27: Intravenous Sedation: Complications

chapter 27 Intravenous Sedation: Complications

A number of complications may occur when the intravenous (IV) route of drug administration is used. Fortunately, most are relatively benign and easily managed. Others, however, are more significant and can lead to serious morbidity or death.

The complications associated with IV drug administration are divided into four groups: (1) those associated with venipuncture, (2) localized complications related to drug administration, (3) general drug-related problems, and (4) drug-specific complications. These are outlined in Box 27-1.


Nonrunning Intravenous Infusion

One of the most common and vexing complications of venipuncture and IV drug administration is the nonrunning or very slowly running IV infusion. Once venipuncture has been successfully completed (e.g., blood returning into the tubing), the tourniquet is removed and the IV drip started. During drug administration, the drip rate should be increased; at other times, the rate should be slowed. The causes of a nonrunning or slowly running IV infusion follow.

Bevel of Needle Against Wall of Vein

It was recommended that the bevel of the needle be facing upward during venipuncture to allow entry through the skin to be as atraumatic as possible. Following entry into the skin, the needle is advanced into the vein with blood returning into the tubing a sign of a successful venipuncture. At this point, the tourniquet is removed and the infusion started. If the IV drip rate that is flowing rapidly until the scalp vein or metal needle is taped into position is noted to slow considerably, it is quite possible that in taping the needle into position, the bevel of the needle was lifted and now lies against the wall of the vein. This will restrict or prevent the flow of fluid from the IV drip into the patient.

To determine whether this is the cause of a slow or nonrunning drip, the needle is carefully untaped and the wings of the butterfly needle gently lifted. This lowers the bevel of the needle off the wall of the vein. If the drip rate increases, the protective cap from the scalp vein needle (Figure 27-2) or a 2 × 2-inch gauze square is carefully placed under the wings of the needle and the needle retaped.

This is not likely to occur when an indwelling catheter is used for venipuncture because there is no bevel on the catheter. However, when a catheter is positioned in either the dorsum of the hand or antecubital fossa, it is possible for the tip of the catheter to lie in a bend in the vein, creating a slow flow of IV solution (Figure 27-3). Determine this by straightening the patient’s wrist or elbow and looking for an increase in the rate of flow of the IV drip. This may be minimized by preventing the patient from bending the joint through the use of an elbow immobilizer or wrist board.


Following successful entry into the vein, the metal needle somehow becomes dislodged while being secured. The dentist or assistant, unaware of this, opens the rate knob, but little or no solution flows. If no solution is flowing, the three causes of nonrunning IVs previously discussed should be considered. If the drip rate is extremely slow and cannot be increased, one should first look at the site where the needle tip is located beneath the patient’s skin. If the needle tip has left the vein and fluid is still flowing, a small colorless swelling will develop at this site. This is termed an infiltration.

In all cases in which an IV drip that was previously running well has either slowed or stopped entirely, the needle should not be removed from the vein until it has been determined definitively that the needle tip is no longer within the vein. The following procedure should be followed to determine the cause of the slow or nonrunning IV drip:


Venospasm is a protective mechanism in which the vein wall reacts to stimulation from the needle by going into spasm. As the needle approaches, the vein appears to disappear or “collapse.” Venospasm is occasionally accompanied by a burning sensation in the immediate area. This burning sensation ends without treatment as venospasm resolves. Venospasm may occur before or after entry of the needle into the vein, securing of the catheter or needle, or starting of the IV drip.


Hematoma is the most common complication associated with venipuncture. It represents the extravasation of blood into interstitial spaces surrounding a blood vessel. The presence of blood in this space leads to localized swelling and discoloration.

When venipuncture is successful, the needle itself acts as an obturator, sealing the hole in the vein wall made during entry of the needle. In some patients, particularly older patients in whom vein walls are less elastic, leakage of blood around the needle may occur during the IV procedure even though the needle tip still lies within the lumen of the vein.

Hematoma may occur at two distinct times during the IV procedure. First, it may develop during attempted venipuncture if the vessel wall is damaged. This is not always preventable. The second cause of hematoma is usually preventable. In this situation, the IV procedure has been completed and the catheter or needle removed from the vein. Improper application of pressure or inadequate duration of pressure at the venipuncture site can result in a hematoma.


Infiltration is similar to a hematoma in that a fluid is deposited into the tissues surrounding the blood vessel. A hematoma is the infiltration of blood outside of a blood vessel. Extravascular injection of a drug is the infiltration of drug outside of the blood vessel. Infiltration is defined as a painless, colorless swelling that develops at the site of the needle (cannula) tip when the IV infusion is started.

In this situation, we are discussing the deposition of the IV infusate into the tissues surrounding the blood vessel. The infiltration discussed here differs from hematoma in that the swelling that develops does not occur until the IV drip is turned on, whereas the hematoma occurs as soon as the vein wall is damaged.

In the continuous IV infusion technique, when infiltration does occur, it only consists of a solution, such as 5% dextrose and water or normal saline, that does not produce any degree of tissue irritation or damage. In contrast, in IV techniques in which the drug is injected directly into a blood vessel, it is much more likely that the drug will produce tissue damage and/or a delayed onset of sedation if deposited outside the blood vessel.

