The Benefits of Oral Rehydration on Orthostatic Intolerance in Children with Postural Tachycardia Syndrome

Abstract

Objective: To evaluate whether equal volumes of oral rehydration solution (ORS) or intravenous (IV) saline provide similar improvements in cardiovascular status during controlled orthostatic challenge when administered to subjects with postural tachycardia syndrome (POTS) with orthostatic intolerance.

Study design: We studied the neurovascular response to fluid loading during orthostatic stress using lower body negative pressure (LBNP) in 10 subjects with POTS with orthostatic intolerance and 15 controls, and on subsequent days before and 1 hour after IV saline infusion or ingestion of ORS.

Results: Subjects with POTS exhibited reduced tolerance to LBNP (P < .0001) compared with controls (Orthostatic Index of 35 715 ± 3469 vs 93 980 ± 7977, respectively). In POTS, following ORS but not saline infusion, cerebral blood flow velocity (CBF_v) was significantly higher than that with no treatment, at -45 mm Hg (P < .0005). Although fluid loading did not confer any advantage in controls, subjects with POTS experienced a significant improvement in orthostatic tolerance following both saline infusion (100 ± 9.7 vs 134.5 ± 17.4; P < .05) and ORS (100 ± 9.7 vs 155.6 ± 15.7; P < .001) when evaluated by normalized orthostatic index (P < .001, compared with untreated baseline).

Conclusions: Maintenance of CBF_v may have resulted in the improved short-term orthostatic tolerance exhibited by the subjects with POTS following ORS administration. ORS is a convenient, safe, and effective therapy for short-term relief of orthostatic intolerance.

Figure 1.

The response of a representative patient with OI to the imposition of a controlled orthostatic challenge using LBNP. The top panel shows that in the absence of supplemental fluid administration (No Fluid), presyncope occurred during exposure to −30 mmHg negative pressure. Following IV saline (Saline, middle panel), and after ingestion of oral rehydration solution (ORS, lower panel), enhanced orthostatic tolerance was achieved as presyncope occurred during exposure to −60 mmHg negative pressure.

Figure 2.

Changes in cardiac output (CO in L/min) in control (top panel) and POTS patients with OI (bottom panel) during imposition of a controlled orthostatic challenge using LBNP following no treatment (No TX – white bars), IV sal ine (Saline – gray bars) and ingestion of oral rehydration solution (ORS – black bars). Treatment effects for controls were not significantly different. For POTS, CO was significantly higher following ORS, compared with no treatment (* = No Tx, p<0.05), both at baseline and −45mmHg and saline had no significant effect.

Figure 3.

Changes in normalized cerebral blood flow velocity (normalizedCBF_V) in control (top panel) and POTS patients with OI (bottom panel) during imposition of a controlled orthostatic challenge using LBNP following no treatment (No TX – white bars), IV saline (Saline – gray bars) and ingestion of oral rehydration solution (ORS – black bars). Because there was no pressure effect, the comparisons reflect the combined effect (i.e., the weighted average) of the CBV_v in the ORS group vs. No Tx. In controls, normalized CBF_v was not significantly reduced at −45 mmHg, nor did fluid administration result in any significant change. In POTS, CBFv following ORS was significantly higher than No TX (ǂ = p<0.0005), which was independent of pressure.

Figure 4.

Changes in normalized orthostatic index (% of that measured without treatment in control (black bars) and POTS patients with OI (gray bars) measured following no treatment (Untreated), intravenous saline (IV Saline) and ingestion of oral rehydration solution (ORS). Neither saline nor ORS increased orthostatic tolerance in untreated controls (p=0.46, N=15); both I.V. saline and ORS significantly improved orthostatic tolerance (* = p<0.05 and ** = p<0.001, respectively, N=10) in POTS subjects.