The Effects of Heated and Room-Temperature Abdominal Lavage Solutions on Core Body Temperature in Dogs Undergoing Celiotomy

Introduction

Hypothermia is common in dogs undergoing celiotomies.¹ In a normal, awake dog, conductive heat loss is negligible because of the small surface area in contact with the ground and the insulated padding on the palmar and plantar aspects of the distal limbs.¹ However, during anesthesia and celiotomy, the recumbent animal has greater surface area in contact with the table, and conductive heat loss increases. The low specific heat of stainless steel surgical tables compared to body tissues enhances conductive heat loss. Heat loss from radiation, convection, and evaporation is also increased during a celiotomy, because greater surface area is exposed when the abdominal cavity is opened. Anesthetic agents disrupt the normal vasoactive responses used to regulate body temperature and also contribute to heat loss during celiotomy.¹ Factors affecting the development of hypothermia in surgical patients include duration of the procedure, choice of anesthetic agents, ambient temperature of the operating room, body condition score of the animal, size of the animal, and the nature of the surgical procedure.^1–4

Numerous studies have documented an increase in anesthetic recovery time and increased morbidity and mortality in hypothermic patients (human and veterinary).^1–9 Hypothermia of even a few degrees can increase recovery times in human surgical patients.¹⁶ For this reason, various methods are used to help maintain an animal’s body temperature during surgery, including circulating hot-water blankets, circulating heated air units, hot-water bottles, warmed intravenous fluids, and warmed inhaled anesthetic gases.^10–13

Successful management of hypothermia in surgical patients requires an accurate means of recording and monitoring changes in core temperatures. Direct means of measuring core temperature, including the implantation of thermisters in a central vein, are limited by their invasiveness and the necessity of maintaining a sterile surgical field.¹³ Therefore, rectal thermography, esophageal thermography, and tympanic thermometers are often used to indirectly determine core body temperatures in animals undergoing abdominal surgery.¹⁴⁷

During celiotomy, the abdominal cavity is typically lavaged with saline solution to dilute and remove contaminants. Warmed solution is recommended and is thought to help increase or maintain body temperature by convection of heat from the lavage solution to the animal.¹⁴¹⁵ While the practice of using warm lavage solution is widely accepted, little is known regarding its effects on an animal’s core temperature. It is unclear if warmed lavage actually increases core temperature following abdominal exploratory surgery or simply slows heat loss; what the optimum temperature of the solution should be; and how long the solution must be present in the abdominal cavity to increase core temperature. The vasodilatation that occurs with warmed lavage may also predispose to additional heat loss during the procedure, as has been documented when warmed irrigants are used during arthroscopic procedures.¹⁶

The purpose of this study was to assess the benefits of warmed peritoneal lavage as a means of improving or maintaining core body temperature in anesthetized dogs during celiotomy. It was hypothesized that a significant difference in final core temperatures would be detected between dogs that received warmed lavage and dogs that received room-temperature lavage solutions.

Materials and Methods

This study was approved by the Mississippi State University’s Institutional Animal Care and Use Committee. Eighteen mixed-breed dogs (10 to 20 kg) scheduled for abdominal exploratory, as part of a veterinary student surgical teaching laboratory, were included in the study. Each dog was positioned in dorsal recumbency on a surgical table. A towel was placed between the table and the dog as insulation to minimize conductive losses to the table. Each dog was premedicated with intramuscular injections of butorphanol^a (0.2 mg/kg) and acepromazine^b (0.05 mg/kg). Anesthesia was induced with an intravenous injection of thiopental^c (6 to 10 mg/kg to effect) and maintained with isoflurane^d in oxygen administered via an endotracheal tube.

At the end of the surgical procedure and prior to performing abdominal lavage, a temperature probe^e was inserted into the esophagus of each dog to the level of the eighth intercostal space. A second probe was placed 6 cm into the rectum. The probes were connected to a physiograph unit^f to continuously record temperature measurements. The temperature probes were calibrated to within 0.1°C using a known temperature water bath prior to insertion into the esophagus and rectum. A tympanic thermometer was used to obtain tympanic temperatures.^g A thermister was also placed in the abdominal cavity at the level of the left kidney and was connected to a physiograph unit to record the temperature of the abdominal lavage solution.^h The temperature of the operating room was also recorded throughout the lavage period.

