L. Hurit. Jackson State University.

Pulsed radiofrequency is the pre- the fascia layer between the omohyoid muscle and the serra- ferred method of neurolysis [13] order viagra soft no prescription. The needle is placed prone position with the hand either by the side or under the in plane to the ultrasound probe viagra soft 100 mg free shipping, and 5 cc volume of local head cheap viagra soft 100 mg line. The procedure is done under fuoroscopic or ultrasound anesthetic is injected with real-time ultrasound imaging. The nerve may be accessed either by classic posterior is confrmed by dye spread and appropriate motor response of technique using the suprascapular notch as an important the supraspinatus and infraspinatus muscles at 2 Hz stimula- landmark or by the anterior approach which requires the tion. The stylet is removed and 2 cc of 1% lido- ular block along with axillary block may be a viable alter- caine is injected. The radiofrequency probe is inserted and native to interscalene block especially in a patient with connected to the radiofrequency generator. Pneumothorax is the most dreaded complication which can be avoided with careful technique and possibly with the use of ultrasound with dynamic visualization of the Precautions needle. Suprascapular nerve block is an easy procedure to perform and a safe technique for providing pain relief from various types of shoulder injuries [32]. Suprascapular nerve block References permits long-lasting, effective analgesia for various condi- tions affecting the shoulder such as rheumatologic disorders, 1. Percutaneous radiofrequency lesioning of the suprascapular nerve for the management of chronic trauma, and postoperative and cancer pain. Pain procedures in clinical peripheral stimulators and pulsed radiofrequency will be practice. Suprascapular nerve shoulder pathologic diseases which will respond positively block for chronic shoulder pain in rheumatoid arthritis. Suprascapular nerve block (using bupivacaine and methylprednisolone acetate) in chronic shoulder pain. Suprascapular nerve block for the treatment of frozen shoulder in primary care: a randomized trial. The effectiveness of ultrasonography- guided suprascapular nerve block for perishoulder pain. Pulsed radiofrequency lesioning • Injury to suprascapular artery and vein of the suprascapular nerve for chronic shoulder pain. Intra-articular cortico- • Transient increase in pain steroid injections versus pulsed radiofrequency in pain shoulder: a prospective, randomized, single-blinded study. Pulsed radio- frequency of suprascapular nerve for chronic shoulder pain: a ran- domized double-blind active placebo-controlled study. Pain relief after arthroscopic shoul- radiofrequency may be useful in selected patients. Ultrasound-guided suprascapular nerve block suprascapular nerve block, intra-articular steroid injection, and a technique. Optimization and stan- suprascapular nerve block, description of a novel supraclavicular dardization of technique for fuoroscopically guided suprascapular approach. Is fuoroscopy-guided suprascapular nerve block better Analgesic effcacy and technique of ultrasound-guided suprascap- than other techniques? Introduction Regional anesthesia has progressed signifcantly since the discovery of cocaine as a local anesthetic. The use of The myriad of conditions that can be managed by chest wall ultrasound Doppler for intercostal nerve block was frst blocks is vast. Since then, the ultrasound technique tal blocks include intercostal neuralgia, Tietze’s syndrome, has been refned to include detailed anatomy of the inter- post-thoracotomy pain syndrome, acute herpes zoster, frac- costal space, different approaches, and visualization tured ribs, metastatic lesions, and postmastectomy syndrome of spread of the medication in real time to avoid [1–3]. Pain due to chest wall trauma including rib fractures is ame- nable to paravertebral and epidural techniques. However, in Pathophysiology the presence of contraindications such as anticoagulation, lack of cooperation, and infection, intercostal nerve blocks Intercostal nerve blocks can be done in a host of clinical provide an excellent alternative for chest wall analgesia in conditions. Patients who develop chest wall pain upper abdominal surgeries are excellent candidates for chronically due to post-thoracotomy