END-STAGE CARE OF THE HUMAN CRYOPRESERVATION PATIENT
by Michael G. Darwin with Charles Platt
Copyright 1994 by Michael G. Darwin. All rights reserved.
Chapter 6: Standby and Transport Logistics
The first step in caring for a critically ill patient is to realize that he is in serious difficulty. This may not be easy, and seemingly inconsequential findings may presage disaster. The gravity of the situation may not be apparent even though there is serious malfunction of one or more systems. A subtle change in a physical sign could be the first indication of general collapse. It has been our personal experience that early warning signs are overlooked or dismissed unless the physician is ever aware of the possibility of serious trouble. There is a recurring tendency even after one has “learned his lesson,” to dismiss an abnormal finding by ascribing it to an unimportant cause. It is not enough to recognize that a physical sign could indicate serious difficulty. The weakest link inpatient care is the tendency of the physician to convince himself that somehow everything will be all right. Every clue must be sifted and analyzed. Every unexpected sign must be understood.
--Stephen M. Ayers, M.D. Care of the Critically Ill, Second Edition
The standard Local Standby Kit (LSK) contains two “E” cylinders of oxygen, capable of powering the Michigan Instruments Heart-Lung Resuscitator (HLR) for approximately thirty minutes. This will usually be sufficient to transport the patient via hearse or ambulance from the hospital or nursing home to a mortuary or other facility where extended external cooling and/or blood washout can be carried out.
Arrangements should be made with the cooperating mortuary (or, if legal death is occurring at home, with the home-hospice program) to provide at least two “H” oxygen cylinders, each of 220 cubic foot capacity, or larger. Always try to conserve E-cylinder oxygen for use when the patient is being moved by a vehicle. If the patient is initially hospitalized, try to use the hospital's oxygen supply while waiting for the mortician or ambulance. In most hospitals, you will find a wall outlet for oxygen in each room. To tap into this supply, you will need to obtain a special adapter or coupling from the respiratory therapy department of the hospital or carry an assortment of adapters for systems commonly in use in your country.
If a wall adapter has a flow restriction device such as a flow meter, it will not provide enough pressure to run the HLR. Only a wall oxygen connector with a DISS fitting (see figure 3-1) can be used.
If the hospital does not have or will not make available this type of fitting, you should ask for an H cylinder or other source of bottled oxygen. Alternatively, you can seek permission to bring a source of bottled oxygen in from outside. Please note that when you are moving an oxygen cylinder through the halls of a hospital, you must always mount it on a proper cylinder truck or hand cart. This is a safety requirement which is vigorously enforced in all hospitals. Once the cylinder is in the patient’s room, it must be secured to the wall or placed in an anti-tip base. Alternatively, if the cart is a four wheel type which allows the cylinder to rest stably at an angle, the cylinder may be left chained to the cart.
A word of caution is in order about getting prompt access to oxygen under emergency conditions in a strange city. Most locales now require a prescription for medical oxygen. You can safely substitute welding gas, but it is rarely available on a 24-hour basis. Therefore, you should always try to plan ahead and have oxygen ordered and delivered to the home or mortuary as soon as you hear that the patient is terminally ill--even if the patient is expected to survive for weeks or months.
Sometimes, of course, it is not possible to plan ahead, and transport technicians should know the procedure for calling in a prescription for oxygen, either as a physician or the agent for a physician. Unfortunately, cylinder oxygen is becoming increasingly hard to obtain on a 24-hour basis. The need for it has been diminished by widespread use of oxygen concentrators (which plug into the wall and make oxygen from room air) and liquid oxygen systems. In many cities and most small towns, rapid, 24-hour delivery of oxygen in cylinders is becoming a thing of the past. Consequently, it's even more critical to plan ahead to ensure a supply.
WARNING: Mortuary personnel are generally unfamiliar with the safe handling of oxygen. The transport technician will need to supervise loading, unloading, and handling of oxygen cylinders with great care. Remember always the risk of a CATASTROPHIC FIRE at the mortuary or en route to it. Within the confines of a vehicle, oxygen concentration can easily rise to a dangerous level. Consequently, you must warn mortuary or other personnel NOT TO SMOKE AS THEY MAY NORMALLY BE ACCUSTOMED TO DOING SO.
