Apex Unit 11 Across the Lifespan Flashcards

Question

Which statement regarding fetal hemoglobin is TRUE? It has an increased affinity for 2,3-DPG. It has a higher P50 than the adult. It is replaced by hemoglobin A at 9 months of age. Erythrocytes containing hemoglobin F have a shorter lifespan.

Answer 1

Erythrocytes containing hemoglobin F have a shorter lifespan Key facts regarding fetal RBCs and HgbF: Fetal RBCs have a lifespan of 70 – 90 days, which is shorter than those with HgbA (120 days). HgbF has a P50 value of 19 mmHg, which is lower than the adult value of 26.5 mmHg. HgbF is unable to bind 2,3-DPG, which explains why it has a higher affinity for oxygen. HgbF is replaced by RBCs containing Hgb A in the first two months of life.

Answer 2

Hypokalemia Massive transfusion is associated with hypocalcemia, metabolic acidosis, and/or metabolic alkalosis. Neonates and children who receive erythrocyte transfusion are at risk for hyperkalemia (not hypokalemia).

Answer 3

48 - 60 mL or 53 - 67 mL (we accepted the wider range) The "correct" range is a function of the equation you use (there are two common ones). We like the following equation: MABL = EBV x [(Hct starting - Hct target) / Hct starting] If you used this equation, the correct range is 48 - 60 mL. The other equation uses Hct average in the denominator: MABL = EBV x [(Hct starting - Hct target) / Hct average] If you used this equation, then the correct range is 53 - 67 mL. For your exam, the item writers should be aware of the different equations in the texts and take this into account when determining the correct response to the question.

Answer 4

Excrete sodium The newborn’s kidney has an immature concentrating mechanism, so it tends to excrete sodium - it is an obligate sodium loser. For the same reason, it partially lacks the ability to retain water and glucose

Answer 5

80 – 90% The total body water for the premature neonate is 80 – 90%.

Answer 6

50 mL Unless you are instructed otherwise, you should use the 4:2:1 rule for fluid calculations on the NCE. Step1: 0-10 kg → Begin with 4 mL/kg/hr Step 2: 10-20 kg → Add 2 mL/kg/hr to the previous total Step 3: > 20 kg → Add 1 mL/kg/hr to the previous total The child in this question weights 15 kg so... Step 1: 10 kg x 4 mL/kg/hr = 40 mL Step 2: 5 kg x 2 mL/kg/hr = 10 mL Answer: 40 mL + 10 mL = 50 mL total

Answer 7

Shorter duration of action for lipid soluble drugs Neonates have a greater percentage of total body water and a lower percentage of fat and muscle mass. Drugs that require fat for redistribution and termination of effect have a longer duration of action (not shorter). A high TBW also means that they require higher doses of water soluble drugs to achieve a given plasma concentration. Since they have lower concentrations of plasma proteins, there will be an increased free fraction of highly protein bound drugs. The cardiac output in the newborn is 200 mL/kg/min. This accounts for a faster circulation time.

Answer 8

A larger dose of succinylcholine The combination of an increased ECF and normal sensitivity of succinylcholine necessitates an increased dose of 2 mg/kg. Its duration is similar between neonates and adults (not increased). The black box warning on succinylcholine warns of hyperkalemia associated with undiagnosed muscular dystrophy in children under eight years old. Considering this, succinylcholine remains a suitable option for rapid sequence intubation, anticipated difficult airway, laryngospasm, or other airway emergencies. The dose for nondepolarizers is the same for neonates and adults on a per kg basis.

Answer 9

2.0 An L/S ratio of 2.0 or greater suggests fetal lung maturity. An L/S ratio less than 2.0 suggests immature fetal lungs and may place the fetus at risk for respiratory distress syndrome.

Answer 10

Metabolic acidosis Pyloric stenosis occurs when hypertrophy of the pyloric muscle creates a mechanical obstruction at the gastric outlet (between the stomach and the duodenum). Vomiting causes the infant to lose H+ and electrolytes, so he will commonly present with: ``` Metabolic alkalosis Hyponatremia Hypokalemia Alkaline urine ``` If vomiting persists, and dehydration is not corrected, impaired tissue perfusion increases lactic acid production (metabolic acidosis).

Answer 11

50% oxygen + 50% air Necrotizing enterocolitis is necrosis of the bowel. The two most important risk factors are prematurity (< 32 weeks) and low birth weight (< 1,500 g). Since many of these babies experience bowel perforation, they present to the OR for bowel resection. Nitrous oxide is contraindicated. That eliminates two of the answer choices. Since they're premature, they're also at risk of retinopathy of prematurity. For this reason, you'll want to decrease the FiO2 to maintain the SpO2 between 89 - 94%. This means that 50% oxygen + 50% air is the best gas mixture for this patient.

Answer 12

Prematurity Explanation: Retinopathy of prematurity causes abnormal vascular development in the retina. The immature retinal blood vessels are at risk for vasoconstriction and hemorrhage. Dysfunctional healing creates scars. As the scars retract, they pull on the retina, causing retinal detachment and blindness. Vasculogenesis occurs 16 - 44 weeks after conception. It's during this time that the patient is at risk for ROP. Prematurity and hyperoxia are the two most significant risk factors.

Answer 13

Ketamine Midazolam Explanation: In experimental animal models, drugs that antagonize the NMDA receptor, stimulate GABA, or both may cause apoptosis. Examples include: ``` Halogenated anesthetics Nitrous oxide Propofol Ketamine Etomidate Barbiturates Benzodiazepines ```

Answer 14

Ductus venosus + Umbilical vein → inferior vena cava Foramen ovale + Right atrium → left atrium Ductus arteriosus + Pulmonary artery → proximal descending aorta The fetal circulation differs from the adult circulation in several ways. In the fetus, gas exchange occurs in the placenta (not the lungs). Also, the circulation is organized in such a way that the blood with the highest oxygen content is preferentially delivered to the heart and brain. This arrangement is dependent on the function of 3 shunts. Ductus venosus: Umbilical vein → inferior vena cava Oxygen rich blood from the placenta bypasses the liver Foramen ovale: Right atrium → left atrium Oxygen rich blood bypasses the lungs and is preferentially delivered to the heart and developing brain ``` Ductus arteriosus: Pulmonary artery (or RV) → proximal descending aorta Lower oxygen blood bypasses the lungs and is delivered to the lower body ```

