Canine and Feline Anesthesia Ch.9 Objectives

Question 1

Describe anesthetic techniques commonly used in small animal practices.

Answer 1

In small animal practice, common anesthetic techniques include inhalation anesthesia with agents like isoflurane or sevoflurane, injectable anesthesia with drugs like ketamine or propofol, and regional anesthesia techniques like nerve blocks or epiduralsGeneral anesthesia - produce analgesia during the period of unconsciousness and, if used along with an analgesic as a part of a balanced protocol, during the preoperative and postoperative periods as well. In addition, general anesthetic procedures can be performed with readily available resources and at a reasonable cost. In dogs and cats, general anesthesia is induced and maintained using balanced protocols, inhalants, intramuscular (IM) protocols, and total intravenous (IV) techniques.

Sedation and neuroleptanalgesia - mild to heavy sedation and neuroleptanalgesia are also frequently used to facilitate diagnostic and therapeutic procedures in small animals that are frightened, aggressive, or in pain.

Local and regional anesthesia - used along with general anesthesia in small animals to provide additional analgesia for dental, abdominal, orthopedic, and occasionally other procedures. Neuromuscular blocking agents are rarely used in general practice but are sometimes used to provide muscle relaxation for ocular and orthopedic procedures in veterinary schools and referral practices.

Question 2

List strategies used to minimize adverse effects when selecting an anesthetic protocol.

Answer 2

To minimize adverse effects when selecting an anesthetic protocol, anesthesiologists should use a multimodal approach, prioritize patient-specific risk assessment, and implement meticulous monitoring and management strategies
* Label all syringes containing injectable anesthetic agents with the name of the patient, the name of the drug, and the drug concentration if more than one concentration is available.
* Administer no more than the minimum dose of drug needed to achieve the desired level of anesthesia.
* Unless told otherwise, administer all IV agents “to effect”

Question 3

Describe how different methods of anesthetic induction and maintenance influence the dynamics of an anesthetic event.

Answer 3

Different anesthetic induction and maintenance methods significantly impact the dynamics of an anesthetic event, influencing the speed of onset, depth of anesthesia, and recovery time, with intravenous (IV) induction generally faster than inhalational, and maintenance strategies varying based on the surgical procedure and patient needs.

Question 4

Prepare a small animal patient, anesthetic equipment, and anesthetic agents and adjuncts for general anesthesia.

Answer 4

To prepare a small animal patient for general anesthesia, assess their health, administer pre-anesthetic medications, set up the anesthesia machine and monitor, and ensure the availability of necessary anesthetic agents and adjuncts.Preparation of a Dog or Cat for General Anesthesia

1. Assess, prepare, and weigh the patient.
2. Determine the protocol (anesthetic agents, doses, and routes and sequence of administration).
3. Calculate the volume of each agent to give (preanesthetic, induction, maintenance, and analgesic agents) and fluid administration rates.
4. Calculate the oxygen flow rates.
5. Prepare equipment required to administer drugs (scales, syringes, needles, anesthetic agents and adjuncts, reversal agents, emergency cart, controlled substance log, and tape to label syringes).
6. Prepare fluid administration equipment (clippers, antiseptic scrub and rinsing agent, catheters, tape, normal saline, catheter cap, administration and extension set, fluids).
7. Prepare equipment for endotracheal intubation.
8. Prepare monitoring equipment, including anesthesia record, stethoscope, monitors, and probes.
9. Assemble and test the anesthetic machine.

Question 5

Describe induction of general anesthesia by intravenous (IV) injection of an ultrashort-acting agent, by mask or chamber induction, or by intramuscular (IM) injection.

Answer 5

General anesthesia induction can be achieved through intravenous (IV) injection of ultrashort-acting agents, mask/chamber inhalation, or intramuscular (IM) injection, each with distinct advantages and disadvantages.

Question 6

Explain cautions and risks associated with each method of anesthetic induction, and strategies to maximize patient safety.

Answer 6

Intravenous Induction

The term “to effect” means that only the amount of injectable anesthetic necessary to produce unconsciousness is given, rather than administering the entire dose calculated on a milligram per kilogram basis. This technique is necessary because the amount of drug needed to induce or maintain anesthesia cannot be precisely predicted for a given patient, and most anesthetic agents have narrow therapeutic indices. For these reasons, IV drugs are given as a series of bolus injections and discontinued when the desired depth is reached—a process known as titration. A competent anesthetist monitors the patient closely and alters the amount of anesthetic given to suit the patient’s requirements, rather than relying solely on a calculated dose.

