Use of the surgical intensive care unit in the preoperative preparation of the high-risk patient

Use of the Surgical Intensive Care Unit in the Preoperative Preparation of the High-Risk Patient Devendra N. Amin, MB, BS (UK), and Thomas J. Iberti, MD, FCCM, FCCP

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REOPERATIVE ADMISSION of a patient to the intensive care unit (ICU) is a relatively new concept. Although becoming a more common practice, many centers do not routinely admit high-risk patients to the ICU preoperatively due to the shortage of ICU nurses and beds and the added expense involved. Thus, at the present time, there are a paucity of studies indicating its clinical usefulness, effect on morbidity and mortality, or influence on length of hospital stay. Therefore, it is the purpose of this article to discuss what is currently practiced at the Mount Sinai Hospital Surgical ICU. This practice is based mostly on clinical experience, and, therefore, only general references will be cited. Hopefully, the subject of preoperative evaluation in the ICU will evolve with the advent of good prospective studies. The added expense and requirement of skilled personnel make it mandatory to clearly identify which patients will benefit from such admission in the future. GENERAL CONCEPTS

It is beyond the scope of this review to discuss the routine evaluation of the high-risk patient. However, it is important to note that the majority of this evaluation (except in the unstable patient) should be performed outside the ICU by the internist, surgeon, and anesthesiologist. Only after it is determined that the patient is a highrisk surgical candidate should the ICU team be consulted. The role of the ICU physician is not to determine who is a high-risk patient, but rather to attempt to reduce the risk of surgery in previously identified patients. On the other hand, the intensivist should actively participate with the patient’s primary physicians in the final determination of operative risk. Frequently, the evaluation in the ICU may add data that will necessitate cancellation or rescheduling of surgery. The need for good communication and a team approach to every preoperative patient cannot be overemphasized.‘*2 Only patients in whom active intervention or alteration in therapy (including volume loading) is planned should be considered for preop-

Journal of Cardiofhomcic Anesthesia,

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erative admission to the ICU. Of course, it is not always possible to clinically determine if therapy will be required, and these patients should be evaluated by the ICU physicians. Patients who will require intraoperative hemodynamic monitoring, but are hemodynamically stable and require no preoperative therapy, are managed by the anesthesiologist in the operating room. Certain patients are high surgical risks, but they do not have underlying disease that is likely to be improved or the risk reduced by preoperative admission to the ICU. Patients in this category include those with severe chronic pulmonary disease or chronic renal insufficiency.3-6 These patients rarely benefit from preoperative admission, and the risk of invasive procedures may outweigh any possible benefit. This risk-benefit ratio is an important part of any evaluation, but is especially important in preoperative ICU admissions. Therefore, prior to any invasive procedure or therapeutic preoperative intervention, a clearly defined goal or endpoint for such an intervention needs to be established. Some patients may benefit from preoperative admission to allow for the safe substitution of intravenous for oral therapy. Examples of such patients would be those with severe hypertension,’ angina,8 or asthma. Frequently, these patients only need the close observation that can be provided by an ICU nurse, and may not require additional preoperative monitoring unless difficulties arise. As mentioned previousry, there currently exist no data that such ICU admissions are beneficial, but future studies should determine From the Departments ofAnesthesiology and Surgery, The Mount Sinai Medical Center, New York, NY. Presented in part at the 27th Annual Bernard H. EliasbergMemorial Symposium, Mount Sinai Medical Center, New York, NY, November 4-5. 1989. Address reprint requests to Thomas J. Iberti, MD, FCC&I, FCCP, Director, Surgical Intensive Care Unit (Box 1062) Mount Sinai Medical Center, 1 Gustave Levy PI, New York, NY 10029-6574. 0 1990 by W.B. Saunders Company. 0888~6296/90/0404-1002$03.00/O

(August), 1990: pp 13- 18

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which, if any, patients should have such admissions to the ICU. RATIONAL USE OF ANY PREOPERATIVE INTERVENTION