syndrome or malig- intercostal nerve blocks [6–11]. Posttraumatic pain with nancy of the chest wall are good candidates for neurolytic fail chest and rib fractures can be treated with these blocks intercostal nerve blocks. In both these scenarios, intercostal blocks are more effective when utilized as a part of the multimodal regime [8]. Chronic pain patients who present with chest wall and History upper abdominal pain are amenable to a series of diagnos- tic blocks prior to radiofrequency lesioning for long-term While William Halstead and Richard Hall are acknowl- control [7, 9, 10]. Terminally ill cancer pain patients with edged as the frst to perform nerve blocks, Vassily von unrelenting chest wall pain due to extensive metastasis may Anrep is credited for being the frst to use cocaine as a require a series of intercostal blocks and chemical neuroly- local anesthetic for intercostal nerve blocks [4]. Braun frst petic neuralgia, post-thoracotomy pain, and intercostal described local anesthetic block of these nerves in 1907. Doulatram Evidence Base Mapping out the entire painful area is necessary before proceed- ing with blocks to avoid missing segments of pain. The use of ultrasound guidance for intercostal block for chronic pain was reported by Curatolo and Eichenberger with the use of an out-of-plane technique [12]. Cryoablation Anatomy of intercostal nerves using ultrasound guidance has showed some promise in isolated cases [13, 14]. These blocks have The anatomy of the intercostal nerves has remained relatively been extensively described in trauma and thoracic or upper constant with little variation. The seventh intercostal nerve terminates at the accurate deposition of dye using ultrasound vs land- the xiphoid process, the tenth intercostal nerve terminates at mark technique as assessed by fuoroscopy. The ultra- the umbilicus, and the twelfth (subcostal) thoracic nerve is dis- sound guidance was associated with intercostal spread for tributed to the abdominal wall and the groin. The subcostal 36 of the 37 injections but only in 26 of the 37 injections nerve (T12) supplies sensory innervation to the abdominal with landmark guidance. Another study [19] comparing wall and combines with L1 to supply sensory innervation to ultrasound-guided intercostal nerve blocks in the 11th and the groin [24, 25]. There are three layers of the intercostal 12th intercostal space for postoperative pain following muscle: external, internal, and innermost intercostal muscles percutaneous nephrolithotomy with controls showed posi- (Fig. The effcacy of intercostal blocks in relieving vein lies in between the internal and innermost intercostal pain and improving ventilator parameters has been dem- muscles. As nerves exit the paravertebral space, they enter the onstrated in multiple studies [1, 3]. However, the current intercostal space and are usually found between the innermost literature has not shown the superiority of ultrasound intercostal muscle and pleura [26]. At the angle of the rib, the technique over other techniques in terms of beneft and nerve lies between the innermost intercostal muscle and the less intravascular and pleural puncture [20–23]. Usually the intercostal nerves There have been studies involving minimally invasive lie inferior to the intercostal artery which is also inferior to the coronary artery bypass grafting which have early discharge intercostal vein and can usually be found on the inferior por- to a step down unit from the intensive care unit [20]. Cadaver studies have found the intercostal Intercostal nerve blocks in combination with pectoral nerve nerve in the midcostal location 73% of the time, subcostal blocks have been used successfully for cardiac resynchroni- 17% of the time, and supracostal 10% of the time [28, 29]. The use of inter- The intercostal nerve separates into bundles and rejoins; costal nerve blocks for implant-based breast surgery has hence, there is not a single discrete intercostal nerve along its also been described with excellent results. Each intercostal nerve single-shot blocks, multilevel continuous intercostal nerve branches into four distal branches anteriorly. The frst branch block catheters are a viable alternative to thoracic epidural is the gray rami communicantes, which communicates to the for multiple rib fractures [22].

