Anesthesia management company Archives - Page 6 of 19 - Xenon Health

It’s a common query our patients spring on us the morning of surgery. “How exactly do the anesthetics you administer put me out?” For intravenous agents we can often get by with a lay explanation of targeted receptors, but for volatile anesthetics the truthful answer has been, “No one really knows.”

Around 1900, Hans Horst Meyer and Charles Ernest Overton independently presented what is now known as the Meyer-Overton correlation: that the minimal alveolar concentration (MAC) of volatile anesthetics is inversely proportional to its lipid solubility. That is, the potency of a volatile anesthetic is proportional to its oil:gas coefficient. This correlation led to the theory that the mechanism of action of anesthetic agents resulted from their interaction with the neuronal lipid bilayer, rather than from a specific lock-and-key model of ligand-receptor binding. This was popular given the varied structural conformations of different anesthetics, making it less likely that they all targeted a common receptor.

The lipid bilayer theory dominated until the 1970s, when Franks and Lieb showed that the Meyer-Overton correlation could be preserved in the absence of lipids: they found that clinical doses of anesthetic inhibited water soluble, lipid-free proteins such as firefly luciferase with potencies that were again inversely correlated to their MAC. A number of potential targets, both ligand-gated (such as GABA) and voltage-gated ion channels have been identified, however receptor binding affinities are low and it remained a point of dispute whether the principle mechanism of anesthesia could be attributed to direct binding to these targets.

In their study published this year, Herold et al used a well described gramicidin-based fluorescence assay (GBFA) to test whether lipid bilayer properties were affected by volatile anesthetics. The model is based on the channel-forming antibiotic gramicidin, which dimerizes across the lipid bilayer to allow ions to pass across it. To do so, its two monomers must expend a certain energy cost to deform the bilayer, as the length of the channel is shorter than the span of the bilayer. Deformations in lipid bilayer properties disturb the ability of gramicidin to dimerize, leading to changes in its ion conduction capacity (as can be measured by a fluorescence assay). The study found no changes in gramicidin channel conduction when exposed to clinically relevant doses of various anesthetics. Toxic doses did cause sufficient alteration of bilayer properties to affect gramicidin conduction.

The jury is still out on the exact mechanism of volatile anesthetics, but recent data are siding against the lipid bilayer as the culprit.

References:

Hemmings HC Jr, et al. Emerging molecular mechanisms of general anesthetic action. Trends Pharmacol Sci (2005)  26(10):503–510.

Herold KF, Sanford RL, Lee W, Andersen OS, Hemmings HC Jr. Clinical concentrations of chemically diverse general anesthetics minimally affect lipid bilayer properties  Proc Natl Acad Sci U S A. 2017 114 (12) 3109-3114

Over the last few decades, chronic pain has become one of the most common reasons people seek medical attention including anesthesia services.  Treatment for chronic pain includes both pharmacologic and non-pharmacologic therapies and tends to be based on a trial and error approach applied to each individual patient.  Unfortunately, regardless of which treatment is selected, only 30-40% of patients demonstrate adequate-to-good pain relief.  For many patients, using a combination of drugs that target more than one pain pathway can reduce dose requirements of each drug and result in better analgesia with fewer adverse effects. Ketamine in low doses can be used to treat chronic pain syndromes, especially those with a neuropathic component.  Based on several randomized controlled trials, chronic pain syndromes that may benefit from ketamine usage include the following: migraines, breakthrough non-cancer pain, central neuropathic pain, chemotherapy-induced neuropathy, complex regional pain syndrome, fibromyalgia, painful limb ischemia, peripheral nerve injury, phantom limb pain, post-herpetic neuralgia, spinal cord injury, temporomandibular pain, trigeminal neuropathic pain, and whiplash.

Ketamine was first developed in the 1960s as a safer alternative to phenycyclidine and subsequently was found to produce profound analgesia and amnesia.  Ketamine acts as an NMDA receptor antagonist with some effects on opioid, muscarinic, and monoaminergic receptors.  An important mechanism of chronic neuropathic pain development includes activation and upregulation of the NMDA receptor from prolonged nociceptive stimulation; thus, ketamine can produce strong analgesia in neuropathic pain states.  There is evidence that NMDA antagonists such as ketamine can stop the onslaught of nociceptive input to the brain and provide an alternative to existing treatments of chronic pain syndromes.  Despite its known potential benefits, there is no consensus on the administration protocol.  Duration of infusion may determine the duration of analgesia, and long term infusions of ketamine may be required for lasting analgesia following treatment.  Ketamine could even be used to reduce chronic pain development in the first place, such as that which may occur following surgery.

