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Administer General Anesthesia

This article, directed at medical students, aims to summarize the steps involved in the administration of general anesthesia.


Steps
  1. Identify Clinical Considerations. Review the history, physical examination and laboratory results to identify the principal clinical considerations for the patient (e.g. limited mouth opening, hypertension, angina, asthma, anemia, etc.). Assign an ASA physical status to the patient. Sometimes just one or two sentences will do the job: Mr. Desai is an otherwise healthy ASA II 81 kg 46 year old man with chronic anemia (hematocrit = 0.29) and controlled hypertension (atenolol 25 mg BID) who is scheduled for a partial colectomy under general anesthesia. He has no allergies and his functional enquiry is negative.
  2. Consultations. Ensure that all required consultations have been done (e.g. diabetic patients may need an endocrinology consult; patients with myasthenia gravis will need a neurology consult). Here are some more random situations where formal or informal consultation may be appropriate: Recent myocardial infarction, Poor left ventricular function (reduced ejection fraction), pulmonary hypertension' metabolic derangements such as severe hyperkalemia, uncontrolled severe hypertension, mitral or aortic stenosis, pheochromocytoma, patients with coagulopathies, patients with a suspected difficult airway
  3. Airway Assessment. Assess the patient's airway using the Mallampati system and examining the patient’s oropharynx. Consider also other criteria (degree of mouth opening, head flexion /extension, jaw size, “mandibular space”). Take a good look for any loose, false or capped teeth. Warn patients with poor dentition that intubation carries a risk of chipped or loosened teeth. Determine if special airway management techniques (such as use of the GlideScope video laryngoscope, Bullard laryngoscope or awake intubation using a fiberoptic bronchoscope) are needed.
  4. Consent. Ensure that the consent for the surgery has been obtained and that it is correctly signed and dated. Patients unable to give regular consent require special consideration: comatose patients, children, psychiatric patients etc. Some centers require separate consents for anesthesia and for blood transfusions. Central to proper consent is that the patient understands his or her options and their respective benefits and risks. It is not sufficient that the patient has merely and agreeably signed all papers placed before him.
  5. Blood Product Planning. Ensure that any needed blood products (packed red cells, platelets, stored plasma, fresh frozen plasma, cryoprecipitate - depending on clinical circumstances) are available. Most smaller surgical cases have blood drawn for “group and screen” – determination of ABO / Rh blood grouping and screening for antibodies that might make crossmatching difficult. Cross and Type: Larger surgical cases often have a number of blood units (usually packed cells) specifically tested for the patient and more or less immediately available (e.g., 4 units of packed cells for cardiac bypass patients in the operating room refrigerator)
  6. Aspiration Prevention. Ensure that the patient has been NPO ("nil per os" - nothing by mouth) for an appropriate length of time, i.e. ensure that the patient has an empty stomach.(Patients without an empty stomach may need a rapid sequence induction, awake intubation, or management with local or regional anesthesia to reduce the chance of regurgitation and aspiration). Pharmacologic means to reduce gastric volume and/or acidity may be appropriate preoperatively, such as a particulate-free oral antacid (sodium citrate 0.3 molar 30 ml po prior to induction of anesthesia) or agents such as cimetidine, ranitidine or famotidine (Pepcid).
  7. Identify Routine Monitoring Needs. All patients undergoing surgery get the following routine monitors: Noninvasive Blood Pressure (manual or automatic), Airway Pressure Monitor / Disconnect Alarm, Electrocardiogram, Nerve Stimulator, Pulse Oximeter, Urometer (if a Foley catheter is placed), Airway Gas Monitor (incl. oxygen analyzer and capnogram), Body Temperature. In addition, spirometry (tidal volume / minute volume) and agent analyzers (% isoflurane % nitrous oxide etc.) are highly desirable. Body temperature may be measured in the axilla, the nasopharynx, the esophagus or the rectum.
