Position the patient supine (some people advocate placing a sandbag between the patient \200\231s shoulder blades, which allows the shoulders to drop back out of the way). Identif y the junction of the medial third and outer two- thirds of the clavicle. Introduce the nee dle just beneath the clavicle at this point, and aim towards the clavicle until contact wit h bone is made. 105 CHAPTER 7.3 Insertion of central venous catheters dle once it has passed beyond the end of the bevel: it may shear off. Use a scalpel blade t o make a small nick in the skin. Hold the blade up and cut away from the wire. If provided, pass the dilator over the wire into the vein. Then remove it, leaving the wire in situ. Pa ss the cannula over the wire into the vein. Make sure that before you push the cannula forw ard the wire is visible at the proximal end. Hold on to the wire at all times, to prevent i t being lost inside the patient For an average adult patient the central venous cannula via the right internal jugular vein does not need to be inserted more than 12 \200\22315cm. Ch eck markings on the cannula. Many are 20cm long and do not need to be inserted up to the hu b. Draw back blood, check the color, pulsatility and the pressure of the back \202 ow of blood, \202 ush all the lumens of the line with heparinized saline and lock off the 3-way taps. At this point the patient can be leveled. Suture the line into place using the ancho rage devices provided and cover with an adhesive sterile dressing. If you appear to have mi ssed the vein on the \201 rst pass, pull back slowly while maintaining suction on the syr inge. You often \201 nd you have gone through the vein and can \201 nd it on withdrawal . Attach a transducer and display the waveform on the monitor. Dispose of your sharps and c lear away your trolley. Obtain CXR to verify central position of the line and check for com plications, including pneumothorax and haemothorax. Document the procedure in the patient \200\231s notes. To locate the vein, redirect the needle closely behind the clavicle and towards the suprast ernal notch. Ultrasound can be used to guide puncture of the vein using a more lateral appr oach. The axillary vein can be identi \201 ed under the pectoral muscles at a depth of 3 \200\2234cm in the average patient. Longer catheters (20cm left and 25cm right) are require d by this approach. Supraclavicular approaches can also be used using both landmark- and ul trasound-guided techniques. Femoral vein The femoral vein lies medial to the femoral artery immedi- ately beneath the i nguinal ligament. It is particularly useful for obtaining central access in small children and in patients with severe coagulopathy. \200 \200 Palpate the femoral artery. To locate the vein, introduce the needle 1cm medial to the femo ral artery close to the inguinal ligament. It is a common mistake to go too low where the s uper \201 cial femoral artery overlies the vein. Ultrasound should be used to identify the vessels (long saphenous vein, deep and super \201 cial femoral arteries) and ensure that the vein is punctured near the inguinal ligament where the artery and vein lie side by side . Procedure Central venous catheterization is almost universally achieved using a catheter ov er a guide wire (Seldinger) technique. This is associated with a lower incidence of incorre ct line placement and complications than cannula over needle techniques. \200 \200 For internal jugular, external jugular and subclavian veins, position the patient supine wi th 10 \200\22320 head down tilt. This distends the vein to aid location and helps prevent air embolism. Monitor ECG in case of dysrhythmias. Universal precautions. Use aseptic tech nique, sterile gown and gloves. Prepare sterile \201 eld. Prepare all equipment. Check wi re passes through the needle freely. Attach 3-way taps to all open ports of the cannula. Fl ush the lumens with heparinized saline. Inject local anesthetic to the entry site. Do not f orget to anesthetize suture sites as well. Identify the target vessel by ultrasound and/or landmark technique. Using a 10ml syringe (partially \201 lled with saline) and nee- dle e nter the central vein by the chosen approach, main- taining suction on the syringe at all t imes. Pass the guide wire through the needle. This should pass freely and without any force into the vein. Watch for arrhythmias. Never pull the wire back through the nee- Position on chest X-ray The catheter should lie along the long axis of the vessel and the t ip should be in the superior vena cava (SVC) or at the junction of the SVC and right atrium , but ideally out- side the pericardial re \202 ection. The pericardium lies below the car ina, so ideally catheter tips should be at or above the level of the carina. Catheters belo w this level may per- forate the heart and cause cardiac