Marcela (guest) 22 Jul 2011 16:27
Does somebody knows a lab where I can send a sports drink to get the osmolarity?
Electrolytes and Acid-Base Balance / Discussion
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Marcela (guest) 22 Jul 2011 16:27
Case 1
A febrile 84-year-old woman is brought from a nursing home to the emergency department of a local hospital. She is severely cachectic, confused, has sagging skin folds, and extremely dry skin. Admission chemistry tests are: serum sodium 168 mmol/L, serum potassium 6.2 mmol/L, chloride 130 mmol/L, and HCO3- 26 mmol/L. The serum osmolality is found to be 360 mOsm/kg of water. A urea nitrogen drawn at admission is 38 mg/dL and the patient’s hematocrit is 58%.
1.Explain the elevated serum sodium and the elevated serum osmolality.
2.Explain the elevated urea-N.
3.What other laboratory studies are indicated?
4.Explain the high hematocrit in this patient.
5.Propose possible reasons for this patient’s abnormal laboratory data.
Case 2
A 40-year-old male presents to the emergency department confused and with the odor of alcohol on his breath. Chemistry tests performed at the time of admission show the following: serum sodium 137 mmol/L, potassium 4.2 mmol/L, chloride 100 mmol/L, and HCO3- 26 mmol/L. The urea-N was 14 mg/dL and glucose was 90 mg/dL. The serum osmolality, however, is 360 mOsm/kg of water.
1.Propose a reason for the patient’s elevated serum osmolality.
2.How would you test your hypothesis?
3.Discuss reasons for serum hyperosmolality in the emergency department patient.
4.Calculate the osmolality based on the above data.
5.Assuming the elevated osmolality is due to ethanol, calculate the patient’s expected blood ethanol concentration.
Case 3
An 8-year-old girl was brought to the hospital with a 4-day history of profuse diarrhea. She was listless and responded rather incoherently to questions. Her skin turgor was poor for a child her age, and her eyes were soft and sunken. Pulse was 114 beats/minute with a BP of 98/66 mmHg. Respirations were deep and at a rate of 26/minute. Hematocrit was 58%. Lungs were clear, and the abdomen was soft without evidence of significant local tenderness. The following laboratory data were obtained:
ABG
pH = 7.13 pCO2 = 18 mmHg
pO2 = 96 mmHg HCO3 = 6 mmol/L
Serum Electrolytes
Na+ = 133 mmol/L K+ = 3.1 mmol/L
Cl- = 115 mmol/L total CO2 = 7 mmol/L
1.What is the nature and etiology of the acid-base disorder in this patient?
2.Is there evidence for and expected degree of compensation for this disorder?
3.Explain the low serum potassium.
4.Is there evidence for abnormalities of electrolyte fluid balance? If so, how might such a disturbance impact serum potassium?
5.Is serum K+ a good indicator of total body K+ for patients with acid-base abnormalities?
6.What are the causes of the high pulse rate, low blood pressure, and high respiratory rate?
7.Why is the serum chloride increased?
Case 4
A 21-year-old woman with an eight-year history of juvenile onset diabetes was brought to the hospital in a coma. She had required 92 units of insulin daily to maintain her blood glucose concentration in an acceptable range and prevent excessive glucosuria. On admission she had a BP of 92/20 mmHg, a pulse of 122 beats/min, and deep respirations of 32/min. Lab data showed:
ABG:
pH = 7.10 pCO2 = 15 mmHg
pO2 = 90 mmHg HCO3 = 4 mmol/L
Serum Chemistry Values:
Na+ = 129 mmol/L K+ = 6.4 mmol/L
Cl- = 95 mmol/L total CO2 = 5 mmol/L
glucose = 1200 mg/dL urea nitrogen = 74 mg/dL
creatinine = 2.3 mg/dL
The serum was strongly positive for ketones.