Multimodal approaches to treating chronic pain are often the most effective. Ketamine is often administered in conjunction with opioid analgesics and can reduce opioid requirements, reduce associated nausea and vomiting, and improve the efficacy of opioid treatment.  Ketamine is an analgesic itself and can be additive or synergistic when interacting with opioids.  It also has potent antidepressant qualities, which may greatly benefit many chronic pain patients who cope with depressive symptoms.  Despite the many potential benefits of ketamine for use in chronic pain management, more evidence is needed to determine its efficacy, and therefore ketamine should be considered only if first- and second-line agents such as opioids and antidepressants are not effective.

The safety and reliability that is a hallmark of modern anesthesia as compared to only a few decades ago has much to owe to the consistency and preparation we bring to our practice. Standard monitors, evidence based guidelines, preoperative patient evaluation and risk stratification, and ready availability of equipment and personnel to be able to respond to an emergency all serve to ensure the ability to detect and respond to potential hazards. Undermining this consistency and resource availability introduces the potential for adverse events, yet this is often what occurs in the catch-all world of anesthesia outside the operating room.

“Out of OR anesthesia” covers a wide range of locations, procedures, and involved personnel. It may include imaging suites such as CT or MRI, interventional radiology settings, endoscopy, electroconvulsive therapy, cardioversion and ICU procedures, just to name a few. As anesthesia care providers, we are increasingly expected to make our services portable, to reproduce the consistency of care we provide in the operating room with fewer resources in an unfamiliar setting.

Our equipment is often limited to what we can carry (or have an anesthesia technician bring to the out of OR location, if we are lucky). Our well stocked drug carts or Pyxis machines are pared down to a few syringes and a drug box, our difficult airway cart and video airway devices left behind for at best an airway box, often
times just the availability of an ambu bag. Anticipation is key, and we must weigh the necessity of preparation with the realistic capacity of what we can bring with us.

A common pitfall is not treating these out of OR locations with enough respect. True, the procedural risks are low, but often general anesthesia is being administered, the risks of which are if anything amplified by the unfamiliar equipment and support staff. There is very little guidance in how we should be conducting these anesthetics. The ASA lays out bare bones requirements for out of OR anesthesia, including a backup oxygen source, suction, ability to bag mask ventilate, access to a crash cart, etc. Ultimately, it is the anesthesia provider’s responsibility to determine what constitutes safe practice in these settings, and we owe it to our patients to be thoughtful as we make our anesthetic plans outside the operating room.

The practice of anesthesia, like its common comparison the aviation industry, has gained a great deal from simulation learning. Ideal for practicing high risk scenarios in a low risk setting, simulations have been shown in studies to accelerate skill acquisition, improve skill retention and reduce extinction of skills. Nontechnical skills such as task management, leadership, teamwork, situational awareness and decision making are also reinforced through simulation, and are particularly useful in emergency patient care. While additional data is needed to elucidate whether simulation makes a positive impact on patient outcomes, it has become integrated into residency and continuing medical education as a vital component of improving patient care and safety.

The evolution of the use of simulation in anesthesiology training has come a long way. Since the 1960s, life-like high-fidelity models have been in development. The incorporation of software based simulators using mathematical models of physiology and pharmacology, simulators were able to interact with mannequin models on a sophisticated level with lifelike responses. As advanced as these models are, they require upfront investment on the part of the simulation center and are limited in how many simulators can be accommodated at one time.

The ABA’s Maintenance of Certification in Anesthesiology Program (MOCA) initially required in Part 4 of their recredentialing process a certain number of hours to be spent in simulation at one of the ABA-endorsed centers nationwide, of which there are fewer than 50. The new MOCA 2.0 is a points based system allowing participants to chose among various activities, of which simulation is optional.