Answer 15

Hypercarbia Trendelenburg position Light anesthesia The balance between PVR and SVR is important in the patient with congenital heart disease, and understanding this concept will help you answer a variety of questions about this patient population. This question asked you about conditions that increase PVR. Notice that each of the examples below decrease vessel diameter, increase pulmonary blood volume, or both. ``` Conditions that increase PVR: Hypercarbia Hypoxemia Acidosis Atelectasis Trendelenburg position Hypothermia Vasoconstrictors Light anesthesia Pain ```

Answer 16

Tetralogy of Fallot Eisenmenger's syndrome Ebstein's anomaly Shunting occurs when there is an abnormal communication between the pulmonary and systemic circulations. Cyanotic Shunt (R → L): A right-to-left shunt allows blood to bypass the pulmonary circulation and enter the systemic circulation. Examples include: Tetralogy of Fallot Transposition of the great arteries Tricuspid valve abnormality (Ebstein's anomaly) Truncus arteriosus Total anomalous pulmonary venous connection ``` Acyanotic shunt (L → R): A left-to-right shunt causes oxygenated pulmonary venous blood to return directly to the lungs instead of being pumped to the body. Examples include: Ventricular septal defect (most common) Atrial septal defect Patent ductus arteriosus Coarctation of the aorta ```

Answer 17

SVR decreased Myocardial contractility increased Tetralogy of Fallot is characterized by four defects: Ventricular septal defect Aorta that overrides the RV and LV Pulmonic stenosis (obstruction to RV ejection) RV hypertrophy Your job is to minimize the R-to-L shunt by satisfying the following goals. Increase SVR Decrease PVR Maintain Contractility and HR Increase Preload

Answer 18

Secundum There are three types of atrial septal defects: Secundum ASDs occur in the middle of the atrial septum and result when the fossa ovalis fails to close. This type of ASD represents ~ 80% of all ASDs. Primum ASDs occur in the lower region of the atrial septum, just above the tricuspid valve. Sinus venosus ASDs are located just below the IVC or less commonly just above the IVC. The most common type of ventricular septal defect is the perimembranous VSD. It is located in the middle of the ventricular septum, just below the septal leaflet of the tricuspid valve.

Answer 19

Right arm Coarctation of the aorta occurs when the aorta narrows in the area of the ductus arteriosus. Since the aorta is narrowed, the LV must generate a higher pressure to overcome the increased aortic resistance. Severe narrowing can limit the amount of blood delivered to the lower half of the body. Although rare, coarctation may occur proximal to the left subclavian artery, reducing perfusion to the left upper extremity. For this reason, the right upper extremity is the best site to measure blood pressure.

Answer 20

Hypoplastic left heart syndrome All patients with a single ventricle require surgical correction with the Fontan procedure. Hypoplastic left heart syndrome is the most common single ventricle lesion.

Answer 21

Age affected < 2 years Onset between 24 - 72 hours Steeple sign It is essential that you understand the similarities and differences between epiglottitis and croup.

Answer 22

0.5 mL of a 2.25% solution Racemic epinephrine and dexamethasone serve as the cornerstone in the treatment of postintubation croup. Racemic epinephrine = 0.5 mL of 2.25% solution diluted in 2.5 mL of 0.9% NaCl Dexamethasone = 0.25 - 0.5 mg/kg IV

Answer 23

Facemask + 1 LMA + 2 Endotracheal tube + 3 Although this child can reasonably proceed to surgery, you should recognize that she is at a higher risk of pulmonary complications. Since mechanical stimulation of the airway increases the risk of bronchospasm 10-fold, you should select the least stimulating airway to satisfy the demands of the surgical procedure. Facemask > LMA >>> Endotracheal tube Having said this, if the child requires a secure airway, you are going to provide a secure airway.

Answer 24

Inhalation induction Foreign body aspiration in a child presents a precarious situation. The primary goals include preventing complete airway obstruction as well as preventing the foreign body from migrating distally in the airway. Positive pressure ventilation can push the foreign body deeper into the bronchial tree, increasing the difficulty of its retrieval. Therefore, a sevoflurane induction that preserves spontaneous ventilation is usually the best approach. Observation of NPO guidelines must be weighed against the risk of airway compromise.

Answer 25

Trisomy 21 Trisomy 21 (Down syndrome) presents with macroglossia (large tongue). This finding increases the risk of upper airway obstruction.

Answer 26

Atrioventricular septal defect Approximately 50% of infants with Down syndrome have coexisting cardiac disease: Most common = Atrioventricular septal defect Second most common = Ventricular septal defect

Answer 27

VACTERL association + Renal dysplasia CHARGE association + Choanal atresia CATCH 22 syndrome + Hypocalcemia

Answer 28

1,000 mL One metabolic equivalent (MET) corresponds to an oxygen consumption of 3.5 mL/kg/min. Walking up two flights of stairs without stopping is equal to 4 METs and consumes ~ 1,000 mL O2/min. Inability to achieve 4 METs is associated with increased perioperative risk.

Answer 29

Dead space Increased dead space necessitates an increased minute ventilation to maintain a normal PaCO2. Aging is associated with a reduction in PaO2, lung elasticity, and chest wall compliance. Taken together, these changes reduce pulmonary reserve and increase the risk of respiratory failure.

Answer 30

Residual volume Functional residual capacity Closing capacity Aging produces the following changes: Increased: RV, FRC, and CC Decreased: VC and ERV Unchanged: TLC

Answer 31

Increased venous capacitance Our veins become stiffer as we age, and this reduces venous capacitance (the volume of blood the veins can hold). In the OR, this manifests as greater blood pressure lability with anesthetic induction or during acute blood loss.

Answer 32

Systolic function Systolic function is usually preserved in the healthy geriatric patient. Why are the other answers wrong? The arterial tree becomes stiffer over time, signifying a reduction in compliance. This increases SVR and SBP. The pulse pressure widens, because SBP increases to a much greater degree than DBP. The aged heart is slower to return Ca+2 into the sarcoplasmic reticulum during diastole, and this slows the rate of myocardial relaxation (decreased lusitropy).

Answer 33

Baroreceptor sensitivity Aging is associated with a decline in baroreceptor sensitivity. This increases the incidence of orthostatic hypotension and contributes to the greater degree of hemodynamic compromise following sympathectomy associated with neuraxial anesthesia. Aging is associated with an increased sympathetic tone and increased plasma norepinephrine concentration. Despite this, end organs are less responsive to adrenergic stimulation.

