Critical Care and Obstetrical Issues Case File
Eugene C. Toy, MD, Manuel Suarez, MD, FACCP, Terrence H. Liu, MD, MPH
Case 36
A 25-year-old woman is noted to be at 26 weeks' gestation. She developed acute pyelonephritis and was hospitalized on intravenous antibiotic treatment the previous day. The patient was doing well until this morning, when she complained of acute and progressive shortness of breath. She has no past medical history of pulmonary problems. On examination, her heart rate (HR) is 130 beats/minute, respiratory rate (RR) is 40 breaths/minute and labored, blood pressure (BP) is 130/85 mm Hg, and temperature 102.6°F. The lung fields reveal diffuse crackles. The patient had an ABG of 7.35, PO2 62 mm Hg, PCO2 40 mm Hg, and HCO3 of 19 mEq/L on 100% oxygen by non-rebreather mask. Shortly after this, the patient is taken to the ICU and intubated and placed on the ventilator.
⯈ What is the most likely diagnosis?
⯈ What are the obstetrical issues in this case?
⯈ Are there any adjustments to the medical management due to pregnancy?
ANSWER TO CASE 36:
Critical Care and Obstetrical Issues
Summary: A 25-year-old woman at 26 weeks' gestation is being treated for pyelonephritis and has developed respiratory failure and rales on pulmonary examination. The patient had an ABG of 7.35, PO2 of 62 mm Hg, PCO2 40 mm Hg, and HCO3 of 19 mEq/L on 100% oxygen by non-rebreather mask. Shortly after this, the patient is taken to the ICU and intubated and placed on the ventilator.
- Most likely diagnosis: ARDS.
- Obstetrical issues: The pregnant patient has different normative values of the arterial blood gas. For instance, the normal pH in pregnancy is 7.45 and normal PCO2 is 30 mm Hg. Thus this patient has significant acidosis and is retaining CO2. The other factor involves monitoring the fetal status and developing a delivery plan if needed.
- Adjustments in management due to pregnancy: In general, treating the medical condition is beneficial for maternal as well as fetal status. Ventilator management is not contraindicated in pregnant women. Some medications should be avoided in pregnancy, such as the quinolone antibiotics and ACE inhibitors.
ANALYSIS
Objectives
- To describe the effect of pregnancy on critically ill patients.
- To describe the considerations of management of the critically ill patient who is pregnant.
- Describe the methods of monitoring fetal status and considerations for fetal intervention in the critically ill patient.
Considerations
This patient is pregnant at 26 weeks' gestation, which is at the lower limits of perinatal viability. The patient was admitted for acute pyelonephritis 1 day previously and has developed acute respiratory failure leading to being intubated and placed on the ventilator. The patient has significant tachypnea and labored breathing, and the ABG is concerning. Pregnancy is associated with physiological alterations in respiratory system, leading to a primary respiratory alkalosis and partially compensated metabolic acidosis. The normal pregnant woman's arterial pH is 7.45. Thus, this patient's arterial pH of 7.35 reflects a substantial acidosis. Likewise, the normal PCO2 in pregnancy is 30 mm Hg due to the increased minute ventilation. This patient's PCO2 of 40 mm Hg is consistent with marked CO2 retention, and impaired ventilation. The patient was appropriately intubated and placed on the ventilator. After stabilization of the maternal status, attention can be paid to fetal status. This is a very important principle: to prioritize maternal well-being prior to addressing fetal issues. A bedside ultrasound to assess for gestational age and fetal weight is important to establish whether the fetus is viable. In general, 24 to 26 weeks is considered to be the lower limits of viability, that is, survival of the baby if delivered. If the fetus is considered potentially viable, then discussion with the patient and family is important to establish whether cesarean intervention for fetal interest would be considered for persistent fetal bradycardia. Additionally, a delivery plan should be established; for instance, should the patient go into preterm labor, whether the delivery would be vaginal or cesarean.
