Preoperative Assessment

(Answer:C) According to the ASA Task Force on Preoperative fasting, breast milk should not be consumed within 4 hours of surgery. Interestingly, non-human milk is considered safe when consumed at least 6 hours prior to surgery.

American Society of Anesthesiologists Task Force on Preoperative Fasting, Anesthesiology 90:896-905, 199

The AHA made several changes to IE prophylaxis guidelines in 2007 that dramatically narrowed the procedures and patients for which prophylaxis is recommended. This came from evidence indicating that prophylaxis only prevents a small number of cases of IE anyway. According to these guidelines, GU or GI tract cases do not need endocarditis prophylaxis (choices A and D). Surgeries that perforate the oral mucosa are still an indication. Risk factors warranting IE prohylaxis include: prosthetic valves, history of IE, congenital heart disease (with specific guidelines - see link below), and valvulopathy developing in a cardiac transplant patient. Choice B is the only procedure and high risk patient according to these guidelines. see link below: http://www.heart.org/HEARTORG/Conditions/CongenitalHeartDefects/TheImpactofCongenitalHeartDefects/Infective-Endocarditis_UCM_307108_Article.jsp

Butylcholinesterase is the enzyme that breaks down succinylcholine, so patients who do not have this enzyme will experience significantly prolonged muscle block after they receive succinylcholine.



The local anesthetic dibucaine inhibits normal butyl cholinesterase, and the degree of the inhibition is called the "dibucaine number."  In a normal patient, dibucaine blocks 80% of enzyme activity, so the dibucaine number is 80. In a patient with a partial mutation, dibucaine blocks only 40-60% of activity, and in a homogenous mutation it blocks 20%.



This patient has a dibucaine number of 21, so this means that his ability to metabolize succinylcholine will be below normal.  Therefore, he will have prolonged muscle block after receiving succinylcholine.



Miller's Anesthesia, 7th Edition, Chapter 29: Pharmacology of Muscle Relaxants and their Antagonists, 2009.

Current evidence suggests that patients taking longterm steroids should receive their normal dose on the day of surgery.  A larger or "stress" dose is only indicated for patients with primary hypothalamus-pituitary-adrenal axis disease.  



Also, adrenal function testing prior to surgery in patients taking longterm steroids has not been shown to reduce incidence of adrenal crisis.  



http://archsurg.jamanetwork.com/article.aspx?articleid=402330

AAA repair is by far the procedure with the highest rate of postoperative respiratory failure -- even greater than thoracic procedures.



Miller's Anesthesia, 7th Edition, Chapter 35: Anesthetic Implications of Concurrent Disease, 2009.

(Answer: C) The guidelines for presurgical fasting are as follows:

Within two hours of surgery: Absolutely nothing
> 2 hours prior to surgery: Clear liquids only-- this includes water, carbonated
beverages, sports drinks, coffee without cream, tea without cream, etc.
> 4 hours prior to surgery: Breast milk
> 6 hours prior to surgery: Light meal, infant formula, nonhuman milk. An example of a light meal is toast or yogurt.
> 8 hours prior to surgery: Any meal.


In this case, the coffee with cream was consumed 3 hours prior to surgery. While coffee by itself is a clear liquid and would be safe greather than two hours prior to surgery, the cream is not a clear liquid and should not be consumed within 6 hours of surgery.

American Society of Anesthesiologists Task Force on Preoperative Fasting, Anesthesiology 90:896-905, 1999

According to the American Diabetes Association, patients should hold metformin the day before surgery as well as the day of the case. This is because metformin can contribute to lactic acidosis if the patient’s renal function is damaged intraoperatively. Patients should hold any other oral hypoglycemics only on the morning of surgery (Glipizide, pioglitazone, etc.) As this patient will be NPO for several hours before the case, taking his normal dose of Lantus will put him at risk for hypoglycemia. Current recommendations are for patients to take ½ to 1/3rd their normal amount of long-acting insulin and for the surgery to be early on the schedule if possible. Hourly blood glucose should be checked intraoperatively. See: http://clinical.diabetesjournals.org/content/19/2/92.full

As a pheochromocytoma is an endogenous production and release of catecholamines, perioperative mortality from dramatic blood pressure swings and their consequences-- ACS, CHF, cerebral hemmorage, and arrhythmias--approaches 45% when untreated.



