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How much daily cortisol is normally secreted from the adrenal glands? How much during stress?
15-20 mg/day; Up to 200-500 mg/day during stress
Perioperative supplemental steroid coverage regimens are either low dose (physiologic) or high dose (supraphysiologic). Describe each regimen.
Low-dose: Cortisol 25 mg IV before induction of anesthesia followed by continuous infusion, 100 mg IV over 24 hours. Supraphysiologic: Cortisol 200-300 mg IV in diveded doses on the day of surgery.
How does minute ventilation change during pregnancy?
Minute ventilation increases by up to 45% during pregnancy.
What respiratory parameter changes most to increase minute ventilation during pregnancy? What physiological factors prompt the increase in minute ventilation during pregnancy?
An increase in tidal volume, with minimal, if any, change in respiratory rate and pattern. This results from increased progesterone and increased CO2 production. Progesterone acts as a direct respiratory stimulant and the progesterone-induced increase in chemoreceptor sensitivity results in a steeper and leftward shifted CO2 ventilatory response curve.
What is the maximum dose of topical cocaine?
200 mg for a 70 kg patient (3 mg/kg)
Treacher-Collins syndrome is associated with cleft palate, as you know, indicating a difficult airway. What congenital heart disease is associated with Treacher-Collins syndrome?
Ventricular septal defect (the most commonly occurring congenital heart disease)
In addition to cleft palate and ventriculoseptal defect, what other conditions are associated with Treacher-Collins syndrome? Is a macroglossia (large tongue) associated with Treacher-Collins syndrome?
Cleft palate (30%), ventriculoseptal defect, malar hypoplasia, colobomas (notching of the lower eyelids), macrostomia (large mouth), malocclusion, and a small oral cavity. Treacher-Collins syndrome is not associated with macroglossia (large tongue) or mental retardation.
What is the earliest sign of magnesium toxicity?
Marked depression of deep tendon reflexes is an indication of impending magnesium toxicity.
State the loading and maintenance doses of magnesium sulfate administered for seizure prophylaxis in pregnancy-induced hypertension.
Loading: 4-6 g over 20-30 minutes Maintenance: 1-2 g/hr, continued for up to 24 hours postpartum.
What specific changes are often seen in the ECG when magnesium levels reach 10 mEq/L?
Prolonged P-R intervals and widened QRS complexes may be observed. Asystole occurs at 20 mEq/L.
List 3 treatments for postintubation laryngeal edema (postintubation "croup").
Mild: Cool, humidified mist and oxygen therapy, ideally administered by a face tent.
More severe: Hourly administration of aerosolized racemic epinephrine, 0.05 mL/kg of 2.25% epinephrine in 3.0 mL of saline. Intravenous dexamethasone (0.25-0.5 mg/kg) may prevent the edema, but the effect takes up to 4-6 hours to manifest.
Identify 10 factors associated with postintubation laryngeal edema ("croup").
1. Age younger than 4 years
2. Tight-fitting endotracheal tube, no audible leak at 15-25 cm H2O
3. Traumatic or repeated intubation
4. Prolonged intubation
5. High-pressure, low volume cuff
6. Patient "bucking" or coughing during intubation
7. Head repositioning while intubated
8. History of infectious or postintubation croup
9. Upper respiratory infection
10. Neck/airway surgery
11. Trisomy 21
What percentage of cardiac output is delivered to the highly perfused organs (heart, lungs, brain, kidneys, and liver)?
Approximately 75% of resting cardiac output is delivered to the vessel-rich organs, although they constitute only 10% of total body mass.
What is retinopathy of prematurity?
Formerly known as retrolental fibroplasia, it's a fibrovascular proliferation overlying the retina that leads to progressive visual loss. ROP occurs almost exclusively in preterm infants. The risk of ROP is inversely proportional to birth weight, and is associated with neonatal oxygen exposure, apnea, blood transfusion, sepsis, and fluctuating levels of carbon dioxide.
At what gestational age does the risk of retinopathy of prematurity become negligible? Why?
After 44 weeks postconception because retinal vasculogenesis is complete between 42-44 weeks postconception.
What is the proportioning system on the anesthesia workstation?
A hypoxia prevention safety device. Manufacturers equip the anesthesia workstations with proportioning systems in an attempt to prevent creation and delivery of a hypoxic mixture. Nitrous oxide and oxygen are mechanically and/or pneumatically linked so that the minimum oxygen concentration at the common gas outlet is between 23 to 25% depending on manufacturer.
How does the Link-25 proportioning system work?
