FEATURES INTENDED TO PREVENT HUMAN ERROR

FEATURES INTENDED TO PREVENT HUMAN ERROR

·        The medical gas pin index and diameter index safety systems ensure that medical gas connections are made correctly.

·        Therefore, one cannot hang a nitrous oxide cylinder in an oxygen hanger yoke or connect a nitrous oxide hose to the oxygen pipeline inlet of the machine.

·        The “fail-safe” valve is a pressure-sensitive device that interrupts flow of all hypoxic gases on the machine to their flow control valves if the supply pressure of oxygen in the intermediate-pressure system (i.e., components downstream of the first stage oxygen regulator that reduces the high pressure in the tank to 45 pounds per square inch gauge [psig] and upstream of the oxygen flow control needle valve) falls below a threshold (˜20 psig in GE machines; 12 psig in Dräger machines).

·        When the pressure of oxygen in the intermediate-pressure system falls below 30 psig, an oxygen supply pressure failure alarm is annunciated.

·        The oxygen flow control knob is “touch coded”; that is, it is fluted and larger in diameter than the other gas flow control knobs and is normally located on the right of all other gas flow control valves.

·        In the Dräger Fabius GS workstation, the gas flow controls are arranged vertically, with the oxygen flow control knob as the lowest.

·        Key-fill systems for anesthesia vaporizers are safety features that also decrease the likelihood of atmospheric contamination during vaporizer filling.

·        The most important of such systems is the Safe-T-Fill system used on desflurane bottles and desflurane vaporizers because filling a vaporizer specific for another agent with desflurane could result in a lethal overdose of desflurane.

·        A pressure relief valve built into the machine common gas outlet, breathing system, or ventilator provides some protection against positive pressure barotrauma.

FEATURES TO CORRECT FOR USE ERROR

·        Gas flow proportioning systems ensure a minimum oxygen concentration of 25% when nitrous oxide and oxygen are being used.

·        Therefore, if the anesthesiologist were to accidentally attempt to increase the flow of nitrous oxide, either the oxygen flow would be increased automatically or the flow of nitrous oxide would be limited according to the flow of oxygen that was set.

·        On older machines, during use of the anesthesia ventilator, changes in fresh gas flow, inspiratory-expiratory (I:E) ratio, or respiratory rate cause changes in delivered tidal volume that might result in overventilation, underventilation, or even barotrauma.

·        On modern systems (e.g., GE workstations that incorporate a ventilator with the Smart Vent feature, Dräger Fabius GS, and Apollo workstations), once the ventilation parameters have been set, they are maintained because the ventilator or circuit automatically compensates for changes in gas flow settings.

·        In the GE workstations with Smart Vent, tidal volume is monitored continually by a computer.

·        If measured tidal volume changes from that set to be delivered, the computer adjusts the volume delivered by the ventilator bellows.

·        Dräger and Datascope Anestar workstations use fresh gas decoupling to maintain a constant tidal volume.

·        In this system, during the inspiratory phase, a decoupling valve closes so that fresh gas entering the breathing system is directed into the reservoir bag and only gas from the ventilator is delivered to the patient.

·        During exhalation, the ventilator chamber refills from the fresh gas flow and the fresh gas that was collected in the reservoir bag during the previous inspiration.

·        A vaporizer interlock system prevents the unintentional simultaneous use of more than one vaporizer.

MONITORING SYSTEMS

·        A monitor of oxygen in the gas delivered to the patient is mandatorily enabled, and the low oxygen concentration alarm is

activated whenever the anesthesia workstation is capable of delivering an anesthetic gas mixture from the common gas

outlet.

Other monitors in the anesthesia workstation include pressure, volume, flow, and gas composition. Some also incorporate

airway gas flow monitoring. The breathing system lowpressure monitor alarm is automatically enabled when the ventilator

is turned on.

ALARM SYSTEMS

Contemporary workstations incorporate an integrated prioritized alarm system with visible and audible alerts when set

parameter limits are exceeded.

