Lippincott's Anesthesia Review: 1001 Questions and Answers
Chapter 13. Neuroanesthesia
Dipty Mangla and Ashish Sinha
1. Total normal cerebral blood flow (CBF) is
A. 25 mL/100 g/min
B. 50 mL/100 g/min
C. 100 mL/100 g/min
D. 150 mL/100 g/min
2. The factor associated with maximum increase in intracranial pressure (ICP) is
A. Increased central venous pressure to 14 mm Hg
B. Hypercarbia with PaCO2 of 50 mm Hg
C. Ventilation with positive end–expiratory pressure (PEEP) of 5 cm H2O
D. Bucking and coughing on endotracheal tube
3. Cerebral perfusion pressure (CPP) (mm Hg) in a patient with intracranial pressure (ICP) of 12 mm Hg, central venous pressure (CVP) of 15 mm Hg, and mean arterial pressure (MAP) of 70 mm Hg will be
4. Treatment of a patient with mannitol can lead to all the following, except
5. A patient is undergoing craniotomy for subdural hematoma. During the procedure, the surgeon requests lowering the intracranial pressure. All the following can be used, except
6. The desired level of PaCO2 in a neurosurgical patient is
A. 30 to 35 mm Hg
B. 25 to 30 mm Hg
C. 20 to 25 mm Hg
D. 15 to 25 mm Hg
7. An absolute contraindication for electroconvulsive therapy (ECT) is
C. Aortic aneurysm
8. Signs of air embolism in a patient include all, except
B. Heart murmur
D. Decreased EtCO2
9. A 65-year-old male is undergoing surgery for medulloblastoma in the posterior fossa of brain. Approximately 1 hour into surgery you notice arrhythmias on the monitors. The next step will be
A. Inform the surgeon
B. Give β-blockers
C. Administer lidocaine
D. Give 100% oxygen
10. Nitrous oxide should be avoided in patients with
A. Subdural hematoma
B. Brain tumor
C. Closed head injury
11. The following fluid should be avoided in a patient undergoing craniotomy
A. Lactated Ringerés
B. Normal saline
C. Dextrose 5%—normal saline
12. Most sensitive method to detect air embolism is
A. Transesophageal echocardiogram (TEE)
B. Decreased end-tidal carbon dioxide
C. Increased end-tidal nitrogen
D. Mill wheel murmur
13. Best measure to reduce cerebral oxygen consumption includes
A. Administration of barbiturates
C. Administration of opioids
D. Institution of hypothermia
14. All of the following decrease cerebral blood flow (CBF), except
15. In a patient undergoing craniotomy, the transducer of arterial line should be zeroed at the
A. Level of hypothalamus
B. Level of heart
C. Level of external auditory meatus
D. Level of atmosphere
16. Jugular venous oxygen saturation
A. Estimates oxygen extraction
B. Is unaffected by systemic hypoxia
C. Involves placement of catheter through inferior vena cava
D. Monitors global oxygenation of both cerebral hemispheres
17. The effect of ischemia on somatosensory-evoked potentials (SSEPs) is
A. Decreased latency, decreased amplitude
B. Increased latency, increased amplitude
C. Decreased latency, increased amplitude
D. Increased latency, decreased amplitude
18. A patient with spinal injury, sustained 3 hours ago, comes to the OR for exploratory laparotomy. Anesthetic management of the patient includes which of the following?
