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Propofol Dosing By Weight May Shortchange Obese Patients

AnesthesiologyClinicians should use bispectral index values to guide propofol induction in patients with morbid obesity, according to Canadian researchers who found that BIS values are better than body weight in this population.

The randomized study, which compared the efficacy of propofol target induction doses calculated using lean body weight (LBW), found the doses based on LBW were consistently lower than those based on the BIS monitoring (Covidien) and resulted in insufficient depth of anesthesia in 60% of cases.

Many anesthesiologists use LBW to determine propofol dosing in bariatric surgery. But Waleed Riad Soliman, MD, PhD, a perioperative fellow in the Department of Anesthesia at Toronto Western Hospital in Ontario, Canada, said his clinical experience suggested this approach was inadequate.

“I observed that patients were not adequately anesthetized and developed tachycardia and hypertension in response to intubation,” Dr. Soliman said.

Dr. Soliman and several colleagues randomized 60 patients undergoing bariatric surgery with a body mass index of at least 40 kg/m2 to receive propofol induction based on their LBW or to be directed according to BIS values. All participants received fentanyl dosed at 3 mcg/kg of LBW and propofol at an infusion rate of 100 mg/kg per hour. In the LBW group, patients received a precalculated propofol dose of 2.6 mg/kg LBW, an approach Dr. Soliman borrowed from a recommendation published in 2011 (Best Pract Res Clin Anaesthesiol 2011;25:27-39).

In the BIS-monitored group, propofol infusion was stopped once BIS dropped to 50. In both groups, anesthesiologists rated the patients’ level of consciousness using the Observer’s Assessment Alertness/Sedation Scale (OAA/S). The study was not blinded.

According to Dr. Soliman, the mean LBW-based precalculated propofol dose was 163.5 mg compared with a mean 225.4 mg propofol required for deep sedation in the BIS group (P<0.05). The mean OAA/S score achieved in those patients with a full propofol dose calculated using LBW was 1 (range 0-3), indicating inadequate sedation. In the BIS group, mean OAA/S scores were 0 (P<0.05 for LBW vs. BIS).

Dr. Soliman said 60% of patients (18 of 30) in the LBW group required additional propofol for induction to achieve deep sedation compared with 3.3% (one of 30) of the BIS patients who required more propofol beyond the dose administered at a BIS value of 50 (P<0.05).

Total induction doses administered in the two groups did not differ significantly; the researchers found a mean 204 mg in the LBW group and 228 mg in the BIS group. There also were no differences in heart rate between the two groups during intubation. However, mean arterial pressure was significantly higher in the LBW group following intubation and through to five minutes after intubation.

Daniel I. Sessler, MD, Michael Cudahy Professor and chair of the Department of Outcomes Research at the Cleveland Clinic, in Ohio, said using total body weight rather than LBW to calculate propofol induction dosing is probably a better strategy in obese patients. Dr. Sessler, who was not involved in the study, pointed to a 1993 publication that supported this view (Anesthesiology 1993;78:657-665).

“The pharmacokinetics of propofol in the obese from those results were clear,” Dr. Sessler said. “Volume of distribution and clearance both increased linearly with body weight, and there was thus no accumulation of the drug. The authors therefore concluded that ‘dosing schemes expressed in mg/kg are the same as those in normal patients.’”

Dr. Soliman’s findings were to be presented at the Canadian Anesthesiologists’ Society’s 2013 annual meeting (abstract 1625814) in Calgary, Alberta. The meeting was canceled because of flooding. 

http://www.anesthesiologynews.com/ViewArticle.aspx?d=Clinical%2BAnesthesiology&d_id=1&i=November+2013&i_id=1012&a_id=24408

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How Does Anesthesia Work?

If you’ve ever had surgery, unless you are super tough, you’ve gone through it with the benefit of anesthetics. But, how do these body-numbing elixirs work?

Prior to the invention of anesthesia in the mid-1800s, surgeons had to hack off limbs, sew up wounds and remove mysterious growths with nothing to dull the patient’s pain but opium or booze. While these drugs may have numbed the patient, they didn’t always completely block the pain, or erase the memory of it.

Since then, doctors have gotten much better at putting us out with drug combinations that ease pain, relax muscles and, in some cases, put us in a deep state of hypnosis that gives us temporary amnesia. Today, there are two primary types of anesthesia drugs: those that knockout the whole body (general) and those that only numb things up locally.

 

Credit: itsmejust | Shutterstock
CREDIT: itsmejust | Shutterstock

If you’ve ever had surgery, unless you are super tough, you’ve gone through it with the benefit of anesthetics. But, how do these body-numbing elixirs work?

