Anesthesia Exam Notes PDF

# Anesthesiology - Goals and Objectives ## Goals The goal of the elective rotation through anesthesiology for the medical student is to introduce them to the perioperative practice and concerns of the anesthesiologist. Regardless of the specialty into which the students may eventually enter, as ph...

# Anesthesiology - Goals and Objectives ## Goals The goal of the elective rotation through anesthesiology for the medical student is to introduce them to the perioperative practice and concerns of the anesthesiologist. Regardless of the specialty into which the students may eventually enter, as physicians, they will care for patients who will undergo a procedure requiring anesthesia at some time in their career and may be asked to participate in the patient's preoperative evaluation and postoperative care. In addition to direct patient care, the use of simulators for both education and clinical evaluation will be utilized. ## Objectives By the end of the rotation in anesthesiology, the student will understand and perform or observe: ### A. Preoperative Patient Evaluation 1. Knowledge of the planned surgery and associated anesthetic concerns including the appropriate choice of anesthesia 2. Medical and surgical history, with specific emphasis on the cardiac and pulmonary histories; allergies and medications 3. Physical examination, including airway evaluation 4. Time of last oral intake on the day of anesthesia and why this is important 5. Assessment of appropriate labs, consults and other studies 6. ASA (American Society of Anesthesiology) Physical Status Classification 7. Informed consent ### B. Intraoperative Care 1. Airway Management - the student should gain experience with bag and mask ventilation, the use of oral and nasal airways, laryngoscopy and tracheal intubation, and placement of laryngeal mask airways. Glidescope, fiberoptic intubation, or other airway devices may also be observed but not performed. Experience will be gained through the use of mannequins, simulators, and direct patient care. Knowledge of pulmonary aspiration and its therapy is also required. 2. General anesthesia – the student should understand the components of general anesthesia and identify the names of intravenous and inhalational anesthetics, neuromuscular blocking agents, narcotics and sedative-hypnotics. The student will learn about the signs, symptoms and treatment of malignant hyperthermia. 3. Regional anesthesia including spinal and epidural anesthesia – the student will learn about techniques, indications, complications and contraindications, and learn about local anesthetics. 4. Intravenous catheter insertion - the student should understand how to choose the site and size of IV catheters and gain experience with their insertion, understand aseptic technique and universal precautions. 5. Arterial catheter insertion - the student should become familiar with the indications, complications and techniques for arterial catheterization. Most will not have the opportunity to perform actual arterial punctures on patients. 6. Central venous catheter insertion - the student should become familiar with the indications, complications and techniques of central venous catheter insertion including the use of the Site Rite, an ultra-sound device used to identify the vascular structures in the neck. Most will have the opportunity to observe but not perform central venous catheter insertion. 7. Pulmonary artery catheter insertion - the student should become familiar with the indications, complications and techniques of pulmonary artery catheterization. Most will have the opportunity to observe but not perform pulmonary artery catheter insertion during their time in cardiac surgery. 8. Monitoring - the student should be able to identify and understand routine anesthesia monitors used to assess ventilation, oxygenation, circulation and temperature. Additional monitors are used to assess neuromuscular blockade and anesthesia depth. 9. Fluid and transfusion therapy - the student should understand intraoperative fluid management and blood transfusion, including transfusion reactions and other complications. ### C. Post-operative Anesthesia Care 1. The student should understand continued emergence issues in the post anesthesia care unit (PACU). 2. The student should understand the two phases of recovery. 