A. Rapid-sequence induction with succinylcholine
B. Hypothermia for better neurologic outcome
C. Managing autonomic hyperreflexia
D. Avoiding corticosteroids
19. The electrophysiological monitor most resistant to anesthetic agents is
A. Somatosensory-evoked potentials
B. Motor-evoked potentials
C. Brain-stem auditory-evoked potentials
20. The most reliable monitor for neurologic monitoring in a patient undergoing carotid endarterectomy is
B. Jugular venous oxygen saturation
C. Awake neurologic exam
D. Stump pressure
21. Anesthetic management of a patient with multiple sclerosis (MS) includes
A. Avoiding hypothermia
B. Avoiding hyperthermia
C. Spinal anesthesia is safe
D. Use of succinylcholine can result in hypokalemia
22. All the following are true for Guillain–Barré syndrome (GBS), except
A. Respiratory paralysis is frequent complication
B. Presence of labile autonomic nervous system
C. Ascending motor paralysis
D. Exaggerated reflexes
23. True statement about autonomic hyperreflexia is
A. Lesions below T10 is responsible for the reflex
B. It can be treated with deep general anesthetic
C. It is associated with vasoconstriction above the site of injury
D. It can be provoked by thermal stimulation
24. A 16-year-old patient with acute lysergic acid diethylamide (LSD) intoxication and head injury comes to emergency room. All the following can be used in anesthetic management, except
25. A 25-year-old patient with severe depression is undergoing an electroconvulsive therapy (ECT). The duration of seizure can be increased by
A. Hypoventilating the patient
B. Hyperventilating the patient
C. Administering succinylcholine
D. Administering rocuronium
26. All of the following are contraindications of electroconvulsive therapy (ECT), except
B. Recent stroke
C. Raised intracranial pressure
D. Severe osteoporosis
27. True statement regarding cerebral physiology is
A. Normal cerebral metabolic oxygen consumption is 5 mL/100g/min
B. Normal Intracranial pressure (ICP) is approximately 15 mm Hg
C. Normal cerebral blood flow (CBF) is 50 mL/100g/min
D. Cerebral autoregulation is strictly maintained at blood pressures between 60 and 150 mm Hg in all patients
28. True statement about cerebrospinal fluid (CSF) is
A. It is formed in the third ventricle
B. It is absorbed in arachnoid granulations present in fourth ventricle
C. Total volume of CSF is about 150 mL
D. Major mechanism of formation is by passive diffusion of ions
29. A precordial Doppler can detect a minimal of ___ mL of intracardiac air:
30. The only inhalational anesthetic that can cause an isoelectric EEG among the following is
D. Nitrous oxide
31. Intraoperative anesthetic management of a patient undergoing cerebral aneurysm repair includes all, except
A. Maintenance of hypotension
B. Mannitol for facilitating surgical exposure
C. Maintaining mild hypothermia
D. Patient remaining intubated for 24 hours postoperatively
32. Which of the following types of neuromonitoring can be done in a patient undergoing transsphenoidal resection of a pituitary tumor?
B. Motor-evoked potentials
C. Visual-evoked potentials
D. Auditory-evoked potentials
33. The drug of choice for treating nausea and vomiting in a patient with parkinsonism would be
34. All the following anesthetic agents can cause seizurelike activity on the electroencephalogram (EEG), except
35. The neuromuscular blocking agent relatively contraindicated in a patient with raised intracranial pressure (ICP) is
36. The afferent input for somatosensory-evoked potentials is carried by which spinal cord tract
B. Dorsal columns
37. You are called to evaluate a 50-year-old patient for brain death. All the following are criteria for brain death, except
A. Apnea for 10 minutes
B. Absence of corneal reflex
C. Presence of spinal reflexes
D. Decerebrate posturing
38. A 30-year-old male is found unresponsive outside a supermarket. The emergency response team finds him in ventricular fibrillation. After 10 minutes of CPR, the emergency response team is successful in reviving the patient. In the emergency room, it is decided to cool the patient to 34°C from 37°C. By this measure, the cerebral metabolic demand will decrease by
39. All the following are relative contraindications to a sitting craniotomy, except
A. Right-to-left cardiac shunt
B. Patent foramen ovale
C. Ventriculoatrial shunt
D. Ventriculoperitoneal shunt
40. An 80-year-old female comes to the ER with closed distal radial fracture. On further questioning, she gives a history of stroke about 2 weeks ago. How long should one wait before it can be assumed that her risk of perioperative stroke is same as a healthy 80-year-old?