  8. Identify Special Monitoring Needs. CVP= central venous pressure PA = pulmonary artery. Determine whether special monitors (arterial line, CVP line, PA line etc.) are needed. Arterial lines allow beat-by-beat blood pressure monitoring, arterial blood gas monitoring and easy access to blood for tests. A CVP line is helpful to assess right-sided cardiac filling pressures. PA-lines are helpful when cardiac output must be measured or when right-sided cardiac pressure data would not be expected to reflect what is happening on the left side. PA catheters measure: (1) CVP waveform (2) PA waveform (3) PCWP (“wedge pressure”) (4) Cardiac Output (5) Right-sided resistance (PVR – pulmonary vascular resistance) (6) Left-sided resistance (SVR – system vascular resistance) (7) PA temperature. Evoked potential studies sometimes are useful to monitor the brain and spinal cord during neurosurgical and orthopedic procedures.
  9. Premedication. Order preoperative sedation, drying agents, antacids, H2 blockers, or other drugs as appropriate. SAMPLE PREMEDICATION ORDERS: Preoperative sedation -Diazepam 10 mg po with sip water 90 min preop; Midazolam 1 mg IV in holding area if requested by patient; Morphine 10 mg / Trilaphon 2.5 mg IM one hr preop (heavier). Drying agent (e.g., prior to awake intubation) - Glycopyrrolate 0.4 mg IM one hr preop. Reduce gastric acidity (e.g., patients at aspiration risk)- Ranitidine 150 mg po evening before surgery and again in am; Cardiac prophylaxis (e.g., mitral stenosis) - Antibiotics as per AHA protocol
  10. Intravenous Access. Start an intravenous (IV) of appropriate size in the hand or forearm(first using local anesthesia for larger IV sizes.)In most cases, a size 20, 18 or 16 gauge IV catheter is hooked up to a bag of Normal Saline (0.9%) or Lactated Ringer’s solution is usually used. A large size 14 is often used in cardiac cases and other large cases, or where the patient is feared to be hypovolemic. Some cases (e.g., trauma cases) will require more than one IV or will require a fluid warmer to avoid hypothermia. In other cases IV access will be via a central line, as in a line placed in the internal jugular vein, an external jugular vein or a subclavian vein.
  11. Equipment Preparation. ANESTHESIA MACHINE CHECK (HIGHLIGHTS ONLY – SEE FULL CHECKLIST): Oxygen Line Pressure, Oxygen Flowmeter, Nitrous Line Pressure, Nitrous Flowmeter, Oxygen Tank Check, Check for Leaks, Vaporizer Check, Check Ventilator. AIRWAY EQUIPMENT CHECK: Suction, Oxygen, Laryngoscope, Endotracheal Tube, Stylet (in ETT) “SOLES”
  12. Drug Preparation. Prepare drugs in labeled syringes. Examples: Thiopental, Propofol, Fentanyl, Midazolam, Succinylcholine, Rocuronuim. Not all these drugs will be drawn up at one in any one case (e.g. usually need only one induction agent).
  13. Prepare emergency drugs for the case: Atropine, Ephedrine, Phenylephrine, Nitroglycerine, Esmolol. Low risk cases may not need any of these drugs to be instantly ready. High risk cases may also require dopamine, epinephrine, norepinephrine and other agents.
  14. Attach Patient Monitors. Prior to induction of general anesthesia the electrocardiogram, blood pressure cuff and pulse oximeter should be attached and baseline vital signs taken. The IV should also be rechecked before the induction drugs are given. After induction / intubation the capnograph, airway pressure monitor, neuromuscular blockade monitor and temperature probe should be attached. Special monitors (CVP, arterial line, evoked potentials, precordial Doppler) may also be needed.
  15. Give Preinduction Drugs. Rocuronium 3 to 5 mg IV may be given to prevent fasciculation (with resulting myalgia) from succinylcholine (a rapid onset ultrashort acting intravenous depolarizing muscle relaxant used primarily for intubation). Small doses of midazolam (e.g. 1 - 2 mg IV) and/or fentanyl (e.g. 50 - 100 mcg IV) may be given to "smooth out" induction. Larger doses may be appropriate where less than usual doses of thiopental or propofol are planned (e.g. in cardiac patients). Preinduction hemodynamic “tuning” using nitroglycerine or esmolol may be needed in hypertensive patients or patients with coronary artery disease.
  16. Induce General Anesthesia. Tell the patient he / she will be going to sleep. Get baseline vital signs. Using thiopental (e.g. 3-5 mg / kg), propofol (e.g. 2-3 mg / kg) or other IV drugs, render the patient unconscious. (Consider using etomidate or ketamine for hypovolemic patients. Consider using fentanyl or sufentanil as the main induction agent for cardiac cases.Use of an inhalation induction with a potent agent such as sevoflurane would also work, but is far less popular in adults.)