Air Embolism

Air embolism is a possible, although extremely unlikely, complication of IV sedation. It is best prevented by using a technique that is free of air: eliminating air bubbles from syringes and from the IV tubing before the procedure and periodically observing the IV infusion bag to prevent it from emptying.

In the highly likely event that one or more small bubbles of air enter into the venous circulation, they will be absorbed by the blood quite rapidly with no clinical sequelae. It is not always possible for all air bubbles to be removed from the IV tubing or syringes, and it is quite probable that small bubbles may enter into the venous circulation of the patient. The patient, noticing the air bubble moving slowly down the IV tubing toward his or her arm, may become quite anxious, believing (from television or movies) that as little as one bubble of air is lethal. Fortunately, this is not so. A rule of thumb in a hospital environment is that a patient can tolerate up to 1 ml/kg of body weight of air in the peripheral venous circulation without adverse effect.1

The typical IV administration set can hold approximately 13 ml of air.2 Because 10 drops of solution (or air) equals 1 ml (adult infusion set), the chances of introducing large volumes of air into the patient’s circulation are extraordinarily low. A 50-kg (110-lb) patient can tolerate 50 ml of air. This is equivalent to 500 to 750 drops of air from an adult IV administration set (10 or 15 drops/ml).

In small children, air embolism is a more significant problem because their bodies cannot tolerate large volumes of air. A 13 kg (30-lb) child is at greater risk of this complication than is a larger patient.


Overhydration of the patient is another not very common problem associated with IV procedures in the dental office. The two most likely candidates for overhydration, however, are children and patients with heart failure. Signs of overhydration include pulmonary edema, respiratory distress, and an increase in heart rate and blood pressure. These are also the signs and symptoms occasionally noted in a patient with acute pulmonary edema.

A rule of thumb for replacement of fluid in a patient is that the initial dose of IV solution administered is equal to 1.5 times the number of hours a patient has gone without food times the patient’s weight in kilograms.3 This is the volume of fluid in milliliters required to replace the fluid deficit created by the patient’s taking nothing by mouth (NPO) before the procedure. If a patient has been NPO for 6 hours before coming to the office, the initial volume of IV solution administered is nine times the patient’s body weight in kilograms. The maintenance dose of IV solution is 3 ml/kg. The problem of underhydration is not significant in the usual outpatient environment.

When IV drugs are administered to pediatric patients, it is recommended that a pediatric infusion set be used. This set, which permits 60 drops/ml instead of the usual 10 or 15, allows for the more precise administration of fluids to the younger, smaller patient or to the adult with more serious heart failure. In many instances, these two classes of patients are not candidates for elective IV moderate sedation in the outpatient dental setting.


Extravascular Drug Administration

When a drug is injected into subcutaneous tissues instead of the blood vessel, three problems may develop:

Pain associated with extravascular drug administration occurs at the site of the needle tip under the skin and tends to remain localized to that area. This distinguishes extravascular injection from IA and IV injections, where a burning sensation radiates either peripherally or centrally. The patient will complain of discomfort as the drug is injected in all three situations.

A potentially greater problem (depending upon the drug and the dosage) is delayed absorption of the drug into the cardiovascular system, especially if larger volumes have been deposited into the tissues. In essence, the drug has been administered subcutaneously instead of intravenously. Uptake of the drug is slow, with an onset of clinical activity occurring anywhere from about 10 to 30 minutes later.

A third problem that might arise is damage to the tissues into which the drug has been deposited. Some drugs used intravenously are potentially irritating to tissues. This is especially true for diazepam and, when it was more commonly used, pentobarbital. The initial response of the tissues is arteriolar and capillary constriction, which decrease the blood supply to the area. If vascular constriction is prolonged or if the chemical is irritating enough, necrosis and sloughing of tissue may occur.


There are two causes of extravascular drug administration. The first is the needle or cannula slipping out of the vein. This usually leads to an immediate formation of a hematoma that is quickly recognized. No drug is usually injected at this time. The second cause is the needle entering the vein and then being pushed through the other side as the dentist attempts to advance it farther into the vein. Blood will have returned into the tubing as the needle entered the vein originally, thereby giving the (false) impression that the needle or catheter tip remains in the vein. However, with removal of the tourniquet, it is unlikely that the blood will leave the tubing, as normally occurs, because the tip of the needle no longer lies in the vein but in subcutaneous tissue. On very rare occasions, the blood will leave the IV tubing and reenter the patient allowing the IV infusion to run even though the needle tip is no longer in the vein. This will occur when the bag of IV solution is quite high above the patient’s heart or if the patient’s skin and underlying soft tissues are not “firm,” allowing gravity to force the solution into the tissues. The latter is seen more often in older, more frail patients.

Use of a continuous IV drip technique really minimizes the possibility of extravascular injection of the drug because an infiltration of infusate produces an immediate swelling. Second, before administration of any drug, it is recommended that patency of the vein be reconfirmed by squeezing the flash bulb or holding the IV bag below the level of the patient’s heart. Despite these precautions, a subtle movement of a patient’s wrist or elbow just after this check but just before drug administration can produce this complication if a rigid metal needle is used. The administration of a 0.2-ml test dose of a drug is a means of detecting this complication before a larger, potentially more damaging bolus of drug is deposited.

Jan 5, 2015 | Posted by in General Dentistry | Comments Off on 27: Intravenous Sedation: Complications
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