Of severe forward and upward displacement of the adducted forensic interest is the mechanism of forceful pulling of arm such as may occur when a motorcycle rider is vaulted the arm purchase generic viagra soft on-line, as may occur in a struggle purchase 100mg viagra soft with visa. Posterior dislocation is characterized by displace- as the humeral head is dislocated inferiorly buy genuine viagra soft on-line. As noted earlier, poste- the head of the humerus normally overlaps the rior dislocation may be related to seizure activity. In these glenoid fossa to form a shadow shaped like a half cases there may also be a compression defect to the artic- moon, which reaches the inferior border of the gle- ular surface of the head of the humerus from continual noid fossa. Elbow Fracture Dislocation Mechanism Anatomy ἀ e majority of elbow dislocations are the result of a fall ἀ e elbow is described as a trochoginglymoid joint, onto the outstretched hand resulting in a combination which has two major actions: fexion–extension and of axial loading, valgus stress, and rotation force to the pronation–supination. Biomechanical studies have shown that elbow sta- the trochlea of the humerus and the trochlea notch of bility decreases with progressive loss of the olecranon the ulna, and the radial head and capitulum of the process of the ulna [25]. A ridge in the trochlear notch articulates ἀ e coronoid process acts as a buttress to prevent with the groove in the trochlea of the humerus. Fat is normally present Etiology within the joint capsule but outside the syn- Elbow fractures occur in approximately 7% of all adult ovium. In young adults the common causes of cavity of the olecranon and coronoid fossa such elbow fracture include motor vehicle incidents, falls that it is not visible on a conventional lateral from a height, and sports-related injuries [34]. Injuries that produce intra-articular patients almost two-thirds of cases occur from falls from hemorrhage cause distension of the synovium a standing height. Of note is the fact that the great majority of Approximately 80% to 90% of elbow dislocations result elbow injuries associated with a positive fat pad in the ulna being displaced posteriorly. Wrist Fracture Dislocation “defensive” fracture is usually caused when the victim’s upper limb is raised to ward of a blow from a weapon. Carpal dislocations as a fracture classically associated with an ofensive-type most commonly result from a fall onto the outstretched injury. However, the report from a series of cases in nose wrist, carpal, and metacarpal fractures. Damage to the articular surface of a metacarpal Forensic Aspects of Upper Limb Injury has been described in clenched-fst injuries, where the assailant’s hand comes into hard contact with a tooth Assault [38]. Eight of 139 forensic pathologist to opine as to whether an injury or patients were shown to have loose intra-articular frag- fracture resulted from an ofensive action by an assail- ments of articular cartilage, whereas tooth indentations ant or a defensive reaction by a victim of assault. Distal commi- examination, however, these changes may be subtle and nuted, and ofen compound fractures of the distal radius easily overlooked. Radial metaphyseal and diaphyseal fractures are typical injuries, whereas the distal radial articular region is also sometimes involved. Defensive-Type Injuries ἀ e ulna is injured more commonly than the radius in Trauma Associated with Seizures direct blows involving the forearm. Fractures may occur from a is clearly a dynamic process with numerous variables, fall or other accident subsequent to a seizure, or can result the forearm is typically pronated so the medial aspect of from the forces generated from the muscle contractions the forearm is vulnerable in a defensive pose. Fractures to the hand occurred in 27 major, deltoid, and latissimus dorsi can culminate in frac- injuries and there were 14 fractures to the radius. Other typical fractures lef side of the body was injured in 67% of the cases and associated with seizures include compression fractures of the right side was injured in 23% of cases. Pediatric supracondylar fractures and been purported to be important in causing airbag-related pediatric physeal elbow fractures. Humerus shaf fractures in young children: Accident the forearm extending across the steering wheel at the time or abuse? Chalidis B, Sachinis N, Dimitriou C, Papadopoulos P, humerus fractures sustained during the use of restraints Samoladas E, Pournara J. Bilateral posterior fracture-dis- in arthrodesis of the interphalangeal joints and a location of the shoulder and other trauma caused metacarpal neck fracture. Pelvic fractures lead to ἀ e pelvis is a stable ring of bones and ligaments that early death from associated damage to major arteries encloses the pelvic viscera (Figure 9. Delayed deaths are more ofen the result of vis is formed by the paired innominate bones and the the systemic efects of visceral injury or multiple system sacrum. In young adults the most common cause of pelvic ἀ e pelvis articulates with the lower limb through fracture is trauma