Preop Flashcards
Insulin adjustment before surgery?
Patients on rapid or short-acting insulin can continue it till the day of surgery without any other changes. Those taking intermediate insulin (usually twice a day dose) should take only 75% of the normal dose the night before surgery and 50% of the normal dose the day of the surgery. With long-acting insulin, the patient needs to reduce their dose by 50% on the morning of the surgery.
rapid-acting (lispro, aspart), short-acting (regular), intermediate (NPH), and long-acting (glargine, detemir).
When to DC Metformin preop?
A common side effect of anti-diabetics is hypoglycemia, especially seen with sulfonylureas (e.g., glipizide). Metformin is excreted through the kidneys, and if metformin builds up due to poor elimination, lactic acidosis can occur. However, studies have shown that there is no increased risk of lactic acidosis in the perioperative period. This has led to the recommendation that metformin be continued until the day of the surgery. The exception is patients with renal dysfunction, who will need to discontinue the metformin 24-48 hours prior to surgery.
The four types of heat loss that occur from a patient to the relatively cold operating environment are: … and their % of total heat loss?
- Radiation 67%
- Evaporation 17%
- Conduction + 4. Convection -> 16%
The main mechanism of heat loss following an initial decrease in core temperature due to redistribution is … and accounts for ~ … of total heat loss.
Radiation, accounting for approximately 67%.
Radiative heat losses occur anytime an object is above absolute zero. The magnitude of the radiation is proportional to the fourth power of the temperature difference between the two sources. T
The main mechanism of heat loss following an initial decrease in core temperature due to redistribution is … and accounts for ~ … of total heat loss.
Radiation, accounting for approximately 67%.
Radiative heat losses occur anytime an object is above absolute zero. The magnitude of the radiation is proportional to the fourth power of the temperature difference between the two sources.
The decision to postpone or proceed with a surgery in a patient with uncontrolled hypertension depends on numerous factors, including …
One must take into account the type of surgery (emergent, urgent, time-sensitive, versus elective), patient risk factors, baseline blood pressure, and signs or symptoms or end-organ damage.
Severe hypertension is defined as BP > 180/110 mmHg, however, surgery may proceed if there are no signs of end-organ damage. However, if the patient has cardiac risk factors and/or is to undergo non-emergent high-risk surgery, then it would not be unreasonable to delay surgery for blood pressure control.
Signs and symptoms of end-organ damage include:
- Chest pain, arrhythmia, dyspnea, orthopnea, peripheral edema
- Headache, vomiting, depressed consciousness, seizure
- Hematuria, proteinuria
- Numbness, weakness, slurred speech
- Retinal hemorrhage, papilledema, blurred vision
- Severe anxiety (out-of-proportion to situation)
Lorazepam dose as premedication?
In doses of 25-50 mcg/kg (max dose of 4 mg) significant amnesia may remain up to 4-6 hours after a dose without excessive sedation, but above 4 mg there is no added benefit and it will prolong sedation. In shorter cases, it may prolong extubation time and as noted earlier does not improve patient satisfaction.
Why Opioids should be limited to patients with pain pre-procedure as a premedication?
Opioids can be used for premedication but use should be limited to patients who have significant pain prior to surgery. Administration without pain can result in dysphoria, may actually sensitize patients to pain, and can increase the risk of postoperative hyperalgesia. There is also a smaller window of safety with opioid medications given their significant respiratory depressive properties, especially when given with other medications (like benzodiazepines). Opioids do not produce anxiolysis or amnesia, thus necessitating other drug administration that may have synergistic effects.
Premedication with Anticholinergic consideration?
Anticholinergic medications have multiple premedication uses including for antisialagogue, antiemetic, and antibradycardia effects.
Scopolamine is a tertiary amine that produces significant sedation with variable effects on amnesia (this improves with administration of benzodiazepines). Side effects include dry mouth, cycloplegia, and it carries the greatest risk of central anticholinergic syndrome (especially in the elderly) among the commonly used anticholinergics in anesthesia. Care should always be taken to review the patient’s current home medications as side effect risks are enhanced in patients already taking anticholinergics preoperatively.
Glycopyrrolate does not cross the blood brain barrier owing to its quaternary amine structure and does not produce sedation but is a very effective antisialagogue and can be used to prevent bradycardia in eye surgery or with succinylcholine use (as in children).
Atropine crosses the blood brain barrier to a lesser degree than scopolamine, so though it carries side effects similar to scopolamine, they occur less often and to a lesser extent
Premedication with the central alpha-2 agonists clonidine and dexmedetomidine benifits and downsides?
It decrease intraoperative MAC of inhaled anesthetics, decrease postoperative opioid consumption, produce sedation, provide anxiolysis, and cause dry mouth.
The primary concern with these medications is the potential risk of significant hypotension and bradycardia as well as withdrawal syndromes after chronic administration.