Interventions made in an attempt to optimize the preoperative status of the cardiac patient (including fluid challenges, inotropes, and vasodilators) require the determination of vital signs, and collection of pulmonary artery catheter data (especially oxygen delivery/consumption) prior to the administration of the therapy and shortly afterward.’ This is done to establish if the cardiovascular therapy has had a positive, negative, or insignificant effect on the patient. This is best done by maintaining an accurate, timed flow sheet or computer trend of the data. Effective use of information from invasive monitoring can only be achieved if the information is accurate. Thus, strict attention to calibration, position, and technique is required. Despite what is frequently published, every medication, especially the inotropes, may have markedly different effects in different patients. If a therapy has no effect, or, especially if it produces a negative effect, it should be discontinued. Too frequently a medication or other preoperative therapy is used without determination of effect. If a beneficial effect has been achieved, then the objective should be to maintain the improved hemodynamics throughout the perioperative period. Finally, any patient admitted preoperatively to the ICU should receive full advantage of such an admission. This would include, in addition to the previously mentioned evaluation and treatment, a familiarization with the facility, orientation by the nursing and physician staff, a discussion of what to expect postoperatively, and answers to any questions. It is also important to meet with the family of each patient in order to discuss what they should expect postoperatively. The importance of such actions in reducing preoperative and postoperative anxiety is not known, WHEN TO ADMIT

This is again a question for which definitive data are lacking. It is the policy here to admit elective surgical patients the day prior to the scheduled surgery. There are several reasons for

this: (1) minimal bed availability; (2) limiting the number of hours of invasive monitoring to reduce the risk of possible catheter infection; and (3) most therapeutic interventions can be performed in this time period. To properly evaluate effects of therapy, at least 12 hours are usually required. However, quite commonly, the initial hemodynamic profile does not reflect the patient’s true baseline due to anxiety and stress, and a longer period of time may be required. If abnormalities are found and changes in therapy are required, this may require serial hemodynamic profiles. It is of limited or no use to admit most patients preoperatively to the ICU unless an adequate time for evaluation is allowed (a major exception to this is the patient with sepsis or septic shock, see below). For emergency surgical procedures, no clear-cut recommendations can be made. Trauma patients rarely, if ever, benefit from preoperative ICU evaluation, because this may result in serious delays. In the best circumstances, the evaluation of routine blood studies and arterial blood gases, as well as insertion of arterial and pulmonary artery catheters, take at least 1 hour. If changes are required, this obviously will lengthen the time in the ICU. This delay must be weighed against the urgency of the surgery. In general, except for trauma patients, it is believed that a 2- to 4-hour delay in order to stabilize the critically ill patient outweighs the risks. WHOM TO ADMIT

Certain types of patients appear to clearly benefit from preoperative ICU evaluation. These include patients with unstable angina,‘0-15 decompensated congestive heart failure,16 severe hypertension,’ renal insufficiency requiring dialysis,3 sepsis,‘7*‘9and aortic vascular disease.2@27 With other patients, such as hemodynamically stable patients with a recent myocardial infarction, or those with chronic ventricular dysrhythmias, the indication for preoperative ICU admission is less clear, and each case needs to be evaluated on an individual basis. Other cases, such as patients with a pheochromocytoma, subarachnoid hemorrhage, or morbid obesity may also warrant ICU admission. Currently, it is perhaps easier to identify

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patients who should not be admitted preoperatively. Examples include patients with malnutrition or stable geriatric patients. However, no absolute policy regarding any generalized patient profile should be established, and each request for ICU admission should be evaluated on an individual basis. NONCARDIAC SURGERY IN CARDIAC PATIENTS