Prior to the invention of anesthesia in the mid-1800s, surgeons had to hack off limbs, sew up wounds and remove mysterious growths with nothing to dull the patient’s pain but opium or booze. While these drugs may have numbed the patient, they didn’t always completely block the pain, or erase the memory of it.

Since then, doctors have gotten much better at putting us out with drug combinations that ease pain, relax muscles and, in some cases, put us in a deep state of hypnosis that gives us temporary amnesia. Today, there are two primary types of anesthesia drugs: those that knockout the whole body (general) and those that only numb things up locally.

 

Local anesthetics block the nerves that connect a particular body part or region to the brain, preventing the nerves from carrying pain signals to your brain. Examples include novocaine shots, which dentists use to numb the nerves in your mouth during a root canal, and epidurals, which allow for a (relatively) painless childbirth by blocking the nerves that originate at the base of the spinal cord and serve the pelvic region.

For serious surgeries that require a patient to be completely unaware, doctors turn to general anesthesia. This renders patients unconscious with no perception or memory of the surgery (though pain from the surgical procedure will be apparent once you wake up). It also limits the physiological responses to surgical cuts, keeping blood pressure, stress hormone release and heart rate constant during the procedure.

The earliest examples of general anesthesia include ether and chloroform. But, there is a fine line between the amount of these drugs needed for surgery and the amount that can be fatal; these drugs were often administered with nothing more than a soaked sponge to the nose, which made it hard to control the dose.

Today, the most common modern general anesthetics are mixtures of inhalable gases, which include nitrous oxide (laughing gas) and various derivatives of ether, such as Isoflurane, Sevoflurane, and desflurane. Skilled anesthesiologists administer the drugs via machines that measure the specific amount necessary to keep the patient out for the surgery, but not forever. Additionally, because the drugs interfere with breathing, patients are often intubated — meaning a plastic or rubber tube is inserted in the trachea to keep the airway open — and kept on a mechanical ventilator.

Despite their necessity in modern medicine, scientists aren’t sure exactly how anesthetics work. The best theory suggests that they dissolve some of the fat present in brain cells, changing the cells’ activity. But, the precise mechanisms remain unknown. For now, next time you find yourself under the knife, just be happy they do.

http://www.livescience.com/33731-anesthesia-work.html

Facts about Anesthesiology and Anesthesiologists

 

Anesthesiology is the practice of medicine dedicated to the relief of pain and the total care of the surgical patient before, during, and after surgery. Without anesthesia, many of modern medicine’s greatest benefits would not exist. More than 25 million surgical procedures are performed each year in the United States. All of those patients were touched by the science of anesthesiology and the skill and dedication of their anesthesiologist.

The anesthesiologist is the perioperative physician (peri meaning “all-around”) who provides medical care to patients throughout their surgical experience. This includes evaluating the patient before surgery (preoperative), consulting with the surgeon, providing pain control and monitoring life functions during surgery (intraoperative), supervising care after surgery (postoperative), and medically discharging the patient from the recovery unit.

The education of today’s anesthesiologists has kept pace with their expanding role in health care. After completing a four-year college program and four years of medical school, they enter a four-year anesthesiology residency-training program. Fellowships in an anesthesia subspecialty involve an additional year of study.

As a result, complications from anesthesia have declined dramatically over the last 30 years. The youngest of premature infants in neonatal units survive intricate, lifesaving procedures while at the same time, 100-year-old patients successfully undergo major surgeries once thought impossible.

Today’s new safe, short-acting anesthetic medications and sophisticated monitoring devices enable anesthesiologists to provide patients with the best medical care possible.

http://medicine.yale.edu/anesthesiology/care/facts.aspx

Anesthesia Fact Sheet

In the Past

 

  • Prior to the 1840s, doctors and dentists did not routinely use anesthesia when operating on patients. Most doctors attempted surgery only when it was absolutely necessary to save a person’s life, and operations were largely limited to amputations and removal of external growths. Although alcohol, opium or other botanicals sometimes helped alleviate the agony, most surgical patients remained conscious and endured excruciating pain.
  • Replica of the inhaler used by William T. G. Morton in 1846 in the first public demonstration of surgery using ether. Credit: Wood Library/Museum, Park Ridge, IL.Replica of the inhaler used by William T. G. Morton in 1846 in the first public demonstration of surgery using ether.

    Wood Library/Museum, Park Ridge, IL.

    In 1846, a dentist publicly demonstrated that ether would put patients to sleep during surgery, and the practice began to spread. Doctors soaked a sponge or a cloth with ether and had patients breathe in the fumes through an inhaler. The fumes knocked the person out, but there was no way to control the amount inhaled. If patients inhaled too little, they could wake up and flail about in pain; if they inhaled too much, they might never wake. To make matters worse, ether is highly flammable, and a spark in the operating room could cause a dangerous explosion. Despite the problems with ether, its use enabled surgeons to perform internal procedures that would have been too painful or complicated to conduct on conscious patients.