Results

Prior to initiation of the lavage, the mean temperature of the combined methods of temperature recording (tympanic, esophageal, and rectal) of the nine dogs in Group 1 (room-temperature lavage solution) was 94.8°F (34.8°C). The combined temperatures ranged from 89.4°F (31.9°C) to 98.4°F (36.9°C). The mean of the combined temperatures of the nine dogs in Group 2 (heated lavage solution) was 93.7°F (34.2°C). The combined temperatures ranged from 89.4°F (31.9°C) to 95.5°F (35.3°C). The difference in initial body temperature reflected the variable duration of the surgical procedure prior to abdominal lavage. At completion of the lavage procedure, the dogs in Group 1 had a mean core temperature of 90.1°F (32.3°C), with a range of 82.7°F (28.2°C) to 94.0°F (34.4°C). The dogs in Group 2 had a mean post-lavage temperature of 97.4°F (36.4°C), with a range of 94.2°F (34.6°C) to 100.6°F (38.1°C). The ambient room temperature throughout the lavage procedure was maintained between 65°F (18.3°C) and 72°F (22°C).

In dogs lavaged with room-temperature saline (Group 1), body temperature was significantly lower by the end of the 15-minute lavage period as measured by the esophageal (P<0.001), rectal (P<0.01), and tympanic (P<0.01) probes. The core body temperature decreased significantly compared to prelavage levels (time 0) at 3 minutes after the initiation of the lavage as measured by the esophageal probe (P=0.031), at 4 minutes as measured by the rectal probe (P=0.027), and at 6 minutes as measured by the tympanic probe (P=0.006).

In dogs lavaged with heated saline (Group 2), body temperature was significantly higher at the end of the 15-minute lavage period as measured by esophageal (P<0.001), rectal (P<0.001), and tympanic (P<0.001) probes. The core body temperature increased significantly compared to prelavage levels at 2 minutes after the initiation of the lavage as measured by the esophageal probe (P=0.009), at 3 minutes as measured by the rectal probe (P=0.022), and at 6 minutes as measured by the tympanic probe (P=0.019).

Esophageal temperatures were significantly higher (P=0.029) in dogs lavaged with heated saline than in dogs lavaged with room-temperature saline beginning at the 6-minute mark of the procedure [Figure 1]. Rectal temperatures were significantly higher (P=0.032) in dogs lavaged with heated saline than in dogs lavaged with room-temperature saline beginning at the 5-minute mark of the procedure [Figure 2]. Tympanic temperatures were significantly higher (P=0.004) in dogs lavaged with heated saline than in dogs lavaged with room-temperature saline after 6 minutes of lavage [Figure 3]. A substantial difference in time was required for a statistically significant change in temperature to occur between Groups 1 and 2 (comparing heated versus room-temperature lavage), as compared to the time required for a significant change to occur in temperature from time 0 when Groups 1 and 2 were independently evaluated. This apparent lag time was caused by the slight difference in the mean core temperature recorded between Groups 1 and 2 at time 0, with the room-temperature lavage subjects having an overall higher initial core temperature than the heated lavage subjects. After 15 minutes of lavage, core temperatures were significantly higher in dogs lavaged with heated saline than in dogs lavaged with room-temperature saline as measured by esophageal (P<0.001), rectal (P<0.001), and tympanic (P<0.001) thermometers.

No apparent change occurred in the temperature of the heated lavage solutions throughout the procedure. The room-temperature lavage solution maintained a constant temperature after attaining a steady-state temperature at around 3 minutes. The room-temperature lavage solution remained largely unchanged except for the 0- to 2-minute time period when the solution temperature increased from 69.7°F (20.9°C) to 85.4°F (29.7°C).

Lavage and core body temperature recordings were discontinued upon completion of the 15-minute lavage period. Grossly, no adverse effects were noted from the heated saline on the abdominal viscera prior to closure of the incisions. All the dogs in this study were euthanized prior to or at the end of surgery, so no specific comments could be made as to the effect of the heated lavage on the recovery of the animal. Several of the dogs were euthanized prior to complete closure of the abdomen, so no comments could be made on the postlavage effects of maintaining core temperature into the recovery period.

Pearson’s correlation coefficients were calculated between the temperature recording methods used in the study. The overall correlation for all dogs of tympanic to rectal and tympanic to esophageal temperatures were r=0.863 and 0.881, respectively. Esophageal and rectal temperature probes had a lower correlation coefficient (r=0.690). These findings were consistent with an individual study group correlation of r=0.849 (tympanic to rectal), r=0.903 (tympanic to esophageal), and r=0.766 (rectal to esophageal) for Group 2 (heated lavage). The correlation coefficients for Group 1 (room-temperature lavage) were r=0.851 (tympanic to rectal), r=0.770 (tympanic to esophageal), and r=0.534 (rectal to esophageal).

