Anesthetic Monitoring PDF

Chapter 6 Anesthetic Monitoring Anesthesia and Analgesia for Veterinary Technicians and Nurses, 6th ed. Thomas and Lerche Learning Objectives—Lesson 6.1 (1 of 2) 1. Explain the principles of anesthetic monitoring, including the reasons for and goals o...

Chapter 6 Anesthetic Monitoring Anesthesia and Analgesia for Veterinary Technicians and Nurses, 6th ed. Thomas and Lerche Learning Objectives—Lesson 6.1 (1 of 2) 1. Explain the principles of anesthetic monitoring, including the reasons for and goals of monitoring. 2. List the physical monitoring parameters, and classify each in one of the following categories: (1) vital signs, (2) reflexes, (3) other indicators of anesthetic depth. 3. List and describe each of the stages and planes of anesthesia. Learning Objectives—Lesson 6.1 (2 of 2) 4. List the monitoring parameters used primarily to determine whether or not the patient is safe, and group them according to whether they primarily assess circulation, oxygenation, or ventilation. 5. Explain and demonstrate assessment of each of the vital signs, reflexes, and other indicators of anesthetic depth.  Monitoring Parameters (1 of 2)  Vital signs: indicate response of animal’s homeostatic mechanism to anesthesia  Heart rate  Heart rhythm  Respiratory rate and depth  Mucous membrane color  Capillary refill time  Pulse strength  Blood pressure  Body temperature  Best indicators of patient well-being  Monitoring Parameters (2 of 2)  Reflexes  Involuntary response to stimulus  Palpebral, corneal, pedal, swallowing, laryngeal, and papillary light reflexes  Other indicators of anesthetic depth  Spontaneous movement, eye position, pupil size, muscle tone, nystagmus, salivary and lacrimal secretions  Parameters offer predictable responses to anesthesia at various depths  May be affected by drugs, disease, or individual response variation  Monitor anesthetized patients as often as possible; continuously is ideal Objectives of Surgical Anesthesia  Patient doesn’t move  Patient isn’t aware  Patient doesn’t feel pain  Patient has no memory of the procedure Stages and Planes of Anesthesia  Three stages (I, II, III, IV)  Stage III divided into four planes  From stage I through stage IV there is a progressive decrease in pain perception, motor coordination, consciousness, reflex responses, muscle tone, and cardiopulmonary function  Stage I  Period of voluntary movement  Patient begins to lose consciousness  Characterized by:  Fear, excitement, disorientation, struggling, panting, urination, defecation  Increased heart rate and respiratory rate  Stage ends with loss of ability to stand and recumbency  Stage II  Period of involuntary movement; the “excitement stage”  Characterized by:  Breathing irregular  Vocalization, struggling, paddling  Increased heart and respiratory rate, pupils dilated, muscle tone marked, reflexes present  Actions are not under conscious control  Stage ends with muscle relaxation, slower respiratory rate, and decreased reflex activity  Stage III in 3 Planes  Plane 1: “light” surgical anesthesia  Not suitable for surgery  Plane 2: “medium” surgical anesthesia  Optimum depth for most surgical procedures  Plane 3: “deep” surgical anesthesia  Excessive depth  Light Stage III  Not adequate for surgery  Regular respiratory pattern, no involuntary limb movements  Eyeballs start to rotate ventrally, pupils partially constricted, decreased pupillary light reflex  Endotracheal tube may be passed and connected to gas anesthetic machine  Other reflexes are still present but decreased response  Medium Stage III (Surgical Anesthesia) (1 of 2)  Suitable depth for most surgical procedures  Characterized by:  Regular and shallow respiration with decreased rate  Blood pressure and heart rate mildly decreased  Relaxed muscle tone  Pedal and swallowing reflexes are absent  Ventromedial eye rotation  Medium Stage III (Surgical Anesthesia) (2 of 2)  Surgical stimulation may produce:  Mild increase