Open Anesthesia Board QOD – Flashcards

b. Hyperbaric oxygen Emergent treatment for stroke secondary to air embolism is hyperbaric oxygen. Cerebral perfusion pressure should be maintained and the patient placed on 100% oxygen while awaiting hyperbaric therapy.

A. Control cerebral edema; avoid hypotension leading to further hypoperfusion injury; avoid cerebral vasodilatation with halogenated anesthetics There is high-level evidence for the efficacy of hemicraniectomy in reducing morbidity and mortality from malignant middle cerebral artery strokes. In this setting, "malignant" refers to life-threatening cerebral edema. Patients have unilateral cerebral edema, may be developing herniation, and may have increased ICP. Intravenous anesthesia with maintenance of cerebral perfusion pressure (i.e., hypertension and euvolemia) is a preferred approach similar to any craniotomy for acute space occupying intracranial lesion. Hyperventilation and hyperosmotic therapy, with mannitol or hypertonic saline, are used concomitantly. The herniation syndrome makes the procedure in this patient an emergency. A pre-emptive hemicraniectomy, prior to clinical neurologic deterioration, would be handled as an urgent but not emergent case.

C. albicans C. krusei is intrinsically resistant to fluconazole and resistance among C. glabrata is increasing. Fluconazole is primarily active against Candida spp. (other than krusei and glabrata), Cryptococcus spp., and Coccidioides immitis. It has limited activity against Blastomyces dermatitidis and Histoplasma capsulatum, and no activity against molds.

b. 10,000 CFU/mL The cutoff point used for the diagnosis of pneumonia is 10,000 CFU/mL for BAL (for endotracheal aspirates the cutoff is 1,000,000 CFU/mL, and for a protected brush specimen the cutoff is 1,000 CFU/mL). Diagnosing a pneumonia with less than 10,000 CFU/mL based on a BAL runs the risk of inappropriately administering antibiotics, and theoretically runs the risk of increased antimicrobial resistance.

a. Calcium chloride 500-1000 mg IV This patient has ECG changes that suggest symptomatic hyperkalemia. All the options listed would effectively lower serum potassium. Glucose/Insulin, hyperventilation, and bicarbonate all function by shifting potassium from the extracellular space into the intracellular space. Unfortunately, each of these interventions takes time (5-10 minute minimum) to be effective. Calcium is a physiologic antagonist and can temporarily stabilize the myocardium. Calcium is effective almost immediately and thus is the initial treatment of choice in this patient.

d. Transesophageal echocardiography Transesophageal echocardiography (TEE) is an effective tool in detecting myocardial ischemia as manifested by left ventricular systolic dysfunction. In fact, echocardiographic evidence of wall motion abnormalities has been shown to precede ECG evidence of ischemia. Furthermore, TEE has also been shown to be sensitive in the detection of ischemia. Central venous pressure and systolic pulmonary artery pressure may change during ischemia, but neither is sensitive nor specific for ischemia.

b. Ligamentum flavum The supraspinous and interspinous ligaments are both midline structures and are not traversed in a paramedian approach. The only structure traversed in both midline and paramedian approaches is the ligamentum flavum. The posterior longitudinal ligament is anterior to the spinal cord and not traversed in either the paramedic or midline approaches.

c. Electrocardiogram and echocardiogram Duchenne's muscular dystrophy (DMD) is the most common and severe form of muscular dystrophy and is an X-linked recessive disease resulting in a mutation in the dystrophin gene. DMD has effects on many organ systems in addition to skeletal muscle, including the heart. Patients frequently develop a dilated cardiomyopathy from fatty infiltration of the myocardium. This may present initially on ECG as prominent Q waves, inverted T waves, or other changes. Echocardiography will show LV wall motion abnormalities as fibrosis progresses and indicates the disease is advancing. Some form of cardiac involvement is present in up to 90% of patients; therefore, a cardiac workup is most appropriate for this patient preoperatively.

