Monitorozás: egy lehetséges definíció



Monitoring: a definition

• Interpretation of available clinical data to help recognize present or future accidents or unfavorable system conditions

• ... not restricted to medicine

(change “clinical data” to “system data” to apply to aircraft, power plants, etc.)

Patient Monitoring

Involves things…

• to measure (physiological measurement, such as BP or HR)

• to observe (e.g. observation of pupils)

• to diagnose (e.g. hypotension may mean shock)

Harvey Cushing (1869-1939) - not just the father of neurosurgery, but the father of monitoring

• Invented and popularized the anesthetic chart

• Recorded both MAP and HR

• Emphasized the relationship between vital signs and surgical events

( increased intracranial pressure leads to hypertension and bradycardia )

Ideal Monitor

• Inexpensive

• Reliable

• No complications

• Tells us something important

• Demonstrated clinical utility

Software

• All modern monitors use software

• Software often has “malfunction” (e.g., leading to system crashes)

• Software sometimes has fatal defects

• Trivial software changes could lead to unexpected (and sometimes deadly) side effects. You should now your software.

Monitoring that has “passed on”

• Ballistocardiography

• Vector cardiography

• Systolic time intervals

• Galvanic skin response

• Classical electroencephalography

• Video stethoscope

[pic][pic][pic]

Monitoring in the present

• Standardized basic monitoring requirements (guidelines) from national societies.

• Integrated monitors available

• Many special purpose monitors available

• Many problems with existing monitors (e.g., cost, complexity, reliability, artifacts)

„Low tech” monitoring

– Manual blood pressure cuff

– Finger on the pulse

– Stethoscope (heart and breath sounds)

– Watching respiratory pattern

– Watching undesired movements

– Looking at the patient’s face

• color

• pupils

Special („high tech”) monitoring

• Pulmonary artery lines (Swan-Ganz catheter)

• Transesophageal echocardiography

• Intracranial pressure (ICP) monitoring

• Electrophysiological CNS monitoring

• Renal function monitoring

• Coagulation monitoring

• Acid-base monitoring

Common clinical problems which are not readily detectable without high-tech monitors

* Hypoxia

* „Wrong gas" incidents during anesthesia

* Medication overdoses

* Air emboli

* Esophageal intubation* (a common cause of anesthesia-related deaths)

* Capnography is the only fully reliable routinely used method to detect esophageal intubation

Monitoring guidelines (ASA)

Standard - required machinery

– Pulse oxymeter

– Apparatus to measure blood pressure, either directly or noninvasively

– Electrocardiography

– Capnography, when endotracheal tubes or laryngeal masks are inserted

– Apparatus to measure temperature

– Appropriate lighting to visualize an exposed portion of the patient.

Detecting medical accidents by monitors

1. Disconnection

2. Hypoventilation

3. Esophageal intubation

4. Bronchial intubation

5. Hypovolemia

6. Pneumothorax

7. Air embolism

8. Hyperthermia

9. Aspiration

10. Acid-base imbalance

11. Cardiac arrhythmias

12. Iv drug overdose

Pulse oximeter

Mass spectrometer

Capnograph

Automatic BP

Stethoscope

Spirometer

Oxygen analyzer

EKG

Temperature

Source: Barash Handbook

Basic monitoring

• Cardiac: blood pressure, heart rate, ECG

• ECG: rate, ST segment (ischemia), rhythm

• Respiratory: airway pressure, capnogram, pulse oximeter, spirometry

• Temperature (pharyngeal, axillary, esophageal, etc.)

• Urine output (if Foley catheter has been placed)

• Nerve stimulator (face, forearm, if relaxants used)

• Auscultation

Airway / Respiratory Axis

• Correct endotracheal tube placement (+ cuff pressure)

• Airway pressure

• Oxygenation

• Ventilation

• Spirometry

• Pulmonary biomechanics

• Airway gas monitoring

• Clinical: respiratory pattern (rate, rhythm, depth, etc.)

Monitoring CO2 = capnographic devices

Arterial CO2 very accurate, but intermittent.

Exhaled CO2 can be intermittent or continuous.

• Infrared Absorption Photometry

• Colorimetric Devices

• Mass Spectrometry

• Raman Scattering

Infrared

• First developed in 1859

• Based on Beer-Lambert law: Pa = 1 - e- ( DC

– Pa is fraction of light absorbed

– ( is absorption coefficient

– D is distance light travels though the gas

– C is molar gas concentration

• The higher the CO2 concentration, the higher the absorption.

