The signs and stages of anaesthesia: No. 1 (1944)

as the patient passes from Consciousness to full anesthesia certain signs appear which make it possible to assess the level it has been reached in this film the classification of the stages of anesthesia is based on that of Goodell and it's applicable to Anesthesia with ether alone or with nitrous oxide the first stage begins with the first breath of anesthetic vapor and ends with loss of consciousness the point at which this occurs is variable and it can be put off for some time by a deliberate effort on the part of the patient the second stage sometimes called the stage of delirium begins with loss of consciousness and continues until the patient is more or less unresponsive to painful stimuli he then passes into the third and most important stage of true surgical anesthesia as this is the stage in which anesthesia is maintained during an operation it subdivided for convenience into four planes light moderate deep and very deep anesthesia below the fourth plane of the third stage the patient enters the fourth stage the stage of impending respiratory failure and death from overdose in the breathing column that follows the vertical line represents time and the diamond shaped symbols represent the extent of diaphragmatic and thoracic movement in each breath the breathing is usually regular while the patient is conscious but it often becomes irregular during the second stage the third stage is marked by the appearance of regular automatic breathing it remains regular throughout the third stage though it changes in character and becomes shallower as anesthesia deepens in the fourth stage it becomes irregular once more and even shallower until finally it ceases all together now we'll consider the breathing in more Det detail on the left side of the vertical timeline we represent the part played by the diaphragm and on the right side the part played by the thorax in the first stage as in normal breathing the two work together in out pause in out pause in the first stage the rate and depth are usually regular but they may be modified by emotion in the second stage they often become irregular a deep breath a short breath a long breath and so on with the third stage comes regular automatic breathing diaphragm and thorax still work together this applies both to the first plane and to the second plane in the third plane the breathing still regular changes in character the intercostal muscles weaken and breathing is taken over increasingly by the diaphragm we'll show each separately to start with the diaphragm contracts as before that expansion of the thorax starts to lag behind here are the movements together as anesthesia travels down the third plane this leg becomes more marked finally as the intercostal muscles become fully paralyzed the chest wall is passively drawn in during inspiration and passively pushed out during expiration in the fourth plane intercostal paralysis is complete and breathing has now been taken over entirely by the diaphragm there may also be a pause between inspiration and expiration in pause out pause in pause out pause this is quite characteristic of very deep anesthesia in the fourth stage the breathing becomes irregular again shallow and gasping and finally fails allog together associated with respiration are other reflexes which may affect the breathing the lenal reflex is active from the start and becomes progressively dulled disappearing in the third plane salivation and mucus production also cease in the third plane reflex vomiting is most liable to occur at the bottom of the second stage but not at all in the third stage now let's follow the respiratory reflexes of the nzed patients through the different stages in the first stage the patient is still conscious and the breathing as you would expect varies greatly but is usually regular during the second stage of a perfect induction breathing would be regular but it's much more common to find irregular breathing as we've already seen the lenel reflex is present so is salivation and mucus production while the vomiting reflex is most active at the bottom of this stage here is typical irregular breathing as the anaus sees it by chest movement and here as it seen by movement of the rebreathing bag sometimes the breathing suddenly becomes very shallow this usually means the patient is just going to vomit swallowing Is frequent due to the irritant effect of ether Vapor LEL spasm may occur in the second stage it may be started by contact with the larynx of strong ether Vapor of saliva or of too large an artificial Airway the change from the second to the third stage is marked by the quite sudden onset of regular automatic breathing its rhythm is so regular that you feel you can predict the time and character of the next breath which will be exactly the same as the one before it and the one after it's probably due to the isolation of the respiratory center from outside influences emotional auditory and tactile it's often deeper than the breathing that has gone before and is of the same type as in normal sleep in the first and second planes of the third stage The lenal Reflex and salivation still persist they don't disappear until well down into the third plane the active Lal reflex means that the regular automatic breathing can still be interrupted by lenel spasm due to a sudden increase in concentration of ether Vapor or to surgical stimuli the third plane is marked by the gradual change over from thoracic to abdominal breathing the intercostal muscles are progressively weakening as a result breathing is taken over more and more by the diaphrag and there is increased abdominal movement this demonst ation shows the difference between normal breathing with thorax and abdomen moving actively and full abdominal breathing with intercostal retraction during inspiration in the theater it may not always be so obvious you can detect it by placing your hand on the chest under the towels and by watching the abdomen notice that the breathing is still regular in the fourth plane intercostal paralysis