Intracranial Hemorrhage

Intracerebral hemorrhage (ICH) accounts for a substantial portion of pregnancy-related mortality. The overall incidence has been roughly estimated to be 6.1 pregnancy-related ICHs per 100,000 deliveries, with ICH accounting for 7.1% of all pregnancy-related mortality. The risk of ICH associated with pregnancy is greatest in the postpartum period. In a multicenter study conducted in the United States, the risk of stroke (both cerebral infarction and ICH) are increased in the 6 weeks after delivery but not during pregnancy itself. Advanced maternal age, African American race, hypertensive diseases, coagulopathy, and tobacco abuse are all independent risk factors for pregnancy-related ICH.

ICH is most commonly due to SAH due to ruptured arterial aneurysms and AVMs. In a study of 154 patients with ICH associated with pregnancy, 77% were secondary to aneurysmal rupture and 23% were due to AVM. Women with AVM bleeds were younger than those with aneurysmal hemorrhage, but no differences were found between AVM and aneurysmal hemorrhage with respect to parity or gestational age at the time of the initial hemorrhage. About 34% patients had hypertension and/or albuminuria at some time during pregnancy, making the differentiation between AVM or aneurysmal ICH and that associated with eclampsia relatively difficult.

Pregnancy does not confer an increased risk of hemorrhage in patients with AVM ; however, the risk of rebleeding is 25% during the same pregnancy, as against a 3–6% risk during the first year in the general population. The risk of aneurysmal SAH was previously believed to be increased during pregnancy, a phenomena contributed by the pregnancy-induced increase in circulating blood volume and cardiac output, and the hormonal changes to the arterial wall. Recent studies, however, do not find an increased association between pregnancy or delivery and the risk of rupture of cerebral aneurysms (1.4% and 0.05%, respectively, comparable to the rates of aneurysm rupture in the general population). Parity may confer a moderate long-term protective effect on the risk of SAH. Once ruptured, prompt aneurysmal obliteration (either surgical clipping or endovascular coiling) should be helpful in decreasing the rate of poor outcomes.

Primary Central Nervous System Tumors

The incidence of brain tumor in the female population is estimated to be around 6 per 100,000. The incidence is not known to be increased in pregnant women, with 85% of such tumors consisting of meningiomas, gliomas, pituitary tumors and vestibular schwannomas. Some of these tumors, such as meningiomas, however, may become symptomatic in the pregnant state due to water retention, engorgement of vessels, and the presence of sex hormone receptors on tumor cells, leading to explosive growth of the tumor. Choriocarcinoma is an aggressive gestational tumor that metastasizes to the brain.

The clinical diagnosis of intracranial neoplasms may be challenging, as the symptoms of headache upon awakening, nausea, vomiting, or seizures could be easily misdiagnosed as hyperemesis gravidarium during early pregnancy or as eclampsia during late pregnancy. However, the presence of an abnormal fundoscopic examination, visual impairment, focal seizures, and lateralizing neurological deficits should alert clinicians to the possibility of an intracranial tumor and prompt further investigations like magnetic resonance imaging to confirm the diagnosis.

In modern day practice, it is feasible in most patients with meningiomas and other benign brain tumors for the pregnancy to continue to term and delivery without endangering the mother of the fetus. Urgent neurosurgical intervention may be required for the management of (1) malignancies, (2) active hydrocephalus, and (3) benign brain tumors associated with signs of impending herniation or progressive neurological deficit.

Pregnancy is also associated with an increased incidence of ventriculoperitoneal shunt complications like shunt displacement and occlusion, owing to an increased intra-abdominal pressure and anatomical changes. Management of such complications depends on the symptoms and gestational age.

Spinal Pathology

Symptomatic disk herniation is reported to have an incidence of around 1:10,000 pregnancies. Severe backache is a common complaint during pregnancy, and is attributable to ligamentous laxity secondary to high serum levels of relaxin and extramechanical stress. Although lumbar disks rarely prolapse de novo during pregnancy, pregnancy may exacerbate a preexisting condition and seems to be a risk factor for postpartum disk prolapse. Joint laxity may also predispose to spondylolisthesis.

It has been observed that 85% of patients with symptomatic disk herniation due to nerve root compression improve with conservative management within 6 weeks. In contrast, women presenting with worsening neurological deficit may require surgical intervention and those with a cauda equina syndrome represent a surgical emergency. Patients may also present for surgery for newly symptomatic spinal tumors and rarely for spontaneous spinal epidural hematoma, vertebral canal abscess, or spinal AVMs.

Traumatic Brain Injury

Trauma is the leading nonobstetric cause of maternal death. It complicates 6–7% of pregnancies and may well involve cranial or spinal injury that will necessitate surgery. Optimal management of the pregnant patient with trauma requires a multidisciplinary approach. Primary goals are aggressive resuscitation of the mother and maintenance of uteroplacental perfusion and fetal oxygenation by the avoidance of hypoxia, hypotension, hypocapnia, acidosis, and hypothermia. What must always be remembered is that resuscitating the mother will resuscitate the fetus!