Answer 34

6% per decade MAC decreases by 6% for each decade of life after 40 years of age. In the 80-year old-patient, MAC is reduced by approximately 25%.

Answer 35

Epinephrine test dose has a higher rate of false negative result Epidural anesthesia is associated with a greater spread of local anesthetic Decreased beta receptor sensitivity in the myocardium reduces the efficacy of an epinephrine test dose (higher rate of false negative results). Epidural anesthesia is associated with greater spread of LA because of a reduction in epidural space volume. Spinal anesthesia is associated with greater spread of LA because of a reduction in CSF volume.

Answer 36

Serum creatinine Serum creatinine remains stable as we age. On the one hand, muscle mass is reduced, so the body produces less creatinine. On the other hand, GFR is reduced so we excrete less creatinine. These changes cancel each other out, leaving the serum creatinine unchanged. Why are the other answers wrong? GFR decreases by 1 mL/min/year after age 40. Age is included in the creatinine clearance formula. This should tip you off that it changes as a function of age. Decreased aldosterone sensitivity impairs the ability to conserve sodium.

Answer 37

Alpha 1-acid glycoprotein Alpha 1-acid glycoprotein binds basic drugs. Its production is increased. Albumin binds acidic drugs. Its production is reduced, particularly in those with poor nutrition. Pseudocholinesterase production is reduced. This can prolong the duration of succinylcholine, especially in men. Hepatic blood flow is decreased. In consequence, less drug is delivered to the liver per unit time. This can prolong elimination of drugs with a high hepatic extraction ratio (fentanyl, lidocaine, metoprolol).

Answer 38

Increased volume of distribution of propofol Faster induction with sevoflurane Total body fat is increased. This accounts for the larger Vd for lipophilic drugs (propofol). Total body water and blood volume are decreased. This accounts for the smaller Vd for hydrophilic drugs (rocuronium). Decreased cardiac output prolongs circulation time. This causes a faster inhalation induction and a slower IV induction.

Answer 39

Heart rate Stroke volume Plasma volume During pregnancy, the cardiovascular system must adapt to support a growing mother and fetus. You will most likely be asked about these changes on boards. Don't freak out when you see that something increases by 40% in one book and that same variable increases by 50 percent in another book. Know the trends! Trust me, I know this is difficult for you type-A folks (I'm one of them). Rant over ... Several weeks after conception, SVR decreases with a compensatory rise in cardiac output and RAAS activity (sodium retention → increased plasma volume). Diastolic BP decreases due to a reduction in SVR. Systolic BP is unchanged. Key Cardiovascular Changes During Pregnancy: Cardiac output (↑ 40 - 50%) Stroke volume (↑ 30%) Heart rate (↑ 15%) ``` Peripheral circulation SBP (no change) DBP (↓ 15%) SVR (↓ 15%) Intravascular fluid volume (↑ 35%) Plasma volume (↑ 45%) Erythrocyte volume (↑ 20%) ```

Answer 40

Third stage of labor You must know how cardiac output changes throughout pregnancy AND during labor and delivery. ``` Cardiac output changes during pregnancy: First trimester = 35% over baseline Second trimester = 50% over baseline Third trimester = 50% over baseline Cardiac output changes during labor (uterine contraction → autotransfusion) ``` First stage of labor = 10 – 25% over prelabor value Second stage of labor = 40% over prelabor value Third stage of labor (after delivery) = 80 – 100% over prelabor value Patients with a history of valvular stenosis or pulmonary hypertension are at greatest risk of hemodynamic compromise when cardiac output is the highest (third stage of labor).

Answer 41

Increases in the mother and decreases in the fetus The oxyhemoglobin dissociation curve tells us the tendency of hgb to bind oxygen, and the P50 is the PaO2 where hgb is 50% saturated by oxygen (normal = 26.5 mmHg). A higher P50 reflects a right shift (right = release) A lower P50 reflects a left shift (left = love) To ensure fetal oxygenation, there has to be an oxygen concentration gradient from mother to fetus. This is accomplished by changes in the P50. Maternal P50 is higher = 30 mmHg (↑ 2,3-DPG) Fetal P50 is lower = 19 mmHg (does not respond to 2,3-DPG) The higher P50 in the mother and the lower P50 in the fetus ensures O2 offloading across the placenta.

Answer 42

7.42 / 30 / 101 / 20 Progesterone is a respiratory stimulant, increasing minute ventilation up to 50 percent (↑ Vt > ↑ RR). Primary event = PaCO2 decreases to ~ 30 mmHg (respiratory alkalosis) Renal compensation = HCO3- decreases to ~ 20 mEq/L (metabolic acidosis) pH is unchanged or very slightly increased A small reduction in physiologic shunt explains the mild increase in PaO2 (~ 100 mmHg). This increases the driving pressure of oxygen across the placenta and improves fetal oxygenation.

Answer 43

Decreased gastric emptying After 20 weeks gestation, the pregnant patient is a higher risk of gastroesophageal reflux, which augments the risk of pulmonary aspiration. In short, this is caused by increased gastric acid production and a decreased esophageal barrier pressure. Gastric acid production is increased by: ↑ Gastrin production by the placenta Lower esophageal sphincter tone is decreased by: ↑ Progesterone ↑ Estrogen Cephalad movement of uterus (alters gastroesophageal geometry) Gastric emptying does NOT change during pregnancy. During labor, however, gastric emptying slows as a function of pain, anxiety, SNS stimulation, and opioids (IV and neuraxial).