An important safety feature of all modern machines/workstations is the preuse checkout. In 1993, the U.S. Food and Drug

Administration (FDA) published anesthesia apparatus checkout recommendations. The machine should be checked by

an educated user. Item no. 1 on the FDA checklist is that an alternative means to ventilate the patient's lungs should be

present and functioning. Therefore, if a problem arises with the machine, the patient's lungs can be ventilated using a selfinflating

resuscitation bag (e.g., Ambu bag). If a machine problem arises and the cause/remedy is not immediately obvious, one should instinctively reach for the resuscitation bag and call for help. A recent analysis of the American

Society of Anesthesiologists Closed Claims Project data found that 35% of adverse outcomes were likely preventable if a

proper preuse checkout had been performed.

Recognizing that not all of the FDA 1993 checkout recommendations can be applied to many of the contemporary

workstations, in 2008, the American Society of Anesthesiologists published guidelines applicable to all anesthesia

delivery systems so that individual departments can develop their own workstation-specific preuse checkout that can be

performed consistently and expeditiously. The 2008 guidelines are intended to provide a template for developing checkout

procedures that are appropriate for each individual anesthesia machine design and practice setting. They discuss which

systems and components should be checked, the checkout interval (e.g., before first case vs. before every case), and who

may be responsible for performing each checkout procedure—the anesthesiologist or technician (Table 59.1). Examples

of user-developed workstation-specific checkouts are available on the American Society of Anesthesiologists'

How is hypoglycemic shock recognized and treated intraoperatively?

·       Hypoglycemia can lead to tissue energy failure and has been associated with hemodynamic collapse and brain injury.

·       Any patient receiving insulin, pramlintide, sitagliptin, or sulfonylureas is at risk for hypoglycemia.

·       Because risk is usually known beforehand, hourly or more frequent monitoring of serum glucose should detect hypoglycemia.

·       If glucose levels are low or decrease rapidly, the fastest treatment is a bolus of intravenous dextrose, 50% solution, administered slowly.

·       In an emergency, one full ampule is the starting dose.

·       In less urgent settings when the serum glucose level is low but not critical, smaller doses can be titrated to serum glucose values.

D. Postoperative Management

D.1. How is diabetes controlled in this patient postoperatively?

·       Unless there is a change in disease status as a consequence of surgery or preoperative care was inadequate, this patient should be transitioned back to her preoperative regimen.

·       Before transitioning, she must recover from the stress response to the surgery.

·       If this were a simple outpatient procedure, such as a cataract extraction, she could return home on her outpatient medication regimen.

·       In this case, however, the effects of tissue injury may not peak for days; diabetes control is thus a dynamic challenge.

·       Regular monitoring of glucose is required (at a minimum checks should be made every 6 hours).

·       She is monitored for hyperglycemia, and her nutrition regimen is adjusted to serum glucose measurements.

·       Hourly glucose measurements and insulin infusion can control hyperglycemia.

·       Most patients can be effectively managed with subcutaneous insulin and less frequent measurements.

·       Insulin dose should take into account preoperative requirements, insulin resistance from the stress response, and caloric intake.

·       Many patients receive intravenous dextrose postoperatively; if they are hyperglycemic on this regimen, dextrose is discontinued.

D.2. Does diabetes increase perioperative risk?

·       Because patients with diabetes are at a greater risk of atherosclerosis, infection, autonomic and cardiovascular instability, and metabolic abnormalities than those without diabetes, perioperative risk is higher in this patient population.

·       After surgery, the diabetic patient is monitored for hyperglycemia and hypoglycemia, ischemic complications, circulatory compromise, and wound and nosocomial infection.

·       As a group, patients with diabetes have an increased risk for complications and poor outcomes from complications.

D.3. What are the common postoperative complications to be expected in a diabetic patient?

·       Hyperglycemia and hypoglycemia, wound infections, and organ ischemia are the most common and worrisome postoperative complications in patients with diabetes.

·       Following myocardial infarction or cerebrovascular accident, hyperglycemia is associated with a worse prognosis.

D.4. Is it necessary to achieve tight perioperative control of glucose?

·       In the critical care setting, there is evidence for improved outcomes with tight glycemic control, variably defined as serum glucose between 80 and 120 mg per dL or higher; other evidence has shown no benefit or even harm.

·       Some advocate for tight glycemic control in cardiac and noncardiac surgery.

·       The risks of hypoglycemia and data from more recent studies have tempered the enthusiasm for tight glycemic control.

·       Potential benefits from tight glycemic control include improvement in metabolic, anti-inflammatory, organ, and circulatory function.

·       Unfortunately, there is little evidence to suggest these benefits are substantial perioperatively.