It's easy to forget this precaution when your prime concern is caring for the patient, but mortuary personnel frequently smoke and are especially inclined to do so at times of stress--such as moving a patient who is on HLR support. Remember, in a closed vehicle where there is a high concentration of oxygen, a lighted cigarette can almost guarantee a serious fire. Remember the Apollo fire!
Access To Ice
You will need 300 to 400 pounds of ice to cool the average160 pound (72 kg) man, plus another 200 pounds for shipping the patient. If the institution which has control of the patient does not have access to this amount of ice or will not make access available, you will have to get it from an outside source.
There are 24-hour ice services in most cities. After you obtain ice from an outside source, a mortuary may keep it for you in one of their freezers (if they have one), or a hospital may allow you to store it in one of their food freezers. Note that if the ice has melted at all along the way, refreezing it may turn it into a semisolid mass, and you'll need an ice pick or screwdriver to break it up.
If you are conducting a standby in the patient's home, you must arrange to have a large supply of ice on hand, or you must find a 24-hour source nearby. Convenience stores such as 7-11 can usually meet this need. If one of these stores is nearby, you may be able to delay buying ice until the patient becomes frankly agonal, so long as enough personnel are available to go out for ice when the time comes.
If there is no reliable source of ice nearby, and no freezer in which to stockpile it for quick access, good quality picnic chests can be used to store ice with relatively little melting. The Igloo brand, with foam-insulated lids, is recommended. You will need six 22-quart chests for an average standby.
Do not use inexpensive, “soft” expanded polystyrene picnic chests that are sold in drugstores and supermarkets. They will leak copiously and will not hold ice for long enough to be economical.
Arranging Prompt Release of the Patient
If the hospital has a staff mortician or diener (lab assistant) who is responsible for handling and processing remains in the morgue, you should contact this person and ask for his help. If you take care of this early on, you'll have a much better chance of obtaining prompt release of the patient. A staff mortician can significantly delay the release of the patient from the hospital if he feels that you have ignored him or treated his authority with insufficient respect.
Whenever possible, try to see that a death certificate is filled out in advance, leaving the lines blank for the cause of death and the signature of the pronouncing physician. If the patient is at home and the hospice is unable to provide round-the-clock nursing service, you will need to make special arrangements for quick pronouncement of death. This is generally done by having a registry nurse in attendance. You will definitely need to clear this with the hospice agency, and possibly with the coroner or medical examiner as well.
Securing a Private Room
If the patient is in an open ward or undivided Intensive Care Unit (ICU) and the institution seems cooperative, you should ask for transfer to a private room or cubicle (preferably near an exit) to minimize disruption and attract as little attention as possible during stabilization and removal. If the patient is unequivocally terminal, reassure the hospital that the cryonics organization (if it is their policy) will pay for the added expense of a private room.
Evaluating the Patient's Condition
Once the basic administrative and physical details outlined above have been dealt with, the team leader should see the patient and to ask to examine the chart. A general assessment of the patient should be made at this time, and the evaluation should be carefully recorded with proper notes.
Is the patient alert and oriented as to person, place, and time? Is the patient comatose? What is the patient's fluid status: edematous, dehydrated, in balance? Whenever possible, obtain a photocopy of the recent medical history and daily “graphic record” from the nursing staff or the attending physician. This may be difficult, and you may have to use the Patient's Directive and Power of Attorney. You should be concerned with the current status and status for the previous 24 hours of the following key items:
- Blood Pressure
- Neurological Status (see Table 1, Glasgow/Pittsburgh Coma Scale)
- Fluid Balance (pulmonary edema?)
- Hematological Status (bleeding or coagulopathies?)
- Laboratory Test Results
- Medications Currently Being Administered (or given during the previous 48 hours)
- Surgical/Diagnostic Procedures
- Unusual Findings
The patient's temperature and fluid balance are of primary importance, since they can profoundly affect the course and quality of resuscitation and stabilization. If a patient is markedly febrile (running a temperature), CPR will be even less effective at meeting metabolic demand than normal. Remember to note this on the transport records. Likewise, the presence of edema will affect the efficacy of CPR due to diminished lung gas-exchange surface area. Severe dehydration could mean inadequate circulating blood volume and thus inadequate blood pressure and tissue perfusion during CPR.
Predicting Cardiac Arrest
Once you have evaluated the patient's condition, you should try and establish a probable time of legal death. Is the patient likely to experience cardiac arrest in a few minutes, a few hours, or a few days? Your assessment will profoundly affect every aspect of the standby operation. Obviously, if the start of ischemia is only minutes away, you will need to summon essential support personnel (such as the cooperating mortician or ambulance service). You will also need to begin drawing up medications.