d. Immune-mediated reaction This patient most likely has a delayed antibody-mediated hemolytic transfusion reaction from the PRBCs given during his surgery. Hemolysis is the most likely cause for the patient's anemia at this time due to lack of signs suggestive of acute blood loss. Such reactions can occur 3-21 days post-transfusion. Laboratory values such as elevated unconjugated bilirubin help lend evidence to this mechanism for his anemia

D. Discontinue transfusion This patient has signs suggestive of an acute transfusion reaction. Despite adequate volume resuscitation and control of surgical bleeding, she is hypotensive, tachycardic and febrile after the initiation of packed red blood cell transfusion. The transfusion should be discontinued and the blood sent back to the blood bank for testing. Febrile transfusion reactions occur in 0.5% of RBC transfusions and 30% of platelet transfusions and are thought to be due to recipient antibodies directed against HLA antigens on donor WBC or platelets. Cytokines released from WBC in stored blood product (especially platelets) may also be a contributing factor. Patients experiencing a febrile reaction have increase in temperature of > 1 C as well as headache and back pain (not obvious in patient under general anesthesia) in addition to signs similar to allergic reaction. The febrile reaction is usually delayed up to 2 hours after the transfusion but is treated successfully with acetaminophen and diphenhydramine. Leukoreduction helps to reduce febrile transfusion reactions. An acute hemolytic transfusion reaction is usually the result of ABO blood group incompatibility and may be fatal. Patients having acute hemolytic reaction present with fever, dyspnea, chest pain, low back pain and sudden hypotension. Under general anesthesia only hypotension and fever may be apparent. Acute renal failure may result; the transfusion should be stopped and volume resuscitation with addition of mannitol or furosemide should be considered.

b. Hypotension/hypoperfusion The use of general anesthesia for acute stroke interventions is requested by many endovascular neurosurgeons, but recent retrospective data points to an association between the use of GA and worse outcome (Froehler, 2012). Prospective studies are needed. In the interim, it appears that hypotension in the setting of GA is the most likely culprit (Davis, 2012). Other possibilities include time delay in mobilizing anesthesia resources, and/or placing a patient on a critical care treatment pathway with associated morbidities (such as ongoing intubation, ventilator associated pneumonia, etc.).

B. Hypertensive Euvolemia HHH therapy has now become hypertensive therapy in the management of cerebral vasospasm. While we want to avoid hypovolemia, it is clear that hypervolemia carries significant morbidity, such as pulmonary complications. Blood pressure is titrated upward until neurologic symptoms subside. The exact blood pressure goal is subjective and tailored to the individual patient. Typical SBP values range from 160-200 mmHg.

c. Adequate intravascular volume Patients with preexisting renal disease are at high risk for further decrement in renal function associated with aortic surgery. Other risks include patients with cardiac disease and those who have aortic cross clamp times (renal ischemia times) greater than 30 minutes. The usual etiology of acute renal failure after AAA repair is acute tubular necrosis. The degree of preoperative insufficiency is the strongest predictor of postoperative dysfunction. Despite the importance of renin-angiotensin system as a contributor to decreased renal blood flow, preoperative therapy with ACEI has not attenuated the decrease in renal blood flow or glomerular filtration rate. Epidural analgesia has also been proposed as a method to reduce the effect of the sympathetic nervous system on kidneys but this has not been shown to prevent or improve changes in renal blood flow. Dopamine and fenoldopam (dopamine-1 agonist) have been touted as preferential dilators of the renal vascular bed, but no outcome evidence indicates that these medications have impact on postoperative renal failure. Diuretics have long been used to prevent renal failure due to animal evidence, but human clinical evidence is lacking. Despite this, mannitol and furosemide are used with frequency in patients undergoing aortic surgery. Animal studies with mannitol show a renal protective effect before the ischemic insult. Mannitol attenuates the decrease in renal blood flow, acts as a vasodilator, increases renal prostaglandin, decreases renal renin, shifts blood to the renal cortex and may be free radical scavenger once the kidneys are reperfused. Furosemide acts to inhibit tubular salt reabsorption and also acts as a vasodilator. Perioperative (preoperative importantly) statin use has been associated with preserved renal function after use of a suprarenal aortic cross clamp. After all of these interventions, perhaps the most important and valuable interventions in preventing further reduction in renal function, are to maintain adequate intravascular volume and left ventricular myocardial function.