  17. Provide Muscle Relaxation. After the patient is unconscious, as evidenced by loss of a lid reflex, use a depolarizing muscle relaxant such as succinylcholine or a nondepolarizing agent such as rocuronium or vecuronium to paralyze the patient in order facilitate endotracheal intubation. Succinylcholine is popular in this setting because of its rapid onset and offset (short duration of effect), but many clinicians never use succinylcholine routinely because of its occasionally lethal side effects related to hyperkalemia and because it is a trigger of malignant hyperthermia in susceptible individuals. The effects of muscle relaxant drugs can be monitored using a nerve stimulator (“twitch monitor”) as well as by observing the patient for unwanted movements. (This step is not needed if a face mask or Laryngeal Mask Airway is used, or if the patient is intubated awake).
  18. Intubate the Patient (Secure the Airway). Using your gloved left hand insert a laryngoscope to visualize the epiglottis and cords and then pass an endotracheal tube (ETT) through the abducted vocal cords with your right hand. Ordinarily the ETT should be positioned with lips around 21 cm for women, 23 cm for men. Inflate the ETT cuff to 25 cm H2O pressure to establish a seal (about 5 ml air will usually suffice), then hook up ETT to patient breathing circuit. Check for equal air entry with stethoscope and check for correct-appearing capnogram. (If an LMA is used, it is inserted without a laryngoscope).
  19. Ventilate the Patient. Although many cases can be done with the patient breathing on their own “breathing spontaneously”, all cases using muscle relaxants need mechanical ventilation for a period. USUAL VENTILATOR SETTINGS: Tidal volume 8-10 ml/kg. Respiratory rate 8-12/min. Oxygen concentration 30%. NOTE Aim for a PCO2 of 35 - 40 mm Hg in normal cases, and 28-32 mm Hg in some patients with increased intracranial pressure. Ensure that all ventilation-related alarms (apnea, high airway pressure, etc.) are enabled and appropriately set.
  20. Look at Oxygenation. Room air is 21% oxygen. Under anesthesia patients are given a minimum 30 percent oxygen (Exception: cancer patients who have taken bleomycin get only 21% oxygen to reduce the chance of oxygen toxicity). 100 percent oxygen with aggressive PEEP (Positive End Expiratory Pressure) may be required in patients with severe respiratory failure (e.g., as in ARDS). Aim for a pulse oximeter reading (arterial oxygen saturation) above 95%. Drops in arterial oxygenation are often due to endotracheal tube displacement into the right bronchus – check for equal air entry in all such cases.
  21. Dial in Inhaled Anesthetic. Provide maintenance anesthesia with nitrous oxide (N2O) 70%, oxygen 30% and a potent inhaled agent such as isoflurane (e.g. 1%). Using blood pressure, heart rate and other indices of anesthetic depth, adjust the inhaled agent concentration as needed (or give increments of IV agents such as fentanyl or propofol). Other volatile agents used in general anesthesia include sevoflurane, desflurane or halothane. Ether is still used in some parts of the world.
  22. Add Intravenous Anesthetics. Add fentanyl, midazolam, propofol or other anesthetic agents as needed according to your clinical assessment of the anesthetic depth. Increments of fentanyl (50 – 100 mcg) will help maintain analgesia. Some clinicians prefer an all IV technique - Total Intravenous Anesthesia, or TIVA. This can be useful in patients with susceptibility to Malignant Hyperthermia (who cannot receive succinylcholine or potent inhaled agents such as desflurane, sevoflurane or isoflurane).
  23. Add Muscle Relaxants. Muscle relaxation is needed for abdominal surgery and many other clinical situations. Using a neuromuscular blockade monitor add muscle relaxants as needed. (The degree of neuromuscular blockade is estimated by examining the finger movement patterns when the ulnar nerve is stimulated electrically with a series of four high-voltage shocks spaced 500 milliseconds apart.) Remember that not all cases require muscle relaxation and that all patients getting muscle relaxants must be ventilated mechanically.
