To the Editor:—
We thank Pfeffer et al. 1for their excellent article on the effect of leg stirrups and intermittent pneumatic compression boots on calf compartment pressures. We wish to raise some points regarding compartment syndrome in association with the lithotomy position.
The results clearly demonstrate that in awake, young volunteers, the weight of the lower limb in generic knee supports causes a rise in calf compartment pressure. The Allen Medical Stirrup system does appear to distribute the weight of the lower limb away from the calf muscles and limit the rise in compartment pressure and, by implication, would reduce the incidence of compartment syndrome. However, the incidence of compartment syndrome is probably very low, and to demonstrate an actual reduction in the incidence of lower limb compartment syndrome would require large numbers of patients.
The individuals at risk from compartment syndrome are frequently elderly and anesthetized and remain in the lithotomy position with the addition of Trendelenburg for several hours. 2The study group was in the lithotomy position for 30 min only. It would be helpful, therefore, to repeat the study in subjects retained in lithotomy for 4 h. However, awake subjects tend to move their legs within the stirrups to prevent discomfort and maintain circulation to the lower limb. Anesthetized patients having surgery in the lithotomy position for several hours are a better model. In a recent study 3of surgical patients having surgery in which both the Allen stirrups and pneumatic compression boots were used, the authors demonstrated a significant rise in lower limb compartment pressure, at variance to the volunteer group of Pfeffer et al.
The addition of the Trendelenburg position has been shown to increase further the compartment pressure compared with the lithotomy position alone. 3Would Pfeffer et al. consider repeating the study and observing the impact of Trendelenburg position in their subjects?
A rise in compartment pressure may not be the only factor that leads to lower limb compartment syndrome. It has been estimated that the fall in lower limb blood pressure is 2 mmHg for every vertical inch in height of the leg above the heart. The actual fall in blood pressure may be more or less than predicted. 4The presence of peripheral vascular disease, intraoperative epidural analgesia, general anesthesia, and deliberate hypotension may further compromise the lower limb blood flow. Thus, while Pfeffer et al. demonstrated a fall in compartment pressure with the use of pneumatic compression boots, pneumatic compression boots may impair peripheral circulation. If compromise of lower limb blood flow is the initiating event that leads to the development of compartment syndrome, then pneumatic compression boots may only increase the risk of compartment syndrome developing. Repeated cycling of a noninvasive blood pressure cuff has been reported to lead to compartment syndrome of the arm, 5and other investigators have considered that pneumatic compression boots may have a role in the development of compartment syndrome. Without data from surgical patients measuring lower limb blood pressure and compartment pressure, it would be premature to conclude that pneumatic compression boots minimize the risk of developing lower limb compartment syndrome.