LINEBURG


<< . .

 34
( 87)



. . >>

toxicity.35 Prolonged use of AED during pregnancy is relatively Some anesthetic agents (e.g. methohexital) are epileptogenic,
safe, except during the late third trimester or labor.36,37 Apnea particularly in the presence of hypocapnia, ketamine, etomidate,
monitoring and observation of the infant for signs of drug with- and aliphatic phenothiazines. Tricyclic antidepressants lower the
drawal are recommended.35,38 seizure threshold. Opioids in high doses cause neuroexcitatory



169
3 Nervous system disorders


Parkinson disease
phenomena in animals but not in humans. Meperidine, and more
so its metabolite normeperidine with its long half-life, can cause
Parkinson disease (PD, paralysis agitans), is a symptom complex
CNS excitability. Laudanosine, a metabolite of atracurium, can be
caused by widespread diffuse lesions in the basal ganglia and cere-
epileptogenic but this is unlikely in humans. Propofol has been
bral cortex, with loss of dopaminergic fibers. Dopamine in basal
implicated in epileptogenesis, with myoclonic activity and opistho-
ganglia normally inhibits extrapyramidal motor neurons from firing.
tonos during clinical use, prompting a warning from the United
Depletion of dopamine produces unopposed action of neuroexci-
Kingdom Committee on the Safety of Medicine.41 However, propo-
tatory acetylcholine resulting in diminished inhibition of extrapyr-
fol effectively stops seizures in humans and animals,42 and seizure
amidal motor output. This diminished inhibition leads to signs of
time is shortened when compared to methohexital for electrocon-
tremor at rest, rigidity, bradykinesia, and disturbances of posture. In
vulsive therapy. Low serum concentrations of amide local anes-
addition, affected patients may become mentally depressed and
thetics are anticonvulsant, but at high serum concentrations (e.g.
develop cognitive and memory deficits that can progress to delir-
lidocaine 10 mg/ml) they cause convulsions. The action of non-
ium. Few cases of pregnancy in women with PD have been reported
depolarizing neuromuscular blockers may be enhanced by the con-
in the literature. Some concerns exist about the consequences of PD
comitant use of AEDs, yet with chronic phenytoin use, there may be
on the evolution of pregnancy and labor as well as the potential for
resistance to pancuronium, but not to atracurium.
teratogenicity44 and toxicity of antiPD medications.45,46
The anesthesiologist must also consider the side effects of AED.
Phenytoin has multiple side effects: hematological (leukopenia,
anemia, agranulocytosis, aplastic anemia) and neurological (peri- Epidemiology
pheral neuropathy). Barbiturates also have similar neurological and
The annual incidence of PD in North America is 20 per 100 00047
hematological (megaloblastic anemia) side effects. Carbamazepine
with a prevalence rate of 190 per 100 000, and a male to female
side effects include an antidiuretic hormone (ADH) effect that may
ratio of 3:2. The onset of PD is usually after age 50 (only 5% of
induce water retention producing emesis and mental confusion,
patients diagnosed before age 40 in Western countries),48,49 with
transient and sometimes persistent leukopenia, and, rarely, agranu-
a peak incidence in the mid-70s, after which the incidence
locytosis and aplastic anemia.27
declines. Familial incidence occurs in 5%. Only 400 women in