tamponade. Catheters placed via th e subclavian veins or left internal jugular vein must not be allowed to lie with the tip ab utting the wall of the SVC. This may cause pain, perforation and accelerated thrombus forma tion. Either advance the catheter to lie in the long axis of the SVC or pull it back to lie in the brachio- cephalic vein. Bear in mind the limitations of CXR; it is use- ful to con \201 rm central passage and no kinking. The close proximity of the SVC to the pleura, asce nding aorta and other structures means that con \201 rmation of the true intra- venous pos ition cannot be inferred from a plain CXR. \200 \200 \200 \200 \200 106 S BODENHAM & A GRATRIX Common problems with central venous access Cannot \201 nd the vein Check position (ultrasound and/or landmarks) and try again. If un successful do not persist with repeated passages of the needle in the hope of hitting the v ein. You may have misinterpreted the landmarks or the vein may be absent, narrowed or occlu ded (e.g. with thrombus). The management of pneumothorax depends upon the size of the pneumothorax and the patient \200\231s condition, particu- larly whether ventilated or not. A small pneumothorax in an u nventilated patient with good gas exchange may be observed, or aspirated using a small-bore cannula and syringe with a 3-way tap. Larger pneumothoraces, those that fail to resolve or those that cause any impairment of gas exchange and/or haemodynamics require a formal ches t drain. Any significant haemothorax should be formally drained as soon as possible. Once b lood has clot- ted in the chest, drainage is dif \201 cult. Seek cardiothoracic/ surgical opinion. Bleeding around the puncture site can occasionally be a persistent problem. If thi s does not resolve with pressure, use a \201 ne suture (e.g. 5/0 Prolene) to tie a purse string around the puncture site. This usually stops the bleeding. Line colonization with ba cteria and fungi is common, but there is no evidence that changing lines on a regular basis (e.g. every 5 \200\2237 days) is of bene \201 t. Aspirating blood (needle in vein?) but cannot pass wire Check needle position by drawing ba ck on the syringe; good \202 ow is essential. Adjust the angle of incidence of the needle to the vein to improve \202 ow. Tip the patient further head down to expand the vein fur ther. Try rotating the needle through 180 and draw back again. Remember the wire must pas s easily without force. If this doesn \200\231t work, repuncture the vein at a slightly dif ferent angle. Is it arterial? Occasionally, particularly if using a technique where the wire passes throu gh the barrel of the syringe, it is dif \201 cult to know whether you have hit the artery or the vein. In this case it is important to avoid passing a large central venous catheter into the vessel until you are sure. Consider the following: \200 Changing catheters over a wire If new central venous catheters are required, these should u sually be placed at a clean site. Occasionally it may be necessary to change a catheter ove r a guide wire using an existing site. The technique is similar to that described above for placing any central venous catheter. The main problem is avoiding contamination of the new catheter. \200 \200 Remove the syringe from the needle and observe for pulsatile \202 ow. Connect a transduce r directly to the needle in the vessel and look at the waveform. Pass the wire into the ves sel and remove the needle. Pass a 16/18G IV cannula over the wire into the vessel and remov e the wire. Attach a transducer or manometer set directly to the cannula. When venous place ment is con \201 rmed, pass the wire back through the IV cannula and continue as before. Cut sutures on the old line before scrubbing. Use universal precautions, aseptic technique, gown and gloves. Clean and prep the area. Pass the wire down the central lumen of the old central venous catheter. (Make sure that the new wire is longer than the old CVP line.) Rem ove the old catheter, leaving the wire in place, and send the tip of the old catheter for c ulture. Clean the puncture site with antiseptic solution. Use the wire to site the new line as required. \200 Arterial puncture \200 \200 Needle only, then simply remove and press. If large-bore cannula, then action depends on ci rcum- stances. If only in situ for a short period then it is usually safe to remove up to 8 French gauge (3mm) and press until bleeding stops. In cases of a larger catheter in situ, carotid puncture in arteriopath, thrombus present, severe coagulopathy or dif \201 culty p ressing (subclavian) leave in situ and give platelets and fresh frozen plasma (FFP) before removing. Seek advice and consider the need for surgical exploration and removal under dire ct vision. Radiological stenting can also be used. \200 The problem with this technique is keeping the new