I. Introduction

University of Babylon
College of Nursing Anesthesia Lec.5
Dr. Naji Yassesr Al-Mayyahi 4th Years _______________________________________________________________

I. Introduction:
In the practice of medicine (especially surgery) and dentistry, anesthesia is a temporary induced state with one or more of analgesia (relief from or prevention of pain), paralysis (muscle relaxation), amnesia (loss of memory), and unconsciousness. A patient under the effects of anesthetic drugs is referred to as being anesthetized.
Anesthesia enables the painless performance of medical procedures that would cause severe or intolerable pain to an unanesthetized patient. Three broad categories of anaesthesia exist:
• General anesthesia suppresses central nervous system activity and results in unconsciousness and total lack of sensation.
• Sedation suppresses the central nervous system to a lesser degree, inhibiting both anxiety and creation of long-term memories without resulting in unconsciousness.
• Regional anesthesia and local anesthesia, which block transmission of nerve impulses between a targeted part of the body and the central nervous system, causing loss of sensation in the targeted body part. A patient under regional or local anesthesia remains conscious. Two broad classes exist:
• Peripheral blockade inhibits sensory perception in an isolated part of the body, such as numbing a tooth for dental work or administering a nerve block to inhibit sensation in an entire limb.
• Central, or neuraxial, blockade administers the anesthetic in the region of the central nervous system itself, suppressing incoming sensation from outside the area of the block. Examples include epidural anaesthesia and spinal anaesthesia.
The purpose of anesthesia can be distilled down to three basic goals or end points:
• hypnosis (a temporary loss of consciousness and with it a loss of memory. In a pharmacological context, the word hypnosis usually has this technical meaning, in contrast to its more familiar lay or psychological meaning of an altered state of consciousness not necessarily caused by drugs—see hypnosis).
• analgesia (lack of sensation which also blunts autonomic reflexes)
• muscle relaxation (…..WIKIPEDIA)
• Immobility---- removal of motor reflexes

•
• General Anesthesia (GA):
Brain doesn’t respond to pain signals or reflexes, completely unconscious and unable to feel pain during medical procedures not only being asleep, GA usually uses a combination of intravenous drugs and inhaled gasses.
• is a medically induced state of unconsciousness with loss of protective reflexes, resulting from the administration of one or more general anaesthetic agents. It is carried out to allow medical procedures that would otherwise be intolerably painful for the patient; or where the nature of the procedure itself precludes the patient being awake.
• A variety of medications may be administered, with the overall aim of ensuring unconsciousness, amnesia, analgesia, loss of reflexes of the autonomic nervous system, and in some cases paralysis of skeletal muscles,. The optimal combination of drugs for any given patient and procedure is typically selected by an anaesthetist, or another provider such as a physician assistant or nurse anaesthetist (depending on local practice), in consultation with the patient and the surgeon, dentist or other practitioner performing the operative procedure.
•
Stages of anaesthesia
Guedel s classification, introduced by Arthur Ernest Guedel in 1937,[12] describes four stages of anaesthesia. Despite newer anaesthetic agents and delivery techniques, which have led to more rapid onset of – and recovery from – anaesthesia (in some cases bypassing some of the stages entirely), the principles remain.
Stage 1
Stage 1, also known as induction, is the period between the administration of induction agents and loss of consciousness. During this stage, the patient progresses from analgesia without amnesia to analgesia with amnesia. Patients can carry on a conversation at this time.
Stage 2
Stage 2, also known as the excitement stage, is the period following loss of consciousness and marked by excited and delirious activity. During this stage, the patient s respiration and heart rate may become irregular. In addition, there may be uncontrolled movements, vomiting, suspension of breathing, and pupillary dilation. Because the combination of spastic movements, vomiting, and irregular respiration may compromise the patient s airway, rapidly acting drugs are used to minimize time in this stage and reach Stage 3 as fast as possible.



Stage 3
In Stage 3, also known as surgical anaesthesia, the skeletal muscles relax, vomiting stops, respiratory depression occurs, and eye movements slow and then stop. The patient is unconscious and ready for surgery. This stage is divided into four planes:
1. The eyes roll, then become fixed;
2. Corneal and laryngeal reflexes are lost;
3. The pupils dilate and light reflex is lost;
4. Intercostal paralysis and shallow abdominal respiration occur.
Stage 4
Stage 4, also known as overdose, occurs when too much anaesthetic medication is given relative to the amount of surgical stimulation and the patient has severe brainstem or medullary depression, resulting in a cessation of respiration and potential cardiovascular collapse. This stage is lethal without cardiovascular and respiratory support.



Physiologic monitoring:
Several monitoring technologies allow for a controlled induction of, maintenance of, and emergence from general anaesthesia.
1. Continuous electrocardiography (ECG or EKG): Electrodes are placed on the patient s skin to monitor heart rate and rhythm. This may also help the anaesthesiologist to identify early signs of heart ischaemia. Typically lead II and V5 are monitored for arrhythmias and ischemia, respectively.
2. Continuous pulse oximetry (SpO2): A device is placed, usually on a finger, to allow for early detection of a fall in a patient s haemoglobin saturation with oxygen (hypoxaemia).
3. Blood pressure monitoring: There are two methods of measuring the patient s blood pressure. The first, and most common, is non-invasive blood pressure (NIBP) monitoring. This involves placing a blood pressure cuff around the patient s arm, forearm, or leg. A machine takes blood pressure readings at regular, preset intervals throughout the surgery. The second method is invasive blood pressure (IBP) monitoring. This method is reserved for patients with significant heart or lung disease, the critically ill, and those undergoing major procedures such as cardiac or transplant surgery, or when large blood loss is expected. It involves placing a special type of plastic cannula in an artery, usually in the wrist (radial artery) or groin (femoral artery).
4. Agent concentration measurement: anaesthetic machines typically have monitors to measure the percentage of inhalational anaesthetic agents used as well as exhalation concentrations. These monitors include measuring oxygen, carbon dioxide, and inhalational anaesthetics (e.g., nitrous oxide, isoflurane).
5. Oxygen measurement: Almost all circuits have an alarm in case oxygen delivery to the patient is compromised. The alarm goes off if the fraction of inspired oxygen drops below a set threshold.
6. A circuit disconnect alarm or low pressure alarm indicates failure of the circuit to achieve a given pressure during mechanical ventilation.
7. Capnography measures the amount of carbon dioxide exhaled by the patient in percent or mmHg, allowing the anaesthesiologist to assess the adequacy of ventilation. MmHg is usually used to allow the provider to see more subtle changes.
8. Temperature measurement to discern hypothermia or fever, and to allow early detection of malignant hyperthermia.
9. Electroencephalography, entropy monitoring, or other systems may be used to verify the depth of anaesthesia. This reduces the likelihood of anesthesia awareness and of overdose.