Evaluation of obstetrics admission to intensive care units (ICUs) may be one of the better ways to approach surveillance of critical illness in pregnancy.
Examination of the conditions leading to obstetric ICU admissions provides some insight into the nature of illnesses related to pregnancy.
Obstetrical hemorrhage and hypertensive disorders are responsible for primary admission to ICU following sepsis and cardiac and pulmonary disease (1).
The appropriate management of critically ill patients requires frequent observation of biophysical parameters.
This includes both invasive and noninvasive hemodynamic monitoring.
This chapter will discuss vascular access techniques for invasive hemodynamic monitoring and point-of-care ultrasound (POCUS) for the management of critically ill pregnant patients.
Arterial and central venous access affords several clinical advantages (Table 1.7.1).
Obtaining these accesses requires knowledge of vascular anatomy, type of catheter, and insertion techniques.
The most common sites for central venous accesses in ICU are internal jugular, subclavian, and femoral. The two most common sites of arterial catheterization are radial and femoral.
Sterile technique including handwashing, using large sterile drape, gown, and gloves is necessary.
Antiseptic agents including povidone-iodine or chlorhexidine gluconate should be applied to skin.
General Catheterization Techniques
Two catheterization techniques are available to obtain vascular access:
Direct technique: Palpation and direct needle puncture, usually with the advancement of a Teflon catheter over the needle into the vessel
Table 1.7.1 Advantages of Vascular Access in Critically Ill Pregnant Patients
Central venous access
Total parenteral nutrition access
Rapid fluid, certain medications (such as vasoactive medications), and blood administration
Lone option in cases in which standard peripheral access cannot be obtained
Continued hemodynamic monitoring Frequent arterial blood sampling
Seldinger technique (2): Using guidewire in this technique
Vessels punctured using a needle with or without syringe attached to the needle
The placement of needle is confirmed with returning of blood flow (pulsatile in cases of arterial puncture).
The advancement of needle ceases.
Flexible guidewire is inserted into the needle and into the lumen of the vessel and advance (there should be no resistance while advancing the wire).
The detail of the procedure will be discussed for each vascular access.
Evidence supporting real-time ultrasound guidance for vascular access facilitates location of the vessel (vein or artery), increases success, and decreases complication rate (3).
Most ultrasound machines have various transducers that can be selected depending on the clinical indications.
Linear transducers also known as “vascular” or “high-frequency” probes have a long, narrow rectangular probe face, generate a frequency range of 5 to 13 MHz (Figure 1.7.1).
This probe is used for obtaining imaging for superficial structures such as vascular structures and soft tissues.
Linear probes are used for procedural guidance owing to high axial resolution.
The internal jugular vein (IJV) is located under the sternocleidomastoid muscle (SCM).
The IJV lies lateral to carotid artery (CA) in most of the patients; however, the relationship between IJV and CA may be abnormal in 10% of the population.
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 CA.
The right IJV is preferred over the left IJV because it provides a more direct course into the right atrium.
The patient’s bed should be raised to a height that is comfortable for the operator.
The patient’s head should be rotated away from the site of planned central venous catheterization to allow for maximum exposure (Figure 1.7.2).
The bed can be placed in Trendelenburg position in 20 to 30 degrees to maintain the head in down position, distending the IJV and minimizing air entrapment.
The ultrasound system should be placed in a clear line of site for the operator to improve ergonomics.
Figure 1.7.1. Linear (vascular) transducer. (Reprinted from Bornemann P. Ultrasound for Primary Care. Wolters Kluwer; 2020.)
The ultrasound probe (linear probe with high frequency) should be placed on the skin with the probe indicator to the left.
Using the transducer, the operator follows IJV and CA along the path from the clavicle to the angle of the mandible to find the ideal location for cannulation (insertion site closer to the clavicle will be closer to the apex of the lung, whereas insertion site closer to the mandible will be closer to the bifurcation of the CA to the internal and external branches).
Once the IJV and CA are identified and differentiated, the ultrasound probe should be centered on the target IJV during visualization of the CA (see Pearls and Pitfalls).
Recommend probe indicator to be oriented to the provider’s left to synchronize the anatomic orientation of the patient and the ultrasound screen.
Manual compression, color flow, and pulsed-wave Doppler can be used to differentiate between venous and arterial structures.
The skin is prepped with an aseptic agent.
The planned site for IJV should be covered with a sterile drape.
Sterile gel and a sheath are placed over the transducer.
With covered transducer, the operator should reidentify the IJV and CA and the probe should be centered on the target IJV.
Using the nondominant hand, the operator stabilizes the transducer.
With dominant hand, local anesthetic medication (e.g., 1% lidocaine) is injected to create skin wheal and then advance under direct visualization of ultrasound to provide more local anesthesia.
The needle is inserted into the patient’s skin maintaining at 45 to 60 degree angle to the frontal plane (i.e., the angle between the needle and the skin) 1 cm away from the transducer indicator (Figure 1.7.3), maintaining constant negative pressure in syringe.
Once the needle is inserted into the skin, the operator may tilt or slide the probe toward the needle to attempt needle tip visualization during needle advancement (as the needle is advanced slowly deeper into the neck, the probe is tilted or slid toward the clavicle to visualize the needle tip as it enters the IJV).
If you bury the needle without blood, gradually withdraw; you may still get into the vein as you may have collapsed it on the way in.
When a vessel is penetrated, the provider should feel an easing of negative pressure applied on the syringe, and a flash of blood is noted at the catheter hub.
Figure 1.7.3. Needle position and relation to ultrasound transducer. (Modified from Cosby KS, Kendall JL. Practical Guide to Emergency Ultrasound. 2nd ed. Wolters Kluwer; 2013.)
Correct needle positioning is demonstrated by visualization of the needle in the middle of the vessel lumen.
The syringe is disconnected from the needle (if the blood is pulsating, the CA has entered. In this situation, remove the needle and tamponade the area for 5-10 minutes).
The guidewire can be passed through the needle and into the IJV.
Both a transverse and longitudinal ultrasound image of the target vein with the guidewire present should be obtained proximal to the puncture site (Figure 1.7.4).
After confirmation of guidewire in the vein, remove the needle while holding guidewire with the other hand.
Make a small nick with the number 11 blade where the wire enters the skin.
Advance dilator over the guidewire with twisting motion.
Remove dilator, holding guidewire and having some gauze 4 × 4 in your hand to apply pressure to a site that will now bleed after dilation.
Place catheter over guidewire; it should advance easily. Hold guidewire at skin entrance and feed it back through distal port of central line (brown cap). When the wire comes out, grab it at the end and finish advancing the catheter.
Remove guidewire and flush all ports.
Suture catheter in place via flange with holes.
The confirmation of the proper catheter placement is via chest x-ray (CXR). The catheter tip should be 2 cm above the junction of the superior vena cava (SVC) and right atrium.
The subclavian vein (SCV) is often used to gain central access.
Brachial vein becomes axillary vein as it passes the teres major muscle and courses inferoposteriorly to the clavicle, becoming SCV at the lateral border of the first rib.
SCV continues to the medial border of the anterior scalene muscle, joins the IJV to form brachiocephalic vein (also referred to as innominate vein), which joins its contralateral counterpart to form SVC.
Landmark-based SCV has long been used for emergency resuscitation when cervical spine abnormalities or airway emergencies preclude IJV access.
The most frequent contraindication is respiratory distress. Anticoagulation treatment presents a major concern at the SVC site because inadvertent subclavian arterial puncture cannot be extrinsically compressed.
As IJV or similar to IJV, ultrasound-guided SCV cannulation approach improves first-pass success and decreases complications (4).
The patient should be placed in a supine position with the arm in the most comfortable position for the procedure.
Maintain a 15 degree Trendelenburg position, with head to the opposite side of the insertion (if no cervical spine injury).
One helpful approach for catheter insertion is to place a rolled towel under the spine and shoulder, if no cervical spine injury, to widen the space between the clavicle and first rib.
The operator should visualize the path of SCV divided into medial, middle, and the lateral thirds along the clavicle line.
Using this method, the junction of medial and middle segments approximates the lateral aspect of SCM insertion on the clavicle.
The ultrasound system should be placed in a clear line of site for the operator to improve ergonomics.
The ultrasound probe (linear probe with high frequency) should be placed on the skin just below the clavicle at approximately its middle third. This will provide a transverse view of SCV and artery (Figure 1.7.5), also pleural line should be identified.
Manual compression, color flow, and pulsed-wave Doppler can be used to differentiate between venous and arterial structures (subclavian artery should be slightly lateral to SCV).
Ultrasound then should move laterally and follow SCV until overlap of vessels is minimized and the pleura is out of the field in order to minimize risk for pneumothorax.
Figure 1.7.5. Short axis of the subclavian vein and artery. SCA, subclavian artery; SCV, subclavian vein.
The needle should be inserted into the skin at a 45 to 60 degree angle to the plane (i.e., the angle between the needle and the skin), maintaining constant negative pressure in the syringe, the remainder of the procedure steps is similar to IJV (see above).
The common femoral vein forms in the femoral sheath, proximal to the joining of the superficial femoral vein, deep femoral vein, and saphenous vein.
Femoral nerve, artery, and vein traverse the femoral triangle by descending beneath the inguinal ligament from lateral to medial.
The femoral vein is 1 to 2 cm medial to the femoral artery.
The location of femoral vein can be estimated by imaging a line from the anterior superior iliac crest to the pubic tubercle and then dividing the line into equal thirds.
The femoral artery lies at the junction of the middle and most medial segment, and the femoral vein can be estimated 1 to 2 cm medial to this point.