The Pre-Emptive Administration Of Ketamine for Controlling Post-thoracotomy Pain

Thoracotomy is one of the most painful surgical incision. Inadequate control of pain can have several detrimental effects, including increased postoperative morbidity and delayed recovery as well as occurrence of post thoracotomy syndrome. Therefore, choosing an effectiveness analgesic regimen for thoracic surgery is critical. Many strategies including intercostal nerve block, intra pleural analgesia, lumbar or thoracic epidural, paravertebral block, intra venous narcotics, intrathecal or epidural narcotics or trans-cutaneous nerve stimulation have been used with varied success. However, the ideal strategy remains an open issue. Different factors including trauma of chest wall, thoracic viscera, diaphragm, and intercostal nerves concur to thoracotomy pain development. Thus, due to multifactorial genesis of pain following thoracotomy a multimodal analgesic approach rather than a single method seems to be more effective because it blocks noxious input at different targets and levels of pain pathways.

Ketamine is an antagonist of N-methyl-D-aspartate (NMDA) receptor that not only abolishes peripheral afferent noxious stimulation, but it may also prevent central sensitization of nociceptors as shown in animal studies. In thoracic surgery, there are contradictory results on the efficacy of ketamine for controlling pain due to different dose, type of surgery/patient, and postoperative analgesic regimen used in the various studies. Mathew et al. in a recent review concluded that adding low-dose ketamine to intravenous morphine analgesia following thoracotomy was safe and could provide a significant better pain relief and reduction of morphine consumption compared to placebo. D'Alonzo et al. found that the administration of a single dose of ketamine prior to chest incision failed to significantly reduce the pain scores and inflammation in the first 24 post-operative hours. Similarly, Yazigi et al. reported that pre-emptive intravenous low-dose ketamine followed by continuous administration during surgery did not decrease acute pain scores and supplemental morphine consumption. Other studies reported that the epidural infusion of Ketamine before thoracotomy or during thoracic surgery provides better postoperative analgesia compared to placebo group or epidural ropivacaine group In the present study, the investigators supposed that the pre-emptive administration of Ketamine would potentiate the effect of intravenous opioid analgesia with reduction of pain scores, inflammatory response and morphine consumption without increasing morbidity in patients undergoing thoracotomy.

This was a single center, double-blind, placebo controlled, parallel-group, prospective study. Patients were randomly assigned to receive 1 mg/kg ketamine (Ketamine Group) or an equivalent dose of normal saline (Placebo Group) before thoracotomy in 1:1 ratio. All patients received postoperatively intravenous morphine administration as additional analgesic regimen Primary end-point was pain relief measured with Visual Analogue Scale at rest. The secondary end-points were the reduction of inflammatory response expressed by plasma c-reactive protein levels, the morphine consumption, and the rate of side effects. The measurements were carried out 6; 12; 24; 36; and 48 post operative hours.