Due to a lack of concise, standardized guidelines for implementation in foot and ankle surgery, these authors provide a literature review and extrapolate recommendations from existing data existing on safe lower extremity tourniquet use. This article is a three-part series covering indications, complications and recommendations for use.
After reviewing indications, precautions and potential complications, we now will address potential recommendations for tourniquet use in lower extremity surgery as compiled by review of the literature.
Key Recommendations Regarding Length Of Tourniquet Time
Non-disrupted inflation duration should be less than or equal to 120 minutes with a reperfusion interval of greater than or equal to 10 minutes every hour (beginning at 120 minutes of tourniquet inflation time). One consistency noted within this review of the literature is that tourniquet-related complications increase as tourniquet time increases;1 this directly relates to the hypoxic environment created by tourniquet inflation and the potential for resultant soft tissue damage.2
In general, animal studies suggest that at two hours of tourniquet inflation, the histologic,3 electrophysiological,4,5 and musculoskeletal impact4,6 of tourniquet use, while present and quantifiable, largely remains reversible.7
Few clinical studies examine tourniquet times greater than two hours. However, those studies with tourniquet inflation exceeding two hours displayed prolonged periods of ischemia that may cause irreversible complications; primarily neurologic.8,9 A systematic review of available literature conducted in 2012 commented on the lack of data available to distinguish at which point from 120 to 180 minutes is tourniquet inflation considered unsafe, later recommending that greater than or equal to 2.5 hours could be considered appropriate if one employs an appropriate ‘breathing period’ from the tourniquet.7 The (lower) pressures at which one uses tourniquets in modern practice may warrant further research in order to set specific time independent parameters for safe tourniquet use and to establish time as a separate factor from pressure. Until such data is available, most surgeons in practice accept the parameters of non-disrupted tourniquet inflation between 90-120 minutes as relatively safe2 with the need for reperfusion intervals assessed after the 120-minute mark.7
What You Should Know About Reperfusion Intervals
There is general agreement that tourniquet inflation should be for as short a time as possible, at as low a pressure as possible to minimize complications. However, there are certain circumstances under which surgery may exceed 120 minutes. For these circumstances, one may consider applying tourniquet “breathing periods.”7,10
A “breathing period” is a time of tourniquet deflation with subsequent re-inflation during the same procedure. This deflation interval allows for temporary reperfusion of the limb, assisting in repletion of the adenosine triphosphate (ATP) depleted during the period of ischemia11 as well as facilitating a shorter time to metabolic recovery with final tourniquet release.2,12,13 By decreasing metabolite load, reperfusion intervals are thought to be tissue protective in surgeries lasting over two hours.13
In an effort to determine optimal reperfusion times for prolonged tourniquet use, Newman demonstrated that hourly release of the tourniquet for 10 minutes ensured rapid metabolic recovery with maintenance of ATP levels in the muscle distal to the tourniquet. When deflating the tourniquet for intervals of only five minutes, tissue pH was more acidotic in the muscles beneath and distal to the tourniquet after subsequent ischemia.3
Pedowitz and colleagues came to a similar conclusion after measuring technetium-99 pyrophosphate uptake in animal skeletal muscle as a marker of muscle injury.4 In this study, researchers demonstrated that two hours of tourniquet-induced ischemia significantly increased technetium uptake in the thigh beneath the tourniquet; however, when employing hourly reperfusion periods of 10 minutes, there was significantly reduced technetium uptake into injured muscle (i.e. less injury observed). As 120 minutes of non-disrupted inflation time appears to be safe, recommendations exist that if one anticipates a need for surgical hemostasis greater than two hours, one may minimize muscle injury with 10 minute reperfusion intervals after each hour of cuff inflation.4,7,12,14,15
How Shape And Size Of Tourniquets Affects Outcomes
Contoured (curved) cuffs permit lower efficacious tourniquet pressures compared to straight cuffs on conical shaped extremities, such as that of the lower extremity, wider cuffs (four to five inches) distribute pressure more evenly to tissue structures, and the cuff should overlap itself on application ideally by seven to 15 cm.12,16
With the lower extremity placement of tourniquets there are generally three respective areas of placement: thigh; calf; and ankle. Of those, thigh and ankle tourniquet placements are common in podiatric surgery. At the respective tourniquet locations, the lower extremity is essentially tapered and conical in shape rather than cylindrical.