On the other hand, if the life expectancy seems likely to be numbered in days rather than minutes, your most immediate priority will be to determine where to situate yourself. I cannot overstate the importance of making a reasonably accurate assessment of when cardiac arrest is likely to occur. Typically, there will be only one set of transport medications available on-site for a local or remote standby. Once the medications have been drawn up, they must be used (even if promptly refrigerated) within no more than 24-48hours. If your estimate of the patient's condition is incorrect, you may find yourself lacking transport medications when they are needed.
The overall level of readiness may be even more important than the issue of when to draw up medications. There is almost no disaster more demoralizing (short of not being able to cryopreserve the patient at all) than being unprepared when the patient experiences cardiac arrest. Here again, assessing the patient with a reasonable degree of reliability is vital, particularly when essential transport personnel must be located off-site for any reason.
Unfortunately, a general assessment is rarely straightforward. Human beings are complex, and many factors will determine when this complex system fails. Nevertheless, there are a few useful guidelines. it should be noted that using these “markers” as predictors with any precision requires both skill and experience. Whenever possible, the transport technician should trust the judgment of those who have the greatest clinical experience. In particular, the nurses caring for the patient may be able to tell with a fair degree of accuracy when the patient will experience legal death. You should ask them for an assessment and give their estimations considerable weight.
Key Factors to Consider
There are two fundamental ways that a patient can experience cardiac arrest: acutely, as a result of very rapid destabilization (perhaps cardiac arrhythmia or hemorrhage), or slowly (perhaps as a result of decompensation and shock).The presence of arrhythmias--which can precipitate sudden cardiac arrest--can be disclosed by discussing the patient's condition with the nursing staff providing care. The range of cardiac conditions that can lead to sudden cardiac arrest is large, and a detailed discussion of the risk factors for sudden cardiac arrest is beyond the scope of this guide. Also, the presence of arrhythmias that are linked to sudden cardiac arrest is usually not going to be very useful in determining with any degree of precision when the patient is going to arrest.
Having said this, there a few specific guidelines that can be given. Some cardiac arrhythmias are a cause for concern only in the context of the patient's overall condition. For example, premature ventricular contractions (PVCs) may occur in a variety of disease states, especially following acute myocardial infarction. Depending upon their nature and frequency, they may or may not be serious. However, in a patient who is entering the agonal shock period, the appearance of PVCs should be great cause for concern. If the PVCs become frequent, occur in runs, or are accompanied by the R-on-T phenomenon, you should be alert for the possibility of impending cardiac arrest. Even if the patient does not arrest as a result of the arrhythmia, it may indicate that shock is deepening and that cardiac arrest maybe close.
One arrhythmia which demands serious attention is ventricular tachycardia (V-Tach). When it is observed in a terminal patient, this arrhythmia must always be viewed as a precursor to ventricular fibrillation and cardiac arrest. Treatment is normally (in a non-terminal patient) immediate and very aggressive, usually through a combination of drugs and cardioversion (electric shock delivered to the heart). When V-Tach is observed in a terminal cryopreservation patient, the transport technician should alert other team members (waking them if necessary), lay out medications, and take all other necessary steps to insure readiness. Since V-Tach can sometimes be sustained for hours, it is probably not wise to draw-up transport medications. However, if the V-Tach is associated with evidence of inadequate perfusion, such as a fall in blood pressure or alteration in consciousness, final preparation of transport medications should be undertaken.
Evaluating Tissue Perfusion
Shock is the pathway to all non-sudden cardiac arrest and the Transport Technician should understand its elements and the many ways in which it can present itself. Simply put, shock is inadequate blood flow or inadequate tissue perfusion as a result of decompensation or frank failure in one or more of the homeostatic mechanisms responsible for delivering blood flow to tissues. Shock can result from the following factors, individually or in combination: inadequate cardiac output secondary to a diseased or failing heart, inadequate distribution of a very large cardiac output, or insufficient blood volume for the heart to pump. In turn, the possible causes of pump failure or inadequate volume could be many. Hemorrhage may deplete circulating volume, and so may altered capillary permeability, which allows vascular fluids to leak out of the circulatory system and into the tissues. Whatever the cause, shock is the proximate cause of all slow death.