Answer 44

Decreased MAC Decreased PaCO2 Increased sensitivity to local anesthetics The old adage says that when you're in doubt, go with progesterone as the cause of the physiologic changes in pregnancy. While that may work if you're given a list of hormones, it falls flat on its face when you're asked a question specific to progesterone. Progesterone Increases: Minute ventilation (↓ PaCO2 & ↑ HCO3- excretion) RAAS activity (↑ blood volume → ↑ cardiac output) Vascular muscle relaxation (↓ SVR & ↓ PVR) Sensitivity to local anesthetics Progesterone Decreases: Airway resistance (↑ bronchodilation) MAC Lower esophageal sphincter tone

Answer 45

Desflurane Lidocaine Magnesium Diffusion is the primary mechanism by which a drug passes from the maternal circulation to the fetus. As a general rule, if a drug diffuses across the blood-brain-barrier, then it will also diffuse across the placenta. ``` Factors that determine the maternal-fetal gradient: Maternal plasma concentration Maternal plasma protein binding Drug ionization Drug lipid solubility Drug molecular weight Tell me more about molecular weight... A drug with a MW < 500 Daltons will easily diffuse across the placenta unless it is highly ionized. A drug that is > 1000 Daltons usually won't cross the placenta. Drugs with poor placental transfer tend to be highly ionized: Succinylcholine Nondepolarizing neuromuscular blockers Heparin Glycopyrrolate Insulin Drugs with significant placental transfer tend to be lipophilic: Benzodiazepines Opioids Volatile anesthetics IV anesthetics (usually not a problem) Local anesthetics (except chloroprocaine d/t rapid metabolism) Atropine Beta-blockers ``` Magnesium isn't lipophilic but it's small, so it can easily diffuse across the placenta. Fetal hypermagnesemia can contribute to skeletal muscle weakness after delivery. Remember that fetal pH is slightly more acidic than the mother’s, so weak bases in the fetal circulation will ionize to a greater degree. This is the basis of fetal ion trapping, and is most likely to occur when increasing maternal alkalosis and increasing fetal acidosis.

Answer 46

Maternal hypokalemia Beta-2 agonists (ritodrine and terbutaline) are tocolytic agents that stop or slow preterm labor. These drugs reduce uterine tone by increasing intracellular cAMP and progesterone release. While you'll likely never encounter these drugs in practice (ritodrine and terbutaline), we included them for historical context along with the fact that learning about them helps solidify the connection between pharmacology and physiology. Maternal side effects: Hyperglycemia results from glycogenolysis in the liver. Hypokalemia results from an intracellular potassium shift. Tachycardia Fetal side effects: The newborn of a hyperglycemic mother is a risk of post-delivery hypoglycemia. The mother’s glucose supply is gone, but the insulin in the neonatal circulation remains. Beta-2 agonists cross the placenta and may increase FHR (Beta-1 crossover effect).

Answer 47

Chloroprocaine To answer this question, we have to know how much of the local anesthetic is available to reach the fetus. Chloroprocaine is an ester-type local anesthetic. Because it is metabolized by pseudocholinesterase in the plasma, very little of chloroprocaine (if any) reaches the fetus. Therefore, fetal ion-trapping is not a significant concern when chloroprocaine is used. Lidocaine, bupivacaine, and mepivacaine are amide-type local anesthetics. They have much longer half-lives, so more of the drug is delivered to the placenta over time.

Answer 48

Afferent pain travels through the hypogastric plexus Pain is transmitted to the T10 – L1 segments of the spinal cord You must be able to differentiate between pain related to the 1st and 2nd stages of labor. Pain specific to the first stage of labor: Afferent pathway = somatic C-fibers → hypogastric plexus Spinal segments = T10-L1 (posterior nerve roots) Quality of pain = diffuse, cramping & dull Specific neuraxial techniques = paracervical block, paravertebral lumbar sympathetic block Pain specific to the second stage of labor: Afferent pathway = pudendal n. Spinal segments = S2-S4 (posterior nerve roots) Quality of pain = well localized & sharp Specific neuraxial technique = pudendal n. block A spinal, epidural, or CSE will provide analgesia for uterine, cervical, and/or perineal pain. A technique that provides analgesia to T10-L1 during the first stage of labor must be extended to cover T10-S4 during the second stage of labor.

Answer 49

Paracervical block Fetal bradycardia is a common complication of a paracervical block, especially if bupivacaine is used.

Answer 50

Bolus 3 percent chloroprocaine in the epidural Pudendal nerve block The dose of a laboring epidural by itself does not provide sufficient analgesia during a forceps delivery. Analgesic options include: Bolusing the epidural with a higher concentration of a rapidly acting local anesthetic, such as 1-2 percent lidocaine or 2-3 percent chloroprocaine. If you were unable to bolus the epidural or if there is no epidural in place, then you could perform a "second-stage" spinal or pudendal nerve block.

Answer 51

50% nitrous oxide + 50% oxygen administered by the patient Inhaled nitrous oxide is making a resurgence as a non-invasive alternative for labor analgesia. A common (and safe) approach is 50% nitrous oxide + 50% oxygen self-administered by the patient via facemask. When administered alone (not with opioids), a 50/50 N2O/O2 mixture is not associated with hypoxia, loss of airway reflexes, or unconsciousness. Additionally, it preserves uterine contractility, and it does not cause neonatal depression Halogenated agents are not used for labor analgesia.

Answer 52

May eat solid food before the epidural is placed Having a baby is serious work! The laboring mother requires adequate nutrition and hydration to support her and the baby during labor. It doesn't matter when mom last ate or drank - she is always considered a full stomach! According to the ASA Practice Guidelines for Obstetric Analgesia, the laboring mother who is healthy may: Drink a moderate amount of clear liquids throughout labor. Eat solid food up to the point a neuraxial block is placed. If there is a high probability of a surgical intervention requiring a general anesthetic, the patient should remain NPO.

Answer 53

Approve the request with the consent of the obstetrician The American College of Obstetricians and Gynecologists (ACOG) Guidelines for Assessment of the Obstetric Patient provide direction for the safe management of obstetric patients. They recommend that the timing of epidural placement should be individualized to each patient, and a patient should not have to wait until she achieves 4 – 5 cm cervical dilation before she can receive analgesia. Therefore, after it is approved by the obstetrician, it is ok to proceed with the epidural placement. Clear liquids may be administered before and after epidural placement. A routine platelet count is unnecessary in healthy patients without a history of abnormal bleeding

Answer 54

Uses a smaller initial dose of local anesthetic The combined spinal-epidural anesthesia (CSE) technique provides the dual benefit of a rapid onset of spinal anesthesia and the ability to prolong the duration of anesthesia with an indwelling epidural catheter. This technique is particularly useful in labor and delivery. The epidural volume extension (EVE) technique involves injection of saline into the epidural space immediately after the local anesthetic is administered into the subarachnoid space. Adding volume to the epidural space compresses the subarachnoid space, and this enhances the rostral spread of the local anesthetic. Said another way, this technique pushes the LA towards the brain to achieve a higher level for a given dose. Administering a smaller dose of local anesthetic in the subarachnoid space provides a more stable hemodynamic profile as well as a faster recovery. The epidural may be dosed if additional anesthesia is required.