from motor vehicle incidents. Other the hip joint and with the lumbar spine via the sacrum causes are falls from a height and industrial accidents. Less commonly, ἀ e integrity of the pelvis is highly dependent upon its bed-bound or wheel chair–confned persons can sufer ligaments. Rarely an acetabular fracture, than the anterior ligaments in maintaining the integrity fracture of the neck of the femur, or hip dislocation may of the pelvis [1]. Pelvic fractures may be divided into simple, stable ἀ e hip joint is a ball and socket joint. Low energy sule called the acetabular labrum extends almost cir- incidents, such as simple falls from a standing height, cumferentially around acetabulum and deepens the tend to cause stable simple fractures, whereas high socket. Capsular ligaments attach the acetabulum to energy trauma, such as motor vehicle incidents, are the femoral neck and intertrochanteric region. Posterior to the Stable pelvic fractures are characterized clinically joint is the ischiofemoral ligament. Higher energy forces will Etiology tend to cause more severe injuries, and may involve both the anterior and posterior aspects of the pelvis resulting Pelvic fractures in adults are associated with signif- in an unstable pelvic ring. In otherwise active and Anterior forces have a propensity to cause separa- healthy individuals, pelvic fractures are an indicator of tion of the symphysis pubis, or fractures to the pubic severe trauma and a marker of potential major pelvic rami and a second posterior fracture in the vicinity of and abdominal visceral damage [2]. Posteriorly result from disruption of major arteries, venous plexuses, directed forces tend to cause iliac or sacral fracture with 159 K13836. Laterally severe blunt force applied to the posterior aspect of the directed forces over the region of the greater trochanter pelvis in a posterior–anterior compression-type injury of the femur can lead to central acetabular fractures. A further rise may be involved in fractures to the region of the greater in degree of force can lead to corresponding fractures to sciatic foramen, the upper part of the ischial tuberosity, the contralateral aspect of the pelvis. Verticallydirectedforcesthroughthefemurordirectly ἀ e internal pudendal artery may be damaged in open to the ischium tend to produce fractures to the ipsilateral book fractures. Fractures around the acetabulum can lead superior and inferior pubic rami, and vertical fractures to rupture of branches of the obturator artery [7]. Fractures that involve shearing injury, with posterior fractures involv- Avulsion fractures are generally a clinical issue rather ing the ilium or anterior sacroiliac disruption can cause than a forensic problem. Avulsion fractures typically damage to the iliolumbar artery, which is in close prox- occur around the pelvis in children and sudden stress imity to the anterior sacroiliac joint [5]. There are fractures to the superior and inferior pubic rami and sacroiliac joint on the right, and a left iliac wing fracture. Typical sites of avulsion frac- A common simple fracture of the pelvis is the isolated ture in the pelvis include the anterior and inferior supe- pubic ramus fracture (Figure 9. Pubic ramus fractures may result from anteri- lower limb beyond the normal range of movement.

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The sac purchase 50 mg viagra soft with visa, entering at the internal ring cheap 50 mg viagra soft fast delivery, may pass into any one or more spaces between layers of the abdominal wall order viagra soft australia. Radical orchiectomy is performed through a herniorrhaphy incision (described above). The spermatic cord is freed and cross-clamped at the internal inguinal ring, transected, and suture-ligated. The testis, with its tunica vaginalis, is then delivered through the incision by blunt and sharp dissection, and the inguinal incision is closed. Sometimes, a testicular prosthesis is inserted and fixed in the scrotum before the inguinal incision is closed. Usual preop diagnosis: Testicular cancer Ligation of spermatic vein is performed through a small, transverse incision 1–2˝ above the internal inguinal ring. Muscles are split and peritoneum reflected medially to expose the spermatic vessels; the vein is identified and ligated. Usual preop diagnosis: Varicocele causing infertility Groin dissection, or inguinofemoral lymphadenectomy (lymph node dissection), is the most critical of the inguinal operations. In these patients, consider causes of increased intraabdominal pressure during H&P. Local anesthesia is acceptable for simple herniorrhaphy, although discomfort may be elicited if the peritoneum is manipulated. Most inguinal procedures are done on an outpatient basis, and the anesthetic should be planned appropriately. Castorina S, Luca T, Privitera G, El-Bernawi H: An evidence-based approach for laparoscopic inguinal hernia repair: lessons learned from over 1,000 repairs. If the tumor can be resected with a safe margin of at least 2 cm, partial penectomy is usually enough. A tourniquet is placed at the base of the penis, which is amputated