Critical Care Obstetrics part 17 pot

Ventilator Management in Critical Illness 149 82 Slutsky AS , Tremblay LN . Multiple system organ failure. Is mechani- cal ventilation a contributing factor? Am J Respir Crit Care Med 1998 ; 157 : 1721 – 1725 . 83 Kolobow T . Acute respiratory failure. On how to injure healthy lungs (and prevent sick lungs from recovering) . ASAIO Trans 1988 ; 34 : 31 – 34 . 84 Martin GS , Bernard GR . Acute respiratory distress syndrome: innovative therapies . Semin Respir Crit Care Med. 2001 ; 2 : 293 – 306 . 85 Frutos - Vivar F , Esteban A , Apezteguia C et al. Outcome of mechani- cally ventilated patients who require a tracheostomy . Crit Care Med 2005 ; 33 ( 2 ): 290 – 298 . 86 Stewart TE , Meade MO , Cook DJ et al. Evaluation of a ventilation strategy to prevent barotraumas in patients at high risk for acute respiratory distress syndrome . N Engl J Med 1998 ; 338 : 355 – 361 . 87 Kuiper JW , Groeneveld ABJ , Slutsky AS et al. Mechanical ventilation and acute renal failure . Crit Care Med 2005 ; 33 ( 6 ): 1408 – 1415 . 88 Cheng IW , Eisner MD , Thompson BT et al. Acute effects of tidal volume strategy on hemodynamics, fl uid balance, and sedation in acute lung injury . Crit Care Med 2005 ; 33 ( 1 ): 63 – 70 . 89 Caldwell - Kenkel JC , Currin RT , Coote A et al. Reperfusion injury to endothelial cells after cold storage of rat livers: protection by mildly acidic pH and lack of protection by antioxidants . Transpl Int 1995 ; 8 : 77 – 85 . 90 Kregenow DA , Rubenfeld GD , Hudson LD et al. Hypercapnic aci- dosis and mortality in acute lung injury . Crit Care Med 2006 ; 34 ( 1 ): 1 – 7 . 91 Varughese M , Patole S , Shama A et al. Permissive hypercapnia in neonates: The case of the good, the bad, and the ugly . Pediatr Pulmonol 2002 ; 33 : 56 – 64 . 92 Pastores SM . Critical illness polyneuropathy and myopathy in acute respiratory distress syndrome: More common than we realize! 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Dildy. © 2010 Blackwell Publishing Ltd. 10 Vascular Access Gayle Olson 1 & Aristides P. Koutrouvelis 2 1 Department of Obstetrics and Gynecology, Division of Maternal - Fetal Medicine, University of Texas Medical Branch, Galveston, TX, USA 2 Department of Anesthesiology, University of Texas Medical Branch, Galveston, TX, USA Introduction Placement and maintenance of vascular access can be an impor- tant adjunct in the care of the critically ill obstetric patient. Arterial and venous access affords the clinician several advantages (Table 10.1 ). Long - term central intravenous (IV) access may also be indicated for gravidas with coexisting disease such as those illustrated in Table 10.2 , for the administration of parenteral nutrition, drugs, or antibiotics [1 – 4] . Establishing central venous and arterial access are acquired skills that require knowledge of catheter types, access routes, insertion techniques and maintenance. Catheter t ype Choosing the venous catheter type and the site for insertion are infl uenced by indication (Table 10.2 ), duration of use, urgency of administration, and the composition of infusate (i.e., osmolar- ity, tonicity, crystalloid, colloid). Catheters with shorter lengths and larger diameters allow for more rapid fl ow rates. For example, coupling of tube diameter (0.71 mm or 22 gauge vs 1.65 mm or 16 gauge) results in almost a quadrupling of the fl ow rate (25 mL/ min vs 96 mL/min) [5] . Multilumen catheters are routinely used for central venous cannulation (Figure 10.1 ). The more com- monly used triple - lumen catheter has an outside diameter of 2.3 mm (6.9 French) and provides three channels (three 18 - gauge, two 18 - gauge plus one 16 - gauge). The opening of each channel is separated from the other by 1 cm or more in order to reduce mixing of infusates. Intravenous catheters are considered to be short - or long - term transcutaneous, or implantable subcutaneously (Table 10.3 ) as well as peripheral or central. A peripheral location is distal to a central vein and contains valves. In contrast, a centrally located catheter contains no valves and is considered to be at the level of the axillary or common femoral vein, and all other veins oriented toward the heart from this level. The use of the terminology “ peripheral ” and “ central ” is also based on the peripheral or central location of insertion and the location of the catheter tip. Central vein cannulation is required to accommodate the large - bore catheters necessary for high - volume administration rates. When administering highly osmolar, sclerotic, or thrombotic IV fl uids, most clinicians agree that the catheter tip should be placed near the heart in the superior or inferior vena cava, although optimal