Autonomics and Orthostatics

Autonomics and Orthostatic Hypotension - Ruey Hu

Background

  • Orthostatic Hypotension (OH) = SBP ↓ > 20 mmHg (or DBP ↓ > 10 mmHg) within 3 min of standing up or head-up tilt to 60% on a tilt table
  • If HR rise is < 15, it’s probably neurogenic OH (nOH)
  • If HR rise >15 within 3 min of standing, it’s non-neurogenic OH
  • In normal ppl, standing causes minimal changes (SBP ↓ less than 10, DBP rises less than 2.5) and HR rises modestly by 10-20
  • Etiology: volume depletion (most common), medications, neuropathy, neurodegenerative disease (Parkinsonism), pump failure (severe AS, arrhythmia)

 

Evaluation

  • Orthostatic vitals sign measurement:
    • Lying BP & HR, then wait 5 mins
    • Sitting BP & HR, then wait 5 mins
    • Standing BP & HR at 1, 3, and 5 mins
      • If pt falls before 5 mins is up, get BP & HR before and after falling
      • If supine HTN present, skip the supine step to avoid risk of stroke
  • Volume status exam, CBC, BMP, EKG, TSH, B12, MMA, LFTs, SPEP/UPEP
  • Rarely neoplastic panels, supine/standing plasma fractioned catecholamine levels and autonomic function testing

 

Management

  • Neurogenic:
    • Conservative measures: TED hose, Elevate HOB and Abdominal binder
    • Drink 16oz of fluid 15 min prior to standing
    • If they have supine HTN, keep HOB 30-45 degrees at all times
  • Outpatients: TED hose and abdominal binder.
    • Add 2.3-4.6g of salt per day to diet (if no contraindications, e.g. CHF)
    • Do non-gravitationally challenging exercises: stationary bike, rower or water activities
    • Avoid high temperatures (which cause peripheral vasodilation)
  • Pharmacologic therapies:
 

Drug

Dose

Mech

Side effects

Fludocortisone (Florinef)

0.1mg QD

↑ by 0.1 mg

Max: 0.3 mg QD

Mineralocorticoid → ↑s blood volume. Also enhances sensitivity of BVs to circulating catecholamines

Edema If Seated or supine HTN, may have to DC or ↓ dose HoK ß Check K b4 start’g & w/I 1-2 wk of dose adjustment, & supplement CI’d by CHF, bc Florinef retains salt

Midodrine

2.5mg TID CC

↑ by 2.5mg

Up to 10mg TID

Peripheral-selective α1 agonist → constricts both aa & vv

cautious severe heart dz, unctrl’d HTN, or urinary retention. SE: supine HTN, pilomotor reactions, pruritus, GI sx, urinary retention. Don’t take 4h prior to bedtime, to limit supine HTN

Droxidopa

100mg

↑ by 100mg

Max: 600mg TID

NE precursor → carboxylated to NE. Can cross BBB.

SE: supine HTN, but less than midodrine Don’t take 4h prior to bedtime, to limit supine HTN

Atomoxetine

10mg or 18mg

SNRI

CI’d by glaucoma and MAOI

 

Additional Information

  • Ephedrine, pseudoephedrine, methylphenidate, and dextroamphetamine are no longer used to treat nOH because of lack of efficacy and intolerable CNS effects
  • Autonomic Function Testing: Available at 4:15pm Tues, Wed, Thurs NPO 4 hours prior
    • Hold oral pressors and antihypertensives 12 hours prior