A rare complication that may not be so rare
Blindness as a result of anesthesia administered during non-eye related surgery is, fortunately, a rare complication. It is not unheard of, however, and seems to be more common in cases involving lumbar surgery. Reports of this result are, in fact, increasing, either because of better reporting techniques or, more likely, because of the increasing frequency of longer, more complicated surgical procedures.[i] The American Society of Anesthesiologist has become sufficiently concerned about this phenomenon that it has established it own closed claims study. [ii] The complication is certainly being more widely reported and discussed.[iii]
Contrary to defense protestations, the fact that this complication is rare does not mean that it is inexplicable or that its cause is unknown. Rather, it is an indication that this complication is usually a result of a number of failings on the part of the anesthesiologist which rarely all occur in the same case. To handle one of these rare and unfortunate cases, the lawyer, and the experts involved, must be aware of these various factors and how they may interact to produce this tragic result.
Most surgeries, and most lumbar surgeries which result in vision loss, occur in the prone position. Anesthesiologists agree that the prone is one of the more difficult and risky positions in which to have a patient during surgery. The patient is more difficult to monitor and is not as accessible. In order to make the site of surgery available to the surgeon, the head and extremities are dependent, lower than the site of surgery and lower than the heart. As far as the eyes in particular are concerned, the anesthesiologist obviously simply cannot see them readily, as in other positions.
It is obvious and well known that the patient’s head and face must be cushioned and padded when in the prone position. Everyone agrees that meticulous care must be taken to be sure that no direct pressure is being applied to the eyes themselves, as direct pressure can be catastrophic. The dangers of pressure on the eyes have been recognized for at least half a century.[iv]
Once upon a time patients seem to have been positioned using mere bed pillows or blankets arranged and placed in such a fashion as to keep the eyes clear, but these days there are a number of headrests specially manufactured to support the face on the bones and obviate any pressure on the eyes themselves. These can be as elaborate as metal horseshoe shaped frames with padding or even metal cages that are screwed into the skull. The more common are thick pieces of foam with usually a T-shaped opening cut out across the eyes and down the nose. There are a number of manufacturers of these. These foam headrests are relatively inexpensive and disposable. Although not universal, a number of anesthesiologists use goggles in addition to the headrest which should avoid any possibility of pressure on the globes.
There is no FDA oversight or approval of these devices. Consequently, they may be designed by doctors or they may be designed by companies that provide operating room supplies. They are generally purchased by hospital purchasing agents with little or no input from the doctors who will actually use them. They do not come in different sizes and so these doctors are called upon to improvise if the patient is smaller or larger than can be accommodated by the headrest. Some come with an opening or cut-out for an endotracheal tube. Others do not. The hospitals do not seem to stock different kinds, so if any adjustment is to be made, it is usually made by the anesthesiologist or a CRNA with a pocketknife. Most of the time, however, with what appears to be a normal individual, no measurement or testing is made before the headrest is used. It is simply assumed that the headrest is the right size and that the opening will accommodate the facial features of the patient; it is placed on the operating table and the patient is placed face down.
Obviously, once the patient is face down, there is no way to readily visualize the manner in which the face is sitting in the headrest. Anesthesiologists and nurse anesthetists will describe how they manually mash the sides of the foam down periodically to try to gauge whether the patient’s eyes are free, but the truth is that there is no way to be absolutely sure unless there were a glass pane in the table and the person monitoring could look up from the bottom and see the eyes. There is no such device to my knowledge. So the anesthesiologist is left to estimate the position of the orbits by peeking at the edges.
If the patient has normal facial features and a good commercial headrest has been used, the patient is probably positioned properly at the beginning of the surgery and the eyes are clear of any pressure. What happens during surgery, however, particularly in back surgery where surgeons may be drilling, tapping, screwing or otherwise manipulating the patient, is that the patient can become twisted or turned slightly or, because of the head-dependent position, the body and face can shift so that the foam is pressing against the eyes. Unless the anesthesiologist is particularly vigilant, this can go unnoticed since, as stated, there is no way to readily see the eyes. The anesthesiologist is, we should remember, also monitoring a number of other things at the same time, as we shall see.