line sterile. Wear two pairs of gloves a nd discard the top pair when you have \201 nished with the old line. Removing central venous catheters To remove central lines ensure that all drugs and infusio ns have been stopped or relocated to other lines. If infection is suspected, send the tip o f the line in a dry specimen pot for culture. Removal of central venous catheters can pre- cipitate air embolism, pneumothorax, haemothorax, embolization of thrombus and bacteraemia/ sepsis. Make sure the puncture site is below the heart and apply pres- sure for at least 5m in; thereafter apply an occlusive water- proof dressing before sitting the patient up. Complications Complications of central venous cannulation depend in part on the route used but include; Early Arrhythmias Vascular injury Pneumothorax Haemothorax Thoracic duct injury (chylothora x) Cardiac tamponade Neural injury Embolization (including guide wire) Late Infection Thrombosis Embolization Erosion/perforation of vessels Cardiac tamponade Choice of catheter There are numerous devices on the market, including cath- eter through n eedle, catheter over needle, catheter through cannula and catheter over wire. The choice of which to use should depend on the indication for its use, availability of equipment and th e skill of the operator. Other choices include single or multi-lumen catheters, catheter ma terial and long- or shor t-term use. 107 CHAPTER 7.4 Common problems with central venous access cations, such as endocarditis, septic thrombosis, tunnel infection or metastatic seeding. W hen a catheter-related infection is documented and a speci \201 c pathogen is identi \201 ed, systemic antimicrobial ther- apy should be narrowed and consideration given for antibi - otic lock therapy, if the central venous catheter or implantable device is not removed. Antimicrobial-impregnated devices are also available, but their overall ef \201 cacy is st ill debated. Catheter-related infections Intravascular catheter-related infections are a ma jor cause of morbidity and mortality. Coagulase-negative sta- phylococci, Staphylococcus au reus, aerobic Gram-negative bacilli and Candida albicans most commonly cause cathe- ter-rel ated bloodstream infection. Management of cathe- ter-related infection varies according to the type of catheter involved. After appropriate cultures of blood and catheter samples, em pirical IV antimicrobial therapy should be initiated on the basis of clinical clues, the se verity of the patient \200\231s acute illness, underlying disease and the potential pathoge n involved. In most cases of non-tunneled central venous catheter-related bacteraemia and f ungaemia, the central venous catheter should be removed. For management of bacteraemia and fungaemia from a tunneled catheter or implantable device, such as a port, the decision to r emove the catheter or device should be based on the severity of the patient \200\231s illne ss, documenta- tion that the vascular access device is infected, assessment of the speci \201 c pathogen involved and the ence of compli- Further reading Stonelake P, Bodenham A. The carina as a radiological landmark for central venous catheter tip position. Br J Anesthesia 2006; 96: 335 \200\2230. Maecken T, Grau T. Ultrasound imaging in vascular access. Critical Care Med 2007: 35: S178 \200\22385. 108 P ANDERSON & A RHODES Pulmonary artery catheter: indications and use Introduction The use of the balloon-tipped, flow-guided catheter to measure the \201 llin g pressure of the left side of the heart was \201 rst described in 1970 by Swan. The use of the device to measure the cardiac output by a thermodilu- tion method was described in t he same paper by Ganz. In the intervening 30 years various other devices have been develope d to measure the cardiac output, but the pulmonary artery (Swan \200\223Ganz) catheter has remained the standard against which the other devices have been judged. Table 7.5.1 Derived haemodynamic parameters Cardiac output Body surface area Cardiac index = Systemic vascular resistance = MAP \200\223 RAP/CO Systemic vascular resistance index = MA P \200\223 RAP/CI Pulmonary vascular resistance = MPP \200\223 PAoP/CO Oxygen delivery (D O2) = CO \227 CaO2 \227 10 Oxygen delivery index (DO2I) = CI \227 CaO2 \227 10 Oxygen u ptake (VO2) = (CaO2 \200\223 CvO2) \227 CO \227 10 Where: CO = cardiac output (l/min) CI = cardiac index (l/min/m2) MAP = systemic mean arterial pressure RAP = right atrial pressu re MPP = pulmonary mean arterial pressure PAoP = pulmonary artery occlusion pressure CaO2 = arterial oxygen content (ml/100ml) CvO2 = venous oxygen content (ml/100ml) Indications Despite >30 years of international experience with the pulmonary artery cathete r, its use has never been vali dated in an adequately powered RCT. Indications for use are therefore based on expert opinion and