Approach To:
The Critically Ill Patient Who Is Pregnant
DEFINITIONS
DELIVERY PLAN: A comprehensive process for vaginal as well as cesarean delivery in the event of labor or need for emergency delivery such as fetal bradycardia.
FETAL MONITORING: Assessment of fetal status with fetal heart rate monitoring, ultrasound for fetal weight, and ultrasound assessment for fetal activity such as breathing, movement, and amniotic fluid volume.
PERIVIABLE: Gestational age at the borderline of viability, usually specified as between 22 to 26 weeks' gestation.
PERIMORTUM CESAREAN: Performing a emergency cesarean on a patient who is either undergoing CPR, or who has or is recently demised.
CLINICAL APPROACH
Physiological Changes in Pregnancy
During pregnancy, the heart is displaced upward and to the left from changes in the shape of the rib cage and from superior displacement of the diaphragm. It also rotates on its long axis. This lateral change in heart position can be misinterpreted on chest x-ray as cardiomegaly. Other changes in the structure of the heart resemble those found as a result of physical training. Physiologic myocardial hypertrophy is a result of expanded blood volume, peaking at 30 to 34 weeks' gestation, and reversing itself after delivery.
Cardiac output (CO) is the product of stroke volume (SV) and heart rate (HR). During pregnancy CO is increased tremendously. By 5 weeks' gestation it rises to 10% over prepregnancy levels and by 34 weeks peaks at some 50% above those levels seen prior to pregnancy. Heart rate begins to rise in the first trimester and continues to rise until it peaks at 15 to 20 beats above normal at 34 weeks. Cardiac output varies greatly with maternal position. It is highest in the knee-chest and lateral recumbent positions and lowest in the supine position (some 30% lower) . Late in pregnancy, because of the development of a dilated paravertebral collateral circulation, venous return from the lower extremities is maintained in the supine position even when the vena cava is completely occluded by the pregnant uterus.
In spite of this, 5 % t o 10% o f pregnant women show signs of "supine hypotension," and experience dizziness, nausea, and even syncope when supine. This may represent a failure of those women to develop an adequate paravertebral collateral system.
Systemic vascular resistance (SVR) diminishes in early pregnancy, reaching its nadir at mid-pregnancy. It gradually rises until term but even then remains approximately 20% lower than prior to pregnancy. This phenomenon is thought to be a direct effect of progesterone on the smooth muscle in the capillary beds, and increased levels of circulating nitric oxide and cyclic adenosine monophosphate also play a role. Since the pregnant woman's blood pressure is a product of her cardiac output and SVR, we see a similar change in blood pressure throughout pregnancy.
Venous blood pressure rises in the lower extremities gradually during pregnancy. Femoral venous pressure rises from 10 cm H2O to 25 cm H2O at term. Consequently edema, hemorrhoids, varicose veins, and an increased risk of deep vein thrombosis are common.
It is often difficult to distinguish between the signs and symptoms caused by physiologic adaptations to pregnancy and those of true cardiac disease. S1 becomes louder by the end of the first trimester, and 90% of pregnant women will develop an S3. Systolic ejection murmurs along the left sternal border develop in more than 90% of pregnant women, and is thought to be caused by increased blood flow across the pulmonic and aortic valves.
Respiratory System Because of increased hyperemia and estrogen levels, the nasopharyngeal mucosa becomes edematous and irritated. Nasal stuffiness, epistaxis, and nasal polyps occur frequently during pregnancy, and resolve spontaneously postpartum.
Due primarily to change in the size and shape of the chest cavity, the following alterations in lung capacities are seen:
- Respiratory rate-unchanged
- Vital capacity-unchanged
- Inspiratory capacity-increased 5 % to 10%
- Tidal volume-increased 30% to 50%
- Inspiratory reserve volume-unchanged
- Functional residual capacity-decreased 20%
During pregnancy, increased levels of progesterone cause a state of relative hyperventilation, resulting in a chronic respiratory alkalosis. This relatively low PCO2 in the pregnant mother is beneficial in clearing CO2 from the fetal circulation.
