Fig. 5.1
Color differenciation of the tubings
The circulatory parameters of the pump: Circulatory support is the essence of the ECMO, to ensure a correct support or replacement of the cardiac function for VA ECMO or to ensure an adequate gas exchange for VV ECMO.
The pump being nonocclusive, the flow rate must always be above 2 L/min. Under that flow rate, there is a risk of backflow, leading to an inefficient ECMO run.
The ECMO flow depends on a few parameters:
The preload: determined by volemia, venous tone, the position, and the size and length of the admission cannula.
The afterload: determined by vascular resistance, the position, size and length of the reinfusion cannula, and the length of the tubing between the pump and the oxygenator.
Cannulae sizes: 17–19 Fr for reinfusion cannuale, 21–23 Fr for admission cannulae, and 5 Fr for the reperfusion line for PVA ECMO.
The parameters are the rotations per minute (RPM) and the blood flow. The therapeutical goal set by the team is the blood flow. For the nurse, writing down these two parameters has no relevance. The correlation of the RPM and blood flow and its evolution through time will allow an effective management of the ECMO run. For example, at 2 pm, the RPM is set up at 4500 L/min for a blood flow at 4 L/min. At 5 pm, for a similar RPM, the blood flow went down to 2.5 L/min. It can be a sign of hypovolemia maybe due to blood loss or the patient may have moved and kinked partially part of the tubing.
The setting of the gas blender: The blender ensures gas exchanges through the oxygenator––oxygen supply is adjusted via the FiO2 and the CO2 removal via the gas flow. It is essential to write down at each round the gas blender settings. In addition to patient’s saturation, ventilator’s settings, and blood gases results, it enables a timely decision-making.
The alarms: They must be set regarding the therapeutic goal. The pump being nonocclusive, it is recommended to maintain the blood flow above 2 L/min to avoid any backflow.
It is also crucial to know on which mode your ECMO is working.
In a free mode, when an alarm is activated, the ECMO will keep working, but when the ECMO is on intervention mode, as soon as an alarm is set on, the ECMO stops working, and an immediate action must be set to resolve the problem. The choice of the mode depends on the human resources; if a nurse, ECMO specialist, or a perfusionist is constantly present at the patient’s bedside, the intervention mode is possible, but if a nurse is taking care of more than one ECMO patients and cannot intervene immediately when the pump stops, the free mode will be safer.
The emergency kit: It should be available at the bedside or in the unit, allowing an immediate response to any adverse events––clamps, emergency hand crank, emergency supplies (appropriate-sized connectors/shears/tubing/rapid access line, fluid, tie-gun and tie-straps/sterile gloves, preprimed pump, etc.)
5.1.2 The Pressure Monitoring
Monitoring pressures is not essential, but it is an additional tool to help the team detect a potential and/or immediate dysfunction of the ECMO. There are no exact target numbers to refer to. Pressures vary depending of the size of the cannulas, the ECMO flow, the patient volemia, etc.
Like explained sooner for circulatory parameters, it is not the number but the evolution of pressures through time that will help the team prevent dysfunctions. Again, it is crucial to write down at each ECMO rounds the pressure numbers in the patient’s chart.
Three pressures are commonly measured (Fig. 5.2).
Fig. 5.2
Pressure monitoring (Courtesy of Maquet®)
P vein or Venous Pressure
It is the prepump pressure. It measures the pressure in the admission cannula. So, it is a negative pressure. It should not excced 100 mmHg.
A quick and significant rise of P vein means the ECMO has difficulty to drain blood from the patient. It can be caused by a hypovolemia or by a kinked and/or occluded admission cannula.
P art or Arterial Pressure
It is the post-oxygenator pressure. It measures the pressure in the reinfusion cannula. It is a positive pressure that should not exceed 200–250 mmHg.
A quick and significant rise in P art may be caused by an increase of the patient’s preload or a sign of a kinked and/or occluded reinfusion cannula.
Δp
It is the pressure difference through the oxygenator. It changes during the ECMO run. The speed of the rise depends mostly on the flow and on a good management of coagulation. It is an indicator of the level of saturation of the membrane of the oxygenator.
Any significant rise of Δp (+20 mmHg/h) must be reported immediately to the medical team. It can be a sign of clotting inside the oxygenator. This could evolve towards a pump failure.
These pressures can be monitored by:
Adding pigtails to the circuit in the appropriate places and connecting them to a pressure monitoring system (similar to the ones used for arterial lines or CVP).