3. The student should understand acute pain management, including narcotic administration and the use of nerve blocks including but not limited to epidural catheters, femoral, interscalene, popliteal and axillary nerve blocks. 4. The student should understand the management of respiratory complications in the PACU including airway obstruction, hypoventilation and hypoxemia. 5. The student should understand the management of circulatory complications in the PACU, including hypotension, hypertension, and dysrhythmias. 6. The student will learn about discharge criteria from the PACU. # Preoperative Evaluation of Patients ## I. Introduction As a perioperative physician, the anesthesiologist must be fully able to evaluate a patient medically, with a full understanding of that patient's impending procedure together with the patient's medical history. Many patients are seen in the preadmission testing centers days before planned surgery or patients may be seen the night before surgery if they are inpatients or minutes before surgery in emergencies. In any case, the preoperative evaluation must include key elements. ## II. Preoperative History A. Establish the patient's problems/diagnosis and the planned procedure. B. Medical history with an emphasis on the cardiovascular, pulmonary, endocrine, hepatic, renal, and neurologic function. (See below for details of the cardiac and pulmonary evaluations) C. Prior surgery and anesthetics including any complications D. Family history of problems with anesthesia to uncover possible history of Malignant Hyperthermia. E. Allergies - distinguish between true allergies and drug intolerances/side effects F. Medications - including herbal therapeutics G. Social Habits - Smoking, ETOH, illicit drugs H. NPO status - nothing per os (last oral intake of fluids and/or solids. ### 1. Cardiac and Pulmonary Evaluations #### 1. Preoperative Cardiac Evaluation - The goal of the preoperative cardiac evaluation is to identify patients at risk for developing perioperative cardiac complications so that steps can be taken to reduce this risk. - Major perioperative cardiac complications include: death, myocardial infarction, congestive heart failure, pulmonary edema, and cardiac arrhythmias. - Perioperative myocardial ischemia also occurs frequently in patients with a history of coronary artery disease, most commonly in the postoperative period. - Patient characteristics have been consistently shown to be associated with a higher incidence of postoperative cardiac complications. These risk factors include the following: history of congestive heart failure, history of coronary artery disease (particularly following a recent myocardial infarction), and advanced age. In general, the more severe the cardiac disease, the higher the likelihood of perioperative cardiac complications. - Not all operations are associated with the same level of risk. High-risk procedures include: major emergency operations (especially in the elderly), aortic and other major vascular surgery, peripheral vascular surgery, and anticipated prolonged surgical procedures associated with large fluid shifts and/or blood loss. #### 2. Preoperative Pulmonary Evaluation - Significant alterations in pulmonary function occur following surgery in both patients with normal lung function and patients with pre-existing pulmonary disease. The goal of the preoperative evaluation is to identify those patients at greatest risk of adverse pulmonary outcomes and to institute preventative measures in the perioperative period designed to minimize these complications. - Bronchospasm may occur during induction of anesthesia or at any time during the anesthetic or postoperatively. Profound bronchospasm may result in the inability to ventilate the patient and result in a life-threatening situation. Patients at major risk of developing bronchospasm include those with a history of: reactive airway disease (with significant history of wheezing), recent upper respiratory infection, and significant prior smoking history (greater than 20 pack-years). Hypoxemia usually develops in patients with preexisting lung disease, most commonly obstructive lung disease. - Major pulmonary complications include: atelectasis, infection, and respiratory failure with prolonged mechanical ventilation. - Alterations in pulmonary function which may lead to major pulmonary complications are the result of a reduction in lung defense mechanisms, alterations in diaphragmatic function, and alterations in lung