Presentation on theme: "BY KARIM YOUSSEF KAMAL, MD Lecturer of Anesthesia, Intensive Care and Pain Management AIN SHAMS UNIVERSITY."— Presentation transcript:
BY KARIM YOUSSEF KAMAL, MD Lecturer of Anesthesia, Intensive Care and Pain Management AIN SHAMS UNIVERSITY
Definition: A peripheral nerve block (PNB) is the injection of a local anesthetic around a nerve or group of nerves with blockade of nerve impulse conduction, causing temporary analgesia and loss of sensory and motor function.
More hemodynamic stability compared with neuraxial blocks. Anticoagulation less of an issue. Increasing popularity due to advances in ultrasound technology. Introduction of perineural catheters prolongs post-operative pain control benefits.
Avoidance of general anesthesia Primary regional anesthetic vs. combination with “light” general anesthetic. Most patients request intra-operative sedation. Decreased PONV, sore throat, delirium, airway obstruction and respiratory depression. Decreased time to discharge from PACU. Increased patient satisfaction.
Post-operative pain control Decreased narcotic requirements and associated adverse side effects (e.g. nausea, pruritis, sedation, confusion, respiratory depression). Earlier recovery of bowel function. Improved tolerance of physical therapy. Improved pain scores in PACU. Increased patient satisfaction.
Infrastructure requirements and potential for surgeon delays. Failed Blocks. Intraoperative awareness and non-operative discomfort (e.g. positioning). Variable duration (approx hours). Rare serious complications (e.g. local anesthetic toxicity, nerve injury).
Ester type: unstable, broken down by pseudocholine esterase. Amide type: stable, broken down be liver enzymes
Intravascular injection (immediate onset) Systemic absorption (delayed onset) Central nervous system signs ◦ 1 st excitation: perioral tingling, tinnitus, agitation ◦ 2 nd depression: blurred vision, slurred speech, loss of consciousness ◦ Seizure Cardiovascular toxicity ◦ Cardiac arrhythmia and/or circulatory collapse ◦ Requires ~ 3x blood concentration that causes seizures
For use in the treatment of life threatening local anesthetic toxicity. Novel therapeutic indication for an old medication (component of TPN). First case reported in 2006, now with over a dozen reported cases. Mechanism of action unknown (“lipid sink?”).
Needle phobia or otherwise uncooperative. Excessive sedation (adults). Infection (local and untreated systemic). Anticoagulation? Pre-existing nerve injury. Surgery specific (e.g. motor block and post- op neurological examination). Block specific (e.g. pulmonary disease and interscalene block).
Monitoring. Availability of resuscitation equipment (suction, airway management). Availability of resuscitation drugs (induction agents, ACLS drugs, lipid emulsion). Pre-procedure confirmation (“timeout”). Aspiration before injection. Incremental injection. Do not inject when paresthesia present.
Anatomy. Loss of resistance and tactile feedback Evoked paresthesia. Nerve stimulator (goal mA). Ultrasound guided.
Children and adults who are already anesthetized when a decision is made that regional block is an appropriate technique. Individuals who are unable to report paresthesias accurately. In performing local anesthetic administration on specific nerve. In placement of stimulating catheters for anesthesia or postoperative analgesia. Patients with chronic pain, in whom accurate needle placement and reproduction of pain with electrical stimulation or elimination of pain with accurate administration of small volumes of local anesthetics may improve diagnosis and treatment.
Motor fibers (Aα)require less current than sensory element (Aδ, C fibers). Cathode(negative)electrode should be attached to the stimulating needle, not anode(positive)electrode. Current less than 0.5 mA is essential to locate the nerve successfully.
Constant current output. The stimulating pulse width should be shorter( sec). A battery indicator is essential. The polarity of the leads should be clearly marked.
Stimulating needle is connected to the cathode. After the skin is disinfected, the needle is advanced towards the nerve with the stimulator at a relatively high current intensity (1–2 mA) and with a pulse width of 100 to 200 μs. This higher current amplitude is necessary to stimulate the nerve at some distance from the needle.
The current intensity decreased as the needle approaches the nerve, threshold current usually at 0.4–0.5 mA. Attempting to observe a twitch at lower intensities (<0.3–0.4 mA) may result in inadvertent intraneural injection.
Once the acceptable threshold current is reached, aspiration for potential intravascular placement is performed. With a negative aspiration a test injection of local anesthetic or normal saline (1–2 mL) is performed. The muscle twitch should diminish following the test injection (Raj test).
The mechanism of the Raj test was previously thought to be due to displacement of the nerve by the injectate. A recent interpretation of the Raj test suggests that ionic solutions influence the response to nerve stimulation.
With pure sensory nerves, the response will be a radiation of paresthesia with each pulse along the distribution of the nerve. Additionally, the pulse width used for nerve localization should be somewhat higher (300 μs–1 ms).