Low blood pressure is often, but not always, associated with shock. A patient who is in shock may have a centrally measured mean arterial pressure of 70 mm Hg, and yet have grossly inadequate perfusion of limbs and even core organs. The critical element is not pressure or even “flow,” but adequate perfusion. In septic shock, for instance, flows maybe very high and yet be inadequate. The point is that the patient has to be considered as a unit and in context, rather than on the basis of any isolated number. The assessment points given below are designed to help you to make that assessment. Beware, there is no “royal road” to achieving clinical skill in patient assessment.
Level of Consciousness
The patient's level of consciousness, considered with the patient's diagnosis and the other factors below, is one of the most valuable and easily evaluated indicators. The body will maintain cerebral perfusion as long as possible, often at the expense of other organ systems. Thus, when compromises in neurological function occur as a result of shock, they are often evidence of the final phase of decompensation. If the patient has been conscious and the level of consciousness deteriorates, it may be an ominous sign that cardiac arrest is approaching.
Similarly, changes in the patient's demeanor may be critical. Combativeness and hallucinations are two of the earliest signs of cerebral hypoperfusion and should be given considerable weight when you evaluate the likely time to cardiac arrest. In order to evaluate these changes objectively, you will need to interrogate the patient. Some guidelines are presented below. When performing an evaluation, always compare the left side of the body with the right and current responses with prior responses.
Assess Response to External Stimuli
- Degree of stimulus required to elicit a response
- Degree of response to the stimuli (use the Glasgow/Pittsburgh Coma Scale; see Table 3-1)
- Presence of weakness or loss of function
- Progression of deterioration
Assess Mental Status and Cognitive Function
- Short-term memory
- Long-term memory
- Orientation to person, place and time
Assess Motor Function
- Compare the left side with the right side
- Muscle strength, pushing or pulling against resistance
- Grip strength
- Motor speech--assess for motor aphasia
In patients who are obtunded or comatose, it is important to evaluate cranial nerve function. Deteriorating cranial nerve function should be considered a warning sign that cardia carrest is usually no more than four to six hours away.
Cranial Nerve Function
- Assess pupil reaction, size and shape. Pupils should be round and equal in size within 1-2 mm.
- Pupil reaction to bright light should be brisk. Shine alight in one eye and check for constriction of the pupil. Check the other eye, too. Through internuncial pathways, it should mimic the response of the eye that is exposed to light. This is known as a consensual response. Pupillary responses should be carefully documented during the agonal phase since failed pupillary reactivity is probably an indication of gross cerebral hypoperfusion or total ischemia.
The lower the combined total score of the two scales, the worse the patient's condition and the shorter the likely time interval to cardiac arrest. Maximum possible score: 30. Minimum possible score: 9.
At the end of this chapter you will find a worksheet to evaluate the patient using the Glasgow/Pittsburgh Coma Scale.
- Assess the corneal reflex by briefly and lightly touching the corneas with a piece of cotton or soft gauze. The eyes should close.
- Assess the blink reflex by touching the eyelashes lightly. The eyes should close.
- Assess the Babinski reflex by stroking the exposed skin of the sole of the foot. Moving upward from the heel, stroke the outer edge of the sole and then stroke across the ball of the foot. The toes should curl down in response. If the big toe moves upward toward the knee and the other toes flare out, the reflex is positive, which is abnormal in someone who has learned to walk and, during shock, may indicate cerebral hypoperfusion.
- Assess joint reflexes by tapping the limb with a reflex hammer to stretch the tendon. In a normal functioning state, the limb should move to shorten the tendon.
One of the first, most important, and easiest things to assess is the patient's circulation. Look for a bluish tint in the mucous membranes of the conjunctivae and the lips, indicating the presence of an increased amount of reduced hemoglobin (central cyanosis). An important caveat about cyanosis is that (as will be discussed in greater detail shortly in the section on pulse oximetry) cyanosis may not be evident even in the presence of marked hypoxia or shock if the patient's hemoglobin is 5g/dl or less. Symptoms which may accompany cyanosis (and/or hypoxia when cyanosis is not present, i.e. during severe anemia) are tachycardia (increased heart rate), tachypnea (increased breathing rate), and dyspnea (shortness of breath) and confusion and/or hostility or combativeness.