a. Nitroprusside Principles of hemodynamic management during the period of aortic cross-clamping in patients with decreased myocardial reserve include reduction in afterload with arteriolar dilators such as nitroprusside and reduction in preload with venodilators such as nitroglycerin. Phenoxybenzamine is longer-acting, orally administered alpha-blocker which is often used in treatment of hypertension in patients with pheochromocytoma. It is not appropriate for use in AAA repair. Care should be taken with reduction in blood pressure in order prevent worsening of visceral ischemia distal to the aortic occlusion. Vasoconstrictors such as norepinephrine and epinephrine may be useful with removal of the aortic cross-clamp in low vascular resistance states. Epinephrine is not usually required as it often increases heart rate and myocardial oxygen consumption while increasing myocardial contractility. Other helpful management options after the cross clamp is removed include volume administration, treatment for hyperkalemia, acidosis and arrhythmias.

d. Stickler Pierre Robin sequence (PRS) is characterized by: 1) Small mandible (micrognathia); 2) Posterior displacement of the tongue (glossoptosis); and, 3) Airway obstruction. It is often, but not always associated with a cleft lip and/or palate. Pierre Robin is called a "sequence" (as opposed to a "syndrome") because everything occurs as a result of mandibular undergrowth in utero. Pierre Robin sequence may occur in isolation, but is often associated with an underlying disorder. The most common syndromes associated with PRS are Stickler syndrome, velocardiofacial syndrome, and Treacher-Collins syndrome. Stickler syndrome is a connective tissue disorder caused by abnormal collagen types II and IX and has autosomal dominant inheritance. It is characterized by "flat" facial appearance with a small nose secondary to midface hypertrophy. Also, extreme myopia and prominent eyes, glaucoma, hearing loss, arthritis, and other problems.

a. Decreased breath sounds, hyper-inflation, hyper-resonance Congenital lobar emphysema is a developmental anomaly of the lung that is characterized by hyperinflation of one or more of the pulmonary lobes. The left lung is more commonly involved and specifically the left upper lobe is the most commonly affected. Infants typically have tachypnea and increased work of breathing, and may have cyanosis. Recurrent pneumonia or poor feeding with failure to thrive are less frequent presentations that may occur in milder forms. Physical examination reveals decreased breath sounds and hyperresonance to percussion. A chest x-ray will reveal hyper-inflation.

a. Roller pump During cardiopulmonary bypass, a mechanical pump is required to circulate blood through the circuit and then back to the patient. In general, 2 types of pumps are utilized for this purpose: roller pumps and centrifugal pumps. Flow of a roller pump is predictable and depends on the revolutions per minute of the pump. Although retrograde flow is not possible, if there is outflow occlusion to the pump, excessive pressure can build, causing the tubing to rupture or the tubing connections to separate. Of course, there are safety checks in place to prevent this from occurring.

b. Retrograde flow is possible with the centrifugal pump The centrifugal pump is quite different than the roller pump. The centrifugal pump operates on a principle of a constrained vortex, where a rotator (impeller) is housed within a rigid container shaped like a cone. Flow depends on the pressure differential created by spinning cones within the pump. In other words, rapidly rotating cones create negative pressure (pressure drop) by the centrifugal action of the rotating core, propelling fluid forward. Flow varies depending on pump preload and afterload. Unfortunately, retrograde flow is possible, but of course, safety checks are in place to prevent this.

