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MONITORING ANIMALS WITH THE USE OF INSTRUMENTATION These machines can be very useful, especially in the situations where the technician can’t always be with the patient through the entire procedure; however you should never completely rely on your machines The following can be monitored via machines: Blood pressure, Central Venous Pressure, Blood Gases, Pulse Oximetry, Capnography, and Electrocardiography EKG Measures the electrical activity of the heart – NOT the mechanical activity. REMEMBER THAT THE EKG CAN CONTINUE EVEN IF YOUR PATIENT’S HEART IS NOT CONTRACTING. This is called electromechanical dissociation. The complexes should be of normal configuration, consistent size, rate, and rhythm If the complexes look abnormal: Alert the Dr. Check the patient! Check the lead placement EKG Cardiac arrhythmia is any pattern of electrical activity that differs from the healthy, awake animal MOST COMMON EKG ABNORMALITIES SEEN WHICH MUST BE ADDRESSED are: 1)Sinus Tachycardia Diagnosed when a patient’s HR under anesthesia is: >200 bpm in cat >180 bpm in small dog > 160 bpm in large dog EKG: SINUS TACHYCARDIA Causes: Can be drug-related (atropine, ketamine), or response to surgical stimulation If animal is also “huffing”, during surgery if reflex activity is present or moving occurs, it may be too “light” Can also occur in situations of hypoxia (early), hypotension, or high CO2 levels Pre-existing conditions of the heart, thyroid, anemia, shock Emergency treatment can include applying pressure to the eyeballs EKG:SINUS BRADYCARDIA 2) Sinus Bradycardia Diagnosed when patient’s HR under anesthesia is: < 60 bpm in large dog <70 bpm in small dog < 100 bpm in a cat Causes: Can be drug related (xylazine, medetomidine, opiods) Increased anesthetic depth, hypoxia (late stages), hypothermia Treatment: Can give reversal agents or atropine Assess other parameters before deciding management EKG: HEART BLOCKS 3) AV Heart Blocks Electrical impulse through the heart is not being transmitted efficiently. 1st Degree: There is a P wave for every QRS complex, but the P-QRS interval is prolonged 2nd Degree: Some P waves are not followed by QRS complexes 3rd Degree: The atria and ventricles are contracting independently. No normal relationship between P waves and QRS complexes EKG:HEART BLOCKS 2nd and 3rd degree blocks can be seen after alpha-2agonist administration, high vagal tone, and some other conditions 4) Ventricular premature contractions (VPCs) Impulse arising from the ventricular muscle causing an uncoordinated heart contraction QRS complexes are wide and bizarre Also caused by hypoxia, heart disease or trauma, electrolyte abnormalities, etc Epinephrine release can stimulate the formation of VPCs Don’t forcibly restrain an animal during the induction of anesthesia! EKG: VENTRICULAR TACHYCARDIA Ventricular Tachycardia: > 3 VPCs in a row, more than 15 in one minute, or VPCs + falling blood pressure EMERGENCY!! Can be treated with Lidocaine given IV EKG:FIBRILLATION Fibrillation Contraction of small muscle bundles within the atria or ventricles Atrial fibrillation No p-waves, high HR, normal QRS complexes Ventricular fibrillation Absence of QRS complexes CARDIAC ARREST IS IMMINENT ECG: Atrial Fibrillation BLOOD PRESSURE Refers to arterial blood pressure Systolic Pressure – produced by the contraction of the ventricles as it propels blood through the aorta, pulmonary artery, and other major arteries Diastolic Pressure – the pressure that remains when the heart is resting between contractions. Mean Arterial Pressure (MAP) - average pressure through the cardiac cycle and best indicator of organ perfusion under anesthesia = diastolic pressure + (systolic-diastolic pressures) 3 BLOOD PRESSURE Pulse pressure – pressure detected by manual palpation the difference between systolic and diastolic pressure Blood pressure can vary with age, breed, species, and instrumentation It is important to monitor TRENDS in blood pressure in addition to actual values BLOOD PRESSURE Normal systolic BP in awake dogs and cats:120 Normal range 90-150 mm Hg Should ideally remain at or above 90 mm Hg in anesthetized patients