con sensus state- ments from a variety of internation al societies. Potential indications for use of the pulmonary artery catheter as described b y Swan and Ganz include: \200 Establishing the etiology of shock states (i.e. cardiogenic vs hypovolaemic vs septic vs ob structive shock) Diagnosis of pulmonary hypertension and assessment of the response to trea tment Differentiation between cardiac and non-cardiac causes of pulmonary oedema Monitoring and management of AMI Monitoring and management of cardiac performance when restoring spon taneous circulation after cardiopul- monary bypass. Monitoring of \202 uid balance in pat ients where this is dif \201 cult clinically, e.g. burns patients, sepsis with capil- lary leak Assessment of response to inotropic drugs or vaso- pressors Peri-operative optimizati on of oxygen delivery in high- risk surgical patients The cardiac output is measured by the thermodilution method described below Thermodilution method for the measurement of cardiac output Cardiac output can be calculate d by using the Stewart \200\223 Hamilton equation (see Table 7.5.2). A bolus of cold \202 uid of known volume and temperature is injected through the proximal port of the pulmonary artery catheter into the superior vena cava. This \202 uid then mixes with the blood in the right ventricle and causes a decrease in the tempera- ture of the blood which is detect ed by a thermistor at the distal end of the pulmonary artery catheter, i.e. in the pul- mon ary artery. \200 Table 7.5.2 The Stewart \200\223Hamilton equation Modi \201 cations of the classic Swan \200\223Ganz pulmonary artery catheter also allow: \200 \200 \200 V(TB \200\223 TI)K1K2 Q = TB(t)dt Continuous measurement of cardiac output Temporary cardiac pacing Continuous monitoring of mixed venous oxygen satura- tion to monitor adequacy of global oxygen delivery. Where: = cardiac output Q = volume of injectate V TB = temperature of blood TI = temperatur e of injectate K1K2 = computational constants TB(t)dt = integral of blood temperature chang e Use of the pulmonary artery catheter Use of the pulmonary artery catheter allows the direct measurement of a variety of haemodynamic parameters: \200 \200 \200 \200 Right atrial pressure Pressures within the right ventricle Pulmonary artery pressures Pulmo nary artery wedge pressure (re \202 ecting the left atrial pressure \200\224see Chapter 7. 5) The cardiac output The change in blood temperature detected by the thermis- tor is plotted against time. The a rea under the curve is inversely proportional to the cardiac output. If the cardiac output is high, there is a large initial change in the blood temperature, which is short lived. If the cardiac output is poor, the initial change in blood temperature is smaller but the cha nge is more prolonged. Usual practice is to perform three measurements in quick succession and to take the mean value of the measured cardiac outputs; this compen- sates for the smal l variations in cardiac output which are seen due to ectopic beats or the respiratory cycle . From these data, various other haemodynamic parameters can be derived (see Table 7.5.1) The measurement of right heart pressures including the pulmonary artery occlusion pressure is described in Chapter 7.5 together with a table of normal values. 109 CHAPTER 7.5 Pulmonary artery catheter: indications and use called for an RCT to assess the effectiveness of the pulmo- nary artery catheter. Since the publication of the Connors study, two rand- omized controlled trials involving the use of the pulmonary artery catheter have been published. The FACTT trial from the ARDSnet group r andomly assigned patients with ARDS to management with either a pulmonary artery catheter o r a central venous catheter. Use of the pulmonary artery catheter did not improve survival or organ function and was associated with more complications than the use of the central ve nous catheter alone. The PAC-MAN trial was a multi-center British study, which randomly ass igned 1041 critically ill patients to management with or without a pul- monary artery cathe ter. Alternative cardiac output moni- tors could be used at the discretion of the treating units. There was found to be no clear evidence of bene \201 t or harm associated with the use of the pulmonary artery catheter. A modification of this technique can be used for the \200\230continuous \200\231 cardiac o utput measurement using a modi \201 ed pulmonary artery catheter. A heating coil is incorp orated into the pulmonary artery catheter to lie within the right atrium and right ventricl e. Every 30 \200\22360s this heats a bolus of blood; this temperature change is again monit ored by a thermistor at the distal end of the catheter, and the cardiac output is calculate d from the temperature/time curve. This technique allows a more rapid assessment of