Cramps and tingling: A diagnostic conundrum.

Tetany a syndrome of sharp flexion of the wrist and ankle joints (carpopedal spasm), muscle twitching, cramps and convulsions, sometimes with an attack of stridor, is due to hyperexcitability of nerves and muscles caused by decreased extracellular ionized calcium. Hyperventilation secondary to anxiety can result in tetany. We report a case of hyperventilation induced tetany 2 h following spinal anesthesia for inguinal hernia repair.

INTRODUCTION

Sudden onset of carpopedal spasms perioperatively following non-thyroid surgery can surprise the anesthesiologist. Tetany due to anxiety induced hyperventilation should be considered in the differential diagnosis.

CASE REPORT

The present case report is about a 30-year-old, 70 kg, 168 cm male patient who was scheduled for right inguinal hernioplasty. He had asthma for the last 10 years and was on regular treatment with salbutamol and beclomethasone rotahalers and was advised salbutamol and beclomethasone nebulizations at bedtime and on the morning of surgery prophylactically even though there was no active wheeze. No other premedication was prescribed.

Spinal anesthesia was administered at L3-L4 inter vertebral space using 17.5 mg of 0.5% hyperbaric bupivacaine. Sensory block up to fifth thoracic dermatome was attained. Transient fall in blood pressure was corrected with intravenous (IV) fluids and one aliquot of 6 mg mephenteramine. As the patient was anxious, midazolam 2 mg was administered IV. He complained of breathlessness and paresthesiae of hands and face. Sensory level of spinal anesthesia was rechecked, which did not show any further ascent and there was no wheeze. Patient was reassured, propped up by 30° and was administered oxygen through a face mask. Blood pressure, SpO2 and electrocardiogram (ECG) were within the normal limits. Surgical procedure lasted for an hour and the patient was shifted to the post-anesthesia care unit (PACU).

Within an hour of PACU admission [Figures 1 and 2], the patient developed painful spasm of both hands and was very restless. Patient was observed to have tachycardia and tachypnea but the blood pressure and oxygen saturation were within the normal limits. Emergency blood gas analysis of a venous sample revealed respiratory alkalosis with pH-7.57, pCO2-16 mmHg, PO2-30 mmHg, HCO3−-14.7 meq/L, Na+-133 mmol/L and low Ca+2- 0.76 mmol/L (normal being: 1.1-1.3 mmol/L), K+- 2.9 mmol/L.

Figure 1

Carpal spasms in the post-operative period due to hyper ventilation induced decrease in ionized calcium

Figure 2

Carpal spasms

5 ml of 10% calcium gluconate IV over 10 min followed by an infusion of 0.5 mg/kg/h and 10 meqs of KCl were administered over 1 h following which patient had symptomatic relief. IV midazolam was repeated to attenuate anxiety. Further post-operative course was uneventful.

DISCUSSION

Anxiety has many adverse perioperative consequences like decreased patient cooperation, activation of sympathoadrenergic reflexes leading to increase in heart rate, blood pressure and development of post-traumatic stress disorder. Hyperventilation is an autonomic response to extreme stress or fear (anxiety). Hyperventilation a condition in which breathing in excess of metabolic requirements results in hypocapnia is secondary to various medical (asthma, chronic bronchitis, emphysema, chronic obstructive pulmonary disease, pulmonary embolism, encephalitis and brain tumors) and psychiatric conditions, is also triggered by acute pain.[123]

Our patient was a known asthmatic and there are reports of dysfunctional breathing in asthmatics.[4] Long term β2 agonist therapy has the propensity to cause a decrease in serum electrolytes (Ca+ 2, K+, Mg+ 2, PO4−) and this could have been compounded by hyperventilation leading to frank tetany.

Normally <10% of gases in the alveoli are replaced with each breath. Hyperventilation leads to rapid exchange of alveolar gases with air, the net effect being drawing more carbon dioxide out of the body leading to hypocapnia. Since carbon dioxide is carried as bicarbonate in blood, loss of carbon dioxide will drive bicarbonate to combine with hydrogen ions to form more carbon dioxide. This causes a decrease in H+ ions leading to respiratory alkalosis.

Respiratory alkalosis dissociates bound hydrogen ions from albumin, which binds with calcium thereby decreasing the freely ionized portion of total serum calcium by 0.05 mmol/L for every 0.1 increase in pH.[56] Hypocalcemia increases neuronal excitability by decreasing the threshold potential needed to activate the sodium channel due to alteration of the electrical state of the channel protein.[7]

Hypomagnesemia occurs due to the same phenomenon as it has similar size and valency, as that of calcium.[5] Intracellular shift of K+ ions leads to hypokalemia. Serum K+ decreases by about 0.5 mmol/L for every 10 mmHg decrease in PaCO2.[2] Tetany can be induced by alkalosis, hypocalcemia, hypokalemia or hypomagnesemia.[1258] Our patient had three of the four causative factors. Serum magnesium levels were not assessed in this case. Hypomagnesemia should be considered, investigated and treated if symptoms of hypocalcemia are resistant to calcium replacement.

Clinical presentation of tetany is highly variable ranging from circumoral numbness, muscle cramps, paresthesiae of hands and feet to laryngospasm, generalized muscle cramps, syncope,[9] seizures (due to cerebral vasoconstriction) and myocardial dysfunction.[8] Trousseau's sign and Chvostek's sign can be used to unmask latent tetany. Our patient had paresthesiae of the upper part of the body, painful spasm of the hands and was spared of pedal spasm probably because of motor block induced by spinal anesthesia.

No gross changes in ECG were apparent in our patient in the single lead displayed on the monitor during the intra operative period. However, we did not obtain a post-operative 12 lead ECG, which would have probably shown the characteristic changes of hypocalcemia and hypokalemia and we proceeded with the treatment instead, based on symptomatology and blood gas analysis.

Venous blood sample was used in our case as sample collection causes relatively less pain and there is excellent correlation between venous and arterial ionized calcium levels even during acidosis and alkalosis.[10] Blood gas analysis of our patient showed respiratory alkalosis with partial compensation, indicated by a low HCO3 − value of 14.7. HCO3 − decreases by 2 meq/L in acute and 5 meq/L for every 10 mmHg fall in pCO2 in chronic respiratory alkalosis[11] which showed that the patient had a background of chronic hyperventilation superimposed by anxiety.

Treatment of the underlying cause is the mainstay of treatment of tetany. Calcium infusions can be used to treat symptomatic hypocalcemia. Rebreathing into a paper bag, which was the traditional treatment for hyperventilation is no longer recommended because of the potential risk of hypoxia.[512]

CONCLUSION

Breathing disorders are common in asthmatics. When chronic hyperventilation and β2 induced electrolyte abnormality is superimposed by anxiety, patients over ventilate enough to cause respiratory alkalosis and hypocalcemic tetany. Breath training and perioperative anxiety should be addressed to prevent such attacks. Hyperventilation and subsequent electrolyte imbalance are to be anticipated in vulnerable patients. Proper counseling, adequate preparation and timely intervention remain the cornerstones for an optimal outcome in such patients.