Mask Induction

For some patients in critical condition, induction by mask may be safer than induction with injectable agents because the anesthetist can decrease anesthetic depth or discontinue the agent by adjusting the vaporizer setting if problems arise.

• Mask induction may result in significant exposure of personnel to waste anesthetic gas, because, no matter how well the mask is fitted, some leakage is inevitable. Therefore adequate room ventilation is necessary to prevent excess inhalation of waste gas (see Chapter 5).
• If the animal resists mask induction, struggling may cause the release of epinephrine, which predisposes the patient to potentially fatal cardiac arrhythmias and hypotension. To avoid this, induce anesthesia by mask only in calm or sedated patients.
• Because of the longer induction time compared with IV administration, mask induction is not appropriate for patients with poor respiratory function (e.g., upper airway disease or obstruction, difficult breathing because of brachycephalic conformation, diaphragmatic hernia, pleural effusion, or pulmonary edema), unfasted patients, or patients at risk for vomiting or regurgitation during induction. These patients must be intubated immediately to prevent serious adverse effects and permit rapid control of the airway and ventilatory support.
• The anesthetist must ensure that the airway is kept open at all times during mask induction. The mask must not occlude the patient’s nostrils, as might happen with a cat or brachycephalic patient if the mask is too small or tight. The anesthetist must not compress the airway or chest during restraint.

Although a mask can be used to maintain anesthesia, the anesthetist is not able to protect the airway, prevent aspiration, provide ventilatory support, or observe respirations as readily as when a tube is present. For these reasons, most anesthetists intubate the patient immediately after induction.

Chamber Induction

Anesthetic chambers allow the induction of anesthesia in even the most uncooperative animal but are associated with complications from stress, trauma, vomiting, airway blockage, and other issues. During chamber induction, it is impossible to assess most monitoring parameters accurately. Thus, the anesthetist must be vigilant and prepared to act quickly if the patient shows signs of compromise.

Intramuscular Induction

• IM injections cannot be titrated or given “to effect.” Usually the entire calculated dose is given at once.
• In general, the dose for IM injection is about twice the corresponding IV dose.
• Drugs administered by the IM route require more time to reach a high enough concentration in the brain to induce anesthesia. IM induction is therefore characterized by a relatively slow onset of anesthesia compared with IV induction (typically 10 to 20 minutes). Occasionally, if drugs are deposited in a fascial plane between muscles, or in subcutaneous (SC) tissue, slow or incomplete absorption may result in an even longer induction or a blunted effect.
• After peak effect, if the patient’s depth of anesthesia is still inadequate, additional drug must be given or an inhalant agent must be administered with a mask until the patient can be intubated. (Remember that some drugs such as propofol, etomidate, and thiopental sodium must not be given intramuscularly.)
• IM induction is characterized by a lengthy recovery period because the animal requires considerable time to metabolize the relatively large dose of drug given by this route.

Question 7

List reasons for, advantages of, and potential complications of endotracheal intubation.