·       Unresolved issues are the best time for tight control, the goals of therapy, the effect of nutrition, and the magnitude and factors in the potential for significant hypoglycemia.

·       The patient is transitioned to her preoperative level of control during recovery, and severe hyperglycemia is prevented by monitoring glucose closely.

·       Glucose levels above 180 mg per dL increase the risk of protein glycation and osmotic diuresis; targeting serum glucose below this value makes physiologic sense.

Protein glycation, diabetes, and aging.

·       Biological amines react with reducing sugars to form a complex family of rearranged and dehydrated covalent adducts that are often yellow-brown and/or fluorescent and include many cross-linked structures.

·       Food chemists have long studied this process as a source of flavor, color, and texture changes in cooked, processed, and stored foods.

·       During the 1970s and 1980s, it was realized that this process, called the Maillard reaction or advanced glycation, also occurs slowly in vivo.

·       Advanced glycation endproducts (AGEs) that form are implicated, causing the complications of diabetes and aging, primarily via adventitious and crosslinking of proteins.

·       Long-lived proteins such as structural collagen and lens crystallins particularly are implicated as pathogenic targets of AGE processes.

·       AGE formation in vascular wall collagen appears to be an especially deleterious event, causing crosslinking of collagen molecules to each other and to circulating proteins.

·       This leads to plaque formation, basement membrane thickening, and loss of vascular elasticity.

·       The chemistry of these later-stage, glycation-derived crosslinks is still incompletely understood but, based on the hypothesis that AGE formation involves reactive carbonyl groups,

·       Subsequent studies by many researchers have shown the effectiveness of aminoguanidine in slowing or preventing a wide range of complications of diabetes and aging in animals and, recently, in humans.

·       Since, the authors have developed a new class of agents, exemplified by 4,5-dimethyl-3-phenacylthiazolium chloride (DPTC), which can chemically break already-formed AGE protein-protein crosslinks.

·       These agents are based on a new theory of AGE crosslinking that postulates that alpha-dicarbonyl structures are present in AGE protein-protein crosslinks.

·       In studies in aged animals, DPTC has been shown to be capable of reverting indices of vascular compliance to levels seen in younger animals.

·       Human clinical trials are underway.

Pramlintide

Pramlintide 

• is an analogue of amylin, a small peptide hormone that is released into the bloodstream by the β cells of the pancreas along with insulin after a meal.[2] 
• Like insulin, amylin is completely absent in individuals with Type I diabetes.[3]
• By augmenting endogenous amylin, pramlintide aids in the cellular absorption and regulation of blood glucose by 
• slowing gastric emptying, 
• promoting satiety via hypothalamic receptors (different receptors than for GLP-1), and 
• inhibiting inappropriate secretion of glucagon, a catabolic hormone that opposes the effects of insulin and amylin. 
• Pramlintide also has effects in raising the acute first-phase insulin response threshold following a meal.
• Both a reduction in glycated hemoglobin and weight loss have been shown in insulin-treated patients with type 2 diabetes taking pramlintide as an adjunctive therapy

How is hypoglycemic shock recognized and treated intraoperatively

How is hypoglycemic shock recognized and treated intraoperatively?

• ·       Hypoglycemia can lead to tissue energy failure and has been associated with hemodynamic collapse and brain injury.
• ·       Any patient receiving insulin, pramlintide, sitagliptin, or sulfonylureas is at risk for hypoglycemia.
• ·       Because risk is usually known beforehand, hourly or more frequent monitoring of serum glucose should detect hypoglycemia.
• ·       If glucose levels are low or decrease rapidly, the fastest treatment is a bolus of intravenous dextrose, 50% solution, administered slowly.
• ·       In an emergency, one full ampule is the starting dose.
• ·       In less urgent settings when the serum glucose level is low but not critical, smaller doses can be titrated to serum glucose values.

How is hyperglycemia treated intraoperatively

How is hyperglycemia treated intraoperatively?