A. 6 days
B. 6 weeks
C. 6 months
D. 6 years
41. A 28-year-old male is being treated in the ICU for raised intracranial pressure (ICP). All the following measures can aid in decreasing ICP quickly, except
B. Hyperventilation to PaCO2 of 30 mm Hg
D. Head elevation to 30 degrees
42. Which of the following agents will have the least effect on somatosensory-evoked potentials (SSEPs)?
D. Nitrous oxide
43. Signs and symptoms of raised intracranial hypertension include all the following, except
D. Irregular respiration
44. Etomidate in a dose of 0.2 mg/kg can lead to all the following, except
A. Abolish ventilatory response to carbon dioxide
B. Increase amplitude and latency of somatosensory-evoked potentials (SSEPs)
C. Decrease cerebral metabolic oxygen demand
D. Decrease cerebral blood flow (CBF)
45. The most important factor governing cerebral blood flow (CBF) is
A. Cerebral metabolic oxygen demand
D. Cerebral perfusion pressure
46. The following graph depicts the relationship between cerebral perfusion and
C. Mean arterial pressure
D. Cerebrospinal fluid pH
47. The following graph depicts the relationship between cerebral perfusion and
C. Mean arterial pressure
D. Cerebrospinal fluid pH
48. A 45-year-old male is seen in the preadmission testing for pituitary adenoma resection surgery. All the following would be expected if this adenoma was causing acromegaly, except
B. Obstructive sleep apnea
C. Difficult airway
49. The fastest measure to decrease intracranial pressure (ICP) in a patient is
50. Therapy for cerebral vasospasm includes
A. Hypertension, hypervolemia, hemodilution
B. Normotension, euvolemia, hypocarbia
C. Hypotension, hypovolemia, hypocarbia
D. Hypertension, hypervolemia, hypocarbia
CHAPTER 13 ANSWERS
1. B. Normal total CBF is about 50 mL/100 g/min. CBF below 20 mL/100 g/min is associated with cerebral ischemia. CBF is modulated by various factors, which include PaCO2, PaO2, blood pressure, intracranial pressure, etc.
2. D. Intracranial pressure is supratentorial CSF pressure measured in the lateral ventricles or cerebral cortex. Normal ICP is 10 mm Hg or less. Between PaCO2 values of 20 and 80 mm Hg, CBF increases by 1 mL/100 g/min and cerebral blood volume increases by 0.05 mL/110g/min per mm Hg increase in PaCO2. Increase in CVP and adding PEEP will minimally increase ICP by affecting venous return. Coughing and bucking can cause a much higher increase in ICP (acute increase) than any of the above factors.
3. B. CPP = MAP − ICP or CVP, whichever is higher.
Thus, CPP = 70 − 15 = 55 mm Hg.
4. A. Mannitol, a six-carbon sugar, is the most commonly used diuretic in neuroanesthesia practice. It is an osmotic diuretic and undergoes little or no reabsorption. It also improves renal blood flow. Side effects include an initial increase in circulatory volume, which can cause pulmonary edema. Diuresis attributed to mannitol can lead to hypovolemia and hypokalemia.
5. C. Treatment of intracranial hypertension includes hyperventilation to PaCO2 of 25 to 30 mm Hg, improving CSF drainage by elevating the head by 30 degrees or surgical placement of CSF drain, using an osmotic diuretic (mannitol), hypertonic saline, decompression craniectomy, barbiturates, and corticosteroids. The latter have been used to decrease cerebral edema, and take a few hours to have effect, but routine use of corticosteroids in managing intracranial hypertension is not recommended.
6. B. PaCO2 is the most potent physiologic determinant of cerebral blood flow. Maximal reductions in ICP can be achieved by decreasing PaCO2 to 25 to 28 mm Hg, and the reduction in ICP lasts up to 24 to 36 hours.
7. B. ECT is commonly used for treatment of refractory major depression. It involves using electricity to shock one or both cerebral hemispheres to induce a seizure lasting 30 to 60 seconds. Contraindications to ECT include pheochromocytoma, recent myocardial infarction (<3 months), recent stroke (<1 month), intracranial mass or increased ICP, angina, poorly controlled heart failure, significant pulmonary disease, bone fractures, severe osteoporosis, pregnancy, glaucoma, and retinal detachment.