Answer 55

Rapid onset of anesthetic action Although it's a rare event, it's possible to accidentally place the epidural catheter in the subdural space (in-between the dura and the arachnoid). Can a test dose rule out subdural catheter placement? No! The test dose will be negative for both intrathecal and intravascular placement. How does a subdural injection present? After a 10 - 25 minute delay (no apparent clinical effect), the patient will develop a high block very rapidly. Because the subdural space is a potential space, its volume is small, so even a small dose of local anesthetic has the potential to create a high block. Respiratory compromise as well as a total spinal are possible. Treatment is supportive (airway control and hemodynamic support) until the block recedes. A subdural injection is also a possible cause of a failed spinal. Since the dose for a subarachnoid block is comparatively much smaller than an epidural, the clinical effect will be negligible.

Answer 56

Placenta previa Placenta previa, abruptio placenta, uterine rupture, and uterine atony increase the risk of obstetric bleeding. Remember that the placenta receives 500 - 700 mL/min or 10% of the cardiac output, so uterine bleeding can become a true emergency. Placenta previa occurs when the placenta covers all or part of the cervical os. The hallmark presentation is painless vaginal bleeding ~ 32 weeks gestation. Risk factors include: previous c-section, advanced maternal age, and multiple parity. Abruptio placentae occurs when the placenta prematurely separates from the endometrium. This always presents with abdominal pain. This may present with or without vaginal bleeding (bleeding may occur behind the placenta). Risk factors: cocaine, methamphetamines, alcohol, hypertension, and multiparity. There is a high risk of DIC. Uterine rupture can range from incomplete to total rupture. This always presents with severe abdominal pain. Referred shoulder pain is the result of diaphragmatic irritation secondary to intraabdominal blood. Uterine rupture can be masked by an existing epidural. Any patient with an existing epidural who develops new onset abdominal pain should be evaluated for uterine rupture. Uterine atony only presents a bleeding problem after delivery.

Answer 57

Uterine atony Hemorrhage is the most common serious obstetric complication, and uterine atony is the most common cause of postpartum hemorrhage. Other causes include: ``` Anatomic abnormalities Uterine inversion Lacerations Disordered coagulation Retained placenta Oxytocin, methergine, prostaglandin, and/or an intrauterine balloon (to tamponade bleeding) are treatments for uterine atony. ``` If the uterine atony is caused by retained placenta, then nitroglycerine is the treatment of choice. It relaxes the uterus and facilitates its manual removal. Because nitroglycerine also relaxes the vasculature (mostly venous), you must take the patient's volume status into account.

Answer 58

Calcium gluconate Furosemide This patient is suffering from hypermagnesemia. The most common etiology of this complication is overdose during magnesium therapy. The first sign of magnesium toxicity is loss of deep tendon reflexes (4 - 6.5 mEq/L or 10 - 12 mg/dL...watch your units!) Hypermagnesemia is treated with calcium gluconate 10 - 15 mg/kg IV and diuresis and/or dialysis. Cardiopulmonary support may be required as well.

Answer 59

Nasal airway The parturient is at higher risk of difficult mask ventilation, difficult laryngoscopy, and difficult intubation. Increased progesterone, estrogen, and relaxin cause vascular engorgement and hyperemia. Combined with an increased extracellular fluid volume, this leads to upper airway swelling, affecting the nasal passages, oropharynx, epiglottis, larynx, and trachea. Epistaxis and airway narrowing can also occur. Your anesthetic plan must take these changes into account: Mallampati score increases during pregnancy. Difficult and failed intubation is 8 times higher in full term patients. The glottic opening is narrowed; a downsized (6.0 – 7.0) endotracheal tube should be used. A short handled laryngoscope (Datta handle) is useful for women with large breasts. Airway manipulation may cause tissue trauma and bleeding. The tissue in the nasopharynx is particularly friable, so insertion of an artificial airway into the nasopharynx should be avoided. Airway edema is made worse by pre-eclampsia, tocolytics, and prolonged Trendelenburg position.

Answer 60

Confirmation of end-tidal carbon dioxide The goals of anesthetic induction for an emergency C-section include securing the airway and delivering the baby as soon as possible. Before induction: The patient is prepped. The entire surgical team is ready. During induction: Rapid sequence induction with cricoid pressure (do NOT mask ventilate). If hemodynamically stable, then propofol 2.0-2.5 mg/kg IV. If NOT hemodynamically stable, then ketamine 1 mg/kg IV or etomidate 0.3 mg/kg IV. After confirmation of successful endotracheal intubation (+EtCO2): Surgery should begin promptly to minimize neonatal depression.

Answer 61

Second trimester In an ideal world, elective surgery is delayed until 2 - 6 weeks postpartum. From time to time, however, non-obstetric surgery must be performed in the pregnant patient. If possible, it should be performed during the second trimester. First trimester: Increased risk to fetal organ development (organogenesis) Second trimester: This is the best time Third trimester: Increased risk of premature delivery GI prophylaxis should be administered to all pregnant patients and left uterine displacement should be used for those in the second and third trimesters. A note on teratogenicity ... There is concern that benzodiazepines administered during the first trimester contribute to cleft palate. While there is some truth to this in mothers receiving high-dose diazepam, Hines says that there is no data to justify this concern when midazolam is used for preoperative sedation.

Answer 62

Anemia Cocaine is an ester-type local anesthetic that inhibits NE reuptake in the presynaptic SNS neuron. Flooding the synaptic cleft with NE increases SNS tone. Chronic cocaine abuse is associated with thrombocytopenia (check platelet count before neuraxial anesthesia). Other risks include tachycardia, dysrhythmias, and myocardial ischemia. Hypotension may not respond to ephedrine in chronic cocaine abusers (d/t catecholamine depletion). Phenylephrine is the best option.

