Keywords
moyamoya syndrome - sickle cell anemia - normovolemia - normocapnia - normothermia
Introduction
Moyamoya disease (MMD) is a rare cerebrovascular disorder of narrowing of the internal
carotid artery (ICA), which reduces cerebral blood flow (CBF) and leads to the development
of abnormal collateral vessels. Adults present with motor deficit, transient ischemic
attacks, infarct, and intracranial hemorrhage. Children have ischemic events triggered
by dehydration, fever, and even crying.
It may be primary (idiopathic) or secondary, also called Moyamoya syndrome (MMS),
which results from an underlying pathology.[1] When MMS secondary to sickle cell anemia (SS) presents for cerebral revascularization
(CR), general anesthesia (GA) administration presents unique implications. We report
anesthetic management of a MMS from SS scheduled for CR.
Case Report
An 18-year-old, 60-kg male, SS patient presented with a history of seizures. Magnetic
resonance angiogram (MRA) revealed narrowing of cervical segment of left ICA, with
occlusion of supraclinoid segment and collateral development (Suzuki grade 3). History
revealed that he received simple blood transfusions on multiple occasions in the past
(including once for sickling crisis) but never exchange transfusion. He underwent
uneventful cholecystectomy in the past. His medications consisted of hydroxyurea before
admission and phenoxymethylpenicillin after admission. Cardiac and pulmonary systems
were normal. His admission hemoglobin was 8.2 g/dL, with 60% sickle cell hemoglobin
(HbSS). Other investigations were normal. Considering the issues associated with direct
revascularization, the neurosurgeon planned for encephaloduroarteriosynangiosis. His
preoperative fasting period was covered with crystalloids infusion. One unit of packed
red blood cells (PRBCs) was transfused the night before surgery, and another was transfused
immediately after induction, raising hemoglobin to 10.3 g/dL. Following anesthesia
induction with fentanyl and propofol and tracheal intubation with rocuronium, anesthesia
was maintained with 50% oxygen, sevoflurane, fentanyl, and rocuronium. Besides routine
monitoring, radial artery was cannulated for monitoring blood pressure (BP) and blood
gas analysis (BGA). Ventilation was targeted to arterial CO2 tension (PaCO2) between 38 and 40 mm Hg. Normothermia was achieved with forced air warmer (FAW)
and warmed fluids infusion. Normal saline and Ringer lactate were infused at 6 mL/kg/h,
and urine output and blood loss were replaced with crystalloids to maintain systolic
BP between 130 to 140 mm Hg. Toward the end of procedure, paracetamol and granisetron
were administered. The surgical procedure of 3.5 hours was smooth. Following reversal
of rocuronium with sugammadex, trachea was extubated, and the awake patient was transferred
to the neurointensive care unit, where to avert sickling, pain was managed with fentanyl,
and satisfactory hydration was maintained. His postoperative period was uncomplicated.
Discussion
RBCs abnormalities in SS produce end-organ damage from microvascular occlusion. Surgery
in sickle cell anemia (SCA) may produce vasoocclusive crisis (VOC), acute chest syndrome,
cardiac failure, etc.[2] When dealing with MMS from SS, the neuroanesthesiologist is faced with the challenges
of delicately balancing various physiological parameters of two coexisting pathologies
to circumvent harm to the patient. Principal perioperative concerns are to maintain
CBF and steer clear of the triggers of sickling. Precautions to avoid sickling provocateurs
must be adopted throughout the perioperative period.
An approach to avert complications of SCA is to reduce HbSS by preoperative transfusion.
However, preoperative transfusion, either simple or exchange, remains contentious.[3] Recently, though, preoperative transfusion has been recommended to increase hemoglobin
to10 gm/dL to keep HbSS below 30%, which provides net benefit of good tissue oxygenation
over downside of raised viscosity.[4] Therefore, we transfused PRBCs preoperatively and also at induction, increasing
hemoglobin to 10.3 g/dL.
Under anesthesia, focus should be on factors responsible for unfavorable outcomes
in these patients. These factors, which either reduce CBF or trigger sickling, are
as follows: hypotension, hypovolemia and dehydration (both increasing blood viscosity),
hypoxia, PaCO2 alterations, and hypothermia.
BP management requires a tightrope walk since both low and high BP is detrimental.
Low BP not only aggravates preexisting diminished CBF but, by reducing oxygen delivery,
also encourages peripheral hypoxia and thereby sickling. Therefore, higher BP is desired
in Moyamoya. Novel monitoring of EEG and near infrared spectroscopy monitoring during
CR, to warn a decrease in CBF or to maintain optimum BP, are still in the investigative
stage.[5]
[6] Since BP in SS patients is generally lower than normal individuals, therefore higher
BP enhances the stroke risk.[7] Thus, avoid BP greater than 140/90 while maintaining good hydration to prevent CBF
reduction. Hence, significance of invasive BP monitoring cannot be overstated. Vasopressors
to augment BP are safe in MMD, but in MMS from SS, fluid loading is preferred over
vasopressors because the latter promotes blood stasis and thereby sickling in periphery.[8] Nevertheless, it is advocated to avoid precipitating a sickling event, treat hypotension
expeditiously with fluids and vasopressor, as appropriate.[9] Various studies have stressed on adequate hydration as the single compelling intervention
to prevent hypotension for better outcomes of such patients.
Besides, poor hydration by increasing blood viscosity encourages erythrocytes polymerization
in capillaries in SS. To prevent dehydration, we covered the perioperative period
(including fasting period) with crystalloids infusion. Furthermore, we replaced urine
output and blood loss with crystalloids. Since consensus is lacking on type of fluids,
we infused both normal saline and Ringer’s lactate. Postoperative vomiting is another
potential source of dehydration, and we prevented that by prophylactic granisetron
administration.
No study has demonstrated a direct link between perioperative hypothermia and sickling.[2] In general, though, it is not unreasonable to consider hypothermia as a risk for
VOC. Mild hypothermia for brain protection has been advocated during CR procedure,
but it remains controversial. Therefore, normothermia should be standard of anesthetic
care in SS patients. We achieved normothermia with FAW and warm fluids’ infusion.
In MMS from SS, maintenance of normocapnia should be the goal because hypercapnia,
as well as hypocapnia, decreases the CBF in regions perfused by collateral vessels,
presumably because of intracerebral steal.[10] PaCO2 levels should be confirmed by BGA, and one should not rely on end-tidal CO2. Importantly, it is desirable to maintain good oxygenation because any episode of
respiratory acidosis would make any accidental hypoxic episode more dangerous.
By adhering to the principles of preventing reduction of CBF and simultaneously instituting
measures to avoid triggers of sickling, our patient had a smooth perioperative course.
In conclusion, successful anesthetic management of MMS secondary to SS was achieved
by good hydration, stable hemodynamics, normocarbia and normothermia.