8. A. Clinical signs of venous air embolism include a decrease in end-tidal CO2, a decrease in arterial oxygen saturation, sudden hypotension, mill wheel murmur, and even sudden circulatory arrest. Presence of a patent foramen ovale, which has an incidence of 20% in adults, can lead to paradoxical air embolism, with the potential of causing coronary ischemia or a stroke.
9. A. For posterior fossa tumor resection, the patient is frequently placed in the sitting or prone position. Monitoring of the patient includes arterial blood pressure line, a central venous catheter (for access, pressure monitoring, aspiration of any air—if required), and a precordial Doppler to detect intracardiac air (venous air embolism). Operations on posterior fossa tumors can injure vital brain-stem respiratory and circulatory nuclei, resulting in hemodynamic fluctuations or depression of ventilation. The surgeon should be informed at the first sign of cardiac arrhythmias.
10. D. Nitrous oxide can diffuse into closed air spaces, which may be of significant clinical consequences. The blood/gas coefficient of nitrous oxide is 0.47, whereas that of nitrogen is 0.015. This means that nitrous oxide is about 33 times more diffusible than nitrogen. As a result, at any given partial pressure, far more nitrous oxide can be carried into a closed gas space than nitrogen removed. Thus, nitrous oxide can quickly expand closed gas spaces, such as middle ear or a pneumothorax.
11. C. In a patient undergoing craniotomy, intravenous fluid replacement should be performed by using glucose-free isotonic crystalloid or colloid solutions. Hyperglycemia is known to worsen ischemic brain injury.
12. A. The most sensitive intraoperative monitor for detecting venous air embolism is TEE. The second best monitor is precordial Doppler sonography, which can detect as little as 0.25 mL of air. Changes in end-tidal respiratory gas concentrations, such as nitrogen and carbon dioxide, and changes in pulmonary artery pressures are less sensitive. Hypotension and mill wheel murmur are late manifestations of venous air embolism.
13. D. Hypothermia is one of the most effective methods for protecting the brain against ischemia. Hypothermia decreases both basal and electrical metabolic requirements throughout the brain, unlike intravenous anesthetic agents or hyperventilation.
14. D. Propofol, barbiturates, and etomidate produce dose-dependent decreases in cerebral metabolic rate and CBF. Ketamine is the only induction agent that dilates the cerebral vasculature and thus increases CBF (50% to 60%).
15. C. In a seated patient, the arterial pressure in the brain differs significantly from left ventricular pressure. Cerebral perfusion pressure is determined by setting the transducer to zero at the level of the ear, which approximates the circle of Willis.
16. D. Jugular venous bulb oximetry involves placing a sampling catheter in the internal jugular vein (IJV). The normal range for mixed venous oxygen saturation at IJV is 50% to 75%. It gives an estimate of balance between oxygen supply and demand of the brain, and measures global cerebral oxygenation (not focal).
17. D. SSEPs reflect the integrity of neuronal pathway from the peripheral nerves through the spinal cord (dorsal columns) to the brain. SSEPs are electrical manifestations of the central nervous system response to external stimulation. Intraoperative changes in amplitude or latency or complete loss of waveforms are indicators of compromised sensory pathway integrity. SSEP amplitude loss greater than 50% or a latency increase greater than 10% is considered significant.
18. A. In the early management of acute spinal injury patients, particular emphasis should be placed on preventing further spinal damage, which may occur during patient movement, airway manipulation, and positioning. High-dose corticosteroids are often administered to help improve neurological outcome. The head and neck should be stabilized using manual inline stabilization, and awake fiberoptic intubation should be considered in high cervical injuries. Patients with high cord transections may have impaired airway reflexes, hypotension, and bradycardia and may be prone to hypothermia in view of generalized vasodilation. Succinylcholine can be used safely in first 24 hours following spinal injury.