the eff ects of treatment on cardiac output than the intermittent ther- modilution technique. There are several potential sources of error when using the thermodilution method to measure car diac output: \200 \200 \200 Intracardiac shunts Too slow injection of cold injectate Impairment of thermistor function by impingement against blood vessel wall Tricuspid valve regurgitation Summary The pulmonary artery catheter can be used to measure and derive a variety of cardio vascular parameters. The clinical value of measuring and manipulating these param- eters ei ther by the pulmonary artery catheter or by newer cardiac output monitors such as the oesop hageal Doppler remains controversial. Even if the absolute readings of cardiac output are ren- dered inaccurate by the presence o f one of the above fac- tors the trends of the readings may still be useful in guiding trea tment. The thermodilution technique directly measures the car- diac output of the right sid e of the heart. At equilibrium it is assumed that the output of the right side of the heart is equal to that of the left side. Further reading Boyd O, Grounds MR, Bennett ED. A randomized clinical trial of the effect o f deliberate perioperative increase of oxygen delivery on mortality in high-risk surgical p atients. J Am Med Assoc 1993; 270: 2699 \200\223707. Pulmonary artery catheter: controversy Despite 30 years of worldwide experience with the pu l- monary artery catheter there is little evidence that it is bene \201 cial to patient ou tcomes and some suggestion that it may even be harmful. In 1996, Connors et al. published a prospective observational study of 5735 patients, 2184 of whom had had their treatment gui ded by the use of a pul- monary artery catheter. The investigators found that the use of th e pulmonary artery catheter was associated with higher mortality rates and increased use of resources, and Connors AF, Speroff T, Dawson NV, et al. The effectiveness of right heart catheterisation i n the initial care of critically ill patients. JAMA 1996; 276: 889 \200\22397. Swan HJ, Ganz W, Forrester J, et al. Catheterization of the heart in man with the use of a \202 ow-directed balloon-tipped catheter. N Engl J Med 1970; 283: 447 \200\22351. 110 P ANDERSON & A RHODES Pulmonary artery catheter: insertion Introduction The pulmonary artery catheter has a small (1.5ml) balloon at the tip, just pro ximal to the distal lumen (Fig. 7.6.1). When inserted into the right atrium this balloon is \201 lled with air and carried by the \202 ow of blood into the pulmo- nary vasculatur e, thus guiding the placement of the cathe- ter. The insertion technique can be divided int o two stages: (i) cannulation of a large vein with an introducer sheath utilizing the techn iques described in Chapter 7.3 and (ii) the passage of the catheter itself. Strict sterile technique should be maintained for the duration of the procedure. ous faults. The balloon should be in \202 ated to test for integ- rity. Each of the lumens of the catheter should be \202 ushed with saline to eliminate air bubbles. The markings on the catheter should be inspected to con \201 rm understanding of the distance marking s ystem used (Fig. 7.6.2) Distance Markings Balloon Heating Coil (Continuous Cardiac Output Monitoring) Balloon Inflation Port Proximal and Distal Injection Ports Monitor Connections Fig. 7.6.2 Pulmonary artery catheter, markings and features. The passage of the pulmonary artery catheter through the right side of the heart and into t he correct position is mon- itored by observing the characteristic real-time pressure trace s on a monitor. Thus the distal lumen of the catheter should be attached to a pressure tran sducer system which allows continuous monitoring of the pressure waveform. Knowledge of the normal pressures on the right side of the heart is invaluable when placing the pulmonary a rtery catheter (see Table 7.6.1) Fig. 7.6.1 The balloon at the tip of the pulmonary artery catheter. Cannulation of a large vein Selection of which vein to cannulate will be determined by oper ator familiarity, the presence of other indwelling vas- cular devices and patient factors s uch as the necessity for cervical immobilization. As a general guide: \200 Table 7.6.1 Normal right heart pressures (mm Hg) Systolic Diastolic Mean Right internal jugular vein allows the shortest and straightest route to the right side of the heart Left subclavian vein offers relatively unrestricted access to the heart Right sub clavian and left internal jugular veins require the catheter to navigate an acute angle to enter the heart Femoral veins can be used if the other sites are unavail- able, but passage of the catheter to the heart is techni- cally dif \201 cult. Right atrium 0 \200\2237 Right ventricle 15 \200\22325 0 \200\2238 Pulmonary artery 15 \200\22325 8 \200\22315 10 \200\22320 