Answer 7

Advantages of Endotracheal Intubation

• Placement of an endotracheal tube is especially beneficial for maintaining anesthesia with inhalant anesthetics.
• When properly maintained, an endotracheal tube helps to maintain an open airway, decreasing the likelihood of airway obstruction caused by patient position, collapse of pharyngeal tissues, foreign material, or any other cause. Because of the importance of maintaining a patent airway, it is customary to leave the tube in place throughout anesthesia and into the recovery period, until the animal regains the swallowing reflex.
• Intubation allows more efficient delivery of anesthetic gas to the animal than does a mask. Because gas flow rates can be lowered, intubation results in reduced exposure of hospital personnel to waste anesthetic gas, and is more economical.
• Use of an endotracheal tube with an inflated cuff reduces the risk of aspiration of vomitus, blood, saliva, or other material that may be present in the oral cavity or breathing passages. This material may accumulate during any procedure; however, the risk of aspiration is particularly high during oral surgery or dentistry and in patients that have not been fasted.
• An endotracheal tube of the correct diameter and length will improve efficiency of gas exchange by reducing the amount of anatomic dead space. Anatomic dead space is composed of the portions of the breathing passages that contain air but in which no gas exchange can occur (i.e., the mouth, nasal passages, pharynx, trachea, and bronchi). With the anatomic dead space minimized, the endotracheal tube ensures that a larger proportion of the gas delivered to the patient reaches the exchange surface in the alveoli.
• The anesthetist can support ventilation in intubated patients by manual or mechanical means. Manual ventilation refers to forced delivery of oxygen and anesthetic gases by squeezing the reservoir bag of the anesthetic machine. Mechanical ventilation refers to use of a mechanical ventilator to achieve the same result. Because of the respiratory depression associated with anesthesia, periodic manual or mechanical ventilation is necessary for most anesthetized patients to ensure adequate gas exchange. Intermittent mandatory manual or mechanical ventilation is required for patients that have been given neuromuscular blocking agents or when the thoracic cavity is open.
• Endotracheal intubation followed by manual or mechanical ventilation is also essential for patients in respiratory or cardiac arrest. For this reason it is advisable to have a laryngoscope and an endotracheal tube of the correct size readily available for all anesthetized patients, even if endotracheal intubation is not planned.

Complications of Endotracheal Intubation

Cuff Not Inflated or Underinflated

• Inability to create a seal between the cuff and trachea
• Difficulty or inability to keep the patient anesthetized
• Aspiration of stomach contents
• Aspiration of foreign material and fluid during dental cleaning
• Pollution of the workspace with anesthetic gas

Tube Diameter Too Small

• Inability to create a seal between the cuff and trachea, leading to the same complications as listed earlier
• Small tubes are more likely to become blocked with mucus
• Increased resistance to breathing and increased respiratory effort

Cuff Overinflated or Tube Diameter Too Large

• Necrosis of the tracheal mucosa
• Possibility of tracheal rupture in extreme situations

Tube Too Long

• If placed past the thoracic inlet, intubation of only one mainstem bronchus occurs, leading to hypoxemia and difficulty in keeping the patient anesthetized
• If extending beyond the mouth, increased mechanical dead space leads to hypoventilation and hypoxemia

Tube Too Short

• Inability to intubate the patient successfully
• Changes in patient position may dislodge the tube from glottis

Overzealous Intubation

• Tracheal irritation leading to tracheitis and postoperative cough
• Trauma or tracheal rupture resulting in pneumomediastinum and/or pneumothorax

Tube Kinked or Obstructed

• Dyspnea and hypoxemia
• Asphyxia and cardiac arrest if not corrected

Tube Not Removed before Return to Consciousness

• Damage to the tube from chewing
• Blockage of the airway
• In extreme situations, a severed portion of the tube can be aspirated or swallowed

Tube Not Cleaned and Disinfected

• Transmission of infectious agents, leading to tracheitis, bronchitis, or pneumonia
• Blockage of the tube with dried mucus or other foreign material

Question 8

Explain how to do each of the following: (1) select and prepare an endotracheal tube (ETT) for placement, (2) place an ETT in a dog or cat, (3) check for proper placement, (4) inflate the cuff, (5) minimize laryngospasm, and (6) extubate a patient during anesthetic recovery.

Answer 8

Selecting an Endotracheal Tube

Endotracheal tubes are available in a wide variety of diameters and lengths. The tube must be of a diameter that is small enough to allow placement without causing trauma to the trachea, but large enough to produce a seal when the cuff is inflated. It must be of sufficient length to reach the thoracic inlet when fully inserted, but must not be so long as to reach the mainstem bronchi or to extend beyond the end of the muzzle when inserted the correct distance. At least three tubes of slightly different diameters should be selected so that you are prepared if your first choice does not fit. The size required by any given patient is influenced by species, conformation, and breed. Next determine if the tube is the appropriate length. The endotracheal tube should ideally extend from the tip of the nose to the thoracic inlet. If it is too short, it may not be long enough to reach the trachea at all. If the tube is too long, one of two problems may occur. If inserted too far, the beveled end may advance into only one mainstem bronchus, thus supplying only one lung with oxygen and anesthetic. If inserted only to the thoracic inlet, the portion of the tube extending from the mouth will increase mechanical dead space. In view of these variations, the following guidelines can be used to estimate the proper size based on patient body weight. Most cats require a 3- to 4.5-mm tube. A dog weighing 20 kg will require a 9.5- to 10-mm tube. Increase or decrease the size by approximately 1 mm for each 5 kg of body weight under or over 20 kg. For example, prepare a 7.5- to 8-mm tube for a 10-kg patient, and a 10.5- to 11-mm tube for a 25-kg patient. This guideline applies to canine patients weighing about 10 to 40 kg.