the United States under age 50 are newly diagnosed as having PD
Anesthetic management during labor
annually, making it rare in women of childbearing age. Only a few
Communication among obstetrician, neurologist, and anesthe-
cases of PD in pregnant women have been reported.48 Since there
siologist is helpful. The prevention and prompt treatment of
is a significant genetic contribution to the pathogenesis of
intrapartum seizures, and provision of effective labor analgesia
PD,50,51 and a trend towards postponing childbearing to a later
to reduce anxiety and hyperventilation are the goals of anesthetic
age with women having babies in their 50s and 60s using assisted
care. Evaluation should be carried out with emphasis on the
reproductive technologies, the number of pregnant women with
adequacy of seizure control, side effects of therapy, the patient™s
PD may increase.
mental and physical status and proposed obstetric management.
Parenteral opioid analgesia can be used. The dose may require
modification to prevent worsening CNS depression in the par-
Etiology
turient potentially sedated from anticonvulsants. However, epi-
The precise cause of primary or idiopathic Parkinson disease is
dural analgesia instituted within accepted guidelines provides
unknown. Gene mutations have been identified in early onset and
superior pain relief and does not depress the CNS. Patients with
familial cases, but epidemiological studies suggest environmental
evidence of a bleeding diathesis require coagulation assessment
factors (i.e. pesticide/herbicide exposure) are the dominant
prior to initiating regional anesthesia. Epidural analgesia is best
cause in most other types of PD.50,51,52 The observation that
established incrementally, avoiding high plasma concentrations
1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a meper-
of local anesthetics, which are epileptogenic.
idine analog derived during illicit drug production, produces PD
in humans and animals, has resulted in increased interest in the
Anesthetic management during cesarean section
role of toxins, and in the development of an animal model for the
The choice of general or regional anesthesia is determined by a
study of new treatments.52,53 Causes of secondary Parkinson
combination of maternal, fetal, and obstetric factors. Postictal
disease are shown in Table 9.4.
and drug-induced somnolence and status epilepticus mandate
general anesthesia (GA), recognizing the potential interaction
between anesthetic agents and AED, and the need to protect the
Pathophysiology
airway. Regional anesthesia is appropriate for elective C/S in a
The histopathology findings of PD consist of a selective and
medically stable patient. As there is a questionable association
between spinal anesthesia and potentiation of seizure activity,29,43 severe degeneration of pigmented neurons in the pars compacta
of the substantia nigra and a moderate degree of gliosis involv-
epidural anesthesia may be preferred, remembering that the risk
ing the locus ceruleus and dorsal vagal nucleus, with variable
for local anesthetic toxicity is greater. Despite the potential pro-
involvement of the nucleus basalis of Mynert.54 Lewy bodies,
blems facing the pregnant epileptic woman, most will have a
concentric, atypical eosinophilic inclusions in the cytoplasm,
stable gestational course and deliver a healthy infant.