Eight units of regular insulin were given IV and 8 units/h were given by IV infusion pump. Her serum glucose concentration fell at a rate of approximately 100 mg/dL each hour. In seven hours her ventilation and blood pH were normal following IV injection of NaHCO3 and vigorous fluid and electrolyte replacement.
1.What is the nature and etiology of the acid-base disturbance?
2.Is there indication for a normal compensatory response?
3.What are serum ketones (ketone bodies)? How are they frequently detected?
4.Explain the abnormal serum potassium result.
5.Explain the low serum sodium result.
6.What is the cause of the low BP upon admission? How does the low BP affect GFR (glomerular filtration rate)?
7.Calculate the patient’s anion gap. Explain.
8.Calculate the patient’s osmolality. Interpret.
Case 5
(Nephrol. Dial. Transplant. 14(1):226-230, 1999)
A 54-year-old male was admitted to emergency department with progressive weakness, somnolence, and shortness of breath 5 days after receiving chemotherapy (ifosfamide 2 g/m2) for recurrence of sarcoma. Past medical history included diabetes mellitus type II that was diet controlled.
Initial labs: creatinine 3.5 mg/dL, K+ 2.3 mmol/L, Na+ 147 mmol/L, Cl- 122 mmol/L, glucose 400 mg/dL.
Initial therapy included isotonic saline, 60 mmol of KCl and subcutaneous insulin. On day 2 similar labs as above were obtained. Blood gases were measured and an initial diagnosis of ketoacidosis was made.
Patient was admitted to ICU with blood pressure of 120/60 mmHg and heart rate regular at 120/min. Respiration rate was 36/min, deep, and labored.
Labs
Analyte
Units
Day 3
Day 4
Reference Range
Na+ mmol/L 160 162 135 - 145
K+ mmol/L 2.3 4.0 3.5 - 5.2
Cl- mmol/L 140 132 97 - 108
Glucose mg/dL 300 307 76 - 110
Creatinine mg/dL 3.7 4.4 0.3 - 1.2
pH 7.24 7.46 7.34 - 7.44
pCO2 mmHg 12 20 35 - 46
pO2 mmHg 122 87 69 - 116
HCO3 mmol/L 5 14 22 - 26
1.The initial therapy included KCl and insulin. Why was the KCl necessary?
2.Were any important lab results missing from the initial studies?
3.How do you interpret the creatinine values?
4.Calculate the anion gap for day 3. Does this support the initial diagnosis of ketoacidosis?
5.What is the nature of this acid-base disturbance?
6.Is there evidence of compensatory mechanisms?
7.Propose a drug-induced mechanism for these laboratory results. Is this adverse reaction typical of this class of drugs?
Case 6
A 25-year-old woman with a history of surgical removal of an adenoma of the pituitary returns to her internist complaining of unquenchable thirst, and excretion of voluminous amounts of urine daily. Laboratory studies drawn in the physician’s office reveal the following: serum sodium 160 mmol/L, potassium 4.8 mmol/L, chloride 125 mmol/L and HCO3- 24 mmol/L. The patient’s serum osmolality is found to be 335 mOsm/kg of water.
1.What further laboratory studies are indicated?
2.What is the most likely diagnosis?
Case 7
A 14-year-old boy who had never been immunized against poliomyelitis contracted the disease late in the summer. He was hospitalized and required the use of a respirator during the acute phase of his illness. When he appeared to be recovering, he was taken off the respirator with no apparent ill effects. Several days later an analysis of his blood revealed the following:
ABG:
pH = 7.32 pCO2 = 70 mmHg
pO2 = 52 mm Hg HCO3- = 35 mmol/L
Serum
Na+ = 136 mmol/L K+ = 4.5 mmol/L
Electrolytes
Cl- = 92 mmol/L total CO2 = 36 mmol/L
1.What is the nature and cause of the acid-base disturbance in this boy? What are other causes of this type of acid-base disorder?