Preparing the Tube

Before an endotracheal tube is used, it must be checked for integrity. It should be clean, sanitized, and free of blockages, holes, deterioration, or other damage. The connector must be securely attached, and the cuff must inflate and hold pressure after the syringe has been detached from the valve. A soft or narrow tube may require use of a stylette, which does not extend beyond the end of the tube, to stiffen it during placement. The tube should be lubricated with a small amount of sterile water-soluble lubricant or with the patient’s saliva immediately before placement.

Intubation Procedure for a Dog or Cat

1. Place the patient in sternal recumbency.
2. Have an assistant grasp the patient’s maxilla behind the canine teeth, extend the neck, and raise the head so that the head and neck are in a straight line. Be sure the lips and whiskers are pulled dorsally and out of the line of sight. The neck should be propped upright and not allowed to sag. The assistant should not push on the ventral aspect of the neck, head, or throat, because this may obscure the view, making intubation difficult.
3. Grasp the tongue with a gauze sponge, and open the mouth fully by firmly pulling the tongue out and down. A mouth gag can be used to hold the mouth open.
4. Adjust the light so that the larynx is well illuminated.
5. If necessary, use the tube or laryngoscope gently to displace the epiglottis ventrally, or the soft palate dorsally, until the glottis can be visualized† (Figure 1).
6. Gently insert the tube past the vocal folds using a rotating motion, but never force the tube! If the tube is too large to pass easily, exchange the tube for one of smaller diameter (Figure 2).
7. After the tube has been placed, gently transfer the patient into lateral recumbency.
8. Check the tube to ensure that it is in the trachea. Then check that it is inserted to an appropriate distance and is oriented to match the natural curve of the trachea.
9. Secure the tube in place with a length of rolled gauze or used IV tubing.
10. Position the tongue so that it hangs loosely from the mouth and is not compressed by the tie.
11. Turn on the oxygen flowmeter(s).
12. Connect the endotracheal (ET) tube connector to the breathing circuit.
13. Inflate the cuff, and check for leaks.
14. Turn on the anesthetic vaporizer, and select the appropriate setting.
15. Commence regular monitoring.
16. Ensure a patent airway by checking the position of the patient and tube. The neck and tube should assume a gentle natural curve.

Checking for Proper Placement

• Visualize the larynx, and confirm that the tube is in the correct location.
• Watch for expansion and contraction of the reservoir bag as the animal breathes.
• Feel for air movement from the tube connector as the patient exhales or when light, quick pressure is applied to the chest wall.
• Watch for fogging of the tube with condensation during exhalation.
• Check that the motion of the unidirectional valves coincides with breathing. The inhalation valve should open as the patient inhales, and the exhalation valve should open when the patient exhales.
• Palpate the neck. The trachea is the only naturally firm structure in the neck. If the tube is inside the trachea, only the trachea will be palpable. If the tube is in the esophagus, both the tube and trachea may be palpable. It is not always easy to feel the tube, however, so mastery of this technique requires practice.
• The ability of the patient to vocalize (growl, whine, or cry) indicates a misplaced tube. This is because vocalization requires the vocal cords to vibrate together, which is impossible if the tube is properly placed.
• Many patients, especially if in a light plane of anesthesia, will cough or exhale forcefully during intubation. This is indicative of proper placement, although not all patients exhibit this sign, especially if anesthesia is deep.
• Connecting a capnograph to the endotracheal tube will reveal an appropriate waveform and level of end-tidal CO2 if the animal is correctly intubated.

Cuff Inflation

To inflate the cuff, first extend the patient’s head to straighten the airway. Attach an air-filled 6-mL or 12-mL syringe to the valve port. Have an assistant close the pop-off valve and gently compress the reservoir bag, watching the pressure manometer. Listen for gas leakage around the tube, which may sound like a soft hiss or gurgling. Slowly inflate the cuff until the leaking just ceases at a pressure of 20 cm H2O but resumes at higher pressures. Avoid overinflation of the cuff, which can result in a variety of mild to serious complications. Inflation should be checked again after 15 or 30 minutes of anesthesia, because tracheal diameter may increase as a result of muscle relaxation, or a slow, undetected leak in the cuff or pilot line may cause the cuff to deflate.