19. C. Somatosensory- and motor-evoked potential monitoring is commonly used to detect ischemia of spinal cord in spine surgeries. Brain-stem auditory–evoked responses monitor ischemia during posterior fossa surgeries. Inhalational agents in general increase the latency and decrease the amplitude of evoked potentials (if used at more than 0.5–0.75 MAC). The effect of inhalational anesthetics on evoked potentials in decreasing order is visual > motor > somatosensory > brain-stem auditory.
20. C. Awake neurological status is the most reliable method to detect cerebral ischemia. In patients undergoing carotid endarterectomy under local anesthesia and mild sedation, global and focal neurological status can be continuously assessed. In patients undergoing carotid endarterectomy under general anesthetic indirect methods to detect cerebral ischemia can be used. These include EEG monitoring, transcranial Doppler, arteriography, and measurement of blood flow using xenon.
21. B. MS is characterized by progressive demyelination in the brain and spinal cord. Stress, anesthesia, and surgery can have detrimental effects on the course of the disease. Elective surgery should be avoided in acute relapse of MS. Regarding the effect of anesthetic technique on MS, spinal anesthesia can exacerbate MS symptoms, epidural anesthesia usually does not affect MS, succinylcholine should be avoided to prevent hyperkalemia, and hyperthermia should be avoided as an increase in temperature may block nerve conduction. Advanced MS may be associated with autonomic dysfunction.
22. D. GBS affects about 2/100,000 people. It is characterized by a sudden onset ascending motor paralysis, areflexia, and paresthesias. Bulbar involvement with respiratory failure is a frequent complication. Succinylcholine should be avoided in these patients, as it can cause hyperkalemia. Regional anesthesia may make GBS worse. Anesthetic management may be complicated by liability of the autonomic nervous system (hypotension or hypertension).
23. B. Autonomic hyperreflexia is seen in patients with spinal cord injury at or above T6. It is characterized by acute generalized sympathetic hyperactivity in response to a triggering stimulus. The triggering stimulus can be any stimulus occurring below the level of the lesion, and is most commonly a distension of hollow viscera (bowel or bladder). Clinical signs include severe hypertension, bradycardia, arrhythmias, profuse sweating, vasodilation above the level of lesion, and pallor and vasoconstriction below the level of lesion. Antihypertensives may have to be utilized to treat the hypertension. Spinal anesthesia (not preferred because of technical difficulty and unpredictable level) or deep general anesthesia has been used in preventing autonomic hyperreflexia.
24. C. LSD is a hallucinogen and causes CNS excitation, sensory distortion, delusions, hallucinations, and euphoria. Autonomic effects, mediated via the hypothalamus, include tachycardia, hypertension, mydriasis, piloerection, salivation, lacrimation, and vomiting. In view of hypertension and tachycardia that can be caused by LSD, ketamine should be avoided.
25. B. Propofol when used for induction in patients undergoing ECT can increase the seizure threshold and decrease the duration of the seizure. Hyperventilation and administration of caffeine or etomidate can increase seizure duration. Muscle relaxants do not affect the threshold or duration of the seizure.
26. A. Contraindications to ECT include recent myocardial infarction (<3 months), a recent stroke (<1 month), an intracranial mass and raised intracranial pressure, angina, poorly controlled congestive heart failure, significant pulmonary disease, bone fractures, severe osteoporosis, pregnancy, glaucoma, and retinal detachment.
27. C. The cerebral metabolic rate is reflected by oxygen consumption, which is about 3 to 3.8 mL/100 g/min. Total CBF averages 50 mL/100 g/min. In normal individuals, CBF remains nearly constant between mean arterial pressures of about 60 and 160 mm Hg. The cerebral autoregulation curve is shifted to right in patients with chronic arterial hypertension. ICP by convention means supratentorial CSF pressure measured in the lateral ventricles or over the cerebral cortex, and the normal CSF pressure is 10 mm Hg or less.
28. C. CSF is formed by the choroid plexuses of cerebral lateral ventricles. In adults, normal CSF production is about 20 mL/hour with a total volume of 150 mL. The CSF is absorbed in arachnoid granulations over cerebral hemispheres. CSF formation involves active secretion of sodium in the choroid plexuses, and not passive diffusion.