Direct pressure on the eyes for an extended period of time is known to cause blindness. This can be demonstrated readily by merely placing your fingers on the eyes and pressing. Once released, vision may take a second or two to come back. It is known that prolonged pressure will result in irreversible visual loss by inhibiting blood flow. Obviously, since experiments are not conducted on humans, the exact amount of time or degree of pressure is not known. However, studies in monkeys have documented visual loss after 60 minutes.[v] The mechanism is simple. The eye could be simplistically thought of as analogous to a balloon. When pressure is placed on the front of the eye, it becomes more difficult for fluid, primarily blood, to be pumped into the eye from the rear. Sufficient pressure for a sufficient period of time will prevent or retard the blood from circulating and hence decrease the oxygen being delivered to the eye and the optic nerve. Such pressure will most often result in a central retinal artery occlusion (CRAO), which gives rise to a tell-tale cherry red spot, which will be apparent on examination of the retina. This almost certainly indicates that there has been direct pressure on the eye. Blindness or visual loss caused by direct pressure is also more likely than that caused by any of the other factors we shall examine to be unilateral, or to differ from one eye to the other, since the eyes would rarely receive identical pressure.
It goes without saying that oxygen must be delivered to all parts of he body for their continued health and survival, and the way that oxygen is delivered is via the blood. Delivery of blood to the eye can be hampered by the presence of external pressure, as discussed above. It can also, or in combination, be the result of a lack of adequate blood pressure which results in insufficient blood, and hence oxygen, being carried to the eye.
Anesthesiologists agree that the goal during surgery is to maintain the blood pressure of the patient as near normal as possible. Of course, the anesthesiologist must first determine what this normal blood pressure is. The blood pressure of the patient is taken at the beginning of the case, when the monitors are first affixed and before any anesthetic agents have been administered, but it would certainly be expected that a patient’s blood pressure at the beginning of surgery might be heightened due to anxiety. In days gone by, patients were brought into the hospital the night before surgery. During this stay, blood pressure was taken several times to determine the patient’s average baseline resting blood pressure, even during sleep. These days, when, because of lack of insurance reimbursement, patients are not brought into the hospital the night before, but rather the morning of surgery, patients are most often brought to the hospital a day or two before the surgery so that their blood pressure can be taken to establish this baseline. Only one reading is taken and doctors will tell you that the patient can also be apprehensive at this time, in the hospital and contemplating surgery, and that this blood pressure reading might also be high. Doctors will complain that, because of lack of insurance reimbursement, they are only allowed to take one such blood pressure reading a day or two before surgery. An argument could be made however that, if the doctors really feel that several readings should be taken over a period of days in order to establish a true baseline, they should do this regardless of insurance reimbursement.
Nevertheless, through whatever method, the anesthesiologist will attempt to determine what the patient’s normal blood pressure is. The stated goal during surgery, then, is to approximate this normal blood pressure. A deviation of 10 to 15 percent below this baseline is probably acceptable, since this approximates the blood pressure of an individual during sleep. As the deviation widens, however, a serious lack of blood flow and, therefore, oxygen, to tissues can occur. It is generally accepted that any time the blood pressure falls below 20% of the baseline, steps should be taken to increase the blood pressure, unless, at the request of the surgeon, blood pressure is being kept intentionally low to minimize blood loss. If this technique is being used, which itself is controversial, it should discussed and the informed consent of the patient obtained beforehand. Certainly, the blood pressure should not be allowed to remain more than 20% below normal for an extended period of time, probably not as long as thirty minutes.[vi]
It is important to remember that we are talking about this individual patient’s baseline, not some average baseline for the general public. Many anesthesiologists seem to think that there is a general baseline for the population and that they are safe in any case as long as they do not let the patient’s blood pressure remain below some specified reading, such as 100/80, for an extended period of time. It is essential to note that it is not this average person’s blood pressure that matters; it is the normal blood pressure of this patient. Particularly if this patient normally has high blood pressure, his body is used to having high blood pressure and so the patient’s blood pressure during surgery must be maintained within the appropriate percentages of normal for that patient. It matters not that the patient’s blood pressure is being maintained within 20% of the average person’s blood pressure; that patient’s tissues are not receiving the amount of blood flow to which they are accustomed.