The majority of preoperative admissions involve patients with cardiac disease.‘0-‘6 Four types of cardiovascular patients may require preoperative KU admission: (1) patients with unstable angina; (2) patients with a history of recent congestive heart failure; (3) patients with moderate to severe valvular disease; and (4) patients with a recent history of myocardial infarction. It is beyond the scope of this review to discuss the physiology and evaluation of these cardiac problems prior to KU admission. Although the pathophysiology of the cardiac disease of these four types of patients varies greatly, certain preoperative determinations and attempts to optimize each condition require similar predetermined goals. There is a need to individualize each patient, and not to use a “cookbook” for the preoperative preparation in the ICU. Despite attempts by numerous authors to establish an optimal range of cardiac output, filling pressures, etc, this should not be the goal of the preoperative admission. An active attempt should be made, using all available data, including those derived from pulmonary artery catheterization, to establish each patient’s oxygen demand, and whether it is being met by the oxygen delivery. Contrary to the maximization philosophy (attempting to achieve the highest possible cardiac output), it is a better approach to have the patient meet his/ her oxygen requirement using the least possible cardiac work. This approach, although controversial, is certainly consistent with the approach to all types of chronic heart diseases, including ischemic heart disease. With this approach, medications such as P-blockers, which decrease myocardial oxygen consumption and reduce stroke work, have been shown to improve postmyocardial infarction survival. It is clear that in the patient with cardiac

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disease, regardless of etiology, the pulmonary capillary wedge pressure (PCWP) has little relationship to the left ventricular end-diastolic volume, due to marked changes in compliance, or valvular disease.28 Similarly, cardiac output can be judged to be insufficient only when used in conjunction with other easily obtainable data. If the mixed venous oxygenation, lactate, and oxygen delivery/consumption are normal, then any cardiac output should be interpreted as adequate.29 As mentioned previously, attempting to maximize a cardiac output that is currently meeting oxygen demands will increase myocardial oxygen consumption and stroke work indices. It is the authors’ opinion that this is exactly opposite the goal of “optimizing” a cardiac patient. Similarly, in cardiac patients (and most other patients), an attempt should not be made to optimize urine output. Perhaps no other ICU tenet is as widely accepted as ensuring adequate urine output. This has some validity, in that prior to pulmonary artery catheterization and other determinations of systemic perfusion, the urine output served as a guide, although poor, of perfusion. While it can be said with some assurance that an adequate urine output probably indicates acceptable perfusion, the opposite is frequently not the case; namely, that a low urine output implies poor perfusion at that point in time. Oliguria, especially in the elderly patient with coexisting heart disease, may have its etiology, not due to low renal blood flow, but secondary to preexisting renal disease, sepsis, acute tubular necrosis, drugs, or other etiology. Readily obtainable data are needed preoperatively prior to “giving fluid” to treat oliguria, including basic kidney function tests, urine electrolytes, urine osmolarity, and pulmonary artery catheterization. From these studies, it is usually possible to determine if the oliguria is secondary to a low flow, volume depletion, or from another etiology unrelated to perfusion. The pulmonary artery catheter allows for a determination of systemic flow, but currently, no clinical method for determination of renal blood flow exists. Therefore, the pulmonary artery data may occasionally miss regional renal blood flow abnormalities while reflecting normal systemic perfusion.” Despite this, in 1990, oliguria per se should not be used as a

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determinant of systemic perfusion in the perioperative patient. VOLUME LOADING THE CARDIAC PATIENT

Fluid loading and optimization in the preoperative period (eg, elective aortic aneurysm repair) have to be tailored to each individual patient’s myocardial compliance characteristics. It is also important to be familiar with the characteristics of the fluid used for optimization. Crystalloids, such as normal saline or lactated Ringer’s solution, have a relatively short half-life within the intravascular space, whereas colloids, such as 5% albumin, can remain in the intravascular compartment for several hours. Close monitoring of the PCWP during the administration of fluid should alert the physician to the presence of a noncompliant ventricle, in which case a disproportionately large increase in the PCWP can be noted (>5 mm Hg). If this is observed, the fluid challenge should be stopped and hemodynamics observed. As with all other elective therapies, iatrogenic injuries should be avoided. Thus, it is never acceptable to push volume until signs of failure appear, then back off. Measurements of heart rate, respiration, PCWP, mean arterial pressure, cardiac output, and arterial and mixed venous blood gases are taken at regular intervals to determine the effect of the volume administered. It remains unclear as to exactly what is the best method to ensure an optimal preoperative cardiovascular condition. Previous studies concentrated on maximization of cardiac index; volume loading with a colloid and crystalloid solution until the maximum cardiac index was achieved for a given volume load or until a specified PCWP was reached (ie, 12 to 18 mm Hg).2’S22As mentioned, many patients undergoing major vascular or general surgery have some degree of left ventricular dysfunction. Maximization of cardiac performance in these patients can result in an unacceptable increase in myocardial oxygen consumption. Hence, a cardiac output that provides an adequate mixed venous oxygen tension is the desired endpoint, rather than the maximum cardiac output achievable. Therefore, in addition to following the cardiac index, it is important to also measure mixed venous oxygenation, oxygen delivery and consumption, as well as (when appropriate) blood lactate levels. A combination of car-

