ANESTHESIA BOARD REVIEW 2023 UPDATE

ANESTHESIA BOARD REVIEW 2023 UPDATE indications for OLV - INDICATIONS FOR ONE LUNG VENTILATION Absolute 1. Protective Isolation a. Massive Hemorrhage b. Infection 2. Control of Ventilation Distribution a. Bronchopleural or bronchopleural cutaneous fistula b. Giant cyst or bullae (risk of rupture with PPV) c. Major bronchial disruption or trauma 3. Unilateral Lung Lavage 4. VATS Relative (Strong) - Surgical Exposure 1. Thoracic aortic aneurysm 2. Pneumonectomy 3. Upper lobectomy Relative (Weak) - Surgical Exposure 1. Esophageal surgery 2. Middle and lower lobectomy 3. Thoracoscopy under general anesthesia fasting guidelines children - endocrine- diabetes - ...Complications of diabetes mellitus include coronary artery disease, cerebrovascular and peripheral vascular disease, autonomic and sensory neuropathies [cardiovascular and GI effects], and joint stiffness, all of which can affect the anesthetic. TMJ and cervical joint stiffness (due to glycosylation of tissue proteins) should be assessed, as 30% of diabetics have difficult intubations endocrine- diabetes - The most feared complication of diabetes is diabetic ketoacidosis (DKA), which is most commonly precipitated by an infection. DKA should be treated with fluid resuscitation, IV insulin (0.2 U/kg initially, 0.1 U/kg/hr after, goal is to decrease by 75-100 mg/dL or 10% per hour), and K+ supplementation (some, but not all, authors recommend bicarbonate if pH is 7.2) Autonomic neuropathy develops in ~ 1/3 of diabetics (50% of those with coexisting hypertension) and may manifest as orthostatic hypotension, reduced HR variability, baseline tachycardia (decreased inhibitory input), deep breathing, and prolonged QT interval. Patients with the above symptoms may be at increased risk for sudden death [Charlson ME et al. JACS 179: 1, 1994], and bradycardia non-responsive to atropine has been described in diabetic surgery patients [Burgos et al. Anesthesiology 70: 591, 1989] endocrine- diabetes - The gastrointestinal system may be affected as well, and patients with autonomic symptoms (ex. gastroparesis) should be considered at risk for pulmonary aspiration Diabetic patients may also be at increased risk for perioperative nerve injuries [Stoelting p. 439], although this has not been definitively established endocrine- thyroid - Most commonly caused by Graves' disease, most-often in women 20-40 years of age (0.2% incidence in parturients). Elective procedures should be deferred until the disease is well-controlled (B-blockers [inhibit peripheral conversion of T4 to T3 in addition to controlling heart rate, goal rate is 85 bpm], antithyroids [methimazole and propylthiouracil, both of which block synthesis of new thyroid hormones but do not affect release of existing hormone. Methimazole works more quickly and has less side effects], +/- iodine [blocks the actual release of thyroid hormone]) endocrine- thyroid - Preoperative evaluation should always include a neck exam, and in some cases, a CT scan. Hyperthyroid patients can be chronically hypovolemic and vasodilated and are prone to an exaggerated hypotensive response during induction of anesthesia, thus pay attention to volume status preoperatively endocrine- thyroid - When selecting (and using) a neuromuscular blocking (or any) drugs, one should be aware of two concerns - first, the potential for muscle weakness (and theoretical possibility of prolonged effect) and second, the potential for tachycardia with reversal Epinephrine and ephedrine should be used with caution endocrine- thyroid (storm) - Hyperthyroid storm (altered mental status, hyperthermia, tachycardia, CHF, shock, and dehydration) can occur intraoperatively but is most common 6-18 hours post-operatively and has a mortality rate of 10-75%. Treat with chilled crystalloid and an esmolol infusion [Thome AC and Bedford RF. Anesthesiology 71: 291, 1989]. Consider 100-200 mg cortisol for hypotension, as well as dexamethasone (inhibits T4-T3 conversion). Propylthiouracil (250-500 mg q6h PO or NG) and sodium iodide (1 g IV over 12 h) are often added, and charcoal, hemodialysis, and plasmapheresis have also been tried endocrine- thyroid (post op complications) - Complications of thyroid surgery include damage to laryngeal nerves, tracheal compression, and hypoparathyoidism. The superior laryngeal nerves supply motors to the cricothyroid muscles (only), as well as supraglottic sensation. The recurrent larnyngeals supply all other muscles in the larynx as well as infraglottic sensation. As patients to say "eeeee" in order to assess these muscles. Tracheal compression is often due to hematoma formation. Hypoparathyroidism is due to surgical removal, and can manifest early as one hour after surgery (stridor, laryngospasm, tingling) endocrine- hypothyroid - Severe, symptomatic hypothyroidism can cause myxedema coma, pericardial effusion, and heart failure - if any of these are present, elective operations should be delayed until thyroid replacement has been initiated and is adequate. That said, mild to moderate hypothyroidism is not an absolute contraindication to surgery Hypothyroid patients require less preoperative sedation and are prone to drug-induced respiratory depression, thus consider benadryl for sedation, as well as metoclopramide for gastric-emptying (which is slowed). Euthyroid