Retrospective Review of Anesthetic Management of Free Flap Reconstructive Surgeries: An Analysis of 162 Cases

Anesthetic Technique

Although several anesthesiologists were involved over 4 years of this study, the anesthetic techniques employed were fundamentally the same for all cases reviewed. Preoperative assessment included elicitation of the patient’s history to ascertain whether they had received chemotherapy which included bleomycin, which could result in gas exchange impairment as the drug is known to cause pulmonary fibrosis. Physical examination included assessment of mouth opening and upper airways to exclude potential intubation problems, and also inspection of peripheral veins, as many of these patients have received chemotherapy and multiple venesections leading to thrombosed veins. Other investigations included full blood count with clotting studies, assessment of blood urea nitrogen, serum creatinine, electrolytes, liver functions, ECG, and chest X-ray.

The patients were premedicated with opioids in combination with benzodiazepines. Anesthesia was induced via an indwelling needle in a peripheral vein with intravenously administered propofol (2 mg/kg), and then the patient was intubated orally or nasally depending on surgical site under a nondepolarizing relaxant, usually intravenous atracurium (0.5–0.8 mg/kg) or vecuronium (0.1–0.4 mg/kg). Cuffed endotracheal tubes were used orally and the nasal tubes were either reinforced or preformed. If difficulty with intubation was anticipated, the patient was anesthetized using an inhalation technique with sevoflurane and direct laryngoscopy attempted, and intubation was achieved with the assistance of either an introducer or a gum elastic bougie. The technique of blind nasal intubation was used earlier on, and fiberoptic bronchoscope was used more often during some of the more difficult intubations. A wide bore nasogastric feeding tube was usually passed after intubation, preferably to allow placement under direct vision. Venous access was provided by an 18 or 20 G cannula in a peripheral vein and a central venous catheter inserted peripherally, whenever required. Access to jugular and subclavian veins was often restricted by the surgical field. A 20 G cannula was placed in a radial artery in cases where major blood loss was anticipated. All patients had a urinary catheter placed.

The convective forced air warmer with blanket was used for temperature regulation, and anesthesia was maintained with nitrous oxide and oxygen with either isoflurane or sevoflurane. Analgesia was provided with either fentanyl or buprenorphine. Inspired gases were warmed and moistened by a condenser humidifier. Monitoring included electrocardiography, pulse oximetry, and also monitoring of inspired oxygen concentration, end tidal carbon dioxide, arterial blood pressure with waveform display, body temperature, neuromuscular blockade, bispectral index, and arterial blood pressure by indirect method. Intraoperatively, fluid maintenance was administered at a relatively high rate of 7–10 mL/kg/hour of crystalloid, usually in the form of either lactated ringer or glucose 5% in normal saline 0.9%. All infused solutions were warmed before infusion.

At the end of surgery, the neuromuscular blockade was reversed with neostigmine, along with glycopyrrolate or atropine and the patient was then transferred to the postanesthesia care unit, while breathing warmed, humidified oxygen-enriched air. An initial intravenous bolus of fentanyl (0.5 μg/kg) with or without midazolam was required to settle these patients, after which postoperative analgesia was generally provided by a fentanyl infusion (1 μg/kg/hour). All patients were given prophylactic intravenous antibiotics both pre- and postoperatively.

Postoperative Management

All these patients were managed postoperatively in high dependency unit setup (‘PACU’). The patients were kept warm, pain-free, and well-hydrated.

Monitoring the flap: clinical observation of skin color, capillary return, temperature, and ultrasound Doppler were monitored for free skin flaps (Table 2).

Temperature Control

Because of the prolonged surgery and sometimes extensive exposure, it can be difficult to achieve temperature control but it is the most important aspect. Though hypothermia has been shown to be effective in temporary storage of free flaps and severed extremities, the effects of hypothermia like rise in viscosity, vasoconstriction, platelet aggregation, etc. reduce flow in the free flap. We recommend maintaining the patient’s body temperature with warming blankets pre- and intraoperatively, and for the first 24–48 hours post surgery. Ambient temperature in the operating room should be relatively high: 24–25°C and the temperature differential between skin and core should be kept to less than 2°C.^3,5

Glucose Control

From available literature regarding albumin leak, acute and chronic hyperglycemia is associated with vascular leakage and thus tissue edema is more likely to be formed. Hence strict glucose control is recommended.³

