Improved mechanical and pnuematic design features 

System monitors with alarms 

Studies show that human error is the dominant problem in anesthetic mishap 

PaO2< 60mmHg

Caused by either patient disease or problems with the delivery system

Ultimately machine problems result in the failure of delivery of adequate  O2 to alveoli

Failure to initiate mechanical ventilation is a very common cause of hypoxia

Decreased FiO2 can be detected with oxygen analyzer 

Oxygen Galvanic Cell (Fuel Cell)

Polarographic Sensors

Paramagnetic Analyzer 

Voltage produced by oxygenation of the lead electrode

Oxygen permeable membrane is used

Sensor lifetime is ~200,000% hours

CO2 can reduce life of cell

Not affected by presently used anesthetic gases 

Used for temperature compensation

Voltage output affected by temperature and pressure 

Uses applied current to reduce O2 to hydoxide anion 

Also uses Teflon oxygen permeable membrane

The change in CURRENT is proportional to O2 in solution 

Altered by circuit pressures 

The two unpaired electrons in O2 allow attraction to a magnetic field

By applying a magnetic field to a stream of gas the pressure of the stream can be changed

O2 concentration can be calculated by changes in stream pressure 

Failure of the liquid O2 reservior

Crossed Pipelines

Closed O2 vavles

Disconnected hoses

Failure of the reserve system 

Cylinder filled with wrong gas

Cylinder Empty

Incorrect cylinder on yoke

Closed O2 valve

Failure of the proportioning system

System leak

Incompetent valves

Inadequate ventilation

Flow meter failure 

Rarely presents a clinical problem when duration of hyperoxia < 24 hrs

May indicate a problem with the system if hyperoxia is unexpected

Easily detected with O2 analyzer

Hypercabia

Apnea

Inadeqaute MV

Failure to Ventialte 

Increased dead space

Incorrectly assembled circuit system

CO2 Absorber failure

Accidential administration of CO2

Inadeqaute fresh gas flow in a non-rebreathing system 

Unidrectional Valve Failure

Increased Areas of Bidirectional Flow

Fresh Gas Flow

APL

Reservior Bag

Bypass Valve OPen

Channeling

Exhaustion 

Leaks cause a loss of fresh gas flow

If under minimum fresh gas flow requirements- 3-fold increase in flow rates if ventilation mode changed 

Usually a result of hyperventilation

With a bellows leak, driving gas can increase minute ventilation 

Occlusions

Inadequate gas in breathing system

Leaks

High Pressure in the breathing System 

Inadeqaute fresh gas flow not meeting uptake requirements

System Leaks

Excessive removal by a faulty scavenger

Excessive removal by a side stream sampler 

Can occur at any one of multiple fittings in circuit

Most common site for a leak is Y-connector

There may be air entrainment as well as fresh gas loss

Closed APL during spontaneous ventilation

Failure of ventilator to vent gas to exhaust system

Scavenger Failure

High pressure alarm should be set no higher than 50-65 cmH2O

Liquid Agent in Fresh Gas Piping

Incorrect vaporizer Filling

Simultaneous Use of more than one Vaporizer

Pumping Effect 

Tilting of vaporizer

One mL of liquid can increase the concentration by 2% or more

A Sevo vaporizer filled with Iso set to deliver 2% will give a concentration of 3.21%

Incorrect filling of a vaporizer with Des would quickly result in lethal concentration 

Interlock device can be defeated with incorrect vaporizer placement

Agents should be placed in order of increasing vapor pressure to minimize cross contamination 

Present day machines use both pneumatically and electrically driven devices

The Anesthesia machine has a back up battery system which can supply 30 mins of power

The ventilator has no back up power supply, and in the event of power failure manual ventilation required 

Supply lasts for 30 Mins

The battery requires 16 hrs to fully charge 

Basal Metabolic Rate

Vascular tone

Muscle Activity 

All factors can be affected by GA

Shivering

Increased plasma catecholamine levels

Left shift of hemoglobin

Coagulopathy

Immunosupression

Hyperglycemia

Decreased Drug Metabolism

Decreased MAC

ECG Changes 

Vasoconstriction

Dysrhythmias

Myocardial Ischemia

J waves

Ultimately V-Fib

Infrared rays emananting from body

Largest source of heat loss

Accounting for 40%

Causes vasodilation 

Reduces the Shivering threshold by 2-4 Degrees C

Redistribution of Heat from Core to Periphery

Steady Decline

Equilibration 

Heat goes from core to periphery

Occurs in the 1st hour

Results in 1-2 degree C temperature decrease 

PA Catheter

Distal Esophagus

Tympanic Membrane

Nasopharynx

Heated blankets

Radiant Warmers

Forced Air Warmers