placement has not been established in prospective human studies [6] . Short - term (less than 2 weeks) transcutaneous catheters are constructed of polyethylene, polyurethane, polycarbonate, vinyl chloride, or silicone and are available in multiple lengths, diam- eters, and lumen numbers. Short - term transcutaneous catheters are suitable for most obstetric patients in the “ diffi cult access ” group (i.e. history of IV drug abuse, IV chemotherapy, hypovo- lemia) and for others with rapidly resolvable clinical conditions. Because of the intended short duration of use, sites on the lower extremities, such as pedal, saphenous, and femoral veins, might be selected; however, decreased mobility and increased risk of catheter dislodgement are among the disadvantages of lower - extremity access locations. Long - term (weeks to months) transcutaneous catheters are usually constructed of more fl exible and less thrombogenic deriv- atives of silicone, and are passed through a subcutaneous tunnel between the points of venous insertion and exit from the skin [7,8] . Frequently, these catheters incorporate a Dacron cuff just proximal to the skin exit site. Catheter tunneling and the Dacron cuff promote tissue ingrowth and fi xation and limit the spread of skin exit - site colonization or infection. Long - term catheters may incorporate a Groshong valve tip [9,10] . Such catheters are blind - ended, but incorporate a side slit near the catheter tip. Positive pressure exerted through the catheter blows the slit walls open outwardly for fl uid or medication administration, while negative pressure draws the slit walls inward for blood sampling. At rest, Vascular Access 153 the catheter is closed, theoretically obviating the need for hepa- rinization between periods of catheter use. Venous sites com- monly used for long - term catheter use include the subclavian, external and internal jugular, basilic, and greater saphenous veins. When the femoral, greater saphenous, or basilic veins are used, the catheter is tunneled to allow for port placement onto the lower chest, abdominal wall, thigh or forearm [11] . Peripherally inserted central venous catheters (PICCs), intro- duced in 1975 [12] , are increasingly popular due to the ease of insertion compared with traditionally placed surgical catheters (e.g. Hickman ports, central venous ports) with potentially fewer complications [13] . Totally implantable venous access systems (TIVAs), generi- cally known as portacath, utilize catheters attached to reservoirs placed into subcutaneous pockets. These systems are indicated for very long - term use (months to years), typically in patients requiring intermittent medications. During catheter use, the res- ervoir is accessed with the use of a special Huber - point needle that uses a non - coring tip. Though surgical insertion is required for implantable catheters, the early and late complications asso- ciated with venous access are reduced with implantable catheters [14] . Ideally, reservoirs for implantable catheters should be placed in a secure, fl at, non - mobile area, preferably overlying a rib. Arterial catheters should be used for specifi c purposes and for short time intervals. Arteries that are accessible to palpation and that can usually be cannulated include (in order of preference) the radial, dorsalis pedis, femoral, axillary, and brachial. In general, for an artery to be suitable for continuous monitoring of intraarterial pressures: (i) the diameter should be large enough to accommodate the catheter without occluding the lumen; (ii) Table 10.1 Advantages of vascular access in the critically ill obstetric patient. Vascular access site Advantages Artery Continued access for: blood pressure monitoring frequent arterial sampling Central venous Rapid fl uid and blood administration Hemodynamic monitoring Table 10.2 Indications for prolonged venous access. Parenteral nutrition and drug therapy Hyperemesis gravidarum Infl ammatory bowel disease Gastroparesis Pancreatitis Cystic fi brosis Short bowel syndrome Heparin (heart valves, deep vein thrombosis) Antibiotics (bacterial endocarditis, osteomyelitis) Chemotherapeutic agents for malignancy Magnesium sulfate Lack of peripheral access Previous intravenous drug abuse Previous prolonged chemotherapy Hemodialysis Figure 10.1 Multilumen catheter insertion set - up. From left to right: small fi nder needle, larger needle, guidewire, scalpel, dilator, triple lumen catheter, anchor and suture. Chapter 10 154 well on dirty skin [20,21] . The most popular antiseptic agents are chlorhexidine gluconate and the povidone - iodine preparation betadine. Betadine is a water - soluble complex of iodine with a carrier molecule. Iodine is