Medical brain notes 7

  Pre-operative evaluation Surgery and anesthesia cause major perturbations to a patient’s homeostasis. The risk of potentially life-threatening complications can be reduced with appropriate pre-operative evaluation and therapy. Because cost concerns have virtually elim-inated pre-operative hospital admission, today the visit may occur just moments before the operation in the case of an emergency or a healthy outpatient, but is better managed in pre-anesthesia clinics to which patients report one or several days before their operation. Surgeons and primary-care physicians can do much to avoid operative delays and cancellations, as well as to reduce the patient’s cost and risk by identifying patients who need a pre-operative anesthesia consulta-tion and by sending all pertinent information, e.g., recent ECG, echo studies, etc., with the patient. The pre-anesthetic evaluation appears to be just another rou-tine of eliciting a history, reviewing all systems, performing a physical examina-

  History We begin with the “H” in “H&P,” obtaining a medical and surgical history. We are particularly concerned with the cardiopulmonary system, and exercise toler-ance is a good measure of current status. We also search for evidence of chronic diseases of other systems. For elective procedures, patients should be in the best condition possible, e.g., no exacerbation of chronic bronchitis or unstable angina. Below, we describe the pre-operative evaluation of some common medical condi-tions. When patients with these, or other rarer, conditions require an anesthetic,  a pre-anesthesia clinic visit a week or so in advance of anesthesia allows time to seek additional information, e.g., study results from the patient’s private physi-cian, perform studies, e.g., cardiac pacemaker interrogation, or obtain consulta-tion from a specialist. Such planning helps keep the operating schedule running smoothly. We inquire about any previous anesthetics, particularly any untoward events such as b

  Physical examination In addition to the cardiopulmonary examination, we carefully evaluate the patient’s airway to predict whether it will be easily intubated (see Airway manage-ment). The physical examination should also seek pre-existing neurologic deficits, particularly if regional anesthesia, e.g., spinal, epidural or nerve plexus block, is considered, and any limitations to flexibility that may present difficulties with positioning the patient. If we plan on regional anesthesia, we need to inspect the anatomy, for example, does the patient have a scoliosis that would make a lumbar puncture difficult, or is his skin infected over the site where we would place the needle?

  Laboratory evaluations and studies Here we must ask the question, “Can the results from additional tests influence my anesthetic and post-anesthetic management?” In the majority of cases, the answer turns out to be “No,” but there are many exceptions. Among them might be a determination of serum potassium if we fear that the patient is hyperkalemic, in which case a succinylcholine-induced release of potassium would be dangerous. Coagulation studies would be needed if we plan regional anesthesia and have reason to worry about a bleeding diathesis or thrombocytopenia. Uncontrolled bleeding into the nerve plexus can cause permanent damage. In general, labora-tory and other studies should be ordered as indicated from the medical history, and only if they might have an effect on intra- or post-operative management, or perhaps if the risk analysis may suggest canceling or altering the procedure itself. For example, suppose we detect a carotid bruit during the pre-anesthetic evaluation of a

  NPO status During induction of general anesthesia, the gag reflex is necessarily abol-ished. Should the patient “choose” that most inopportune time to suffer gastro-esophageal reflux (or worse yet, emesis), there is a high likelihood the stomach contents could end up in the lung, causing a chemical pneumonitis or even acute suffocation from the lodging of solid particles in the bronchial tree. In addition to pharmacologic means (see Pharmacology), we minimize this risk by having the patient report for surgery with an empty stomach. Patients are asked to refrain from eating solid foods for 6–8 hours prior to elective surgery. While there is evi-dence that clear liquid ingestion is cleared rapidly and not dangerous in those patients with normal digestion (it may even  raise  the pH of the stomach con-tents above the pH 2.5 danger zone), it remains customary to tell patients who are scheduled for an elective operation in the morning not to eat or drink any-thing for at least 6 hours (fo

  Planned procedure The planned surgical, diagnostic, or therapeutic procedure influences the anesthetic management, sometimes producing problems for which we must be prepared. For example, the neurosurgeon may trigger a wild release of cate-cholamines when destroying the trigeminal ganglion in a percutaneous procedure that lasts only minutes. How are we going to protect the patient from the expected sympathetic storm? Or, how can we guard against a sudden and substantial rise in peripheral arterial resistance when the surgeon clamps the aorta in prepar-ation for the resection of an aortic aneurysm? The planned procedure also has implications for, among other things, intra-operative positioning of the patient, potential need for blood replacement, anticipated severity of post-operative pain (is a regional anesthetic an option?), and need for intensive care after surgery.