New ECMO consoles have added the pressure monitoring function to their controllers, without the need to add any connectors to the ECMO circuit.
A pressure number alone is not a significant element; it is a tool that can help the team manage and assess the patient’s ECMO run in addition to clinical exam, circuit control, and patient’s blood panel. For example, a rise of 60 mmHg in the Δp in an hour could be a sign of clotting in the oxygenator, but this number alone cannot justify the replacement of the oxygenator. It has to be completed by blood gases to assess the ability of the oxygenator to perform gas exchanges efficiently.
5.2 Adapting the Specifics of ECLS to the Regular Monitoring of the Patient in a Critical Care Unit
5.2.1 Pain and Sedation
ECMO patients are now more commonly awake and even extubated sooner [1]. It is mostly the case for VA ECMO patients: they can be awakened just after ECMO implantation; some teams even implant the ECMO on nonsedated and extubated patients with local anesthetics. For VV ECMO patients, they are always deeply sedated the first few days due to the major lung damage.
The ECMO membrane lung is trapping medications, altering pharmacokinetics and pharmacodynamics of analgesics and sedatives such as propofol, midazolam, or opioids [2]. Higher doses of sedatives and analgesics must then be administered to obtain an appropriate sedation and comfort of the patient. Hence, protocols of management of pain and sedation should be reassessed for ECMO patients.
5.2.2 Infection
Like any other device inserted inside the patient, the cannulas can be a source of infection. ECMO cannulas, being of large diameters, enhanced the risk. The site of cannulation worsens this potential complication: drowning can soil jugular cannulas, stool contaminates femoral cannulation, and central cannulation is directly inside the heart of the patient.
Early detection is of paramount importance; the nurse should check:
Daily white blood count and cell blood culture
At each round, the integrity of the cannula dressing
A daily assessment of the insertion point of the cannulas, looking for redness, swelling, bleeding, or potential infection
In central lines, the use of chlorhexidine gluconate-impregnated sponge reduces the infection rate, diminishes the frequency of dressings up to 7 days, and allows a visual on the insertion point [3]. It can be done with the ECMO cannulas (Fig. 5.3).
Fig. 5.3
Transparent chlorhexidinie gluconate impregnated dressing
5.2.3 Skin Care
Skin care is a constant challenge for ICU nurses. ICU patients have always been good candidates for developing pressure sores: they are lying in bed most of the day, often sedated; infection and heparin infusion can provoke skin abrasion or hematoma; and edemas are unavoidable, specially for patients with heart failure.
ECMO patients, in addition to these preexisting skin alterations, must face other potential skin damages: cannula’s sutures are tight and through time lesions can appear. Edema plus the pressure of the cannula on the skin can lead to unavoidable pressure sores.
Protecting the skin from the cannulas can be done with foam dressings or hydrocolloids already used for regular patients. To fix the cannulas without damaging more skin, some attachment devices like the horizontal tube attachment are composed of hydrocolloid, allowing skin protection and an additional fixation (Figs. 5.4 and 5.5).
Fig. 5.4
Horizontal tubing attachement device (Courtesy of Hollister®)
Fig. 5.5
Horizontal tubing attachement device on an ECMO patient
5.3 Preventing Complications
ECMO is a miniaturized version of the extracorporeal circuits used in the operating room for thoracic surgery. An ECMO run is therefore the source of minor to major complications, endangering the patients.
One of the key points of ECMO management is to prevent and make an early detection of these complications. All the ICU caregivers (doctors, nurses, perfusionists, physiotherapists, respiratory therapists, help nurses) must be trained to acknowledge the signs of an early bleed, an infection, and a dysfunction of the ECMO.
5.3.1 Bleeding
Bleeding is frequent and can be massive during any ECMO run. The blood of the patient is in contact with an inert and nonbiological material, so continuous systemic anticoagulation by nonfractionated heparin infusion is necessary to prevent fibrin and clot formation in the ECMO circuit. During implantation, a bolus of 5000 UI of heparin is most commonly injected to the patient, enhancing the risk of bleeding. In the immediate postimplantation phase, the challenge is to be able to balance the control of postoperative bleeding as well as minimizing the formation of clots in the ECMO circuit. Bleeding can also be worsened after an open heart surgery or transplant.