Hydration

To maintain adequate microcirculatory perfusion of the transplanted tissue, a hyperdynamic circulation with a high cardiac output, peripheral vasodilatation, and a large pulse pressure is required. Both the donor and the recipient sites have insensible fluid losses and blood losses. Mild-to-moderate hypervolemia reduces the sympathetic vascular tone and dilates the supply vessels to the flap. Though the oxygen delivery to the tissues is probably optimal at a hematocrit level of around 30, most patients can tolerate a drop in hematocrit up to 18–20%, targeting the central venous values of 10–15 cm H₂O or 3–5 cm H₂O above baseline.³

Control of Blood Pressure

During major tumor resection, controlled hypotension is required to improve the surgical field and reduce the blood loss. Other measures which include are (I) positioning to improve the venous drainage and (II) local anesthetic infiltration. Blood pressure can be controlled by various anesthetic techniques like combination of inhalational agent (sevoflurane/isoflurane) and opioids infusion (fentanyl) ± NTG infusion ± propofol/dexmetomidine. Mean arterial blood pressure should be maintained at a normal or slightly elevated level during harvesting and anastomosis of the flap to ensure an adequate perfusion pressure through the graft tissue bed. Hypotension is usually secondary to blood loss or vasodilatation and should be treated with fluid replacement.³

Microvascular Circulation

Both crystalloid and colloid infusions are used. We prefer Dextran as it has been shown to be more efficient plasma substitute than both the large volumes of colloids and crystalloids and dextran appears to have beneficial effects on the microcirculation. It has an antithrombotic effect through a reduction in platelet adhesiveness. It also causes a depression of factor VIII activity. Thus, dextran has an advantage in terms of thromboprophylaxis but the amount that can be given has to be limited during major blood loss. Hypertonic saline solutions have been the subject of recent interest. It appears to be an effective plasma volume expander and has beneficial cardiovascular effects but due to lack of available literature we prefer Dextran.⁷ Our policy in adults is to infuse Dextran-40 in doses of 1–2 mL/kg/hour from the moment the anastomosis is established till 24–36 hours postoperatively. Extensive blood loss can occur during a prolonged procedure and may be covert (e.g., latissimus dorsi donor site). Packed cells to be transfused only if the hemoglobin level falls below 8 g/dL or hematocrit less than 18–20%.³

Urine Output

A urine output of 1–2 mL/kg/hour should be maintained intraoperatively and postoperatively with appropriate fluid management. Diuretics are best avoided in these operations because volume depletion compromises flap survival.³

Acid–Base Balance and Serum Electrolytes

As these procedures are of prolonged duration, it mandates blood gas analysis at preset intervals and corrections to be done accordingly. In our institute, we do blood gas analysis every 3–4 hourly. Hypoxia and hypercarbia inadvertently affect microcirculation and thus, graft survival.

Analgesia

We use intravenous opioids, regional block, or a combination of these two. NSAIDs are usually avoided in the acute perioperative period because of the risk of bleeding and flap hematoma formation.

Regional anesthesia usually consists of a brachial plexus block for upper limb or lumbar epidural for lower limb flaps. Advantages of regional analgesia include excellent analgesia and vasodilatation with improved flap blood flow during and after the operation, reduction in the stress response to surgery and anesthesia, decreased blood loss, reduced incidence of deep vein thrombosis, a hastened postoperative recovery and can prevent vasospasm after replantation. However, there are some major concerns regarding the regional anesthesia, especially epidural anesthesia in microvascular free tissue transfer. As the flap is denervated, sympathectomy produced by an epidural may decrease microcirculatory blood flow in free flaps by decreasing MAP (and hence perfusion pressure) and by diverting the blood away from the flap to normal intact tissues (‘steal’ phenomenon). This was particularly a concern in hypovolemic patients. We used the epidural towards the end of the case when the blood pressure was satisfactory and the cardiovascular system was adequately filled. We used small increments of 0.125% or 0.25% bupivacaine followed by an infusion of 0.15% bupivacaine with or without fentanyl (2 μg/mL).

Anticoagulation

The use of various anticoagulants and volume expanders is employed to reduce the probability of vascular thrombosis. Some have been shown to produce an advantage in experimental models, and also potential clinical benefit in retrospective analysis. However, because the rate of thrombosis is quite low with good techniques, detection of a difference between groups is difficult. Despite considerable research on thrombosis in, e.g., cardiovascular disease, antithrombotic regimens in microvascular surgery are generally empiric and few randomized blinded controlled studies exist. The three most commonly used substances include heparin, aspirin, and low-molecular-weight Dextran (also a volume expander).

Heparin

Heparin is used in microvascular surgery both systemically and topically in irrigation solutions.^2,4 Though due to limited literature we have not used unfractionated heparin, we prefer Enoxaparin 0.4 mL subcutaneously.

Aspirin

Low-dose aspirin is usually recommended for prophylaxis in microvascular free flap surgery.^2,4