Airway and Respiratory Mechanics

Some of the most noteworthy changes occur in the respiratory mechanics during pregnancy. The oxygen consumption increases about 20–40% at term and the functional residual capacity decreases up to 20%, both contributing to a rapid oxygen desaturation during periods of apnea, as occurs during induction of anesthesia. Therefore, at least 2 min of preoxygenation and denitrogenation with a tightly fitting face mask is mandatory before the induction of general anesthesia during pregnancy. Maternal obesity, preeclampsia, or both can accentuate the risk of hypoxemia associated with the induction and emergence from general anesthesia.

Progesterone-mediated increases in respiratory rate and minute volume result in reduced arterial partial pressure of carbon dioxide (PaCO ₂ ) of around 30 mmHg. Maternal pH, however, remains within normal limits due to compensatory renal excretion of bicarbonate. During anesthesia PaCO ₂ levels should be maintained within these norms. Care needs to be exercised while manipulating PaCO ₂ during neurosurgery, as significant reduction in PaCO ₂ below 25 mmHg may reduce uteroplacental perfusion and shift the maternal oxygen–hemoglobin dissociation curve to the left, with resultant reduced oxygen delivery to the fetus.

Airway changes during pregnancy include capillary engorgement of the respiratory mucosa and friability of oropharyngeal tissues (due to soft tissue edema caused by accumulation of extracellular fluid), predisposing the upper airway to trauma, bleeding, and obstruction. The size of the glottic opening is reduced; gentle laryngoscopy and the use of small endotracheal tubes (6–7 mm ID), therefore, is the dictum. Difficult airway is commonly encountered, and the incidence of failed intubations is eight times higher in the pregnant as compared to the general population.

Cardiovascular System

Hemodynamic changes during pregnancy include a 40–50% increase in blood volume and cardiac output and a 20% reduction in hematocrit due to dilution, resulting in dilutional anemia. A decrease in systemic vascular resistance by the second trimester decreases both diastolic and systolic blood pressure. At term, maternal blood volume reaches 90 mL/kg, an increase of 1000–1500 mL in most women. These changes are necessary to provide adequate uteroplacental perfusion and anticipate blood loss during delivery.

Aortocaval compression is of concern to the anesthesiologist during and after the second trimester. The combination of systemic hypotension due to decreased venous return, increased uterine venous pressure, and uterine arterial hypoperfusion severely compromise uterine and placental blood flows. When combined with the hypotensive effects of regional or general anesthesia, aortocaval compression can readily produce fetal asphyxia. In addition, chronic partial caval obstruction in the third trimester predisposes to venous stasis, phlebitis, and edema in the lower extremities, thereby increasing the already elevated risk of deep vein thrombosis. These considerations emphasize the need for left uterine displacement during anesthesia and surgery, most effectively accomplished by tilting the operating table 30 degrees to the left or placing a roll under the patient’s right hip.

Gastrointestinal System

The upward and anterior displacement of the stomach by the gravid uterus, combined with the reduced gastroesophageal sphincter tone by the elevated progesterone levels, place the parturient at a high risk for regurgitation and pulmonary aspiration. A history of active reflux or obesity poses additional risk. All pregnant patients are therefore considered full stomach, and adequate aspiration prophylaxis with either a nonparticulate antacid or a combination of a histamine H2–blocking drug and metoclopramide is administered prior to induction.

Renal and Hepatic Systems

Increased renin and aldosterone levels promote sodium and water retention during pregnancy, contributing to an increased edema in the previously asymptomatic intracranial tumors, leading to worsening signs and symptoms.

Renal plasma flow and the glomerular filtration rate increase as much as 50% during the first trimester, causing a decline in serum creatinine and blood urea nitrogen. Slight elevations of these parameters may therefore be a cause of concern in the pregnant population.

Minor elevations in serum transaminases, alkaline phosphatase, and lactic dehydrogenase may be observed in the third trimester; 25–30% decrease in serum cholinesterase activity may be seen at term, but rarely produces prolongation of succinylcholine’s action.

Pregnancy is associated with a hypercoagulable state that may be beneficial in limiting blood loss at delivery. All clotting factors (excluding XI and XIII) are increased during pregnancy.

Central Nervous System Changes

The minimum alveolar concentration (MAC) of inhalational anesthetics decreases progressively by as much as 40% during pregnancy, due to a surge in endorphin levels and the sedating effects of progesterone. The requirement for inhalational anesthetics therefore decreases considerably in a pregnant patient for surgery.

The dose requirements for local anesthetics may be reduced by about one-third in the pregnant population at term. The reduced volume of cerebrospinal fluid (CSF) secondary to epidural venous engorgement may cause a more extensive spread of the local anesthetic, thereby reducing the dose by 30%. Also, the increased pressure in the epidural space facilitates diffusion across the dura and produces higher concentration of local anesthetic in the CSF.

An increase in the epidural venous pressure caused by the increased intra-abdominal pressure and direct vena cava compression, predisposes a preexisting pathology in the valveless epidural veins to rupture in the presence of abrupt pressure changes like sneezing, coughing, or a forceful Valsalva maneuver.

The epidural arterial vessels are equally prone to rupture and produce a hematoma, due to the degenerative changes in vessel walls produced by progesterone and estrogen during pregnancy.