The literature notes that the combination of using a tourniquet that is as wide and contoured as possible permits a reduced pressure gradient across the cuff thereby reducing the required tourniquet pressure for arterial occlusion.1,17 Additionally, selecting a tourniquet with overlap length that minimizes fluctuations in pressure perioperatively is optimal, though no statistical justification for a measurement range has been identified.
Shape. For this tapered shape in the lower extremity, contoured tourniquet cuffs are ideal as they afford lower occlusion pressures when compared to straight cuffs of equal width.14,18,19 On average, a pressure reduction of 20 mmHg can take place with a wide, contoured cuff versus a standard width cylindrical cuff.19 One may attribute this reduction in limb occlusion pressure to the increased surface contact area via better fit, creating more equal distribution of pressure from center to distal tourniquet edges once inflated. Contoured tourniquets may also have the additional benefit of decreased displacement once inflated, theoretically reducing distraction during operative time and keeping the surgical field consistently visually optimized.
Width. There is an inverse relationship in the lower extremity between occlusion pressure and tourniquet width, denoting that the greater the tourniquet width, the lower the tourniquet pressure needed for arterial occlusion. Conversely, a narrower tourniquet width requires higher tourniquet pressures for appropriate arterial occlusion.3,17-23 One can attribute this inverse relationship to the increased efficiency in pressure transmission to deeper tissues when applied through a greater surface area (i.e. a wider cuff).21 When limited to the arterial occlusive pressure of a tourniquet, wider tourniquets have the additional benefit of increased duration tolerance and decreased perceived tourniquet pain.23 With respect to decreased limb occlusion pressure (LOP), studies comparing widths ranging from four to 10 cm as ‘narrow’ note a superiority of ‘wide’ cuffs ranging from 12 to 18 cm.3,17,18,20-23
Length. There is no standard guideline for cuff length. This should ideally be a flexible measurement based on each patient case; however there are suggestions of cuff length overlap in literature. Unclear as to the origin for the justification for this measurement range, Derner and Buckholtz in 1991 recommended that tourniquet cuff length should overlap six to eight inches in order to produce a more accurate tourniquet gauge perioperatively.15 More recently, various literature has quoted an ideal overlap between seven and 15 cm.12,14,16
What Do We Know About The Impact Of Tourniquet Location?
With many podiatric cases that include solely the foot (i.e. forefoot-, midfoot-, and hindfoot-exclusive cases), there exists the option to place a tourniquet at the thigh, calf, or distal ankle. While there is much research on the direct implications of using a tourniquet at those specific locations, there is a lack of data outlining the risk probability of using a tourniquet in one location versus another. For example, there is research that addresses risk probability of a DVT using a tourniquet in the lower extremity but there is minimal-to-no research that directly stratifies such an adverse event with variable location (thigh, calf, or ankle). One area found in which risk does associate with tourniquet location is tourniquet pain which supports the use at the ankle rather than the calf (thigh location was excluded from these studies).24,25
With extensive research existing on optimal tourniquet use, adverse event probability related to tourniquet location is an area for further study in order to describe optimal tourniquet use and provide better postoperative outcomes.
How Do Surgeons Actually Determine Tourniquet Pressure?
A primary recommendation is to calculate the limb occlusion pressure (LOP) to identify the appropriate tourniquet pressure for a specific patient, including an appropriate safety margin. A secondary recommendation we determined based on our literature review reports that the following fixed ranges are ‘acceptable’ for lower extremity tourniquet use if LOP is not utilized to calculate the lowest efficacious pressure:
• thigh use = 300mmHg;
• calf use = 200mmHg (approximately 91 percent efficacious at maintaining a bloodless surgical field); and
• ankle use = 250mmHg.
With various tourniquet-related complications encountered and documented, it is imperative to use pressures that maintain effective tourniquet function while limiting the amount of risk associated with tourniquet use. To do so, one should employ the minimum pressure at which the tourniquet is still functionally optimal (i.e. the minimum pressure required to stop arterial blood flow into the limb distal to the cuff). There are two measurement methods described to obtain this minimum pressure value: the limb occlusion pressure (LOP) or the arterial occlusion pressure (AOP).