volumes following certain types of operations and alterations in gas exchange. - Lung defense mechanisms are impaired secondary to: reduced ciliary motility secondary to volatile anesthetic gases, intubation, hyperoxic gas mixtures, and inhalation of cold, dry gas; alterations in mucous production, with both increased quantity and viscosity of secretions; and impaired cough reflexes. - Alterations in diaphragmatic function may be profound in patients undergoing upper abdominal surgery and may last for one week or more. - Alterations in gas exchange occur commonly and are due to multiple factors including: ventilation-perfusion mismatch (areas of lung which are hypoventilated but perfused), intra-pulmonary shunting (areas of totally non-ventilated but perfused lung), alveolar hypoventilation (secondary to effects of anesthetics), and reduction in mixed venous O2. Most of these changes occur acutely and resolve within 24 hours following superficial surgery but may persist for days following upper abdominal or thoracic surgery. - Risk factors for postoperative pulmonary complications include: smoking history, independent of its association with COPD, upper respiratory infection, starvation malnutrition and COPD. - Pulmonary function tests are not predictive of postoperative morbidity except in lung resectional surgery. A good history and physical is the most important preoperative pulmonary evaluation. Only patients with obstructive lung disease have been shown unequivocally to be at increased risk postoperatively. The risks associated with restrictive lung diseases or pulmonary hypertension is unknown. - Significant physical findings would be signs of acute airflow obstruction and increased secretions, specifically, wheezing and rhonchi. Screening CXR’s are rarely of benefit in the absence of abnormal history or physical findings. ## III. Physical Exam A. measurement of vital signs B. overall observation of the patient as it may relate to the positioning of the patient C. heart D. lungs E. abbreviated neurological exam when regional anesthesia is considered F. airway examination 1. Dentition - inspect for loose or chipped teeth, presence of caps, bridges, or dentures 2. Airway Evaluation - extremely important! Anatomy which is associated with anticipated difficult airway includes: limited neck extension, limited temporomandibular joint mobility, short neck, large tongue and micrognathia. - The Mallampati scale² was developed to classify the upper airway in terms of size the tongue and the pharyngeal structures visible upon mouth opening. While sitting, the patient is asked to open his/her mouth and protrude their tongue.  Class I: soft palate, fauces, uvula, pillars Class II: soft palate, fauces, portion of uvula Class III: soft palate, base of uvula Class IV: hard palate only ## III. Laboratory Examination A. Routine labs for healthy asymptomatic patients are no longer recommended. Labs should be obtained based on history and physical findings. B. Labs may also be obtained based on the anticipated procedure, e.g. a baseline' hemoglobin/hematocrit should be obtained prior to surgery which is expected to have a significant blood loss. C. Pregnancy tests are sometimes routinely done in woman of childbearing age to prevent exposure to potentially teratogenic anesthetics in the first trimester. D. Additional recommended studies include an EKG for those over 40 years old regardless of the health of the patient because of the increasing prevalence of CAD in this age group. E. Routine coagulation studies and urinalysis are not cost effective in asymptomatic, healthy patients. ## IV. ASA (American Society of Anesthesiologists) Physical Status Classification A. This classification was developed not to assign risk but used to describe the overall condition of the patient based on their physical condition, independent of the planned operation. - PS-1 A normal, healthy person - PS-2 A patient with mild systemic disease (no functional limitation) e.g. hypertension, controlled diabetes without end-organ involvement, extremes of age, obesity, smoker. - PS-3 A patient with severe systemic disease which results in functional limitation, e.g. poorly controlled hypertension, diabetes with end-organ involvement such as vascular compromise, angina, prior myocardial infarction, pulmonary disease, which limits activity. - PS-4 A patient with severe systemic disease which is a constant threat to life, e.g. congestive heart failure, history of recent myocardial infarction, unstable angina, advanced pulmonary disease, renal or hepatic dysfunction, diabetes with end organ dysfunction. - PS-5 A moribound patient who is not expected to survive without the operation, e.g. a ruptured abdominal aneurysm, pulmonary embolus, head injury with increased intracranial pressure. - PS-6 A declared brain-dead person whose organs are being removed for donor purposes. - E Any patient in whom an emergency operation is required. 