Pediatric Diaphragm Thickness Trial
Condition: Child
Study type: Interventional

Summary: 
      The evaluation of diaphragm function in ventilated patients is not easy. One option is to use
      esophageal pressure (Pes) measurements but recently, diaphragmatic ultrasound has proven
      itself as a useful tool in this setting. In adults the thickening fraction (TF), which
      describes the difference in thickness between end-inspiration and end-expiration, correlates
      with the diaphragmatic pressure-time product per breath (PTPdi), an esophageal
      pressure-derived work of breathing parameter. There is a lack of data that tells us whether
      the same is true in children. This physiological study intends to look at the correlation
      between esophageal pressures and thickening fraction assessed by ultrasound in a pediatric
      cohort of patients.
    

Detailed description: 
      The gold standard in evaluating lung mechanics is the esophageal pressure. And although
      diaphragm ultrasound has been reported to be feasible in assessing diaphragm activity in
      sedated patients, no study has thus far looked at the relationship between the ultrasound
      parameters (i.e. thickening fraction) and the esophageal pressure. This is a single-centre
      physiological cohort study to evaluate the feasibility of using the thickening fraction as a
      parameter for diaphragm activity during spontaneous breathing in sedated children. Data will
      be collected during an elective surgical procedure with a patient under general anesthesia.
      If the patient's legal representative provides written informed consent, the patient is
      enrolled in the study before start of the anesthetic procedure and the trial ends on the
      moment of removal of the laryngeal mask.The registration of the physiological data will not
      interfere with the surgery.The thickening fraction (using ultrasound) and pressure
      measurements will be performed simultaneously and repetitive during different loads on the
      respiratory system.Esophageal pressures (Pes) will be measured with a single air-filled
      balloon catheter(AVEA™ smarthcath pediatric 7 Fr, Vyaire Medical Inc., IL, USA). The balloon
      catheter will be inserted nasally after the induction of anesthesia. The catheter will then
      be connected to a pressure transducer (FluxMed, MBMED, Argentina). The appropriate placement
      will be checked by commonly used methods. Firstly, the appropriate depth of insertion will be
      estimated by measuring the nose-ear-xyphoid distance, which is the distance from the nose to
      the diaphragm. Secondly, the balloon catheter will be inserted more deeply than this
      predicted distance, placing it in the stomach, and a positive pressure swing when mild
      abdominal pressure is exerted on a slightly inflated balloon will be noted. Thirdly, when
      retracted into the esophagus, cardiac reflections on the pressure monitor will appear.
      Fourth, when applying positive pressure ventilation, we will look for a positive deflection
      on the pressure curve. The output from the pressure transducer will be saved from the Fluxmed
      respiratory mechanics monitor. Pes will be measured over at least five consecutive breaths
      selected at the end of the pressure recordings. Ultrasound recordings will be done with the
      BK 3500 ultrasound machine, using a linear high-resolution probe. The parameter measured is
      the distance between the pleura and peritoneum as seen on a 2D image. The thickness using
      B-mode ultrasound imaging at end expiration on 10cm H2O of positive end-expiratory pressure
      (PEEP) and on zero PEEP (ZEEP) will be assessed. Furthermore, the thickness with Mmode
      imaging, both at end-inspiration (TEI) and end-expiration (TEE) will be measured. A
      transducer will be placed on the right side of the body in the midaxillary line at the level
      of the 8th and 9th intercostal space, the so-called zone of apposition. The probe will be
      positioned perpendicular to the skin, and temporary markings will be applied to the skin.
      Subjects are positioned in a supine position. TEE will be measured just before the thickening
      start and TEI measured at maximal thickening. Measurements will be averaged out of three or
      more consecutive breaths. The thickening fraction (TF) is calculated as (TEI - TEE)/TEE and
      expressed as a percentage. Digital images will be stored and re-interpreted by a separate,
      blinded interpreter.The thickening fraction recordings will be repeated during different
      loads on the respiratory system, with varying the depth of anesthesia (mean alveolar
      concentration of anesthetic vapor - MAC) and different added respiratory loads with a
      threshold valve and different levels of PEEP. An anesthesia circle circuit with standard
      pediatric tubing will consistently be used. The lowest dose of opioids will be used to the
      extent clinically possible.

      Condition #1: during positive pressure ventilation, no spontaneous breaths Condition #2:
      spontaneous, MAC 1.5, PEEP, no added respiratory load Condition #3: spontaneous, MAC 1.5,
      PEEP 10, no added respiratory load (only Tdi, no TF) Condition #4: spontaneous, MAC 1.5,
      ZEEP, no extra added respiratory load Condition #5: spontaneous, MAC 1, ZEEP, no added
      respiratory load Condition #6: spontaneous, MAC 1, ZEEP, 7 cm H2O added respiratory load
      Condition #7: spontaneous, MAC 1, ZEEP, 15 cm H2O added respiratory load

      These different conditions will alter the work of breathing the diaphragm has to perform and
      will allow us to better correlate thickening fraction with esophageal pressure.Preceding this
      study, a reproducibility study will assess intra-observer reproducibility for the researcher
      doing the ultrasound measurements.

      A power analysis is not possible, as this is the first study comparing these parameters in
      children. Data will be analyzed using the SPSS statistical software package (SPSS Inc., IL,
      USA). Continuous variables will be reported as median (interquartile range). Friedman test
      and Wilcoxon paired tests (with post hoc Bonferonni correction) will be used to assess
      differences between related variables. Correlations between TF and Pes will be calculated
      using the Spearman method and performed for the entire data set (including all four
      respiratory conditions of each patient) because of the limited sample size. Two-tailed p
      values less than 0.05 will be considered significant.

      All precautions will be taken to prevent complications due to placement of the balloon
      catheter but nevertheless all adverse events will be assessed.
    

Intervention name(s): Diaphragmatic echography; Measurement of esophageal pressure; Registration of respiratory mechanics
Intervention type(s): Procedure; Procedure; Diagnostic Test
Intervention description(s): Echography of the diaphragm at the zone of apposition. End-inspiratory and/or end-expiratory thickness of the diaphragm will be measured in M-mode.; Pressure will be measured in the lower third of the esophagus using an esophageal balloon and pressure transducer.; Pressures and volumes will be registered by the Fluxmed respiratory monitor (MBMED, Argentina)
Intervention model: Single Group Assignment
Intervention model description: a single-centre physiological cohort study to evaluate the feasibility of using the thickening fraction as a parameter for diaphragm activity during spontaneous breathing in sedated children.
Masking: None (Open Label)
Primary purpose: Diagnostic
Keywords: diaphragm thickening fraction; oesophageal pressure