in heart rate, blood pressure, or respiratory rate  Patient remains unconscious and immobile  Pupillary light response is sluggish; pupil size is moderate  Deep Stage III (1 of 2)  Deep anesthesia—excessive for most procedures  Characterized by:  Low heart and respiratory rates, decreased tidal volume  Reduced pulse strength  Increased capillary refill time (CRT)  Poor to absent papillary light reflex; central eyeballs; moderately dilated pupils  Reflexes are totally absent; muscle tone is very relaxed  Deep Stage III (2 of 2)  Early stage of anesthesia overdose  Characterized by:  Abdominal breathing  Fully dilated pupils; dry eyes  All reflexes are absent  Marked depression of the cardiovascular system, pale mucous membranes, increased CRT  Flaccid muscle tone  Stage IV  Period of anesthetic overdose  Characterized by:  Cessation of respiration  Circulatory collapse  Death  Resuscitate immediately to save the patient Assessment of Anesthetic Depth  Reflexes  Swallowing, laryngeal, pedal, palpebral, corneal  Pupillary light reflex or dazzle reflex  Present, decreased, depressed, or absent  Spontaneous movement  Muscle tone  Eye position, pupil size  Nystagmus  Salivary and lacrimal secretions  Heart and respiratory rates Assessment of Anesthetic Depth: Reflexes  An unconscious response to a stimulus  Conscious animals and protective reflexes  Decreased reflexes to stage III, plane 3 level anesthesia (when there are few to none)  Reflexes evaluated  Swallowing, laryngeal, pedal, palpebral, corneal, papillary light reflex  Reported as present, decreased, or absent  Swallowing Reflex  A normal response to food or saliva in the pharynx  Monitored by viewing the ventral neck region  Present in light surgical anesthesia  Lost in medium surgical anesthesia  Returns just before the patient regains consciousness  Used to determine when to pull the endotracheal tube  Laryngeal Reflex  Epiglottis and vocal cords close immediately when larynx is touched by an object  Prevents tracheal aspiration  Observed during intubation if animal is in the light plane of anesthesia  Makes intubation difficult  Especially in cats, pigs, and small ruminants  May cause laryngospasm in cats, pigs, and small ruminants  Palpebral Reflex  The blink reflex in response to a light tap on the medial or lateral canthus  May be elicited by lightly stroking the hairs of the upper eyelid  Present in light anesthesia  Often lost during medium anesthesia, although the exact point varies  Slow palpebral response in horses indicates adequate surgical anesthetic depth  Ruminants tend to have a slightly stronger reflex than horses  Pedal Reflex  Flexion or withdrawal of limb in response to squeezing, twisting, or pinching a digit or pad  Used in small animals only  Varies from subtle muscle contraction to full withdrawal of limb  Varies with depth of anesthesia  Present in light anesthesia  Absent in medium anesthesia  Requires a high-intensity stimulus  Corneal Reflex  Retraction of eyeball within orbit and/or a blink in response to corneal stimulation  Touch the cornea with a drop of sterile saline or artificial tears  Most useful in large animals; difficult to elicit in small animals  Present in light and medium anesthesia; absent in deep or excessive anesthesia  Used primarily to determine if a LA patient is too deep  Pupillary Light Reflex (PLR)  Constriction of pupils in response to bright light shined on one retina  Present in light and medium anesthesia; absent in deep anesthesia  Dazzle reflex  Blink response to bright light shined on retinas  Same significance as PLR  Lost very early in anesthesia  Other Indicators of Anesthetic Depth  Spontaneous movement  Muscle tone  Eye position  Pupil size  Nystagmus  Salivary and lacrimal secretions  Heart and respiratory rates  Response to surgical stimulation Learning Objectives—Lesson 6.2 (1 of 4) 6. List normal values for each physical monitoring parameter, and identify values that should be reported to the attending veterinarian. 