at least 2 cm proximal to the tumor. The corpora cavernosa are sutured, and the tourniquet is released, followed by inspection for bleeding. The edges of the urethra are sutured to the ventral skin, and the lateral and dorsal skin edges are approximated over the ends of the corpora cavernosa. Usual preop diagnosis: Squamous cell carcinoma of the penile skin Insertion of penile prosthesis is performed for impotence. Preop evaluation should be directed toward the detection and treatment of these conditions prior to anesthesia. Sacral anesthesia (saddle block) is sufficient; lumbar epidural anesthesia may be less reliable than spinal or caudal at blocking sacral fibers. Usual preop diagnosis: Metastatic prostate cancer Vasovasostomy is the reestablishment of the continuity of the vas deferens and restoration of fertility following a previously performed vasectomy. The site of previous vasectomy is identified and excised and the two ends of the vas deferens anastomosed. It is bilateral and requires the use of either the operating microscope or magnifying loupes. Usual preop diagnosis: Infertility 2° vasectomy Hydrocelectomy: The testis, with the surrounding hydrocele (Fig. The wall of the hydrocele is excised and the edges sutured around the epididymis to prevent recurrence. Variant procedure or approach: Aspiration used as a temporizing approach because recurrence is almost 100%. Usual preop diagnosis: Hydrocele Spermatocelectomy: A spermatocele is a cyst of the epididymis, usually excised with the part of the epididymis from which it arises. Variant procedure: Aspiration as a temporizing maneuver until the operation can be performed. Usual preop diagnosis: Spermatocele or epididymal cyst Insertion of testicular prosthesis: A small incision is made in the scrotal skin, and a pouch is created by blunt dissection in dartos fascia. The prosthesis is placed in the pouch and fixed to the dartos fascia to prevent prosthesis migration. Usual preop diagnosis: Absent testis, either congenital or following orchiectomy Reduction of testicular torsion is an emergency operation that must be performed within 6 h of occurrence to prevent irreversible ischemic damage to the testis. Through a small scrotal incision, the testis is reduced and fixed to the dartos fascia to prevent retorsion. Many of these procedures are done on an outpatient basis, and the anesthetic should be appropriately planned to facilitate early discharge. A transverse or longitudinal perineal incision is made and carried down to the urethra, which is dissected free from surrounding tissues. The strictured area is excised and end-to-end anastomosis is performed over a catheter. Repair of a long urethral stricture may require placement of a patch from the scrotum, foreskin, or buccal mucosa. Variant procedure: Transurethral incision and dilation, which is associated with a 30–50% recurrence rate. Usual preop diagnosis: Urethral stricture, usually posttraumatic Urethrectomy: Partial or total urethrectomy is done through a longitudinal perineal incision. The urethra is dissected free of surrounding tissues and followed proximally and distally from the membranous urethra to the external urethral meatus. In total urethrectomy, a tubularized skin graft is interposed between membranous urethra and perineal skin. Usual preop diagnosis: Urethral carcinoma Insertion of artificial urinary sphincter, performed for incontinence, consists of a perineal incision, through which a cuff is inserted around the bulbar urethra. A suprapubic incision is made to place the reservoir and pump, which inflates and deflates the cuff. Usual preop diagnosis: Urinary incontinence Transperineal prostate seed implantation (brachytherapy): High doses of radiation can be delivered to the prostate by implanting radioactive seeds directly into the prostate gland. Using a transrectal ultrasound probe, radioactive seeds (iodine 125 or palladium 103) are implanted into the prostate (Fig. The patient is placed in lithotomy position, and a rectal ultrasound probe, with a perineal grid attached, is introduced to image the prostate. This procedure is done by a combined team of radiation oncologists and urologists. Lumbar epidural anesthesia may be less reliable at providing sacral anesthesia and offers no advantages over the above techniques for shorter procedures, although caudal anesthesia may be an acceptable alternative. They include the following: Repair of vesicovaginal fistulas: The vaginal approach is usually recommended for small and distally located vesicovaginal fistulas; otherwise, a transabdominal repair is performed (see Open Bladder Operations, p. An incision is made in the anterior vaginal wall around the fistula, which is excised. Bladder and vaginal walls are separated and closed with interposition of tissues or flaps to separate the incisions and prevent recurrence. Variant approach: Transabdominal repair of vesicovaginal fistula (see Open Bladder Operations, p. Usual preop diagnosis: Vesicovaginal fistula Operations to correct stress urinary incontinence: Many procedures have been designed to correct female urinary incontinence.

