There is no doubt that the use of monitoring devices may yield information that adds to patient safety. However, if these devices are used inappropriately, they may confuse or mislead the physician.
Clinical monitoring starts with preoperative assessment of the surgical patient. This includes full history, clinical examination and necessary investigations. A summary of this preoperative consultation should be included in the patient record with a notation of the ASA status.
Before commencing any anaesthetic, there should be a thorough check of all the equipment which may be needed by the anaesthetist.
The anaesthetic record serves as a monitor for both the patient and the anaesthetist with a number of important functions. Basically, the anaesthetist is the only indispensable monitor for the patient, being responsible for his/her safety and well-being during the perioperative period.
A monitor consists of three components; a sensor, a system for data collection and organization and a system for interpretation. Any component may be “human” or may be some electrical or mechanical “device”. There are four classes of monitors. In class I monitors, all components are “human”. In class II monitors, the sensor is a “device”. In class III monitors, the sensor and data collector are “devices”. In class IV monitors; all components are “devices”.
Classes of monitors:
Data collection / organization
Currently, the most fundamental monitors are those of class I and II. Class III monitors still requires human interpretation. Although class IV monitors are composed of component “devices”, they should work under the control of the human anaesthetist.
Class I monitors represent “the human monitors” as all their components are human in nature in the form of human senses as vision, audition and touch. In conjunction with the human monitors of the anaesthetist, the patient can share as being a monitor for him/herself.
Examples are diabetic surgical patients and those undergoing TURP or carotid endarterectomy under regional anaesthesia.
Class II monitors introduces mechanical or electrical sensors to extend the human senses of the anaesthetist for monitoring vital functions of his/her patient. Examples are the stethoscope and the manual sphygmomanometer. Both monitors are simple, mobile, cheap and easy to use. They can be considered close friends to the physician and the most minimum monitoring standards for patient care.
A class III monitor includes a “device” for sensing, a “device” for data collection and organisation, while interpretation is a “human” process. Examples are the non-invasive automated sphygmomanometer, the invasive cannula / transducer / amplifier / display arterial blood pressure monitoring system, the ECG, the pulse oximeter, the capnogram, the electronic thermometer, the nerve stimulator, the monitors for anaesthetic depth, the monitors for brain and spinal cord functions, the echocardiogram, thromboelastography, the central venous and pulmonary artery catheters, gastric tonometry and the monitors of respiratory and haemodynamic functions.
Monitors of class IVhaving sensed (by a device), collected and organized the data (by a device), interpret them (by a device) and then present the interpreted data to the physician. They use feedback open or closed loop systems including controllers to dose drugs to the patients to maintain desired target values. In spite of this, the data should be supervised by the attending physician, so that his/her skills may complement those of the controller and the monitor.
The major roles performed by the anaesthetist during administering general anaesthesia are the maintenance of drug induced unconsciousness, muscle relaxation and perioperative analgesia.
In either open or closed feedback loops, the difference between the input (target or desired) and the output (measured) values is treated as an integrated error to be corrected by the controller through changing anaesthetic concentration through a vaporizer or infusion rate through an infusion syringe or pump. This can be compared to an imaginary loop which includes the anaesthetist who corrects the error between the input and output values by manually changing the vaporizer setting or the drug infusion rate.
For Control strategies in Anaesthesia refer previous article. (Automated Anaesthesia- Control Techniques in Anaesthesia – Anaesthesia Pearls November 2013)
For patient monitoring, the important “device” is the presence of a vigilant anaesthetist. The patient needs simple monitoring if s/he belongs to ASAI class, the operation is simple, brief, minimally invasive and needs no muscle relaxation. The anaesthetist carefully observes the reservoir bag with fingers on the pulse and measuring BP by a manual sphygmomanometer. A pulse oximeter is also essential for monitoring oxygenation. More escalated monitoring is needed for patients of ASA II or more class, with longer operations, extremes of age or body weight, expected blood loss and fluid shifts together with the need of muscle relaxation.
The amount of monitoring devices should be tailored to the patient needs including ECG, capnography, thermometry, peripheral nerve stimulation or monitoring of expired anaesthetic concentrations. Spirometry, invasive monitoring of cardiac filling pressures by central venous or pulmonary artery catheters and monitoring ABG’s may be added if mandatory.
MONITORING AND PATIENT SAFETY: Mohamed Ezzat Moemen, Founder & Emeritus Professor of Anaesthesia & Intensive Care, Faculty of Medicine Zagazig University.First Edition 2004
CONTROL TECHNIQUES IN ANAESTHESIA
The main goals of clinical anaesthesia are the maintenance of drug induced unconsciousness, muscle relaxation and analgesia. Although intra-operative analgesia is an integral part of general anaesthesia, its role for post-operative pain relief is indispensible.
