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

Summary

This video explains the stages of anesthesia, detailing key signs such as breathing patterns, reflex responses, and pupil reactions. It outlines the progression from the first stage (induction) through to the fourth stage (overdose and respiratory failure). The video emphasizes how changes in breathing, reflexes, and eye signs can help assess anesthesia depth. Special attention is given to how different stages affect the patient's breathing and how reflexes like the laryngeal, corneal, and conjunctival reflexes evolve. Understanding these signs is crucial for monitoring anesthesia safely during surgical procedures.

Takeaways

• 😀 The classification of anesthesia stages is based on Goodell's model and applies to both ether alone and ether with nitrous oxide.
• 😀 Stage 1 involves regular breathing, emotional modifications, and a gradual transition to unconsciousness. Reflexes such as the lash and conjunctival reflex are active.
• 😀 Stage 2, also called the stage of delirium, is characterized by irregular breathing and active laryngeal reflexes. The vomiting reflex is most active at the bottom of this stage.
• 😀 The third stage (surgical anesthesia) is the most critical, with anesthesia maintained for surgical procedures. It is subdivided into four planes, from light to very deep anesthesia.
• 😀 In the third stage, diaphragm and thorax coordination changes, with diaphragm taking over as anesthesia deepens. Intercostal muscles weaken, leading to more abdominal breathing.
• 😀 In Stage 4 (overdose), breathing becomes irregular, shallow, and may cease altogether, leading to respiratory failure and cyanosis. The patient’s reflexes and breathing patterns significantly change.
• 😀 Eye signs are crucial for assessing depth: in Stage 2, the eyes are moving or diverging, while in Stage 3, they become fixed and central. In Stage 4, pupils are dilated and non-responsive to light.
• 😀 The most reliable sign for assessing anesthesia depth is breathing, with automatic regular breathing being a key indicator in the third stage and irregular, shallow breathing in Stage 4.
• 😀 Reflexes such as the lash, conjunctival, and corneal reflexes disappear progressively as anesthesia deepens, with the corneal reflex absent in the third stage and pupil dilation appearing in the fourth stage.
• 😀 Pre-medication with morphine or atropine can influence pupil size and breathing patterns, making these drugs important considerations when assessing anesthesia depth.

Q & A

What is the first stage of anesthesia, and what are the key physiological changes observed?

The first stage of anesthesia begins with the first breath of anesthetic vapor and ends with the loss of consciousness. During this stage, breathing is usually regular, though it can be modified by emotional responses. The diaphragm and thoracic muscles work together in a normal rhythm. Reflexes such as laryngeal reflex and salivation are active, and pupils are small and responsive to light.

What characterizes the second stage of anesthesia, also known as the stage of delirium?

The second stage of anesthesia begins with the loss of consciousness and ends when the patient becomes unresponsive to painful stimuli. Breathing becomes irregular, and the patient may display involuntary movements such as gasping or shallow breathing. Reflex vomiting is common, and the laryngeal reflex is heightened. The eyes may move rapidly or diverge widely, and pupils remain small but react briskly to light.

How is the third stage of anesthesia divided, and what changes occur in the patient during this stage?

The third stage of anesthesia is the most important for maintaining anesthesia during surgery. It is divided into four planes: light, moderate, deep, and very deep. During this stage, breathing becomes regular and automatic, with the diaphragm gradually taking over from the intercostal muscles. Reflexes such as the laryngeal reflex persist, though they diminish as anesthesia deepens. The pupils become slightly larger and the reaction to light becomes sluggish. The eyes remain fixed and central.

What is the significance of the fourth stage of anesthesia, and what are the key physiological signs?

The fourth stage represents an overdose of anesthesia, where the respiratory system fails. Breathing becomes irregular and shallow, and may eventually cease. The diaphragm may continue to function, but thoracic muscles are paralyzed. Reflexes, including laryngeal and corneal, are absent, and the pupils become fully dilated with no response to light. This stage requires immediate intervention to prevent respiratory failure.

What role does breathing play in assessing the depth of anesthesia?

Breathing is the most continuous and reliable sign for assessing the depth of anesthesia. Anesthetists listen for changes in breathing patterns to gauge the patient’s status. Regular and automatic breathing is typical in the deeper stages of anesthesia, while irregular and shallow breathing may indicate issues such as vomiting or respiratory failure. Any changes in breathing are important and should be promptly addressed.

How do pupil reactions change as anesthesia deepens?

Pupils are small and responsive to light in the second stage of anesthesia. As anesthesia deepens, the pupils become larger and less reactive to light, losing their response entirely by the third or fourth plane of the third stage. In the fourth stage, the pupils are fully dilated and non-reactive to light, a sign of deep overdose.

What is the significance of eye movements and position in assessing anesthesia depth?

In the second stage, the eyes may move rapidly or diverge widely. As anesthesia deepens, the eyes become fixed and central. This change occurs in the first plane of the third stage, marking the transition from irregular eye movement to a more stable and predictable position. Eye signs are useful for confirming the patient’s level of anesthesia, but they can be influenced by factors like premedication.

What are the key reflexes to monitor during anesthesia, and how do they change across stages?

The key reflexes to monitor include the lash reflex, conjunctival reflex, and corneal reflex. The lash reflex disappears during the second stage, while the conjunctival reflex diminishes and is lost by the second plane of the third stage. The corneal reflex is lost by the third plane of the third stage. These reflexes help indicate the depth of anesthesia, with their presence confirming that the patient is in a certain stage, and their absence indicating deeper anesthesia.

How does premedication with drugs like morphine or atropine affect the depth of anesthesia?

Premedication with morphine or atropine can alter reflexes and pupil size. Morphine tends to constrict the pupils and depress breathing, while atropine dilates the pupils and stimulates breathing. The presence of these drugs should be considered when interpreting signs of anesthesia depth, as they may alter normal patterns.

What are some common pitfalls when assessing anesthesia depth, especially for beginners?

A common pitfall for beginners is misinterpreting the depth of anesthesia based on eye signs alone. For example, the eyes may appear to be in the second plane with fixed, central positioning, but the patient may still be on the verge of vomiting. Also, beginners may not fully appreciate the impact of premedication on reflexes and breathing patterns, which can lead to misjudging the patient’s status.