When a patient is agonal and the body is attempting to compensate for failure of one or more homeostatic mechanisms, circulation to the brain and core organs tends to be maintained at the expense of other areas. Usually, the body shunts blood flow away from organ systems which can tolerate periods of reduced or absent flow, such as the limbs, skin, and the gastrointestinal system. In such patients, the peripheral circulation usually becomes compromised in a very consistent fashion. As the more distal parts of the body (such as the lower extremities) begin to experience failed perfusion, you should notice pallor, cooling, and an increase in capillary refill time beyond two seconds. The nail beds will loose their normal pink color and become cyanotic, and the arms and legs will become cool to the touch.
When capillary refill times increase to four or more seconds, the limbs assume a mottled purplish appearance. In some cases there may even be signs of dependent lividity where blood in the limb, under the influence of gravity, settles into the most dependent part of the tissues. This is normally a postmortem change but it may also be seen inpatients with very protracted agonal courses; particularly in AIDS patients, the extremely elderly, and in patients dying of dehydration. If you notice these changes in a patient's circulation--particularly in conjunction with abnormalities in vital signs (low blood pressure or pulse),you should expect that cardiac arrest will occur within a few hours at most.
Primary vital signs are generally defined as blood pressure, pulse rate, and respiratory rate. In many situations, these signs may be a reliable guide to the agonal time course. Of course, the patient's underlying condition and status will also have considerable relevance. For instance, extreme tachycardia (elevated heart rate) will be tolerated far longer in a young marathon runner in shock after an accident than in an 86-year-old heart-attack victim. Still, there are certain vital signs which cannot be tolerated by any individual. A peak systolic blood pressure of 50 mm of mercury or less is seldom tolerated by the heart for more than an hour. Terminal patients (i.e., those in whom no resuscitation intervention is planned) with peak systolic pressures of 50 mm or less should be considered frankly agonal and in imminent danger of cardiac arrest. Sustained peak systolic pressures below 80 mm Hg should also be considered cause for concern, particularly in the presence of other abnormal vital signs (tachycardia, bradycardia, or Cheyne-Stokes respiration) or evidence of peripheral vascular shutdown. On the other hand, if a patient's systolic blood pressure is 70 mm Hg while the other vitals appear stable and central and peripheral perfusion are good, the low blood pressure is probably not predictive.
NOTE: Blood pressure readings are given as the systolic pressure over the diastolic pressure; for example, 120/70. A few adults may have very low normal blood pressure, even as low as 70 systolic. The difference between the patient's normal pressure and the current pressure may be more relevant than an absolute value.
It is very important to remember that for arterial pressure to be measured reliably, you need a central catheter rather than a cuff. Quite commonly, a cuff-measured pressure may be nonexistent or very low, while a reading of central arterial systolic pressure may be 80 or even 100 mm Hg.
Tachycardia and bradycardia are also indicators of impending cardiac arrest, particularly when considered in light of other vitals signs. Typically, heart rates higher than 150 to 175 bpm are not sustainable for more than a few hours. Heart rates over 120 bpm are cause for concern, particularly if the blood pressure is less than 100 mm Hg or other signs of decompensation such as peripheral vascular shutdown are present.
In the case of bradycardia, it must always be assessed in the context of the patient's overall condition. Some patients can tolerate heart rates in the range of 30 to 40bpm for extended periods of time, particularly if the bradycardia is a result of a conduction defect(s) and has developed over a long period. Alternatively, a patient in serious distress who is classified as “dying” and has a heart rate of 40 bpm (down from a normal or elevated heart rate) should be considered at high risk for imminent cardiac arrest.
The respiratory rate varies so widely, it cannot be used as an indicator by itself. However, Cheyne-Stokes syndrome (a respiratory pattern consisting of stepped, sonorous intakes of air; see Glossary for details) is a frankly agonal sign when coupled with other abnormalities in vitals. If it is present, the transport technician should prepare for cardiac arrest within 24 to 48 hours or less. Very low respiratory rates or respiration characterized by increasingly long periods of apnea (transient cessation of breathing) should also be considered prognostic of impending cardiac arrest. The “death rattle” is a fairly distinctive bubbling or gurgling respiration which results from a combination of impaired consciousness and mucous accumulation. This is a very reliable sign that cardiac arrest is near, although there are occasional exceptions. Finally, the presence of so-called classical shock, as indicated by hypotension (low blood pressure) with tachycardia and diaphoresis (sweating), should be considered a serious warning sign. If the patient's skin is cold and clammy, respirations are fast and shallow, and blood pressure is low, the patient can be considered in shock and not far from cardiac arrest.