7. Explain setup, operation, care, maintenance, and troubleshooting of an esophageal stethoscope, electrocardiograph, Doppler monitor, oscillometric blood pressure monitor, pulse oximeter, and capnograph. 8. Describe the information derived from anesthetic gas monitoring, oxygen monitoring, and anesthetic depth monitoring. Learning Objectives—Lesson 6.2 (2 of 4) 9. Interpret output and data from an esophageal stethoscope, electrocardiograph, Doppler monitor, oscillometric blood pressure monitor, pulse oximeter, and capnograph. 10. Describe how to determine the blood pressure using a Doppler monitor, oscillometric blood pressure monitor, or arterial catheter and transducer. Learning Objectives—Lesson 6.2 (3 of 4) 11. Identify the following rhythms on an electrocardiographic tracing: normal sinus rhythm (NSR); sinus arrhythmia (SA); sinus bradycardia and tachycardia; first-, second-, and third-degree atrioventricular (AV) heart block; supraventricular premature complexes (SPCs) and ventricular premature complexes (VPCs); supraventricular and ventricular tachycardia; atrial and ventricular fibrillation; and QRS and T-wave configuration changes. Learning Objectives—Lesson 6.2 (4 of 4) 12. Identify machine-generated data that should be reported to the VIC. 13. Identify abnormal monitoring parameters, and list common causes of abnormal monitoring parameters. 14. Use monitoring parameters to determine anesthetic depth. 15. Explain adverse consequences of hypothermia, and identify strategies to prevent hypothermia. Determining Whether the Patient is Safe (1 of 2)  Assess vital signs  Physical Touch, hearing, vision  Mechanical instruments Electrocardiograph Blood pressure monitor Capnograph Doppler blood flow monitor Pulse oximeter Determining Whether the Patient is Safe (2 of 2)  Vital signs groupings  Circulation Heart rate and rhythm, pulse strength, CRT, mucous membrane color, blood pressure  Oxygenation Mucous membrane color, CRT, hemoglobin saturation, inspired oxygen, arterial blood oxygen  Ventilation Respiratory rate and depth, breath sounds, end-expired carbon dioxide levels, arterial carbon dioxide, blood pH  Indicators of Circulation: Heart Rate (1 of 2)  Physical assessment  Palpation of apical pulse through the thoracic wall  Palpation of the peripheral pulse  Auscultation with stethoscope: more difficult in recumbent, anesthetized animals  Mechanical assessment  ECG machine  Blood pressure monitor  Intraarterial line and transducer  Indicators of Circulation: Heart Rate (2 of 2)  Bradycardia  Depressant effect of most anesthetics  Excessive anesthesia depth  Adverse effects of drugs  Tachycardia  Inadequate anesthetic depth  Pain  Hypotension  Blood loss  Shock  Hypoxemia  Hypercapnea  Indicators of Circulation: Heart Rhythm  Assessed along with heart rate  Normal sinus rhythm vs. sinus arrhythmia  First- or second-degree heart block  Causes of arrhythmias  Drugs  Medical states or diseases  Instruments Used to Monitor Heart Rate and Rhythm  Esophageal stethoscope  Thin flexible catheter attached to audio monitor or conventional stethoscope  Electronically amplifies heart sounds  Inserted into esophagus to level of the fifth rib and adjusted for maximum sound  Electrocardiograph monitor  A graphic representation of the electrical activity of the heart  Used to detect arrhythmias, which are common in anesthetized animals  Differentiate normal from abnormal and dangerous from harmless rhythms  Commonly Encountered Cardiac Arrhythmias  Sinus arrhythmia (SA)  Sinus bradycardia  Sinus tachycardia  AV heart block (first, second, third degree)  Premature complexes  Supraventricular premature complexes (SPCs), Supraventricular tachycardia, Ventricular premature complexes (VPCs), Ventricular tachycardia  Fibrillation  Indicators of Circulation: Capillary Refill Time (CRT)  Rate of color return to oral mucous membrane after application of gentle digital pressure  Indicates