Maternal blood volume comprises the plasma volume and the red blood cell mass. This total blood volume begins increasing as early as 6 weeks' gestation and plateaus at 30 to 34 weeks of pregnancy, increasing by some 40% to 50% in most gravidas. Plasma volume begins to increase at 10 weeks' gestation and plateaus at 30 weeks' gestation, while the red blood cell mass begins increasing at 10 weeks and continues its rise until term. The reasons for these expansions remain unknown. The use of iron supplementation has been shown to enhance the increase in RBC mass from 18% to 30% by term. Since at mid-pregnancy the plasma volume increases more than that of red blood cell mass, there appears a transient physiologic anemia of pregnancy. A gradual decline in platelets has been observed throughout pregnancy, but 98% of pregnant women will have platelet counts of >116,000/mm3. Values below this should be evaluated for causes of thrombocytopenia.
Renal Changes Renal plasma flow begins to rise early in pregnancy becoming 75 % higher than prior to pregnancy by 16 weeks' gestation. Glomerular filtration rate rises as early as 5 to 7 weeks and reaches a level 50% greater than in the nonpregnant female. The altered mechanism of handling glucose in the proximal tubules during pregnancy remains to be completely understood. Glucose excretion into the urine occurs in most pregnant women. While the nonpregnant female excretes <100 mg/d, in pregnancy this can reach 1 to 10 g of glucose per day.
Respiratory Diseases in Pregnancy
Asthma exacerbations are typically slightly decreased in pregnant women with mild disease, while those with severe disease may have worse deterioration. Because of the uterine pressure on the diaphragm, there is decreased pulmonary reserve. Treatment of the asthmatic pregnant patient is identical to that of the nonpregnant patient, beginning with β-agonist respiratory therapy and steroids, and progressing to magnesium sulfate. Methylxanthines are also considered safe for use in pregnancy. Epinephrine is relatively contraindicated in pregnancy due to its possible vasoconstrictive effects on the uterine arteries.
Influenza mortality is increased in the pregnant woman due to respiratory changes as well as the relatively immunocompromised state. Thus, obstetrical patients are one of the key groups that should receive annual influenza immunization. The live attenuated nasal vaccine is contraindicated in pregnancy. Those women who have suspected or confirmed influenza should promptly receive anti influenza therapy. Oseltamavir (tamiflu) or zanamivir (Relenza) are safe in pregnancy. These agents are best begun within 2 days of the beginning of infection, and are taken for 5 days. The pregnant patient may have fulminant and severe disease, and prompt admission and respiratory support should be enacted if the patient deteriorates. In a large series of patients with H1N1 influenza in pregnant and postpartum women in California, 10% of those with infections were hospitalized, which is 4 times higher than the general population. Eighteen were admitted to the ICU (20% of those hospitalized), and 8 patients died; 75% of these deaths were complicated with medical illnesses, and none had received anti-viral medication within 48 hours of disease.
Airway Difficulties
Several anatomic changes occur throughout pregnancy such as weight gain, including increase in breast size, respiratory tract mucosal edema, and capillary engorgement of nasal and oropharyngeal mucosa and laryngeal tissues. Decreased functional residual volume of up to 50% with concomitant increase in oxygen needs can lead to rapid development of hypoxemia in the hypoventilating patient. The progesterone effect o f the GI tract can also lead t o delayed gastric emptying and decreased lower esophageal sphincter tone, which increases the risk of aspiration. Laryngeal edema makes intubation more difficult, and many anesthesiologists advocate "downsizing" the ET tube. Also, because of the risk of bronchospasm or further distortion of the airway anatomy, there may be only one good attempt to place the endotracheal tube. Use of the laryngeal mask airway (LMA), which is a supraglottic airway device that is designed to fit in the hypopharynx, may be useful. Every obstetrical airway should be considered a difficult airway. Difficult anatomy and rapid oxygen desaturation should be anticipated.
