title: Feasibility of continuous multiorgan variability analysis in the intensive care unit.
abstract: OBJECTIVE
  The aim of the study was to evaluate the feasibility of continuous heart and respiratory rate variability (HRV and RRV, respectively) monitoring in critically ill patients derived from electrocardiogram (ECG) and end-tidal capnography (etCO(2)) waveforms.
  
  
  METHODS
  Thirty-four patients (age, 56.5 ± 15.9 years; Acute Physiology and Chronic Health Evaluation II score, 22.8 ± 6.7) underwent continuous recording of ECG and etCO(2) waveforms from intensive care unit admission and intubation to discharge or maximum of 14 days. Overlapping 5-minute windows were analyzed with a wide range of variability measures (time, frequency, entropy, and scale-invariant and nonlinear domains). Waveform data quality, presence of disconnections and arrhythmias, quality of beat and breath detection, and subsequent variability computations were evaluated.
  
  
  RESULTS
  Patients were enrolled for 11.0 ± 3.6 days. The proportion of missing waveform data among all patients was (median [interquartile range, maximum]) 2.9% (1.3%-9.7%, 36.4%) for ECG and 3.1% (1.1%-11.4%, 84.5%) for etCO(2). Heart rate variability data loss (ie, proportion of windows removed) was 1.3% (1.0%-2.1%, 5.9%) due to disconnection, 0.6% (0.1%-3.9%, 39.5%) due to atrial fibrillation, and 6.6% (1.4%-17.9%, 89.0%) due to data cleaning. Respiratory rate variability data loss was 7.3% (2.9%-11.6%, 47.7%) due to disconnection (or apnea) and 5.5% (2.9%-8.4%, 56.4%) due to cleaning. Continuous individualized multiorgan variability analysis processing resulted in HRV and RRV computations for 81.2% ± 25.0% and 87.5% ± 11.9% of available ECG and etCO(2) waveform data, respectively.
  
  
  CONCLUSIONS
  The quality of continuously recorded ECG and etCO(2) waveforms in critically ill patients is adequate for subsequent continuous variability monitoring in this pilot study. The clinical utility of continuous variability analysis merits further investigation.
authors.affiliation: Ottawa Hospital Research Institute, Ottawa, Ontario, Canada K1H 8L6.
authors.forename: Beverly
authors.initials: B
authors.lastname: Bradley
authors.forename: Geoffrey C
authors.initials: GC
authors.lastname: Green
authors.forename: Izmail
authors.initials: I
authors.lastname: Batkin
authors.forename: Andrew J E
authors.initials: AJ
authors.lastname: Seely
mesh_terms: D000328:Adult; D000368:Aged; D019296:Capnography / Q000379:methods*; D003422:Critical Care / Q000379:methods*; D016638:Critical Illness; D004562:Electrocardiography; D005240:Feasibility Studies; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods; D010865:Pilot Projects; D015203:Reproducibility of Results; D056152:Respiratory Rate / Q000502:physiology*