Hyperventilation Syndrome

02/07/2014

An 18 yo male with a past medical history sig for Anxiety, Depression and OCD presented to the ED on 02/07 with a chief complaint of "my heart is racing and I feel as if I can't catch my breath". Pt stated that he had recently been discharged from West Penn inpatient psych 2 days ago. He was admitted for anxiety attacks, made progress and was doing well until he had been d/c home. For the past day he has been experiencing palpitations and a sense of impending doom. EKG showed tachycardia at 140 bpm and normal sinus rythm with no changes in ST waves, blood pressure was 98/82, tachypnea at 24, Tox screen was negative, CBC normal and CMP showed hypokalemia at 2.3 and hypophosphatemia at 1.5 and low bicarb at 18. Calcium and Mg were nomal. Pt had no other medical problems, was recently started on Abilify, Vistril 2 weeks ago and Ativan prn. He denies smoking, drinking or drugs, glue/paint sniffing. He hasn't had any nausea or vomiting but has had 2 lose bowel movements since yesterday. Physical exam was remarkable for tachycardia only. We, Nephrology, were consulted for the pt's hypokalemia and hypophosphatemia. 

My attending sent me to start the consult. This was a humbling case and reminded me of how little I still know (that happens every day, actually). I was heading down the path of problems with the kidney function itself or possibly a side effect of the new medications (Abilify has a very small, < 1%, side effect of hypokalemia)."The pt has low bicarb and hypokalemia... perhaps he has aquired Renal Tubular Acidosis type II". I wanted lab work that looked at the kidney's ability to function normally such as urine ph and urine lytes. My attending agreed and we went to see the pt together. While in the room, the attending noted that pt took a few deep sighs/min. The pt also told the attending that he has been experiencing numbness and tingling around the mouth and and his thumbs would tighten up. This is where I went wrong. I didn't notice the sighing when I interviewed the pt and he didn't tell me about the tingling or carpal spasms, but I didn't think to ask about them either. My attending was suspicious that respiratory alkalosis may be the cause for his electrolyte abnomalities and ordered an ABG. ABG came back with a PH of 7.52, CO2 of 25 and HCO3 of 17. I learned that this pt's electrolyte abnormalities were caused by Hyperventilation Syndrome most likely secondary to Anxiety. 

Hyperventilation Syndrome

Etiology

Psychopatholgy-The association between hyperventilation syndrome and psychological pathologies (such as panic/anxiety disorder) is strong and the most likely the cause of our pt's hyperventilation and subsequent electrolyte disturbance. As I looked back in the ED records, he had been admitted 1 year ago due to a biking accident with no record of depression or anxiety. At that visit, he had normal electrolytes which makes a disorder of the kidney less likely the cause of his low potassium and phosphate. 

Regulatory systems-Abnormalities in the reticular activating system have been proposed as a cause for hyperventilation syndrome. When asked to breath through a mouthpiece, pt's with abnormal control can have induced hyperventilation and may point to overactivation of the reticular activating system. 

Epidemiology

Up to Date reports that there is a strong correlation with hyperventilation syndrome and anxiety/panic attacks. The prevalence of hyperventilation syndrome has been reported to range from 25 to 83 percent in patients with an anxiety disorder but only about 11 percent in patients with nonpsychiatric medical comorbidities. 

Clinical Presentation

Up to Date states that the cardinal feature of hyperventilation syndrome is a transient increase in minute ventilation. Patients with hyperventilation syndrome present with a variety of somatic and nonsomatic complaints related to the increased respiration.

Somatic signs and symptoms 

Dyspnea-pt complained of this

Light-headedness

Paresthesias-pt complained of perioral parathesisas

Chest pain

Palpitations-pt complained of this

Diaphoresis

Carpopedal spasm-pt complained of carpal spasms

Diagnosis

There is no gold standard and is based mostly on clinical suspicion. Of course, you need to r/o serious underlying causes of hyperventilation (get chest xray and EKG)

Treatment

If psych is the underlying cause, the treatment is based on reassurance, pt education and cognitive-behavioral therapy. Prevention of further anxiety and panic attacks is key. 

So, the patient had Hyperventilation Syndrome but why did he have the electrolyte abnomalities (hypophosphatemia, hypokalemia and decreased HCO3)?

Hypophosphatemia-CO2 is the biggest source of acid in the body because it binds H20 in the blood and forms carbonic acid which then dissociates into H+ and HCO3-.When you hyperventilate, you blow off more CO2 and become alkalotic. Since CO2 diffuses freely across cells, the intracellular PH easily becomes alkalotic. Alkalosis stimulates an enzyme phosphofructokinase which then stimulates glycolysis. Glycolysis increases the formation of phosphorylated carbohydrate compounds in the liver and skeletal muscle. The source of the phosphate needed is in the serum. Thus, you use up serum phosphate and you will see a drop in serum phosphate = Hypophosphatemia!!!

Hypokalemia-In the presence of alkalemia, hydrogen leaves the intracellular space into the extracellular space to try and help achieve a normal PH. Potassium must enter the cell in exchange for the hydrogen leaving the cell to maintain electroneutrality. Thus, you see a drop in drop in serum potassium. 

Decreased HCO3-this is simply the metabolic compensation for the respiratory alkalosis. 

Great case!! I learned a lot with this one!