High-Flow Nasal Cannula Reduces Effort of Breathing But Not Consistently via Positive End-Expiratory Pressure.

BACKGROUND: High-flow nasal cannula (HFNC) therapy reduces the effort of breathing in patients with bronchiolitis, but the mechanisms are not understood. Theorized mechanisms include dead space washout and positive end-expiratory pressure (PEEP) application. RESEARCH QUESTION: What are the mechanisms of action of HFNC therapy in patients with bronchiolitis? STUDY DESIGN AND METHODS: Prospective, single-center study of children 3 years of age or younger with bronchiolitis from January 2020 through March 2021. Flow was titrated between 0.5 and 2 L/kg/min. Electrical impedance tomography measured end-expiratory lung impedance (EELZ) change as an end-expiratory lung volume (EELV) change surrogate and change in tidal impedance difference (ΔZ) as a tidal volume (VT) surrogate. A subset showed manometry measuring esophageal pressure change (ΔPes; transpulmonary pressure surrogate) and pressure rate product (PRP; effort of breathing metric). We hypothesized that EELV and VT would not change and that effort would reduce via respiratory rate (not ΔPes). Measurements were reported as the difference from 0.5 L/kg/min. RESULTS: We studied 22 patients in total, 10 with esophageal manometry. Median EELZ increased by 0.36 arbitrary unit (AU), 2.42 AU, and 4.8 AU at 1 L/kg/min, 1.5 L/kg/min, and 2 L/kg/min (P = .01, 2 L/kg/min vs 0.5 L/kg/min), which corresponded to a median increase in EELV of 1.8 mL/kg between 0.5 and 2 L/kg/min. Seven patients showed an increase in EELZ of > 5 AU, 12 showed no change in EELZ (± 5 AU), and three showed a decrease in EELZ of > 5 AU. ΔZ (ie, VT) did not change from 0.5 L/kg/min to 2 L/kg/min (median change, 0.29 AU; P = .48). Median PRP decreased by 78 cm H2O/min from 0.5 L/kg/min to 2 L/kg/min (P = .02), with all patients demonstrating a reduction in PRP, with a nonsignificant change in ΔPes (P = .68). INTERPRETATION: Increasing HFNC in children with bronchiolitis reduces the effort of breathing, but no consistent increase occurs in end-expiratory lung volume and no significant change occurs in VT or transpulmonary pressure. This suggests that PEEP application is not the primary mechanism of action of HFNC in children with bronchiolitis.

Symptomatic catheter-associated thrombosis in pediatric trauma patients: Choose your access wisely.

BACKGROUND: Traumatic injury and the presence of a central venous catheter are 2 of the strongest risk factors for venous thromboembolism in children. The purpose of this study was to determine the incidence of symptomatic, catheter-associated thrombosis in critically injured children. We hypothesized that femoral venous catheters are associated with a greater rate of thrombotic complications when compared with all other central venous access points. METHODS: We reviewed a retrospective cohort (2006-2016) of injured children (≤18 years) admitted to a pediatric intensive care unit with central access placed ≤7 days from admission. Symptomatic, catheter-associated thrombosis was determined by radiographic evidence. Poisson regression was used to compare the incidence of catheter-associated thrombosis per 1,000 catheter days between femoral and nonfemoral catheters. All comparisons were 2-tailed with α = 0.05. RESULTS: We examined 209 pediatric trauma patients with central access (65% femoral, 19% subclavian, 11% arm vein, and 5% internal jugular). Femoral catheters were removed earlier (median [interquartile range] 4 [2-7] vs 8 [3-12] days, P < .001) and were larger in diameter (5 Fr [4-7] vs 4 Fr [4-4], P < .001) when compared with all other catheters. Catheter-associated thrombosis was more frequent in femoral versus nonfemoral catheters (18.4 vs 3.5 per 1,000 catheter days, P = .01). CONCLUSION: Femoral venous catheters are associated with a greater incidence of symptomatic, catheter-associated thrombosis in pediatric trauma patients. When central venous access is indicated for injured children, the femoral site should be avoided. If a femoral venous catheter is necessary, use of a smaller catheter should be considered.

Measurements Obtained From Esophageal Balloon Catheters Are Affected by the Esophageal Balloon Filling Volume in Children With ARDS.

BACKGROUND: Esophageal balloon inflation volume may affect the accuracy of transpulmo-nary pressure estimates in adults, but the effect is unknown in pediatrics. Using a combination bench and human study, we sought to determine a range of optimal filling volumes for esophageal balloon catheters and to derive a technique to inflate catheters to yield the most accurate estimates of pleural pressure. METHODS: In the laboratory study, we evaluated 4 pediatric and adult esophageal balloon catheters, a liquid-filled catheter, and a micro-tip catheter, both with and without a model esophagus. We compared the measured esophageal pressure for each type of catheter within a pressurized chamber. Esophageal balloon catheters were also tested by manipulating the esophageal balloon inflation volume, and we attempted to derive a filling-volume technique that would assure accuracy. We then tested the feasibility of this technique in 5 mechanically ventilated pediatric subjects with ARDS. RESULTS: In the laboratory study, smaller inflation volumes underestimated the chamber pressure at higher chamber pressures, and larger inflation volumes overestimated the chamber pressure at lower chamber pressures. Using an optimal filling-volume technique resulted in a mean total error that ranged from -0.53 to -0.10 cm H2O. The optimal filling-volume values for the pediatric catheters were 0.2-0.6 mL, and 0.4-0.8 mL for the adult catheters. When correctly positioned and calibrated, the micro-tip transducer and liquid-filled catheters were within ± 1 cm H2O of chamber pressure for all ranges of pressure. In the clinical study, high variability in measured esophageal pressure and subsequent transpulmonary pressure during exhalation and during inhalation was observed within the manufacturer's recommended esophageal balloon inflation ranges. CONCLUSIONS: Manufacturer-recommended esophageal balloon inflation ranges do not assure accuracy. Individual titration of esophageal balloon volume may improve accuracy. Better esophageal catheters are needed to provide reliable esophageal pressure measurements in children.

Increase in oxygen consumption after albuterol inhalation in ventilated infants and children.

OBJECTIVE: To determine if inhaled albuterol (salbutamol) increases oxygen consumption (V'O2) in children and, if so, the duration of this effect. DESIGN: Oxygen consumption was measured by indirect calorimetry using the Argon dilution technique with a respiratory mass spectrometer. After measurement of baseline values, albuterol was administered and subsequent measurements were performed at 10 minutes, 1 hour, 2 hours, 3 hours, and 4 hours. SETTING: Multidisciplinary PICU in a university teaching hospital. PATIENTS: Eleven intubated infants and children (five girls, six boys) with a mean age of 20 months (range, 1 mo to 8 yr) and a mean weight of 10.7 kg (range, 3.1-23 kg) who required therapeutic albuterol inhalations. INTERVENTION: Nine hundred micrograms of albuterol (10 puffs) was administered by a metered-dose inhaler into a spacer through the inspiratory arm of the ventilator circuit near to the patient, during 10 mechanically assisted breaths. MEASUREMENTS AND MAIN RESULTS: All children showed an increase in V'O2 within 10 minutes (mean increase 48.6%). The increased V'O2 was still elevated (42.3% above baseline) at 1 hour, but 3 hours after albuterol inhalation, the V'O2 was back to baseline in all patients. Heart rate increased significantly at 10 minutes, 1 hour, and 2 hours after inhalation. CONCLUSION: There is a large increase in V'O2 after albuterol inhalation. This effect lasts up to 3 hours.