patients may receive their usual dose of thyroid medication on the morning of surgery (remember, however, the t½ of T4 is about 8 days). endocrine- hypothyroid - Hypothyroid patients, who have diminished cardiac output, blunted baroreceptor reflexes, and decreased intravascular volume, are at risk for severe hypotension. Induction may be best accomplished with ketamine. Consider pancuronium as a paralytic agent (chronotropic effects). Intubation may be compliated by a large tongue Do NOT give volatile anesthetics to hypothyroid patients, as they are at risk for severe myocardial depression. Instead, consider nitrous oxide plus intravenous agents (ex. benzodiazepines). There no evidence that hypothyroid patients have reduced MAC requirements. Monitoring should focus on temperature control and cardiac output (i.e. avoiding congestive heart failure). In cases of refractory hypotension, one should always be cognizant of the possibility of acute adrenal failure Recovery from general anesthesia may be delayed by hypothermia, respiratory depression, or slowed drug biotransformation, and hypothyroid patients often require prolonged mechanical ventilation. Because of the risk for respiratory depression, opiates may need to be avoided in favor of ketorolac for postoperative analgesia pediatrics- basics - black bag on circuit, latex-free IV setup (clear masks are OK, as are ETT, LMA, and pink tape) Warm the room Peds Bear hugger Overhead Warming lights Age appropriate headrest and monitors IV setup in room Ventral supports: improved lung volumes, oxygenation, and compliance, esp in obese patients6 Ventilation and perfusion are more uniform in prone position → ↓ V/Q mismatch → Improved oxygenation7 prone position - hemodynamic response to prone position ↓Stroke volume, ↓ Cardiac index ↑SVR, ↑PVR HR, PAOP, Right atrial pressure: no change Recommend invasive hemodynamic monitors in patients with precarious cardiovascular status POVL - prone position, nerve injury - Mechanisms ↑ stretch, compression → ischemia Occur despite adequate protection1,12 → other factors? Prone patient Supraorbital, facial, mandibular nerves Brachial plexus and its peripheral components perioperative nerve injury - Neurovascular compromise: •Compression or stretching of intraneural vasa nervorum - neural ischemia •Nerve has a long or superficial course between two points of fixation •Stretching and compression combined - worst •Tissue edema from IV fluid may contribute to neurovascular compression Coexisting medical problems which may contribute to injury: •Diabetes mellitus Uremia •Alcohol abuse Polycythemia vera •Vitamin deficiency Acromegaly •Coagulopathy/ Hypothermia Hypothyroidism perioperative nerve injury, mgmt - • Determine if sensory or motor (sensory is usually transient) • Avoid stretch and recheck in 5 days • Contact patient frequently • If persistent after 5 days- neurology consult Nerve conduction studies EMG If motor, do consult immediately beach chair - Advantages Decreased incidence of brachial plexus injuries vs. lateral decubitus Better surgical exposure Problems Decreased MAP, CVP, PAOP, SV, CO, PaO2 Increased PVR, TPR beach chair - Compensation While Awake: SVR increases 50-80% BP unchanged, or slightly increases CPP (cerebral perfusion pressure) decreases ~15% Spontaneous ventilation --> improved venous return from cerebral circulation Under Anesthesia: Vasodilation prevents SVR increase BP decreases CPP may decrease MORE than 15% due to vasodilation, impaired venous return Positive pressure ventilation --> impaired venous return from cerebral circulation Position-related IJ compression --> impaired venous return from cerebral circulation beach chair - Cerebral Autoregulation, Perfusion Usual teaching: CBF constant with MAP 50-150mmHg Autoregulatory range shifts upward with h/o HTN Better minimum MAP may be a range: 70-93mmHg, with a mean of 80 +/- 8 mmHg MAP at brain in sitting position very different from arm NIBP: MAP at brain is actually lower by the pressure gradient between site of BP measure (e.g., arm) and brain. If using ABP, set transducer at level somewhere between external auditory meatus (base of brain) and top of head (most cephalic portion of cerebral cortex). To estimate, subtract 1mmHg per 1.25 cm (or 0.77mgHg decrease per cm) above top of BP cuff Positioning: Avoid compression/obstruction of major vessels (arteries and veins) of the neck Gas embolism can also cause hypotension and generalized circulatory instability preop thoracic - You should always evaluate the patient to determine whether he could withstand pneumonectomy even if radiologically only a lobectomy or limited resection is contemplated. On thoracotomy, a surgeon may be forced to do pneumonectomy because of an unexpected node over the pulmonary artery. If you have decided the patient cannot withstand pneumonectomy, this should be addressed with the surgeon ahead of thoracotomy. Step 1: Routine PFTs. If the patient meets the following criteria, no further workup is necessary: FEV1 > 2 liters FEV1/FVC > 50% MVV > 50% of predicted RV/TLC <50% preop thoracic - Step 2: If the patient does not meet the above criteria on routine PFT, and if the FEV1 volume is less than 2 liter, we need to perform split lung function testing. Lungs with tumor may not be contributing to total FEV1 volume and thus... Continues...