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Intraoperative Monitoring of the Anesthetized Patient

The administration of an anesthetic agent creates a condition wherein there is a loss of bodily sensation with or without loss of consciousness . After administration, of the anesthesia there is a loss of voluntary control, followed by complete relaxation, no muscular rigidity, and deep regular breathing. Under these circumstances the patient undergoing a surgical procedure has given up control of his existence and is depending upon the vigilance and skill of the physicians in attendance. The most important monitor in the operating room is the anesthesiologist. Monitoring is intended to provide early warning of adverse changes or trends during the operation so that irreversible damage can be prevented.


Standards for basic intraoperative monitoring have been adopted by the American Society of Anesthesiologists, last amended on October 13, 1993. Standard I requires that qualified anesthesia personnel shall be present at all times during he procedure. Standard II requires that the patient's oxygenation, ventilation, circulation, and temperature shall be under continued evaluation.

1. Oxygenation

The anesthesiologist must ensure adequate oxygen concentration in the inspired gas and the blood during all anesthetics. During administration of general anesthesia using an anesthesia machine, the concentration of oxygen in the patient breathing system must be measured by an oxygen analyzer with a low oxygen concentration limit alarm in use. With regard to blood oxygenation a quantitative method of assessing oxygenation, such as pulse oximetry must be employed.

2. Ventilation

The anesthesiologist must ensure adequate ventilation of the patient during all anesthetics, and every patient must have the adequacy of ventilation continually evaluated. While qualitative clinical signs such as chest expansion, observation of the reservoir breathing bag, and auscultation of breath sounds may be adequate, quantitative monitoring of the CO2 content and volume of expired gas is encouraged. When an endotracheal tube is inserted , its correct positioning in the trachea must be verified by the clinician and by identifying the carbon dioxide in the expired gas. When ventilation is controlled by a mechanical ventilator, there must be a device which is in continuous use, capable of detecting any disconnection of the components of the breathing system. The device should give an audible signal when the alarm threshold is exceeded.

3. Circulation

The anesthesiologist must ensure the adequacy of the patient's circulatory function during all anesthetics. Every patient must have an electrocardiogram which continuously displays during the entire intraoperative period. Blood pressure and heart rate must be determined and evaluated at least every 5 minutes. In addition to the above, circulatory function must be continually evaluated by palpation of pulse, auscultation of heart sounds, and some form of peripheral pulse monitoring.

4. Body Temperature

In order to maintain appropriate body temperature during the anesthetics, there must be a readily-available means to measure the patient's temperature.

Recording of Data

An indispensable part of anesthetic care is the anesthesia record. All anesthetic events must be documented for medical and legal purposes. This record is the only contemporaneous and continued record that provides a detailed account of what took place during the course of intraoperative treatment and management of patients. It is the means by which patient responses can be analyzed, and provides the basis for appropriate treatment action. The anesthesia record provides spaces for recording fluid and blood replacement, estimated blood loss, urinary output, body temperature, ECG findings, endtidal PCO2 , arterial blood gases, and central venous pressure. It is important that a record exist of when the last vital signs were determined. The record is useful in planning subsequent anesthetic management. While patient care takes precedence over record keeping, doctors must make every effort to keep the anesthesia record as current as possible. Information recorded on the basis of the anesthesiologist's memory will be suspect.

Complications During Anesthetics

There are numerous complications that can occur during the intubation of the trachea. During direct laryngoscopy and intubation of the trachea, there can be dental and oral soft tissue trauma, hypertension and tachycardia, cardiac dysrhythmias, myocardial ischemia, and inhalation of gastric contents. While the tracheal tube is in place, there can be tracheal tube obstruction, endobronchial intubation, esophageal intubation, tracheal tube cuff leak, barotrauma, nasogastric distension, accidental disconnection from the breathing circuit, tracheal mucosa ischemia, and accidental extubation. The immediate and delayed complications after extubation of the trachea include laryngospasm, inhalation of gastric contents, sore throat, laryngitis, laryngeal edema, laryngeal ulceration tracheitis, tracheal stenosis, vocal cord paralysis, and arytenoid cartilage dislocation.


Monitoring equipment designed to provide objective data relevant to the anesthetized patient's well-being is extremely valuable and is improved upon each day, but in the last analysis there is a demand upon the anesthesiologist for continued vigilance to obtain both objective and subjective and objective information from the anesthetized patient.

This informational piece was prepared by Silverman & Fodera. If you would like more information on this topic, call us at (800) 220-LAW1, or use the "Do I Have A Case?" link on this web site.