170
Chapter 9



Table 9.5 Clinical side effects of the administration of
Table 9.4 Causes of secondary Parkinson disease
levodopa to 60 nonpregnant patients with Parkinson
Drugs Dopamine receptor antagonists (e.g.
*
disease55
antipsychotic and antiemetic drugs)
Symptom No. of patients
Encephalopathy Posttraumatic pugilist™s encephalopathy
*

Vascular disease Small vessel multi-infarct state
*
Nausea 51
Infections Postencephalitic
*
Vomiting 31
Prion disease
Anorexia 19
HIV
Postural hypotension 14
Miscellaneous Carbon monoxide intoxication
*
Cardiac dysrhythmia 12
Hydrocephalus
Myocardial infarction 1
Parathyroid diseases
Psychic manifestations 10
Paraneoplastic diseases
Involuntary movements 37
Laboratory abnormalities
HIV ¼ human immunodeficiency virus
Leukopenia 5
Positive LE cell preparations 1
although not specific to PD, may be found in the cerebral cortex
Elevated serum urea nitrogen 3
especially when dementia is present. Similar changes are seen in
Elevated SGOT 7
the basal ganglia. It is thought that the symptoms in patients with
PD are due to a disturbance in the regulation of the input to the LE ¼ lupus erythematosus; SGOT ¼ serum glutamic oxaloacetic
thalamic nuclei from the cerebellum and the basal ganglia, >transaminase
particularly the globus pallidus, substantia nigra, and other nuclei
should be used with caution during pregnancy as it crosses the
in the subthalamic region.
placental barrier and may be metabolized in fetal tissues, including
the brain and spinal cord. Early fetal exposure to levodopa or
Clinical presentation and diagnosis
dopamine may alter normal fetal neuronal development.56
Dopamine agonists (pergolide, pramipexole, ropinirole, caber-
Parkinson disease is characterized clinically by alternating rest
goline), now used earlier in the disease management, act directly
tremor, cogwheel rigidity of muscles, and bradykinesia. Other
on the dopamine receptors independent of degenerating dopami-
signs are a mask-like facies, dysarthria, stooped posture, gait
nergic neurons. They have a longer half-life than levodopa, provide
abnormalities, slowness and poverty of movements, diminution
more sustained striatal stimulation, reduce incidence of motor
of associated movements, disturbances of postural control, and
complications,57 and are neuroprotective. Catechol-O-methyl-
autonomic nervous system dysfunction. Diagnosis is generally
transferase (COMT) inhibitors (tolcapone, entacapone) reduce
based on the classical signs of the disorder. Functional imaging
the metabolism of levodopa and are used as adjunctive treatment.
single photon emission computed tomography and positron
Monoamine oxidase (MAO) B inhibitors, selegiline and rasagiline,
emission tomography improve diagnostic accuracy, especially
have been used successfully to increase dopamine levels and may
in patients unresponsive to PD therapy.
offer some neuro-protection.58,59 However, these drugs should be
avoided in patients taking an antidepressant because of potentially
Treatment
serious CNS toxicity that may represent the serotonin syndrome.60
There are no reports of these drugs being used in parturients with
Treatment of PD is symptomatic and individualized. The available
PD. Amantadine, an antiviral drug, may help rigidity, but its role is
therapeutic measures include nonpharmacologic and pharmacolo-
limited in pregnancy as its use has been associated with complex
gic treatments, and surgical procedures. Nonpharmacologic inter-
fetal cardiovascular lesions.61 The mode of action is unknown.
ventions (patient education, exercise, and other supportive
Surgery, either stereotactic (thalamotomy, deep brain stimula-
therapies) are fundamental elements of the overall management of
tion) or fetal tissue implantation, is indicated for patients who
patients with PD and will lead to a comfortable and better lifestyle.
cannot be satisfactorily managed with medications alone. A par-
The aim of pharmacological treatment is to restore dopamine
turient is unlikely to undergo surgery while pregnant.
balance and reduce acetylcholine-induced neuronal effects.
Levodopa, a dopamine agonist, remains the most effective drug
in the treatment of PD.46,55 Levodopa, in combination with carbi-
Pregnancy in patients with Parkinson disease
dopa, an effective inhibitor of the activity of dopa decarboxylase,
Pregnancy in patients with PD is rare and its precise incidence
prevents peripheral breakdown of levodopa in the liver allowing a
unknown. At the moment there are insufficient reports of par-
higher concentration of dopamine to reach the blood“brain bar-
turients with PD to ascertain the impact of pregnancy on PD and
rier. Peripheral side effects (see Table 9.5) are diminished when
of PD on pregnancy. One report suggests that pregnancy may
this combination is used. The sustained release formulation of
levodopa-carbidopa (Sinemet’ CR) produces constant plasma exacerbate PD and have a long-term negative impact on the
course of the illness.62
dopamine levels and a more even clinical response. Levodopa



