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Equilibration Time Required for Respiratory System Compliance and Oxygenation Response Following Changes in Positive
Craig D Smallwood1,2,3, Brian K Walsh1,2, John H Arnold1,2
1Division of Critical Care Medicine, Department of Anesthesia, Perioperative and Pain Medicine, Boston Children's Hospital, Boston, MA.
Insights
In pediatric patients on mechanical ventilation, dynamic compliance improved within 38 minutes of increasing positive end-expiratory pressure (PEEP), while oxygenation took 71 minutes. The time for oxygenation to improve with PEEP varied based on illness severity.
Area of Science:
- Pediatric Critical Care Medicine
- Respiratory Physiology
- Mechanical Ventilation
Background:
- Positive end-expiratory pressure (PEEP) increases are used to enhance oxygenation by recruiting and stabilizing alveoli.
- The temporal dynamics of PEEP's effects on oxygenation and pulmonary compliance in children are not well-established.
Purpose of the Study:
- To quantify the time required for maximal oxygenation and pulmonary compliance changes in pediatric patients receiving mechanical ventilation following PEEP adjustments.
- To investigate the influence of illness severity on these response times.
Main Methods:
- Retrospective analysis of continuous data from mechanically ventilated pediatric subjects.
- Calculation of time to 90% (T90) of maximum change for oxygenation and dynamic compliance after PEEP increases.
- Comparison of T90 values and analysis of the effect of oxygen saturation index on response times.
Main Results:
- Dynamic compliance changes occurred significantly earlier (T90 = 38 minutes) than oxygenation changes (T90 = 71 minutes; p < 0.001).
- Oxygenation response time was dependent on illness severity, with greater lung dysfunction associated with longer response times (p = 0.001).
Conclusions:
- Significant time lags exist between improvements in pulmonary compliance and oxygenation following PEEP increases in pediatric patients.
- These findings highlight the importance of considering illness severity when interpreting oxygenation responses to PEEP in mechanically ventilated children.
Objectives:
Increases in positive end-expiratory pressure are implemented to improve oxygenation through the recruitment and stabilization of collapsed alveoli. However, the time it takes for a positive end-expiratory pressure change to have maximum effect upon oxygenation and pulmonary compliance has not been adequately described in children. Therefore, we sought to quantify the time required for oxygenation and pulmonary system compliance changes in children requiring mechanical ventilation.
Design:
Retrospective analysis of continuous data.
Settings:
Multidisciplinary ICU of a pediatric university hospital.
Patients:
Mechanically ventilated pediatric subjects.
Interventions:
A case was eligible for analysis if during a 90-minute window following an increase in positive end-expiratory pressure, no other changes to the ventilator were made, ventilator and physiologic data were continuously available and a positive oxygenation response was observed. Time to 90% (T90) of the maximum change in oxygenation and compliance was computed. Differences between oxygenation and compliance T90 were compared using a paired t test. The effect of severity of illness (by oxygen saturation index) upon oxygenation and compliance was analyzed.
Measurements And Main Results:
A total of 200 subjects were enrolled and 1,150 positive end-expiratory pressure change cases were analyzed. Of these, 54 subjects with 171 positive end-expiratory pressure change case were included in the analysis (67% were responders).Changes in dynamic compliance (T90 = 38 min) preceded changes in oxygenation (T90 = 71 min; p < 0.001). Oxygenation response differed depending on severity of illness quantified by oxygen saturation index; lung dysfunction was associated with a longer response time (p = 0.001).
Conclusions:
T90 requires 38 and 71 minutes for dynamic pulmonary compliance and oxygenation, respectively; the latter was directly observed to be dependent upon severity of illness. To our knowledge, this is the first report of oxygenation and compliance equilibration data following positive end-expiratory pressure increases in pediatric mechanically ventilated subjects.
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