• CO2 absorption takes place at 425 nm

• N2O, H2O, and CO can also absorb at this wavelength

• Two main types: side port and mainstream

Capnography vs Capnometry

Capnography

• Measurement and display of both ETCO2 value

and capnogram (CO2 waveform)

• Measured by a capnograph

Capnometry

• Measurment and display of ETCO2 value (no waveform)

• Measured by a capnometer

Absorption bands

[pic]

Side port

• Gas is sampled through a small tube

• Analysis is performed in a separate chamber

• Very reliable

• Time delay of 1-60 seconds

• Less accurate at higher respiratory rates

• Prone to plugging by water and secretions

• Ambient air leaks

Mainstream

• Sensor is located in the airway

• Response time as little as 40 msec

• Very accurate

• Difficult to calibrate without disconnecting (makes it hard to detect rebreathing)

• More prone to the reading being affected by moisture

• Larger, can kink the tube.

• Adds dead space to the airway

• Bigger chance of being damaged by mishandling

Colorimetric

• Contains a pH sensitive dye which undergoes a color change

in the presence of CO2

• The dye is metacresol purple and it changes

to yellow in the presence of CO2

• Low false positive rate,

higher false negative rate

• Acidic solutions, e.g., atropine,

lidocaine will permanently change the color

Waveform phases

% CO2

Exhaled volume

Phase I – airway gas Phase II – transitional gas Phase III – alveolar gas

Single Breath CO2 (SBCO2)

% CO2

Exhaled Volume

Normal capnogram

[pic]

• Phase I - the beginning of exhalation

• Phase I - represents most of the anatomical dead space

• Phase II - where the alveolar gas begins to mix with the dead space gas and the CO2 begins to rapidly rise

• The anatomic dead space can be calculated using Phase I and II

• Alveolar dead space can be calculated on the basis of: VD = VDanat + VDalv

• Significant increase in the alveolar dead space signifies V/Q mismatch

• Phase III corresponds to the elimination of CO2 from the alveoli

• Phase III usually has a slight increase in the slope as “slow” alveoli empty

• The “slow” alveoli have a lower V/Q ratio and therefore have higher CO2 concentrations

• In addition, diffusion of CO2 into the alveoli is greater during expiration.

• End tidal (ET) CO2 is measured at the maximal point of Phase III.

• Phase IV is the inspirational phase

Abnormalities

• Increased Phase III slope

– Obstructive lung disease

• Horizontal Phase III with large ET- art. CO2 change

– Pulmonary embolism

– ( CO

– Hypovolemia

• Sudden ( in ETCO2 to 0

– Dislodged tube

– Vent malfunction

– ET obstruction

• Sudden ( in ETCO2

– Partial obstruction

– Air leak

• Exponential (

– Severe hyperventilation

– Cardiopulmonary event

Abnormalities

• Gradual decrease

– Hyperventilation

– Decreasing temperature

• Sudden increase in ETCO2

– Sodium bicarbonate administration

– Release of tourniquet

• Gradual increase

– Fever

– Hypoventilation

• Increased baseline

– Rebreathing

– Exhausted CO2 absorber

Limitations

• Critically ill patients often have rapidly changing dead space and V/Q mismatch

• High mean airway pressures and PEEP restrict alveolar perfusion, leading to falsely decreased readings

• Low cardiac output will decrease the reading

Applications

• Metabolic

– Assess energy expenditure

• Cardiovascular

– Monitor trend in cardiac output

– Can use as an indirect Fick method, but actual numbers are hard to quantify

– Measure of effectiveness in CPR

– Diagnosis of pulmonary embolism: measure gradient

Pulmonary applications

• Effectiveness of therapy in bronchospasm

• Confirm endotracheal tube placement

• Can predict successful extubation

Capnography – diagnosis of air embolism

Aetiology - passive

Open venous sinuses

– Neurosurgical cases in sitting position

– Spinal surgery eg. laminectomy

– Central venous catheters

Aetiology - active

• Rapid blood transfusion under pressure

• Laparoscopy (carbon dioxide)

• Femoral canal operations

• Gas cooled lasers

Signs

• Hirtelen eszméletvesztés, csökkent légzési széndioxid

• Alacsony perctérfogat

• Hypoxia

• Bradycardia

Diagnosis

• Capnography

• Doppler

• Oesophageal stethoscope

„Mill wheel murmur”

• Fall in oxygen saturation

[pic]

Prevention

• Care with fluid infusors

• Remove all air from infusion bags

• Level one type infusors

• Air filter

• Air detector

• Care with positioning

• Maintain site of surgery below level of heart where possible

• Care with central venous lines

• Closed systems eg. pressure transducers

• Minimum number of connection

• Change connections below heart level

• Remove lines with patient head down in expiration

• If blood doesn’t come out air will go in!