Figure 6-4: Correlation of mean arterial pressure (MAP) and heart rate in a patient dying from dehydration and pulmonary insufficiency (secondary to end-stage adenocarcinoma of the lungs) with clinical signs and occurrence of cardiac arrest.
Urine Output/Fluid Status
Urine output is probably the second most important general indicator of the progression of shock. When a dying patient becomes oliguric (defined as less than 30 cc of urine output per hour) or anuric (no urine output), it is a sign that the kidneys are no longer receiving adequate blood flow and cardiac arrest can be expected within hours or, at the extreme, a day or two. Note that oliguria and anuria can only be assessed accurately and reliably if the patient has a bladder catheter.
Some moribund patients may have a naturally low urinary output, resulting in long periods (up to a day) between each instance of urination and the next. This should not be mistaken for anuria.
There are clinical laboratory tests and measurements which can help in assessing the time to cardiac arrest, but when a terminal patient is receiving orthodox treatment, these tests are seldom performed. If a patient still has some chance of recovery and is receiving acute care in an ICU or CCU, you are more likely to get useful data such as the following:Arterial Oxygen Tension: A paO2 (the concentration of oxygen in the blood) of less than 70 mm Hg in a patient breathing 100% oxygen on a ventilator is an indicator that cardiac arrest may be imminent.
Blood Lactate: Metabolic acidosis with elevated blood lactate levels (over1 mEq/dl) indicates inadequate perfusion.
pH: Blood pH of less than 7.25 (with normal pCO2 levels) isanother indication of terminal shock.
[insert tables and captions]
Table 3-2 gives normal and crisis values for blood gases and chemistries. Memorizing these values is essential for rapid assessment of a patient's status in a difficult emotionally stressful situation. The Transport Technician should commit these values to memory and review them frequently.
You should now understand that it's seldom easy to determine when a patient is going to experience cardiac arrest. Recently, a tool has come into use in the cryonics community which promises to objectify this process somewhat and provide a more reliable measure of when a patient is becoming frankly agonal by providing a very reliable indicator of the patient's overall perfusion status. This device is the pulse oximeter. It has a number of advantages over all of the assessment techniques described above. It is simple, accurate, noninvasive, painless, and easy to use, giving continuous information about a patient's pulse and perfusion status. The pulse oximeter consists of either two or three components: the oximeter module, a cable with sensor (which is applied to the patient), and if the unit is portable with internal, rechargeable batteries: it will have a separate power supply/charger!.
Figure 6-5: Pulse Oximeter: oximeter, photodetector, sensor placement.
The sensor contains two diodes emitting red and infrared light which is picked up by a photodetector after it has passed through human tissue. In some pulse oximeters, the detector is placed opposite the emitting diodes, with an earlobe or fingertip in between. In other units, the light is detected after it has penetrated tissue and reflected off internal bone, typically in the patient's forehead. Some units combine both modes of operation, to allow maximum flexibility of probe placement. This is especially important for cryonics purposes where poor perfusion may persist for many hours. In such cases, you should be able to use areas such as the bridge of the nose or the forehead, where perfusion usually persists until the very end.
Regardless of whether the unit uses transmittance, reflectance, or both, it works on the principle that oxygen content will alter the light-absorbing characteristics of hemoglobin in the arterial blood supply. Thus, the pulse oximeter provides a reliable guide to arterial oxygen saturation, at the same time that it monitors the patient's pulse.
Usually, there will be an alarm that can be preset to values for pulse rate and saturation selected by the operator. There will be another alarm preset to values which cannot be overridden.
In a terminally ill cryonics patient, assuming the patient and family are cooperative, pulse oximetry should be used as soon as possible and should be continued for as long as possible. There are no exceptions to this rule. Any patient who has been diagnosed as terminal is at increased risk of sudden cardiac arrest, and pulse oximetry enables a constant 24-hour vigil.
The importance of this cannot be overstated. Decompensation may occur suddenly, particularly in cases where the patient is elderly, has heart disease, has active or potential for active bleeding, or has chronic obstructive pulmonary disease (such as emphysema or pulmonary fibrosis). The emergency can easily occur when no one is around or when a sitter or registry nurse has fallen asleep.
Similarly, younger patients who are at risk of sudden decompensation, such as those with heart disease, arrhythmias, electrolyte imbalance, or risk of bleeding(such as patients with gastric or esophageal tumor involvement) must be continuously monitored to avoid cardiac arrest occurring without advanced warning.