29. B. A precordial Doppler can detect as little as 0.25 mL of intracardiac air. A precordial Doppler is the next best sensitive indicator to detect intracardiac air after a transesophageal echocardiogram.
30. A. Isoflurane can produce an isoelectric EEG at 2 to 2.5 MAC, while enflurane typically produces a spike and wave pattern at 2 to 3 MAC. Seizure activity may be seen on EEG with 3% enflurane in a hypocapnic patient. Halothane causes slowing of EEG activity with increasing concentration until 4 MAC, after which it produces uniform activity. Increasing sevoflurane concentration from 2 to 5 MAC changes the cortical EEG pattern from a high-amplitude slow wave to burst suppression to an isoelectric EEG interspersed with spikes.
31. D. Intraoperative management of cerebral aneurysms should include availability of blood, avoidance of hypertension during induction, central venous pressure and arterial blood pressure monitoring, mannitol after the dura is opened to help surgical exposure, elective hypotension as it decreases transmural pressure across the aneurysm (avoiding rupture), administration of thiopental and mild hypothermia for cerebral protection, and awake extubation depending on neurological status.
32. C. The transsphenoidal or bifrontal craniotomy approach may be used to gain access to pituitary gland. The former (transsphenoidal approach) has several advantages including elimination of frontal lobe retraction, microsurgical removal of small adenomas, reduced blood loss, and shorter hospital stay. Patients are intubated endotracheally (oral), and oropharyngeal packing is done to prevent bleeding into the esophagus. Additionally, epinephrine or cocaine may be injected submucosally to reduce bleeding. The cavernous sinus forms the lateral border of the sella turcica and includes the internal carotid artery, venous structures, and cranial nerves III, IV, V, and VI. Therefore, visual-evoked potentials may be monitored in the OR for early detection of visual pathway damage.
33. A. Parkinson disease is a movement disorder that affects individuals 50 to 70 years of age. It is caused by progressive loss of dopamine in the nigrostriatum. Patients have bradykinesia, postural instability, rigidity, facial masking, and a resting pill-rolling tremor. Antidopaminergic activity associated with butyrophenones, phenothiazines, and metoclopramide can worsen symptoms and thus these should be avoided.
34. D. Ketamine, etomidate, and enflurane can cause seizurelike activity on the EEG. Thiopental increases the threshold and decreases the duration of seizure activity.
35. C. In a patient with increased intracranial pressure, a nondepolarizing muscle relaxant is commonly used to facilitate controlled ventilation and tracheal intubation. Rocuronium and vecuronium are commonly used as they provide the greatest hemodynamic stability. Succinylcholine and atracurium (due to associated histamine release) may increase ICP, particularly if intubation is attempted before deep general anesthesia. Hyperventilation prior to intubation is utilized to decrease the ICP.
36. B. Somatosensory-evoked potentials are transmitted through the following pathway:
peripheral stimulus → peripheral nerve → dorsal root ganglia → first-order fibers in the ipsilateral posterior column to dorsal column nuclei → second-order fibers crossing to the opposite side → medial lemniscus to the thalamus → third-order fibers continuing to the frontoparietal sensory-motor cortex.
37. D. Brain death is irreversible cessation of all brain activity. Generally accepted clinical criteria for brain death include presence of coma, absence of motor activity, absence of brain-stem reflexes (papillary, corneal, vestibule–ocular, and gag/cough), absence of ventilatory effort (PaCO2 >60 mm Hg), exclusion of hypothermia or effect of sedatives, isoelectric EEG, and absence of cerebral perfusion by angiography.
38. B. Cerebral metabolic rate decreases by 6% per degree Celsius decrease in body temperature below 37°C. Hence, a 3°C drop in temperature will decrease the cerebral metabolic rate by 18%.
39. D. The incidence of venous air embolism in sitting craniotomies is about 20% to 40%. The presence of right-to-left shunt can cause paradoxical air embolism. Air embolism can have catastrophic consequences, such as coronary ischemia and stroke. Thus, sitting position should be avoided in patients with a right-to-left shunt, patent foramen ovale, or ventriculoatrial shunt.
