Oxygenation of a Crystalloid Cardioplegic Solution

_____________ _ The purpose of this study is to compare the effectiveness of an alternative method of oxygenating a crystalloid cardioplegic solution to the use of a bubble oxygenator. Five hundred milliliters of 100% oxygen was introduced, using sterile technique, into 100 ml bags of Ringer's solution at varying temperatures (20°, 10°, and 4°C). The contents of the bags were shaken for one minute by hand and then cooled to 4°C or maintained at that temperature using a Shiley CSD 103 Cardioplegia Delivery Set. This method of oxygenation was compared to constant bubbling of 100% oxygen into Ringer's solution in a Shiley S70 bubble oxygenator at 4°C. Samples of oxygenated solution from the bubble oxygenator were collected over a 60 minute time period. After 30 minutes the values stabilized and the last 12 samples were used as the reference for the bubble oxygenator. Samples of the solutions cooled using the Shiley CSD 103 were taken when the temperature stabilized at 40C. All4°C samples were then analyzed for p02 using an IL 326 blood gas analyzer and the values compared for the various techniques. The results of this study showed the following p02 values: 570 20°-+4°C 10°-+4°C 4°-+4°C n 12 12 12 12 xmmHg ±SO 1183±28 795±59 983±26 1116±18 The conclusion drawn from this study is that the use of Ringer's solution oxygenated and maintained at 4°C is a cost effective alternative to the use of a bubble oxygenator to increase the p02 in crystalloid cardioplegic solutions. Introduction _____________ _ Since 1955, when Melrose, Bentall, and their colleaguesu introduced the idea of "elective cardiac arrest," cardiothoracic surgeons have been using varDirect communications to: William E. Hodges, Jr., ECT Program, Medical University of South Carolina, 171 Ashley Ave., Charleston, SC 29412 134 ious cardioplegic solutions for the purpose of inducing cardiac arrest during open heart surgery. 11 Since it was felt that the high potassium cardioplegic solutions did more harm than good to the heart, cardiothoracic surgeons in the United States went for a period of about thirteen years from the early 1960s till1973 without using cardioplegia during open heart surgery. 12 Cardioplegia use in the United States returned after a study in 1973 by Gay and Ebere on the functional, metabolic, and morphological effects of hyperkalemic crystalloid cardioplegia. In 1978 Follette and Buckberg suggested the addition of blood to the cardioplegic solution. Theoretically to increase the oxygen carrying capability this blood cardioplegic solution may increase myocardial protection during aortic cross clamping by the release of oxygen carried by the hemoglobin molecules. 9 Another studyl using blood cardioplegia has suggested any temperature below 20°C actually would reduce the ability of the hemoglobin to release oxygen and therefore the effectiveness of blood cardioplegia. Since 1981, oxygenation of crystalloid solutions' ,' 19 has been suggested as an alternative method of providing oxygen to the ischemic myocardium during aortic cross clamping. Three of these studies' ' 19 oxygenated the cardioplegia by bubbling as they circulated. By using a bubble oxygenator or a modified cardiotomy to oxygenate the crystalloid solution, an additional cost of $100-$300 will be incurred by the patient. In an era of DRGs and a constant attempt to reduce cost, a cost effective method of oxygenating crystalloid cardioplegia would be desirable. The purpose of this study is to develop a comparable method of oxygenating crystalloid cardioplegia and to introduce a cost effective method of oxygenating crystalloid cardioplegia to a known p02 and oxygen content. The null hypothesis to be tested is that there is no difference between the p02 and the oxygen content produced by the methods studied. Materials and Methods ________ _ In this study four methods of preparing oxygenated crystalloid cardioplegia were compared, Table 1 Uncorrected p02 for the Four Methods S70A 20°C to 40C l0°C to 4°C n xmmHg + SD 12 1183 + 28 12 795 ± 59 Table 2 12 983 ± 26 12 1116 ± 18 Calculated Oxygen Content for the Four Methods S70A 20°C to 4°C l0°C to 4°C n 12 12 12 12 x ml/dl + SD 3.55 + 0.09 2.38 ± 0.17 2.95 ± 0.07 3.34 ± 0.06 In the first method 1000ml of Ringer's Solutiona (RS) was recirculated and chilled to soc at one 1/min through a Shiley S70A bubble oxygenatorb with an oxygen flow rate of one 1/min. RS was used because it is a balanced electrolyte crystalloid solution typical of those that can be used to make a crystalloid cardioplegic solution. At five minute intervals five samples were drawn and analyzed for p02. When there was no measurable change in the p02 for three consecutive samples, 12 samples were drawn and recorded. In the second method four bags of room temperature (20°C) RS were oxygenated in the following manner: Air was removed via a 19ga needle placed into the injection port of the RS bag. Next, using a gas filter, 100% oxygen was bubbled into the bag until the bag became distended (50mmHg). The oxygenated solutions were then shaken by hand for 60 seconds and introduced into a Shiley Cardioplegic Solution Delivery Set CSD-103b. The RS was recirculated with the cooling coil submerged in an ice bath till the temperature reached 4°C (a needle probe< was inserted into the injection port of the CSD-103 and temperature was monitored by a Tete-thermometer temperature boxd). Once the desired temperature was reached, three samples from each bag were taken and analyzed for p02. In method three and four, four RS bags were cooled in a refrigerator to 10°C and in ice to 4°C respectively. These bags were then oxygenated and analyzed for p02 in the previously described manner. All samples were analyzed using the IL Micro 13 blood gas analyzer" which was calibrated for the higher limit with 95% oxygen and for the lower limit with 20% oxygen to insure accuracy at higher p02• All data a Travenol Labs, Inc. Deerfield, IL 60015 b Shiley, Inc. Irvine, CA 92714-5751 c Yellow Springs Instrument Co., Inc. Antioch, OH 43710 d Instrumentation Laboratory Inc., Lexington, MA 02173 e Systat, Inc. Evanston, IL 60202 f American Bentley, Irvine, CA 92714 are reported uncorrected and oxygen contents were calculated from the noncorrected data. Statistical Analysis Analysis of variance (p < 0.05) was used to determine statistical significance between the four groups. The Student-t test (p < 0.05) was used to determine statistical significance between methods 2,3, and 4 and the bubbler method. The IBM Systatl statistical package was used to analyze the data. Results _______________ _ The results of this study are summarized in Tables 1 and 2. Note the similarity between the bubbler method and method four. Analysis of variance indicated there was a statistically significant difference in the methods. The S70A group and the group of 4°C RS maintained at 4°C were significantly different. Discussion _______________ _ The advantages of oxygenated crystalloid cardioplegia over nonoxygenated crystalloid cardioplegia have been noted in several studies. • Bodenhamer et aP observed a significant decrease in the mean postreperfusion adenosine triphosphate (ATP) levels of canine hearts perfused with nonoxygenated crystalloid cardioplegia as compared to the canine hearts perfused with a fully oxygenated solution. Also noted was a significant increase in the myocardial water content in the nonoxygenated group but not in the oxygenated group. Ultrastructural evaluation of these hearts showed severe ischemic damage in the nonoxygenated group as compared to the normal appearance of the oxygenated group. 16 In 1985 Guyton et aP indicated that oxygenation of a crystalloid cardioplegic solution led to an improved recovery of regional function in the left anterior descending and circumflex regions after 15 and 30 minutes of ischemia respectively. This study also noted that the mean 12 hour post operative creatine kinase