Goals of General Anesthesia
Administering general anesthesia provides three benefits: (a) hypnosis, putting the patient to sleep; (b) analgesia, relieving pain; and (c) relaxation, easing the muscles sufficiently to perform the procedure, primarily in abdominal and some orthopedic cases.6
An anesthetist's primary goal is to anesthetize patients and have them recover without ill effects from the anesthesia. Whether this happens depends a great deal on the anesthetist's abilities and how carefully he follows the rules for safely anesthetizing patients (Table 15-2).
Table 15-2 Ten Rules for Safely Anesthetizing Patients ||Download (.pdf)
Table 15-2 Ten Rules for Safely Anesthetizing Patients
Assess the patient carefully to be aware of any underlying medical condition or medication that might interfere with the anesthesia or surgery.
If possible, keep the patient NPO for ≥6 hours before the procedure. (Modify for infants and small children.) Small sips of water taken with a preanesthetic medication are acceptable. Also consider this course for procedures done under local or regional blocks, since you may have to switch to using general anesthesia during the procedure.
Use a tilting OR table, so that you can put the patient in a head-down position if there is a risk of emesis. During surgery, turning the patient on his side may not be an option.
Check available drugs and equipment before you start. The truism is that, whatever you don't have available or that doesn't function properly will be what you need in a crisis.
Have suction instantly available. This is the most-often-neglected piece of equipment. Check that the parts are assembled, the equipment is turned on or ready to be quickly turned on, and the vacuum works. When you don't have suction available, it is almost certain that you will need it—quickly.
Keep the patient's airway clear. Use a nasal or an oral airway, as needed. If the patient doesn't need it, he will spit out an oral airway.
Be ready to control ventilation. No matter what anesthetic you use (including ketamine), you may need to assist ventilations with a BVM, with or without a controlled airway device such as an LMA or ET tube.
Have an IV running. This is not only therapeutic, but also an excellent precaution if something goes awry. In a crisis, it is far easier to begin administering medications or fluids through an established IV than to struggle to insert one.
Continually monitor the pulse, BP, and skin color (and the color of any blood from the surgical site). A precordial or esophageal stethoscope, a BP cuff that is used on a regular basis (q5min), and good observation are all that is required for basic monitoring.
Have an assistant in the room who can help in an emergency.
Four of the five essential elements for general anesthesia may need to be improvised or omitted in austere situations: premedication, monitoring, induction medications, and oxygen. Additionally, alternative maintenance drugs (anesthetics) or delivery methods may need to be used.
Premedication provides mild sedation for the patient and counteracts some side effects, primarily excess salivation and increased vagal tone.
A wide variety of narcotics, benzodiazepines, phenothiazines, and other medications may be used for premedication. Try to use sedating anticholinergics (e.g., those with antihistamine activity) if the normal medication cannot be used. Premedications are usually administered parenterally, but many may be given orally.
Promethazine 50 mg (1 mg/kg) tablets (which also have anticholinergic activity) can be used in adults for nausea and very mild sedation. Give promethazine about 2 hours before anesthesia. This medication is particularly good if ketamine is used as a general anesthetic. Diazepam tablets, 10 to 20 mg (0.15 to 0.25 mg/kg), can be used as a tranquilizer before either regional or general anesthesia. Oral diazepam has a more rapid and reliable onset than does intramuscular (IM) diazepam.8 Diphenhydramine (Benadryl) is cheap, and almost always available. It can be given parenterally or orally, and is both sedating and anticholinergic.
Considered by many anesthesiologists to be the only essential preoperative medication, atropine 0.4 to 0.6 mg dries secretions and diminishes vagal tone on the heart. Atropine may be administered IM 30 to 40 minutes before induction or diluted and given IV immediately before anesthesia.6 Atropine can also be administered orally in tablet form (0.5 mg in an adult) at least 20 minutes before the general anesthetic is administered. There is no harm if the patient takes it with a small amount (~20 mL) of water.8
In austere situations, anesthesia with only the most basic monitoring (even more basic than what you're thinking) is the norm. Often the only monitoring is checking the pulse: either constantly with an esophageal or precordial stethoscope (improvised models of both instruments are described in Chapter 5, Basic Equipment) or at least every 5 minutes while taking a BP. You can also monitor the pulse by laying a finger just anterior to the tragus of the ear to feel the superficial temporal artery pulsate. Also, monitor the patient's skin color, capillary refill, and the color of any blood from the surgical site, since this requires little or no apparatus. A wisp of cotton taped near the nostril is a useful indicator that the patient is still breathing.6
Esophageal stethoscopes are particularly important during thoracic procedures. Only one earpiece is needed, although a modified stethoscope can also be used. Precordial stethoscopes (that can also be placed over the back) are particularly important to use during procedures on babies. Likewise, only one earpiece is needed, but the bell should be securely taped to the patient before the procedure begins.