171
3 Nervous system disorders


Anesthetic management neuromuscular blocking agents and masking of tremors, prevents
postoperative nausea, vomiting, and prolonged ventilation.69 The
Anesthetic management is generally determined by the poten-
use of regional analgesia (combined spinal“epidural or epidural)
tial interaction between anesthetic drugs and antiPD medica-
for labor pain is logical and should theoretically reduce leg stiff-
tions. Therapy for PD should be initiated before surgery and
ness, although the epidural placement could be difficult in a rigid
continued the morning of surgery to decrease drooling, the
parturient with tremors. Intrathecal or epidural morphine might
potential for aspiration, and ventilatory weakness. Reinstituting
worsen rigidity through a central effect due to its low lipid solu-
therapy soon after surgery is crucial as the half-life of levodopa
bility. Decreased intravascular fluid volume and levodopa treat-
is short. Interruption of therapy for more than 6 to 12 hours can
ment may cause hypotension and cardiac dysrhythmias during
result in severe skeletal muscle rigidity that may interfere with
the induction of neuraxial anesthesia, requiring the aggressive
ventilation. It is important to avoid drugs, such as phenothia-
administration of crystalloid or colloid solutions and
zines, butyrophenones (droperidol), and perhaps large doses of
vasopressors.55,66,67
opioid, that inhibit dopamine release or compete with dopa-
mine at receptors in the basal ganglia. Patients who do not
General anesthesia
receive levodopa prior to anesthesia are more prone to develop
neuroleptic malignant syndrome (NMS), if the anesthetic tech-
General anesthesia for C/S might be indicated in patients with
nique includes antidopaminergic drugs (metoclopramide,
severe tremors, or rigidity, or dementia, as these could lead to
droperidol).
inadequate surgical conditions or technical difficulty in perform-
An obstructive ventilatory pattern has been observed in one-
ing a neuraxial block. The anesthesiologist should always make
third of patients with PD.63 Upper airway dysfunction is com-
sure that treatment is optimal.
mon, making patients more prone to retained respiratory
Aspiration of pharyngeal contents into the trachea may result
secretions, atelectasis, and aspiration. Opioid-induced chest
from dysphagia compounded by excessive salivation. These
wall rigidity warrants caution. Morphine is known to inhibit
patients benefit from a rapid sequence induction of anesthesia
dopamine release at a presynaptic level.64 Alfentanil is known
with appropriate measures to prevent pulmonary aspiration.
to produce acute dystonic reactions in untreated patients
Cimetidine or ranitidine given an hour prior to induction reduces
with PD.65
acid production, and sodium citrate, a nonparticulate antacid,
In patients treated with levodopa, orthostatic hypotension,
given 20 minutes prior to induction neutralizes the acid present in
cardiac dysrhythmias, and even hypertension can occur during
the stomach. Atropine, as an antisialologue, and ipratropium, as a
regional, as well as GA.55,66,67 Rigidity and pulmonary edema have
bronchodilator, can be used perioperatively to reduce pulmonary
been reported following the use of a combination of fentanyl and
secretions and, theoretically, relieve any airway obstruction
droperidol in patients on levodopa.68 Anesthetizing a patient on
resulting from excessive parasympathetic activity, but they do
selegiline, an MAO B type inhibitor, provides a challenge to the
not prevent aspiration. Atropine is a more logical choice as it
anesthesiologist. The interaction of MAO inhibitors and meper-
crosses the blood“brain barrier and its central effects oppose
idine may cause profound respiratory depression, hypotension,
the prominent cholinergic effects seen in these patients. The
agitation, excitement, restlessness, hypertension, headache,
anesthesiologist must balance the advantage of rapid onset of
rigidity, convulsions, hyperpyrexia, and coma.69
neuromuscular blockade with succinylcholine in the dysphagic,
The use of ketamine is controversial in patients treated with
pregnant PD patient against a possible hyperkalemic response (a
levodopa as it can result in tachycardia and hypertension, or
single case report).73 Muzzi and colleagues failed to substantiate
possibly worsen the rigidity due to interaction with the opioid
this increase in potassium in nonpregnant patients.74
receptor. Despite these concerns, ketamine has been used with-
Chest wall rigidity and hypokinesia result in a restrictive pat-
out difficulty.70 Nitrous oxide displaces labeled dihydromor-
tern of respiratory deficit,75 and postoperative spasticity may
phine from opioid receptor sites in the brain so it may
result in airway obstruction requiring ventilation. Involuntary
precipitate or worsen muscle rigidity in patients who are receiv-
movements (a generalized coarse phasic tremor with tonic
ing opioids.71 There is no absolute contraindication to the use of
rigidity) after GA can be confused with either worsening of PD
any particular anesthetic technique; however, one must be
symptoms or thermoregulatory shivering. Postoperative shiver-
aware of potential interaction among dopamine receptor
ing is mostly transient. In the postoperative period, especially a
antagonists and opioids, alone or in combination with nitrous
day after surgery, patients with PD may develop confusion and
oxide. One should avoid metoclopramide because of its antido-
hallucinations. The precise mechanism of this postoperative con-
paminergic effects. Ondansteron does not appear to worsen the
fusion is unknown.76
symptoms of PD, unlike dopamine receptor-blocking neurolep-
tic drugs.72
Central nervous system neoplasms
Brain tumors occur rarely in young patients and so are uncom-
Regional anesthesia
mon in pregnancy (approximately 90 pregnant patients in the
US per year).7,77 The types of tumor are identical to those seen
Regional anesthesia for C/S has some obvious advantages over
in nonpregnant women of the same age77,78 and they may be
GA: cardiovascular stability, fewer drug interactions, avoids