Cardiac Disease in Pregnancy
Hypertensive diseases in pregnancy are common, affecting approximately 8% of obstetrical patients. These can be gestational hypertension which is isolated elevated blood pressure, preeclampsia (hypertension with proteinuria), or superimposed preeclampsia on chronic hypertension. Preeclampsia alters the hemodynamic parameters by increasing systemic vascular resistance and decreasing intravascular volume. Thus, preeclamptic women are more sensitive to volume changes, either blood loss which can lead to hypotension, or fluid overload leading to pulmonary edema.
Peripartum cardiomyopathy is a 4-chamber dilated cardiomyopathy of unknown etiology affecting women in pregnancy or postpartum. Affected patients present with congestive heart failure, and noted on chest radiograph to have a markedly enlarged cardiac silhouette. The cardiac output is below 45% and other causes of ventricular dysfunction are ruled out. Many cases are discovered late after onset of severe symptoms, and thus, a high index of suspicion is needed. Treatment in pregnancy is aimed at stabilization of maternal status. The mainstays of treatment are digoxin, loop diuretics, afterload reduction with hydralazine and nitrates, and β-blocker use. ACE inhibitors and ACBs are contraindicated in pregnancy due to fetal renal effects. Unless a patient is decompensating, expectant management of the preterm patient (less than 37 weeks) is advisable. For those women who are decompensating, careful hemodynamic monitoring and support and coordination of care with anesthesiologist, cardiologist, and high-risk obstetrician in an ICU labor and delivery setting are required. The prognosis depends on recovery of left ventricular function, which occurs in about 50% of patients. Mortality can approach 10% in those patients with worsening heart failure. As many as 80% of women who become pregnant again may develop congestive heart failure with future pregnancies.
Liver Disease in Pregnancy
Acute fatty liver of pregnancy is an extremely dangerous condition characterized by microvesicular steatosis of the liver, thought to be due to mitochondrial dysfunction of fatty acid oxidation, which leads to fat accumulation in hepatocytes. Liver insufficiency results, and if it is not diagnosed and promptly treated with delivery, then maternal and neonatal morbidity or mortality results. Women with AFLP are more likely to have heterozygous long chain 3-hydroxyacyl-coenzyme A dehydrogenase (LCHAD) deficiency. Patients present with nonspecific symptoms such as malaise, nausea and vomiting, and possibly right upper quadrant pain. Hypoglycemia and fulminant liver failure with encephalopathy can also be present. The physical examination may or may not manifest hypertension or jaundice. The laboratory analysis is important and usually shows elevated liver function tests and decreased glucose levels. Disseminated intravascular coagulopathy (DIC) and hyperbilirubinemia may also be present. Delivery is the cornerstone of therapy. Renal function should also be monitored.
Sepsis in Pregnancy
Infection is more common in pregnancy due to the patient's immunosuppressed state. The most common cause of sepsis is pyelonephritis, typically due to Escherichia coli, particularly caused by to O127 subtype; however, a large number of gram-negative rods are possible etiologies. Endotoxin release causes hypotension due to peripheral vasodilation. The most common cause of sepsis in the postpartum patient is postcesarean endometritis. Pregnant women have a higher mortality than nonpregnant patients. Early diagnosis, aggressive antibiotic therapy, supportive therapy, and removal of the source of the sepsis are important. The decision of delivery is difficult due to the fact that the gestation may be premature; nevertheless, the pregnancy may alter the cardiovascular hemodynamics such as decreasing the venous return. Fetal status should be monitored carefully. Placental perfusion in fetus depends on maternal mean arterial pressure.