The Link-25 system is found on conventional Datex-Ohmeda machines. The heart of the system is the mechanical integration of the nitrous oxide and oxygen flow control valves. It allows independent adjustment of either valve, yet automatically intercedes to maintain a minimum 25% oxygen concentration with a maximum nitrous oxide-oxygen flow ratio of 3:1. The Link-25 automatically increases oxygen flow to prevent delivery of a hypoxic mixture. A 14-tooth sprocket is attached to the nitrous oxide flow control valve and a 28-tooth sprocket is attached to the oxygen flow control valve. A chain physically links the sprockets. When the nitrous oxide flow control valve is turned through two revolutions, or 28 teeth, the oxygen flow control valve will revolve once because of the 2:1 gear ratio. The final 3:1 flow ratio results because the nitrous oxide flow control valve is supplied by approximately 26 psig, whereas the oxygen flow control valve is supplied by 14 psig. Thus, the combination of the mechanical and pneumatic aspects of the system yields the final oxygen concentration. The Link-25 proportioning system can be thought of as a system that increases oxygen flow when necessary to prevent delivery of a fresh gas mixture with oxygen concentration of less than 25%.
List 5 conditions that can "fool" the proportion limiting systems.
1. Wrong supply gas
2. Defective pneumatics or mechanics
3. Leaks downstream
4. Inert gas administration
5. Dilution of inspired oxygen concentration by volatile inhaled anesthetics
What type of gas can lead to delivery of a hypoxic mixture on a workstation equipped with a proportioning system? What is mandatory when such a gas is present?
An inert, third gas, such as He, N2 or CO2, can cause delivery of a hypoxic mixture because contemporary proportioning systems link only nitrous oxide and oxygen. Use of oxygen analyzer is mandatory (or preferentially a multigas analyzer, when available) if the operator uses a third gas.
Describe myocardial preconditioning.
A short-term rapid adaptation to brief ischemia such that during a subsequent, more severe ischemic insult, myocardial necrosis is delayed. The infarct-delaying properties of ischemic preconditioning have been observed in all species studied. Five minutes of ischemia is sufficient to initiate preconditioning, and the protective period lasts for 1-2 hours.
Describe the cellular mechanisms mediating myocardial preconditioning.
Pharmacological activation of the adenosine receptors (particularly a1and a2 subtypes) initiates preconditioning via intracellular signal transduction mechanisms involving protein kinase C and adenosine triphosphate-dependent potassium channels. Other factors involved include the sodium:hydrogen exchanger, inhibitory G proteins, and tyrosine kinase.
What agents can trigger or modulate the myocardium preconditioning response? Which agent antagonizes this?
Volatile anesthetics, adenosine, or opioid agonists mimic preconditioning. Ketamine antagonizes the protective effect of preconditioning and thus should be used with caution in patients at risk for myocardial infarction in the perioperative period.
What blood product "should" be ABO compatible, but is not strictly mandatory?
Platelets (which bear both ABO and HLA). Incompatibility shorten lifespan.
Consider the patient in the lateral decubitus position with no axillar roll and a pulse oximeter on the dependent hand. What is the most likely cause for apparently low SaO2 from the pulse oximeter?
The axillary neurovascular bundle is compressed, comprising blood flow to the extremity.
What is the most effective measure for pain associated with pancreatic cancer?
Celiac plexus block with alcohol or phenol
What two amide local anesthetics and one ester local anesthetic are most often used for infiltration anesthesia?
Amides: Lidocaine (0.5% to 1.0%), Bupivacaine (0.125% and 0.25%) Ester: Procaine (0.5% to 1.0%)
What oxygen sources and delivery pressures are acceptable for transtracheal jet ventilation? What sources and pressures are not adequate for transtracheal jet ventilation?
High-pressure: 15-30 psi of oxygen (central hospital supply or regulated cylinder) can be delivered directly to the catheter, with insufflations of 1 to 1.5 seconds at a rate of 12 insufflations per minute. If a 16 gauge catheter has been placed, the system will deliver a tidal volume of 400 to 700 mL. At a delivered pressure of 50 psi, a 16 gauge delivers 500 mL of oxygen per second. In most instances, 25 psi is a sufficient inspiratory pressure. Low pressure systems cannot provide enough flow to expand the chest adequately for oxygenation and ventilation (Ambu bag, 6 psi; common gas outlet, 20 psi).
List 3 most frequently encountered complications of mediastinoscopy, in order of greatest to least incidence.
Hemorrhage, pneumothorax (usually right sided) and recurrent laryngeal nerve injury (permanent in up to 50% of cases)
Which vaporizer is a dual circuit gas vapor blender? To what feature does the duel circuit apply?
