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Chapter: Essential Anesthesia From Science to Practice : Clinical management : Pre operative evaluation

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Common disorders - Anesthesia Clinical management

Anesthetic and operative procedures constitute a physiologic trespass with which the patient can deal better, if not simultaneously challenged by correctable derangements that sap his strength and threaten his homeostasis.

Common disorders

We encounter many patients with pre-existing medical conditions. Anesthetic and operative procedures constitute a physiologic trespass with which the patient can deal better, if not simultaneously challenged by correctable derangements that sap his strength and threaten his homeostasis. Ideally, the surgeon would already have addressed these questions. However, that is not always the case, and the anesthesiologist needs to assess the medical condition of the patient. The answers to the question, “Is the patient in the optimal condition to pro-ceed with anesthesia and operation?” are not always clear-cut. For example, a patient with transient ischemic attacks is scheduled for a carotid endarterec-tomy. The patient also has coronary artery disease and unstable angina. Should we risk the possibility of a stroke by first putting the patient through a heart operation, or should we risk a myocardial infarction by first doing a carotid endarterectomy? Consultations with other experts help in resolving such difficult issues.

Trauma emergency

Rapid assessment of the airway and fluid status precedes, or coincides with, the most urgent: stemming of hemorrhage. Once we have secured an airway and established a route for administering fluids, we can contemplate anesthe-sia, realizing that a patient in hemorrhagic shock will tolerate and require very little anesthesia. The mechanism of the trauma may suggest additional studies (Table 1.3).



Diabetes

 

We focus on the many end-organ effects of diabetes, as well as the patient’s glu-cose control (HgbA1c). Those with poor control should be considered for pre-admission. Pre-operative studies should include assessment of metabolic, renal, and cardiac status. In general, diabetic patients should be scheduled early in the day.

Because of the 30% incidence of gastroparesis in this population, diabetics are often pretreated with metoclopramide to speed gastric emptying and are induced with a ‘rapid sequence induction’ (see General anesthesia). Intra-operative man-agement aims to match insulin requirements, recognizing the fasting state and the effects of surgical stress.

Coronary artery disease

In 2002, the American College of Cardiology and the American Heart Association (ACC/AHA) published updated guidelines for the perioperative cardiovascular evaluation of patients for non-cardiac surgery. These so-called “Eagle criteria” should be applied only when the results are likely to impact care. We should always ask the patient about their exercise tolerance; the ACC/AHA recommendations attempt to quantify this by using metabolic equivalents (METs), which enables us to classify patients on a scale of 1 (take care of yourself around the house) to 10+ (participate in strenuous sports). A useful dividing line is 4 METs (climb a flight of stairs). In general, patients unable to do more than 4 METs represent a group at high risk of cardiovascular complications. The algorithm in Fig. 1.2helps in assigning risks and identifying those patients who require additional cardiac evaluation. In addition to their functional capacity, the algorithm incorporates medical status (Table 1.4) and the procedure planned (Table 1.5).




Pacemaker/AICD

Pacemakers are life saving for many patients with heart rhythm disturbances. There are many types available, with a range of functionality (see Table 1.6). The addition of an automatic internal cardiac defibrillator goes one step further. Unfortunately, these life-saving devices may fail to function properly in the presence of electrical devices, e.g., electrocautery. Many patients carry a card identifying the pacemaker make and model. Some can also provide a report from a recent electronic interrogation that specifies proper function and remain-ing battery life. More often than not, we do not have that information. A chest radiograph can reveal pacer make and model, as well as lead location. In symp-tomatic (lightheaded spells, palpitations, hypotension) or in pacer-dependent patients, a pacemaker interrogation (by a specialist with proprietary communi-cation equipment) may be necessary. If this is not an option, a current ECG might be helpful, if it demonstrates pacer spikes in appropriate locations.



Pulmonary disease

The patient with pre-operative pulmonary disease faces risks of intra-operative and post-operative pulmonary complications including pneumonia, bron-chospasm, atelectasis, respiratory failure with prolonged mechanical ventilation, and exacerbation of pre-existing lung disease. The risk of these complications depends on both the patient and the procedure.