Trauma in Pregnancy
Approximately 6% to 7% of all pregnant patients experience trauma of some type, with the highest risk in the third trimester. Most of these are accidental, although some are intentional. The most common type of trauma is falls, which comprise about half of the cases. The most common cause of fetal death is maternal shock, and the second most common cause is placental abruption. Blunt trauma does not seem to increase the risk of death more than that of the nonpregnant patient. Attention to the patient is systematic and similar to that of the nonpregnant individual, initially focused on the ABCs and then addressing overt or hidden hemorrhage. Uterine rupture due to direct abdominal trauma is rare, but it should be suspected in a patient with a history of prior cesarean, uterine tenderness, rapid onset of maternal hypotension or shock, and a nonreassuring fetal heart rate pattern. After maternal status is assured, attention can be directed to fetal well-being. Fetal ultrasound and fetal heart rate monitoring are important. Because of the maternal soft tissue, fetal injury is rare with blunt trauma.
In the case of penetrating trauma, fetal mortality is higher, especially in those with abdominal injury. Fetal injury occurs in up to 70% of third-trimester cases, and fetal loss occurs in approximately half of cases, whereas maternal mortality occurs in <5 % of cases. Most experts recommend exploratory laparotomy with penetrating trauma to the abdomen to assess for possible uterine laceration, or fetal injury. Imaging should be performed as needed on the pregnant patient. Plain film radiographs may be performed with appropriate shielding. If available, MRI is preferable rather than CT to decrease radiation exposure. Nevertheless, CT of the chest, for instance, only emits 1 rad of radiation energy; exposure of a pregnancy to <10 rads is not considered to be dangerous to the developing fetus. Diagnostic peritoneal lavage has not been found to be consistently accurate in pregnancy and is typically not used.
Perimortem Cesarean
Perimortem cesarean is performed primarily for 2 reasons: (1) for certain maternal death due to severe head injury or other non-resuscitatable cause, the indication is to save the fetus, or (2) for maternal cardiac arrest due to a potentially resuscitatable cause, for both maternal and fetal benefit. Examples of the second category include cardiac arrest or severe blood loss, and the cesarean section removes the fetus so as to remove a nonvital organ from the maternal circulation. This facilitates the resuscitation, allowing better venous return and easier chest compressions. With either reason, the cesarean needs to be done within 4 minutes of cardiac arrest to support neurologic function of the fetus. The key to rapid delivery is the use of large of incisions. A midline vertical incision is made from the xiphoid to the pubis through all layers of the abdominal wall. If the placenta is in an anterior position, the surgeon cuts through it and addresses the bleeding only after the fetus is delivered. Typically, a midline vertical incision through the upper uterine segment is made and the neonate delivered, suctioned, and cord clamped and cut. Thereafter, resuscitation of the pregnant patient can be resumed.
Amniotic Fluid Embolism
Amniotic fluid embolism (AFE) is a rare obstetrical emergency where the suspected etiology is that amniotic fluid and fetal cells and hair entering into the maternal circulation, leading to maternal hypotension and cardiovascular collapse. An anaphylactic reaction presents acutely associated with pulmonary artery spasm and hypertension, elevated right ventricular pressure and hypoxia. Half of affected women will die within 1 hour of presentation. A second phase then ensues if the patient is successfully resuscitated: florid DIC and massive hemorrhage with uterine atony. Therapy is early recognition, and supportive therapy such as oxygenation, CPR, crystalloid, blood products and pressor agents as needed, and aggressive treatment of associated coagulopathy. Emergency cesarean in women with cardiac arrest unresponsive to resuscitation may be required. Unfortunately, AFE is associated with an 80% maternal mortality.
CLINICAL CASE CORRELATION
- See also Case 8 (Airway Management and Respiratory Failure), Case 19 (Sepsis), and Case 35 (Hypertensive disorders in pregnancy).
COMPREHENSION QUESTIONS
36.1 A 30-year-old woman is noted to be at 12 weeks' gestation. An arterial blood gas is performed due to symptoms of shortness of breath. In interpreting the ABG, which of the following statements is most accurate regarding its normal value in pregnancy?