2 (E should be added to the PS class when it is an emergency) ## V. Informed Consent A. The patient must be given a reasonable explanation of the options available for the anesthetic management: general, regional, local or topical anesthesia; intravenous sedation; or a combination of local and sedation. MAC is "monitored anesthesia care", previously called local standby, is just monitoring by the anesthesiologist or nurse anesthetist or more often, monitoring plus sedation while the surgeon uses local infiltration. Regardless of the chosen technique, consent must always be obtained. Not all risks need to be detailed but only those that are most likely to be of concern for similar patients having similar procedures. B. Patient questions should be answered. C. An explanation of what to expect should also be routine. 1. Stoelting and Miller, Basics of Anesthesia (Philadelphia: Churchill Livingstone, 2000), 111 2. Stoelting and Miller, Basics of Anesthesia (Philadelphia: Churchill Livingstone, 2000), 114 # General Anesthesia ## I. What is General Anesthesia? "the sleeplike state that makes painless surgery possible" (Oliver Wendell Holmes, 1846) ## II. Four Components of General Anesthesia (GA) A. Unconsciousness B. Amnesia C. Analgesia D. Muscle relaxation ## III. Three Phases of GA – Induction, Maintenance and Emergence A. Induction - the transition from the awake state to unconsciousness. There are two methods of induction including intravenous and inhalation. 1. Intravenous induction - administering an intravenous bolus of an anesthetic agent such as propofol to render a patient unconscious. 2. Inhalational induction – having a patient breathe a potent inhaled anesthetic, such as sevoflurane to render a patient unconscious. This method is used most often in pediatric anesthesia and for adults with needle phobias. 3. Inhalational inductions take longer than intravenous (1-2 minutes vs. 20-30 seconds) B. Airway Management - an essential skill for the anesthesiologist a. the airway includes structures that lie between the alveoli of the lungs and the atmosphere b. respiratory gases enter the airway by way of the nose or mouth before passing through the pharynx c. All anesthetic agents produce a dose dependent respiratory depression that can lead to apnea. If untreated, apnea rapidly leads to hypoxemia, which, if prolonged, can produce significant patient morbidity and mortality. 1. Central apnea results from the respiratory depressant effects of anesthetic agents on the respiratory centers of the cerebral medulla. Induction of anesthesia almost always causes central apnea, which is diagnosed by the absence of respiratory effort in the part of the patient. Treatment includes ventilation with bag and mask, tracheal intubation, or reversal of the agent causing the central apnea. A laryngeal mask airway (LMA) can also be placed and the patient is then allowed to resume spontaneous ventilation. 2. Obstructive apnea occurs when gas flow into the alveoli is impeded by mechanical obstruction of the airway. Airway obstruction is most commonly caused by the tongue occluding the pharynx. a. Other causes of airway obstruction include malignancies of the pharynx, larynx, or trachea, foreign bodies, laryngospasm, mucous plugging, and bronchospasm. b. Obstructive apnea is treated by relieving the obstruction c. Airway obstruction can be relieved by neck extension, chin lift, jaw thrust, or placement of either an oral or nasal airway. Oral and nasal airways provide a physical separation between the tongue and palate or pharynx, which provides a channel for the passage of respiratory gases. d. Ventilation - because respiratory depression and apnea are common during anesthesia, evaluating a patient's airway is of paramount importance to help identify those patients who will be difficult to mask ventilate or difficult to intubate. Rarely (0.0001 -0.02%), a patient will be impossible to either ventilate or intubate. Identifying this group is necessary to avoid an airway disaster. Difficulty with mask ventilation can sometimes occur. 