Answer 63

Fetal head compression Fetal heart rate monitoring provides an indirect method to assess for fetal hypoxia. Fetal oxygenation is a function of uterine and placental blood flow. The fetus responds to stress with peripheral vasoconstriction, hypertension, and a baroreceptor mediated reduction in heart rate. There are three patterns of fetal decelerations: early, late, and variable. Early: Uterine contraction compresses the fetal head. Head compression increases vagal tone to reduce HR. Occurs with each uterine contraction. Onset and offset parallels uterine contraction. Late: Related to decreased uteroplacental perfusion. FHR decreases after peak uterine contraction then returns to baseline after completion of the contraction. Caused by maternal hypotension, hypovolemia, acidosis, preeclampsia. Requires urgent assessment of fetal status. Variable: FHR shows no consistent pattern with uterine contraction. Umbilical cord compression causes a baroreceptor mediated ↓HR. Decelerations are typically self-limiting. Fetal compromise will prolong the FHR recovery time. Persistent decelerations require urgent assessment of fetal status.

Answer 64

Atrial septal defect Tetralogy of Fallot is the most common cyanotic congenital heart defect. There are four abnormalities associated with this disease: Right ventricular outflow tract obstruction - due to a narrowed or stenotic pulmonic valve Right ventricular hypertrophy - due to pressure overload from the RV obstruction Ventricular septal defect - due to septal malalignment An overriding aorta that receives blood from both ventricles Because there is a resistance at the PA outflow tract, blood is shunted across the VSD. This creates a R → L shunt (cyanotic). Since blood bypasses the lungs, arterial hypoxemia ensues. The shunt is made worse by conditions that: Increase PVR (hypercarbia, acidosis, hypoxemia, PEEP) Decrease SVR (volatile agents, histamine release) Increase myocardial contractility A R → L shunt speeds the onset of action of IV drugs. A R → L shunt slows the onset of volatile agents (more so with less soluble agents). Ketamine is great for these patients, because it preserves SVR. While it can increase contractility and PVR, these effects are not clinically significant in this context.

Answer 65

Pulmonary stenosis with atrial septal defect Tetralogy of Fallot An outflow tract obstruction occurs when there is a resistance to ejection of ventricular blood. Shunt lesions with outflow tract obstruction include: Tetralogy of Fallot Ebstein's anomaly Pulmonary stenosis with atrial or ventricular septal defect Eisenmenger's syndrome Shunt lesions without outflow tract obstruction include: ``` Atrial septal defect Ventricular septal defect AV canal defect Patent ductus arteriosus Aortopulmonary window ```

Answer 66

Ventricular septal defect VSD is the most common congenital defect in the neonate. This can be diagnosed by echocardiography with Doppler or cardiac catheterization with angiography. The direction of blood flow across the ventricular septum is a function of SVR and PVR. If SVR is higher, then there will be a L → R shunt (non-cyanotic). If PVR is higher, then there will be a R → L shunt (cyanotic). Remember that a L → R shunt increases RV volume and workload. Over time, the increased pulmonary blood flow increases PVR, and if left untreated, PVR can become higher than the SVR leading to a R → L (cyanotic) shunt. If you are presented with a question about the most common congenital defect with a certain disease (and you are unsure of the correct answer) VSD is a smart choice. Examples might include Treacher Collins syndrome or Tetralogy of Fallot.

Answer 67

Resuscitation with 0.9 percent NaCl Fetal lungs don't mature until 35 weeks gestation, so neonates born before this time are at risk of inadequate surfactant production and the development of respiratory distress syndrome. Type II pneumocytes produce surfactant. It increases lung compliance by reducing alveolar surface tension (law of Laplace). Without surfactant, alveolar collapse reduces FRC and RV. This leads to V/Q mismatch, hypoxemia, and metabolic acidosis. Therapy for RDS begins with nasal CPAP. Although this modality often eliminates the need for more invasive maneuvers, continued respiratory distress warrants tracheal intubation and exogenous surfactant. Since oxygen delivery is the name of the game, Hct should be maintained above 40 percent. Crystalloid resuscitation causes a dilutional anemia, which reduces DO2. Albumin 5 percent is a better choice (10-20 mL/kg at a time), because a smaller volume can achieve a similar expansion of the intravascular space. Complications that often accompany RDS include: pneumothorax, acidosis, and sudden CV decompensation. A preductal a-line is preferred.

Answer 68

Dexamethasone 0.5 mg/kg IV Postintubation laryngeal edema (postintubation croup) typically presents within 30 - 60 minutes following extubation. The child experiences hoarseness, a barky cough, and stridor. ``` Treatment includes Cool and humidified oxygen 0.5 mL of 2.25% solution diluted in 2.5 mL of 0.9% NaCl Heliox (helium + oxygen mixture) Dexamethasone 0.25 - 0.5 mg/kg IV ``` Dexamethasone does not provide acute treatment, because it requires 4 - 6 hours to achieve peak effect.

Answer 69

Laryngeal mask airway Risk factors for the development of postintubation laryngeal edema include: Age < 4 years Endotracheal tube cuff leak absent above 25 cm H2O pressure (a monometer is useful to intermittently measure cuff pressure) Traumatic or multiple intubation attempts Prolonged intubation Head or neck surgery Head repositioning during surgery History of infectious or postintubation croup Upper respiratory tract infection Trisomy 21 Remember that nitrous oxide can easily diffuse into the ETT cuff. This can increase the cuff pressure during intubation, impairing perfusion of the tracheal mucosa.

Answer 70

There is an increased risk of difficult intubation Risk of aspiration is increased Commonly associated with other genetic disorders. Airway specific risk include: Airway obstruction Difficult laryngoscopy Difficult mask ventilation if there are additional craniofacial abnormalities Aspiration The Dingman-Dott mouth retractor can reduce venous drainage and cause tongue engorgement. This increases the risk of post-extubation airway obstruction.

Answer 71

60 weeks (we also accepted 52 weeks) Neonates are at risk of apnea following surgery and anesthesia. Patients less than 60 weeks post conceptual age should be admitted for 24 hour observation with an apnea monitor. Hines states 52-60 weeks is the cutoff, but Miller and Barash say 60 weeks. While we accepted both answers, if you see a question similar to this on the NCE, 60 weeks is your best bet.