A. The arterial pH will likely be lower, and PCO2 unchanged as compared to the nonpregnant patient.
B. The arterial pH is unchanged, and PCO2 will likely be increased as compared to the nonpregnant patient.
C. The pH will be higher and PCO2 will be lower than the nonpregnant patient.
D. The pH and PCO2 are both unchanged as compared to the nonpregnant patient.
36.2 A 28-year-old G1P0 woman at 34 weeks' gestation is noted to have a 2-day history of malaise and nausea and vomiting. On examination, she appears slightly icteric. Her BP is 140/90 mm Hg. Lab results reveal that SGOT is 200 IU/L, and bilirubin is 5 mg/dL. Which of the following would be most consistent with acute fatty liver of pregnancy?
A. Urine protein of 500 mg over 24 hours
B. Peripheral blood smear showing schistocytes
C. Blood glucose of 40 mg/dL
D. Amylase level of 3 times normal value
36.3 A 31-year-old G2P1 woman at 40 weeks' gestation is in active labor. She is on oxytocin augmentation of labor due to slow labor progress. The nurse notes that the patient is not responsive and has no pulse and no blood pressure. CPR is initiated. Which of the following is the most likely diagnosis?
A. Acute fatty liver of pregnancy
B. Amniotic fluid embolism
C. Diabetic ketoacidosis
D. Uterine rupture
ANSWERS TO QUESTIONS
36.1 C. The normal arterial blood gas in pregnancy reveals a primary respiratory alkylosis with partial metabolic compensation. Thus, the arterial pH is higher than the nonpregnant state (7.45) and the PCO2 is lower as compared to pregnancy (30 mm Hg vs 40 mm Hg in nonpregnancy). To compensate for this
change, the kidneys excrete bicarbonate, and thus the serum bicarbonate is lower than the nonpregnant patient (19 mEq/L vs 24 mEq/L).
36.2 C. This patient presents as acute fatty liver of pregnancy with the malaise, and nausea/vomiting, icterus, and mildly elevated blood pressure. Hypoglycemia is often present. With significant disease, the patient can have an elevated serum ammonia level and encephalopathy.
36.3 B. Amniotic fluid embolism. This patient presents with the acute onset of hypotension, cardiovascular collapse, and hypoxia. If resuscitated, the patient may enter into a state of hemorrhage and DIC.
CLINICAL PEARLS
⯈ The physiological changes of pregnancy must be considered in interpreting the lab results.
⯈ As compared to the nonpregnant patient, the intravascular volume and cardiac output increases 50% in pregnant women.
⯈ The pregnant woman has a primary respiratory alkalosis and partial compensatory metabolic acidosis.
⯈ The priority should be to assess and stabilize maternal status prior to addressing fetal issues.
⯈ Fetal status should begin with accurate gestational age determination. A primary decision point is to determine whether the fetus is viable, and whether there would be emergency cesarean intervention for fetal issues.
⯈ A delivery plan should be developed should the patient require delivery.
⯈ A fetal monitoring status should be developed.
⯈ There are few medications that are contraindicated in pregnancy.
References
American College of Obstetricians and Gynecologists (ACOG). Asthma in pregnancy. ACOG practice bulletin; no. 90. Washington DC: American College of Obstetricians and Gynecologists (ACOG); Feb 2008.
Louie JK, Acosta M, Jamieson DJ, Hone in MA. Severe 2009 H1N1 influenza in pregnant and postpartum women in California. N Engl} Med. 2010;326:27-35.
Sliwa K, Hilfiker-Kleiner D, Petrie MC, et al. Current state of knowledge on aetiology, diagnosis, management, and therapy of peripartum cardiomyopathy: a position statement from the Heart Failure Association of the European Sociery of Cardiology Working Group on peripartum cardiomyopathy. Eur ] Heart Fail. Aug 2010;12(8):767-778.
Stein PD, Matta F, Yaekoub AY. Incidence of amniotic fluid embolism: relation to cesarean section and to age.] Womens Health (Larchmt) . Mar 2009;18(3 ):327-329.
Tuffnell DJ. United Kingdom amniotic fluid embolism register. BJOG. Dec 2005;112(12):1625-1629.
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