Temperature gradients and rewarming time during hypothermic cardiopulmonary bypass with and without pulsatile flow

Pulsatile Versus Nonpulsatile Cardiopulmonary Bypass Flow: An Evidence-Based Approach

OBJECTIVE

To derive evidence-based recommendations for the use of pulsatile perfusion (PP) technique for the reduction of mortality and nonfatal complications after elective coronary artery bypass grafting surgery (CABG).

OUTCOMES

Incidence of total mortality, myocardial infarction (MI), stroke, and renal failure during hospital stay.

EVIDENCE

Medline, Embase, and the Cochrane controlled trial register (CCTR) on the Cochrane library were searched from the earliest achievable date of each database to March 2005. No language restrictions were applied. Retrieved reprints were evaluated according to a priori inclusion criteria, and those included were critically appraised using established internal validity criteria. BENEFITS AND HARMS: Only one fair quality randomized controlled trial demonstrated the beneficial effect of PP in reducing the incidence of total mortality and MI. No studies demonstrated the beneficial effect of PP in reducing the incidence of stoke or renal failure. One randomized controlled trial demonstrated that PP was associated with increased hemolysis compared to nonpulsatile (NP) perfusion.

CONCLUSION

The evidence is conflicting and therefore does not support making recommendation for or against routinely providing the PP to reduce the incidence of mortality or MI. The evidence is insufficient to recommend for or against routinely providing the pulsatile profusion to reduce the incidence of stroke or renal failure.

Thermal energy balance as a measure of adequate rewarming from hypothermic cardiopulmonary bypass

OBJECTIVE

To determine whether the amount of heat (thermal energy) used actively to rewarm patients on cardiopulmonary bypass (CPB) was a better indicator of adequate rewarming from hypothermic CPB than core temperature.

DESIGN

Prospective study.

SETTING

Single hospital.

PARTICIPANTS

Fifty-four sequential patients undergoing hypothermic CPB.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Thermal energy balance (TEB) (net heat supplied to or removed from the body, from initiation to termination of CPB) was measured using previously validated apparatus. Adequacy of rewarming was assessed by measuring the coldest postoperative core (tympanic membrane) temperature and the time to rewarm postoperatively to a core temperature of 37.0 degrees C. Core temperature on termination of CPB did not correlate with the degree of postoperative hypothermia as judged by time to rewarm postoperatively to 37.0 degrees C (r = 0.14; p = 0.33), but did correlate with coldest postoperative core temperature (r = 0.47; p = 0.0003). TEB correlated better with time to rewarm to 37.0 degrees C (r = 0.43; p = 0.001) and coldest postoperative core temperature (r = 0.58, p = 0.0001).

CONCLUSION

TEB is a better predictor than corresponding values of core temperature on termination of CPB in predicting the coldest postoperative temperature and time to rewarm to 37 degrees C.

Tissue heat content and distribution during and after cardiopulmonary bypass at 17 degrees C

We measured afterdrop and peripheral tissue temperature distribution in eight patients cooled to approximately 17 degrees C during cardiopulmonary bypass and subsequently rewarmed to 36.5 degrees C. A nasopharyngeal probe evaluated trunk and head temperature and heat content. Peripheral tissue temperature (arm and leg temperature) and heat content were estimated using fourth-order regressions and integration over volume from 30 tissue and skin temperatures. Peripheral tissue temperature decreased to 19.7+/-0.9 degrees C during bypass and subsequently increased to 34.3+/-0.7 degrees C during 104+/-18 min of rewarming. The core-to-peripheral tissue temperature gradient was -5.9+/-0.9 degrees C at the end of cooling and 4.7+/-1.5 degrees C at the end of rewarming. The core-temperature afterdrop was 2.2+/-0.4 degrees C and lasted 89+/-15 min. It was associated with 1.1+/-0.7 degrees C peripheral warming. At the end of cooling, temperatures at the center of the upper and lower thigh were (respectively) 8.0+/-5.2 degrees C and 7.3+/-4.2 degrees C cooler than skin temperature. On completion of rewarming, tissue at the center of the upper and lower thigh were (respectively) 7.0+/-2.2 degrees C and 6.4+/-2.3 degrees C warmer than the skin. When estimated systemic heat loss was included in the calculation, redistribution accounted for 73% of the afterdrop, which is similar to the contribution observed previously in nonsurgical volunteers.