How To Calculate And Apply The Limb Occlusion Pressure (LOP)
1. Use arterial doppler to identify source (dorsalis pedis or posterior tibialis artery); and then
2. Inflate the tourniquet in increments until you can no longer perceive the doppler signal.
This measurement allows one to account for patient-specific factors, such as blood pressure, limb circumference, limb shape, cuff application and design, as well as tissue characteristics.1,7,18,26-28 When using LOP in practical application, it is judicious to apply an additional pressure safety margin to account for physiologic variations and/or other environmental changes that may occur normally over the duration of a surgical procedure.1
Prior studies attempted to define optimal safety margins for lower extremity tourniquet use with relatively good success and bloodless surgical fields.18,27,29 Taking into account these previous studies and optimal safety values, Younger and colleagues developed a formula for pressure safety margin that does not require the operator to enter the limb type or size (see figure 1 below).17
Using this algorithm for the safety margin range applied to LOP, Younger and team found success rates of approximately 95 percent in good bloodless surgical field outcomes in 40 patients using thigh tourniquets. Additionally, in comparison to the typical thigh pressures seen intraoperatively (300 to 500mmHg) this formula was able to achieve a tourniquet pressure reduction of 19 to 42 percent.17
How To Calculate And Apply Arterial Occlusion Pressure (AOP)
Another method to calculate the effective minimum tourniquet pressure is the arterial occlusion pressure (AOP). One should note that this suggested method has differing descriptions in the literature (both descriptions outlined below):
1) AOP = [(systolic pressure - diastolic pressure) (limb circumference)/3(cuff width)] + diastolic pressure.22
2) AOP = [SBP + 10]/KTP30
SBP: Patient’s systolic blood pressure
KTP: Tissue padding coefficient
The first formula is derived from a 1993 paper published by Graham and colleagues, using blood pressure, limb circumferential, and cuff width to gauge the appropriate pressure setting per individual patient.22 Younger, Estebe and their respective colleagues reported that using this method of AOP with a 50 to 75mmHg safety margin, can decrease tourniquet pressures by 20 to 40 percent in the adult population in comparison to arbitrary default pressures.14,17 The disadvantage to this method is the potential necessity of pressure adjustment intraoperatively based on blood pressure fluctuations. Though similar to the LOP disadvantage, the way in which one measures LOP can account for the variables of padding underneath the tourniquet whereas that specific factor is unaccounted for in this AOP formula.
The second AOP measurement is based on SBP and extremity circumference. It is a formula derived from Tuncali and colleagues’ study using an 11 cm wide tourniquet on extremity circumferences ranging from 20 to 75 cm to create the above equation and establish the corresponding tissue padding coefficient (KTP; coefficients found in the paper appendix).30 However, this formula has a theoretic disadvantage, as the tourniquet design used to establish the equation has a fixed width of 11 cm and is a straight design cuff; preventing the use of different tourniquet widths or designs (i.e. contoured) with equation outcome accuracy.
Therefore, we recommend LOP as the method for calculating tourniquet pressure as it has the flexibility of use in more diverse situations (i.e. with different tourniquet designs) while still lowering the intraoperative tourniquet pressures to meet individual case requirements effectively.
Despite the current advantages to estimating LOP for tourniquet pressure settings (such as decreased risk of tourniquet complications) versus using a fixed pressure range like that commonly observed in modern practice, a survey of 317 podiatric surgeons revealed only seven percent consider LOP when selecting cuff pressure.31
One possible reason for this lack of LOP usage is the presumed increase in operating room time to establish the LOP.17 Using a photoplethysmograph sensor signal (pulse oximeter) on the toe, Pedowitz and team found that intra-op establishment of LOP required less than five minutes per patient.18 Similarly, Tuncali and colleagues averaged approximately three minutes (178.81 ± 25.46 seconds) to establish accurate LOP intra-operatively32,33 and, impressively, Younger and team averaged around 20 ± 6 seconds.34 With advancements in technology there is potential for methods producing shorter LOP calculation time (approximately 30 seconds),17,19,35,36 eliciting more advantages to using LOP as a standard for identifying the appropriate individualized tourniquet pressure.
Nevertheless, surgeons rarely calculate the minimum pressure for effective tourniquet use; more often, we see a fixed value for thigh, calf or ankle placement. If this is the case, we should critically evaluate the research from which we obtain these numbers. The authors attempted to extract the most common pressure or ranges (from 2000 onward) published on human lower extremity tourniquet usage where there was comment on both tourniquet pressure and hemostasis, given that the most common advantage to tourniquet inflation today is the ability to have a bloodless surgical field.
• A commonly noted effective tourniquet pressure at the thigh was 300mmHg. We found no mentioned need for increase in tourniquet pressure at this value with adequate hemostasis from studies listed (see table 1 below). One should note that other significantly lower pressures listed in this table reveal up to 90 percent success in maintaining bloodless surgical field.