  Anesthetic choice In addition to the above assessment, the anesthetic plan must consider the wishes of both patient and surgeon, as well as  our  individual skill and experience. Does the patient have special requests that need to be taken into account? For example, some patients would like to be awake (maybe the President so he doesn’t have to pass control of the US to the Vice-President), others asleep, and others do not want “a needle in the back.” Some patients present special problems, for example Jehovah’s Witnesses who do not accept blood transfusions, based on their interpretation of several pas-sages in the Bible (for example Acts 15:28, 29). A thoughtful and compassion-ate discussion with the patient usually finds the physician agreeing to honor the patient’s wishes, an agreement that may not be violated. The caring for children of Jehovah’s Witnesses brings an added concern and may require ethics consultation and perhaps even referral to a court. Again, these issues are be

  Peri-operative beta blockade The last few years have seen increasing interest in the prophylactic use of beta-blockade to reduce peri-operative cardiac morbidity, particularly in patients at high risk for a cardiac event and undergoing major elective non-cardiac surgery. The target of this therapy is a heart rate of 70 beats/min and systolic BP of 110 mmHg – if tolerated by the patient. If the patient is not currently on beta-blockers, a cardioselective agent (atenolol or metoprolol) is recommended. Unless contra-indicated, this blockade should be initiated  as early as possible  and maintained throughout the hospitalization and after discharge (at least 30 days and probably longer). Antihypertensives Angiotensin-converting enzyme (ACE) inhibitors (and angiotensin II antagonists) have been linked to severe and refractory intra-operative hypotension under anesthesia. Unless the patient has very severe hypertension, many recommend discontinuation of these medications the day before sur

  Informed consent Up into the 1950s, anesthesia claimed about one life of every 2000 anesthetics given. Particularly during the last 30 years, the frequency of anesthesia-related complications leading to morbidity and mortality has decreased markedly, but unfortunately not to zero. No one knows the actual incidence of preventable anesthetic deaths; currently quoted numbers range from 1 in 20 000 to 1 in 200 000 anesthetics; a reasonable estimate probably lying somewhere in the middle of these figures Anesthetic risks are usually smaller than the risks associated with surgical interventions, but they loom large when general anesthesia or heavy sedation is required for a non-invasive and essentially risk-free diagnostic examination. For example, when a small child needs anesthesia to hold still for a CT scan or MRI study, anesthesia poses the only risks. Many drugs used in general anesthesia interfere with ventilation – think of respiratory depression from narcotics, surgical anesthesia

  Airway management We have made remarkable advances in techniques to secure a patent airway, and have developed new equipment and methods to monitor breathing. Yet, respiratory complications remain the leading cause of anesthesia-related deaths, with the majority related to failure to obtain control of the airway. Here we will discuss: (i) how to evaluate the airway of a patient; (ii) the impact of the planned procedure designed to protect the airway; and (iii) how to manage the airway. First, let us explain why all this matters. Any time we anesthetize a patient, we must be prepared to take over his ven-tilation at a moment’s (or less) notice because anesthesia can interfere with the patient’s ventilation in so many ways. We may have weakened, with muscle relax-ants, the patient’s ability to breathe. We may have put him into a deep coma, anesthetizing his respiratory center and relaxing the muscles in his mouth and pharynx so that his air passage is obstructed. We might have suppress

  Examination of the airway Direct laryngoscopy (see below) requires neck flexibility, a mouth that can open widely, and no excessive pharyngeal tissue or a large tongue to get in the way. These features cannot be measured directly, but the following steps help us to assess problems that might arise during laryngoscopy: ·             Assess mouth opening: inter-incisor distance should exceed 4 cm in an adult. ·             Determine the mentum–hyoid ( > 4 cm) or thyromental ( > 7 cm) distance: shorter distances suggest an anterior or very cephalad larynx, which would be difficult to visualize by laryngoscopy. ·             Investigate the posterior pharynx (modified Mallampati Classification) by hav-ing the sitting patient fully extend his neck, maximally open his mouth, and stick out his tongue with or without phonation. Figure  2.1 shows how we classify the visible structures. ·             Determine the ability to move lower in front of the upper incisors, which is a good sign

Mask–ventilation Simple as it seems, the ability to mask–ventilate a patient is  the  essential airway management technique that needs to be practised and learned by every health-care provider. Most important is the patient’s head position: Do not let the patient’s neck flex and thus potentially occlude the airway, which makes mask–ventilation difficult to impossible. Proper mask technique includes the following: (i)         Select an appropriate size mask to fit over the patient’s nose and mouth and provide an airtight seal without pressure on the eyes.   (ii)      Place the head in sniffing position (occiput elevated, neck extended) or directly supine, with the neck neutral to slightly extended.   (iii)    Positioning yourself at the patient’s head, apply the mask to the face with a pincer grip by thumb and index finger of the left hand. Place the third finger on the mentum and pull the chin upward. The fourth finger remains on the mandible so as not to compress the soft tissue, with

  Laryngeal mask airway Developed in the 1980s, the laryngeal mask airway (LMA; Fig.  2.3 ) has supplanted tracheal intubation for many general anesthetics. The device is basically the progeny of a facemask mated with an endotracheal tube, allowing positioning of the mask just above the glottic opening. While we have available a version intended to protect the airway from gastric aspiration (LMA Proseal®), none can guarantee it. The major advantages of the LMA over tracheal intubation are the lower level of skill required for placement, decreased airway trauma (especially of the vocal cords), and reduced stimulation such that lightly anesthetized, sponta-neously breathing patients can tolerate the device. Also, the properly positioned LMA places the laryngeal inlet in clear view for a fiberoptic scope, making tra-cheal intubation through the device a popular technique in the management of the difficult airway. To place the LMA, we induce anesthesia without paralysis, then 1.          p