Laryngospasms

Laryngospasm can be prevented by using one or more of the following strategies.

• Apply no more than 0.1 mL of 2% injectable lidocaine directly to the glottis before placement. Aerosolize it with a 25- to 26-gauge needle, or apply 2 to 4 drops on the arytenoid cartilages with a tomcat catheter attached to a 1-mL syringe. Wait 30 to 60 seconds for the lidocaine to take effect before attempting intubation. As an alternative, a small amount of lidocaine gel can be gently applied with a sterile cotton swab.
• Be sure the patient is adequately anesthetized before attempting to intubate the patient, because increased anesthetic depth decreases the incidence and severity of laryngospasm.
• Prepare carefully, wait for the glottis to open before attempting placement, and try to get the tube in the first time. Repeat attempts worsen laryngospasm.
• Never force the tube! This can lead to severe and potentially life-threatening complications including tracheal rupture, pneumothorax, and pneumomediastinum.

Extubating

To prepare the patient for extubation, deflate the cuff by drawing out all the air until the pilot balloon is empty. Untie the tube so that it can be rapidly removed. At all times during recovery, keep the patient’s neck in a natural but extended position to protect the airway. Some anesthetists prefer to deflate the cuff and untie the gauze or tubing before signs of arousal are seen so that the tube can be quickly removed when swallowing occurs. In dogs, extubation should occur when the swallowing reflex returns. In cats, extubation should occur when the patient shows signs of impending arousal, such as voluntary movements, swallowing, or active reflexes. A notable exception to this general rule is brachycephalic dogs. In these patients, many anesthetists prefer to delay extubation until the patient is able to lift its head unassisted, as early extubation may lead to respiratory distress from upper airway obstruction.

Question 9

Describe maintenance of general anesthesia by administration of an inhalant agent, injection of repeat IV boluses of an ultrashort-acting agent, or constant rate infusion (CRI).

Answer 9

Anesthetic Maintenance in a Dog or Cat

General anesthesia is maintained with inhalant or injectable agents. As with anesthetic induction, there are subtleties in the way each agent is handled to ensure that the patient is at an optimum anesthetic depth and is safe. The administration of these agents is summarized here.

Maintenance with an Inhalant Agent

• Choose the initial dial setting on the basis of the anesthetic depth following intubation.
• Make periodic changes in the vaporizer dial setting based on monitoring parameters.
• If the anesthetic depth is slightly too light or deep, make small dial changes of approximately 0.5% to 1% increments with isoflurane or sevoflurane.
• If the patient’s anesthetic depth is significantly light (e.g., the patient exhibits spontaneous movement, swallowing, active reflexes, strong muscle tone), increase the oxygen flow to 50 to 100 mL/kg body weight per minute, and set isoflurane at 3% to 5% or sevoflurane at 4% to 6% (induction levels) until signs of increased depth are evident.
• If anesthetic depth is significantly too deep (e.g., absent reflexes, flaccid jaw tone, central dilated pupils), then increase the oxygen flow to 50 to 100 mL/kg body weight per minute, turn off the vaporizer, and monitor the patient carefully until signs of decreased depth are evident. As soon as depth starts to decrease and the patient is safe, resume the anesthetic.

Maintenance with Repeat Boluses of Propofol, Alfaxalone, or Another Ultrashort-Acting Agent

• Monitor the patient every few minutes.
• Administer additional boluses as needed to effect, typically every 3 to 5 minutes.
• The necessary volume for each bolus varies but is often approximately one tenth to one quarter of that required for induction.
• Maintain the patient at an optimal plane and avoid overdose.

Maintenance with a CRI of Propofol or Alfaxalone

• Place an IV catheter, attach an administration set, and begin IV fluid administration.
• Calculate the volume of anesthetic needed to last the anticipated length of the procedure.
• Draw this volume into a syringe.
• Place the syringe in a syringe pump and program in the infusion rate in milliliters or microliters per minute, or in milliliters or microliters per hour (the manual will indicate accepted units).
• Attach the syringe to the port of a winged infusion set primed with anesthetic to be administered.
• Place the needle of the winged infusion set into the injection port of an IV administration set near the catheter.
• After induction and intubation, start the syringe pump at the calculated rate.
• Based on the results of monitoring parameters, make subtle changes in the infusion rate as needed to maintain the patient in surgical anesthesia.

