Anesthesia of the Surgical Patient

1. Anesthesia of the Surgical Patient January 19, 2009

2. Key Points • The role of the anesthesiologist has expanded to become the perioperative physician. • The specialties of critical care medicine and pain medicine have grown out of the expanded field of anesthesiology. • New and improved airway and intubation devices, such as the laryngeal mask airway and the video laryngoscope, have led to improved management and control of routine and difficult airways.

3. Anesthesia • Embodies control of three great concerns of humankind: consciousness, pain, and movement. • Combines the administration of anesthesia with the perioperative management of the patient's concerns, pain management, and critical illness. • The fields of surgery and anesthesiology are truly collaborative and continue to evolve together, enabling the care of sicker patients and rapid recovery from outpatient and minimally invasive procedures.

4. History of Anesthesia • Along with infection control and blood transfusion, anesthesia has enabled surgery to occupy its fundamental place in medicine. • Ether • Nitrous oxide • Chloroform • Cocaine • Barbituates • Halothane, enflurane, isoflurane, sevoflurane • Depolarizing vs non-depolarizing paralytics

5. Pharmacology • The relationship between the dose of a drug and its plasma or tissue concentration. • It is what the body does to the drug. It relates to absorption, distribution, metabolism, and elimination. • The route of administration, metabolism, protein binding, and tissue distribution all affect the pharmacokinetics of a particular drug.

6. Pharmacokinetics • Administration of a drug affects its pharmacokinetics, as there will be different rates of drug entry into the circulation. • Distribution is the delivery of a drug from the systemic circulation to the tissues. • Molecular size of the drug, capillary permeability, polarity, and lipid solubility. • Plasma protein and tissue binding. • The fluid volume in which a drug distributes is termed the volume of distribution (Vd). • Metabolism is the permanent breakdown of original compounds into smaller metabolites.

7. Pharmacodynamics • Pharmacodynamics , or how the plasma concentration of a drug translates into its effect on the body, depends on biologic variability, receptor physiology, and clinical evaluations of the actual drug. • An agonist is a drug that causes a response. • A full agonist produces the full tissue response, and a partial agonist provokes less than the maximum response induced by a full agonist. • An antagonist is a drug that does not provoke a response itself, but blocks agonist-mediated responses. • An additive effect means that a second drug acts with the first drug and will produce an effect that is equal to the algebraic summation of both drugs. • A synergistic effect means that two drugs interact to produce an effect that is greater than expected from the two drugs' algebraic summation.

8. Pharmacodynamics • The potency of a drug is the dose required to produce a given effect. • The efficacy of any therapeutic agent is its power to produce a desired effect. • Dose-response curves show the relationship between the dose of a drug administered and the pharmacologic effect of the drug. • The effective dose (ED50) would have the desired effect in 50% of the general population. • The lethal dose (LD50) of a drug produces death in 50% of animals to which it is given. • The ratio of the lethal dose and effective dose, LD50/ED50, is the therapeutic index.

9. Unconsciousness Electroencephalogram Benzodiazepines Sevoflurane Nitrous oxide —c Amnesia Clinical signs   Midazolam Desflurane Anxiolysis   Diazepam Isoflurane   Lorazepam Enflurane Barbiturates Halothane Propofol Etomidate Ketaminea Analgesia Heart rate Opioids Sevoflurane Nitrous oxide Amides Esters Blood pressure   Morphine Desflurane   Lidocaine   Cocaine Respiratory rate   Meperidine Isoflurane   Bupivacaine   Procaine Clinical signs   Hydromorphone Enflurane   Mepivacaine   Chloroprocaine   Fentanyl Halothane   Prilocaine   Tetracaine NSAIDs   Ropivacaine   Benzocaine   Ketorolac Regional peripheral nerve blocks Parecoxib Muscle relaxation Nerve stimulator Depolarizing agent Sevoflurane —b   Brachial plexus Paralysis Tidal volume   Succinylcholine Desflurane   Sciatic Hand grip Nondepolarizing agents Isoflurane   Femoral 5-second head lift Enflurane   Cervical plexus Clinical signs   Pancuronium Halothane Regional central nerve blocks   Vecuronium   Rocuronium   Spinal   Atracurium   Epidural Cis-atracurium   Mivacurium

10. Local Anesthetics • Local anesthetics are divided into two groups based on their chemical structure: the amides and the esters. • Lidocaine, bupivacaine, mepivacaine, prilocaine, and ropivacaine have in common an amide • Lidocaine has a more rapid onset and is shorter acting than bupivacaine; however, both are widely used for tissue infiltration, regional nerve blocks, and spinal and epidural anesthesia. • Cocaine, procaine, chloroprocaine, tetracaine, and benzocaine have an ester linkage • The common characteristic of all local anesthetics is a reversible block of the transmission of neural impulses when placed on or near a nerve membrane. • Local anesthetics block nerve conduction by stabilizing sodium channels in their closed state, preventing action potentials from propagating along the nerve.