1. Common causes of difficult mask ventilation include obesity, history of sleep apnea, maxillofacial trauma, pathology of the pharynx and larynx, and the presence of a large tongue. Preoperatively, patients should be asked about difficulty with prior anesthetics, history of sleep apnea, and the presence of airway pathology. e. The laryngeal mask airway (LMA) is placed in the hypopharynx and does not protect the lungs from aspiration. Limit peak airway pressure during bag ventilation to less than 25 cmH2O to avoid gastric distention. f. Tracheal intubation involves placing an endotracheal tube into the trachea via either the mouth or nose. Intubation is usually performed by inserting a laryngoscope into the mouth, displacing the tongue into the submandibular space to expose the vocal cords, and placing the endotracheal tube into the trachea. As with mask ventilation, intubation can be very easy or impossible. 1. Laryngoscopic views - graded from grades I - IV. Grade I view (80-95%) – exposes the entire laryngeal aperture Grade II view (1-4%) – allows exposure of just the posterior portion of the laryngeal aperture but usually allows a successful intubation. Grade III view (0.05 -0.035%) – exposes only the epiglottis Grade IV view (0.0001 – 0.02%) – exposes only the soft palate  2. Other alternative methods of endotracheal intubation may include the use of a bougie, light wands, Glidescope, fiberoptic scopes, and intubating LMAs. 3. The two most common laryngoscope blades used are the Miller and MacIntosh (MAC). C. Maintenance - the time from induction to emergence. Multiple drugs may be used to maintain the components of general anesthetics including a pure inhalational agent with or without the addition of other IV drugs to potentiate the 4 components of general anesthesia already provided by the inhalational agent. D. Emergence - transition from the anesthetic state to the awake state upon completion of the surgery. If intubated (breathing tube placed in the trachea) for the surgery, the patient is the extubated (breathing tube removed from the trachea) once they are awake enough to follow simple commands, have adequate minute ventilation and demonstrate adequate muscle strength. ## IV. Pharmacology A. Pharmacokinetics - "what the body does to the drug" including uptake, distribution and elimination by metabolism or excretion. The volume of distribution equals the amount of drug in the body divided by the plasma drug concentration. After the initial bolus of drug, the plasma drug level decreases due to redistribution of the drug from organs with high blood flow (heart, brain, kidney) to tissues that have a large mass relative to their blood flow (muscle and fat). Half-life is the time required for the drug plasma concentration to decrease by 50%. Elimination rate is the rate at which the drug is eliminated from the body per unit of time. B. Pharmacodynamics - "what the drug does to the body" as demonstrated by the dose-response relationship. The desire site of action of anesthetic agents is the brain. Drugs must cross the blood-brain barrier to reach the receptors to produce their effects. Lipid-soluble drugs cross the blood-brain barrier more rapidly than water-soluble drugs and therefore have a more rapid onset of action and a more rapid of effect. ## V. Inhalational (Volatile) Anesthetics A. Volatile Anesthetics (VA) - include halothane, enflurane, isoflurane and nitrous oxide (N2O). VAs are liquids at room temperature and converted to gases through the use of agent-specific vaporizers. B. МАС - "Minimal Alveolar Concentration" is the alveolar concentration that prevents movement in 50% of patients in response to a standardized stimulus (e.g. surgical incision). The higher the MAC, the less potent the volatile agent. Therefore, halothane is the most potent with a MAC of 0.75% and desflurane is the least potent with a MAC of 6%. MAC values are expressed as a percentage of 1 atm. Listed are the MAC values for the common volatile anesthetics. 