18

18 CASE 18


A 40-year-old male comes to his primary care physician complaining of blurred vision and a headache.


The patient has a 6-year history of hypertension and hyperlipidemia. The hypertension has been poorly controlled because of noncompliance. The patient works in a manufacturing plant and has smoked 1 pack of cigarettes per day for the past 20 years.



PHYSICAL EXAMINATION



VS: T 37°C, P 68/min, R 22/min, BP 210/150 mm Hg and the same in all four extremities, BMI 28

PE: The patient is anxious and complains of an inability to concentrate because of the headaches. He does not remember urinating during the past day and is unable to provide a urine sample for analysis. A presystolic murmur (fourth heart sound) is evident. Funduscopic examination shows swelling of the optic nerve in both eyes (papilledema).


LABORATORY STUDIES



SMA-12: BUN 160 mg/dL (normal: 7-20 mg/dL); Creatinine: 8.2 mg/dL (normal: 0.8 to 1.4 mg/dL)

Blood gas analysis: PO2 90 mm Hg, PCO2 33 mm Hg, HCO3− 12 mEq, pH 7.30

Plasma renin activity: 25 ng/mL/hr (normal: 1.9 to 3.7 ng/mL/hr)

ECG: Normal sinus rhythm, left axis deviation, no shift in ST segment

Cardiac enzymes (myosin, CK-MB): Normal


DIAGNOSIS


Malignant hypertension



PATHOPHYSIOLOGY OF KEY SYMPTOMS


The kidneys provide chronic regulation of blood pressure through the processes of pressure diuresis and pressure natriuresis. Normally, hypertension produces few if any symptoms. Malignant hypertension is an example of a hypertensive emergency in which the elevated blood pressure is life threatening.


The presenting symptoms of blurred vision and headache are caused by cerebral edema. The abnormally large arterial pressure exceeds the autoregulatory range of the cerebral circulation and results in an increase in cerebral capillary pressure. Increasing capillary pressure causes a net filtration of plasma into the central nervous system (CNS), resulting in cerebral edema. Increased pressure within the cranial vault causes neurologic impairment and papilledema, a bulging of the optic nerve that is visible through a funduscope.


Malignant hypertension causes target organ damage, particularly to the kidney. The patient is likely in renal failure, indicated by the elevation in blood urea nitrogen and creatinine, the lack of urine production, and the metabolic acidosis. Metabolic acidosis is characterized by an acidic pH, a decrease in plasma HCO3− levels, and a compensatory decrease in PCO2. The kidneys normally excrete slightly acidic urine, and, consequently, impaired renal function usually leads to a metabolic acidosis (Fig. 18-1).


image

FIGURE 18–1 Acid-base nomogram showing arterial blood pH, arterial plasma HCO3−, and PCO2 values. The central open circle shows the approximate limits for acid-base status in normal people. The shaded areas show the approximate limits for the normal compensations caused by simple metabolic and respiratory disorders. For values lying outside the shaded areas, one should suspect a mixed acid-base disorder.


(Adapted from Cogan MG, Rector FC Jr: Acid-Base Disorders in the Kidney, 3rd ed. Philadelphia, WB Saunders, 1986.)

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Jul 4, 2016 | Posted by in PHYSIOLOGY | Comments Off on 18

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