratory inductive plethysmography), and EEV and Cdyn in the gravity-dependent and nondependent hemithoraces (electrical impedance tomography) were measured throughout. Early mRNA markers of lung injury were analyzed using quantitative real-time PCR.Results:From 15 min of life, AaDO2 was lower in SEP group (P < 0.005; two-way ANOVA). SEP resulted in higher and more homogeneous Cdyn (P < 0.0001). Mean (SD) EEVRIP at 5 min was 18 (9) ml/kg and 6 (5) ml/kg following SEP and SI, respectively (P = 0.021; Bonferroni posttest); this difference was due to a greater nondependent hemithorax EEV. There was no difference in markers of lung injury.Conclusion:An SEP at birth improved gas exchange, lung mechanics, and EEV, without increasing lung injury, compared to the SI strategy used.

Indicators of optimal lung volume during high-frequency oscillatory ventilation in infants

Objectives:During high-frequency oscillatory ventilation, an understanding of the relationship between lung volume and lung mechanics may help clinicians better apply ventilation. The objectives of this study were: 1) to describe the relationship between lung volume and lung function parameters during mapping of the deflation limb of the pressure–volume relationship in infants receiving high-frequency oscillatory ventilation, and 2) to determine whether these parameters might be useful in targeting an optimal volume to apply ventilation. Design:Observational physiological study. Setting:Tertiary neonatal intensive care unit in a pediatric hospital. Patients:Fifteen infants receiving high-frequency oscillatory ventilation and muscle relaxants. Interventions:The deflation limb of the pressure–volume relationship was mapped in each infant, after recruitment to total lung capacity, using stepwise airway pressure decrements. Total lung capacity and closing volume were defined by oxygenation response. Measurements and Main Results:Lung volume (respiratory inductive plethysmography), oxygen saturation, transcutaneous carbon dioxide, and indicators of lung mechanics were recorded at each pressure. A distinct bell-shaped relationship between lung volume and carbon dioxide, minute ventilation, and tidal volume (both at airway opening and by inductive plethysmography) could be identified on the deflation limb, with an improvement of 21.6 mm Hg (CO2), 168 mL2/sec (minute ventilation), 0.25 mL/kg (airway opening tidal volume), and 13.7% (plethysmography tidal volume) compared with total lung capacity levels. The mean (SD) optimal volumes and pressures for these parameters were significantly lower than total lung capacity, occurring at volumes between 38.6 (39.8)% and 62.8 (31.1)% of total lung capacity, and 28 (36.3)% and 41.3 (38.7)% of pressure at total lung capacity (p < 0.05; Bonferroni post-test). These coincided with the lowest pressure and volumes that maintained the oxygenation benefit of recruitment. Conclusions:Transcutaneous carbon dioxide, tidal volume, and minute ventilation may assist in refining strategies to identify optimal lung volume.

Lung protective ventilation in extremely preterm infants.

The lungs of an extremely preterm infant ≤28 weeks gestation are structurally and biochemically immature and vulnerable to injury from positive pressure ventilation. A lung protective approach to respiratory support is vital, aiming to ventilate an open lung, using the lowest pressure settings that maintain recruitment and oxygenation and avoiding hyperinflation with each tidal breath. For infants with severe respiratory distress syndrome and persistent atelectasis, lung protective ventilation requires recruitment using stepwise pressure increments, followed by reduction in ventilator pressures in search of an optimal point at which to maintain ventilation. Several studies, including a single randomised controlled trial, have found this lung protective strategy to be more effectively administered using high‐frequency oscillatory ventilation rather than conventional ventilation. Many extremely preterm infants have minimal atelectasis and low oxygen requirements in the first days of life, and the ventilatory approach in this case should be one of avoidance of factors including overdistension that are known to contribute to later pulmonary deterioration. From a practical perspective, this means setting positive end‐expiratory pressure at the lowest value that maintains oxygenation and restricting tidal volume using a volume‐targeted mode of ventilation.

