Monitoring during Anesthesia Flashcards
What do you need to know?
what is normal
how old is the patient?
species?
what drugs did the patient recieve?
what is the procedure?
what is normal for this specific patient?
what do we monitor?
CNS
CVS
respiratory
renal
temperature
other? -case dependent
CNS monitoring
- need to maintain good anesthetic depth
- check for reflexes:
- eye (palpebral, corneal, nystagmus, lacrimation)
- jaw tone
- anal reflex
- pedal reflex
- EEG and other monitoring not used regularly
evaluating plane of anesthesia:
- species and individual variations
- position of eye
- movement
- muscle tone
- certain reflexes
- response to surgical stimulation
- nystagmus (usually in horse)
- shivering (light)
- eye reflexes present
light plane of anesthesia
- central eye position
- cessation of limb movements
- muscle tone remains
- response to surgical stimulation (either movement or breathing/hemodynamic response)
- nystagmus (horse)
- eye reflexes present
- shivering
- moist cornea
medium plane of anesthesia (goal)
- no spontaneous movement
- no reflex movement
- no change in hemodynamic or breathing in response to surgical stimulation
- moderate muscle tone
- decrease in tidal volume
- no palpebral reflex
- no shivering
- ventromedial rotation of the eye
- small pupil aperture
- moist corneas
deep plane of anesthesia
- decrease in tidal volume
- abdominal breathing may be noted
- eyes fixed centrally
- no pedal reflexes
- no spontaneous or reflex movement
- bradycardia/hypotension and worsening of hemodynamic function
- no palpebral and corneal reflex
- dilated pupil
- dry cornea (dead…)
CV monitoring
maintain perfusion to body organs and maintain a normal rhythm and rate
use clinical skills as well as specific equipment to monitor HR, BP, etc
evaluating mucous membranes
- pale pink/pink: normal
- white/pale: anemia, vasoconstriction, lack of circulating fluid
- cyanosis: lung disease, decrease in oxygen flow to the breathing circuit, endobronchial intubation
- red/bright pink: hypercapnia
evaluating CRT
- the time it takes for blood flow back into the capillary bed after it is manually compressed with a digit of the anesthetist
- may be deceptive in determining peripheral perfusion: may refill from engorged veins as well as arteries
- normal < 1-2 seconds
evaluation of pulse
- information about the rate, rhythm and pulse quality
- subjective
- SA: lingual, femoral and digital
- LA: facial, transverse facial, digital arteries
equipment/techniques used to monitor CVS
- esophageal stethoscope
- ECG
- BP monitoring
- pulse ox
- central venous pressure
- urine output
esophageal stethoscope
- blind-ended tube that is passed into the esophagus at the level of the heart and is connected to ear pieces to which you can listen to
- can evaluate rhythm, rate
- cannot evaluate adequacy of circulation
- can be annoying to the anesthetist
ECG
- electrical activity of the heart
- heart rate and rhythm
- not good for evaluation cardiac function or disease
-
placement of leads
-
LA-lead I
- RA-right jugular farrow
- LA- ventral midline under heart apex
- RL- any site remote from heart
-
LA-lead II
- RA-right elbow
- LA-left elbow
- LL-left stifle or abdomen
-
LA-lead I
common arrhythmias
sinus tachycardia
sinus bradycardia
second degree AV block
VPCs
normal HR for different species:
dog 70-140
cat 110-140
horse 30-45
cattle 60-80
sheep 70-130
goat 90-160
BP monitoring
- maintain adequate perfusion to the vital organs
- a mean BP should be maintained above 60 mmHg (70 in horses)
- two methods:
- direct
- indirect
direct BP
- provides real time beat by beat pressure monitoring
- invasive: place an arterial catheter which is connected to tubing then to a pressure transducer
- aseptic technique when placing arterial lines
- hematoma formation common
-
arteries used:
- dogs: femoral, dorsal pedal
- cats: dorsal pedal, tail
- horse: facial arteries, transverse facial, great metatarsal
- cattle: middle coccygeal, median auricular
- sheep/goat: median auricular artery
indirect BP monitoring
- sphymomanometry
- occlusion of artery by inflatable cuff and return of BF distally to the cuff as the pressure of the cuff is reduced
- when pressure is reduced, 1st sound heard is systolic P
- cuff measure at which BF ceases to increase with decreasing cuff P is diastolic P
- stethoscope, doppler pulse detectors
- systolic should be > 80 mmHg
why is cuff size important when measuring BP?