Blood loss is, of course, an inevitable part of surgery. Blood loss, by definition, lowers blood pressure, since when the volume of blood is decreased, there is less pressure within the circulatory system. The anesthesiologist will counteract this drop in fluid levels by administering replacement fluids. Normal saline, lactated ringers and chrystalloid solutions are all used to replace blood volume and support blood pressure. Blood products are also used to replace the blood that is lost. Some blood may be recovered from the patient during surgery with the use of a cellsaver device. The patient may have stored his or her own blood in anticipation of surgery and blood bank blood can be used, although this may be the last option due to concerns about disease transmission.
If blood is replaced with non-blood products, the blood pressure can be maintained, since the volume of fluid within the circulatory system is maintained, but since blood contains oxygen in the form of hemoglobin and non-blood replacements do not, this net blood loss translates into a net oxygen loss. In this instance, even though the blood pressure might be maintained at an acceptable level, the blood which is being carried to the tissues is deficient in oxygen and so tissue damage can still occur.
Another consequence of the replacement of blood with non-blood fluids is that these fluids can cause generalized swelling as these fluids are absorbed by the tissues. This generalized swelling can also make blood circulation difficult. As tissues swell, pressure results on arteries passing through this tissue, making it more difficult for the heart to pump blood and oxygen throughout the body. In addition, in areas such as the eye where blood vessels must travel through openings in the skull, a swelling of the tissue around that opening can constrict the blood vessels, to the point of inhibiting or even preventing blood from passing through these openings to the eye. The dependent position of the head during spine surgery in the prone position exacerbates the problem.[vii]
Still another difficulty of the prone position is the ventilation of the patient. Almost always the respiration of the patient is being controlled. An endotracheal tube has been placed and a ventilator is being used to breathe for the patient. This is necessary in most cases due to the anesthetized state of the patient and to keep the patient from moving, but it is particularly important when the patient is in the prone position since the patient is lying on his or her chest, making it difficult to breathe. The carbon dioxide level of the patient is monitored by sampling air expired by the patient during exhalations. This carbon dioxide level should not exceed 40. If it exceeds this level for any considerable period of time, it is an indication that the patient is not receiving enough oxygen. Obviously, the blood cannot carry oxygen to the body if the blood is not receiving sufficient oxygen from the outside. Hence this CO2 level must be monitored and not allowed to rise. If it increases significantly over 40, either the frequency of ventilation or the amount of oxygen being given to the patient must be increased.
Toward the end of the case, the patient is usually weaned off of the ventilator. Care should be taken not to do this too early when the patient is in the prone position since, as we have seen, the patient will have more than the normal difficulty breathing on his or her own and CO2 levels can rise dangerously.
The oxygen level in the blood can, of course, be monitored even more directly during surgery. In most cases, the blood pressure is being monitored by the use of an arterial line, a catheter which has been inserted in an artery. With this line in place, it is simple to draw blood samples and test the hemoglobin and hematocrit levels in the blood. It is important to maintain these levels so that adequate oxygen is present in the blood, even if blood must be given to the patient to do so. This, with the CO2 monitoring, can give a good picture of the level of oxygen which is being supplied to the tissues by the blood. Particularly in a long procedure, blood gases should be taken periodically and certainly when any unexplained rise in carbon dioxide is detected.
While any one of the above risk factors might not be sufficient to cause blindness or even vision loss in a patient, a combination of two or more can be deadly. Slight pressure on the eyes may not cause visual loss if not for a prolonged period. Even significant deviations from baseline blood pressure can be tolerated if not for a prolonged period. Blood loss may not result in a decrease in hemoglobin and hence oxygen levels sufficient to cause problems.
But low blood pressure for a continuing period of time, coupled with a decrease in oxygen levels in the blood during a prolonged surgery can cause damage to tissues, particularly those as susceptible to injury as the eye. If too much non-blood fluids are given, causing swelling and constriction of blood flow, the problem can be compounded.[viii] Then, even slight pressure on the eyes from outside can contribute greatly to a lack of perfusion in the eye and to the optic nerve. The result can be a condition known as posterior ischemic optic neuropathy, in short, an injury to the optic nerve behind the eye which results from a lack of oxygen.
Blindness following lumbar surgery is sufficiently common to be recognized as a known complication. It is not a freak, inexplicable occurrence or an act of God. The factors causing it are known and generally a combination of two or more of these factors must be present for damage to occur. For more than one of these factors to be present, the anesthesia care being provided to the patient must generally be sloppy and below the standard of care. The lawyer handling such a case and the experts employed must be able to look at all of the factors together to demonstrate how this tragic consequence occurred.