  • The introduction of less flammable anesthetic gases made operating rooms safer, and the discovery of intravenous anesthetic agents such as sodium thiopental made it possible for surgeons to control the dose. But well into the 1950s, doctors still usually sedated their patients using some type of anesthetic gas and monitored them with nothing more sophisticated than a stethoscope. Dangerous side effects were common and included heart rhythm and breathing problems, lowered blood pressure and nausea and vomiting.
  • For many decades after anesthetics became a routine part of surgery, practically nothing was known about how they work. Virtually all scientists believed that anesthetics blocked nerve cell signaling by disrupting fatty molecules in the membranes that envelop cells. This theory, first put forward in the early 1900s, dominated research on anesthetics for much of the 20th century. Anesthetics are difficult to work with in the laboratory, and the lack of tools to study them at the molecular level contributed to this period of slow scientific progress.

 

Today

 

  • Every year, millions of Americans undergo surgery safely with general anesthesia, although some risks remain. Many of these procedures, which have improved the health, longevity and quality of life of the U.S. population, would not have been possible without modern anesthetic techniques.
  • Scientists have learned that general anesthesia consists of several components, including sedation, unconsciousness, immobility, analgesia (lack of pain) and amnesia (lack of memory). They have developed agents that can provide each of these elements separately, which enables anesthesiologists to tailor the regimen to each procedure and patient.
  • Advances in cell biology, genetics and molecular biology have transformed anesthesiology into an active area of research. Scientists have largely abandoned the idea that anesthetics work by acting on fatty molecules in cell membranes. The bulk of the evidence now supports the idea that the drugs target specific protein molecules embedded in nerve cell membranes and interfere with neurotransmission. Researchers now believe that each anesthetic acts on a different set of molecules to bring about its characteristic effects.
  • New general anesthetics, both inhaled and intravenous, act quickly and disappear rapidly from the bloodstream, so patients can go home sooner after surgery.  Side effects are less common and usually not as serious as they once were. Despite these improvements, general anesthetics are still among the most dangerous drugs used by doctors, particularly for elderly patients and those with certain chronic, systemic diseases, such as diabetes.
  • The discovery that local and regional anesthetics can be used to block specific nerves has provided doctors with an alternative to general anesthesia for many procedures, especially minor ones.  With local and regional anesthetics, patients can remain conscious and comfortable during surgery. But these anesthetics can have side effects, and delivering them to the right spot is sometimes difficult.
  • Anesthesiologists have become leaders in the area of patient safety. Their training includes practice responding to emergency situations using computer-controlled mannequins called patient simulators.

    Anesthesiology students training with a patient simulator. Credit: Jeffrey Taekman.Anesthesiology students training with a patient simulator.

    Jeffrey Taekman.

    Patient simulators have lifelike features such as a pulse, blood pressure and heart and breath sounds, and they are programmed to respond to drugs and other medical interventions much like a real patient would.

  • Anesthesiologists carefully monitor patients throughout surgery using electronic devices that continually display vital signs. Major advances in monitoring include the continuous measurement of blood pressure, blood oxygen levels, heart function and respiratory patterns. These advances have dramatically improved the safety of general anesthesia and make it possible to operate on many patients who were previously considered too sick to undergo surgery.
  • The role of the anesthesiologist has expanded beyond the operating room to include caring for patients during postoperative recovery. Anesthesiologists also provide anesthesia for nonsurgical procedures such as endoscopy and various cardiac interventions, as well as during labor and delivery. In addition, anesthesiologists are often called upon by other specialists for advice on how to manage pain.

 

Tomorrow

 

  • As scientists learn more about the molecular mechanisms by which anesthetics cause their various effects, they will be able to design agents that are more targeted, more effective and safer, with fewer side effects.
  • Observations of the short- and long-term effects of anesthetics on subsets of the population, such as the elderly or cancer survivors, will reveal whether certain anesthetics are better than others for members of those groups. Research on how a person’s genetic makeup influences the way he or she responds to anesthetics will enable doctors to further tailor anesthesia to individual patients.
  • Research will yield a better understanding of why surgery sometimes triggers life-threatening postoperative events such as heart attack, kidney failure and respiratory distress. This may allow anesthesiologists to preempt and better respond to these dangerous conditions.
  • Scientists will gain a better understanding of the mechanisms that underlie pain and consciousness from knowledge of how anesthetics affect these physiological states. This could lead to new ways to alleviate pain and to new treatments for conditions associated with a decrease or loss of consciousness, such as epilepsy and coma.  Studies of the mechanisms of anesthesia may also provide insights into the nature of consciousness itself.

 

http://www.nigms.nih.gov/Education/factsheet_Anesthesia.htm