The cases of patients suffering from complex knee injuries vary in complexity and severity. These patients may have isolated lower extremity injuries or can present with more complex injury patterns involving multiple organ systems. This dichotomy presents challenges to both the surgical team and the anaesthesia team because patients may be stable for treatment in an outpatient setting with surgical intervention performed on a semielective basis, or they may present in a more urgent manner and require anaesthesia for emergent reduction of a knee dislocation, fasciotomy, vascular repair or early stabilisation with damage control orthopaedics and delayed reconstruction after initial evaluation.
This chapter discusses the perioperative approach to the patient with a complex knee injury and reviews options for anaesthesia (including regional and general anaesthesia), techniques to mitigate blood loss and techniques to maintain appropriate fluid management.
Anaesthesia Considerations for Patients with Knee Injuries
Because of the potential variability of patients receiving care for complex knee injuries, careful coordination between the surgical team and the anaesthesia team must be achieved. Anaesthesia care for complex knee surgery requires increased skill and an orthopaedic anaesthesia provider with proficiency in a wide range of techniques, including general anaesthesia, central neuraxial anaesthesia and peripheral regional anaesthesia. Although many complex knee surgeries are performed on an elective basis, these patients may also present emergently after a polytraumatic injury, and therefore providers must also be comfortable with managing a challenging airway in a wide age range, caring for patients at increased risk for haemodynamic instability and deep venous thrombosis (DVT) or fat emboli, and must be willing to participate in a range of highly variable operative procedures. ,
When required, patients with complex knee injuries should be evaluated for life-threatening injuries via the advanced trauma life support (ATLS) protocol. If required, preoperative cardiac evaluations (such as electrocardiography) should be considered, and all providers must maintain a high index of suspicion for associated injury patterns in other organ systems in the polytraumatised patient. In all patients the injury history, injury pattern, medical history, anaesthesia history, pertinent imaging related to the injury and any associated comorbid conditions should be reviewed in preparation for appropriate anaesthesia.
Both in the acute setting and at times when surgical intervention can be delayed, surgical coordination is paramount between the surgical and anaesthesia teams. It is important to for the surgeon to communicate with the anaesthesia provider regarding the planned surgical positioning, expected blood loss, potential use of a tourniquet, the nature of the procedure and the pertinent steps, the expected surgical duration and the need for pre- or postoperative regional anaesthesia. When this early communication is accomplished, it allows for appropriate choice of anaesthesia and minimises complications before, during and after surgery.
Anaesthetic Choice and Perioperative Analgesia
The anaesthesia team plays a crucial role not only in maintaining homoeostasis throughout the surgical procedure but also in providing assistance in controlling pain both during and after the surgery. Complex knee surgery can be associated with significant postoperative pain and because of that a variety of anaesthetic techniques are considered to provide adequate analgesia. These include oral or systemic medications, intraarticular or periincisional injection, central neuraxial (spinal or epidural) anaesthesia and regional anaesthesia (commonly referred to as a block ). , Although each anaesthetic approach promotes safe and effective analgesia, each is associated with advantages and disadvantages, which makes a single gold standard approach difficult to achieve.
Choosing the appropriate anaesthetic technique relies on knowledge of the planned procedure and patient history and comorbidities. Although general anaesthesia is typically chosen for complex knee surgeries, patients with associated head and neck trauma or reactive airway disease may not be candidates for a general anaesthetic and could benefit from central neuraxial anaesthesia. In contrast, patients with depleted intravascular volumes, coagulopathy or chronic anticoagulant use would not be appropriate candidates for spinal or epidural anaesthesia given the sympathetic blockade and bleeding risk that occurs with these techniques. , , In addition, regional blocks are often beneficial in these settings, and although they are infrequently used in isolation, they can be an excellent augment to general or spinal anaesthesia to reduce intraoperative and postoperative opioid use.
The use of spinal epidural or central neuraxial anaesthesia can also be considered to allow for adequate pain control throughout the surgical procedure. This approach is effective at controlling pain during the procedure but does have limitations as mentioned. In addition to patient historical factors, the use of spinal anaesthesia typically allows the patient to be awake for a significant portion of the surgery. In emergent settings or during extended surgical procedures, this may induce patient anxiety or discomfort and therefore may not be an appropriate option. , If spinal or epidural anaesthesia is chosen, communication with the anaesthesia team is essential to ensure that the catheter is placed at a lower lumbar level to provide appropriate coverage at the level of the knee, such that the L4, L5 and sacral nerve roots are appropriately blocked.