1. Halothane 0.75 2. Isoflurane 1.2 3. Sevoflurane 2.0 4. Desflurane 6.0 5. Nitrous Oxide 105 C. Characteristics - all volatile anesthetics are dose-dependent respiratory depressants and can trigger malignant hyperthermia in susceptible patients. ## VI. Intravenous Anesthetics A. Propofol – the most commonly used IV anesthetic, replacing thiopental (Pentothal), which is still used by many primarily in obstetrics. Propofol requires the use of a sterile technique when preparing it and may cause pain on injection. It is preferred in outpatient anesthesia because it causes less nausea and vomiting. As with thiopental, propofol produces a decrease in blood pressure. It can be used as a sedative and as a general anesthetic. B. Etomidate - used in hemodynamically unstable patients for induction because it has minimal hemodynamic effects. It is used just for induction of anesthesia because repeated doses can cause adrenal suppression. Like propofol, etomidate can cause pain on injection. C. Ketamine - stimulates the sympathetic nervous system and is the only intravenous agent that can cause an increase in blood pressure and heart rate. Ketamine can produce post-op hallucinations and excessive salivation. D. Midazolam (Versed) is mainly used as an anxiolytic agent administered prior to the induction of anesthesia, but can also be used as an induction agent rarely. It produces antero-grade amnesia, not retrograde. ## V. Opioids A. Most common opioids used in anesthesia are: fentanyl, morphine, sufentanil, alfentanil, remifentanil, hydromorphone and meperidine. B. Mechanism of action - opioids produce analgesia by binding to opioid receptors, of which there are 4 types: mu, kappa, delta and sigma. Opioids are predominantly mu receptor agonist. Although both opioid agonists and antagonists bind to opioid receptors, only agonists are capable of receptor activation. Opiate-receptor activation inhibits the presynaptic release and postsynaptic response to excitatory neurotransmitters (e.g. acetylcholine and substance P) C. Side effects - includes dose-dependent respiratory depression, bradycardia, increased incidence of nausea and vomiting, spasm of the sphincter of Oddi, and chest wall rigidity. D. Naloxone (Narcan) – a pure opioid antagonist, used to reverse the effects of opioids including respiratory depression. ## VI. Neuromuscular Blocking Agents (NMBA) or Muscle Relaxants A. NMBA are used to facilitate tracheal intubation, improve surgical exposure and operating conditions and prevent patient movement. NMBA bind to the acetylcholine (Ach) receptors located at the post-synaptic nerve terminals of skeletal muscle, preventing Ach from binding the receptors and therefore they prevent muscle contraction. B. Two classes of NMBA a. Depolarizing agent - Succinylcholine 1. Succinylcholine is the only depolarizing muscle relaxant in clinical use 2. It has the most rapid onset of action (30-60 sec.) and the shortest duration of action (5-10 min) and is used mostly in rapid sequence inductions. 3. Action is terminated by diffusion away from the neuromuscular junction. It is metabolized in the plasma by pseudocholinesterase. 4. Succinylcholine can induce malignant hyperthermia. 5. Succinylcholine should not be used in patients with a recent history of stroke or spinal cord history, myopathy or burns because it may precipitate hyperkalemia and cardiac arrest. 6. Succinylcholine is an agonist b. Non-depolarizing agents - curare, pancuronium, vecuronium, atracurium, cisatracurium, rocuronium and mivacurium 1. Non-depolarizing agents are competitive antagonists and therefore function as inhibitors. 2. These agents can be reversed by administering an cholinesterase inhibitor, also called an anticholinesterase (e.g. neostigmine and edrophonium), which prevents the degradations of acetylcholine (Ach), thereby making more Ach available at the neuromuscular junction to compete with the NMBA 3. Although the anticholinesterase is given to increase Ach availability at the nicotinic receptors of skeletal muscle, it will also affect muscarinic receptors, particularly at the heart causing vagal-like bradycardia that can progress to sinus arrest. This effect is minimized by the concomitant administration of an anticholinergic (e.g. atropine or glycopyrrolate) C. Peripheral Nerve Stimulator – used to monitor the degree of paralysis. (See Monitors) ## VII. Malignant Hyperthermia (MH) - is a rare, inherited myopathy characterized by an acute hypermetabolic state within muscle tissue following the induction of general anesthesia. There is an abnormality in the reuptake of calcium by the endoplasmic reticulum resulting in sustained muscle contraction and hypermetabolism, with metabolic acidosis, tachycardia, hypercarbia, hypoxemia and hyperthermia. One may also see cyanosis, muscle rigidity and arrhythmias. Anesthetic agents which may trigger MH include all volatile agents and Succinylcholine. If it occurs, the triggering agent must be stopped and Dantrolene must be given. # Monitoring ## 1. Routine Monitors ### A. Electrocardiography (ECG) - represents the sum of the electrical vectors taking place during depolarization and repolarization of the heart. Leads most commonly monitored are II and V5 in a five lead configuration. 