slowly released from the carrier mol- ecule, thus reducing any irritating effects. Due to this slow release, the preparation should be left in contact with the skin for at least 2 minutes [20 – 22] . In one study, a 2% aqueous solution of cho- rhexidine gluconate demonstrated superior antiseptic properties compared to 10% providone - iodine and 70% alcohol [16] . However, different concentrations of chorhexidine gluconate may not have the same effi cacy. Shaving at catheter insertion sites is not recommended as it abrades the skin and promotes bacterial colonization. If hair removal is necessary, it should be clipped. After the catheter has been inserted and secured, a dressing should be placed over the site. Gauze or transparent dressings may be used as both approaches have similar rates of catheter - related infection. Catheterization t echniques – g eneral Three catheterization techniques are available to obtain vascular access: direct, modifi ed and classic Seldinger techniques. The direct approach involves palpation and direct needle puncture, usually with the advancement of a Tefl on catheter over the needle and into the vessel. The Seldinger [23] technique involves the use of a guidewire. This approach is used to replace the needle during percutaneous arteriography. Once the vessel has been punctured and the return of blood fl ow (pulsatile in cases of arterial punc- ture) is achieved, needle advancement ceases and a fi ne, fl exible there should be adequate collateral circulation; (iii) the site should be such that catheter care can be facilitated; and (iv) the site should not be prone to contamination. Preparing for c atheter i nsertion Before cannulation of any vessel, it is necessary to assure patency of the vessel. Contraindications to vessel cannulation include infection or infl ammation at the site, arterial – venous or aneurys- mal malformations, and arterial graft. Coagulopathy is a relative contraindication to cannulation. In the presence of coagulopathy, the use of Doppler to identify the location of vessels reduces complications. Catheter insertion has been demonstrated in 242 patients with corrected coagulopathy and 88 with uncorrected coagulopathy. In these cases, most bleeding after cannulation was controlled with a suture at the catheter insertion site, and the only variable signifi cantly associated with a bleeding complication was a platelet count < 50 × 1 0 9 /L (P = 0.02) [15] . In addition, local pressure and use of topical thrombin spray may be used to control peripheral but not central bleeding. Skin p reparation Cutaneous antisepsis is paramount. This includes but is not limited to handwashing, education of personnel, and the use of sterile technique to include large sterile drape, gown and gloves [16 – 19] . Antiseptic agents that reduce skin microfl ora for skin preparation include alcohol, iodine, chlorhexidine gluconate, and hexachlorophene. Alcohol has a broad spectrum of antibacterial activity but has no detergent action, and therefore may not work Table 10.3 Central venous catheter types. Type Short term Long term Implantable Location Transcutaneous Transcutaneous Subcutaneous Duration Less than 2 weeks 4 weeks or longer Months to years Venous site Peripheral Pedal Saphenous Femoral Central Subclavian External jugular Internal jugular Cephalic Facial Saphenous Femoral Same as central long term. Huber point needle required for access to reservoir Material Polyethylene, polyurethane, vinyl chloride, silicone Silicone Cuff No cuff Dacron Lumen Varies Single/double Indication Diffi cult access Chronic illness Chronic illness Risks/benefi ts Dislodgement of catheter Decreased patient mobility Increased patient mobility Tip Open Groshong valve Vascular Access 155 wire is inserted through the needle and into the lumen of the vessel. The sharp needle is then removed and a polyurethane - type catheter is threaded over the wire and into the vessel. Commercially produced catheters that incorporate an integral guidewire and employ the modifi ed Seldinger technique are also available. Beards and associates [24] compared these three insertion tech- niques in 69 critically ill patients. The direct puncture technique was associated with the highest failure rate, followed by the modi- fi ed and classic Seldinger techniques, respectively. The direct puncture technique also took signifi cantly longer, used more catheters, and required more punctures per successful insertion than did the modifi ed or classic Seldinger techniques. These authors also observed that polyurethane catheters were signifi - cantly less likely to block and require reinsertion than were the Te fl on catheters. As a result, they strongly endorsed use of