Figure 6-6: Vital signs and pulse oximetery data in a 55-year old male AIDS patient. This patient was in peak physical condition 2-years prior to onset of his illness (runner/weightlifeter). Note the extended period of time which these reserves allowed the patient to tolerate poor perfusion.Pulse Oximetry Crisis Values
You should become more vigilant when oxygen saturation drops to 90% or below. If the patient becomes agitated or is moved, this may result in false low saturation readings. However, they may also signal the onset of cerebral hypoxia, and you should take great care to do a complete evaluation including a pulse oximetry reading.
As saturation declines below 80%, cardiac arrest is usually imminent (typically 24 hours or less), and changes in vital signs, mentation, and tissue perfusion will become more pronounced.
Setting Up and Troubleshooting the Pulse Oximeter
A variety of oximeters may be in use throughout the cryonics community in the coming years. For specific guidance, follow the manufacturers' instructions carefully. In general, however, the following guidelines should apply:
Check the cable and probe.
Clean the probe with alcohol as recommended by the manufacturer.
Change the site used for measurement every four to six hours as needed to reduce vasoconstriction and accompanying false “low” readings. (This will also reduce the chance of ischemic damage to the skin from compression by the probe or probe holder.)
If the room is brightly lit, there will be a risk of false readings. Guard against this by covering the site where the probe is applied in such situations.
Initially, if the patient finds forehead or earlobe monitoring uncomfortable or distressing, you can apply the probe to a finger or toe. As the perfusion status deteriorates, however, the patient's level of consciousness may diminish to the point where you can shift the probe to an ear lobe without causing undue distress. Ultimately, as even the ear lobe experiences diminished perfusion, the forehead or the bridge of the nose can be used.
Caveats on Pulse Oximetry
Perhaps the most important caveat to pulse oximetry is that it can only be effective if you use it. In fact, if you use the pulse oximeter inconsistently, this may create a false sense of confidence. Similarly, if the unit is not operating properly it constitutes a serious hazard. In the complete absence of pulse oximetry, other methods of monitoring the patient will be used; but this will not be the case if you are placing your trust in the monitoring equipment.
One final caveat is also in order. Pulse oximetry is not a reliable indicator of hypoxia or inadequate tissue perfusion in cases of severe anemia where the patient's hemoglobin is less than 8 g/100 ml. In such instances, hemoglobin oxygen saturation may be reported by the oximeter as adequate (as indeed it is), but the amount of hemoglobin available to deliver oxygen to the tissues is not adequate, and oximetry will not indicate the true state of affairs until very near the time of cardiac arrest (minutes to an hour). Thus, incases of severe anemia, you must use other methods in addition to pulse oximetery to assess the patient's perfusion status.
Similarly, in cases where the amount of abnormal hemoglobin (carboxyhemoglobin, methemoglobin or sulfhemoglobin) is greater than 3% to 4%, pulse oximetry will not be a reliable indicator. Increased bilirubin levels which occur in jaundice secondary to liver failure (a common occurrence in end-stage cardiac, cancer, and hepatic disease patients) can also cause false readings, indicating low saturation. Saturation may also be “falsely” depressed in cases of peripheral vascular disease or when vasoconstricting medication is being used.
Graph Your Data
Taking all the readings and gathering the data as outlined above is important and is the first step. However it is of only limited usefulness unless the data is presented in away that lets you spot trends. Thus it is very important that you graph data in real time. Heart rate, blood pressure (preferably as mean arterial pressure (MAP)) respiratory rate and mixed blood oxygen saturation should all be plotted graphically, preferably on the same sheet of graph paper. This will allow you to spot trends early and begin making preparations.
Study the graphics of the two patients' agonal vitals presented in this chapter. In both cases trends were important. In one case (patient A-1049) the trend of increased heart rate and steadily dropping blood pressure was highly predictive. This is almost a textbook case; when the patient's systolic blood pressure dropped below 50 mmHg she expired very shortly thereafter. Maintaining a graphic record can tip you off to the beginning of the final spiral of decompensation precious hours before you might have noticed it otherwise.
A Final Note
Generally, shock is not tolerable for more than a few hours, particularly in chronically ill and debilitated patients. You should rely on nursing staff to assess whether a patient is experiencing shock and how much time may remain until cardiac arrest.