width of cuff should be ~40 % of circumference of limb
bigger width than circumference: underestimate BP
smaller width than circumfrence: overestimate BP
too tight: underestimate
too loose: overestimate
oscillometric method
- cuff is inflated to a pressure and pressure is slowly released as the monitor detects the oscillations in the cuff caused by BF under cuff
- as pressure decreases, there is an increase in BP and oscillations
- systolic: rapid increase in amplitude of oscillations
- mean: lowest cuff pressure at which maximum oscillation occurs
- diastolic: rapid decrease in oscillation after max oscillation
- MAP > 60 mmHg
measuring cardiac output
- invasive method (thermodilution)
- requires special and expensive equipment
- not used routinely
- CO = SV x HR
pulse oximetry
- arterial oxygen saturation
- heart rate monitoring
- placed on tongue, ears, digits
- measures light absorption of two different wavelengths at fast intervals during pulsation
- detects reduced hemoglobin and oxyhemoglobin
- sensitive to movement, cold, vasoconstriction
- should be maintained >95%
at what percent do you consider the patient to be hypoxemic?
<90%
central venous pressure
- pressure within the thoracic vena cava
- balance between venous blood volume and contractility of the heart
- decreased CVP = hypovolemia
- increased CVP = fluid overload
-
normal
- SA: 2-7 cmH2O
- LA: 15-25 cmH2O
urine output
- dependent on CO, blood volume, and renal function
- not used often in anesthesia
- need to catheterize in order to quanitify
- normal 1-2 mL/kg/hr
monitoring respiratory system
- maintain oxygenation and remove CO2
- respiratory rate
- chest excursions
- abdominal effort
- tidal volume can be subjectively evaluated based on movement of rebreathing bag and thoracic excursions
- monitor MM color
normal respiration rates
dog 10-30
cat 24-42
horse 8-15
cow 12-35
sheep 15-40
goat 15-25
pig 10-45
equipment/techniques for monitoring respiration
ventilometer/respirometer
blood gas analysis
capnograph
pulse ox
ventilometer/respirometer
measures the tidal volume and minute volume of the patient
normal tidal volume 10-15 mg/kg
creates dead space, can accidentally extubate patient
blood gas analysis
measures levels of oxygen and CO2 in arterial blood
provides acid-base status
can also measure electrolytes/glucose/lactate
capnography
- measures the end tidal CO2 and the inspired CO2 tension
- connected between the patient and the breathing system
- provides info on: adequacy of ventilation, CVS, patient’s metabolism
- useful to measure: hypoventilation, hyperventilation, apnea, disconnection, rebreathing, obstruction, embolism
phases of capnogram
Phase I: inspiratory baseline
Phase II: expiratory upstroke
Phase III: expiratory plateau
Phase IV: inspiratory downstroke
Phase I
- inspiratory baseline
- represents the inspiration of fresh gas with CO2
- the baseline should stay at the level that corresponds to zero concentration (mmHg) of CO2
- normal end tidal CO2 = 35-45
Phase 2
- expiratory upstroke
- occurs shortly after the inspiration ends
- upstroke is caused by the rapid washing out of the fresh gas in the anatomic space and then replacement by CO2-rich alveolar gas
- should be steep
Phase 3
- expiratory plateau
- represents continuous exhalation
- line will be perfectly horizontal if ventilation and perfusion were perfectly matched
- however, ventilation and perfusion are not perfectly matched
- this results in CO2 slowlly increasing as the gas from the lung areas with lower ratio of ventilation to perfusion reaches the sampling site
phase 4
- inspiratory downstroke
- occurs shortly after expiration ends and represents the rapid washing out of the CO2 by fresh gas as inspiration starts
- should be steep
pulse ox to monitor respiratory system
lower oxygen tension means lower arterial oxygen saturation
will also see low saturation with pulmonary embolism
body temperature
- hypothermia and hyperthermia should be avoided
- thermistor/thermocouple inserted into the esophagus (core temp)
- can use a rectal thermometer
- maintain >94 deg F
- rule out malignant hyperthermia in pigs
anesthetic complications due to hypothermia:
decrease in anesthetic requirements
not responding to anticholinergics
prolonged recovery
cardiopulmonary depression