2.What are the normal compensatory mechanisms in response to this acid-base disturbance?
3.Is there evidence that these compensatory mechanisms are operative in this case?
4.Differentiate compensatory responses in acute and chronic respiratory abnormalities of acid-base metabolism.
5.What is included in the measurement of total CO2 in serum?
6.Bicarbonate is generally included in the test panel: pH/blood gases. How is the bicarbonate value determined and what is its relationship to total CO2 in serum?
7.Why is serum chloride decreased?
Table 1: Classification and Characteristics of Simple Acid-Base Disorders
Primary Change
Compensatory Response
Expected Compensation
METABOLIC
Acidosis ↓↓↓ cHCO3- ↓↓ pCO2 pCO2 = 1.5 (cHCO3-) + 8 ± 2, pCO2 falls by 1-1.3 mmHg for each mmol/L fall in cHCO3-, Last 2 digits of pH = pCO2 (e.g., if pCO2 = 28, pH = 7.28), cHCO3- + 15 = last 2 digits of pH, cHCO3- = 15, pH = 7.30
Alkalosis ↑↑↑ cHCO3- ↑↑ pCO2 pCO2 increases 6 mmHg for each 10 mmol/L rise in cHCO3- , cHCO3- + 15 = last 2 digits of pH (cHCO3- = 35, pH = 7.50)
RESPIRATORY
Acidosis
Acute ↑↑↑ pCO2 ↑ cHCO3- cHCO3- increases by 1 mmol/L for each 10 mmHg rise in pCO2
Chronic ↑↑↑ pCO2 ↑↑ cHCO3- cHCO3- increases by 3.5 mmol/L for each 10 mmHg rise in pCO2
Alkalosis
Acute ↓↓↓ pCO2 ↓ cHCO3- cHCO3- falls by 2 mmol/L for each 10 mmHg fall in pCO2
Chronic ↓↓↓ pCO2 ↓↓ cHCO3- cHCO3- falls by 5 mmol/L for each 10 mmHg fall in pCO2
Modified from Narins RG and Gardner LB, Simple acid-base disturbances, Med. Clin. North Am. 65:321-346, 1981 [Tietz Textbook of Clinical Chemistry, 3rd edition, table 32-4, p. 1115].
Ch10-Fig4.jpg
Figure 4: Acid-Base Map: area of normal values is labeled N; map actually extends further up than shown (to a pH of 6.6) and further to right than shown (to a pCO2 of 180 mmHg); numbered lines represent isopleths for bicarbonate (in milliequivalents per liter); from Goldberg M et al., Computer-based instruction and diagnosis of acid-base disorders: a systematic approach, JAMA 223:269-275, 1973, p. 270
Case 3
An 8-year-old girl was brought to the hospital with a 4-day history of profuse diarrhea. She was listless and responded rather incoherently to questions. Her skin turgor was poor for a child her age, and her eyes were soft and sunken. Pulse was 114 beats/minute with a BP of 98/66 mmHg. Respirations were deep and at a rate of 26/minute. Hematocrit was 58%. Lungs were clear, and the abdomen was soft without evidence of significant local tenderness. The following laboratory data were obtained:
ABG
pH = 7.13 pCO2 = 18 mmHg
pO2 = 96 mmHg HCO3 = 6 mmol/L
Serum Electrolytes
Na+ = 133 mmol/L K+ = 3.1 mmol/L
Cl- = 115 mmol/L total CO2 = 7 mmol/L
1.What is the nature and etiology of the acid-base disorder in this patient?
2.Is there evidence for and expected degree of compensation for this disorder?
3.Explain the low serum potassium.
4.Is there evidence for abnormalities of electrolyte fluid balance? If so, how might such a disturbance impact serum potassium?
5.Is serum K+ a good indicator of total body K+ for patients with acid-base abnormalities?
6.What are the causes of the high pulse rate, low blood pressure, and high respiratory rate?
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