the classic Seldinger technique and polyurethane catheters. During catheterization, proper positioning of the patient is important. The patient should be in the Trendelenburg position and rolled slightly to the left in the later stages of pregnancy when the inferior vena cava is susceptible to compression by the enlarged uterus. If the patient is intolerant of the Trendelenburg position, the legs can be raised. Local anesthetic is infi ltrated into the site for needle insertion, incisions or dissection for subcutane- ous pockets. After venous puncture, the syringe is removed care- fully, while the operator covers the needle hub to prevent excessive bleeding and entry of air. Covering the needle hub is especially important with central venous punctures. With the Seldinger technique a guidewire is placed through the needle, and the needle is withdrawn. Next, a stiff dilator is generally threaded over the wire and passed one or more times in order to dilate the tract to the vein, after which a dilator – catheter assembly is threaded over the wire into correct position, and the wire and dilator are removed. Correct placement is supported by confi rm- ing free aspiration of blood from the catheter and free fl ow (by gravity alone) of an appropriate crystalloid solution through the catheter. Long - term transcutaneous catheters are generally placed using a peel - away sheath modifi cation of the Seldinger technique. After dilation of the tract, a dilator – sheath assembly is advanced over the wire into the chosen vein, and the wire and dilator are removed. A Silastic catheter is then threaded through the peel - away sheath. Upon proper positioning, the handles on the peel - away sheath are rotated perpendicular to its long axis until the sheath cracks. Pulling the sheath handles apart, the sheath is then simultaneously peeled in half along its long axis and removed while the catheter is carefully held in place. In cases of arterial cannulation, successful line placement can be confi rmed by the appearance of pulsatile blood fl ow or, if any doubt exists, by blood gas analysis. Vessels suitable for cannula- tion include radial, femoral, brachial, axillary, dorsal pedis and superfi cial temporal arteries. For blood pressure monitoring, the catheter is connected to a transducer with a three - way stopcock and high - pressure tubing which is connected to a pressure bag containing normal saline and heparin (1500 U/500 mL). The high - pressure tubing is necessary to prevent damping of blood pressure readings. The heparinized saline is administered through the pressurized bag at a rate of approximately 2 – 5 mL/h to prevent the catheter from clotting off. It is critically important to purge all pressure lines and stopcocks before connecting the arterial line to prevent arterial air embolism. All set - ups should also have a purge or fl ush device that can be used to clear any blood that may back up into the pressure tubing as well as to clear the catheter itself and the stopcock after blood sampling. Complications of arterial cannulation include vessel spasm, infection, thrombosis, bleeding, and hematoma. Special t echniques for c atheter i nsertion Several authors have described utilizing real - time ultrasound to facilitate the location of a vein and to lessen the incidence of mechanical complications related to central catheter insertion [25,26] . The use of ultrasound during the central venous access placement, particularly in diffi cult patients, is becoming more commonplace. The placement of the transducer in the area of interest, whether internal jugular (Figure 10.2 ) or femoral, facili- tates identifi cation of the venous vessel. The dramatic enlarge- ment of the superior vena cava during a Valsalva maneuver readily identifi es the enlarged and yet compressible venous vessel as compared to the non - compressible, pulsating artery. Schummer et al. conducted a study demonstrating a mechani- cal complication rate of 12% during catheter insertion using the Seldinger technique [27] . The complications encountered by this experienced group included inadvertent arterial puncture, pneu- mothorax, malposition, and failed cannulation. Ultrasound has the potential to decrease this complication rate. Fluoroscopic guidance has also been reported to be of assistance with catheter placement. Finally, right arterial electrocardiography can be used to facilitate proper catheter tip placement [6] . Complications – g eneral A wide range of immediate and delayed complications can be associated with central venous and arterial catheters (Tables 10.4 & 10.5 ). Specifi c complications related to catheter use are dis- cussed individually within each subsection. Catheter m