Discussion

Mild hypothermia is common in animals undergoing any surgical procedure, particularly celiotomy.¹ The significant heat loss during abdominal surgery is attributed to the increased surface area present for heat exchange, the retardation of normal thermodynamic control of the body by anesthetic agents, and the direct exposure of the core body compartment to ambient room temperatures.¹⁴⁵⁷ Evidence suggests that hypothermia increases morbidity and mortality in animals and should be prevented whenever possible.^35–791213 When hypothermia occurs, effective treatment is needed to reduce complications.

Currently, many efforts that address perioperative hypothermia focus on preventing heat loss to the environment through the use of external heating systems. These methods effectively reduce heat loss from the periphery of the body, but they do not improve the animal’s core temperature in many cases. Surface heating systems do not increase core temperatures unless the temperature of the heating system exceeds the patient’s core temperature. The heat must then pass through a thermal gradient to effectively increase core temperature. Additionally, complications occur when surface heating systems are used at higher temperatures. Surface burns are reported in animals with prolonged exposure to heating pads set at 42°C.¹⁹ This consequence is greater during surgery, because animals are unable to shift their bodies to avoid prolonged exposure to the heating pads. The disruptive effects of anesthesia on peripheral circulation in animals may also increase the likelihood of thermal injury from surface heating systems.

Other methods of rewarming hypothermic surgical and nonsurgical patients have been evaluated.^1251011 Extracorporeal warming and bypass technology are superior to external heaters, heated insufflation gases, and warmed lavage.¹²¹⁷¹⁸ However, their use is limited in animals by their expense, invasiveness, and the need for experienced personnel to operate the necessary equipment.¹⁷ As a result, more practical methods of rewarming animals have been sought. In humans, peritoneal lavage with warmed isotonic saline has been an excellent method of rewarming severely hypothermic patients compared to external warming methods and the use of heated inhalation agents.² In a controlled comparison between peritoneal lavage and heated inhalation agents in severely hypothermic humans (i.e., core temperature of 25°C), warmed peritoneal lavage required an average of 193 minutes to rewarm the people, compared to 332 minutes for heated inhalation.² Gastric and thoracic lavage has also been shown to be more effective in increasing core temperature than exposure to an elevated ambient temperature, heated surface warmers, or heated insufflated gases in dogs.¹⁸ These findings suggest that the use of warmed peritoneal lavage may increase the animal’s body temperature and decrease postoperative recovery time and morbidity.⁵⁷ Results of the study reported here confirmed that the use of warmed peritoneal lavage solutions increased body temperature in dogs undergoing celiotomy. Factors that may influence the efficacy of abdominal lavage include temperature of the solution, duration of the lavage, and the animal’s initial body temperature. In this study, at least 2 to 6 minutes of lavage with saline at 110±4°F (43±2°C) were required to significantly increase body temperature.

The optimum temperature of a peritoneal lavage solution for effectively increasing body temperature in dogs without causing injury to abdominal viscera is unknown. The room-temperature lavage used in Group 1 in this study actually decreased body temperature in dogs after only 3 to 6 minutes (depending on the method of temperature measurement). As expected, room-temperature lavage solutions were ineffective for warming, and they are not recommended for clinical use. This study demonstrated the importance of not allowing solutions intended for use as abdominal lavage to cool in the operating room prior to administration. The heated saline solution used in this study was 110±4°F (43±2°C), and it effectively increased body temperature in dogs.

A limitation of the study was that the nonsurvival aspect of the laboratory exercise did not allow evaluation of core temperatures during closure of the abdominal incision or an evaluation of the effect on the overall recovery time. Further research in these areas is required. The study described here also did not investigate lavage solutions at higher temperatures. Intuitively, the use of warmer lavage solutions would decrease the time required for rewarming; however, the use of lavage solutions that are excessively warm could cause thermal injury to abdominal tissues.¹⁹

The duration of lavage required to effectively increase core temperature in a dog during celiotomy depends on the dog’s initial body temperature, the temperature of the lavage solution, and the magnitude of continued heat loss. The continued application of a warmed lavage solution increases the dog’s temperature as long as the solution is warmer than the animal’s core temperature. Throughout the lavage period, the abdomen remains open, and heat loss continues through radiation, convection, conduction, and evaporation. The application of a heated solution causes vasodilatation, which may increase heat loss from the viscera.¹¹⁶ The loss of heat from the abdomen caused by vasodilatation may impact the overall effectiveness of heated lavage to maintain normothermia during closure of the abdominal incision. This effect was not addressed in the study reported here. In this study, lavage with saline solution at 110±4°F (43±2°C) significantly increased core temperature after 2 to 6 minutes. Core temperature continued to increase throughout the 15-minute lavage period. Practically, the surgeon must weigh the advantages of continuing peritoneal lavage to further warm the animal against the risks of increased anesthetic and surgical time.