Tec 6. The pressure in the vapor circuit is electronically regulated to equal the pressure in the fresh gas circuit. At a constant fresh gas flow rate, the operator regulates vapor flow using a conventional concentration control dial. When the fresh gas flow rate increases, the working pressure increases proportionally. For a given concentration setting even when varying the fresh gas flow rate, the vaporizer output is constant because the amount of flow through each circuit remains proportional.
Define "standard of care".
Conduct and skill of a prudent practitioner that can be expected by a reasonable patient. Also defined as reasonable care by a professional. Standard of care is a very important medicolegal concept because a bad medical result due to failure to meet the standard of care is malpractice.
How is the standard of care established? What two sources are typically consulted to establish the standard of care?
What a jury says it is. Beliefs of expert witnesses (de facto standards of care) as well as published standards of care, guidelines, practice parameters, and protocols are commonly used.
You decide an LMA is appropriate for the airway management of the 9-kg patient, but a 1.5 LMA is not available; will you use a size 1 or a size 2 LMA?
The manufacturer recommends for the clinician to choose the largest size that will fit comfortably in the oral cavity, and then inflate to the minimum pressure that allows ventilation to 20 cm H2O without an air leak.
Describe a transverse rectus abdominus muscle flap procedure for autologous breast reconstruction.
TRAM replaces the breast with an ellipse of abdominal skin and subcutaneous tissue based on the rectus abdominus muscle. The procedure creates a natural appearing breast from the patient's own tissue. The abdominal donor site is closed as though the patient has undergone abdominoplasty ("tummy tuck").
What drugs should be avoided in the transverse rectus abdominus muscle breast reconstruction procedure?
Vasopressers and N2O (during the abdominal closure)
Describe the Whipple procedure for pancreatectomy indicated by pancreatic carcinoma.
Pancreaticoduodenectomy, followed by a pancreaticojejunostomy, hepaticojejunostomy, and a gastrojejunostomy
What electrolyte disturbances are expected during the Whipple procedure?
Hypocalcemia, hypomagnesemia, hypokalemia, and possible hypochloremic metabolic alkalosis
What is the Murphy eye on a tracheal tube? What is the purpose of the Murphy eye?
A hole through the tracheal tube wall opposite to the bevel. The purpose is to provide an alternate pathway for gas flow if the bevel becomes occluded.
What is the name for tracheal tubes that lack a Murphy eye?
Magill-type tubes. The cuff can be placed closer to the tip of the tube.
What does the ASTM require of tracheal tubes?
A radio-opaque marker must be placed at the patient end of the tube or along the entire length of the tube to determine the position of the tube after intubation.
Identify 4 reasons why positive pressure ventilation of 25 cm H2O would not be sufficient to ventilate an individual.
1. Upper airway is obstructed 2. The patient has sufficient muscle tone to prevent chest expansion 3. The individual has decreased pulmonary compliance 4. The individual has increased pulmonary resistance
What nerve can be blocked in a popliteal fossa block?
The sciatic nerve can be localized in the upper area of the popliteal fossa. The goal is to block the sciatic nerve before it branches into the tibial and peroneal nerves.
List indications for popliteal fossa block.
Foot and ankle surgery, short saphenous vein stripping, and in the pediatric population. This block provides improved calf tourniquet tolerance and an immobile foot, compared to ankle block.
What type of muscle is found in the gastrointestinal tract? Identify the arrangement of this muscle in the GI tract.
The tunica muscularis of the gastrointestinal tract is composed of 2 layers of smooth muscle: the inner layer is circular, the outer layer is longitudinal. Specialized circular muscles are called sphincters.
Which zona of the adrenal cortex is the only one capable of synthesizing aldosterone? Why is this true?
Zona glomerulosa, only one to contain aldosterone synthase
List contraindications for cricothyrotomy.
Neonates and children younger than 6 years of age, and in patients with laryngeal fractures
Give 3 contraindications to use of a pulmonary artery catheter.
1. Complete left bundle branch block
2. Wolff-Parkinson-White syndrome
3. Ebstein's malformation
What type of muscle is the pyloric sphincter?
Smooth muscle
List the electrolyte disturbances associated with anorexia nervosa.
Hypokalemia, hyponatremia, hypochloremia, and metabolic alkalosis as a result of vomiting and laxative & diarrhetic abuse.
Considering the ventilator in pressure control mode: what parameter fluctuates with each cycle? What patient parameters determine the fluctuation?
Inspiratory pressure is greater than the positive end expiratory pressure. In this mode, tidal volume fluctuates with alterations in patient compliance, pulmonary resistance, and with patient-ventilator asynchrony.
Which neuromuscular relaxant is most often associated with triggering allergic (anaphylactic) reactions?
Succinylcholine
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