172
Chapter 9


benign or malignant, primary or metastatic. The majority are brain or those requiring decompression. Anticonvulsants and
gliomas, followed by meningiomas, acoustic neuromas, and corticosteroids are used, when indicated. Spinal hemangiomas
less common tumors such as choriocarcinoma, which is unique and meningiomas with rapidly progressing symptoms are treated
to pregnancy. Spinal tumors are rare, representing 12% of CNS with decompression laminectomy, but vertebral resection and
neoplasms during pregnancy. Prognosis varies according to the intradural surgery may be required.
type of tumor. Gliomas arise from astrocytes and oligodendro-
cytes and vary in degree of malignancy from slow growing to
Effect of pregnancy and obstetric management
highly anaplastic, producing tissue damage and a mass effect.
Meningiomas are benign tumors that grow slowly from the Pregnancy may cause enlargement of meningiomas and acoustic
membranes covering brain and spinal cord, ultimately produ- neuromas possibly from fluid retention, increased blood volume,
and engorgement of blood vessels.10 The hormones of pregnancy
cing a mass effect. Acoustic neuromas are slow-growing, benign
tumors arising from the vestibular portion of the eighth nerve may facilitate tumor growth, since 90% of meningiomas and
and are often seen in patients with neurofibromatosis. Pituitary some gliomas have progesterone receptors. Maternal hyperten-
tumors are benign and slow growing, producing a variety of sion, increases in ICP, and seizure activity must be controlled
hormones (growth hormone, adrenocorticotrophic hormone, throughout pregnancy and especially during labor. Method of
prolactin), and visual-field defects from compression of the delivery for a parturient with brain tumor remains controversial,
optic chiasm. Choriocarcinoma, an invasive, malignant tumor and is likely to be influenced by the presence of high ICP. Many
of trophoblastic origin, is prone to metastasis and may develop obstetricians prefer to deliver patients with brain tumors by C/S if
there is increased ICP;81 however, similar maternal and fetal out-
after a molar pregnancy, abortion, ectopic gestation, or term
pregnancy. Metastatic brain lesions are found in 3“20% at the comes can be achieved with pain-free labor and assisted vaginal
time of initial diagnosis of choriocarcinoma.79,80 In the spinal delivery.82 Tewari et al. described eight parturients with malig-
cord, hemangiomas and meningiomas are the most common nant brain tumors diagnosed during pregnancy; all had a neuro-
tumors, producing symptoms related to compression of sur- logic crisis between 27 and 32 weeks. Six of these patients were
delivered emergently, and four of the patients died.83 If the symp-
rounding structures.
toms could be controlled pharmacologically these authors
recommended C/S in the early third trimester followed immedi-
Clinical presentation and diagnosis ately by neurosurgical intervention.

Nonspecific symptoms from brain tumors include constant
Anesthetic management
headache and persistent nausea and vomiting secondary to
increased intracranial pressure (ICP). In the pregnant patient
The anesthetic management is guided by the presence or absence
these must be differentiated from common headache and morn-
of symptoms and signs of elevated blood pressure (BP) and ICP.84
ing sickness. Most patients demonstrate lateralizing signs,
Pain during labor and pushing can increase ICP, while good pain
including hemiparesis, sensory loss, visual-field defects, and
control by regional analgesia helps minimize any fluctuations.
aphasia. Seizures, focal or generalized (with or without a focal
This analgesic benefit has to be balanced against the risk of
onset), are also common with low-grade gliomas and meningio-
brain-stem herniation following an inadvertent dural puncture.85
mas and must be differentiated from other causes. Patients with
Epidural injection of local anesthetics increases epidural-space
spinal-cord tumors causing compression can present with pain-
pressure possibly causing a worsening of symptoms.86 Wakeling
less weakness and numbness of the legs, followed by paralysis
described exacerbation of CNS symptoms, dizziness, paresthe-
and loss of sphincter function. Magnetic resonance imaging scan-
siae in both hands, and transient rigid immobility, after an epi-
ning is used to define mass lesions and is preferred over CT, which
dural in a parturient with an unknown large cerebello-pontine
is less sensitive and requires shielding.
angle tumor and obstructive hydrocephalus.87

<< . .

 34
( 87)



. . >>

Copyright Design by: Sunlight webdesign