Answer 72

464 mL Classic resuscitation guidelines recommend replacing the NPO deficit, evaporative loss, blood loss, as well as providing a maintenance rate. Since there was no blood loss noted in the stem, assume there wasn't any. Don't read into the question! Maintenance = (10 kg x 4 mL/kg) + (8 kg x 2 mL/kg) = 56 mL x 3 hrs = 168 mL NPO = 56 mL x 4 hr = 224 mL Evaporative loss = 2 mL/kg x 2 hrs = 72 mL (don't include the 1st hour) Total fluid administration = 464 mL

Answer 73

52 mL/hr Unless you're told otherwise, you should use the Holliday-Segar formula (4:2:1 rule) on the NCE. The hourly maintenance rate is calculated as the sum of: The 1st 10 kg = 4 mL/kg/hr The next 10 kg = 2 mL/kg/hr Each additional kg over 20 kg = 1 mL/kg/hr This patient weighs 16 kg, so... (10 kg x 4 mL/hr) + (6 kg x 2 mL/hr) = 52 mL/hr

Answer 74

Tachycardia Intracerebral hemorrhage The fetus can experience pain as early as seven weeks gestation. Even though the neonate has an immature sympathetic nervous system (an increased PNS tone), pain activates the SNS manifesting as tachycardia and hypertension. In fact, the combination of hypertension, an immature cerebral autoregulatory response, and a fragile cerebral vasculature predispose the neonate to intracerebral hemorrhage. Other causes of intracerebral hemorrhage include: hypoxia, hypercarbia, hyperglycemia, hypoglycemia, hypernatremia, and wide swings in blood pressure.

Answer 75

Prematurity Retinal maturation begins at 16 weeks gestation and is complete between term and 44 weeks gestation. Vasculogenesis begins at the macula then continues outwards towards the edges of the developing retina. In the preterm neonate, retinal maturation continues for a longer period during extrauterine life. The immature retinal blood vessels are at risk vasoconstriction and hemorrhage. Dysfunctional healing leads to scar formation and ultimately retinal detachment. The risk of ROP varies inversely with gestational age and birth weight. If you have to pick the most significant risk factor for ROP, then we suggest prematurity. If the question asks about modifiable factors, then hyperoxia would be the correct choice (since you can't control when the baby is delivered, but you can control how much O2 you administer).

Answer 76

Inhibition of glucuronyl transferase Hyperbilirubinemia Bilirubin is a byproduct of RBC breakdown. Any condition that increases serum bilirubin can cause kernicterus (fetal encephalopathy). ``` Glucuronyl transferase (phase II rxn) metabolizes bilirubin. This pathway is not mature at term. leaving the newborn vulnerable during the first few days of life. Risk factors: prematurity, low plasma protein concentration, and acidosis. Treatment of hyperbilirubinemia includes phototherapy and exchange transfusion (rarely needed). ```

Answer 77

Hypoglycemia Newborns have a limited supply of glycogen, and this small supply can quickly exhaust during acute stress. Risk factors for hypoglycemia include < 48 hours of age, small for gestational age, and being born to a diabetic mother. The risk of hypoglycemia becomes less of an issue after the 1st week of life. Hypoglycemia in children older than one week should raise suspicion of an underlying disorder, such as hyperinsulinism. Signs of hypoglycemia typically manifest when serum glucose falls below 30 – 40 mg/dL in newborns < 72 hours old and 40 mg/dL in those older than 72 hours. A good number to keep in your head is 40 mg/dL. General anesthesia masks these signs. Treatment consists of IV 10% dextrose (2 mL/kg). If seizures are present, then dose is doubled (4 mL/kg) in order to provide adequate substrate to the brain. After the bolus, a D10 infusion at 8 mg/kg/min is titrated to maintain serum glucose > 40 mg/dL. Glycosuria leads to osmotic diuresis, dehydration and increased serum osmolarity that can ultimately lead to intracerebral hemorrhage.

Answer 78

Sodium excreters At birth, GFR and tubular function are far from mature, and the ability to handle free water and excess solute is diminished. A consequence of this is that newborns have a high fluid turnover. Since they are unable to reduce their urine output below 1 mL/kg/hour during the first week of life, fluid requirements can be as high as 150 mL/kg/day. Neonates are obligate sodium excreters. The renin-angiotensin-aldosterone system attempts to conserve sodium, however the immature distal tubules fail to fully respond to aldosterone. The response to antidiuretic hormone is diminished as well. Nagelhout says GFR matures by 6 – 12 months, however there are other sources that say it can be as late as 2 years. Tubular function matures by 2 years.

Answer 79

Biliary atresia Biliary atresia is the result of a defect in the extrahepatic bile duct system that impairs bile flow. ``` It presents within weeks of birth. Signs include: Persistent jaundice (> 14 days) Dark urine Acholic stool (pale or clay colored) Hepatomegaly Splenomegaly (late sign) ``` Surgical correction includes: Kasai's operation (portoenterostomy) Liver transplantation Indeed, biliary atresia is the most common indication for liver transplantation in children less than two years of age.

Answer 80

Requires earlier surgery compared to omphalocele Gastroschisis and omphalmocele are congenital defects of the abdominal wall which permit externalization of the abdominal viscera. Most cases are diagnosed by prenatal ultrasound. Compared to omphalocele, gastroschisis: Is associated with a periumbilical cord (usually the right). Is usually a smaller defect in the abdominal wall. Does not have a hernia sac covering the abdominal viscera. Requires earlier surgery (usually within 24 hours of birth) Is less common. Is more commonly associated with premature birth.

Answer 81

Radiation + Cover head with plastic Conduction + Place a foam pad on the OR table Evaporation + Humidify anesthetic gases Neonates are particularly susceptible to heat loss as a result of a large surface area to body mass ratio, limited fat stores, thin skin, and inability to shiver. Up to 60 percent of the heat is lost via the head. Nonshivering thermogenesis (metabolism of brown fat) is a mechanism by which the neonate maintains its body temperature. This process is mediated by the SNS (beta-3). Brown fat is stored in the scapulae, axillae, mediastinum, and retroperitoneal space. Preterm babies have a smaller reserve of brown fat. Anesthetic agents impair NST.