is complete and the entire breathing is taken over by the diaphragm here the Seesaw movement of chest and abdomen is obvious breathing is regular but it's shallower and often jerky there is often a pause between inspiration and expiration due possibly to interference with the hering Brer reflex in the fourth stage the breathing once more becomes irregular besides being irregular it's shallow and gasping with contraction of the accessory muscles of respiration the so-called Trail tug the respiratory Center is depressed and will shortly fail unless the anesthetic is withdrawn owing to the inefficient character of the breathing carbon dioxide accumulates and cyanosis will develop unless a high proportion of oxygen is given the Lash reflex is contraction of the lids when the eyelashes are stroked the conjunctival reflex is contraction of the lids when the conjunctiva is touched gently with a clean finger the corneal reflex is contraction of the lids when the corneal is touched before considering the other signs let's summarize these three the Lash reflex disappears during the second stage of an theia and its presence merely confirms that the patient is very lightly anesthetized the conjunctival reflex is brisk in the second stage gradually diminishing in intensity and is lost by the second plane of the third stage the coral reflex is lost by the third plane of the third stage both these reflexes are very variable while their presence confirms that anesthesia is above a certain depth their absence means nothing nothing the next sign to consider is the position of the eyes and the eye movements if the eyes are looked at in the second stage they'll be found to be moving briskly from side to side or widely Divergent the Divergence or the movement lessens as anesthesia deepens but is still present in the first P of the third stage when the extrinsic muscles are paralyzed the eyes come to rest in the center and the patient has now by definition reached the second plane normally they remain fixed and Central from now on this chart sums up the position of the eyes and the eye movements there is brisk movement or wide Divergence in the second stage Less in the first plane of the third stage and none from then on the size of the pupils and their reaction to light are also important the anesthetist can normally detect the reaction to light when he pulls the lids back briskly but in the demonstrations that follow the eyes have been photographed in darkness by infrared Rays a light is then turned on and the reaction of the pupil is easily seen because of the reduced illumination the pupils are larger than they would appear in ordinary light in the second stage they are small and moving and react briskly to light in the first plane of the third stage they're still small with slight movement and the light reaction remains brisk this holds for the second plane also though now the pupils are fixed in Central in the third plane the pup are larger and the reaction to light is lessened notice that in spite of deeper anesthesia this pupil is not Central this dilation continues in the fourth plane and as it's due to the gradual paralysis of the sphincter Iris the life reaction is now sluggish in the fourth stage the muscle becomes completely paralyzed the pupil is fully dilated and no longer reacts to light the fully dilated pupils of the fourth stage must be distinguished from a sudden dilation which occurs in the second stage if the patient is about to vomit then the pupils react briskly to light again the chart sums up the size of the pupils small until the third plane and dilating from then on and the sudden dilation in the second stage if the patient is about to vomit the light reflex is brisk in the second stage and becomes more sluggish through the third stage until it's lost by the beginning of the fourth stage this composite chart shows all the ey signs grouped together in the second stage the Lash reflex The conjunctival Reflex and the corneal reflex are active the eyes are moving or Divergent the p are small except when vomiting is about to occur and they react to light in the first plane of the third stage the Lash reflex is lost the conjunctival and cornal reflexes are still present the eyes are moving slightly or are Divergent the pupils are small and react to light in the second plane the conjunct IAL reflex goes but the cornal reflex is still present the eyes are fixed and Central the pupils are still small and react to light in the third plane The cornal Reflex disappears the eyes are still fixed and Central with the pupil slightly larger in the fourth plane the pupils are fairly widely dilated with a sluggish light reaction in the fourth stage they're fully dilated with no reaction to light in assessing the depth of of anesthesia from the eye signs remember that premedication with morphine or atropine will affect the size of the pupils after morphine the pupils will be smaller than normal after atropine they will be larger a single examination signifies very little it's change in size of pupils that's important the most valuable sign is the breathing because that is the only one that is continuously available the experienced anesthetist listens almost subconsciously to the breathing and is instantly aware of any change he then proceeds to find out why the Chang has occurred it may be louder and deeper is a response to surgical stimuli or shallower from impending vomiting or from respiratory failure or there may be the first sounds of lenel stridor or other obstruction one common Pitfall for beginners is that in lightening anesthesia the eye signs May L behind the patient may be one moment apparently in the second plane with fixed Central eyes and a minute later may be on the point of vomiting finally don't forget the effect of premedication morphine contracts the pupils and also depresses the breathing atropine dilates the pupils and stimulates breathing the standard will vary with the amount of either drug that has been given an alteration in any reflex is more significant than it State at the first inspection e