Monitoring In Anesthesia

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Monitoring In Anesthesia:

Monitoring In Anesthesia Dr Walid I Hamimy Department of anesthesia Cairo University

Objectives:

Objectives What are the standard monitors? What is the physical principle of each? Anesthetic Implications !!!!

Goals:

Goals Safety Perioperatively Physiologic stability Early identification of problems for early correction Proper monitoring  risk

ASA standards for basic anesthesia monitoring:

ASA standards for basic anesthesia monitoring Qualified provider should be available throughout anesthesia Oxygenation Oxygen analyzer Oximeter Ventilation Capnography Ventilator alarms Circulation ECG Blood pressure Temperature Observe Color of patient Chest movements Color & amount of blood in operative field

Monitors for Oxygenation:

Monitors for Oxygenation

Why Do We Monitor Oxygen?:

Why Do We Monitor Oxygen? Overall assessment of the whole system Oxygen supply to the patient Oxygen uptake by the lungs Oxygen delivery to the tissues via the circulation Oximetry Oxygen Monitor

Oxygen:

Oxygen Oxygen in gas mixture FiO2 Oxygen monitor Oxygen in blood PaO2 Oxygen electrode CaO2 Lex Oxygen con SaO2 Oximeter

Oxygen monitor:

Oxygen monitor Rapid detection of hypoxic mixture Calibration daily (usually by the 21% of room air) Ideal location depends on the response time Slow Inspiratory limb Rapid patient connection limb to check inspiratory & expiratory

Oxygen monitor:

Oxygen monitor Paramagnetic oxygen analyser Fuel cell

Oxygen monitor: Physical principle:

Paramagnetic O2 analyser all gases are diamagnetc (repelled from magnetic field) Except O2 & NO which are paramagnetic (being attracted to a magnetic field) Oxygen monitor: Physical principle

Paramagnetic O2 analyzer:

Paramagnetic O2 analyzer N2 N2 N2 N2 N S

Oxygen Monitor: Physical principle:

Oxygen Monitor: Physical principle Galvanic Oxygen Analyzer (Fuel cell) Silver cathode Lead anode Oxygen is first reduced to generate a current proportional to its concentration Response time 20 s Accuracy to within  3%

Oxygen electrode:

Oxygen electrode For measurement of PaO2 Either trans-cutaneous or through arterial blood sample

Oxygen electrode Clarke electrode:

Oxygen electrode Clarke electrode Polarography: Application of a small voltage (0.6 V- 600 mV) will reduce Oxygen releasing electrons. Consists of Platinum cathode Silver/Silver Chloride anode dipped in buffered electrolyte to minimize the effect of CO2 Reduction of O2  electrons  flow of current proportion to O2 tension

Oxygen electrode Clarke electrode:

Oxygen electrode Clarke electrode

Trans-cutaneous PaO2:

Trans-cutaneous PaO2 Heating of skin to 45 o to be Hyperdynamic Continuous Non invasive Warm up period of 15 min Response time 15 s Thin skin more reliable

Oximeter:

Oximeter

Oximeter:

Oximeter Measures SaO2 by spectrophotometry in intact tissue Accuracy to within  2% Based on Beer-Lambert law “ The amount of absorption of light  the quantity of the substance ” Isobestic point

PowerPoint Presentation:

Red Zone Infra Red Zone Red uced Hb absorbed more by Red light Oxy Hb absorbed more by Infrared light I.B I.B

Structure:

Structure Probe Attached to Finger Ear lobe nasal bridge Wrapped around a digit Two light emitting diodes Red & Infra-red light diodes Single detector on the opposite side

Display:

Display Pulse waveform Heart rate Saturation of Oxygen Constant absorbance due to tissues, venous & capillary blood Variation in transmitted light absorbance for each wave length is assumed to be due to arterial pulsation Rate of pulsation (variation) is read as heart rate

Advantages of Oximeters:

Advantages of Oximeters Simple to use Non invasive No warm up time Not affected by pigmented skin