When considering possible central neuraxial anaesthetic options, both the effectiveness of analgesia and patient satisfaction are comparable for spinal and epidural anaesthesia; , however, the surgeon must evaluate several factors when considering this type of anaesthetic approach. Many complex knee procedures are performed in the ambulatory surgery setting and therefore necessitate discharge the same day that surgery is performed. Central neuraxial techniques may increase time to discharge and limit the ability of the patient to ambulate and perform early range of motion, which are often crucial to the early recovery phase and to allow for discharge home after surgery. , ,
Because of the limitations related to central neuraxial anaesthesia, complex knee surgery is typically performed with a combination of general anaesthesia and regional anaesthesia with blockade of one or more peripheral nerves. Several regional anaesthetic options exist for knee surgery, and providers have previously considered blockade of the large nerves of the lower extremity such as the femoral or sciatic nerve. Such blocks encompass both the sensory and motor function of these nerves and therefore not only deliver regional anaesthesia but also may induce paralysis of the innervated muscles, which may help in facilitating ease of surgical exposure and access to deeper structures.
Sciatic blocks have been less commonly used for isolated procedures to the knee; however, femoral nerve blocks (FNB) remain common. The femoral nerve is the largest branch of the lumbar plexus and originates from the dorsal divisions of the ventral rami of lumbar nerve roots of L2, L3 and L4. The femoral nerve is the major motor nerve to the anterior compartment of the thigh, supplying the pectineus, sartorius, rectus femoris, vastus lateralis, vastus medialis, vastus intermedius and articularis genu. In addition, the femoral nerve supplies cutaneous innervation of the knee and thigh via the intermediate femoral cutaneous nerve, medial femoral cutaneous nerve and saphenous nerve. , Because of the extensive innervation of the femoral nerve and its close proximity to the lateral femoral cutaneous nerve (LFCN) and obturator nerve, blockade of the femoral nerve has typically been performed with high volumes of anaesthetic in an effort to achieve a threefold block of all three nerves in the location. , Although some studies have demonstrated limited effectiveness in achieving blockade of the LFCN and obturator nerve, femoral nerve blockade is highly effective and relatively easily achievable under ultrasound guidance.
Femoral nerve block has demonstrated excellent analgesia after surgical procedures around the knee, including anterior cruciate ligament (ACL) reconstruction; however, because of the diffuse effect achieved by FNB, there are potential drawbacks. In the patient population commonly treated for complex knee injuries, early mobilisation and range of motion of the knee are paramount to limit risk of thromboembolism and arthrofibrosis. Returning to normal ambulation is also of paramount importance. Because of the motor blockade of the quadriceps muscles and associated quadriceps paralysis that can occur with FNB, such early mobilisation can be challenging, and this can lead to an increased risk of falls, even in young healthy patients undergoing outpatient procedures.
In an effort to limit the effects of the diffuse blockade of the femoral nerve while achieving similar levels of analgesia, the use of an isolated saphenous nerve block or adductor canal block has gained popularity. Because of the increased sophistication of ultrasonographic techniques, providers are able to provide an isolated cutaneous blockade of the saphenous branch of the femoral nerve at the level of the midthigh with limited associated motor effects. This isolation of a cutaneous nerve has demonstrated good effectiveness in controlling pain several different procedures around the knee, including knee arthroplasty, knee arthroscopy and ACL reconstruction. , However, the main purported benefit of this nerve block is the theoretical benefit of increased quadriceps function after surgery. That being said, the degree to which adductor canal blocks preserve the function of the quadriceps muscle, and therefore the ability to safely ambulate or perform range-of-motion exercises after surgery, is controversial. Several studies have demonstrated that adductor canal blocks yield limited or no quadriceps dysfunction or paralysis compared with FNB. However, even despite the isolated cutaneous blockade, other studies have demonstrated decreased quadriceps function and even quadriceps paralysis after adductor canal block, thus limiting the potential effectiveness of this block compared with the more diffuse blockade provided by an FNB.
At present it is recommended that surgeons coordinate potential anaesthetic options with the anaesthesia providers at their institution. Based on the available literature, use of each of the techniques mentioned in this chapter are reasonable and can be tailored based on patient factors and expertise available at each institution. At this time our preferred methodology is a combined approach using general anaesthesia and an adductor canal block. To assist in perioperative analgesia, periincisional local anaesthetic injection and oral pain medications are also used to ensure pain is well controlled.
Intraoperative Fluid Management
Although decisions regarding perioperative analgesia are important for patient satisfaction and early rehabilitation, perioperative maintenance of adequate intravascular volume is important to achieve optimal outcomes during and after surgery. During the surgical procedure, anaesthesia providers will use a combination of factors including blood pressure, heart rate, central venous pressure, and urine output to monitor intravascular volume and ensure adequate resuscitation. , More complex calculations and measurements are typically not required during the vast majority of complex knee procedures, but appropriate fluid management must take into account the fasting time that the patient has endured before surgery and should also account for periods of dehydration and preoperative cardiac output when necessary. , There is not a uniformly accepted algorithm for intraoperative fluid administration; however, choosing the appropriate type, amount, and timing of intraoperative fluid allows for intravascular volume control during surgery, and limits postoperative morbidity.