Sound is mechanical vibration of particles in a physical medium (air, blood, fat, etc). Sound comes in three "flavors": infrasound, audible sound, and ultrasound, based on its frequency There are 5 major steps that ultrasound takes before an image can be made: sound generation, transmission, reception or reflection, reflection to transmission, reception to processing image production 8-12 MHz (multifrequency) linear probe (this probe alone will suffice for 90% of practical nerve blocks)
Propagation through dense objects e.g. bone is poor with nearly the entire ultrasound beam reflected (hyper echoic (bright) image ). Fat and tendon have low reflectivity thus they form hypo echoic (dark) images. The outline of an object is generally best delineated when the ultrasound beam is at 90 degrees. Generally speaking, nerves appear in the transverse (cross sectional) view as round to oval shaped structures that are nodular and they can be hypo echoic or hyper echoic depending on location. On the transverse view, peripheral nerves in cross section often appear to have an internal honey comb texture.
Ultrasound is generated when multiple piezoelectric crystals inside a transducer rapidly vibrate in response to an alternating current. To generate a clinically useful image, ultrasound waves must reflect off tissues and return to the transducer. The transducer, after emitting the wave, switches to a receive mode. When ultrasound waves return to the transducer, the piezoelectric crystals will vibrate once again, this time transforming the sound energy back into electrical energy.
High frequency beam has a narrower beam width Resolution refers to the ability to clearly distinguish two structures lying beside one another.
Low frequency = greater depth of penetration but lower resolution
Acoustic impedance =resistance of a medium to the sound transmission Attenuation = loss of wave energy traveling through a medium of different acoustic impedance Cycle = the combination of one rarefaction and one compression equals one cycle Doppler effect =sound + movement -> modified frequency Echogenicity = capacity of a structure in the path of an ultrasound beam to reflect back sound waves Frequency = the number of cycles per unit time. frequency is the reverse of wavelength. The higher the frequency, the smaller the wavelength.
Hyperechoic = an ultrasound image with echoes stronger than normal or than surrounding structures; images are bright on monitor; examples are bone and pleura. Hypoechoic = an ultrasound image with weaker echoes than the surrounding structures; images are dark on monitor; examples are vessels and cyst. Interface = boundary between two substances that transmit sound at different velocities. Velocity = speed at which sound waves travel through a particular medium; velocity = frequency x wavelength; ultrasound velocity through human soft tissue = 1540 m/sec. Wavelength = the distance between the onset of peak compression or cycle to the next.
Linear vs curved. High frequency vs low frequency.
“ In-Plane ” Safer Always see tip of needle Out-of-Plane ” May be easier. Risk losing sight of needle tip.
Superficial nerves need shallow settings. Deep nerves need deep settings.
Resolution Set by the transducer frequency. Gain Near Far Color doppler Shows blood flow.
Can save to hard drive or disk. Able to print out hard copy. Able to save video. New reimbursement requirements Must have proof that block was done with ultrasound if you billed for it.
Regardless of the machine or transducer selected, there are four basic transducer manipulation techniques, which can be described as the “PART” of scanning: Pressure (P): Various degrees of pressure are applied to the transducer that are translated onto the skin. Alignment(A): Sliding the transducer defines the lengthwise course of the nerve and reference structures. Rotation(R): The transducer is turned in either a clockwise or counterclockwise direction to optimize the image (either long or short-axis) of the nerve and needle. Tilting(T): The transducer is tilted in both directions to maximize the angle of incidence of the ultrasound beam to the target nerve, thereby maximizing reflection and optimizing image quality.
Safety - no radiation. Visualize nerves. Visualize surrounding structures. Avoid complications. Visualize spread of local anesthetic. May be more reliable and quicker onset of action. Visualize the internal anatomy. Advance the needle under real time guidance (dynamic images). Observe the local injection (accuracy).
Any block technique works if you are good All current RCTs are small Ultrasound decreases:: Onset time Number of needle passes Discomfort if stimulation is avoided Decreased LA volumes Increased successful rate
All about peripheral nerve block are true except: a) More hemodynamic stability compared with neuroaxial blocks. b) Anticoagulation less of an issue. c) Introduction of perineural catheters prolongs post- operative pain control benefits. d) Postoperative nausea and vomiting are common. All of the following are amide type local anesthetic except: a) Lidocaine. b) Mepivacaine. c) Prilocaine. d) Cocaine.
One of the following drugs are used in the treatment of local anesthetic toxicity: a) Amiodarone b) Digitalis c) Atropine. d) Intralipid infusion. Current intensity that is necessary for successful nerve block: a) O.2mA. b) 0.3mA. c) 0.4mA d) 0.5mA. All of the following are true except: a) Ultrasound decreases local anesthetic dose requirements. b) Ultrasound decreases discomfort if stimulation is avoided. c) Ultrasound decreases successful rate. d) Ultrasound decreases number of needle passes.