Monday February 4 2008
Human surgery is not equivalent to surgery in mice
Patients going into surgery should control their alcohol intake beforehand, according to a report in The Guardian. Drinking “even moderate amounts prior to surgery could slow down recovery and weaken the immune system", the newspaper said.
The newspaper story is based on a German study looking at mice that had a form of “surgery” after exposure to alcohol. The mice that had alcohol had more severe post-operative lung infection. However, it is not possible to tell how this “surgery” could relate to any surgical procedure carried out in humans, or how the dose of alcohol given to the mice in one week could relate to quantity and frequency of alcohol consumption in an adult.
Heavy drinking is well known to be related to poorer health and it is sensible for people to try and keep their alcohol consumption within recognised limits. It is unclear from this study whether alcohol consumption should be avoided completely around the time of surgery.
Where did the story come from?
Dr Claudia Spies and colleagues from the medical institutes in Berlin carried out this study. The research was funded in part by the German Research Society. It was published in the peer-reviewed medical journal: Alcoholism: Clinical and Experimental Research.
What kind of scientific study was this?
This was a laboratory study in mice in which researchers developed a mouse model of surgery to explore immune responses and lung disease after alcohol exposure. It is known that long-term alcoholic patients have a greater risk of complications after surgery, particularly with pneumonia.
Researchers exposed 32 laboratory mice to alcohol or to a control injections of saline. On the eighth day, all mice had surgery under sterile conditions and whilst under anaesthetic. Two days after surgery the mice were randomised, and half were exposed to the bacteria that causes pneumonia (K. pneumoniae), or to saline.
After 24 hours of exposure to the bacteria, all mice were killed so that their organs could be removed for assessment. Researchers recorded the body weight, impairment, symptoms of infection and other characteristics of the mice on the first and last day of the experiment
What were the results of the study?
There was no difference in clinical characteristics between the mice groups on the first day of the experiment (before exposure to alcohol or surgery). However, at the end of the experiment (after alcohol exposure, surgery and exposure to bacteria) the researchers found there to be significant differences between the alcohol-treated mice and non-alcohol treated mice, and between those infected with bacteria and those not.
The most important result was that in mice who were infected with bacteria, those that had been exposed to alcohol previously had more pronounced lung injury than those who were not exposed to alcohol. They also had higher levels of two proteins (called cytokines), interleukin-6 and interleukin-1, in their lungs, which promote inflammation. However, there was no significant difference in the numbers of bacteria in the lungs or in the concentration of other immune chemicals in the spleen. In the liver, there was a lower concentration of inflammatory protein in the infected mice treated with alcohol.
What interpretations did the researchers draw from these results?
The researchers conclude that, as expected, the exposure of mice to bacteria causing pneumonia results in lung infection. However, the infection is more severe in alcohol-treated mice, and these mice showed increased levels of the two proteins linked to inflammation. The researchers conclude that the one week of ethanol treatment “may have provoked a weakened immune response in the lung, leading to more pronounced organ damage”.
What does the NHS Knowledge Service make of this study?
There are limitations to what can be learnt from this study, as results from animal studies do not necessarily translate into similar results in humans. In addition, there are methodological limitations to this study, some of which the researchers raise:
- In assessing the damage to the lungs caused by exposure to infection, the researchers used a subjective measure. They say that the finding that increased levels of interleukin-6 led to greater lung damage need to be confirmed by further studies using a more objective scoring system.
- The significance of the surgery in this experiment is difficult to see. All mice had abdominal “surgery”, but the results relate to the effect of bacteria on lung health.
- The researchers only measured the concentrations of two proteins involved in response to the pneumonia infection – interleukin-6 (IL-6) and interleukin-10 (IL-10). There are other types of these chemicals secreted by cells of the immune system that may play a part in the response to infection. These chemicals are also thought to be activated by surgery; however, in this experiment researchers did not measure them before exposing the mice to pneumonia. In humans, different markers would be used to consider the severity of a pneumonia infection, such as white blood cell count, other inflammatory markers in the blood, temperature, fluid balance, and clinical examination of the patient.
The relevance of this particular study to people undergoing surgery is limited. It is known that continued heavy alcohol drinking is related to poorer health and it is sensible for people to try to moderate their alcohol consumption to within recognised limits. Whether alcohol consumption should be avoided around the time of surgery in particular remains unclear.
Sir Muir Gray adds...
And stop smoking: in fact get as fit as you can before you become ill.