IMPLICATIONS

Temperature afterdrop after bypass at 17 degrees C was 2.2+/-0.4 degrees C, with approximately 73% of the decrease in core temperature resulting from core-to-peripheral redistribution of body heat. Cooling and rewarming were associated with large radial tissue temperature gradients in the thigh.

Postbypass hypothermia and its relationship to the energy balance of cardiopulmonary bypass

Using a newly developed computerized intraoperative data acquisition system, the apparent adequacy of rewarming and its relation to the energy exchange between the patient and the bypass system was investigated. Retrospective analysis of comparable patients identified two groups that had, at the end of surgery, either a nasopharyngeal temperature (NPT) of 36 degrees C or more ("warm" group, n = 19), or a NPT of 35 degrees C or less ("cold" group, n = 19). Temperatures from the nasopharynx, thenar eminence skin, and bypass pump arterial and venous lines were continually recorded and sent to the computer data base together with the pump flow rate. There were no significant differences between the groups regarding time on perfusion, time taken to cool, time of hypothermia, or the time interval from end of perfusion to the end of surgery. However, rewarming time was greater in the warm group (P less than 0.01). The cold group were subjected to more profound hypothermia (P less than 0.001), and had lower NPTs and skin temperatures at the end of bypass (P less than 0.0001 and P less than 0.01, respectively). However, the difference between NPT and thenar skin temperature in each group at either the end of bypass or the end of surgery was the same. The net energy exchange between patient and pump was significantly different (mean in warm, 130 kJ [SD = 530]; in cold, -389 kJ [SD = 427]; P less than 0.003). In conclusion, the adequacy of rewarming can be expressed in terms of the energy exchanged in the bypass system, and cannot be assessed by the nasopharynx:skin temperature gradient.

A pulsatile pump for cardiopulmonary bypass and its clinical use

A pulsatile pump driven by a coil spring, which was designed and constructed by us, is described in this report. It consists of two main parts, a disposable blood chamber and a driving section. The blood chamber has two leaflet valves and a piston, which is covered with two bellofram rolling diaphragms and moves into the housing to draw in and eject the blood. The driving section consists of three cams, an electric motor and a coil spring. The ejection force is wholly produced by the compressed coil spring and is transmitted to the piston in the blood chamber by a rod. This pump allows the ejection pressure, the beat rates, and the stroke volume all to be changed independently. The performance of the pump was tested by using a circulation model where the beat rate was adjusted from 30 to 250 bpm. The output subsequently increased from 0.8 l/min to 5.7 l/min and the stroke volume, from 20.4 ml to 36.7 ml. This new pump has been used for clinical cardiopulmonary bypasses in 24 patients of open heart surgery and the pressure traces during perfusion resembled those of the patients' own hearts.

Recent advances in cardiopulmonary bypass and the clinical application of myocardial protection

Basic scientific research has provided the impetus to develop cardioplegic solutions that offer excellent myocardial preservation. Future research will continue to develop methods for better delivery of cardioplegia to all myocardial regions. In addition, earlier detection of evolving ischemic damage during aortic cross-clamping might provide a basis for earlier intervention to reverse developing myocardial injury. At the present time, the cardiac surgeon has many cardioplegic solutions and delivery systems from which to choose. Only by understanding the principles involved in myocardial preservation will the surgeon be able to develop a system that will work best in his or her clinical practice.

Pulsatile and nonpulsatile cardiopulmonary bypass: review of a counterproductive controversy

In the controversy over pulsatile and nonpulsatile perfusion, most authors have failed to recognize the fundamental physical differences between the two methods. Pulsatile perfusion is polymorphic and its form varies with both the pulsatile source and the vascular system being perfused; nonpulsatile perfusion is by definition unvarying and uniform. While many studies of hemodynamics, metabolism, organ function, microcirculation, and histology show benefits derived from pulsatile perfusion, others do not. The simplest explanation for these conflicts is that different investigators employ different forms of pulsatile perfusion, only some of which are effective. Failure to quantitate adequately the pulsatile components of flow in these studies prevents differentiation between effective and ineffective forms of pulsatile flow and makes comparison of studies difficult. Future research in this area should be directed toward definition of effective pulsatile perfusion by adequate measurement of the pulsatile components of perfusion.