Surfactant before the first inflation at birth improves spatial distribution of ventilation and reduces lung injury in preterm lambs

The interrelationship between the role of surfactant and a sustained inflation (SI) to aid ex utero transition of the preterm lung is unknown. We compared the effect of surfactant administered before and after an initial SI on gas exchange, lung mechanics, spatial distribution of ventilation, and lung injury in preterm lambs. Gestational-age lambs (127 days; 9 per group) received 100 mg/kg of a surfactant (Curosurf) either prior (Surf+SI) or 10 min after birth (SI+Surf). At birth, a 20-s, 35 cmH2O SI was applied, followed by 70 min of positive pressure ventilation. Oxygenation, carbon dioxide removal, respiratory system compliance, end-expiratory thoracic volume (via respiratory inductive plethysmography), and distribution of end-expiratory volume and ventilation (via electrical impedance tomography) were measured throughout. Early markers of lung injury were analyzed using quantitative RT-PCR. During the first 15 min, oxygenation, carbon dioxide removal, and compliance were better in the Surf+SI group (all P < 0.05). End-expiratory volume on completion of the sustained inflation was higher in the Surf+SI group than the SI+Surf group; 11 ± 1 ml/kg vs. 7 ± 1 ml/kg (mean ± SE) (P = 0.043; t-test), but was not different at later time points. Although neither achieved homogenous aeration, spatial ventilation was more uniform in the Surf+SI group throughout; 50.1 ± 10.9% of total ventilation in the left hemithorax at 70 min vs. 42.6 ± 11.1% in the SI+Surf group. Surf+SI resulted in lower mRNA levels of CYR61 and EGR1 compared with SI+Surf (P < 0.001, one-way ANOVA). Surfactant status of the fetal preterm lung at birth influences the mechanical and injury response to a sustained inflation and ventilation by changing surface tension of the air/fluid interface.

The Effect of Suction Method, Catheter Size, and Suction Pressure on Lung Volume Changes During Endotracheal Suction in Piglets

We aimed to identify the effect of suction pressure and catheter size on change in lung volume during open and closed endotracheal suction. Anesthetized piglets (n = 12) were intubated with a 4.0-mm endotracheal tube. Lung injury was induced with saline lavage. Three suction methods (open, closed in-line, and closed with a side-port adaptor) were performed in random order using 6, 7, and 8 French gauge (FG) catheters, at vacuum pressures of 80, 140, and 200 mm Hg. Lung volume change was measured with respiratory inductive plethysmography. Overall, open suction resulted in greater lung volume loss during and at 60-s postsuction than either closed method (p < 0.001). When open and closed methods were analyzed separately, volume change was independent of catheter size and suction pressure with open suction. With closed suction, volume loss increased with larger catheter sizes and higher suction pressures (p < 0.001). With an 8-FG catheter and suction pressure of 140 or 200 mm Hg, volume loss was equivalent with open and closed suction. Lung volume changes are influenced by catheter size and suction pressure, as well as suction method. With commonly used suction pressures and catheter sizes, closed suction has no advantage in preventing loss of volume in this animal model.

Negative tracheal pressure during neonatal endotracheal suction.

Endotracheal tube (ETT) suction is the most frequently performed invasive procedure in ventilated newborn infants and is associated with adverse effects related to negative tracheal pressure. We aimed to measure suction catheter gas flow and intratracheal pressure during ETT suction of a test lung and develop a mathematical model to predict tracheal pressure from catheter and ETT dimensions and applied pressure. Tracheal pressure and catheter flow were recorded during suction of ETT sizes 2.5–4.0 mm connected to a test lung with catheters 5–8 French Gauge and applied pressures of 80–200 mm Hg. The fraction of applied pressure transmitted to the trachea was calculated for each combination, and data fitted to three nonlinear models for analysis. Tracheal pressure was directly proportional to applied pressure (r2 = 0.82–0.99), and catheter flow fitted a turbulent flow model (R2 = 0.85–0.96). With each ETT, increasing catheter size resulted in greater catheter flow (p < 0.0001) and thus lower intratracheal pressure (p < 0.0001). The fraction of applied pressure transmitted to the trachea was accurately modeled using ETT and catheter dimensions (R2 = 0.98–0.99). Negative tracheal pressure during in vitro ETT suction is directly proportional to applied pressure. This relationship is determined by ETT and catheter dimensions.