Intravenous cannulation of adolescents does not affect the modulation of autonomic tone assessed by heart rate and blood pressure variability

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Abstract
Invasive arterial monitoring alters autonomic tone. The effects of intravenous (IV) insertion are less clear. The author assessed the effects of IV insertion on autonomic activity in patients aged 11 to 19 years prior to head-up tilt by measuring heart rate, blood pressure, heart rate variability, blood pressure variability, and baroreceptor gain before and after IV insertion with continuous electrocardiography and arterial tonometry in patients with orthostatic tachycardia syndrome (OTS, N=21), in patients who experienced simple fainting (N=14), and in normal control subjects (N=6). Five-minute samples were collected after 30 minutes supine. Fifteen minutes after IV insertion, data were collected again. These 5-minute samples were also collected in a separate control population without IV insertion after 30 minutes supine and again 30 minutes later. This population included 12 patients with OTS, 13 patients who experienced simple fainting, and 6 normal control subjects. Heart rate variability included the mean RR, the standard deviation of the RR interval (SDNN), and the root mean square of successive RR differences (RMSSD). Autoregressive spectral modeling was used. Low-frequency power (LFP, 0.04–0.15 Hz), high-frequency power (HFP, 0.15–0.40 Hz), and total power (TP, 0.01–0.40 Hz) were compared. Blood pressure variability included standard deviation of systolic blood pressure, LFP, and HFP. Baroreceptor gain at low frequency and high frequency was calculated from cross-spectral transfer function magnitudes when coherence was greater than 0.5. In patients with OTS, RR (790±50 msec), SDNN (54±6 msec), RMSSD (55±5 msec), LFP (422±200 ms2/Hz), HFP (846±400 ms2/Hz), and TP (1550±320 ms2/Hz) were less than in patients who experiences simple fainting (RR, 940±50 msec; SDNN, 84±10 msec; RMSSD, 91±7 msec; LFP, 880±342 ms2/Hz; HFP, 1720±210 ms2/Hz; and TP, 3228±490 ms2/Hz) or normal control subjects (RR, 920±30 msec; SDNN, 110±29 msec; RMSSD, 120±16 msec; LFP, 1600±331 ms2/Hz; HFP, 2700±526 ms2/Hz; and TP, 5400±1017 ms2/Hz). Blood pressure and blood pressure variability were not different in any group. Standard deviation, LFP, and HFP were, respectively, 5.24±0.8 mm Hg, 1.2±0.2, and 1.5±0.3 for patients with OTS; 4.6±0.4 mm Hg, 1.2±0.2, and 1.4±0.3 for patients who experienced simple fainting; and 5.55±1.0 mm Hg, 1.4±0.2, and 1.6±0.3 for normal control subjects. Baroreceptor gain at low frequency and high frequency in patients with OTS (16±4 msec/mm Hg 17±5) was comparable to that in patients who experienced simple fainting (33±4, 32±3) and that in normal control subjects (31±8, 37±9). Heart rate variability differed between patients with OTS and patients who experienced simple fainting or normal control subjects, and blood pressure and blood pressure variability were not different, but no parameter changed after IV insertion. There were no differences from the groups that did not receive IV insertions. Data suggest, at most, a limited effect of IV insertion on autonomic function in adolescents.