Wedge pressure 6 \200\22312 The pulmonary artery catheter is inserted through the introducer sheath and advanced until a right atrial pressure trace is identi \201 ed on the monitor. The distance to the right atrium varies depending on the insertion point of the introducer sheath. Typically the righ t atrial trace will be found at an insertion depth of 15 \200\22320cm from the internal jug ular veins, 10 \200\22315cm from the subclavian veins and 30 \200\223 40cm if the femoral r oute is used. At this point the balloon is in \202 ated with 1.0 \200\2231.5ml of air and the in \202 ation port locked. The distance marking on the catheter should be noted. The c atheter is now slowly advanced whilst monitoring the pressure trace. The typical right vent ricle pressure waveform should be seen after advancing the catheter approximately a further 10cm, and this should change to the pulmonary artery waveform between 10 and 20cm beyond t hat (Fig. 7.6.3). Most commercially available introducer sheaths are inserted by the modified Seldinger techn ique. Where appropriate, the insertion of the introducer sheath can be guided by ultrasound . It must be remembered that an introducer sheath is of large diameter (up to 8.5 French) a nd that the consequences of accidental arterial cannula- tion are likely to be more severe than would be the case with a standard central venous catheter. A sterile sleeve is af \201 xed to the introducer sheath through which the pulmonary artery catheter will be passe d. This will allow aseptic manipulation of the catheter once it is in situ. Passage of the pulmonary artery catheter Before starting the insertion procedure, the pulmo nary artery catheter should be visually inspected for any obvi- 111 CHAPTER 7.6 Pulmonary artery catheter: insertion There are certain circumstances in which the PAoP will not accurately re \202 ect the left ventricular end-diastolic pressure. These include: \200 Mitral valve stenosis \200 Mit ral valve incompetence \200 Pulmonary venous obstruction, e.g. from pulmonary \201 bros is Tip of the catheter lying outside of Wests \200\231 zone 3, i.e. the pulmonary capillary bed is compressed by the pressure within the alveoli at some point during the respiratory cycle. 40 mmHg RA RV PCW PA 20 0 Contraindications Absolute contraindications to placement of a pulmonary artery catheter in clude the presence of prosthetic tricus- pid or pulmonary valves, endocarditis of tricuspid or pul- monary valves and the presence of right heart thrombus. Caution is advised in pati ents with recent cardiac arrhyth- mias and those with coagulopathy. Fig. 7.6.3 Pressure trace during insertion of a pulmonary artery catheter. Note that the principle differences between the right ven- tricle and pulmonary artery wave forms are the higher diastolic pressures and the presence of a dicrotic notch in the pulmon ary artery waveform. Both of these observa- tions are due to the presence of elastic tissue in the walls of the pulmonary artery. If the expected pressure changes are not seen after advanc- ing the catheter the appropriate distance, it is possible that the catheter is coil ing within the chamber and there is a risk of knotting. The balloon should be de \202 ated and the catheter withdrawn slowly to the starting depth before in \202 ating the balloon and trying again. The balloon should always be de \202 ated before withdrawing the cathete r to pre- vent damage to surrounding structures and minimize the risk of knotting. Once in the pulmonary artery, the catheter should be advanced a further 10cm or so until the typica l wedge pressure trace is seen (Fig. 7.6.3). This is the pulmonary artery occlusion pressur e (PAoP). Once the PAoP has been measured (see below) the balloon should be de \202 ated; if the typical pulmonary arterial waveform does not reap- pear then the catheter should be slowly pulled back until it does. The balloon should never be left in \202 ated or the cat heter in the wedged position because this can lead to erosion of the artery wall and subseq uent artery rupture or to pulmonary infarction. When the insertion procedure is complete, a CXR should be performed to confirm the correct position of the catheter and to identify co mplications of central venous access. Complications The complications of pulmonary artery catheter place- ment can be divided int o those caused by the initial venepuncture which are common to all such procedures (see Cha pter 7.3), and those due to the passage or pres- ence of the pulmonary artery catheter itse lf. Complications due to the passage of the pulmonary artery catheter include: \200 \200 Cardiac arrhythmias. Right bundle branch block occurs in up to 5% of insertions. Patients w ith pre-existing left bundle branch block are at risk of complete heart block Cardiac perfo ration Damage to the tricuspid and