Normal diastolic BP in awake dogs and cats: 80 Normal range = 50-90 mm Hg Normal MAP: 90-100 mm Hg -Should be maintained above 60 mm Hg in anesthetized patients - This is the best indicator of blood perfusion to the internal organs BLOOD PRESSURE MONITORING INDIRECT BP MONITORING Method most commonly used in private practice Noninvasive, less technically difficult than direct monitoring 2 types of monitors: DOPPLER – determines SYSTOLIC PRESSURE ONLY by detecting the echo of RBCs passing through an artery Probe is placed on the leg or tail of an animal and a cuff is used to compress an artery and then detect the pressure at which blood flow resumes OSCILLOMETRIC – determines, systolic, diastolic, and MAP by detecting the oscillations within the cuff caused by the pulsation of the artery beneath the cuff INDIRECT BP MONITOR: OSCILLOMETRIC INDIRECT BP MONITOR: OSCILLOMETRIC Less labor intensive than Doppler monitors but tend to be less consistent in their ability to register blood pressures for smaller patients Set to automatically cycle every 2 to 3 minutes -1 minute cycles tend to create an ischemic challenge to the extremity INDIRECT BP MONITOR: OSCILLOMETRIC Cuff width should be 30%-50% of limb circumference for dogs and cats -Excessively wide cuffs will lead to an under-estimation of blood pressure -Excessively narrow cuffs will lead to an over-estimation of blood pressure Location of cuff is important -Most consistent cuff location for small patients is the midforeleg, tailbase -Don’t hesitate to try all locations as needed -Good locations for larger animals include metacarpus, metatarsus, and distal tibia just above tarsus INDIRECT BP MONITOR: DOPPLER -More consistently effective when monitoring small patients -Measures systolic pressure only -Hair is clipped at the probe site -The depression in the probe must be filled with ultrasound gel -Once you hear the swishing sound, tape the probe in place -Both excessive and inadequate pressure can create difficulties measuring accurately INDIRECT BP MONITOR: DOPPLER -It is often possible to obtain readings by first wetting the site with alcohol, then applying coupling gel to the site and the probe without clipping any hair -The cuff is placed just proximal to the probe -Cuff width is as important with doppler BP measurement as with oscillometric BP measurement -Cuff width should be 30-50% of limb circumference for dogs -Excessively wide cuffs will lead to an underestimation of blood pressure -Excessively narrow cuffs will lead to an overestimation of blood pressure -5 readings are taken, the highest and lowest are thrown out. The average of the other 3 are used to determine the SAP. http://www.youtube.com/wa tch?v=Li4oGhfKmDQ http://www.vasg.or g/doppler_use.htm DIRECT BP MONITORING Used less than indirect methods in private practice Indwelling catheter is placed in femoral or dorsal pedal artery Catheter is connected to a manometer or pressure transducer via a fluid-filled tubing and the pressure is displayed http://www.vasg.org/direct_arterial_pressures.htm WHAT CAN I DO IF THE BLOOD PRESSURE IS TOO LOW? Check the patient! Decrease the inhalant anesthetic setting Increase the IV fluid flow rate (check with the Dr. first of course) Check the cuff to ensure proper placement/positioning Location Selection: cuff size should be 30-50% of the circumference of the selected location. So, hold the cuff up to the desired location and turn it sideways – it should go roughly halfway around the limb or tail. Finally…. Hetastarch, Dopamine, Dobutamine ….to be used in emergencies! CENTRAL VENOUS PRESSURE -Measurement of the blood pressure in a central vein -anterior vena cava -Assesses how well the blood is returning to the heart and the ability of the heart to receive and pump blood -Helpful in monitoring animals with right sided heart failure and preventing overhydration in animals receiving IV fluids CENTRAL VENOUS PRESSURE www.dcavm.org/08techmar.html http://books.google.com/books?id=LtGS0t1MIskC&pg= PA410&lpg=PA410&dq=manometer+veterinary+medici ne&source=web&ots=BIOCQL_14Z&sig=MZnEtUSN6v pdi4TTnNjYkAduva4&hl=en&sa=X&oi=book_result&r esnum=9&ct=result#PPA410,M1 BLOOD GASES Refers to