Induction and Maintenance with an IM Injection

• Calculate the volume to be administered.
• Administer the agent via the IM route.
• Place the patient in a quiet area for 15 to 20 minutes, where it can be monitored.
• After peak effect, check the anesthetic depth and start the procedure if depth is adequate.
• If the anesthetic depth is inadequate, give additional drug intramuscularly or intravenously or administer an inhalant agent by mask.

Question 10

List principles of providing for patient positioning, comfort, and safety during anesthetic maintenance.

Answer 10

Patient Positioning, Comfort, and Safety

During anesthetic induction and maintenance, a number of considerations must be observed to ensure that the patient is not harmed.

• During induction the animal should be supported as it loses consciousness. Particular care should be taken to be sure that the animal does not strike its head on the table during induction or transfer to surgery.
• After IV induction, as soon as the patient is intubated, remove the needle and syringe to avoid accidental overdose in the event that the syringe plunger is accidentally pushed while the patient is being moved.
• Immediately after intubation, lay the patient in lateral recumbency, then secure and cuff the tube.
• Before preparing the patient for surgery, the anesthetist must ensure that the patient’s endotracheal tube is correctly placed (i.e., in the trachea) and that the cuff is functional and inflated. Once the surgical preparation begins, it is difficult to reposition the animal to allow re-intubation without compromising aseptic technique.
• Check the endotracheal tube for kinks or bends. An open airway must be maintained at all times.
• Any time an intubated patient is turned over, the endotracheal tube should be temporarily disconnected from the anesthetic circuit. Rolling or twisting the animal while it is still connected to the circuit may cause the endotracheal tube to twist and collapse, resulting in an airway obstruction, or may cause the distal end of the tube to traumatize or lacerate the trachea.
• The hoses of the anesthetic machine should be supported so that there is no drag on the endotracheal tube. This could result in tracheal trauma or displacement of the tube. Displacement is of particular concern when using a supraglottic airway device.
• The position of the hoses and endotracheal tube should be checked during patient transfer and after repositioning. Hyperflexion of the neck should be avoided because it may lead to endotracheal tube obstruction.
• The reservoir bag should be placed so that it is clearly visible at all times.
• When positioning the animal on the surgery table, the anesthetist should ensure that the animal assumes as normal a posture as possible. In particular, hyperextension or hyperflexion of the limbs should be avoided because either may result in permanent neurologic injury.
• Heavy drapes or instruments must not compress the chest of a small patient, because this may interfere with respiration.
• Do not overtighten leg restraint ropes, or circulation may be compromised.
• Place the patient on a heat-retaining surface such as a warm-water circulating blanket. Do not use an electric heating pad, which can burn the patient!
• If one lung is diseased, place the normal side up whenever possible, to maximize oxygen exchange.
• Tilting the surgery table so that the patient’s head is down gives the surgeon easier access to some abdominal organs, particularly the uterus and ovaries. However, the anesthetist should be aware that more than a 15-degree elevation of the caudal aspect of the body may cause the abdominal organs to compress the diaphragm, which may compromise heart and lung function. Head-down tilted positions should be avoided entirely in animals with breathing difficulties, especially those with diaphragmatic hernia.
• Artificial tear solution or other corneal lubricant should be instilled into the eyes of an anesthetized patient every 2 to 3 hours, unless the patient is undergoing ocular surgery. This is particularly important if an anticholinergic is used. General anesthesia decreases tear secretion for a period of up to 24 hours after anesthesia, and some dogs may need periodic application of a corneal lubricant for up to 36 hours after recovery. Cats maintain some tear production throughout anesthesia; however, lubrication is advisable if an anticholinergic or ketamine is given.

Question 11

List factors that affect patient recovery from anesthesia, the signs of recovery, appropriate monitoring during recovery, and oxygen therapy during recovery.