peripheral tissue blood perfusion  >2 seconds is prolonged and indicates poor perfusion  May result from epinephrine release, low blood pressure, hypothermia, cardiac failure, excessive anesthetic depth, blood loss, shock  Results in reduced temperature of affected part(s)  Indicators of Circulation: Blood Pressure (BP)  Force exerted by flowing blood on arterial walls  Evaluates tissue perfusion during anesthesia  Factors involved: Heart rate, stroke volume, vascular resistance, arterial compliance (elasticity), blood volume  Varies throughout cardiac cycle  Hypotension vs. hypertension  Indicators of Circulation: Pulse Strength  Used as a rough indicator of blood pressure  Determined by the difference between systolic and diastolic blood pressure, vessel diameter, and other factors  Palpate a peripheral artery  Lingual, femoral, dorsal pedal, carotid, facial, auricular  Appropriate arteries vary by species  Reduced in anesthetized animals  A subjective interpretation  Blood Pressure Monitors (1 of 2)  Direct  Reading obtained via indwelling catheter inserted into an artery (facial or aural) and attached to a pressure transducer and monitor  Most commonly used in equine practices and research facilities  Provides continuous reading throughout the cardiac cycle  Most accurate  Indicators of Oxygenation: Mucous Membrane Color (1 of 2)  Assessed by observing the gingiva  Varies from patient to patient  Evaluate before each procedure to determine baseline for patient  Rough assessment of oxygenation and tissue perfusion  Alternate sites: tongue, conjunctiva of lower eyelid, mucous membrane lining of prepuce or vulva  Indicators of Oxygenation: Mucous Membrane Color (2 of 2)  Pale mucous membranes: blood loss, anemia, poor capillary perfusion  Cyanotic membranes (blue to purple): respiratory arrest, oxygen deprivation, pulmonary disease  Affected by body temperature, vascular resistance, gum disease  Physiology of Oxygen Transport  Adequate oxygen necessary for metabolic processes  Components of total oxygen content  Free, unbound oxygen molecules dissolved in plasma (minor content)  Oxygen chemically bound to hemoglobin in erythrocytes (four binding sites/hemoglobin molecule)  Most oxygen is carried by hemoglobin  100% saturation: all available hemoglobin binding sites are filled with oxygen  Indicators of Oxygenation: Measuring Blood Oxygen (1 of 2)  Calculated oxygen content  Measures both bound and dissolved oxygen  An accurate measurement expressed as mL/dL  (CaO2) = (Hb × 1.39 × SaO2/100) + (PaO2 × 0.003)  Partial pressure (PaO2)  (normal = 90 to 110 mm Hg arterial blood)  Measures unbound oxygen dissolved in plasma (N = ~1.5% total content)  Expressed as mm Hg and varies in arterial, capillary, or venous blood  Highest in arterial blood; lowest in venous blood  Indicators of Oxygenation: Measuring Blood Oxygen (2 of 2)  Percent oxygen saturation (percent SaO2)  Percentage of total number of available hemoglobin binding sites occupied by oxygen molecules (normal ≥97% total content)  Varies in arterial, capillary, or venous blood  Highest in arterial blood; lowest in venous blood  Partial Pressure and Oxygen Saturation  A nonlinear direct relationship  As one decreases so does the other, but not at the same rate  As partial pressure decreases the oxygen saturation also decreases, but not as rapidly  Indicates oxygen availability in animals with normal hemoglobin levels  Measuring Partial Pressure and Oxygen Saturation  Blood gas analyzers measure partial pressure  Pulse oximeters measure oxygen saturation  PaO2 and SaO2 are elevated in anesthetized patients breathing pure oxygen  Low PaO2 and SaO2 observed during anesthesia can indicate hypoxemia and the need for oxygen supplementation or assisted ventilation  Pulse Oximeter  Measures the saturation of hemoglobin and the heart rate  Red and infrared wavelength light technology with digital readout  >95% saturation normal in patient breathing pure oxygen 