Guidelines for the intraoperative management of patients undergoing spine surgery

Authors: Karl Zheng and Martin Angst

General considerations

Surgical procedures are divided into three classes based on the extent of surgery: Minor, major, and complex. Considerations for the intraoperative management of patients’ undergoing spine surgery are class-specific.  Procedures are listed in the table:

Access

Consider establishing vascular access as suggested:

• Minor surgery: 18-20G IV cannula, A-line only if medically indicated
• Major surgery: 16 and 18-20G IV cannulas, A-line recommended
• Complex surgery: 2 x 14-16 IV cannulas or central venous line (cordis), A-line.

Fluid management

The overall aim is to keep patients euvolemic, while avoiding excessive fluid administration. Fluids should be titrated on an “as needed basis” to maintain euvolemia. In the absence of tools directly assessing fluid status (e.g. TEE) integration of various clinical indicators will allow inferring a patient’s fluid status (arterial blood pressure, pulse pressure variation, acid/base balance, clinical assessment of peripheral perfusion, trends in CVP). Consider using colloids early in major and complex surgery (after administration of 1-2 liters crystalloids) to avoid soft tissue edema.

• Crystalloids: Balanced solutions (e.g. LR) are preferred in combination with normal saline to limit sodium load.
• Colloids: Colloids preferentially expand intravascular volume and limit volume load of the interstitial space. This is particularly relevant in patients who are in prone position for extended periods of time. These patients have an increased risk of postoperative visual loss. Large volumes of crystalloids may increase such risk. Significant soft tissue edema is also associated with slower bowel recovery and raises concerns regarding the patency of a patient’s airway at the end of surgery. The use of albumin 5% is recommended. The use of hetastarch is discouraged in major and complex surgery as it may impair renal function and worsen coagulopathy.

Blood pressure management

The overall aim is to avoid decreases in arterial blood pressures (BPart) > 20% from baseline (baseline = typical blood pressure at rest without stress). Stricter control of blood pressure may be required in patients with myelopathy or trauma to the spine, i.e., maintaining a mean arterial pressure ≥ 80-90 mmHg. Generally, consider taking the following sequential actions if BPart decreases > 20%:

• Reduce the amount of anesthetics as many anesthetic agents decrease systemic vascular resistance (use age-adjusted MAC and evaluate individual patients’ true anesthetic requirements). The use of 50% nitrous oxide (minimal impact on SVR) is suggested to spare volatile anesthetics. A total of 0.7-1.0 MAC is often sufficient to prevent awareness and provide adequate surgical conditions.
• Opioids are mainly used to control hemodynamic variables during general anesthesia. Opioids to not exert preemptive analgesic effects. As such, the liberal use of opioids during general anesthesia has no beneficial effects on postoperative pain. However the liberal use of opioids during general anesthesia may aggravate arterial hypotension. Towards the end of surgery opioids should be titrated to provide postoperative pain control.
• Consider starting a continuous infusion of a vasopressor at a low dose. The use of phenylephrine at a rate ≤ 0.4 mcg/kg/min is suggested. The use of higher rates has to be balanced against the risk of concealing intravascular volume depletion. This is particularly important in patients with significant blood loss.
• Appropriate amounts of fluids should be used to restore euvolemia if a decrease in BPart  > 20% is due to intravascular volume depletion (normal SVR).

Transfusion of blood products

While there is some controversy regarding the threshold hematocrit (Hct) or threshold hemoglobin (Hb) that should be maintained during surgery and trigger administration of blood, a threshold of 24% (Hct) or 8gr/dl (Hb) is suggested for major and complex surgeries. Consider administering blood at Hct ~ 27% or Hb ~ 9gr/dl if blood loss is continuous to maintain a Hct ≥ 24% or a Hb ≥  8gr/dl. Suggested thresholds provide a margin of safety as blood loss can be continuous. If blood loss is rapid and extensive administering blood products may be dictated by hemodynamic parameters rather than specific Hct or Hb targets.