  24. Fluid Management. Ensure adequate hematocrit, coagulation, intravascular volume and urine output by giving adequate IV fluids and blood products. For most cases run an IV of Normal Saline or Ringer’s solution at 250 ml/hr to start, then adjust to meet the following goals: In first two hours of case, replace any preoperative fluid deficit (e.g. NPO for 8 hours x 125 ml maintenance fluid needed per hour kept NPO = 1000 ml to give in first 2 hrs) Meanwhile, for entirety of case replace “third space” surgical losses at 2 - 10 ml/kg/hr (e.g., 2 for carpal tunnel repair, 5 for lap chole, 10 for bowel surgery.) Maintain urine output over 50 ml / hr or 0.5 to 1.0 ml/kg/hr Maintain hematocrit in safe range (above 0.24 in everyone; at or above 0.3 in selected patients at risk).
  25. Monitor Depth of Anesthesia. Unintended intraoperative awareness during surgery, while rare, is a monumental tragedy to the patient and can trigger post-traumatic stress disorder. It may happen when a vaporizer inadvertently empties or other problem (e.g. infusion pump failure).occurs. Remember that awake surgical patients cannot signal their distress if they are paralyzed with muscle relaxants. Using clinical assessment, ensure that the patient is unconscious. This is more of an art than a science, but takes into account autonomic findings such as BP and HR and the amounts of drugs given to date. Use of a potent inhaled agent like isoflurane is especially likely to ensure unconsciousness. A BIS monitor (Bispectral Index Monitor) is frequently advocated as a monitor of anesthetic depth.
  26. Prevent Hypothermia. Perioperative hypothermia can be a serious problem for some patients. For example, patients who shiver in the recovery room after surgery use excessive oxygen and may “put a strain on the heart” (induce myocardial ischemia in patients with coronary artery disease). Keep core temperature above 35 Celsius using fluid warmers, forced air heaters or just keeping the room warm. Measure axillary, rectal or oropharyngeal temperature to ascertain the degree of hypothermia. Temperature monitoring also helps detect the occurrence of an episode of Malignant Hyperthermia (a hypermetabolic syndrome).
  27. Emergence. When the surgery is nearing completion, discontinue the anesthetic agents and reverse any neuromuscular blockade (e.g. neostigmine 2.5 - 5 mg IV with atropine 1.2 mg or glycopyrrolate 0.4 mg IV). Neostigmine is never given alone (or your patient will get severe bradycardia or cardiac arrest). Use a neuromuscular blockade monitor (nerve stimulator) to ensure that any muscle relaxation has been well-reversed. Allow spontaneous ventilation to resume. Check respiratory pattern visually and via capnograph. Wait for consciousness to return.
  28. Extubation. Once the patient is awake and obeying commands, suction out the oropharynx with a large-bore mouth sucker, remove air from the ETT cuff with a 10 ml syringe, and pull out the ETT. Apply 100% oxygen by face mask after extubation. Supply jaw-thrust, oral airway, nasal airway or other airway interventions as needed to maintain good spontaneous breathing. Keep a close eye on the patient’s breathing and on the pulse oximeter (keep above 95%).
  29. Transport to PACU (Recovery Room). When the case is over and the paperwork done, bring the stretcher into the OR and put the patient on it without pulling out lines and disconnecting monitors. Don't forget the oxygen tank and oxygen mask. Monitor patients breathing visually. Keep a finger on a pulse while moving the patient (in appropriate cases), but use a transport monitor for sick patients or for big surgical cases (eg, cardiac surgery). Give report to RNs in PACU as well as to the anesthesiologist managing the PACU (complex cases). PACU = Post Anesthetic Care Unit
  30. Arrange Postoperative Care. Before leaving, take care of any remaining paperwork. This includes analgesic orders (e.g. morphine 2 - 4mg IV prn), oxygen orders (e.g. nasal prongs 4 liters/min or face mask 35% oxygen), antibiotics, feeding orders, fluid orders and post-operative tests such as electrolytes and hematocrit. Be sure to identify any special concerns you have about the patient. Where appropriate, discuss current clinical situation with patient’s family.



Tips
  • DRUG DOSAGE NOTE. Doses and volumes discussed here apply to normal adult patients. Adjustments for pediatric patients, frail patients, and patients with impaired renal, hepatic, respiratory or cardiac status will be needed. Drug interactions may also influence dosing needs. Remember that clinical drug dosing (and timing) is as much an art as a science.



Warnings
  • This article is directed at medical students.

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