0071643192.pdf

HEMATOLOGY, ONCOLOGY, ALLERGY,

AND IMMUNOLOGY

DIAGNOSIS

■ Co-oximetrycan differentiate between oxy-, deoxy-, carboxy-, and methe-

moglobinemias and allows confirmation of the diagnosis.

■ In patients with methemoglobinemia the partial pressure of O 2 in the

blood is usually normal, and an ABG typically yields a normal PaO 2 and

O 2 saturation.

TREATMENT

■ Methylene blue(1–2 mg/kg IV) facilitates the reduction of Fe3+changes

to Fe2+.

Sulfhemoglobinemia

Pathophysiology and causes are similar to methemoglobinemia, though usu-

ally less severe because sulfhemoglobinemia causes a rightward shift of the O 2

dissociation curve, favoring the release of O 2 (whereas methemoglobinemia

causes a leftward shift).

CAUSES

■ Nitrates, sulfonamides, trinitrotoluene

DIAGNOSIS

■ Co-oximetrywill identify the presence of an abnormal hemoglobin but

cannot differentiate between met- and sulfhemoglobin. Adding cyanide to

the blood sample changes the absorption pattern of methemoglobin and

allows for the identification of sulfhemoglobinemia.

TREATMENT

■ Supportive care

■ Transfusions may be necessary for severe toxicity.

■ Methylene blue does not reduce sulfhemoglobin. Because of the poten-

tial side effects of methylene blue (including paradoxical methemoglo-

binemia), an effort should be made to differentiate between sulf- and

methemoglobinemia.

ONCOLOGIC EMERGENCIES

Hypercalcemia of Malignancy

In the setting of cancer, hypercalcemia results from bone destruction (metas-

tasis, multiple myeloma), paraneoplastic syndrome (parathyroid hormonelike

substance), or osteoclast activation (lymphoma, leukemia).

SIGNS/SYMPTOMS

■ Generally present when levels exceed 12 mg/dL

■ Polyuria, nephrolithiasis, anorexia, nausea, vomiting, constipation, weak-

ness, confusion, pathologic fracture

DIAGNOSIS

■ Chemistries, serum PTH level

■ ECG with shortened QT interval

Paradoxical

methemoglobinemia—excess

methylene blue can cause

methemoglobinemia.

Inhaledhydrogen sulfide

(H 2 S) acts as a mitochondrial

toxin similar to cyanide and is

treated with nitratesin order

to induce a

methemoglobinemia. The

primary described mechanism

of toxicity is not via

sulfhemoglobinemia.

Symptoms of hypercalcemia:

Stones, bones, abdominal

groans, and psychiatric

overtones

Causes of Hypercal-

cemia—

MISHAP

Malignancy

Ingestion vitamin D,

calcium

Sarcoidosis

Hyperparathyroidism

Alkali-milk syndrome

Paget disease,

paraneoplastic

syndrome