pulmonary valves The catheter may knot if allowed to coi l in one of the heart chambers during insertion. \200 \200 Complications due to the presence of the pulmonary artery catheter include: \200 Pulmonary artery rupture. A large observational study suggested that the incidence of pulmo nary artery rup- ture was 0.031%. Pulmonary infarction may occur if the balloon is left in \202 ated for prolonged periods of time or if the catheter migrates distally and occludes a small branch artery. Infection. Venous air. \200 Pulmonary artery occlusion (wedge) pressure When the pulmonary artery catheter is in the we dged position there is an uninterrupted column of blood between the distal lumen of the cat heter and the left atrium. At the end of diastole, when the mitral valve is open, this colu mn of blood extends to the left ventricle, thus the pressure in the left ventricle at end d iastole is transmitted to the transducer system along an uninter- rupted column of \202 u id. The PAoP can therefore be used as a marker of left ventricular preload at the end of ex piration when arti \201 cial intrathoracic pressure manipulations can be discounted. Further reading Harvey S, Harrison DA, Singer M. Assessment of the clinical effec- tiveness of pulmonary artery catheters in managementof patients in intensive care (PAC-Man): a rand omized controlled trial. Lancet 2005; 366: 472 \200\2237. Kearney TJ, Shabot MM. Pulmonary artery rupture associated with the Swan \200\223Ganz catheter. Chest 1995; 108: 1349 \200\22352. Mermel LA, Maki DG. Infectious complications of Swan \200\223Ganz pulmonary artery catheter s. Pathogenesis, epidemiology, prevention, and management. Am J Respir Crit Care Med 1994; 149: 1020 \200\22336. 112 P QUINTON & A CRERAR-GILBERT Echocardiography the received f is referred to as the Doppler shift (fd) and is given by the Doppler equatio n; Echocardiography provides invaluable and prompt infor- mation about systolic and diastolic function, \201 lling status and the function of the intracardiac valves and the great ves sels. This has a signi \201 cant in \202 uence on decision making and management in the I CU. fd = 2.fo.v.cos /c Where: v is the velocity of blood \202 ow; is the angle between th e ultrasound beam and blood \202 ow; c is the ultrasound velocity in that medium; fo is t he transmitting frequency. The Doppler shift can therefore be used to measure the velocity of blood \202 ow. Physics of ultrasound \200 Sound is an example of a longitudinal wave oscillating back and forth through a transmittin g medium at a \201 xed velocity, resulting in zones of compression and rarefaction. Ultra sound includes that proportion of the sound spec- trum above 20kHz. Echo machines use frequ encies of 2 \200\22310MHz. The wavelength ( ) is inversely related to the frequency (f) by the sound velocity (c) so that c = f. Sound velocity in a given material is constant but varies in different materials. Ultrasound propagates poorly in air. c in blood is 1570m/s, soft tissue 1540m/s and air 330m/s. v = fd.c/2fo.cos v is most accurately measured when is zero and the ultrasound beam is in line with the blood \202 ow. Doppler calculations cannot be made when the ultrasound beam is perpendicular to the \202 ow of blood as the cosine of 90 is zero. As long as is <20 then the measurement error is <6%. Doppler calculated velocities are displayed g raphically on the echo machine with v on the x-axis and time on the y-axis. This process re quires a formidable amount of electronic processing. Color Doppler is a real-time colorized display of blood \202 ow superimposed on a 2D image. This also requires an enormous amou nt of computation and is used to iden- tify turbulent \202 ow within the heart that may o ccur, for example, with valvular pathology. Imaging by ultrasound \200 Ultrasound waves are generated by piezoelectric crys- tals in a transducer that vibrate whe n an alternating cur- rent is applied. Imaging is achieved by emitting ultrasound pulses fr om the transducer which are reflected by a boundary between two tissue structures and recei ved by the same transducer, generating a current which is processed to generate an image. W avelength is a determinant of image quality as the spatial resolution is limited to approxi mately one . Therefore, shorter s (obtained with higher fs as c is constant) produce be tter resolution. However, higher fs give reduced tissue penetration and thus a reduced imag e depth. The pulsed ultrasound signal is described by the pulse repetition frequency (PRF). This must be set so that there is suf \201 cient time for the pulsed wave to be trans- mi tted, re \202 ected and received in order to display all objects uniquely within a typical 10cm viewing window. There must only be a single pulse present between the transducer and the re \202 ected object at any point in