·           Chronic pulmonary disease Both chronic obstructive pulmonary disease(COPD) and asthma can increase the risk. Therefore, well before anesthesia and surgery we should treat the patient to bring him into the best possible condition, given his lung disease.

·           Smoking Even without evident lung disease, smoking increases the risk of pul-monary complications up to four times over that or non-smokers. Eight weeks of smoking cessation isf required to reduce that risk, though carboxyhemoglobin will virtually vanish after only 24 smoke-free hours.

·           General health There are general risk indices that predict pulmonary compli-cations well. In fact, exercise tolerance alone is an excellent predictor of post-operative pulmonary complications.

·           Obesity Obese patients present more airway management difficulties for severalreasons: (i) mechanical issues related to optimal positioning; (ii) redundant pharyngeal tissue complicating laryngoscopy; (iii) many suffer from obstructive sleep apnea (and its sequelae: pulmonary hypertension/cor pulmonale); and (iv) in obese patients it can be extremely difficult or impossible to mask–ventilate the lungs due to the weight of the chest wall. Obesity also increases the risk for thromboembolic phenomena. Post-operatively, however, obesity has not proven to increase the risk of pulmonary complications.

·           Surgical site Proximity of the surgical site to the diaphragm is the single mostimportant predictor of pulmonary complications. Thoracic and upper abdom-inal operative sites confer a 10–40% incidence. This can be reduced perhaps 100-fold with laparoscopic techniques.

·           Surgery duration Operations lasting<3 hours are associated with fewercomplications.

·           Intra-operative muscle relaxants Pancuronium, specifically, has been associatedwith an increased incidence of pulmonary complications; this is related to its long half-life and risk of residual muscle weakness.

·           Results of pre-operative testing Routine pre-operative pulmonary function tests(PFTs) are not indicated, unless the patient is undergoing lung resection. If available, however, the risk of complications increases when the forced expira-tory volume in 1s (FEV1) or forced vital capacity (FVC) are <70% predicted, or when the FEV1/FVC is <65%

Asthma

Pre-operatively, our goals are to reverse bronchospasm and inflammation, pre-vent an asthma exacerbation, clear secretions, and treat any infection. We specif-ically ask about any increased inhaler use, recent hospitalizations or Emergency Department visits for bronchospasm, a recent change in sputum amount or color, or a recent cold. All of these factors increase the risk of peri-operative bron-chospasm. If the patient is scheduled for thoracic or upper abdominal surgery (with a very high risk of pulmonary complications), spirometry can identify patients at greatest risk.

Glucocorticoids may be helpful in those patients who do not respond ade-quately to 2 agonists. Patients who are steroid dependent will often have suppressed adrenal cortical function and require supplemental steroids in the peri-operative period.

Chronic renal failure

Chronic renal failure (CRF) involves both the excretory and synthetic functions of the kidney. When the kidney fails to regulate fluids and electrolytes, the net result is acidosis, hyperkalemia, hypertension, and edema. Meanwhile, the lack of syn-thetic function results in anemia (due to decreased production of erythropoietin) and hypocalcemia from a lack of active vitamin D3 (this also leads to secondary hyperparathyroidism, hyperphosphatemia, and renal osteodystrophy). Azotemia can cause platelet dysfunction.

Medications that are renally excreted will be affected by CRF, and most should be avoided. In particular, meperidine (pethidine, Demerol®) should not be given as its metabolite (normeperidine) can accumulate and cause seizures. The pre-ferred muscle relaxant is one that does not depend on renal function for its metabolism (atracurium, cis-atracurium for surgical relaxation).

We check electrolytes on these patients pre-operatively and prefer they undergo dialysis within the preceding 24 hours. We must resist the temptation to hydrate a patient who is intravascularly ‘dry’ following dialysis, as they cannot excrete excess fluids. Replacement fluids should not contain potassium (normal saline is preferred over Ringer’s lactate) as these patients are at risk for hyperkalemia. CRF patients are also at increased risk for coronary artery and peripheral vascular disease.


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