Intra-operative unconsciousness and muscle relaxation can be achieved by automatic control while post-operative patient- controlled analgesia (PCA) is a sort of manual control.
Control of Unconsciousness:
One of the main tasks of the anesthetist during surgery is to control anaesthetic depth. At the ether era, anaesthetic depth was defined by Guedel classification. Nowadays, anaesthetic depth shows good correlation with EEG, BP, HR, endtidal concentrations of anaesthetic agents, oesophageal motor activity or somatosensory or auditory evoked potentials. However, BP proved to be the most reliable guide for assessing anaesthetic depth and dosing inhaled vapours. The mean reason for automating the control of anaesthetic depth is to release the anaesthetist so that s/he can devote attention to other tasks as controlling fluid balance, ventilation and drug application which cannot yet be adequately automated, thus increasing the patient safety.
Computer controlled drug administration:
Drug administration by computer can be designed as either closed loop or open loop systems.
Closed Loop Anaesthesia:
A controller is designed and implemented on a personal computer. The controller makes use of an error between desired and actual values of BP, through negative feedback control. Correcting this error can be achieved by an inhalation anaesthetic as isoflurane delivered by an electronic vaporizer, or by iv agent as propofol or alfentanyl delivered by a computerized infusion pump. The anaesthetist supervising the controller does not interfere in the system and all workers have proved supreme haemo-dynamic stability with closed loop system exceeding the findings when BP is manually controlled during general anaesthesia.
Open Loop Anaesthesia:
It has no input signal but it uses mathematical models and equations to produce predicted drug concentration in the blood. With this system the anaesthetist selects the blood concentration considered appropriate for the individual patient and the pharmacokinetic model is used to calculate the infusion rate required to achieve this target concentration. A target controlled infusion model calculates the distribution and elimination of the drug and the infusion rates necessary to achieve and maintain a target blood concentration. The infusion rates are transmitted to a pump which then delivers the drug iv to the patient.
Patient Controlled Aanalgesia (PCA):
PCA can be considered a type of closed infusion system where the patient provides the input signal to control the administration of the analgesic drug. He is considered an integral part of the closed system as the actual versus desired values of pain relief. This has proved to be an effective technique for treating postoperative pain.
Control of muscle relaxation:
The degree of neuromuscular block is usually monitored by observing the muscle response to nerve stimulation, commonly the ulnar nerve. Bolus doses of neuromuscular blocker are usually administered intermittently based on this response. However, this method inevitably leads to fluctuations in the degree of neuromuscular block, particularly with recently introduced short-acting agents. To reduce this effect, continuous infusion of neuromuscular blocker may be used, but differences in pharmacodynamics and pharmacokinetics between patients make it difficult to choose the correct infusion rate to maintain the desired level of neuromuscular block. Closed-loop control offers the ability to provide a stable level of neuromuscular block allowing for variations in individual responses to neuromuscular blocking agents.
Early work on feedback control of drug infusion for muscle relaxation was carried out experimentaly on sheep, followed by successful human clinical trials A Datex relaxograph, a mathematical model, a syringe driver and the patient are the components of a closed loop control which offers the ability to provide a stable level of neuro-muscular block allowing for variations in individual response to neuro-muscular blocking agents.
Starting by a loading relaxant dose, a controlled relaxant rate is infused in the patient through this closed system to be stopped before the end of surgery and reversing the relaxant effect.
Advanced controllers: Recently, multivareable anaesthesia has been possible by using more than one controller in the system. Again, an optimum controller uses a comparator for directing one controller or the other to the best correction of the error between input and output.
The major problem of feedback control in anaesthesia is that there are enormous patient to patient variations in dynamic model parameters. Thus, it is difficult to design a fixed controller suitable for all patients. This led to the investigation of self-adaptive and self-organizing control strategies for intelligent control of mechanical ventilation, anaesthetic depth, muscle relaxation and other parameters.
Through the early decades of the coming century, control strategies will expand the concept of automation. However, an advance in microprocessor technology has started to bring automation to all levels of application. Intelligent control systems with the ability of decision-making will gradually take larger shares in automatic control of anaesthesia and intensive care.
System Automatically Delivers Anesthesia Medications During Surgery
A team of French anesthesiologists has developed an automatic delivery system of propofol and remifentanil, which they recently tested in a multi-center trial involving 196 surgical patients. The researchers reported in Anesthesia & Analgesia that the system, which uses a Bispectral Index (BIS) monitor as a guide, performed better than manual administration.