Disadvantages of Oximeters:

Disadvantages of Oximeters Read inaccurately in the presence of Carboxy , methemoglobin & bilirubin !!!! Hypothermia Severe hypotension Excessive incident light

Sources of error :

Sources of error Sensor Inadequate light transmitted (nail polish, onychomycosis) Surrounding light Movement or diathermy causing "noise" in received signal Processing Increasingly unreliable with low SpO2 Haemoglobin High concentration of MetHb (down towards 85%), COHb (up towards 100%) or other species Other light-absorbing species in blood (methylene blue, other dyes) Blood flow (Shock, hypotension & hypothermia)

Monitors for Ventilation:

Monitors for Ventilation Capnography Ventilator alarms

Why monitor CO2:

Why monitor CO2 Global well-being The excretion of CO2 is the final common pathway of metabolism Risk management Nothing is called minor anesthesia Airway is the commonest problem Specific diagnostic patterns

Carbon dioxide:

Carbon dioxide E T CO2 Capnography P a CO2 CO2 electrode Trans cutaneous Arterial blood sample

Capnography:

Capnography E T CO2 correlates well with PaCO2 in the absence of pulmonary disease PaCO2 = 40 mm Hg E T CO2 = 35 mm Hg Infra red gas analyzer

Infra red gas analyzer Capnography:

Infra red gas analyzer Capnography CO2 or any other gas containing 2 dissimilar atoms absorb infra red radiation Amount of absorption is related to conc. Infra red is passed through 2 tubes Sample Reference

Infra red gas analyzer Capnography:

Infra red gas analyzer Capnography

Types of capnography:

Types of capnography According to position in circuit: in-line out of circuit at the end of a sampling tube. In-line analyser (Main stream) Advantages No sampling tube to block Disadvantages bulk. needs to be heated. windows fogging up. can't be used on non- intubated patients Sampling (Side stream) The sampling variety has the big disadvantage of a sampling tube which tends to get blocked with condensation. Some companies offer a special tube that allows water to escape. expensive

Normal Tracing:

Normal Tracing At first there is a rapid rise as the dead space gas comes out of the major airways. Then, there is a plateau which is allowed to have a slow rise. Finally, there is a rapid decline as the next breath enters the patient

Poor plateau:

Poor plateau Kinked tube Herniated cuff Bronchospasm Any obstruction that limits expiration

Curare cleft:

Curare cleft Usually seen with high CO2 It is a diaphragmatic twitch pulling some fresh gas past the sampling tube Not to be confused with cardiogenic oscillations

Cardiogenic oscillations:

Cardiogenic oscillations Caused by the beating of the heart against the lungs Said to be more readily seen as relaxant wears off and tone returns to chest and abdominal walls and diaphragm. It is more common in paediatrics because the heart takes up relatively more space in the chest

Camel Capnography:

Camel Capnography Unequal emptying of lungs Lateral position Tube touching carina

CO2 Trends:

CO2 Trends Slow decrease in CO2 Hyperventilation Fall in body temperature Falling lung or body perfusion Sudden drop to 0 Kinked ET tube Kinked or disconnected sampling tube Patient extubated Total anaesthetic circuit disconnect In a ventilated patient: ventilator failure

CO2 Trends:

CO2 Trends Sudden drop not to 0 Leak in circuit eg deflated cuff Obstruction eg acute broncho-spasm. Leak in sampling tube drawing in room air Exponential decrease Circulatory arrest: cardiac or hypovolaemic Embolism: air or clot Sudden severe hyperventilation

CO2 Trends:

CO2 Trends Gradual increase in CO2 Hypoventilation Absorption of CO2 from peritoneal cavity Rapidly rising body temperature Sudden increase in CO2 Injection of sodium bicarbonate Release of tourniquet Sudden increase in blood pressure

Capnography: Importance:

Capnography: Importance Correct placement of a tube Adequate ventilation Rebreathing Air, fat & pulmonary embolism -- decrease Malignant hyperthermia Normocapnia should be ensured in the elderly and Carotid artery surgery