Answer 11

The length of the recovery period

• The length of the anesthetic period. As a general rule, the longer the patient is under anesthesia, the longer the expected recovery.
• The condition of the patient. Lengthy recoveries are seen in animals that have almost any debilitating disease (particularly liver and kidney disease).
• The type of anesthetic given and the route of administration. Lengthy recoveries are more common if an injectable agent is given intramuscularly rather than intravenously.
• The patient’s temperature. Hypothermic patients are slow to metabolize and excrete anesthetic drugs.
• The breed of the patient. Certain dog breeds (e.g., greyhounds, salukis, Afghan hounds, whippets, and Russian wolfhounds) are slow to recover from certain anesthetic agents, especially barbiturates.

Signs of Recovery

An animal recovering from general anesthesia gradually progresses back through the anesthetic stages and planes. As the animal moves from deep to moderate to light anesthesia, vital signs and reflexes change in predictable ways. The heart rate, respiratory rate, and respiratory volume increase. After assuming a ventromedial position, the eyeballs move back to a central position. Reflex responses return, and muscle tone strengthens. The animal may shiver, swallow, chew, or attempt to lick. Shortly after swallowing reflexes return, the animal will normally show signs of consciousness, including voluntary movement of the head or limbs and possibly vocalization.

While passing through stage II, some patients may exhibit a variety of alarming signs including head-bobbing, delirium, hyperventilation, head-thrashing, and rapid limb paddling, especially if not premedicated. Occasionally a patient may attempt to stand and fall or may appear blind and bump into the sides of the cage. Some patients (particularly those recovering from ketamine anesthesia) may chew at their paws or claw their faces. Animals showing these signs of a “rough” or “stormy” recovery usually return to normal within a short time, but steps must be taken to prevent self-trauma or disruption of the surgical wound. Administration of preanesthetic medications before the procedure often prevents or moderates these signs, but additional tranquilization or administration of analgesics during the postoperative period may be necessary in these patients.

Monitoring

During recovery, the patient must be watched continuously at close range because a recovering animal may develop hypoxemia, cardiac arrhythmias, or other complications, yet show no signs that are evident to the casual observer. Evaluation from across the room is not acceptable because problems such as vomiting, chewing the tube, and airway occlusion occur with some regularity and must be managed without delay to prevent serious consequences. These problems are discussed in detail in Chapter 13.

To minimize these risks, the patient should be positioned in the cage so that mucous membranes and respiration can be observed. Vital signs should be evaluated at least every 5 minutes. Abnormal vital signs or a delayed return to consciousness may indicate a variety of serious conditions that must be treated promptly by the veterinarian, such as shock, hemorrhage, hypoglycemia, or hypothermia.

Oxygen Therapy

As soon as the anesthetic depth decreases sufficiently, most recovering patients begin to shiver. Shivering is a protective response to hypothermia that raises the body temperature. During shivering, contracting muscle tissue converts oxygen and chemical fuel into heat. Consequently, muscle contractions associated with shivering increase oxygen consumption. Oxygen administration during recovery is necessary to meet these needs and to compensate for residual respiratory depression until anesthetic depth decreases. Oxygen should be administered via the endotracheal tube at a rate of 50 to 100 mL/kg/min (0.5 to 1 L per 10 kg body weight up to a maximum of 5 L/min) for 5 minutes after discontinuation of the anesthetic or until the animal swallows. This route of administration allows waste anesthetic gases to be scavenged and gives the anesthetist the ability to bag the patient during recovery to help reinflate collapsed alveoli.

If the patient is at a light depth of anesthesia and must be extubated, oxygen can be administered by mask. Some patients do not tolerate a mask without becoming agitated, however, and may require an alternative means of oxygen delivery. The following options are alternatives to the use of a mask during the postoperative period.

• An oxygen source such as the Y-piece or the fresh gas inlet of a non-rebreathing system can be placed near the nasal openings.
• An Elizabethan collar can be placed around the patient’s neck, with an oxygen line secured to the inside of the collar. The front of the collar is covered with cellophane, with a small ventilation hole. A flow rate of 1 L/min provides approximately 30% to 40% oxygen.
• Oxygen can be delivered via a nasal catheter. A lubricated soft red rubber catheter (5 to 10 French depending on the size of the patient) is introduced into the ventral nasal meatus. Intranasal proparacaine or 2% lidocaine can be used to desensitize the nasal tissues to allow insertion. The catheter is advanced to the level of the carnassial teeth and attached to the dorsum of the nose with tissue glue (cyanoacrylate). A flow rate of 100 to 150 mL/kg provides approximately 30% to 50% oxygen. Alternatively, nasal prongs used in human hospitals may be used. They can be secured to the patient with tissue glue or staples.
• The patient can be placed in an oxygen cage.