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As the pressure wave travels distally buy 100mg viagra soft mastercard, an increase in systolic amplitude can be noted cheap viagra soft 50mg line, whereas the diastolic amplitude decreases initially up to midthoracic level buy viagra soft online pills, then increases again. These differences can impact important measurements such as those of aortic gradients. Accordingly, in general, it is advisable to measure the central aortic pressure at the level of the coronary arteries. This also avoids interference with the effect of pressure recovery, which can become relevant in patients with mild to moderate aortic stenosis, particularly when the aorta is small. Elevated a wave (any increase in ventricular filling) Tricuspid stenosis Decreased ventricular compliance as a result of ventricular failure, pulmonic valve stenosis, or pulmonary hypertension D. Cannon a wave Atrial-ventricular asynchrony (atria contract against a closed tricuspid valve, as during complete heart block, following premature ventricular contraction, during ventricular tachycardia, with a ventricular pacemaker) E. Prominent y descent Constrictive pericarditis Restrictive myopathies Tricuspid regurgitation J. Cannon a wave Atrial-ventricular asynchrony (atria contract against a closed mitral valve, as during complete heart block, following premature ventricular contraction, during ventricular tachycardia, or with a ventricular pacemaker) E. Prominent x descent Tamponade Subacute constriction and possibly chronic constriction Right ventricular ischemia with preservation of atrial contractility I. Prominent y descent Constrictive pericarditis Restrictive myopathies Mitral regurgitation J. Elevated systolic pressure Primary pulmonary hypertension Mitral stenosis or regurgitation Congestive heart failure Restrictive myopathies Significant left-to-right shunt Pulmonary disease (pulmonary embolism, hypoxemia, chronic obstructive pulmonary disease) B. Reduced systolic pressure Hypovolemia Pulmonary artery stenosis Subvalvular or supravalvular stenosis Ebstein anomaly Tricuspid stenosis C. End-diastolic pressure elevated Hypervolemia Congestive heart failure Diminished compliance Hypertrophy Tamponade Regurgitant valvular disease Pericardial constriction D. Diminished or absent a wave Atrial fibrillation or flutter Tricuspid or mitral stenosis Tricuspid or mitral regurgitation when ventricular compliance is increased F. Dip and plateau in diastolic pressure wave Constrictive pericarditis Restrictive myopathies Right ventricular ischemia Acute dilation associated with tricuspid or mitral regurgitation G. Systolic pressure elevated Systemic hypertension Arteriosclerosis Aortic insufficiency B. Widened pulse pressure Systemic hypertension Aortic insufficiency Significant patent ductus arteriosus Significant rupture of sinus of Valsalva aneurysm D. Reduced pulse pressure Tamponade Congestive heart failure Cardiogenic shock Aortic stenosis E. Pulsus paradoxus Constrictive pericarditis Tamponade Obstructive airway disease Pulmonary embolism G. Spike-and-dome configuration Obstructive hypertrophic cardiomyopathy Cardiac Output Measurements Although extremely important, often requested and tested, cardiac output measurements represent only estimates of the true cardiac output on the basis of several assumptions. Three methods are used in the catheterization laboratory: thermodilution, Fick, and ventriculography. Thermodilution Method Thermodilution is based on the principle of washout of a temperature change induced by injection of a defined fluid volume cooler than the body temperature. In practice a bolus of liquid (usually 10 mL of normal saline kept at room temperature) is injected into the proximal port of the catheter, and the change in temperature from baseline is measured by a thermistor at the distal end of the catheter and displayed as a function over time. Cardiac output correlates inversely with the area under the curve and can be calculated when the temperature and specific gravity of the injectate and the blood as well as the volume of the injectate are known (eFig. Configurations of thermodilution curves in high and low cardiac output states (middle) and with improper injection technique (bottom). However, thermodilution is less