In the 2016 American Society of Anesthesiologists meeting, the ASA announced the upcoming release of a new screen-based simulation education program called Anesthesia SimSTAT. The program was developed in partnership with CAE Healthcare, a medical simulation company which has produced physical mannequin-based systems across a wide range of specialties. What is unique about SimSTAT is its ease of accessibility. It can be accessed via laptop via a web browser on both PC and Mac, requiring only an internet connection without need for plugins or installations.

SimSTAT will introduce on its release five learning modules at feature 3D graphics and interactive mechanics. A game based approach rewards points for successful navigation of the various cases. The user has unlimited attempts to improve competency in varied settings including the operating room, obstetric anesthesia, and the PACU. Rapid objective feedback is provided, along with practice guidelines and other resources.

Users are able to select an avatar to act as the anesthesiologist in five different scenarios. Three modes exist: orientation, which introduces the user to his environment; feedback, which allows the user to run through the scenario with frequent hints and guidance; and assessment, which runs the module without providing help or interruption. Nearly everything in the environment is interactive, with graphics for airway examination and sound bites for heart and lung sounds, fully functional ventilator dials, and an electronic medical record which updates when actions are taken by the anesthesiologist. The interface is intuitive, with the ability to access various actions either by clicking directly on the relevant object (e.g. clicking the IV pole to administer fluids or blood) or finding it on the navigation bar at the bottom of the screen.

Two scores are generated at the end of each module: an action score which represents the actions taken by the user and whether they were appropriate in timing and circumstance, and a physiological score which measures the deviations the patient’s vitals incur from acceptable parameters.

Due to release in 2017, SimSTAT promises many of the benefits of hands-on simulation combined with the convenience of being able to complete the modules anywhere, anytime. The program is currently in its beta testing phase and is preparing for general release in the upcoming months. Its target audience is primarily those seeking continuing medical education credits, specifically part 4 of MOCA; but there has been interest in using the modules as an educational platform for trainees as well. Those interested in receiving updates on its ongoing development can join the mailing list by contacting screenbasedsimulation@asahq.org.

Patients undergo spine surgery for many different conditions, and these surgeries range from minimally invasive procedures to prolonged operations involving multiple spinal levels.  Anesthesia for spine surgery can present with many challenges, including difficult airway management, multiple patient cardiopulmonary comorbidities, significant blood loss, and pain control after surgery.  Anesthetic goals include providing optimal surgical conditions, reducing blood loss, avoiding spinal cord ischemia, and facilitating intraoperative neurophysiologic monitoring.

Preoperative evaluation includes special attention to airway anatomy and cervical spine instability.  Spinal deformities can result in compromised respiratory function, necessitating blood gas analysis and pulmonary function testing, and pulmonary hypertension could result from severe kyphoscoliosis.  Preoperative history and physical should include elicitation of sensorimotor deficits, which should be carefully documented.  Laboratory workup should include at least a baseline hemoglobin, coagulation factors, and type and screen.

Selection of anesthetic technique often is affected by neurophysiologic monitoring, which often includes motor and/or somatosensory evoked potentials that is facilitated with avoidance of volatile anesthetics and neuromuscular blockade.  A total intravenous anesthetic technique can be done with propofol and remifentanil infusions.  In anticipation of blood loss, two large bore intravenous catheters should be placed and connected to a fluid warmer. An arterial line might be required for continuous blood pressure monitoring and frequent blood draws. If vasoactive drugs are needed, a central venous catheter should be placed.  Awake intubation with a fiberoptic scope may be needed depending on anticipated airway challenges.  Induction and intubation are usually performed on the stretcher, and the patient is then repositioned prone onto the operating table with careful attention to position of the endotracheal tube.  Pressure points must be carefully padded and checked throughout the surgery to avoid optic injury and peripheral neuropathies, and jaw clenching necessitates a carefully secured bite block.

Many potential complications should be considered, especially during major spine surgeries.  The anesthesiologist should plan for the potential for massive blood loss, which may be reduced by the use of antifibrinolytic agents and controlled hypotension, depending on surgeon preference.  The anesthesiologist must carefully monitor and titrate blood pressures with consideration of the potential for spinal cord ischemia. Ischemic optic neuropathy is the most common cause of perioperative visual loss, a rare but devastating possibility.  Postoperative care may include admission to the intensive care unit, especially if the patient remains intubated due to concern for airway edema.