1. Jørgensen A, Gaustad SE, Møllerløkken A, Brubakk AO
GENERAL ANESTHESIA INCREASES MORTALITY AND BUBBLE FORMATION DURING DECOMPRESSION
Jørgensen A, Gaustad SE, Møllerløkken A, Brubakk AO
Department of Circulation and Medical Imaging, Medical Faculty, Norwegian University of Science and Technology, Trondheim, Norway
INTRODUCTION
HYPOTHESIS
RESULTS
CONCLUSION
Formation of bubbles in blood and tissues is the basis for injury to divers after decompression, a condition known as decompression sickness (DCS) (Eftedal OS et al., 2007). The number of bubbles formed during decompression is dependent on tissue nitrogen uptake and elimination, which might be influenced by ambient temperature (Gerth WA et al., Navy Experimental Diving Unit, 2007) and the level of activity (Dujic Z et al., 2005).
General anesthesia is commonly used in animal experiments studying DCS and bubble formation (Møllerløkken et al., 2006), and all general anesthetics so far tested markedly impairs the normal thermoregulatory control with inhibitory effects on shivering and peripheral vasoconstriction resulting in a profound reduction in core temperature (Sessler DI, 2008). Mack and Lin showed in unanesthetized rats that hypothermia lead to decreased nitrogen elimination from the body, suggesting that changes in regional blood flow in tissues like skin, skeletal muscles and adipose tissue accounted for most of this reduction, and that a reduction in heart rate accounted for 1/3 of the decrease (Mack and Lin, 1986).
This study investigates for the first time the effect of general anesthesia on core temperature and its influence on vascular bubble formation and survival after a saturation dive in a dry hyperbaric chamber.
Rats anesthetized during the dive compared to controls had significantly more bubbles, fig. 2A (Bubbles∙cm-2, 6.9 ± 4.6 vs. 1.7 ± 3.6 SD, p < 0.001), and higher morality fig. 2B (67% vs. 13%, p < 0.001). General anesthesia induced a rapid core temperature drop, fig. 3, and there was a high significant correlation and a linear relationship between core temperature and heart rate and respiration rate, fig 4. .
General anesthesia during a saturation dive in a hyperbaric chamber is hypothesized to increase bubble formation and mortality by decreasing the rate of nitrogen elimination during decompression, due to an effect of a decreased core temperature and immobility.
This study has demonstrated for the first time that rats in general anesthesia during a simulated dive in a hyperbaric chamber, have a significantly increased bubble formation and mortality. The explanation of these findings might be an effect of decreased core temperature, decreased heart rate/cardiac output and respiration, inactivity, and hence reduced nitrogen elimination during decompression. This study addresses the importance of strict ambient and core temperature monitoring and regulation when performing diving and altitude experiments studying bubble formation and decompression sickness in conscious and anesthetized animals.
METHODS
Thirty-six female Sprague-Dawley rats, body weight 266g ± 8SD, were divided into two groups: Group I (n = 21) were anesthetized using general anesthesia (Midazolam 0.5mg·100 g-1/Fentanyl 5µg·100 g-1/Haldol 0.33mg·100 g-1, s.c.). Group II (n = 15) were not anesthetized during the dive. The rats were compressed to 700kPa breathing air, stayed at the bottom 50 min to near saturation (Lillo RS and Parker EC, 2000), and were decompressed linearly at 50kPa·min-1 (12 min), fig. 1. Chamber and room temperature were held constant at 22°C. Core temperature, heart rate and respiration rate was measured during the experiment. Bubbles were measured in the pulmonary artery using ultrasound. Bubble formation was graded according to a method described by Eftedal and Brubakk and converted to bubbles∙cm-2 (Eftedal OS and Brubakk AO, 1997).
Figure 2. Upper line is showing a 1.2°C core temperature drop in conscious rats during a 62 min chamber dive. Lower line is showing a 8.0°C core temperature drop during 60 min in general anesthesia. Ambient temperature was 22°C.
REFERENCES
Eftedal OS, Lydersen S, Brubakk AO. The relationship between venous gas bubbles and adverse effects of decompression after air dives. Undersea Hyperb Med 2007;34:
Gerth WA, Ruterbusch VL, Long ET. The influence of thermal exposure on diver susceptibility to decompression sickness. In. Panama City: Navy Experimental Diving Unit; 2007.
Dujic Z, Palada I, Obad A, Duplancic D, Bakovic D, Valic Z. Exercise during a 3-min decompression stop reduces postdive venous gas bubbles. Med Sci Sports Exerc 2005;37:
Mollerlokken A, Berge VJ, Jorgensen A, Wisloff U, Brubakk AO. Effect of a short-acting NO donor on bubble formation from a saturation dive in pigs. J Appl Physiol 2006;101:
Sessler DI. Temperature monitoring and perioperative thermoregulation. Anesthesiology 2008;109:
Mack GW, Lin YC. Hypothermia impairs but hyperthermia does not promote inert gas elimination in the rat. Undersea Biomed Res 1986;13:
Lillo RS, Parker EC. Mixed-gas model for predicting decompression sickness in rats. J Appl Physiol 2000;89:
Figure 2. Rats in general anesthesia versus conscious control rats during a simulated chamber dive had significantly more bubbles detected in the pulmonary artery (fig 2A), and a higher mortality rate (fig 2B) during 60 min post dive observation. Bubbles∙cm-2 are presented as mean ± SD.
Eftedal O, Brubakk AO. Agreement between trained and untrained observers in grading intravascular bubble signals in ultrasonic images. Undersea Hyperb Med 1997;24:293-9.
ACKNOWLEDGEMENTS
This study was supported by the Norwegian Petroleum Directorate, Norsk Hydro, Esso Norge and Statoil under the ‘dive contingency contract’ (No ) with Norwegian Underwater Intervention (NUI). The assistance of statistical calculations by Astrid Hjelde is gratefully acknowledged.
CONTACT INFORMATION
Arve Jørgensen, Department of Circulation and Medical Imaging, Faculty of Medicine, Norway, University of Science and Technology T: F: E:
Figure 4. There was a linear relationship and a positive correlation between core temperature and heart rate (rs = 0.96, p = 0.000) and core temperature and respiration rate (rs= 0.76, p = 0.004) during general anesthesia.
Figure 1 is showing the diving profile, 50 min at 700 kPa, 12 min linear deco.