accurate in patients with significant tricuspid or pulmonic regurgitation, intracardiac shunts, low cardiac output, or irregular rhythms. Fick Method The Fick method relies on the principle that blood flow is proportional to the difference in the concentration of oxygen between arterial and venous blood and the rate of oxygen uptake in the lungs (Fig. Fluid containing a known concentration of an indicator (Cin) enters a system at a given flow rate, adding to the concentration of the indicator already present and thereby raising the concentration of the indicator in the outflow (Cout). In a steady state, the rate of indicator leaving the system must equal the rate at which it enters plus the rate at which it is added. When oxygen is used as the indicator, cardiac output can be determined by measuring oxygen consumption (V̇), arterial oxygen content (CaO ), and mixed venous oxygen content (2 ). Although the oxygen content in blood samples can be reliably measured, measurement of oxygen consumption may represent a source of variability, especially if steady-state conditions are difficult to establish. It is determined by a polarogram, which is connected to the patient by a plastic hood or mouthpiece and tubing and relates the difference between the oxygen concentration in the expired air and the known concentration of oxygen in room air. This can lead to large errors, however, as much as 40% in cardiac output estimates, compared with the measured 40 oxygen consumption. Ventriculographic Method As a third method, the cardiac output can be calculated based on determination of the stroke volume multiplied by the heart rate. The stroke volume equals the difference between end-diastolic and end- systolic volumes. The borders of the contrast-filled left ventricle are traced in end diastole and end systole, and these two-dimensional (2D) values are converted into three-dimensional (3D) volumes based on calibration algorithms with grids and phantoms. Inaccuracies can easily be introduced in the calibration and tracing steps as well as heartbeat irregularities (e. The ventriculographic method, however, is preferred in patients with significant aortic or mitral regurgitation. Even though it represents an oversimplification of the complex cardiovascular hemodynamics, it has proved very useful in clinical practice. Accordingly, the pressures at the proximal and the distal ends of a vascular bed are measured, and the difference is divided by the cardiac output: mean pressure gradient (mm Hg)/mean flow (L/min). However, it is a less accurate means to assess the severity of pulmonary vascular disease. An additional assessment often performed in the catheterization laboratory is whether any resistance elevation can be induced, as by exercise, or reduced, as by sodium nitroprusside systemically or inhalation of nitric oxide in the pulmonary circulation. Whether any resistance elevation is fixed or reversible, however, is an important question in various clinical scenarios (e. A more accurate measure to describe the dynamic relationship between pressure and flow is vascular impedance, which accounts for blood viscosity, pulsatile flow, reflected waves, and arterial compliance. However, it requires simultaneous measurement of pressure and flow data and is not easy to obtain. Thus, vascular impedance has not gained widespread acceptance as a routinely reported variable. Clinical Aspects and Integration Into Patient Care Evaluation of Valvular Stenosis The cardiac catheterization takes an important part in the evaluation of patients with valvular stenoses, especially if there is discordance in the degree of severity by physical examination and noninvasive tests such as echocardiography. For a number of cases, determination of the pressure gradient will suffice, but the valve should be calculated as well. Determination of Pressure Gradients Aortic Valve Stenosis (see Chapter 68) Although easily accessible, the femoral artery pressure, recorded through the access sheath, should not be used for the calculation of the gradient across the aortic valve because it is unreliable, for various reasons (Fig. Another option is to use a multipurpose catheter, which is kept in ideal aortic position, and a pressure wire that is advanced through the catheter just across the aortic valve.