40. B. Regional blood flow and metabolic rate are normal after 2 weeks following a stroke. Alterations in CO2 responsiveness and blood–brain barrier abnormalities require more than 4 weeks to be corrected. Thus, most clinicians postpone elective surgery for at least 6 weeks following stroke.
41. A. Definitive treatment of intracranial hypertension is ideally directed at the underlying cause. Treatment modalities include fluid restriction, head elevation, osmotic agents and loop diuretics, moderate hyperventilation (up to 24–36 hours), avoidance of hypotension, hypoxia and hypercarbia, and corticosteroids. The latter is used to decrease cerebral edema in patients with known intracranial tumors, and take a few hours to take effect.
42. A. Inhalational volatile anesthetics produce an increase in latency and decrease in amplitude of evoked potentials. Nitrous oxide produces a decrease in amplitude with no change in latency. Propofol decreases amplitude and an increase in latency of SSEPs. Muscle relaxants have no effect on SSEPs. Narcotics cause dose-dependent decrease in amplitude and increase in latency.
43. B. Increased intracranial pressure (ICP) can lead to altered mental status, intractable vomiting, and focal or global neurological deficits. Clinical signs include hypertension, bradycardia, irregular respiration, and pupillary changes (papilledema may be seen on fundoscopy). Cushing triad consists of raised ICP, hypertension, and bradycardia.
44. A. Etomidate decreases cerebral metabolic rate, CBF, leading to a decrease in intracranial pressure. It enhances SSEP. It is a sedative hypnotic but lacks analgesic properties. Ventilation is affected to a lesser extent with etomidate when compared to barbiturates or benzodiazepines. Induction doses usually do not result in apnea.
45. A. Increased metabolic activity leads to an increase in CBF. Regional CBF parallels metabolic activity and can vary from 10 to 300 mL/100 g/min. For example, motor activity of a limb is associated with a rapid increase in regional blood flow of the corresponding motor cortex.
46. A. CO2 gas tension has the greatest influence on cerebral blood flow (CBF). Between a PaCO2 of 20 and 80 mm Hg, CBF changes approximately 1 to 2 mL/100 g/min per mm Hg in PaCO2.
47. B. Marked changes in PaO2 affect cerebral blood flow (CBF), although minimally. Hyperoxia is associated with only minimal decreases in CBF. On the other hand, hypoxemia (PaO2<50 mm Hg) greatly increases CBF.
48. A. The acromegalic patient suffers from general overgrowth of skeletal, soft, and connective tissues. This results in coarse facial features and enlarged hands and feet. Patients may also have a difficult airway because of overgrowth of soft tissues of upper airway, enlargement of tongue and epiglottis, overgrowth of mandible with increased distance from lips to vocal cords, and glottic and subglottic narrowing. These changes may also lead to obstructive sleep apnea. Patients also are prone to hyperglycemia, hypertension, congestive heart failure, increased lung volumes, increased ventilation–perfusion mismatch, peripheral neuropathy, skeletal muscle weakness, osteoarthritis, and osteoporosis.
49. D. The quickest way to reduce ICP in a patient is hyperventilation, often to a PaCO2 of 25 mm Hg. Reduced PaCO2 (hypocarbia) causes cerebral vasoconstriction leading to a reduction in cerebral blood flow and cerebral blood volume. However, hyperventilation is only used as a temporizing measure only in periods of acute raised ICP.
50. A. Cerebral vasospasm occurs in about one-third of patients surviving the initial aneurysmal rupture, and carries a high degree of morbidity and mortality. The degree of vasospasm depends on the degree of initial subarachnoid hemorrhage. Vasospasm usually develops 3 to 14 days postsubarachnoid hemorrhage results in narrowing of cerebral blood vessels and decreased blood flow distally. This may lead to an ischemic deficit and cerebral infarction, if left untreated. Therapies for cerebral vasospasm include “triple-H therapy” (hypertension/hypervolemia/hemodilution), balloon angioplasty, and intra-arterial nicardipine and other vasodilators.<CT>