Pyelonephritis, Unresponsive Case File
Eugene C. Toy, MD, Patti Jayne Ross, MD, Benton Baker III, MD, John C. Jennings, MD
CASE 23
A 20-year-old G1P0 woman at 29 weeks’ gestation is hospitalized for acute pyelonephritis. She has no history of pyelonephritis in the past. She has been receiving intravenous (IV) ampicillin and gentamicin for 48 hours. She complains of acute shortness of breath. On examination, her temperature is 99°F, heart rate is 100 beats per minute (bpm), respiratory rate (RR) is 24 bpm and labored, and blood pressure (BP) is 120/70 mm Hg. Right costovertebral angle tenderness is elicited. The fetal heart tones are in the range of 140 to 150 bpm. The urine culture reveals Escherichia coli sensitive to ampicillin.
» What is the most likely diagnosis?
» What is the most likely mechanism for this patient’s condition?
ANSWER TO CASE 23:
Pyelonephritis, Unresponsive
Summary: A 20-year-old G1P0 woman at 29 weeks’ gestation is undergoing treatment of pyelonephritis with an appropriate antibiotic regimen and now complains of shortness of breath.
- Most likely diagnosis: Acute respiratory distress syndrome (ARDS).
- Mechanism: Endotoxin-mediated pulmonary injury.
ANALYSIS
Objectives
- Understand the clinical presentation of pyelonephritis.
- Know that the primary treatment of pyelonephritis is intravenous antibiotic therapy.
- Understand that endotoxins can cause pulmonary damage, leading to ARDS.
Considerations
The patient is a 20-year-old woman at 29 weeks’ gestation, who presented with pyelonephritis. She was started on intravenous ampicillin and gentamicin. Urine culture confirmed the diagnosis of infection with E. coli. The patient now complains of dyspnea and tachypnea. The most likely etiology for her respiratory symptoms is ARDS, with pulmonary injury secondary to endotoxin release. This typically occurs after antibiotics have begun to lyse the bacteria, leading to endotoxemia. Endotoxins can damage a variety of organs including lung, heart, liver, and kidney. The pathophysiology of ARDS is leaky capillaries, which allow fluid from the intravascular space to permeate into the alveolar areas. Chest x-ray may reveal patchy infiltrates; however, if the disease process is early, the chest radiograph may be normal. Treatment includes oxygen supplementation, careful monitoring of fluid status, and supportive measures. Occasionally, a patient may require intubation, but typically, the condition stabilizes and improves with time.
APPROACH TO:
Pyelonephritis in Pregnancy
DEFINITIONS
PYELONEPHRITIS: Kidney parenchymal infection, most commonly caused by gram-negative aerobic bacteria, such as E. coli.
ENDOTOXIN: A lipopolysaccharide that is released upon lysis of the cell wall of bacteria, especially gram-negative bacteria.
ACUTE RESPIRATORY DISTRESS SYNDROME: Alveolar and endothelial injury leading to leaky pulmonary capillaries, clinically causing hypoxemia, markedly increased alveolar– arterial gradient, and loss of lung volume.
CLINICAL APPROACH
Pyelonephritis in pregnancy can be a very serious medical condition, with an incidence of 1% to 2% of all pregnancies. It is the most common cause of sepsis in pregnant women. Studies show an increase risk of pyelonephritis in pregnant women who are young, Hispanic or Black, less educated, who smoke and have late entry to prenatal care. Pyelonephritis can lead to preterm labor, preterm delivery, and ARDS. The patient generally presents with complaints of dysuria and abrupt onset of flank tenderness, fever, chills, and, possibly, nausea and vomiting. Urinalysis typically shows pyuria and bacteriuria; a urine culture revealing >100 000 colonyforming units/ mL of a single uropathogen is diagnostic. About 15% to 20% of women may also have bacteremia. The most common organism is E. coli, seen in about 80% of cases. Klebsiella pneumoniae, Staphylococcus aureus, Enterobacter, and Proteus mirabilis may also be isolated.