11. Local Anesthetic Toxicity • CNS – tinnitus, slurred speech, seizures, and unconsciousness • CV - hypotension, increased P-R intervals, bradycardia, and cardiac arrest • Bupivacaine 3 mg/kg • Lidocaine 5 mg/kg • Epinephrine is a vasoconstrictor, reduces local bleeding, and keeps local anesthetic in the nerve proximity for a longer period of time. • Onset of the nerve block is faster • Quality of the block is improved • Duration is longer • Less local anesthetic absorbed in bloodstream – reducing toxicity

12. Spinal Anesthesia • Injected directly into the dural sac surrounding the spinal cord • Possible complications include hypotension, especially if the patient is not adequately prehydrated • High spinal block requires immediate airway management • Spinal headache is related to the diameter and configuration of the spinal needle, and can be reduced to approximately 1%

13. Epidural Anesthesia • Local anesthetics are injected into the epidural space surrounding the dural sac of the spinal cord • Achieves analgesia from the sensory block, muscle relaxation from blockade of the motor nerves, and hypotension from blockade of the sympathetic nerves as they exit the spinal cord • Provides only two of the three major components of anesthesia—analgesia and muscle relaxation • Anxiolysis, amnesia, or sedation must be attained by supplemental IV administration of other drugs • Complications are similar to those of spinal anesthesia

14. General Anesthesia • A triad of three major and separate effects: unconsciousness (and amnesia), analgesia, and muscle relaxation • A combination of IV and inhaled drugs

15. Intravenous agents • IV agents that produce unconsciousness and amnesia are frequently used for the induction of general anesthesia. • They include barbiturates, benzodiazepines, propofol, etomidate, ketamine. • Barbiturates are anticonvulsant & decrease cerebral metabolism • Propofol has short duration and rapid recovery • Benzos reduce anxiety and produce amnesia • Etomidate has rapid induction and awakening • Ketamine produces analgesia and amnesia

16. Analgesia • Narcotic • Non-narcotic • Toradol • Ketamine

17. Neuromuscular Blocking Agents • Depolarizing – Succinylcholine • Rapid onset and offset • Non-depolarizing • Pancuronium – long acting • Rocuronium, vecuronium, cis-atracuronium – intermediate • Reversed by neostigmine, edrophonium, pyridostigmine

18. Inhalational Agents • Provide all three characteristics of general anesthesia: unconsciousness, analgesia, and muscle relaxation • A dose-dependent reduction in mean arterial blood pressure • Minimum alveolar concentration (MAC) is a measure of anesthetic potency • The ED50 of an inhaled agent • The higher the MAC, the less potent an agent is

19. Intraoperative Management

20. Pre-op evaluation • The detailed medical history • The physical examination is targeted primarily at the CNS, cardiovascular system, lungs, and upper airway • Concurrent medications • Preoperative laboratory data and specific testing for elective surgery should be patient- and situation-specific

21. Risk Assessment • An integral part of the preoperative visit is for the anesthesiologist to assess patient risk. • Risk assessment encompasses two major questions: (a) Is the patient in optimal medical condition for surgery? and (b) Are the anticipated benefits of surgery greater than the surgical and anesthetic risks associated with the procedure? • Research into factors that correlate with the development of postoperative morbidity and mortality has recently gained great interest

22. Risk Assessment Table 47-6 American Society of Anesthesiologists Physical Status Classification System P1 A normal healthy patient P2 A patient with mild systemic disease P3 A patient with severe systemic disease P4 A patient with severe systemic disease that is a constant threat to life P5 A moribund patient who is not expected to survive without the operation P6 A declared brain-dead patient whose organs are being removed for donor purposes

23. Mallampati Classification

24. Comorbidities • Ascertain the patient's severity, progression, and functional limitations induced by ischemic heart disease or pre-existing CAD • Infection, noxious particles, and gases can exacerbate COPD • However, anesthetic techniques have improved, and it has been shown that patients with severe lung disease can safely undergo anesthesia • Virtually all anesthetic drugs and techniques are associated with decreases in renal blood flow, the glomerular filtration rate, and urine output

25. Comorbidities • The patient with liver disease requires an understanding of the many physiologic functions of the liver: synthesis of albumin, coagulation factors, metabolism of drugs • may influence the selection of volatile anesthetics • The three metabolic and endocrine conditions that are most prevalent in patients undergoing surgery are diabetes mellitus, hypothyroidism, and obesity • Patients with diabetes are at an increased risk for perioperative myocardial ischemia, stroke, renal dysfunction or failure, and increased mortality • Increased wound infections and impairment of wound healing also is associated with the pre-existence of diabetes in patients undergoing surgery

26. Airway Mgmt Algorithm

27. Airway Mgmt Algorithm

28. PONV

29. Malignant Hyperthermia • MH is a life-threatening, acute disorder, developing during or after general anesthesia • genetic predisposition • Triggering agents include all volatile anesthetics and the depolarizing muscle relaxant succinylcholine • The classic MH crisis entails a hypermetabolic state, tachycardia, and the elevation of end-tidal CO2 in the face of constant minute ventilation • Respiratory and metabolic acidosis and muscle rigidity follow, as well as rhabdomyolysis, arrhythmias, hyperkalemia, and sudden cardiac arrest • A rise in temperature is often a late sign of MH

30. Malignant Hyperthermia • Treatment must be aggressive and begin as soon as a case of MH is suspected • Stop all volatile anesthetics and give 100% O2 • Hyperventilate the patient up to three times the calculated minute volume • Begin infusion of dantrolene sodium 2.5mg/kg IV • Repeat as necessary to titrate for clinical signs • Continue dantrolene for atleast 24 hours • Give bicarbonate to treat acidosis if dantrolene ineffective • Treat hyperkalemia with insulin, glucose, and calcium • Avoid calcium channel blockers reat hyperkalemia with insulin, glucose, and calcium • Continue to monitor core temperature • Call MH hotline