disc index and oxygen consumption relative to delivery gives a better picture of overall circulatory function. Increasing cardiac output beyond that necessary to meet oxygen demands should not be the goal of preoperative management. PREOPERATIVE SEPTIC SHOCK

Most preoperative evaluations are similar to that reviewed previously for the cardiac patient, or involve volume loading. However, the emergency patient in septic shock is much different. Despite the apparent urgency to have the patient in septic shock undergo surgery (eg, perforated viscous, abdominal abscess, peritonitis), this patient should have surgery temporarily delayed until hemodynamics, perfusion, and acid-base status are corrected.16-‘9S29It is simplistic to believe that delaying surgery for 1 to 2 hours will necessarily worsen outcome, especially when many of the actions of the bacterial endotoxin cascade have already been manifested. The goal in these patients should be to insure a safe operative course, and limit further end-organ damage that may be caused by hypoperfusion, acidosis, or hypoxemia, and result in multisystem organ failure. This type of patient should be emergently admitted to the ICU, intubated and hyperventilated (to help correct the usual metabolic acidosis), and have arterial and pulmonary arterial catheters placed. Fluid therapy is critical in the initial treatment/resuscitation of septic shock; however, it is not necessary to administer 8 to 10 L of volume, as is commonly advocated. There are several reasons for this: (1) most septic shock patients arriving in the ICU have already been given large amounts of volume by the emergency department staph (2) septic patients, especially those who are elderly, have noncompliant ventricles and cannot tolerate large volumes without serious cardiopulmonary compromise; (3) massive edemalanasarca may worsen oxygen dynamics; and (4) few studies have demonstrated a beneficial effect from massive volume loading. Although this approach of “limiting” volume may be viewed as radically different from most recommended approaches, it should be noted that the mortality of septic shock patients (approximately 50%) has not changed in the last 20 years.

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As with other therapy, fluid should be given until no further demonstrable benefit can be established by further administration (ie, reduction in blood lactate, improvement in metabolic acidosis, or improvement in oxygen consumptiondelivery ratio). Trends in blood lactate levels, combined with oxygen delivery/consumption and mixed venous oxygenation values, are the best ways to determine adequacy of systemic perfusion. Goals of septic shock resuscitation should include optimization of perfusion with judicious use of volume, inotropes, and blood, and correction of dangerous acid-base and electrolyte disturbances. Close interpretation and monitoring of blood lactate, mixed venous oxygenation, and oxygen delivery and consumption allow for evaluation of the effectiveness of interventions. Frequently, these patients may have respiratory compromise due to metabolic acidosis, or a primary pulmonary process. These patients are rou-

tinely intubated and ventilated, even if oxygenation and ventilation are adequate, in order to reduce the work of breathing (up to 20% of the cardiac output may go to the muscles of respiration in respiratory distress), and to further use a reduction in PC02 to increase serum pH. Bicarbonate infusions are not usually used to treat acidosis in septic patients. If, despite resuscitation, the septic patient remains markedly hypotensive, acidotic, and hyperlactatemic, surgical intervention will invariably be hopeless. CONCLUSION

The use of the ICU for preoperative admission of the high-risk surgical patient is an evolving area. With the advent of more major surgical procedures in high-risk patients, this type of admission will probably increase. Future studies are needed to more clearly delineate those patients who will benefit from such admissions.

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