Chronic hypotension and hyponatraemia

Spinal cord injuries (SCI) at T6 and above disrupt autonomic nervous system (ANS) function, lowering peripheral vascular resistance. This can cause chronic hypotension. Sustained low blood pressure can stimulate the secretion of antidiuretic hormone (ADH) and may result in hyponatraemia.

Hyponatraemia is defined as a serum sodium concentration of less than 135 mmol/L.

Other factors that can influence sodium concentrations are:

excessive fluid intake
renal compromise
hypothyroidism
medications including diuretics, opioids, selective serotonin reuptake inhibitors (SSRIs) and non-steroidal anti-inflammatory drugs (NSAIDs)
inadequate salt intake
obstructive or central sleep apnoea
acute or chronic lung disorders, causing hypercapnia.

References

Song, P., Dong, F., Feng, C., Shen, Y., Wang, Y., Zhang, R., Ge, P., & Shen, C. (2018). A study of predictors for hyponatraemia in patients with cervical spinal cord injury. Spinal Cord, 56(1), 84–89. https://doi.org/10.1038/s41393-017-0023-1