alposition Catheter malposition can be a complication of any vascular can- nulation. Optimal catheter tip location has not been established via prospective human studies but most practitioners believe the superior vena cava, proximal to the right atrium, to be the ideal location [6] . Catheter tips located in smaller, more proximal veins are more likely to be associated with venous thrombosis and stenosis, while catheter tips positioned in the heart may be associ- ated with cardiac arrhythmias, perforation, tamponade, valvular injury, or endocarditis. PICC catheter tip malpositioning from an Chapter 10 156 Carotid Artery Right I.J. Figure 10.2 Ultrasound image of the IJV. The IJV can be visualized beneath the sternocleidomastoid muscle and adjacent to the carotid artery. Table 10.4 Complications of central venous catheters. Immediate Delayed Insertion failure Venous thrombosis Malposition Pulmonary embolism Air embolism Superior vena caval syndrome Catheter embolism Venous stenosis Cardiac arrhythmia Arteriovenous fi stula Pneumothorax Arterial pseudoaneurysm Hemothorax Catheter thrombosis Hydrothorax/chylothorax Catheter dislodgement/breakage Tracheal/esophageal injury Catheter - related infection Femoral nerve injury Endocarditis Brachial plexus injury Cardiac perforation Phrenic nerve injury Cardiac tamponade Vagus nerve injury Suppurative thrombophlebitis Recurrent laryngeal nerve injury Clavicular osteomyelitis Stellate ganglion injury Table 10.5 Complications of arterial catheters. Hematoma Hemorrhage Catheter occlusion Catheter dislocation Infection Embolism Ischemic injury Thrombosis Pseudoaneurysm Arteriovenous fi stula antecubital approach is the most frequently seen with a rate of 21 – 55% [28] . Among the most devastating consequences of cath- eter malposition is cardiac tamponade. This uncommon yet potentially catastrophic complication must be considered after insertion of all central catheters. Postinsertion chest radiographs are universally recommended, with possibly the exception of the image - guided central venous catheter insertion [29 – 32] . These radiographic studies should demonstrate midline placement of the catheter tip in the center of the SVC, and not abutting the arterial or ventricular wall. Thrombosis, s tenosis and o cclusion Thrombosis of the great veins is frequently asymptomatic and therefore under - recognized and under - reported [33] . In SCV catheterization, the complication is clinically diagnosed with a frequency of less than 5%, but is diagnosed by contrast venogra- phy in 20 – 40% of patients [29] . Thrombosis appears to be related to several factors. The fi rst consideration is the relative diameters of the catheters and vessel. Generally, the smaller the diameter of the catheter relative to the vessel size, the lower the incidence of thrombosis. Additional factors include duration of use, catheter material, shape of catheter tip, number of cannulation attempts, low cardiac output, hypotension, use of vasopressors, peripheral vaso - occlusive processes, and Raynaud ’ s disease [24,34] . Catheter occlusion can result from the formation of a fi brin plug at the catheter tip. This is part of a fi brin sleeve that forms around essentially all IV catheters present for more than a week [29,35] . When withdrawing blood samples, the dead space in the system should be appreciated, and a suffi cient quantity of blood to account for this should be withdrawn and discarded before actual specimen collection. It also is very important to purge the Vascular Access 157 maintained in a 20 – 30 ° Trendelenburg position. This maintains the head in a “ down ” position, distending the IJV and minimizing air entrapment. A trianglular region created by two heads of the SCM and the clavicle is then identifi ed (Figure 10.3 ). The carotid artery is palpated medial to the IJV and medial and posterior to the SCM and is retracted medially. An 18 - gauge cannulating needle, attached to a syringe, is inserted at the apex of the triangle, bevel facing up, and at a 30 – 45 ° angle to the skin (Figure 10.4 ). The needle is advanced toward the ipsilateral nipple. If the vein is not encountered by a depth of 5 cm, the needle is withdrawn 4 cm and advanced again in a more lateral direction. When a vessel is entered a fl ash of blood is noted at the catheter hub. If the blood is pulsating, you have entered the carotid artery. In this situation, remove the needle and tamponade the area for 5 – 10 minutes. When the carotid artery has been punctured, no further attempts should be made on either side because puncture of both arteries can have serious consequences. system after specimen collection, lest the line clot off. Clots adherent to the