Pregnant women with acute pyelonephritis should be hospitalized and given intravenous antibiotics. Cephalosporins, such as cefotetan or ceftriaxone, or the combination of ampicillin and gentamicin are usually effective. IV antibiotics should be continued until fever and flank tenderness have substantially improved, and then the patient may be switched to oral antimicrobial therapy. Suppressive therapy should be prescribed for the remainder of the pregnancy as recurrent infection may develop in 30% to 40% of women after treatment of pyelonephritis. This can be achieved using nitrofurantoin 100 mg orally on a daily basis. A repeat urine culture should be obtained to ensure eradication of the infection. If clinical improvement has not occurred after 48 to 72 hours of appropriate antibiotic therapy, urinary tract obstruction (ie, ureterolithiasis) or perinephric abscess should be suspected. Ultrasound and/or computed tomography imaging may be helpful in this situation to assess for hydronephrosis, stone, or abscess.
Approximately 2% to 5% of pregnant women with pyelonephritis will develop ARDS, defined as pulmonary injury due to sepsis, usually mediated by endotoxins. The endotoxins derived from the gram-negative bacterial cell wall enter the blood stream, especially after antibiotic therapy is initiated, and may induce transient elevation of the serum creatinine as well as liver enzymes. Also, the endotoxemia may cause uterine contractions and result in preterm labor. Diffuse bilateral or interstitial infiltrates are typically seen in chest radiograph (Figure 23– 1).
The treatment of ARDS is supportive care, with priorities on oxygenation and careful fluid management. In severe cases, mechanical ventilation may be required to maintain adequate oxygen levels.
Prevention
Normal physiologic changes in the urinary tract system occur in pregnancy that may increase the risk of infections. Progesterone induces relaxation of the smooth muscle that makes up part of the renal calyces and ureters. Some vesicoureteral reflux also occurs during pregnancy which can add to the increased risk of upper tract infection. Up to 8% of pregnant women will have asymptomatic bacteriuria, persistent, actively multiplying bacteria within the urinary tract. When untreated, about 25% of women will develop pyelonephritis in the pregnancy. In contrast, when asymptomatic bacteriuria is identified and treated in the first trimester, the risk of pyelonephritis is reduced to 1% to 4%. For this reason, a urine culture should be performed in the first trimester, or entry into prenatal care, and follow-up cultures performed to ensure eradication of the urinary tract infection. The recurrence rate for asymptomatic bacteriuria (ASB) is about 30%; therefore, periodic surveillance is necessary after treatment to prevent recurrent infections.
Figure 23–1. Acute respiratory distress syndrome. Chest radiograph depicts acute respiratory
distress syndrome with diffuse pulmonary infiltrates. (Reproduced with permission from Kasper DL,
et al. Harrison’s Principles of Internal Medicine. 16th ed. New York, NY: McGraw-Hill; 2005:1593.)
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CASE CORRELATON
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COMPREHENSION QUESTIONS
23.1 A 36-year-old G1P0 woman at 27 weeks’ gestation is noted to have fever, right flank tenderness, and pyuria. She is diagnosed with pyelonephritis. A urine culture is performed. Which of the following is the most commonly isolated etiologic agent causing pyelonephritis in pregnancy?
A. Proteus speciesB. Candida speciesC. Escherichia coliD. Klebsiella species
23.2 A 21-year-old G1P0 woman at 15 weeks’ gestation is noted to have fever of 101°F (38.3°C), BP of 80/ 40 mm Hg, and decreased urine output. Which of the following is the most common cause of septic shock in pregnancy?
A. Pelvic inflammatory diseaseB. PyelonephritisC. Wound infectionD. Mastitis
23.3 When a pregnant woman with pyelonephritis does not improve on adequate antibiotic therapy for 48 hours and experiences continued severe flank tenderness and fever, which of the following should be next considered?