Note that a patient that is intubated and breathing oxygen from an anesthetic machine receives close to 100% oxygen. This is beneficial for the relatively short duration of most procedures, but prolonged inhalation of high levels of oxygen (e.g., greater than 50% oxygen for more than 24 hours) can be toxic.

Question 12

Describe general nursing care during the postanesthetic period.

Answer 12

In the postanesthetic period, patients require general nursing care to ease recovery, ensure their safety, and prepare them for return to the hospital ward. The anesthetist should be sensitive to the fact that the animal has no means of understanding the events that have produced the disorientation, fear, and discomfort that often accompanies the return to consciousness. Quiet, calm handling, reassurance, and attention to the patient’s comfort level are therefore essential.

The anesthetist can take several steps to minimize patient discomfort during recovery. All ties restraining the animal to the surgery table should be removed before the animal regains consciousness. The anesthetist should ensure that all accessory procedures, such as bandaging, chest tube placement, and urinary catheterization, have been completed and that all monitoring equipment probes, cuffs, and electrocardiographic electrodes have been removed. The anesthetist should also be gentle when moving a recovering patient, so as not to increase discomfort and pain.

The IV catheter should be left in place until the endotracheal tube has been removed and it is clear that the patient is recovering normally. This provides venous access in the event that the patient’s current condition or an unexpected complication necessitates administration of IV drugs or fluids.

Patient recovery may be hastened by gentle stimulation in the form of talking softly to the patient, gently patting or rubbing the chest, turning the patient, or gently moving the endotracheal tube. These actions stimulate breathing and increase the flow of information to the reticular activating system (RAS) of the brain—the area responsible for maintaining consciousness in the awake animal. A lack of stimulation of the RAS may cause drowsiness in the conscious animal. It is therefore speculated that stimulation of this area may help the animal to awaken. A recovering patient should also be turned every 10 to 15 minutes to prevent pooling of blood in the dependent lung and tissues—a condition called hypostatic congestion. When the intubated patient is turned from one side to another, the breathing circuit must be briefly detached from the endotracheal tube, and the head and neck should be turned as a single unit to minimize the risk of tracheal damage by the tube. Although not proven, there may be a risk of causing the stomach to twist if a patient is turned by moving the limbs over the body from one side to the other. For this reason, some professionals recommend turning a patient by sliding the limbs under the body instead, especially if the patient is a member of a breed prone to gastric dilatation–volvulus.

Never leave a recovering patient in an open cage or on a table unattended, because once spontaneous movement returns, a recovering patient may fall and be injured. Food and water should not be left in the cage during recovery because it is possible for a recovering animal to drown in a water bowl or suffocate in a food bowl. Some patients may be able to drink soon after standing; however, most have little appetite for food for several hours after recovery anyway. Vomiting during the recovery period is not uncommon, but provided the patient is conscious, this is seldom dangerous.

Nursing care of hypothermic patients should include the provision of heat. This can be accomplished by a variety of means including warm air or water blankets, heat lamps, warm water bottles, and incubators. Never use electric heating pads, which have a significant potential to burn a recovering patient. Box 9-6 lists recommended heat sources. Recovering patients are unable voluntarily to move away from a heat source if it is excessive; therefore the anesthetist must prevent burns by ensuring that the heat source never exceeds 42° C (approximately 107.6° F). Gradual rewarming is preferred to rapid rewarming because the latter may cause dilation of cutaneous vessels, leading to hypotension.

Analgesics should be administered as requested by the veterinarian, preferably before the onset of pain. If analgesia is adequate, the patient should be able to sleep comfortably and should demonstrate minimal signs of discomfort. A change in the dose or frequency of administration or use of a different or additional agent may be necessary if postoperative pain is not well controlled.

After recovery the anesthetist must provide ongoing care and prepare the patient for release or continued hospitalization. Most small animal patients should be given nothing by mouth for the first hour or two and no food for at least several hours. On discharge, the client should be instructed to reintroduce water gradually after arriving home and to feed a small meal after several hours. Exceptions to these guidelines include very small and neonatal patients, which require reintroduction of water and food more rapidly.