• A commonly noted effective tourniquet pressure at the calf was 200mmHg, which maintained a bloodless surgical field at least 91 percent of the time from studies listed (see table 2 below).
• A commonly noted effective tourniquet pressure at the ankle was 250mmHg, which proved to be an effective pressure value without breakthrough bleeding from studies listed (see table 3 below).
Tourniquet pressure ranges are so vastly different within current practice that it is difficult to determine if these numbers are based on attending preference, hospital policy or rooted in evidence-based research. These differences are highlighted through many surveys conducted over the years regarding tourniquet use in practice.
In 2003 Kalla and team conducted a survey among foot and ankle surgeons in the US and Canada, with 317 responses on current trends in tourniquet use.31 For the most common pressures utilized, ankle and calf tourniquet pressures ranged from 201 to 350mmHg with the majority of ankles (72 percent) and majority of calves (57 percent) using between 201 to 250mmHg. Thigh cuff users also reported pressures from 201 to 351mmHg, however the majority of (62 percent) utilized higher pressures around 301-350mmHg.
In 2005 Younger and colleagues conducted a similar survey targeted at accredited American Orthopaedic Foot and Ankle Society (AOFAS) surgeons.37 This survey evaluated what aspects of tourniquet use have essentially unanimous acceptance and which vary; finding primarily that AOFAS members cited complications (strikethrough, nerve injury, etc.) and contraindications (graft, DVT, infection, etc.) specific to tourniquet use with consistency; however the variance most notable was tourniquet pressure setting. To determine tourniquet pressure settings, 43 percent of surgeons factored in blood pressure and limb size, and only nine percent considered the limb occlusion pressure.37
Another survey conducted among orthopedic surgeons, both in the academic and community settings, supported the notion that evidenced-based medicine is not the primary source by which one derives appropriate tourniquet pressure.38 Approximately 50 percent of responding surgeons were unfamiliar with literature on safe tourniquet use. This survey further demonstrated that respondents who were aware of literature on safe tourniquet use frequently used higher pressures than currently supported by literature.38
The response to these surveys on lower extremity tourniquet usage emphasizes the variance within the surgical community on tourniquet pressures used in practice and the methods by which we conclude appropriate pressure. A movement for improving patient safety has led to decreased tourniquet pressures in podiatric practice distancing us from the now seemingly high pressures of 500mmHg to 1000mmHg previously used in the lower extremity.39 However, the disparity apparent between current surgical practice and current literature on tourniquet use, begs the question as to if the numbers we use in practice now could be more tailored based on randomized clinical trial data to further optimize patient safety.
Discussion And Concluding Thoughts
Pneumatic tourniquets are used in an estimated 15,000 orthopedic and non-orthopedic surgical procedures daily in the United States and elsewhere.1 Despite a long history and widespread use the tourniquet is by no means a benign instrument, and, though low in probability, is associated with a barrage of potential complications. As with any complication, taking preventative measures and having an awareness of complication existence can help reduce the frequency of their occurrence.
With extensive use of tourniquets, an innate assumption that knowledge on tourniquet safety is also widespread would seem straightforward; yet many studies and research questionnaires point to this not being the case.31,37,38,40 Evaluating why this disparity exists, we must consider the formal instruction surgeons receive on tourniquet application, of which we believe there is none. As with many other surgical skills, we find that it is common for a senior surgeon to teach tourniquet application to matriculating residents, possibly creating a heterogeneous educational experience that will carry into surgical practice.
To reduce complications and provide the best patient safety, it is necessary for surgeons to have a well-rounded knowledge of appropriate tourniquet application and to employ such measures in daily practice. With the creation of the guidelines found throughout this review, it is our hope to help narrow the academic and practical gap and create evidence-based practices that provide the safest patient outcomes. This literature review was intended to extrapolate recommendations from data existing on safe lower extremity tourniquet use as well as provide a comprehensive background on the practice. From the review conducted, a table with our current recommendations on safe lower extremity tourniquet use is provided in table 4 below.
Dr. Wilson is a third-year Podiatric Medicine and Surgery resident at St. Mary’s Medical Center in San Francisco, Calif.
Dr. Oloff is the Podiatric Medicine and Surgery Residency Program Director at St. Mary’s Medical Center in San Francisco, Calif. He is an attending physician at the Palo Alto Medical Foundation in Burlingame, