Practical critical care techniques (Proceedings)

August 1, 2011

Steven L. Marks, BVSc, MS, MRCVS, DACVIM

Article

Emergency and critical care medicine is one of the fastest growing fields within veterinary medicine. The standards and quality of care continue to rise and the pet owning community is expecting state of the art care for their pets. This driving force has led to 24 hour care centers and emergency care centers providing excellent patient care all over the USA and Canada. Many of these facilities are performing advanced diagnostic and therapeutic techniques and not simply acting as triage and stabilization units.

Until recently, many procedures that should and could be performed on critically ill patients were not included in the core curriculum at most veterinary schools. With this in mind, the following presentation will review some basic procedures that may aid in management of the critically ill patient.

Nasal oxygen supplementation

Nasal oxygen supplementation is a safe and effective technique for providing oxygen supplementation for the critically ill patient. There are numerous clinical indications for oxygen therapy and variable techniques to provide oxygen support. If there is doubt whether a patient requires oxygen, a therapeutic trial is suggested. The advantages of nasal oxygen supplementation include; ease of administration, ease of patient monitoring, non-invasive technique and no special equipment requirements. The disadvantages of this technique include; lack of patient tolerance, epistaxis, aerophagia and the inability to know the exact fraction of inspired oxygen.

The technique is quite simple and requires minimal equipment. Any type of flexible tube sizes 3.5-8.0 F can be used. Urinary catheters and pediatric feeding tubes work well. The nasal mucosa should be desensitized with topical anesthetic (lidocaine or proparacaine), which should be allowed to take effect over several minutes. The anatomic landmarks utilized are the external naris and the vertical ramus of the mandible. The tube is passed into the ventral nasal meatus to the vertical mandibular ramus. The tube can be attached via cyanoacrylate (super glue) and or sutures to the external naris and the muzzle over the frontal sinus. An E-collar may be used for patients that will not tolerate this technique to prevent dislodgement. If used for extended periods of time, the oxygen should be humidified.

Introsseous catheter

The use of an intraosseous or intramedullary catheter is valuable in the critically ill animal when venous access is not available. Fluid therapy as well as emergency drugs can be administered via this route. There are several anatomical sites that can be utilized. These sites include the greater tubercle of the humerus , the trochanteric fossa of the femur, as well as the medial aspect of the proximal tibia. Purpose made intraosseous catheters are available or any standard bone marrow needle can be used. In young animals hypodermic or styletted spinal needles may be used. In most cases these catheters can be placed with light sedation and infiltration with local anesthesia. The area where the catheter is to be placed is shaved and aseptically prepared. The region should be infiltrated with lidocaine making sure to infiltrate the periosteum. A small stab incision is made in the skin with a scalpel and the bone marrow needle is driven into the bone using a screw like motion. The size of the needle can vary depending on the size of the patient. Usually 16-18 gauge needles work best. To avoid a cortical bone plug it is important to keep the stylet in place if using a styletted needle. Once placed, aspiration can be performed to check placement and saline can be infused. This area can be covered with 4" x 4" gauze with antiseptic or antibiotic ointment and bandaged.

Recently a new technique has been introduced for rapid introsseous catheter placement. The EZ-IO® infusion system uses a slow speed, hand held, battery operated drill that places a purpose made bone marrow catheter.

Rapid venous cutdown

An emergency venous cutdown is performed in order to provide emergency vascular access. This technique is quite simple and requires minimal surgical skill. The patient is sedated (when necessary) and placed in lateral recumbency. The lateral saphenous vein is the vein of choice in the dog and medial in cats. The vessel should be visualized prior to starting. The area is shaved and aspeptically prepared. A skin incision is made by using a #11 with the cutting edge up. It is important to try and visualize the path of the vessel in order not to transect the vessel. The incision should not be made directly over the vessel, but off to the side.

The skin incision should expose a length of the vessel. Using blunt/ sharp dissection with curved mosquito forceps the vessel should be cleared of perivascular fascia until the mosquito forceps can be placed under the isolated vessel.

Once the vessel is isolated, a venotomy is performed using a #11 scalpel blade with the cutting edge up. A catheter introducer or "vein pick" is used to open the venotomy site and slide a 14-16 gauge angiocatheter into the vessel lumen. Prior to placing the catheter into the vessel, the stylet is retracted into the lumen of the catheter so the vessel will not be damaged. The mosquito forceps can be retracted in order to straighten the vessel as the catheter is advanced into the vessel. Catheter placement should be checked by flushing with saline. The skin margins are then opposed and a bandage applied to wrap the catheter. This catheter can be utilized for emergency drugs or rapid fluid administration.

Thoracocentesis

Thoracocentesis can be easily performed in most dogs and cats. This technique is used for the emergency removal of fluid or air from the pleural space but can also be used as a diagnostic tool. Different techniques can be utilized including using a catheter, hypodermic needle or butterfly catheter.

It is easiest to use a needle or catheter, which is attached to a fluid extension set, a three-way stopcock and syringe. By using an extension set between the needle and syringe, movement is not reflected onto the needle avoiding damage to the visceral pleura.

At North Carolina State University thoracocentesis is divided into two basic techniques, diagnostic thoracocentesis and therapeutic thoracocentesis.

Diagnostic thoracocentesis is performed by using a 3 cc syringe and a 20-22 gauge hypodermic needle.

This procedure can generally be done without sedation in most animals. The animal can be in sternal recumbency or standing. An area is shaved and aseptically prepared on the thorax. The needle is introduced into the skin and negative pressure is applied. The needle is then slowly introduced through the intercostal muscles of intercostal space 7-8 on the cranial rib margin, remembering that the intercostal vessels are located on the caudal edge of the rib. When a pneumothorax is suspected, the needle should be introduced in the dorsal ½ of the thorax. With pleural effusion the needle can be introduced in the ventral ½ of the thorax. When the needle enters the pleural space, there will be a distinct loss of negative pressure. At this point either air or fluid should enter the syringe. The patient should be closely monitored after thoracocentesis for signs of respiratory difficulty and tachypnea.

Therapeutic thoracocentesis is a more aggressive technique and follows the diagnostic procedure. This procedure requires the use of a 14-16 gauge 5.25 inch angiocatheter. Using aseptic technique, 3-4 additional side fenestrations are cut into the catheter using a #11 blade. The positioning and anatomic location are as for the diagnostic thoracocentesis. The entry site on the cranial rib margin of intercostal space 7-8 is infiltrated with local anesthetic and a stab incision is made into the skin with a #11 scalpel blade. A 3 cc syringe is attached to the catheter and negative pressure is applied once the catheter is in the skin and subcutaneous tissue. The catheter is slowly advanced until negative pressure is lost. This indicates entry into the pleural space. At this point the entire catheter is advanced approximately 1/8 inch further into the pleural space. Now while holding the stylet hub still, the catheter is advanced enough to cover the stylet trocar. Once this had been performed the angle of the catheter is changed and the catheter is fully advanced off the stylet and an extension and aspiration set is attached.

The advantage of this technique is rapid and safe removal of fluid or air from the pleural space and this catheter can remain as a temporary chest drain.

Chest drain

The chest drain or chest tube can be easily placed in animals with pleural space disease that has been refractory to repeated thoracocentesis. In most cases other than moribund patients, sedation, general anesthesia and or local anesthesia are required. There are several different tube types that can be placed. The preferred chest drain is a styletted or trocar chest tube, the prototype being produced by Argyle®. The advantage of using this tube type is that the tube can be placed easily and will not kink due to the stylet and trocar that comes with the tube. The disadvantage is that these tubes can be traumatic and expensive. Other types of tubes that can be used include plain feeding tubes. Sizes vary from 16 F to 24 F depending on the size of the intercostal space. These tubes require placement with a large pair of forceps such as Carmalt forceps. The advantage of the feeding tube is that they are less expensive. The disadvantage is they may kink when advanced into the thorax.

The tube should be placed on the side of thorax which is most affected. Bilateral chest drains may be required in some cases. The hemithorax is clipped and aseptically prepared. An assistant should pull the animals skin in a cranial direction. A spot is chosen between intercostal spaces 7-10 and mid-thorax. Lidocaine should be infiltrated intradermally and extending into the intercostal muscle and pleura. A small incision is made in the skin extending into the muscle. Care should be used to avoid the intercostal vessels running along the caudal edge of the ribs. The chest drain is placed by pointing the trocar or Carmalt forceps towards the opposite elbow and firmly introducing the tube into the thorax. The tube should be pre-measured to know how much tube to advance. Once the tube is advanced, the assistant can release the skin and the tube is automatically carried approximately 2 intercostal spaces caudally from the entry site. This avoids the need to tunnel the tube subcutaneously. A Chinese finger trap tie is used along with a butterfly to secure the tube. The tube must be clamped and then included in a body wrap.

Abdominocentesis

This technique is used to remove fluid from the abdomen for diagnostic or therapeutic purposes. Fluid analysis and cytology can be helpful in assessing the etiology of an abdominal effusion and in cases of significant effusion may decrease respiratory distress due to pressure on the diaphragm. The procedure is very straight forward and can be performed in the conscious animal. The animal can be standing or in lateral recumbency. The ventral abdomen should be shaved and aseptically prepared. The umbilicus is the major landmark and the right quadrant is used in order to avoid the spleen. Needles or catheters ranging in size from 14-21 gauge can be used. It is common to introduce the needle without a syringe initially and then collect the sample via gravity or attach a syringe. Gentle spinning of the needle may assist fluid collection. Over the needle catheters can also be used in this situation. With larger gauge catheters, extra fenestrations can be cut to assist in fluid removal. Fluid analysis and cytology can be performed to help determine the etiology of the effusion.

Diagnostic peritoneal lavage

This is a modification of abdominocentesis. When unable to obtain a positive abdominal tap, fluid can be introduced into the abdomen. It is generally sufficient to use 10 ml/kg body weight of warm saline. This fluid can be introduced into the abdomen via a needle or catheter. The animal is then gently agitated, and fluid is then removed. This is a very sensitive technique for evaluating the abdominal cavity. Fluid analysis and cytology may be helpful in assessing the fluid.

Central venous pressure

This is an easy procedure that can be performed on all critically ill patients. The basic requirement is that a long central catheter be placed in the jugular vein. This technique allows you to estimate right atrial filling pressures and intravascular volume. The catheter is attached to an extension set, which goes to a 3-way stopcock. A fluid bag with a fluid administration set is attached to the other side of the stopcock and a manometer is placed in the upright port of the stopcock. Initially the stopcock is positioned off to the manometer and fluid is flushed through the jugular catheter. Then the stopcock is positioned off to the patient and the manometer is allowed to fill. Lastly the stopcock is positioned in the off position to the fluids and a continuous fluid column exists between the manometer and the jugular vein. The 0 of the manometer is set at the level of the right atrium with the animal in lateral or sternal recumbency. Normal values are between 0-5 cm of water. Relative changes may be more important that absolute values. Perhaps the best use of this technique is to monitor CVP in response to a fluid challenge.