A. Obstruction of the urinary tractB. Anaerobic organismsC. Hemolytic uremic syndromeD. Factitious fever
23.4 Asymptomatic bacteriuria is best identified by which of the following?
A. Careful questioning for dysuria or urinary frequencyB. Urine culture on the first prenatal visitC. Urine culture at 35 weeks’ gestationD. Urinalysis for any patient with family history of urinary tract infection (UTI)
ANSWERS
23.1 C. Escherichia coli is the most commonly isolated bacteria in pyelonephritis. Proteus and Klebsiella may also be found, but they are not the most common. Pregnant women with acute pyelonephritis should be hospitalized and given IV hydration and antibiotics. Cephalosporins, or the combination of ampicillin and gentamicin, are usually effective. The patient should be treated with IV medicines until the fever and flank pain resolve, and then switched to oral medication for the remainder of the pregnancy. Candida species are more often associated with vaginitis and not an infection associated with the urinary tract or kidneys.
23.2 B. Pyelonephritis is the most common cause of septic shock in pregnancy. Endotoxins derived from the gram-negative bacterial cell wall enter the bloodstream, especially after antibiotic therapy, and may induce transient elevation of serum creatinine as well as liver enzyme levels. The endotoxemia may cause uterine contractions and place a patient into preterm labor. Another complication that may arise is the development of ARDS, pulmonary injury due to sepsis. Mastitis typically occurs postpartum and, though rare, if left untreated can lead to abscess formation or sepsis. The agent most commonly responsible for mastitis is S. aureus, typically acquired from the back of the baby’s throat during breastfeeding. An unattended wound infection can lead to postpartum sepsis as well; especially, after cesarean delivery. Pelvic inflammatory disease typically does not lead to sepsis; however, if a tubo-ovarian abscess forms and then ruptures, the patient is likely to go into septic shock. This is a surgical emergency that could be fatal.
23.3 A. Urinary obstruction, such as with a stone, should be considered with continued fever and flank tenderness after a 48- to 72-hour course of appropriate antibiotic therapy. Pyelonephritis is typically caused by aerobic bacteria such as E. coli, Klebsiella, Proteus, and S. aureus. H emolytic uremic syndrome (HUS) is a disease characterized by hemolytic anemia, acute renal failure (uremia), and thrombocytopenia, but is not associated with pyelonephritis; however, like pyelonephritis, its etiology is usually due to E. coli (in HUS, a strain of E. coli that expresses a Shiga-like toxin). Patients typically present with bloody diarrhea rather than fever and flank pain. Factitious fever is also not associated with pyelonephritis, since the fever associated with this infection is legitimate.
23.4 B. Urine culture for every patient at the first prenatal visit helps to identify asymptomatic bacteriuria. Treatment prevents sequelae such as preterm labor and pyelonephritis during pregnancy. Careful questioning would not be of much use since the bacteriuria is asymptomatic. A urine culture at 35 weeks would not be helpful either; by this point, the asymptomatic bacteria may have already led to unfavorable consequences such as preterm labor or pyelonephritis. It is cost-effective and a good practice of preventative medicine for patients to get a urinalysis at every prenatal visit, regardless of family history which does not affect the likelihood of having bacteriuria.
CLINICAL PEARLS
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» The most common cause of septic shock in pregnancy is pyelonephritis. » When dyspnea occurs in a pregnant woman who is being treated for pyelonephritis, ARDS should be considered. » When pyelonephritis is unresponsive after 48 to 72 hours of antibiotics, resistant organisms, obstructed urinary tract (stone), or perinephric abscess should be considered. » Endotoxin release from gram-negative bacteria is the cause of acute respiratory distress syndrome associated with pyelonephritis. |
REFERENCES
Cunningham FG, Leveno KJ, Bloom SL, Hauth JC, Rouse DJ, Spong CY. Renal and urinary tract disorders. In: Williams Obstetrics. 24th ed. New York, NY: McGraw-Hill; 2014:1033-1038.
Cunningham FG, Leveno KJ, Bloom SL, Hauth JC, Rouse DJ, Spong CY. Renal and urinary tract disorders. In: Williams Obstetrics. 24th ed. New York, NY: McGraw-Hill; 2014:1051-1068.
Wing DA, Fasset MJ, Getahun D. Acute pyelonephritis in pregnancy: an 18-year retrospective analysis. Am J ObstetGynecol. 2014;210:219.e1-6.
Hooton, TM. Urinary tract infections and asymptomatic bacteriuria in pregnancy. UpToDate Inc. Update December 19, 2011; Accessed 5.02.2012.
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