• ·       The high end of a normal range for fasting serum glucose is 110 mg per dL; however, hyperglycemia in inpatients need not be treated until it reaches a higher level.
• ·       The one good agent for treating intraoperative hyperglycemia is intravenous insulin.
• ·       Onset takes minutes, peak effect is achieved in 15 to 30 minutes, and duration of effect is less than an hour, facilitating titration.
• ·       Insulin may be administered by continuous infusion or as intermittent boluses; the bolus consumes less lead time and eliminates the risk of pump misprogramming or malfunction.
• ·       Subcutaneous insulin is less ideal for use during general anesthetics or complex procedures because variable peripheral blood flow will alter the uptake and duration of action.
• ·       Most other therapies for DM2 are not fit for intraoperative use.
• ·       Oral agents cannot be easily administered, are not reliably absorbed, and have too long a duration of action to be practical perioperatively.
• ·       They may be taken on the day of surgery before minor procedures.
• ·       In this case, sitagliptin should be discontinued to avoid hypoglycemia.
• ·       Metformin, a biguanide, increases the risk of lactic acidosis during periods of hypoperfusion. 

• ·       Metformin is discontinued for 3 or more days before extensive procedures when a large-volume blood loss is possible.

Breathing Systems

1. Which of the following offers the most resistance?

A. Nonrebreathing valve

B. Co2 canister

C. Tracheal tube

D. Y-piece

E. Breathing tubes

2. The functions of the breathing system include the following:

A. Conveying oxygen and anesthetic gases to the patient

B. Delivering positive pressure

C. Removing waste and anesthetic gases from the patient

D. Conveying excess gases to the scavenging system

3. Resistance to breathing through a breathing system is influenced

By

A. Laminar flow

B. Gas flow rate

C. Turbulent flow

D. Length of the breathing tubes

4. Rebreathing may be influenced by

A. Fresh gas flow

B. Arrangement of components in the breathing system

C. Mechanical dead space

D. The size of the reservoir bag

5. Effects of rebreathing include

A. Reduced loss of heat and water from the patient

B. Reduced inspired oxygen

C. Less fluctuation in inspired anesthetic agent concentration

D. Decreased inspired carbon dioxide

6. Factors that cause a discrepancy between the composition of the inspired gas mixture and that of the fresh gas include

A. Rebreathing

B. Leaks in the breathing system

C. Uptake of anesthetic agent by components of the breathing system

D. Increased fresh gas flow

7. Factors that can cause a discrepancy between the volume of gas discharged from a ventilator or reservoir bag and that inspired by the patient include

A. Fresh gas flow

B. Compression of gases in the circuit

C. Leaks

D. Distention of breathing system components

8. The reservoir bag

A. Allows use of lower fresh gas flows

B. Provides a means for delivering positive pressure

C. Can ser ve as a monitor of spontaneous respiration

D. Can cause excessive pressure if the apl valve is not open

9. Concerning the peak pressure than can be generated in the breathing system if there is a reservoir bag in place,

A. If the reser voir bag is less than 1.5 l in size, the pressure shall not be less than 30 cm h2o

B. If the reser voir bag is larger than 1.5 l, the pressure shall not be less than 45 cm h2o

C. If a 1.5-l bag is expanded to four times its normal size, the pressure shall not be greater than 50 cm h2o

D. If a bag over 1.5 l is expanded to four times its size, the pressure shall not be greater than 65 cm h2o

10. Functions of breathing tubes include

A. Acting as a reser voir in certain systems

B. Protection against excessive pressure

C. Providing a flexible connection between the different parts of the breathing system

D. Expanding during spontaneous breathing to prevent rebreathing

11. During spontaneous respiration,

A. The apl valve should be kept partially closed

B. Most apl valves open automatically

C. An obstruction in the scavenging system may result in gas being removed from the breathing system

D. Obstruction of the air intake valve in the scavenging system can result in positive pressure in the breathing system

12. With a PEEP valve in the breathing system,

A. An increased exhalation effort is necessary if the patient is Breathing spontaneously

B. An increase in tidal volume may be seen with mechanical Ventilation

C. The amount of PEEP can be either fixed or adjustable

D. A spring-loaded peep valve must be kept in the upright position

13. Which of the following connectors are male?

A. Those on the breathing tubes

B. Those on the reser voir bag mount

C. Those on the mask

D. Those on the y-piece connecting to the breathing tubes

14. Deposition of bronchodilators in the patient’s tracheobronchial Tree is enhanced by

A. Use of a spacer

B. A low inspirator y flow rate

C. Low humidification

D. An expirator y pause

15. Causes of localized turbulent flow include

A. Constrictions in the flow channel

B. Valves

C. Cur ves

D. Gas at a flow rate below the critical number