catheter tip, or even the vessel lumen, can be dislodged during fl ushing. Flushing protocols, with and without heparin, have been devised to reduce catheter thrombosis [33,36] . The use of a fi brinolytic agent administered through the catheter has also been shown to be successful in reopening thrombosed catheters [37 – 41] . Additional treatment of catheter - related deep vein thrombosis may also involve catheter removal [42,43] . Embolism Air embolism is a rare but potentially fatal complication of central venous catheters with an estimated incidence of less than 1% but with a mortality rate as high as 50%. If the air embolus is of the magnitude of 50 mL or greater, the outcome is more likely to be fatal. Symptoms of an air embolus can include seizures, hemipa- resis, and focal neurologic signs. An air embolus may be reduced by aspirating through the central line or placing the patient in Trendelenburg and in the left lateral decubitus position in the hopes of containing the air in the right ventricle until other mea- sures can be enacted. In stable patients, treatment can be sup- portive and include administration of 100% oxygen. Rewiring central venous catheters can also be particularly hazardous. Attention to technique and position must also be employed during this seemingly innocuous procedure. Vesely [44] reviewed complications for 11 583 central venous catheter insertions. Air embolism only occurred in 15 cases, the majority of which had undetectable, mild, or moderate symp- toms that resolved with supplemental oxygen. Only one case in their series was fatal. Specifi c v enous a ccess s ites Internal j ugular v ein ( IJV ) The IJV is located under the sternocleidomastoid muscle (SCM), and, at its junction with the subclavian vein (SCV), helps form the brachiocephalic vein. Anatomic variation in the course of the IJV has been noted, and the relationship between the IJV and the carotid artery may be abnormal in 10% of the population [45] . Typically, when the head is turned away from the intended side of cannulation, the IJV forms a line from the pinna of the ear to the sternoclavicular joint and brings the IJV to a more anterior position relative to the carotid artery [8,46] . The IJV is a common route for central venous access. Its advantages include the ease by which this vessel can be compressed in the case of hemorrhage and the decreased risk of pneumothorax. The right IJV is pre- ferred because the thoracic duct is avoided as well as providing a more direct course to the right atrium [45] . The anatomic rela- tionship of the left IJV to the left brachiocephalic vein makes it diffi cult to negotiate vessel angles and increases the risk of steno- sis and thrombosis. Two insertion techniques, the median and posterior approaches are available for IJV cannulation. With the median approach the head is turned away from the cannulation site with the body Figure 10.3 Positioning for internal jugular vein cannulation. The head is turned away from the insertion site. A triangle is formed by the junction of the heads of the SCM at the apex, and their insertions at the clavicle. Figure 10.4 Anterior approach to internal jugular vein cannulation. The carotid artery is palpated and retracted medially while the needle is inserted at the tip of the triangle and advanced toward the ipsilateral nipple. Chapter 10 158 Neurologic complications are rare, but have been documented in association with IJV catheterization. The close anatomic rela- tionship between the lower brachial plexus and the IJV can con- tribute to the potential for nerve damage, and is more commonly associated with a traumatic cannulation attempt [50] . External j ugular v ein ( EJV ) The EJV is formed by the junction of the retromandibular and posterior auricular veins. It runs obliquely across the SCM along a line extending from the angle of the jaw to mid - clavicle. The EJV joins the SCV at an acute angle under the area of the clavicle [46] . The primary advantage of using the EJV for venous access is the decreased risk of pneumothorax. The disadvantages include diffi culty in advancing a catheter, and vein perforation due to the acute angle with the SCV. The patient is placed supine or in the Trendelenburg position and the head is turned away from the side of insertion. The vein can best be identifi ed by applying pressure just above the clavicle and allowing the vein to engorge. Unfortunately, even under the best of conditions, 15% of patients will not have an identifi able EJV [51] . Once identifi ed, the vein should be stabilized between the thumb and forefi nger at a level midway between the clavicle and jaw and the catheter inserted with the bevel up. The length of the catheter