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Anaesthesiology
Commonly Used Monitoring Techniques
Built from Barash Clinical Anesthesia, 9th Edition
What’s inside
15 sections · 193 slides
Overview
- Purpose of anaesthesia monitoring
- Scope of this topic
- Framework used for each monitor
- Evidence and cost of monitoring
Standards for Basic Anesthetic Monitoring
- ASA basic monitoring standards
- Standard I: qualified personnel
- Standard II: the four variables evaluated
- Oxygenation requirements under Standard II
- Ventilation requirements under Standard II
- Circulation and temperature requirements
Monitoring of Inspired Oxygen Concentration
- Three types of oxygen analyser
- Paramagnetic oxygen analysers
- Galvanic cell oxygen analysers
- Polarographic oxygen analysers
- Placement of the oxygen sensor in the circuit
- Performance requirements and calibration
- Alarm limits at machine checkout
- Indications for inspired oxygen monitoring
- Limitations of inspired oxygen monitoring
Monitoring of Arterial Oxygenation by Pulse Oximetry
- Variables measured by a pulse oximeter
- Shape of the oxyhaemoglobin dissociation curve
- Rightward shift of the dissociation curve
- Application of the Beer-Lambert law
- Extraction of the pulsatile arterial signal
- Functional saturation measured by pulse oximetry
- Fractional saturation measured by a co-oximeter
- Functional versus fractional saturation
- Effect of methaemoglobin on the reading
- Effect of carboxyhaemoglobin on the reading
- Factors that corrupt the oximeter signal
- Interference from theatre equipment
- Indications and reported accuracy
- Questions pulse oximetry cannot answer
- Desaturation as a late sign of apnoea
- Pulse oximetry with non-pulsatile circulation
- Pulse oximetry in infants and children
Monitoring of Expired Gases
- Historical gas-analysis techniques
- Principle of infrared absorption spectrophotometry
- Infrared transmission spectra of carbon dioxide and nitrous oxide
- Five components of an infrared gas analyser
- Simultaneous multi-gas measurement
- Critical events revealed by gas analysis
- Detection of critical events by gas analysis
- Detection of critical events by gas analysis (continued)
- Capnometry and capnography defined
- Phases of the normal capnogram
- End-tidal to arterial carbon dioxide gradient
- Abnormal capnogram shapes
- Capnography and endotracheal tube placement
- Sudden loss of the carbon dioxide waveform
- Abrupt versus gradual falls in end-tidal carbon dioxide
- Rebreathing on the capnogram
- Physiological determinants of end-tidal carbon dioxide
- Factors that may change end-tidal carbon dioxide during anaesthesia
- Factors that may change end-tidal carbon dioxide during anaesthesia (continued)
- Monitoring inspired and expired agent concentration
- Minimum alveolar concentration
- End-tidal agent monitoring and awareness
- Nitrogen monitoring and its loss
- When end-tidal carbon dioxide misrepresents arterial carbon dioxide
- Capnography in neonates and small infants
Invasive Monitoring of Systemic Blood Pressure
- Generation of the arterial pressure trace
- Sources of error in fluid-coupled systems
- Damping and natural frequency
- Acceptable damping for a given natural frequency
- Consequences of underdamping and overdamping
- Optimising the transducing system
- Choice of arterial cannulation site
- Arterial cannulation and direct blood pressure monitoring
- Arterial cannulation and direct blood pressure monitoring (continued)
- Value of the Allen test
- Techniques for arterial cannulation
- Zeroing and levelling the transducer
- Transducer level in the beach-chair position
- Vascular complications of arterial cannulation
- Indications for an arterial catheter
- Contraindications to arterial cannulation
- Safe handling of arterial line blood and tubing
Intermittent Noninvasive Monitoring of Systemic Blood Pressure
- Korotkoff sounds
- The oscillometric method
- Sequence of oscillometric pressure determination
- Contraindications to cuff placement
- Cuff injury during prolonged surgery
- Cuff size and limb position errors
- Non-pulsatile flow and cuff measurement
- Alternative cuff sites and site-dependent readings
Monitoring of Central Venous and Right-Heart Pressures
- Uses of a central venous cannula
- Central venous pressure as right ventricular preload
- Unreliability of right-sided pressures for left ventricular filling
- Advantages of the pulmonary artery catheter
- Progression of pressures from central vein to left ventricle
- Components of the normal central venous pressure trace
- Abnormal a waves
- Abnormal v waves
- Central venous versus pulmonary artery monitoring
- Pressure waveforms during catheter flotation
- West zones of the lung
- Verifying that the catheter tip lies in zone III
- Indications for a pulmonary artery catheter
- Conditions that invalidate the wedge pressure
- Dysrhythmias during catheter passage
- Pulmonary artery rupture
- Reported incidence of catheter complications
- Adverse effects associated with pulmonary artery monitoring
- Adverse effects associated with pulmonary artery monitoring (continued)
- Choice of central venous access site
Monitoring of Cardiac Output by Pulmonary Arterial Catheter
- Indicator dilution principle
- Bolus thermodilution cardiac output
- Continuous cardiac output monitoring
- Error from a catheter not advanced far enough
- Other sources of thermodilution error
- Indications for measuring cardiac output
- Assumptions behind thermodilution
Monitoring of Cardiac Output by Arterial Waveform Analysis
- Motivation for less invasive cardiac output
- Non-invasive finger cuff cardiac output
- The volume-clamp principle
- The Windkessel model of the artery
- Blood flow into and out of a Windkessel artery
- Areas under the systolic and diastolic pressure curve
- Proportionality of systolic and diastolic flows to their areas
- Stroke volume from the pressure-curve areas
- The calibration constant k
- Indices reported by uncalibrated devices
- Indications for arterial waveform cardiac output
- Signal quality requirements
- High-output states and vascular tone
- Aortic valve lesions and waveform analysis
Monitoring of Body Temperature
- Thermoregulation under anaesthesia
- Four routes of heat loss
- Physiological consequences of perioperative hypothermia
- Sites for measuring core temperature
- Mean body temperature
- Limitations of skin and rectal temperature
Monitoring of Processed EEG Signals
- Electroencephalography for cerebral ischaemia
- Applying the forehead sensor
- Beta-power ratio
- Power concentration in the gamma band
- Burst suppression ratio
- Open algorithm for processing the EEG into a depth score
- Interpreting the displayed number
- Agent dependence of the processed EEG score
- Indications for processed EEG monitoring
- Contraindications to processed EEG sensors
- Evidence on processed EEG and intraoperative awareness
- Awareness and anaesthetic exposure in children
Monitoring Neuromuscular Blockade
- Rationale for monitoring neuromuscular blockade
- The two steps of neuromuscular monitoring
- Quantitative neuromuscular monitors
- Three categories of neuromuscular monitor
- Mechanomyography and acceleromyography
- Technique at the ulnar nerve
- Consensus recommendation on neuromuscular monitoring
- Underuse of neuromuscular monitoring
- Hazard of facial stimulation sites
- Practical limitations of acceleromyography
- Practical limitations of electromyography
Future Trends in Monitoring
- Three trends in monitoring device design
- Anaesthesia information management systems
- Algorithmic inference of clinical data
- Obligation of clinical judgement
Key Points
- Key points on oxygen and gas monitoring
- Key points on pressure and flow monitoring
- Key points on temperature, brain and judgement
- The unchanging principle of monitoring
- References
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- References (continued)
- Barash, Cullen, and Stoelting's Clinical Anesthesia, 9th Edition