• Prophylactic use of tranexamic acid (10mg/kg bolus) should be considered for major surgery (discuss with surgeons), and is strongly recommended for complex surgery (10mg/kg bolus followed by an infusion of 1mg/kg/h). However, use of tranexamic acid should be discussed with the surgeons if patients have a history of thromboembolic events or suffer from malignancies.
• A cell saver should be available for major and complex surgery except for cancer-related surgeries.
• Consider the use of FFP after administering 4-6 units of red packed blood cells (RBCs) or as clinically indicated.  Administration of FFP and RBCs in a ratio of 1:1 to 1:2 is suggested.
• Consider administration of platelets (one apheresis product) after transfusion > 6 RBCs, a platelet count < 100,000/mcl, or as clinically indicated. Consider administration of platelets for each additional administration of 6 RBCs.
• Consider administration of cryoprecipitate (10 units) after transfusion of 10 RBCs to maintain a plasma fibrinogen level > 100 mg/ml.
• Consider calling for help and initiating Massive Transfusion Protocol in case of massive and/or uncontrollable bleeding.

Prophylaxis of postoperative nausea and vomiting

A special consideration concerns the use of steroids (dexamethasone). Steroids have to be avoided in patients undergoing spinal fusion as they may impact bone healing. Discussing the use of dexamethasone with surgeons is strongly recommended.  PONV prophylaxis should follow departmental guidelines using risk stratification (http://ether.stanford.edu/policies/PONV_prophylaxis_guidelines.html).The risk for developing PONV is predicted by four factors:  The use of postoperative opioids, being a non-smoker, being of female sex, and having a history of PONV or motion sickness. Each factor adds 1 point to a maximum score of 4. The number of agents for preventing PONV is equal to the risk score. Agents to consider are:

• Ondansetron (4mg)
• Dexamethasone (4mg) in non-fusion procedures
• Propofol
• Scopolamine patch (1.5mg)
• Haloperidol (1mg)

Pain management

The major aim is to provide adequate pain control (pain at rest ≤ 3/10, pain during movement ≤ 5/10) using a multi-modal approach. While opioids are an important component of the multimodal approach, opioid-sparing techniques are encouraged to avoid opioid-related adverse effects including prolonged postoperative constipation and drowsiness. Latter may impede patient mobilization. Certain components of a typical multimodal approach require special considerations in patients undergoing spine surgery. In particular, the use of a COX2 inhibitor (celecoxib) has to be avoided in patients undergoing spinal fusion. As such, its use should be discussed with surgeons. Non-steroidal anti-inflammatory drugs (e.g. ketorolac) should be avoided.

• Patients should be started on acetaminophen (1gr PO) before surgery. Patients will receive acetaminophen around the clock (1gr PO q6h) until they are switched to an oral combination product containing an opioid and acetaminophen (e.g. Percocet).  Dose adjustments may be necessary in the very elderly and in patients with impaired liver function.
• Consider the use of celecoxib (200mg PO) before surgery for non-fusion procedures.
• Consider the use of an intraoperative ketamine infusion (0.5mg/kg bolus followed by an infusion rate of 0.25mg/kg/hr). Stopping the infusion 30-45 minutes before the end of surgery is recommended to facilitate emergence from anesthesia. The use of ketamine is encouraged in patients undergoing major and complex surgeries. It is strongly recommended in patients with history of chronic and multiple pain complaints. The intraoperative use of ketamine exerts opioid-sparing effects of ~40% during the postoperative period and is very rarely associated with hallucination.
• Consider the use of an intraoperative lidocaine infusion (100mg bolus followed by an infusion rate of 1-2mg/kg). A lidocaine infusion is recommended for patients undergoing major or complex surgery.
• The use of gabapentin before surgery is controversial. Gabapentin can cause postoperative drowsiness and impair patient mobilization. However, gabapentin may particularly benefit patients with a history of chronic and multiple pain complaints. Consider preoperative administration of gabapentin (600 mg PO) in patients with a history of chronic pain.

Neuro-monitoring

Patients requiring neuro-monitoring including motor-evoke potentials should not receive neuromuscular blockers, except for endobronchial intubation. If baseline potentials are recorded before turning a patient prone short-acting succinylcholine should be used (discuss with neuro-monitoring team). A standard anesthetic plan not interfering with the monitoring of evoked potentials includes the use of 0.5 MAC of a volatile anesthetic, <50% N₂O, and a remifentanil infusion targeted to a patient’s anesthetic needs. Patients requiring EMG monitoring (Nuvasive XLIF, MIS TLIF) should not receive any non-depolarizing neuromuscular blockade even for intubation. Use succinylcholine instead.