Treatment

• 100% oxygen

• Stop doing whatever caused it

– surgeon, equipment, position

• Flood air entry point with saline

• Remove air if central venous catheter in situ

• Be ready with CPR to break up airlock

Central Nerve System Monitoring

• Clinical: sensorium, reflexes, “wake up test”

• Electroencephalography: raw EEG, compressed spectral arrays (CSA), 95% spectral edge, etc.

• Evoked potentials (esp. somatosensory EPs)

• Monitoring for venous air emboli

• Intracranial pressure (ICP) monitoring

• Transcranial Doppler studies (MCA flow velocity) (Research)

• Jugular bulb saturation (Research)

• Cerebral oximetry (Research)

Temperature Monitoring

Temperature Monitoring - Normothermia

• Normal human temperature ~ 37°C

• Normal temperature varies ~ 1-1.5°C

• Core temperature controlled to ~ 0.2°C

• Tonic thermoregulatory function - shunting of core blood to the periphery; 1°C - 1.5°C change in core temperature in 1st hr.

Core temperature = temperature of inner organs (surface + 4-5 0C, depends on the site)

Depends on:

Anatomy - rectum: 37.1± 0.4

oral cavity: 36.7± 0.4

axillary: 36.5 ± 0.4

Covering clothes

Tissue water content

Lifestyle

Daytime (higher in the late afternoon – emotions, work, etc.)

Rationale for use

• detect/prevent hypothermia /hyperthermia

• monitor deliberate hypothermia

• adjunct to diagnoses

• monitoring CPB cooling/rewarming

Sites

• Esophageal

• Nasopharyngeal

• Axillary

• Rectal

• Bladder

Temperature Monitoring - Mild Hypothermia 1-3 oC

• Reduced resistance to infection

– decreased oxidative killing by neutrophils

– decreased O2 delivery to tissues

– protein wasting

– decreased collagen synthesis

• Reduces platelet function

• Decreases activation of coagulation cascade

• Increased blood loss

• Increased transfusion requirement

• Increased adverse cardiac events

• 3x increase in wound infection

Kurz et al, NEMJ 1996;334:1209-15

Temperature Monitoring - Normothermia Goal in Surgery

Keep all surgical patients ≥ 36°C for the entire perioperative period unless protective hypothermia is indicated.

Temperature Monitoring - Scaling

1. Zero on the Fahrenheit scale = the temperature of a mixture of equal parts ice, water, and salt.

2. Zero point on the Celsius scale (also known as centigrade) = the freezing point of water.

3. Zero on the Kelvin scale (natural point for a temperature scale) = the point at which all particle motion stops. Unit = "Kelvin”, the magnitude of 1 K= magnitude of 1 oC.

Temperature Monitoring

A. Mechanical devices

1. Mercury thermometer

- exponential curve

- set time: 3-4 min, 10 min in axillary

- precision: ± 0.1 0C (between 35-42 0C)

2. Liquid crystall (home diagnostics)

3. Infrared thermograpy

- breast pathologies,

- inflammation

- research

- vertebrae (nerve problems/arthritis)

- circulatory pre-disposition (varicose veins)

Infrared = electromagnetic wavelength between 0.7 µm and 1, frequency is 300GHz or more.

Infrared thermography = equipment or method, which detects infrared energy emitted from an object, converts it to temperature, and displays image of temperature distribution.

In: R.D. Hudson, Jr. "INFRARED SYSTEM ENGINEERING" (John Wiley & Son, 1969)

B. Electronic devices

[pic]

1. Platinium-based sensors (resistance changes linearly between 0 0C - 100 0C )

2. Thermistor (tainted metal oxide semiconductors with negative temperature coefficients) - resistance decreases with elevated temperature.

# exhibit a large output signal that results in a high degree of precision

# are exceptionally stable and capable of maintaining in-calibration performance for long periods of time, and

# are inherently more accurate than thermocouples

3. Temperature-sensing integrated circuits: amplifiers with built-in temperature-sensitive semiconductor elements.

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