At present, the American Society of Anesthesiologists recommends that patients avoid clear liquids (not including alcohol) for 2 hours and that they be fasting for at least 6 hours before most elective surgical interventions ( Table 38.1 ). Although there is little evidence that fasting for up to 10 hours reduces intravascular volume, and knee surgery does not have the same insensible fluid loss or third spacing that other procedures around the abdomen or thorax would, it is still recommended that patients continue oral intake of clear liquids as able until 2 hours before surgery to avoid dehydration and mitigate the need for aggressive intravenous rehydration.
|Time Before Surgery||Fasting Recommendations Before Surgery|
|2 h||Clear liquids (not including alcohol) only|
|4 h||Breast milk is acceptable|
|6 h||Nonhuman milk, infant formula or a light meal consisting of toast or cereal with clear liquid|
|8 h or more||A heavy meal consisting of fried foods, fatty foods or meat products|
Most patients undergoing elective complex knee surgery are relatively healthy and are safely maintained in a euvolemic state with an intravenous (IV) administration of a simple crystalloid solution. Although normal saline (0.9% sodium chloride solution) is the most commonly used to resuscitate intravascular volume during periods of hypovolaemia or dehydration, anaesthesia providers typically choose a colloid solution with an electrolyte composition similar to plasma. To achieve a composition similar to plasma, crystalloid is often combined with a balancing buffer such as lactate, and such solutions are commercially available as PlasmaLyte or Ringer’s lactate (these solutions are commonly referred to as balanced electrolyte solutions). , Solutions containing hypertonic mixtures are contraindicated in most clinical settings, solutions with potassium are contraindicated in hyperkalaemia secondary to the risk of ventricular dysrhythmia and dextrose or other sugars are typically avoided to limit the risk of hyperglycaemia. It should be noted that commercially available balanced crystalloid solutions typically contain calcium, which can induce the coagulation cascade, and therefore should be limited if used in the same IV tubing for patients requiring blood transfusion or other blood products.
Colloid solutions (such as human plasma or fresh frozen plasma) can also be used to maintain similar levels of euvolaemia; however, these products are typically less cost effective and there is limited evidence that colloid administration provides advantages over the use of a buffered crystalloid solution. Similarly the administration of albumin or synthetic colloids (hydroxyl starches) have limited evidence for use in the elective surgical setting but may provide benefit in certain acute traumatic cases. ,
For the majority of patients undergoing minimally or moderately invasive surgeries lasting less than 2 hours, 1000 to 2000 mL of IV balanced electrolyte solution is sufficient to maintain a relatively euvolemic state. However, some providers choose to use the long-standing ‘4-2-1’ rule such that fluids are replaced at a rate of 4 mL/kg per hour for the first 10 kg of patient weight, followed by an additional 2 mL/kg per hour for the next 10 kg, and then an additional 1 mL/kg per hour for every kilogram thereafter (e.g., a 70-kg patient would require 110 mL/hour of fluid replacement). With more invasive surgery or surgeries that require more time, strategies focusing on direct 1:1 replacement of lost volume are chosen. In these instances, blood loss, urine output and other potential fluid losses are calculated and are also typically monitored with intraarterial waveforms to determine appropriate levels of fluid replacement and the patient’s response to administration. In these situations, blood transfusions may also be necessary to maintain the intravascular volume when haemoglobin drops to less than 7 to 8 g/dL or haematocrit to less than 21% to 24%. If larger amounts of blood loss or prolonged surgical time are expected, it is imperative to discuss this with the anaesthesia provider before surgery to ensure appropriate fluid resuscitation is available during the surgical procedure.
Management of Blood Loss During Complex Knee Surgery
In addition to efforts from the anaesthesia team to assist in appropriate fluid management and pain control, surgeons must be aware of techniques to minimise blood loss and promote a stable environment. Most complex knee surgeries do not require intraoperative or postoperative blood transfusion; however, surgical procedures for treatment of complex knee injuries often involve one or more incisions for exposure of anatomy or to harvest grafts for ligamentous or cartilaginous reconstruction ( Fig. 38.1 ). Use of such incisions induce more surgical bleeding such that the surgical field of view can become obscured and can be associated with increased blood loss compared with more minimally invasive procedures that involve isolated arthroscopy. Because of this, strategies such as tourniquet use, topical agents and systemic medications to mitigate bleeding and maintain a well-visualised surgical field are of utmost importance.