5.3.1.1 Prevention
To prevent bleedings, a very strict control of the hemostasis is necessary: the heparin infusion rates have to be titrated to obtain an aPPT ratio between:
1.8 and 2 times normal level for VA ECMO patients depending on their cardiac condition; the antifactor Xa can also be a better indicator of the heparin management
1.5 and 1.8 times normal level for VV ECMO patients
2 and 2.2 times normal level for ECMO circuits with more than two cannulas like VAV, central cannulation
5.3.1.2 Clinical Signs and Treatment
Bleeding on ECMO can be local or generalized:
The Ear, Nose, and Throat (ENT) area: Bleedings in this area are almost unavoidable. Mouth care is then difficult, and sometimes ineffective. With a nose bleed, the nurse can start by digitally pressuring the nostrils for a 5-min period. If the bleeding persists, insert a resorbable hemostatic wick in each nostril. If this technique fails too, the last resort is to insert a nasal compression probe (it is possible to use a urinary catheter). By inflating the balloon of the probe, a compression is made in the posterior fossa, stopping the bleeding.
For the mouth, oral care stays crucial even if it seems ineffective. The mouth of the patient should still be gently suctioned to remove drooling, blood, and clots, and cleaned with smooth mouth sticks but only with water. Mouthwashes usually contain alcohol, which can maintain the bleeding and provoke a burning sensation to the patient. In the most severe bleedings, ENT specialist can perform a packing of the mouth: the entire oral cavity and throat will be then packed with hemostatic wicks. Oral care is then impossible, but to avoid pressure ulcer on the palate and tongue, the “packing” must be humidified with saline every 4–6 h and completely removed after 48 h.
The dressings: Bleedings can occur on all the patient’s dressing, insertion point of IV lines, suction drains, and ECMO insertion point. The use of hemostatic dressings can avoid redoing the dressings several times a day.
The neurological status of the patient: Look for any signs of intracranial hemorrhage––bilateral pupillary response, level of consciousness, patient’s reaction to the decrease of sedatives [4].
The aspect of the lung secretions: Intra-alveolar hemorrhage can occur. Bleeds can be related to the disease itself, especially for patients on VV ECMO with severe ARDS, but it can also be caused by a disseminated intravascular coagulation (DIC) for patients on VA ECMO. It is recommended for patients on VV ECMO to use a humidifier on the ventilation tubing. Warming and humidifying the bronchial tree could minimize clot formation.
The aspect of the urine: Although rare, presence of blood in urine can occur. The urine color is then bright red. Be careful not to cofound it with the “dark reddish” color of the urine in case of hemolysis.
The digestive tract: Presence of blood in stools can be seen. If there is a doubt, use hydrogen peroxide on a stool sample. If foam appears, it means there is blood. In the absence of external bleeds or in severe DIC cases, a gastric lavage should be performed to check the presence or absence of blood.
General treatment: It is essential that the team understands and finds the right balance between pro- and anticoagulants to manage the patient properly. The daily blood count can assess the blood loss and the need to transfuse the patients with packed red blood cells or platelets. It is still a debate in the ECMO community to determine the cutoff for red blood cells transfusion; some teams (La Pitié Salpêtrière is part of them) recommend to transfuse only when the hemoglobin is under 7 g/dL; others argue that an ECMO patient should have a normal hemoglobin to allow an optimized oxygenation, so that the transfusion limit will be 12 g/dL.
For long, ECMO teams have been reluctant to discontinue heparin during ECMO runs. Experiences from several teams and data show that in case of severe hemorrhage and if the patient is nonresponsive to transfusion and a decrease rate of the heparin infusion, the discontinuation of the heparin is possible [5] for hours and even days, with a strict control of the aPPT and a thorough check of the oxygenator and cannulas looking for clots and thrombin. In a worst case scenario, using recombinant factor VIIa has been done safely by several teams with a major decrease of bleedings, but must be a last resort therapy with an extreme caution and surveillance of the ECMO circuit [6–8]
5.3.2 Thromboembolic Risk
Good and effective anticoagulation treatment not only avoids bleeding but also prevents formation of clots and thrombin. They are the results of cells lysed by the turbulence of the ECMO pump and the stagnation of blood. They are easily visible with a flashlight within the tubing and connectors: dark clots and white fibrin strands can be easily observed.
Meticulous surveillance is of paramount importance: detection, documentation, and the evolution of clots and fibrin can prevent major adverse events like brain damage or ECMO failure due to pump or oxygenator thrombosis (Figs. 5.6, 5.7, and 5.8).
