Anesthetic Considerations for Orthognathic Surgery: PROCEDURE

In: Anesthesia

25 Feb 2010

The patient is brought to the theater on a tilting trolley with the head on a pillow. The patient is properly positioned on the trolley with the head at the end of the trolley and shoulders on the edge of the pillow. Noninvasive blood pressure, ECG, and oxygen saturation monitoring are commenced. Preoxygenation of the patient is carried out. An intravenous line is established and is connected to an intravenous infusion of crystalloids, Ringer lactate solution, from a pump infusion set. Dexamethasone, 0.1 mgAg is given intravenously prior to induction of anesthesia in order to reduce postoperative swelling. Induction of anesthesia is usually carried out with an intravenous induction agent such as pro-pofol or thiopentone. If difficult intubation is to be expected, an inhalational induction is carried out with a potent inhalational anesthetic such as halothane or sev-oflurane and the ability to ventilate the patient is determined prior to giving any muscle relaxant. If intubation is predicted to be extremely difficult, an awake intubation is carried out. This is rare in elective orthognathic surgery. Once the patient is asleep and it is determined that the patient can be manually ventilated, a nondepolarizing muscle relaxant such as rocuronium is given. The patient is ventilated until the muscle relaxant acts. Otrivin (p-xylometazoline hydrochloride) or 4% cocaine is sprayed into either one nasal passage or both, the latter if a nasogastric tube is to be inserted via the second nasal passage. The sprayed Otrivin or cocaine is flushed along the nasal passage by ventilating the patient with the anesthetic gases. Otrivin and cocaine produce vasoconstriction of the nasal mucosa and prevent bleeding during nasal intubation or passage of the nasogastric tube. Otrivin is preferred to cocaine because it does not cause a significant rise in blood pressure after instillation. Preferably, a nonkinking endotracheal tube, the end of which is lubricated with jelly, guided by a malleable stillete is inserted. Once the tip of the tube is in the pharynx, the stillete is removed. It must be noted that occasionally one may have to bend the stillete sharply to pass the tube through the nasal passage. If the tube is passed through the fiberoptic bronchoscope, then a stillete is not necessary. Once the tube is inserted, the position of the tube may be confirmed by connecting it to the breathing circuit via an end-tidal carbon dioxide probe and checking for the presence of carbon dioxide in the expired gases.

A nasogastric tube is inserted if the jaws are to be wired together. It is inserted prior to inflation of the cuff of the endotracheal tube since the latter interferes with the passage of the nasogastric tube. The nasogastric tube, usually 16 gauge, lubricated with jelly is passed either blindly or with the help of the Magill’s forceps through the other nasal passage into the stomach. The position of the nasogastric tube is checked by injecting air through the nasogastric tube and listening over the stomach for the sound of air bubbling through the gastric fluid. Once the nasogastric tube is in position, the cuff of the endotracheal tube is inflated. Both the endotracheal tube and the nasogastric tube are taped to the nose. Here one must be careful not to tape the tube tightly to the tip of the nose. It should be curved and preferably not touching the tip of the nose. Taping should ensure that the tube is not pulled back and pressing on the tip of the nose by surgeons who assist from the head end. The eyes are covered. Once the tube is fixed, using a Magill’s forceps, the throat is gently packed with ribbon gauze soaked in saline and wrung dry by hand. An arterial line is inserted in order to measure the accurately during hypotensive anesthesia.

Following insertion of an arterial line, the patient is disconnected from the breathing system and the monitors and is taken to the theater and transferred to a soft mattress on the operating table. Positioning of the patient is extremely important in orthognathic surgery. The head is extended. A reclining position is adopted with the head high. It is raised to about 10-15° from the horizontal. This position helps venous drainage from the operation site. Every further inch the head is raised from the heart, the blood pressure drops by 2 mm Hg. The reclining position helps the blood flow, and the soft mattress prevents excessive pressure to the skin of the back, preventing soreness and ulceration that may occur at the end of the operation. The patient is covered with a warm air blanket to maintain body temperature as near normal as possible. canadian pharmacy viagra