1. Lead II is used for monitoring the atria, P waves, rhythm disturbances and inferior wall ischemia. 2. Lead V5, which lies in the 5th intercostal space of the anterior axillary line, is useful for detecting anterior and lateral wall ischemia 3. Disorders which can be detected by ECG intraoperatively: ischemia, dysrhythmias, electrolyte abnormalities, infarctions, chamber hypertrophy, drug toxicity, pacemaker malfunction, and conduction abnormalities ### B. Pulse Oximeter 1. Pulse oximetry uses absorption differences in oxygenated/deoxygenated blood to provide a noninvasive, continuous, intraoperative approximation of arterial oxygenation. 2. Oxyhemoglobin absorbs more light at 960nm, while deoxyhemoglobin absorbs more light at 660 nm (Lambert-Beer Law). An oximetry probe, which consists of a constant light source and a light receiver (photodiode), is placed on a body location, which receives pulsatile blood flow (i.e. finger or an ear lobe). Depending on the patient's SaO2, some light will be absorbed, microprocessors compute SpO2. PaO2 is then surmised accordingly. 3. Pulse oximetry tends to be inaccurate at low arterial oxygen saturations and demonstrates a noticeable lag time following a rapid change in SaO2. Inaccuracies also occur with patient shivering, digital nerve block, ambient light, motion, methylene blue administration, methemoglobinemia, carboxyhemoglobin, hypothermia, and low perfusion. 4. Pulse oximetry is inexpensive, noninvasive and can be an invaluable aid in quickly detecting early hypoxia.  PaO2 is the partial pressure of oxygen in arterial blood. The oxyhemoglobin dissociation curve is sigmoidal shape and relates PaO2 to oxyhemoglobin saturation. The normal adult P50 is the PO2 at which hemoglobin is 50% saturated and equals 26.8 mmHg. Normal PaO2 of about 100 mmHg results in an O2 saturation of about 98%. The steeper part of the curve shows that as saturation decreases there is a marked decrease in the PaO2. ### C. Capnography 1. Capnography provides a graphical and numerical determination of end tidal carbon dioxide (ETCO2) concentration of expired and inspired gases. 2. Capnography helps confirm adequate ventilation of sedated/anesthetized patients by continuously sampling breathing circuit gases. 3. Capnography has multiple clinical uses: a. It is the gold standard for endotracheal tube placement confirmation. b. The stomach may contain a limited amount of CO2 from swallowed expired air or mask ventilation so the endotracheal tube placement confirmation may require three or four breaths to "wash out" trapped gastric CO2. The clinician's inability to recognize an esophageal intubation can have a catastrophic outcome. c. A reliable monitor of ventilator controlled decrease of PaCO2 in the setting of increased intracranial pressure. d. A sudden reduction/ elimination of ETCO2 may indicate severe bronchospasm, cardiac arrest, lowered cardiac output, pulmonary embolism, breathing circuit disconnect, venous air embolism, mucous plug, V/Q mismatch and increased dead space. e. The shape of the curve provides information on pulmonary pathology (asthma, COPD), equipment failure (incompetent valves, exhausted CO2 absorbent, spontaneous respiratory effort by the patient. ### D. Arterial Blood Pressure 1. providing an anesthetic is an absolute indication for arterial blood pressure monitoring 2. Mean Arterial Pressure (MAP)=Systolic BP + 2(Diastolic BP)/3 3. BP should be checked every 3-5 minutes intraop and every 10-15 minutes in the PACU 4. Two types of noninvasive blood pressure monitoring a. Ausculatory method - using a BP cuff and stethoscope b. Oscillometric method - an automatic cuff used in the OR 5. Invasive arterial blood pressure monitoring a. Indications - elective hypotension, anticipation of wide intraoperative blood pressure swings or large fluid shifts, end-organ disease or surgery necessitating precise beat to beat blood pressure regulation, need for multiple arterial blood gases or other labs, inability to use noninvasive BP monitors. b. Complications - ischemia to the hand/digits, loss of digits, hematoma, thrombosis, infection, skin necrosis, embolization of plaque or air bubbles, bleeding and accidental intra-arterial drug injection. c. Cannulation sites - radial (most commonly used), ulnar, brachial, axillary, femoral, dorsalis pedis and posterior tibial arteries. ### E. Temperature 1. Temperature monitoring aids in the maintenance of appropriate body temperature during all anesthetics. 