Inaccurate estimation:

Inaccurate estimation Rapid respiratory rate Chronic pulmonary disease Severe Hypotension & blood loss

PowerPoint Presentation:

Capnography and EtCO2 Factors affecting ETCO 2 : Increased ETCO 2 Decreased ETCO 2 Changes in C O 2 Production Hyperthermia Sepsis Thyroid storm Malignant Hyperthermia Muscular Activity Hypothermia Hypometabolism Changes in CO 2 Elimination Hypoventilation Rebreathing Partial airway obstruction Exogenous CO 2 absorption (laparoscopy) Hyperventilation Hypoperfusion Embolism Transient increases in ETCO 2 may be noted after: IV bicarbonate administration, release of extremity tourniquets, or removal of vascular cross-clamps.

Trans-cutaneous PaCO2:

Trans-cutaneous PaCO2 It is a monitor for CO2 excretion in tissues Best for acutely ill neonates Less useful as an emergency warning device due to slow response time

CO2 electrode Severinghaus:

CO 2 electrode Severinghaus Incorporates a H + sensitive glass with electrodes on either side of it this glass is in contact with a thin film of sodium bicarbonate solution CO 2 + NaHCO 3 ---- H 2 CO 3 which lowers the pH proportional to the CO 2 conc. The response time is 2 minutes which is slower than pH electrode to allow time for diffusion of CO 2

pH electrode:

pH electrode H + replace the metallic cations of the pH sensitive glass ---> potential difference proportional to the H+ conc. 2 electrodes Mercury- Calomel (Reference electrode emersed in a KCl solution Silver-Silver chloride emersed in a solution of constant pH (HCl)

Precautions:

Precautions Temperature must be stable standardize against 2 buffers of known pH flushed with saline to avoid contamination with plasma proteins

Monitors for Circulation:

Monitors for Circulation Arterial blood pressure measurement ECG

Measurement of ABP:

Measurement of ABP Indirect Sphygmomanometer Oscillometer Piezoelectric crystal Ultrasonic method (Arteriosonde) Direct Arterial cannulation and mechano-electric transducer

Indirect Measurement:

Indirect Measurement Sphygmomanometer (Riva Rocci) 1896 Manual intermittent technique Modified to return to flow technique Rapid estimate of systolic blood pressure only Most widely used “ Korotkoff technique ” Korotkoff sounds 5 phases Diastolic pressure at phase IV or V

Limitation to Auscultatory method:

Limitation to Auscultatory method Long or loose stethoscope tubings Aneroid manometers should be calibrated Cardiogenic shock or vasopressor infusion Pseudohypertension (Shivering) Calcific arteriosclerosis (False high pressure) Inappropriate cuff size Rapid cuff deflation

Automated intermittent technique:

Automated intermittent technique Consistent reliable values for SBP, DBP & MAP Provide alarm systems Free the operator to perform other duties

Oscillometry:

Oscillometry 1 st described by Recklinghausen in 1931 During cuff deflation, variation in cuff pressure resulting from arterial pulsation Peak amplitude of pulsations MAP

Ultrasonic method:

Ultrasonic method Depending on Doppler principle Determine blood flow distal to the cuff Operator dependent (!!! Accuracy)

Direct Measurement:

Direct Measurement Arterial cannulation Transducer Tubings

Indications:

Indications CVS instability Massive fluid shifts Intracranial surgery Serious myocardial dysfunction Facilitate CVS manipulation Cardiovascular surgery Induced Hypotension Frequent arterial sampling Thoracic surgery ICU

Pressure transducer:

Pressure transducer

Hazards & Complications:

Hazards & Complications Hematoma Arteriospasm Air or clotted-blood emboli Anaphylaxis from local anesthestic Sepsis Hemorrhage Arterial occlusion Vasovagal response Pain

Temperature Measurement:

Temperature Measurement

Measurement of Temperature:

Measurement of Temperature Definition Temperature Expression Heat Energy All physical properties of matter are temperature dependent Temperature scales Celsius Scale Kelvin Scale Fahrenheit scale

Conversions:

Conversions o C = o K o F = ( o C x 9/5) + 32 o C = ( o F - 32) x 5/9 0 o C = 32 o F 35 o C = 95 o F 36 o C = 96.8 o F 42 o C = 107.6 o F

Why monitor temperature ?:

Why monitor temperature ? Normal temperature 36.5 – 37.5  temperature VC  temperature sweating & VD GA Reduce lower threshold to 33-35 o C Increase Upper threshold to 38 o C

When to monitor temperature ?:

When to monitor temperature ? General Anesthesia > 30 minutes Regional anesthesia Body cavity surgery Long extensive procedures Patients given blood products Overt infections & pre-existing fever Autonomic instability

Types Of Thermometers:

Types Of Thermometers 1) Expansion 2) Electric 3) Optical

Expansion Thermometers:

Expansion Thermometers Physical Principle Solids change their dimensions by heat Liquids & gases change their volume Types Liquid filled thermometers Bimetallic thermometers Bourdon gauge thermometer

Liquid filled thermometers:

Liquid filled thermometers Mercury in glass Most common outside the OR Accuracy + 0.1 o C Disadvantages Limited range Fragility Slow response time No permanent record Repeated shaking is necessary

Bimetallic strip thermometer:

Bimetallic strip thermometer 2 thin metal strips different coefficients of linear expansion Welded together to form a spiral one end is fixed and the other end is attached to a pointer Used in measurement of atmospheric temperature It is not accurate

Bourdon gauge thermometer:

Bourdon gauge thermometer Hollow ribbon of metal in the form of a coil winds and unwinds with temperature changes Similar to the bimetallic thermometer

Electric Thermometers:

Electric Thermometers Thermocouple (Seebeck effect) Platinum resistance thermometer Thermistor thermometer

Thermocouple:

Thermocouple Seebeck effect --- A circuit of 2 dissimilar metal Copper & Constantan (alloy of copper & Nickel) 2 junctions maintained at different temperatures Cold junction (maintained constant) hot junction (Measuring probe) EMF is generated and current will flow Current proportional to the temp. gradient Thermopile = several thermocouples arranged in series

Advantages of thermocouple:

Advantages of thermocouple Robust construction Rapid response Reasonably accurate The probe is very small

Platinum resistance thermometer:

Platinum resistance thermometer Metal (platinum) Resists corrosion high positive thermal coefficient of resistivity Wheat-stone bridge Most accurate ( + 0.0001 o C) Used as a standard for calibration

Thermistor thermometer:

Thermistor thermometer Semiconductor (Oxides of Nickel or Manganese or Cobalt) Negative thermal coefficient of resistivity Most sensitive Rapid response time Needs calibration every several months

Optical Thermometers:

Optical Thermometers Physical principle: “ IR radiation is emitted from hot skin then collimated by a lens to fall on a detector ” Temperature sensitive (Thermistor or thermocouple) --- Radiometer Small areas for Thermographic scanning Photosensitive (Indium antimonide) Photo-conductive material that emits small current when IR falls on it Optical filters to exclude other sources Suitable for thermographic scanning (Rapid response time)

Problems of skin temp. measurement:

Problems of skin temp. measurement Incomplete contact with the skin Heat from the skin passes to the thermometer and the skin temp. falls

Sites of body temperature measurement:

Sites of body temperature measurement Esophageal Lower Best for blood temperature Rectal useful guide to core temperature Lags behind the esophageal temp. during cooling Nasopharyngeal or Tympanic (Brain) Nasal (Respiratory rate) (intubated Patients) Big toe (Skin temperature)

Surface-core temperature gradient should not exceed 3-5 oC. In shock states the difference > 5oC:

Surface-core temperature gradient should not exceed 3-5 o C. In shock states the difference > 5 o C

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