1. Basic Anesthetic Monitoring
ASA Standards for Basic Anesthesia Monitoring
Prepared by
Dr. Mahmoud Abdel-Khalek

2. Basic Anesthetic Monitoring
The primary goal of anesthesia is to keep the patient as safe as possible in the perioperative period
Anesthesia and surgery are serious invasions on the physiologic stability of the human body
Careful monitoring of the patient during and after surgery allows the anesthesiologist to identify problems early, when they can still be corrected
Proper monitoring of the patient can reduce the risks involved in anesthesia and surgery
Some of the physiologic disturbances that occur in the perioperative period include: apnea, respiratory depression, airway obstruction, cardiac depression, hypertension, hypotension, hypervolemia, hypovolemia, arrhythmias, blood loss, fluid shifts, weakness, bradycardia, tachycardia, hyperthermia, and hypothermia

3. Standards of Care Proper monitoring standards are well-defined
The most widely accepted current anesthesia monitoring standards are those that have been published by the by the American Society of Anesthesiologists (ASA)
The ASA standards were initially published in 1986, and were updated afterwards

4. The ASA Standards for Basic Anesthetic Monitoring
Standard I states that a qualified anesthesia provider will be present with the patient throughout the anesthetic
Standard II states that the patient's oxygenation, ventilation, circulation, and temperature will be continually monitored
Assessment of oxygenation involves two parts: measurement of inspired gas with an oxygen analyzer and assessment of hemoglobin saturation with a pulse oximeter and observation of skin color
Assessment of ventilation is by clinical assessment and preferably capnography

5. The ASA Standards for Basic Anesthetic Monitoring
Tracheal intubation must be verified clinically and by detection of exhaled CO2
Mechanical ventilation must be monitored with an audible disconnect monitor
Assessment of circulation involves continuous ECG monitoring, blood pressure measurement at least every five minutes, and continuous monitoring of peripheral circulation by such means as palpation, ausculation, plethysmography, or arterial pressure monitoring
The patient's temperature must be measured if changes are anticipated, intended, or suspected

6. Oxygen analyzers
Oxygen Analyzers Oxygen analyzers are an integral part of the newer anesthesia machines
The purpose of the oxygen analyzer is to confirm that oxygen is being delivered to the patient and that concentration of oxygen in the gas mixture is adequate
The oxygen analyzer provides one last check before the gas mixture is delivered to the patient
For the analyzer to be useful, it must be calibrated and the low-limit alarm must be working
The two main types of oxygen analyzers are galvanic (fuel cell), and the polarographic

7. Pulse Oximeters
Pulse oximetry have been a major advance in improving the safety of anesthesia
The pulse oximeter provides continuous monitoring of hemoglobin saturation using a two-wavelength light absorption technique
The monitor filters out the effects of ambient light, tissue, skin pigment, tissue, and venous blood It focuses on the pulsatile absorption which due to pulsatile arterial blood
Pulse oximeters were developed in the early 1980's and rapidly proved their value in anesthesia
Pulse oximetry allows rapid, beat-by-beat, noninvasive monitoring of blood oxygenation
Disadvantages of pulse oximetry are that it is motion sensitive, and that substances like carbon monoxide, methemoglobin, and some dyes affect the readings

8. Capnography
The most common method of exhaled CO2 measurement is sidestream infrared (IR) capnography
Gas from the circuit is drawn into an infrared measurement chamber CO2, N2O, H20, and inhaled anesthetic agents all absorb infrared light, but at slightly different frequencies
Newer monitors have precise light sources and filters that specifically measure the individual gases These monitors provide breath-by-breath gas analysis
Problems with IR capnographs are that moisture can cause blockage of the gas path, and that they can't measure oxygen or nitrogen

9. Automatic blood pressure monitors
Current automatic noninvasive blood pressure monitors work on the oscillometric technique
The cuff inflates well above the systolic pressure and then deflates slowly The monitor first senses oscillations as the cuff drops to systolic pressure
The point at which the oscillations are the strongest is read as the mean pressure
Most of these devices calculate the diastolic pressure after they measure the systolic and mean pressures
The system is normally very reliable and accurate, but motion (especially shivering) on the part of the patient or the surgeon leaning against the cuff will cause false readings or failure to get a reading
Patient injury is possible if the tubing becomes kinked Values may be in error if the cuff is not the proper size

10. ECG Monitor
The ECG monitor can provide a lot of information to the anesthesiologist
Arrhythmia detection and identification of tachycardia and bradycardia are important uses
The ECG monitor may also provide the first indication of myocardial ischemia However the absence of ST depression does not guarantee that ischemia is not present
Lead placement is important in ischemia detection
The most sensitive lead is lead V5, detecting about 75% of ischemic episodes Lead II plus lead V5 raise the detection rate to 80%, whereas leads II, V4, and V5 together detect 98% of ischemic events
Current top-of-the line monitors do automated ST analysis which is more reliable than individual practitioner assessment as long as the measurement points are correct

11. Ventilation Monitors
Current anesthesia machines have ventilator disconnect alarms and built-in spirometers
The spirometers have high and low limit alarm settings
Continuous measurement of exhaled tidal volume can detect circuit leaks and hypoventilation
The spirometers on the anesthesia machines may give false readings if moisture blocks the inner workings
Current anesthesia machines also have overpressure alarms and overpressure "pop-off" valves

12. Temperature Monitors Monitoring of skin temperature is nearly useless
Upper esophageal and nasopharyngeal temperature are affected by airway temperature
Lower esophageal temperature is normally a good reflection of core or blood temperature
Tympanic membrane temperature is also a good indication of core temperature but it is not practical in the operating room environment

13. Peripheral Nerve Stimulators
Peripheral nerve stimulation (PNS) monitoring is not required by the ASA standards However, it is an important safety monitor in patients who a receiving neuromuscular blocking drugs
Train-of-four monitoring assesses the level of nondepolarizer blockade and double-burst stimulation assesses return of strength at the end of the case
Clinical monitoring of neuro- muscular blockade during an anesthetic is difficult without a PNS monitor
Clinical assessment of strength is important, however, at the conclusion of an anesthetic before a final decision is made to extubate the patient