The controller allows the automated delivery of propofol and remifentanil and maintains BIS values in predetermined boundaries during general anesthesia better than manual administration.
Closed-Loop Coadministration of Propofol and Remifentanil
McSleepy: Automated Anesthesia System
Canadian Researchers at McGill University in Montreal, Quebec and the McGill University Health Centre (MUHC) have developed an automated anesthetic system and believe they were the first in the world to perform a surgery with such a machine. The new system, named ‘McSleepy’.
The anesthetic technique was used on a patient who underwent a partial nephrectomy, a procedure that removes a kidney tumor while leaving the non-cancerous part of the kidney intact, over a period of three hours and 30 minutes.
To manipulate the various components of general anesthesia, the automated system measures three separate parameters displayed on a new Integrated monitor of anesthesia (IMATM): depth of hypnosis via EEG analysis, pain via a new pain score, called AnalgoscoreTM, and muscle relaxation via phonomyographyTM, all developed by ITAG. The system then administers the appropriate drugs using conventional infusion pumps, controlled by a laptop computer on which “McSleepy” is installed.
Using these three separate parameters and complex algorithms, the automated system calculates faster and more precisely than a human can the appropriate drug doses for any given moment of anesthesia.
“McSleepy” assists the anesthesiologist in the same way an automatic transmission assists people when driving. As such, anesthesiologists can focus more on other aspects of direct patient care. An additional feature is that the system can communicate with personal digital assistants (PDAs), making distant monitoring and anesthetic control possible. In addition, this technology can be easily incorporated into modern medical teaching programs such as simulation centers and web-based learning platforms.
McSleepy developer uses “KIS” to increase precision and safety of intubation
Apr. 15, 2011 — Researchers have introduced the first intubation robot operated by remote control.
First there was McSleepyTM. Now it’s time to introduce the first intubation robot operated by remote control. This robotic system named The Kepler Intubation System (KIS), and developed by Dr. Thomas M. Hemmerling, McGill University Health Centre (MUHC) specialist and McGill University Professor of Anesthesia and his team, may facilitate the intubation procedure and reduce some complications associated with airway management. The world’s first robotic intubation in a patient was performed at the Montreal General Hospital earlier in April, 2011by Dr. Hemmerling.
“The KIS allows us to operate a robotically mounted video-laryngoscope using a joystick from a remote workstation,” says Dr. Hemmerling who is also a neuroscience researcher at the Research Institute of the MUHC. “This robotic system enables the anaesthesiologist to insert an endotracheal tube safely into the patient’s trachea with precision.”
The insertion of an endotracheal tube allows artificial ventilation, which is used in almost all cases of general anesthesia. Correct insertion of this tube into patients’ airways is a complex manoeuvre that requires considerable experience and practice to master. “Difficulties arise because of patient characteristics but there is no doubt that there are also differences in individual airway management skills that can influence the performance of safe airway management,” says Dr. Hemmerling. “These influences may be greatly reduced when the KIS is used.”
After successfully performing extensive tests in the airways of medical simulation mannequins, which closely resemble intubation conditions in humans, clinical testing in patients has now begun.
“High tech equipment has revolutionized the way surgery is done, allowing the surgeon to perform with higher precision and with almost no physical effort – I believe that the KIS can do for anesthesia what these systems have done for surgery”, says Dr. Armen Aprikian, Director of MUHC’s Department of Urology who performed surgery on the first patient treated using the KIS.
Insertion of an endotracheal tube into the airway is sometimes performed by non-anaesthesia physicians with less than ideal experience who do not have the occasion to routinely perform this procedure. In addition, endotracheal intubations are also performed outside the hospital setting, for example in emergency situations, where intubating conditions are much more difficult. The Kepler Intubation System has the potential to help in these situations and make intubation more accessible, controlled, and safe.
This device is a first prototype in a completely new field of robotic intervention. Future work will focus on providing tactile feedback, so that the operator develops a “feel” for what is happening and thus accelerate a learning curve. In addition, Dr. Hemmerling and his team would like to automate even more of the intubation process with KIS; ideally, once inserted into the patient’s mouth, KIS would, without human guidance, independently move the endotracheal tube into correct position into the patient’s trachea.
“We think that the Kepler Intubation System can assist the anesthesiologist’s arms and hands to perform manual tasks with less force, higher precision and safety. One day, it might actually be the standard practice of airway management,” concludes Dr. Hemmerling, whose laboratory developed the world’s first anesthesia robot, nicknamed McSleepy™, in 2008, which provides automated anesthesia delivery.