Preventing vasoconstriction with phenoxybenzamine (non-selective a-antagonist) has been shown to reduce mortality to 0-3%. 



If a patient receives a b-blocker without alpha blockade, he may have experience alpha mediated vasoconstriction and have an extremely dangerous elevation in blood pressure.



Barash, Clinical Anesthesia, 6th Edition, Chapter 49: Endocrine Function, pg. 1295

Patients who have had a cardiac catheterization--especially with a drug eluting stent (DES) require long-term antiplatelet therapy to prevent restenosis. Now, a hip replacement is an elective procedure with a high risk of bleeding, so if at all possible, the patient should discontinue his plavix prior to the case. The problem is, this increases the patient’s perioperative risk of MI due to stent thrombosis, which carries a high mortality rate.

Current guidelines are that a DES requires treatment with plavix for a minimum of 12 months before discontinuing it for an elective procedure. For bare-metal stents (BMS), guidelines are to wait at least one month. Since this patient’s stent was placed 6 months ago, he could safely discontinue the plavix with a BMS now and in 6 months with a DES.

Chassot PG, Perioperative antiplatelet therapy: The case for continuing therapy in patients at risk of myocardial infarction. British Journal of Anesthesia, 2007; 99:316-3

Ideal body weight (IBW) is an idea made by insurance companies for the weight for each gender and height that has the lowest mortality. The formula is:



IBW (kg) = height (cm) - x, where x = 100 for adult males and 105 for adult females.



Barash, Clinical Anesthesia, 6th Edition, Chapter 47: Anesthesia and Obesity, pg. 1231, 2009.

Patients receiving drug eluting stents should defer elective surgery for at least 12 months as electron micrographs show significantly increased patency with time. Discontinuing plavix during this early period is associated with a significant risk of thrombus formation, myocardial infarction, and death. After 12 months though, for elective surgery, current guidelines are to discontinue plavix for at least 7 days. The other medications listed are thought to be benefitical perioperatively (especially beta blockers-- class I recommendation), so they should be continued on the morning of surgery.

Barash, PD and Cullen BF, Clinical Anesthesia, 6th Edition, Chapter 42: Anesthesia for Vascular Surgery, pg. 1111-2.

There is strong evidence that statins reduce perioperative cardiac risk. The DECREAE-III trial of 2009 showed that patients receiving fluvastatin had a reduced incidence of perioperative MI as well as 30-day non-fatal MI, and 30-day cardiac death. It is thought that statins stabilize plaques and reduce vascular inflammation. In this case, the patient should be told to take her Fluvastatin with a small sip of water.

Schouten O, Boersma E, Hoeks SE, et al.; Dutch Echocardiographic Cardiac Risk Evaluation Applying Stress Echocardiography Study Group. Fluvastatin and perioperative events in patients undergoing vascular surgery. N Engl J Med. 2009;361(10):980–989.

The STOP-Bang screening questionnaire is an 8-question survey that categorizes a patient’s risk for OSA as high or low. The risk factors are as follows: 1. Loud snoring 2. Feeling tired during the daytime 3. Someone observing the patient stopped breathing during sleep 4. Being treated for HTN 5. BMI > 35 6. Age > 50 7. Neck circumference > 40 cm 8. Being male Four of these were listed above. See: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3325050/

Butylcholinesterase is the enzyme that breaks down succinylcholine, so patients who do not have this enzyme will experience significantly prolonged muscle block.



The local anesthetic dibucaine inhibits normal butyl cholinesterase, and the degree of the inhibition is called the "dibucaine number."  So in a normal patient, dibucaine blocks 80% of enzyme activity, so the dibucaine number is 80.  In a patient with a partial mutation, dibucaine blocks only 40-60% of activity, and in a homogenous mutation it blocks 20%.



Miller's Anesthesia, 7th Edition, Chapter 29: Pharmacology of Muscle Relaxants and their Antagonists, 2009.

Pre-operative fluid deficit is a function of weight and the time that a patient was NPO. For maintenance, the first 10kg of a patient's weight should receive 4ml/hr, the second 10kg 2ml/hr, and every kg after that 1mg/hr. This patient weighs 100kg, so 40+20+80 = 140. She was NPO for 12 hours, so 140 x 12 = 1.68L.



