Use of peripheral temperature as a guide to post-operative circulating adequacy.
Various monitors are used to judge the circulatory status of a post-operative patient to detect and treat the imbalance in the circulatory status at the earliest. It is well-known that a patient who is cold and clammy is in a poor circulatory status but coldness is subjective and does not quantitate the circulatory failure. We, therefore, decided to find out whether any meaningful relationship exists between the peripheral temperature and the circulatory status of the patient.
An attempt has been made in this study to evaluate the role of peripheral temperature monitoring with other parameters such as blood pressure, central venous pressure and urine output to diagnose and treat the circulatory impairment in the post-operative period. We have selected a group of patients undergoing major cardiothoracic operations as these are the ones in whom maximum circulatory disturbances are likely to occur in the post-operative period.
One hundred and twenty-five patients undergoing major cardiothoracic surgery comprise the material for the present study. There were 75 (60%) males and 50 (40%) females in the group. Fifteen patients (12%) were below 10 years of age, 80 (64%) were between 10 and 20 years and 30 (24%) were above 30 years of age.
The youngest patient was 4 months old while the oldest was 65 years of age.
Recording of temperature
Skin temperature was monitored by applying a special probe to the great toe, while simultaneously, rectal probe recorded the core temperature. These probes were connected to a thermocouple unit which gave instantaneous accurate reading of temperature in centigrades.
This study was carried out in cardiac post-operative intensive care unit where room temperature was stabilised to around 270C most of the time. A control study of variations of peripheral temperature in normal individuals was carried out; however, it is not presented here. In our opinion the relative variation between the core temperature and the peripheral temperature is of great significance than its comparison with the normal values.
Effects of drugs, mainly isoprenaline and adrenaline, were also taken into account. Decisions to discontinue, re-institute or accelerate these drugs were taken mainly on the basis of peripheral temperature.
Apart from the peripheral and core temperatures other vital signs such as blood pressure, central venous pressure and respiratory rate, were monitored and charted at regular intervals. Specially made charts were used to record these observations. A quick glance at these charts enabled the clinician to visualise the progress or deterioration in the general condition of the patient.
[Table - 1] depicts the various types of surgical procedures employed in our 125 patients in whom toe temperature was monitored.
Peripheral temperature gave an early indication of low cardiac output status. Thirty-six out of 125 patients in our series required support of ionotropic drugs like adrenaline and isoprenaline. Timely administration of ionotropic drugs improved the general condition of patients rapidly which was also obvious by the rise in peripheral temperature. Normalisation of other parameters followed the peripheral temperature. Twenty-five patients in this series died giving a mortality of 20 per cent. Out of these 25 patients, external temperature of 21 patients remained low inspite of all supportive drugs. In the remaining 4, the external temperature did not give us any indication of severity of the patients' condition. Toe temperature monitoring helped us to diagnose cardiac tamponade in two cases earlier than we would have done otherwise.
charts [Fig. 1], [Fig. 2], [Fig. 3] ,[Fig. 4]
[Fig. 1]. shows an uneventful recovery following ASD closure. There was no significant difference between the core and peripheral temperature recordings.
[Fig. 2.] is a tracing of a patient operated for mitral valve replacement who had low peripheral temperature with normal rectal temperature while shifting to recovery ward. Isoprenaline was started inspite of the fact that other parameters remained relatively normal. Quick response was seen by a rise in the peripheral temperature and increase in the urine output. Isoprenaline was discontinued slowly after peripheral temperature and adequate urine output were maintained. The patient had an uneventful recovery.
[Fig. 3] shows the tracings of a case of aortic valve replacement. Low cardiac output as suggested by the fall in the peripheral temperature was treated with isoprenaline. Excessive drainage gave a clue to cardiac tamponade and the patient was explored. It is interesting to note that the usual teaching of rise in C.V.P. in cardiac tamponade need not be true in all cases. Improvement in the peripheral temperature after relief of cardiac tamponade is characteristic.
[Fig. 4] is a tracing of a 6 year old boy on whom total correction of Fallot's tetralogy was done. Peripheral temperature remained low throughout inspite of all measures. After 10 hours of operation, the patient expired.
The routine methods of cardiovascular monitoring, though found useful in determining the general condition of the patient, are often found to be inadequate to predict the prognosis of a patient. Also these monitors allow significant time lag to institute preventive measures if general condition of the patient deteriorates. Blood pressure is the easiest and most popular monitor. However, it is by no means a correct indicator of tissue perfusion. It is well known that the blood pressure is maintained near normal in early stages of shock by peripheral vasoconstriction. Blood pressure recording in infants is often difficult, particularly if the child is tending to go in shock. Though central venous pressure was thought to be a very reliable guide, it has its own pitfalls. It does not give any idea of left ventricular function. Urine output, if monitored continuously, is a good index of tissue perfusion. Urinary excretion of 0.5 ml/hour/kg of body weight is considered to be satisfactory. However, patients undergoing open heart surgery are often taken on cardiopulmonary bypass with a bloodless prime. These patients often have satisfactory urine output even though myocardial function is inadequate. Skin and core temperature can be measured without much discomfort to the patient. These can give a quick idea about inadequate peripheral circulation and allow the medical team to take appropriate measures before the condition becomes irreversible. The figures shown in this presentation demonstrate the effectiveness of this technique.
Joly and Weil, in 1969, have used temperature of the great toe as an indication of the severity of shock since the measurement of great toe temperature is not significantly affected by the patient's movement. Toe temperature can be measured without reference to the patient's mental status. Finger temperature is not a good guide especially when the patient rubs his finger against bed. Authors have shown that a significant correlation exists between the cardiac output and the toe temperature. They have also been able to predict the prognosis in about 67% by early measurement of toe temperature. Toe temperature is a reliable indicator of cardiac output and indirectly an indicator of systemic blood flow in terms of tissue perfusion. In addition to aiding in the assessment of blood flow, toe temperature permits a helpful indication of prognosis. If toe temperature, 3 hours after admission is less than 270C or the difference between the toe and the ambient temperatures is less than 20, the prognosis is not good. Increase in the skin temperature is likely to improve with satisfactory cardiac output.
Seki et al, in 1974, have studied the regional changes of skin temperature in the leg after open heart surgery. They have measured the skin temperature at patella, mid-anterior aspect of the ankle and the sole of the big toe. The difference in the patellar and ankle temperature was an accurate indicator of prognosis. A large percentage of patients with a positive difference survived while others with a negative difference died. A correlation of cardiac index to the skin temperature was best on the first postoperative day.
Thus, toe temperature provides an objective information not only in patients with shock but also on the post-operative circulatory adequacy. With minor investment in instrumentation it is a valuable addition for clinical monitoring. It is a reliable, non-invasive and relatively cheap monitor in any intensive care area. The only disadvantage of this method is the inability to foresee dysrrhythmias. A sudden death following an episode of cardiac arrhythmia in an otherwise stable patient does not allow sufficient time for the peripheral temperature to fall. This was the cause in four patients in whom peripheral temperature had failed to give a slightest idea about poor prognosis.
Thanks are due to the K.E.M. Hospital and Seth G.S. Medical College Research Society and the Dean, K.E.M. Hospital and Seth G.S. Medical College, Bombay, for permitting us to report the data.