measurement of blood pH and dissolved oxygen and carbon dioxide gas in arterial or venous blood. -Indicate how well the patient is obtaining oxygen and delivering it to the tissues and how well the lungs are expelling carbon dioxide -All of these depend on the respiratory function of the patient. BLOOD GASES OXYGEN OXYGEN EXISTS IN 2 FORMS IN THE BLOOD: Free molecule dissolved in plasma (PaO2) Measured by a blood gas analyzer Values below 60 mm Hg indicate hypoxia!! To treat: supplement oxygen, assist ventilation Chemically combined with hemoglobin in RBCs (SaO2 or SpO2) Measured by a pulse oximeter Values below 90% indicate hypoxia!! To treat: supplement oxygen, assist ventilation BLOOD GAS ANALYZER Not commonly used in private practice Blood sample should be taken from an artery Sample is placed on ice and should be run within 2 hours of collection PULSE OXIMETER Inexpensive, noninvasive, portable, easy to use Clip is placed on a thin strip of tissue that is nonpigmented and hairless Most commonly the tongue, but can also use the pinna, rectal mucosa, toe webbing, lip, vulvar fold, Achilles tendon, under base of tail PULSE OXIMETER Values should ideally read 97% or greater under anesthesia Animals that are not anesthetized can also be connected to a pulse oximeter Used during emergencies in animals with respiratory distress. BLOOD GASES: CARBON DIOXIDE PaCO2 = The portion of carbon dioxide that is dissolved in plasma (Carbon dioxide partial pressure in the arteries) Blood gas analyzers tell how well the patient is eliminating CO2 An awake patient’s levels are usually less than 45 mm Hg. It is common to see levels of 45-60 mm Hg in an anesthetized patient because the animal doesn’t breathe deeply enough to eliminate the usual amount of CO2 If greater than 60 mm Hg, hypoventilation is present. Assess other parameters to determine oxygenation and assist ventilation if necessary CARBON DIOXIDE Carbon dioxide build-up can result in respiratory acidosis Commonly seen levels are 7.2-7.3 as compared to normal values of 7.35-7.45 Blood pH is measured via blood gas analyzers CAPNOGRAPHY A capnometer is placed on the endotracheal tube: it monitors the amount of CO2 that is expired Noninvasive Info is displayed as a graph CAPNOGRAPHY Measure End Tidal CO2 As inspiration occurs, CO2 should be around zero Hypercapnea = ET CO2 greater than 55 mm Hg CO2 canister needs changing, hypoventilation (should correct when patient is bagged) Hypocapnea = ET CO2 less than 35 mm Hg Tachypnea, dead space, too much assisted ventilation, improper endotracheal tube placement/connection Correcting Blood Gas Abnormalities The main reason for a low SpO2 in an anesthetized patient is decreased ventilation 1) The animal is not breathing well and you need to assist it Respiratory rate should be 8 – 20 breaths /min for the average patient (avg = 10-12 bpm). Small patient may need more breaths. You can ventilate the patient by closing the pop – off valve, squeezing the bag to inflate the lungs. NEVER SQUEEZE THE BAG TO MORE THAN 20 cm H20!!! Try just occasional breaths at first – the more breaths you give, the less the patient’s brain will stimulate the patient to breathe on it’s own. Use the patient and the pulse ox as a guide. Correcting Blood Gas Abnormalities 2) The patient has ventilation/perfusion mismatch – the oxygen isn’t getting to the areas in the lungs where the blood is Check that the machine is hooked up properly Check that the oxygen is turned on/in tank Check that the endotracheal tube is placed correctly and the cuff is properly inflated. If the tube is in too far, the gas/O2 will only go to one side of the lungs. 3) The patient’s pulse is weak Check that the patient isn’t too deep Check the blood pressure and act accordingly (see section on blood pressure) Correcting Blood Gas Abnormalities 4) The sensor is slipping off the patient 5) The sensor has been at one location for a long time and is too dry or is pinching off blood supply to the area. The following locations may be used for the pulse ox. probe: tongue, lips, ear, toe webbing, prepuce, and vulva. 6) The patient may have a preexisting lung disease 7) Bradycardia or severe arrhythmias