2. Sites - esophageal, nasopharynx, skin, rectum, bladder, pulmonary artery catheter. 3. Definition of hypothermia - body temperature less than 36 degrees Celsius. 4. Complications of hypothermia - dysrhythmias, increased peripheral vascular resistance, coagulopathy, poor wound healing, decreased drug metabolism, leftward shift of the hemoglobin-oxygen saturation curve, and delayed awakening from general anesthesia. ## II. Additional Monitors ### A. Peripheral Nerve Stimulator (Twitch Monitor) 1. Since there is a considerable variation in a patient's sensitivity to muscle relaxants, a nerve stimulator is an excellent, non-invasive monitor to evaluate the extent of muscle relaxation. 2. Indications – to assess adequacy of paralysis prior to direct laryngoscopy, to assess adequacy of paralysis and appropriate amount of NMBA during surgery and to ensure adequacy of recovery of neuromuscular function prior to extubation. 3. Two electrodes are placed over the ulnar or facial nerve, usually and four twitches are delivered (called a train-of-four). Unparalyzed patients have all four twitches of equal intensity. Following the administration of a non-depolarizing NMBA, patients become paralyzed and the twitches are lost or decrease in intensity. Patients should be maintained so that they have 1 or 2 of the four twitches during general anesthesia. ### B. BIS (Bispectral Index) Monitor 1. The incidence of intraoperative awareness is judged to be about 1 in 500. The BIS monitor processes the patient's EEG activity and converts it to a single number, which represents the patient's state of awareness. The scale is from 0 to 100, where 100 represents the awake state and 0 represents the absence of brain activity. Numbers between 40 and 60 are considered optimal for a health patient undergoing routine general anesthesia and surgery. 2. The BIS is most useful in situations where there would be a greater possibility of intraoperative awareness, such as trauma, obstetrics, and cardiac surgery. It is not considered the gold standard to prevent intraoperative awareness. ### C. Central Venous Pressure 1. Indications – for guiding fluid replacement in patients with hypovolemia or shock, infusion of any irritating IV drugs, TPN, aspiration of air emboli, placement of pacemakers and venous access in patients with poor peripheral venous access. 2. Sites for central venous access - Subclavian, internal jugular, femoral, and external jugular veins. 3. Contraindications - coagulopathy or ipsilateral carotid endarterectomy 4. Complications - pneumothorax, hemothorax, air embolism, infection, vascular damage, hematoma formation, dysrhythmias. ### D. Pulmonary Artery Pressure 1. Indications - controversial, the effectiveness of this monitor remains mostly unproven in many groups of surgical patients. Consider its use whenever the cardiac index, preload, volume status, or the degree of mixed venous blood oxygenation needs to be known, particularly in patients in which these parameters may be important in situations of high risk for hemodynamic instability (e.g. recent MI, aortic aneurysm repair) 2. Contraindications same as for central venous plus LBBB, Wolff-Parkinson-White syndrome, pulmonary artery rupture, severe dysrhythmias, and pulmonary infarction. ### E. Urinary Output 1. Indications - patients with CHF and shock, lengthy surgeries and surgeries with anticipated large fluid shifts. 2. Urine output should be roughly 0.5 to 1 ml/kg/hr. 3. Possible causes of decreased urinary output would include: pre-renal (e.g. dehydration, low cardiac output), renal (e.g., chronic renal failure) and post-renal (e.g., obstruction of the urinary catheter). # Fluid and Transfusion Therapy 1. Intravenous fluids can be divided into two general categories: crystalloid and colloid solutions. ### A. Cryst