time in order to avoid range ambiguity. With a c in tissue of 1540m/s this means that at a depth of 10cm the PRF must be no more than 7.7kHz . The strength of re \202 ection at an interface depends on the difference in acoustic im pedance (AI) between two media. AI is the product of density and the c within the medium. T here is a large AI mismatch between tissue and air, preventing imaging within the lung. Thi s also occurs between the transducer and tissue, necessitating a layer of gel between tissu e and transducer. Indications for echocardiography in the ICU \200 Haemodynamic instability: ventricular failure, hypovolae- mia, vasodilation, acute valvular dysfunction, cardiac tamponade, pulmonary embolism Aortic dissection Infective endocarditi s Source of systemic embolus Unexplained hypoxaemia \200 \200 \200 Indications for transthoracic echo (TTE) \200 Imaging of the ascending aorta which is not visualized by transoesophageal echo (TOE) due t o interposition of the left main bronchus. Imaging of the left ventricular (LV) apex which is frequently foreshortened by TOE. Accurate measurement of the pressure gradient across th e aortic valve which is frequently underestimated with TOE where alignment of the Doppler b eam can be suboptimal. When TOE is contraindicated. Indications for TOE \200 Conditions that prevent image acquisition with TTE such as in the presence of hyperin \202 ated lungs, surgical dressings, wounds, drains, prone position or excess fat tissue. Exami nation of posterior structures which are better visualized with TOE such as thoracic aorta, pulmonary veins, left atrium, mitral valve. Pathologies where TOE is more sensitive than T TE, e.g. left atrial thrombus, interatrial septal defects, cardiac tamponade. In conditions where diagnosis and treatment require more detailed information such as in suspected aorti c dissection, infective endocarditis, complex mitral valve pathology. Doppler \200 Doppler is used in echocardiography principally to look at aspects of blood \202 ow. The Doppler effect is the apparent change in f in waves that occurs when the source and observe r are in motion relative to each other, with the f increasing when the source and observer approach and decreasing when they move apart. This shift in f from the transmitted to 113 CHAPTER 7.7 Echocardiography CFM \200 Contraindications to TOE To assess the size of the regurgitant jet. For mitral regur- gitation (MR) a jet area >50% of the left atrial area is severe and for aortic regurgitation (AR) a jet width >40% of the LV out \202 ow tract. Note that this method tends to underestimate the severity of eccent ric (wall hugging) jets of MR. Absolute Relative Peforated viscus Atlantoaxial joint disease Oesophageal stricture Prior chest irradiation Oesophageal tumors Hiatus hernia Active upper GI bleeding Doppler \200 Oesophageal diverticula To assess systolic \202 ow reversal in the pulmonary veins (MR) or the descending thoraci c aorta (AR). Oesophageal scleroderma Recent upper GI surgery Systemic embolization \200 TOE is the most sensitive and speci \201 c technique for determining the source and potent ial mechanism of sys- temic embolization for patients with cerebral ischaemic events or per ipheral infarction. TOE can identify cardiac sources of embolism including atrial and ventr icular thrombi, vegetations, tumors, atrial septal defects or aneurysms, and atheromatous d isease of the aorta. In critically ill patients with AF, TOE is necessary to exclude the pr esence of thrombus before cardioversion when a long period of anticoagulation is not possib le. Indications in the ICU Pulmonary embolism (PE) \200 Echo can provide bedside diagnosis in the unstable ICU patient with massive PE when transpo rtation outside the ICU for angiography or CT may be unsafe. TOE has a sensitivity of 80 \200\22392% and a speci \201 city of almost 100%. Echocardiographic features of massive PE are; (i) Acute cor pulmonale; speci \201 cally mid-cavity hypoki- nesia with preserved fu nction at the apex in con- trast to RV dysfunction due to other causes in which wall motion is abnormal in all regions. Infective endocarditis (IE) \200 The major criteria for the diagnosis of IE are persistent bacteraemia with typical organism s with echocardio- graphic evidence of endocardial involvement. Echocardiographic features of IE are: (i) an oscillating intracardiac mass which may be on a valve and/or supporting s tructure, or in the path of a regurgitant jet or iatrogenic device (ii) Central emboli in the proximal pulmonary arteries; particularly the main and the right pulmonary artery (detection of left-sided emboli is limited by the poor propagation of ult rasound through air in the left bronchus). Valvular dysfunction Echo can be used to assess valvular lesions using 2D imag- ing, Dopple r and color \202 ow mapping (CFM).