Answer 82

Three months Minimum alveolar concentration (MAC) varies with age. Infant 1 - 6 months: MAC is higher than the adult Infant 2 - 3 months: MAC peaks at its highest level Neonate (0 - 30 days): MAC is lower than the infant Premature: MAC is lower than neonate The MAC requirement pattern for sevoflurane is different. 0 days to 6 months: MAC = 3.2 percent 6 months to 12 years: MAC = 2.5 percent

Answer 83

A maximum inspiratory force better than – 25 cm H2O Flexion of the knees to the chest The neonate isn't going to follow commands prior to extubation, so we must rely on other measures that do not require cooperation. Although it doesn't provide an objective measure, many practitioners rely on visual inspection. Grimacing, elbow and hip flexion, and bringing the knees to the chest seem to correlate with adequate recovery. Although a head lift > 5 seconds is appropriate for an adult, a neonate does not have the muscle strength to raise his head. A TOF ratio > 90 percent suggests a full recovery. A maximum inspiratory force (MIF) less than -25 cm H2O predicts adequate recovery from neuromuscular blockade. Since this is a negative number, a MIF of -30 is better than a MIF of -25

Answer 84

Calcium gluconate The initial treatment for hyperkalemia is to antagonize the membrane effect of potassium. Hyperkalemia brings resting membrane potential closer to threshold potential. The myocyte is more easily depolarized, and this increases the risk of lethal arrhythmias. Calcium chloride or calcium gluconate raises the threshold potential, and this restores the distance between resting membrane potential and threshold potential. Other treatments for severe hyperkalemia include: Transcellular shift: Sodium bicarbonate 1 - 2 mmol/kg per dose Glucose 0.3 - 0.5 g/kg as 10% glucose solution + insulin 1 unit per 4 - 5 g glucose IV Albuterol Hyperventilation ``` Potassium excretion: Kayexalate 1 g/kg per dose (PO or enema) Furosemide 1mg/kg per dose IV Dialysis Hemofiltration ```

Answer 85

45 years Closing volume is the point at which dynamic compression of the airways begin. Said another way, it is the volume above residual volume where the small airways begin to close during expiration. Things that increase closing volume include: CLOSE-P ``` COPD LV failure Obesity Supine position Extreme age Pregnancy Closing capacity = Closing volume + Residual volume In the supine patient, CC exceeds FRC at ~ 45 years of age, and in the standing position this occurs at ~ 66 years of age. ```

Answer 86

Age This one shocked us a little bit too! Age is the most significant risk factor for cancer. The incidence of cancer is below 2% in the teen years and increases to 25% after age 65.

Answer 87

The most significant risk factor is increasing age It is common following cardiac surgery Postoperative cognitive dysfunction (POCD) presents insidiously over a period of weeks to months (delirium usually occurs early in the postop period). Patients complain of impaired concentration, psychomotor skills, and comprehension, and this can lead to chronic alteration in activities of daily living. Diagnosis consists of postoperative neuropsychological testing. The cause is unknown, but it may be related to cerebral hypoperfusion, inflammation, and general anesthesia. Advanced age is probably the most significant risk factor for developing POCD. Other risk factors include: cardiac surgery, low level of education, high ASA status, pre-existing cognitive deficit, major surgery, long duration of surgery, and postoperative infection. Nagelhout says that inhalation anesthetics are preferred over IV agents. Hines disagrees, and says that due to the dearth of evidence, there is no reason to avoid specific agents. There is no treatment for POCD, but luckily most cases are mild and tend to resolve after ~ 3 months.

Answer 88

Can be precipitated by urinary retention Is treated by fixing the underlying medical cause and is the most common postoperative CNS complication in the elderly In the elderly, delirium is the most common CNS complication postoperatively and can be seen as frequently as 60 percent in some procedures (femoral fractures). Delirium presents early in the postoperative period and can last from days to weeks. Causes of DELIRIUM include: ``` Drug use (what new drugs have been introduced) Electrolyte imbalance Lack of drugs (Withdrawal) Infection (UTI and respiratory) Reduced sensory input Intracranial dysfunction Urinary retention and fecal impaction Myocardial event, male gender ```

Answer 89

Pulse pressure Plasma norepinephrine concentration Vascular elasticity is reduced in the elderly. This makes the vessels "stiffer" so we can say that their compliance is decreased. Arterial stiffness increases SBP to a greater degree than it does DBP, so pulse pressure becomes wider. The plasma NE concentration is increased, however this causes adrenergic receptor downregulation - there is a resistance to adrenergic stimulation. Lusitropy is the process of myocardial relaxation. Impaired ventricular Ca+2 homeostasis and a hypertrophied myocardium result in a slower rate of ventricular relaxation. These factors contribute to the diastolic dysfunction that is common in the elderly. Heart rate decreases as a function of age (max HR = 220 - age). This population is less able to increase HR in response to hypoxia, hypotension, and hypovolemia.

Answer 90

Diphenhydramine Parkinson's disease is associated with a loss of dopaminergic neurons in the substantia nigra in the basal ganglia. DA inhibits the firing rate of extrapyramidal neurons. Loss of dopaminergic fibers creates a relative increase in acetylcholine activity in the extrapyramidal neurons. The patient exhibits signs of motor excitation, such as resting tremor and rigidity. Bradykinesia is one of the cardinal signs of Parkinson's disease. Knowing the pathophysiology makes the treatment obvious. There are 2 pharmacologic broad options: 1.) reduce Ach with an anticholinergic such as benztropine or diphenhydramine and/or 2.) increase DA with levodopa or selegiline. If a patient experiences an exacerbation of Parkinsonian signs during the perioperative period, the most appropriate choice is a drug with anticholinergic properties. Drugs that exacerbate Parkinsonian signs include: droperidol, metoclopramide, and chlorpromazine. Increasing age is the most common cause of Parkinson's disease, however additional contributing factors include: manganese exposure in welders and genetic predisposition.

Answer 91

Minute ventilation Lung compliance Closing capacity Respiratory parameters that increase with age include: Lung compliance Closing capacity Minute volume Residual volume FRC Respiratory parameters that decrease with age include: ``` Vital capacity, forced VC Expiratory reserve volume Inspiratory reserve capacity Elasticity of the lung Chest wall compliance Lung mass ```

Answer 92

Gardening Walking up a flight of steps without stopping One metabolic equivalent is equal to the oxygen consumption by an awake patient while sitting. By convention, one MET is equal to an oxygen consumption of 3.5 mL/kg/min. Two METs equals 7 mL/kg/min, three METs equals 10.5 mL/kg/min and so on. We can estimate the functional status of the cardiopulmonary system by determining how many metabolic equivalents a patient can perform. Mortality drops by 11 percent for each additional MET a patient can do. Assuming that cardiac status is optimized, patients who can achieve at least 4 METs can be cleared for surgery.