should not exceed 15 cm. Undue force at the time of catheter insertion can result in perforation of the EJV at the angle in which is enters the SCV. Manipulation of the shoulder may facilitate passage of the J - wire past the clavicle without asserting undue pressure [52] . In addition, upon meeting resis- tance at the EJV - SCV junction, the J - wire can be withdrawn approximately 0.5 cm proximal to the junction. The triple - lumen catheter may then be slowly advanced over the J - wire. The success of this maneuver may lie in the smaller diameter of the catheter tip [53,54] . Complications of EJV cannulation include thrombo- sis, superior vena cava perforation, and hydrothorax [47,55] . Subclavian v ein ( SCV ) The SCV is often used to gain central access. As a continuation of the axillary vein, the course of the SCV runs underneath the clavicle and along the outer surface of the anterior scalene muscle. At the level of the thoracic inlet, the SCV joins the IJV to form the brachiocephalic vein [8,46] . To cannulate the vein, the patient is placed in the supine position, maintaining a 15% Trendelenburg position, with the head facing toward the site of insertion and the arms pronated, slightly fl exed, and down at the sides. One helpful approach for catheter insertion is to place a rolled towel under the spine and shoulder. This type of positioning serves to widen the path between the fi rst rib and the clavicle. Next, the operator should visualize the path of the subclavian artery divided into medial, middle, and lateral thirds along the clavicular line (Figure 10.6 ). Using this method, the junction of the medial and middle segment approximates the lateral aspect of the SCM insertion on the clavicle. Using this point for needle insertion may decrease the risk for pneumothorax. The bevel should initially be pointing upward. The catheter tip is “ walked ” along the underside of the With the posterior approach, the body position is the same but the physician should plan an insertion site 1 cm superior to the point where the external jugular vein (EJV) crosses over the lateral edge of the SCM. In the posterior approach, the needle is then inserted at the 3 o ’ clock position, with the bevel up, and is advanced along the underbelly of the SCM and then aimed toward the SCM at its sternal insertion and the suprasternal notch (Figure 10.5 ). The IJV should be encountered 5 – 6 cm from the skin surface with this approach. If the advancing attempt does not produce a fl ash of blood in the hub of the needle, applying slow continuous negative pressure while withdrawing the needle potentiates identifi cation of venous blood, thus identifying the vein. However, the absence of pulsatile blood fl ow does not nec- essarily ensure venous access has been achieved. Ideally, a pres- sure wave should be transduced to confi rm a venous waveform [45,47] . In addition to the previously described approaches, tunneled central venous catheters have also been described using the IJV versus the SCV. The IJV approach was easier to perform with fewer complications [48] . Complications of IJV cannulation include hematoma, carotid artery puncture, nerve damage, air embolus, and cardiac tamponade. As previously noted, ultrasound guidance for vessel location is favored by many physicians. Investigations utilizing ultrasound guidance for access of the IJV provide the most compelling evi- dence in support of this approach. Karakitsos et al. [49] per- formed a prospective randomized trial of 900 subjects, evaluating cannulation of the IJV using ultrasound guidance versus standard landmark methods. After controlling for multiple factors, real - time ultrasound - guided catheter insertion of the IJV was signifi - cantly associated with reductions in carotid puncture hematoma, hemothorax, pneumothorax, catheter - related infection, access time from skin to vein and number of attempts when compared to standard landmark methods. Figure 10.5 Posterior approach to internal jugular vein cannulation. In the posterior approach the needle is advanced along the underbelly of the SCM aiming at the suprasternal notch. . Management in Critical Illness 149 82 Slutsky AS , Tremblay LN . Multiple system organ failure. Is mechani- cal ventilation a contributing factor? Am J Respir Crit Care Med 1998 ; 157 : 172 1 – 172 5. Crit Care Med 2005 ; 171 : 388 – 416 . 117 Shorr AF , Sherner JH , Jackson WL et al. Invasive approaches to the diagnosis of ventilator - associated pneumonia: A meta - analysis . Crit Care. postpartum minute ventilation and weaning . Am J Obstet Gynecol 1995 ; 172 : 326 (part 2). Abstract. 153 Murray MJ , Cowen J , DeBlock H , et al. Task Force of the American College of Critical