Difficulties in assessing the effects of lavage solution on core body temperature include the accurate measurement of core temperature without the invasive implantation of thermistors and measuring core temperature without compromising sterility of the surgical field. In this study, temperature measurements were obtained using esophageal, rectal, and tympanic temperature probes. Esophageal and rectal temperature measurements vary slightly from measurements taken via thermistors implanted in a central vein.²⁰ This difference has been attributed to factors such as the metabolic processes within the stomach and colon, inconsistent placement of the temperature probes, the sensitivity of the equipment used, and the presence of fecal material within the rectum that may insulate the probe from the surrounding tissues.²⁰²¹ The rectal probe may also be affected by the temperature of the lavage solution as it is poured into the abdomen. The rectal temperature probes were consistently inserted 6 cm into the rectum to limit these variables. In the study reported here, the esophageal temperature probe was inserted to the level of the eighth intercostal space in order to place it directly over the heart and to reduce artifactual increases in temperature readings caused by metabolic activity in the stomach.²¹ Temperatures were recorded from three separate body locations to reduce the possibility that variation at an individual site would influence the results.

Differences were observed in the times at which the various temperature recording probes detected a change in body temperature. The rectal and esophageal probes consistently detected increases or decreases in temperature earlier than the tympanic thermometer. This faster detection may have arisen because the anatomical positions of the rectal and esophageal probes were closer to the body’s core. However, these probes were also in closer proximity to the lavage solution and may have been influenced by the temperature of the solution itself. Also, the tympanic thermometer was incapable of reading temperatures <92°F and would have failed to obtain some readings in the more hypothermic animals.

This study documented the efficacy of warmed peritoneal lavage solution in increasing body temperatures in dogs during celiotomy. The optimum temperature of the peritoneal lavage solution was not determined, although a solution warmer than the normal core temperature of the animal is required to allow sufficient transfer of heat. A peritoneal lavage solution heated to 110±4°F (43±2°C) effectively increased body temperatures in dogs undergoing celiotomy in the study reported here.

In this study, a lag time of 2 to 3 minutes was noted between initiation of room-temperature lavage and reaching a steady-state temperature of abdominal lavage solution. This period of temperature fluctuation likely occurred from a shift in heat from the animal to the lavage fluid, because the increase in temperature of the lavage fluid coincided directly with the reduction in body temperature as recorded by the temperature probes. This same effect can be anticipated with the use of warmed saline.

The length of time the abdomen should be lavaged to warm the animal depends on several factors, including the initial temperature of the animal, the temperature of the lavage solution, the weight of the animal, and body conformation. Larger animals and animals with higher fat stores in the abdomen require more heat energy to effectively increase their body temperatures, thus requiring potentially longer lavage periods to achieve an appreciable difference.² The exact effects of body condition and size of the animal were beyond the scope of this study, so a standard range of body weight was used as a means to limit variability.

The volume of lavage used in clinical applications, and thus the length of duration of the lavage prior to closure of a celiotomy varies depending on animal size and level of contamination of the surgery. A more contaminated surgery usually requires a higher volume of lavage solution to be used in order to reduce the negative effects of the contamination. When lavage is indicated for dilution of contamination, the use of heated lavage solution is recommended in order to limit hypothermia and improve recovery time.

Variability exists between surgeons for closure times of abdominal incisions, and it is possible that a significant amount of heat could be lost during closure of the abdomen. Additional studies are needed to document an optimal time for closure of the incision in the linea. In this study, a minimum of 2 to 6 minutes was required for effective heat exchange to begin between the lavage solution and the tissues. It can be assumed that once the heated solution is removed from the abdominal cavity, heat losses will continue until closure is completed and anesthesia is discontinued.

Conclusion

The use of heated abdominal lavage was an effective means of improving core temperatures in mildly hypothermic animals during celiotomy procedures. Significant increases in core temperatures were obtained after several minutes using a lavage solution heated to 110±4°F (43±2°C). Heated lavage was superior for maintaining or obtaining normothermia in animals compared to room-temperature lavage. Further research is required to determine an optimal lavage temperature and time. The vasodilatory effects of heated lavage may increase the rate of heat loss from the abdominal cavity following the lavage procedure; therefore, closure of the abdominal cavity should commence as soon as the lavage procedure is completed.

Acknowledgments

The authors thank Dr. Carolyn Boyle for completion of statistical analysis and Mr. Shandon Gifford for technical assistance in gathering data.