The ventilator and the monitoring devices are at the foot end of the patient. This gives enough room for the surgeons to move about at the head end. Anesthesia is maintained by ventilating the patient’s lungs with nitrous oxide oxygen and isoflurane, and an analgesic is given for analgesia. Fentanyl or alfentanil is given as an infusion since this reduces the stress response and prevents surges of blood pressure. Apart from the initial dose of the muscle relaxant, usually no incremental doses are needed during orthognathic surgery. The arterial blood pressure, ECG, pulse, oxygen saturation, end tidal carbon dioxide, temperature, inspired oxygen, and fluid balance are monitored continuously and recorded intermittently. If the operation is to exceed 5 hours, a urinary catheter is inserted and urine output is monitored. At the request of the surgeons, an antibiotic, usually penicillin or, if bone is to be harvested, a cephalosporin such as cephlexine, is given intravenously for antibiotic cover. Fluids are given, preferably through a blood warmer. The basic fluid requirement in orthognathic surgery is around 4 mlAg/h. The blood lost is usually replaced with three times the loss in crystalloids. If colloids are given, an equivalent amount to the loss is given. In measuring blood loss, it is important to take into consideration the enormous amounts of saline used to cool the burs. The saline bottles are weighed prior to use with burs and reweighed to calculate the loss when required. Thus, the blood loss should be calculated as follows: amount of blood loss = (fluid in the suction bottles + fluid from swab weighing) – (fluids used for irrigation, ie, what is used from the saline container on the nurse assistant’s tray + fluids used with the burs). Hemoglobin content of the blood is measured during the operation using a Hemocue hemoglobinometer and, if the hemoglobin concentration falls below 8 g/dL, a unit of packed cells is given.

In orthognathic surgery, oozing of blood occurs from the connective tissues and the bones. Sometimes this may be severe, obstructing the view of the operator. Thus, it is a type of surgery where induced hypotension is beneficial. Induced hypotension not only improves the surgical field but also reduces the blood loss. A head-up position of 10-15° definitely helps by aiding venous return.

In orthognathic surgery, the most common nerve effected is the trigeminal nerve, the stimulation of which results in activating the sympathetics in the medulla, which in turn stimulate the cardiac sympathetics, giving rise to tachycardia. Thus, the most common rhythm during orthognathic surgery is tachycardia. Therefore, the best drug for induced hypotension is a p blocker. However, the biggest problem with (3 blockers is that they may also produce bronchospasm. The incidence varies according to the selectivity of the drug. However, none are purely p selective.

The most common drugs used for hypotensive anesthesia during orthognathic surgery are labetolol and es-molol. In combination with isoflurane, they reduce the blood pressure to the required level. However, if the patient has a history of asthma, these hypotensive agents are avoided. In such cases, hypotension is carried out with posture and isoflurane. The time to start the hypotensive technique is the time at which the surgeon incises the mucosa. Maximum hypotension in young, healthy adults is limited to a mean arterial pressure (MAP) of 50 mm Hg. The pressure to which it is lowered depends on the surgical field and not the numerical value of the blood pressure. Since the aim of hypotension is to provide a relatively bloodless field for the surgeon, as soon as this is achieved, a further drop in blood pressure is avoided. Hypotension is carried out only during the period in which it is going to help the surgeon operate and is terminated when the plating of the os-teotomized segments has begun.

Usually patients scheduled for vertical subsigmoid osteotomy of the mandible have intermaxillary fixation or jaws wired together at the end of the operation. Though plating has reduced the incidence of intermaxillary fixations, still a surgeon may decide to have a patient in intermaxillary fixation at the end, if the osteotomized segments are unstable despite being fixed with plates. If a patient is to have intermaxillary fixation, the patient is given an antiemetic prior to the end of surgery. Further, before the wires are fixed, the surgeon sucks out the throat and removes the throat pack. buy cialis soft tabs

At the end of the operation, the patient is placed in a head-down position, the throat pack is removed in patients who are not on intermaxillary fixation, and the pharynx is suctioned. Once the patient begins to breathe, the patient is turned on the side and suctioned again. When on the side, there is always some bleeding since the blood accumulated in the nasal sinuses during maxillary osteotomies flows out. After suctioning, the patient is extubated and a nasal airway is inserted to facilitate breathing. Then the patient is transferred to a tilting trolley and is taken to the recovery room lying on the side and with head down. Oxygen is given through a ventimask and blood pressure, ECG, and oxygen saturation are monitored during the transfer.

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