Fractal ventilation enhances respiratory sinus arrhythmia

BACKGROUND: Programming a mechanical ventilator with a biologically variable or fractal breathing pattern (an example of 1/f noise) improves gas exchange and respiratory mechanics. Here we show that fractal ventilation increases respiratory sinus arrhythmia (RSA) – a mechanism known to improve ventilation/perfusion matching. METHODS: Pigs were anaesthetised with propofol/ketamine, paralysed with doxacurium, and ventilated in either control mode (CV) or in fractal mode (FV) at baseline and then following infusion of oleic acid to result in lung injury. RESULTS: Mean RSA and mean positive RSA were nearly double with FV, both at baseline and following oleic acid. At baseline, mean RSA = 18.6 msec with CV and 36.8 msec with FV (n = 10; p = 0.043); post oleic acid, mean RSA = 11.1 msec with CV and 21.8 msec with FV (n = 9, p = 0.028); at baseline, mean positive RSA = 20.8 msec with CV and 38.1 msec with FV (p = 0.047); post oleic acid, mean positive RSA = 13.2 msec with CV and 24.4 msec with FV (p = 0.026). Heart rate variability was also greater with FV. At baseline the coefficient of variation for heart rate was 2.2% during CV and 4.0% during FV. Following oleic acid the variation was 2.1 vs. 5.6% respectively. CONCLUSION: These findings suggest FV enhances physiological entrainment between respiratory, brain stem and cardiac nonlinear oscillators, further supporting the concept that RSA itself reflects cardiorespiratory interaction. In addition, these results provide another mechanism whereby FV may be superior to conventional CV

Beat-by-beat cardiovascular index to predict unexpected intraoperative movement in anesthetized unparalyzed patients: a retrospective analysis

International audienceOBJECTIVE: Unexpected intraoperative movement may be detrimental during delicate surgery. This study tested retrospectively an algorithm based on beat-by-beat circulatory variables (incorporated into a Cardiovascular depth of anesthesia index: CARDEAN in relationship to unexpected movement, and compared its performance to that of the electroencephalogram (EEG)-derived index: BIS-XP 4.0. METHODS: 40 ASA I or II patients presenting for knee surgery had EEG (BIS XP 4.0), beat-by-beat (Finapres) finger non-invasive blood pressure (BP), conventional brachial BP and electrocardiogram (EKG) monitors attached. Anesthesia was induced and maintained with propofol and remifentanil. Before incision, the propofol concentration was set to maintain BIS < 60. From incision to emergence, the anesthesiologist was denied access to BIS or Finapres. Anesthesia adjustment was titrated at the discretion of the anesthesiologist according to conventional signs only: brachial BP, EKG, eyelash reflex, movement. Occurrences of movement and eye signs (divergence of eyeballs, tears, corneal reflex, eyelash reflex) were observed. The CARDEAN algorithm was written retrospectively and tested vs. BIS. RESULTS: 11 movements occurred in 8 patients. CARDEAN > 60 predicted movement in 30% of the cases, 15 to 274 s before movement (sensitivity: 100%, specificity: 95%; relative operating curve ROC = 0.98; prediction probability pk = 0.98). BIS > 60 predicted movement in 19% of cases (sensitivity: 64%; specificity: 94%, ROC: 0.85, pk: 0.85). CONCLUSION: Retrospectively, a cardiovascular index predicted unexpected intraoperative movements. Prospective validation is needed