d. Transgastric mid-papillary short axis view Transesophageal echocardiography (TEE) is an effective tool in detecting myocardial ischemia as manifested by left ventricular systolic dysfunction. In fact, echocardiographic evidence of wall motion abnormalities has been shown to precede ECG evidence of ischemia. Furthermore TEE has also been shown to be sensitive in the detection of ischemia. The transgastric mid-papillary short axis view is recommended for monitoring of ischemia because it shows portions of the myocardium that are perfused by all three main coronary arteries: the right, left anterior descending and circumflex arteries. It should be noted that this view does have its limitations as it does not provide information about the right ventricle, or the basal or apical segments of the left ventricle.

b. Benzodiazepines Delirium in the ICU may be to be related to benzodiazepine use. Benzodiazepine use appears to be associated with an increase in delirium when compared to dexmedetomidine - both the Maximizing Efficacy of Targeted Sedation and Reducing Neurological Dysfunction (MENDS) [Pandharipande et al.] and the Safety and Efficacy of Dexmedetomidine Compared to Midazolam (SEDCOM) [Riker et al.] studies suggest that dexmedetomidine may decrease delirium when compared to benzodiazepines.

b. 24h stool nitrogen Healthy individuals consume and excrete nearly identical amounts of nitrogen. Critically ill patients, who are catabolic, tend to excrete more nitrogen than they consume (thus the nitrogen balance is negative). In critically ill patients, it is therefore useful to compare nitrogen intake to nitrogen losses, which primarily occur in the form of urinary excretion. In order to accurately measure nitrogen balance, change in BUN must also be accounted for. Knowledge of nitrogen intake (divide g protein by 6.25 to get g nitrogen), urinary excretion, and the change in BUN over 24h allows one to calculated the nitrogen balance and assess the adequacy of nutritional support.

d. Ventricular fibrillation Synchronized electrical cardioversion is most effectively employed to convert patients with unstable supraventricular tachycardias. The electrical shock is "synchronized" with the QRS complex in order to avoid shocking the heart during the vulnerable refractory period: It avoids an "R on T" episode. During ventricular fibrillation, there is no QRS complex and thus the device would fail to discharge.

d. Intercostal Systemic absorption of a local anesthetic is determined by the site of injection, the concentration and volume of local anesthetic, the addition of vasoconstricting additives, and the pharmacologic profile of local anesthetic. Generally speaking, the more vascular the region the higher the blood levels after injection. Absorption from the intercostal space is rapid, with plasma concentrations peaking as quickly. Many people use the acronym "ICE-BS" (Intercostal -- Caudal -- Epidural - Brachial plexus - Spinal) to remember fastest to slowest systemic absorption.

b. Carbamazepine Trigeminal neuralgia is characterized by intense, stabbing pain in the distribution of the trigeminal nerve. The symptoms are usually unilateral. The patient may experience exacerbations with more frequent attacks, followed by remissions with fewer and less frequent attacks. Carbamazepine is the first line treatment for trigeminal neuralgia.

b. Fibrinogen Fibrinogen will reach a critical level (i.e., below 100 mg/dL) after loss of about 1.5 blood volumes. Other coagulation factors typically reach critical levels after about 2 to 2.5 blood volumes.

c. Forearm supination At the level of the axillary artery, the brachial plexus has divided into three cords (medial, lateral, and posterior), which are named in relationship to the axillary artery. These three cords travel with the axillary artery within the axillary sheath. The musculocutaneous nerve, however, as a terminal branch of the lateral cord, travels separately and is NOT located inside the axillary sheath. Thus, it must be blocked separately from an axillary brachial plexus block. Assuming that a musculocutaneous nerve block has not been performed, we would not expect to see a motor block of the biceps muscle, and elbow flexion and forearm supination, as well as cutaneous sensation to the lateral forearm, would be intact.