Both IV and inhalation agents are often used for induction. Ketamine needs no induction agent.
Benzodiazepines, although not often used for induction, can be used for this purpose. Diazepam, often the most readily available benzodiazepine, can be used as an IV induction agent, although it has a longer onset and longer duration (i.e., longer "hangover") than most other agents.9 The newer benzodiazepines generally work faster and have shorter half-lives.
The most feared complication during induction is laryngospasm. Since a neuromuscular blocking agent may or may not be available, provide constant positive pressure with an anesthesia bag or a bag-valve-mask (BVM). This normally breaks the spasm. If not, spray the cords with lidocaine, and be prepared to do a cricothyrotomy (rarely needed).
In austere situations, oxygen is frequently unavailable, and so is considered a luxury. If oxygen is scarce, use it only to preoxygenate patients who will undergo brief apneic procedures, to induce and intubate small children10, and to supplement anesthesia at altitudes >9000 feet (2743 meters). Also provide it for patients with laryngospasm, acute desaturation, significant anemia (Hgb <9 g/dL), or heart or lung disease, and to those in shock.9
Also consider using oxygen when (a) inducing anesthesia in a patient using ether and air; (b) giving anesthesia with more than 8% ether; (c) doing a Cesarean section (C-section), but use only until the baby is delivered; (d) patients have any respiratory disease or considerable airway secretions; and (e) the preoperative BP has fallen by >30%.
Theoretically, all patients may go through four stages (plus substages, or planes) of anesthesia, no matter which agent is used (Table 15-3). Ether is the anesthetic that shows all the classic stages, so the pattern with ether is described more fully under "Ether" in Chapter 16, Anesthesia: Ketamine, Ether, and Halothane.
Table 15-3 Signs of General Anesthesia Stages and Planes (Levels of Stages) ||Download (.pdf)
Table 15-3 Signs of General Anesthesia Stages and Planes (Levels of Stages)
Response to surgical stimulus
II. Excitement (Delirium)
Lash reflex goes*
III. Surgical Anesthesia
Lid reflex gone*
IV. Medullary Paralysis
Pupil of anoxia*
When anesthesia is given with basic equipment and few medications, tracking anesthetic stages can be a useful safeguard against over-medication.
Anesthetics vary widely in their effects, so staging must be used with the particular drug's effects in mind. The general pattern follows the oversimplified, but useful, concept that anesthetics suppress the central nervous system from above downward, as blood concentration increases. This progression (stages) is based upon the patient's body movements, respiratory rhythm, oculomotor reflexes, and muscle tone. The classic anesthetic stages are detailed in the following paragraphs.
There is suppression of the highest cerebral centers, with the patient gradually losing the sensation of pain. Patients remain conscious and rational, and have decreased pain perception. Muscle tone, breathing, and pulse are normal. Stage 1 anesthesia is indicated for obstetric analgesia, and as a supplement to local anesthesia for minor procedures.
Stage 2: Excitement (Delirium)
This stage begins when patients lose consciousness and become excited, struggle, and (possibly) become difficult to control. Patients retain their gag reflex and can protect their airway, although they breathe irregularly and may hold their breath. Their pupils generally become dilated. Their abdominal muscles contract during expiration. They lose their eyelash reflex and have roving eye movements and dilated but reactive pupils. They retain reflex responses to any painful or irritating stimuli, including noxious anesthetic vapors.
Stage 3: Surgical Anesthesia
In this stage, patients no longer respond to painful stimuli. Muscular relaxation progressively increases, spontaneous respiration diminishes, and patients lose their protective gag reflex. Non-anesthesiologists need only recognize two planes: acceptable ("Light") and too deep.11
Plane: Light Surgical Anesthesia
This is the optimal anesthetic level for most patients during surgery. Patients' breathing becomes regular again, although they will inspire deeply every 2 to 3 minutes. The eyes no longer move and, as the anesthesia level deepens, the pupils gradually dilate. The patient no longer moves and muscular tone decreases. The abdomen and chest move synchronously. An artificial airway or endotracheal (ET) tube may be inserted in this plane—but not earlier.
Plane: Deep Surgical Anesthesia (Too Deep)
In this plane of anesthesia, patients' intercostal muscles become progressively paralyzed, eventually having paradoxical movement (moving in with inspiration). Sudden inspirations pull on the mediastinum and trachea, drawing it downward (the "tracheal tug"). Patients' pupils become progressively less reactive to light. Abdominal surgery is actually very difficult at this anesthesia level if the patient is not pharmacologically paralyzed.
Stage 4: Medullary Depression (Way Too Deep)
During stage 4, the brainstem's respiratory center becomes depressed, which causes patients to stop breathing and lose all muscle tone. Their pupils are fixed and dilated. The heart may (as with chloroform) or may not (as with ether) be dangerously depressed.6 If a patient stays in this stage too long, his heart stops and he dies.11