2014 ACC/AHA perioperative guidelines make a few key recommendations regarding valvular heart disease in general.
It is recommended that any patient with suspected moderate or greater degree of valvular stenosis or regurgitation undergo preoperative echocardiography if there has been no echo in the last year or there is a significant change in physical examination since the last echocardiogram. Stenotic and regurgitant lesions can be thought of broadly as either being volume overload or pressure overload.
AR causes to investigate preoperatively?
Aortic regurgitation (AR) has numerous causes. Most common causes are endocarditis, rheumatic fever, bicuspid AV, aortic root dilation, aortic dissection and collagen vascular disorders (Marfan, Ehlers-Danlos). AR results when the aortic valve leaflets do not coaptate properly leading to leaking of blood back into the left ventricle during diastole. This regurgitated blood results in a decreased cardiac output and the possibility of volume overload of the LV. Aortic regurgitation is commonly diagnosed following auscultation of a diastolic murmur (heard best along the right sternal boarder) combined with a widened pulse pressure and decreased diastolic blood pressure. According to the ACC/AHA recommendations, left-sided regurgitant lesions are better tolerated than stenotic lesions. Patients with decreased ejection fractions (< 35%), those with ischemic causes of regurgitation, history of diabetes mellitus, and/or carotid endarterectomy have worse outcomes.
When thinking about the anesthetic implications of AS disease, one should think about the following variables: heart rate, contractility, preload, and afterload.
- Severe aortic stenosis is defined as a valve area less than 0.8 cm2 and a transvalvular pressure gradient higher than 50 mmHg.
- The “triad” of symptoms include: angina, syncope, and shortness of breath (dyspnea). The degree of symptoms does not correlate with the degree of stenosis.
- HR: normal sinus rhythm should be maintained since loss of the left atrial contraction will result in a dramatic decrease in stroke volume and blood pressure. A normal to slower heart rate is beneficial to allow as much time for ventricular filling as possible. Furthermore, elevations in heart rate can lead to ischemia due to decreased diastolic time.
- Contractility: want to maintain, avoid depression of contractility which can lower stroke volume.
- Preload: want to have adequate volume.
- Afterload: must be maintained distal to the stenotic lesion to ensure coronary perfusion. A decrease in blood pressure can lead to myocardial ischemia which will further worsen contractility.
- Cardiac resuscitation is not typically effective in patients with AS; code situations must be avoided as it is generally not possible to created adequate stroke volume with chest compression in these patients.
When thinking about the anesthetic implications of AR disease, one should think about the following variables: heart rate, contractility, preload, and afterload.
- The magnitude of regurgitant volume depends on the diastolic time and the pressure gradient across the aortic valve (dependent on systemic vascular resistance).
- HR: must be kept above 80 bpm to prevent increases in the time for regurgitation. Decreased heart rates, which will increase diastolic time, will allow more regurgitation.
- Contractility: want to maintain.
- Preload: need adequate volume loading to ensure enough volume can move forward. Want to avoid overloading patient because this will increase regurgitant volume.
- Afterload: want to lower systemic vascular resistance which will attempt to prevent more regurgitation.
ACC/AHA guidelines
The first decision you need to make: is this emergency surgery? If not, does he have “active cardiac conditions,” which are essentially the old “major risk factors.” These are: unstable or severe angina, myocardial infarction (MI) within a month, heart blocks (mobitz II or type III), major ventricular arrhythmias, supraventricular arrhythmias (such as a-fib/ flutter) with rapid ventricular rate (RVR), active or severe heart failure, or severe valvular stenotic disease. If any of these are present they need to be addressed prior to surgery. After you have determined that the patient does not have an active cardiac condition you ask yourself is this a low risk surgery, if so, you can proceed without further workup at this point. If it’s an intermediate or high risk surgery then you need to risk stratify further. If the patient can muster up 4 mets of activity without symptoms (climb a flight of stairs), the patient has essentially passed a stress test and you can proceed with surgery. Our patient cannot do this (minimal activity due to pain). Now we have to further stratify him by “clinical risk factors,” formally called “intermediate risk factors,” back when the guidelines were more straight forward. Clinical risk factors are: ischaemic heart disease, compensated heart failure, diabetes (especially insulin dependent), renal insufficiency (especially CKD with creatinine greater than 2.0), and CVA. If the patient has none of these risk factors, he is deemed good to go without further cardiac evaluation (may need pulmonary evaluation still, but that’s a different story). A patient with 1-2 of these clinical risk factors qualify for a stress test, should the patient and cardiologist feel it will change management (versus continuing medical management with heart rate control). Three or more clinical risk factors essentially has the same management except you should think a little bit harder about getting a stress test (you think I’m making this up!). Therefore, our patient has no active cardiac conditions but two clinical risk factors, therefore the recommendation is to proceed with the case with heart rate control or consider a stress test. The ABA typically errs on the side of safety, so I would recommend you choose to consult for stress test and not “proceed with heart rate control” just yet (even if the patient was asymptomatic). Given the fact the patient cannot generate 4 mets (due to leg pain) a treadmill stress test will certainly fail and you should proceed with a dobutamine stress test. Lets now fast forward to the 2014 ACC/AHA guidelines.