Barash, Clinical Anesthesiology, 6th edition, Chapter 10: Cardiovascular Anatomy and Physiology, 2009.

A cataract repair is a low-risk surgery. According to the American Heart Association (AHA) 2007 Guidelines, patients having low-risk surgery who do not have an active cardiac condition can proceed to surgery without further testing. The following are active cardiac conditions according to those guidelines: 1. Angina at rest or with minimal exertion 2. Decompensated CHF 3. Significant arrhythmia such as a symptomatic bradycardia, symptomatic ventricular arrhythmia, Mobitz II atrioventricular block, and third-degree atrioventricular heart block. 4. Severe valvular disease such as symptomatic aortic stenosis or mitral stenosis. ACC/AHA 2007 Guidelines for Perioperative Cardiovascular Evaluation and Care for Noncardiac Surgery. See: http://circ.ahajournals.org/content/116/17/e418.full

The AHA has stratified non-cardiac surgeries into low, medium, and high risk of perioperative cardiac events. Low risk surgeries include endoscopic procedures, cataract repairs, and breast surgeries. These have a reported cardiac risk of
Intermediate risk surgeries have a reported cardiac risk of 1-5%, and these include carotid endarterectomy (choice A), orthopedic surgeries (choice B), intrathoracic surgery, prostate surgery, and intraperitoneal surgery (choice C).

High risk surgery has a greater than 5% risk of cardiac event and includes aortic or other major vascular cases as well as peripheral vascular surgery-- such as a femoral-popliteal bypass (choice D).

ACC/AHA 2007 Guidelines for Perioperative Cardiovascular Evaluation and Care for Noncardiac Surgery. Available at: http://circ.ahajournals.org/content/116/17/e418.full

This patient has known peripheral vascular disease and needs his metoprolol for rate control; continuing his beta blocker is a Class I recommendation.



Also, the North American Symptomatic Carotid Endarterectomy Trial (NASCET), patients taking aspirin and plavix had a significantly lower stroke rate when compared to patients taking either drug alone or patients without any anticoagulation.



Barsh, Clinical Anesthesia, 6th Edition, Chapter 42: Anesthesia for Vascular Surgery, pg 1118, 2009.



http://www.nejm.org/doi/full/10.1056/NEJM199108153250701 

Most breast surgeries are considered low-risk. According to the American Heart Association (AHA) 2007 Guidelines, patients having low-risk surgery who do not have an active cardiac condition can proceed to surgery without further testing. The following are active cardiac conditions according to those guidelines: 1. Angina at rest or with minimal exertion 2. Decompensated CHF 3. Significant arrhythmia such as a symptomatic bradycardia, symptomatic ventricular arrhythmia, Mobitz II atrioventricular block, and third-degree atrioventricular heart block. 4. Severe valvular disease such as symptomatic aortic stenosis or mitral stenosis. ACC/AHA 2007 Guidelines for Perioperative Cardiovascular Evaluation and Care for Noncardiac Surgery. See: http://circ.ahajournals.org/content/116/17/e418.full

The maximum allowable blood loss is a function of the patient's pre-procedure blood volume, hematocrit, and minimum allowable hematocrit. This patient has a history of myocardial infarction, so the minimum recommended hematocrit for him is 30. The first step toward this calculation is knowing the patient's pre-procedure blood volume. For a man, blood volume is approximately 75ml / kg. As this man weighs 73 kg, his blood volume is 73 x 75 = 5475. Now, the hematocrit is 35, and as this patient has a history of coronary artery disease, the minimum hct allowable for him is 30. The formula is [Hct(original) - Hct(minimal)] / Hct(original), so (35 - 30 ) / 35 = 0.143. This fraction x blood volume = 0.143 x 5473 = 0.782.

Miller RD and Pardo MC, Basics of Anesthesia 6th Edition, Elsevier Publishers, Philadelphia PA, 2011.

While previous guidelines said that men over 40 and women over 50 should receive a screening EKG, the 2011 guidelines say that age alone is not an indication.  Instead, the patient's comorbidities, the invasiveness of the surgery, and the history and physical should determine if the patient needs an EKG.



Practice Advisory for Preanesthesia Evaluation, American Society of Anesthesiologists, pg8, 2011.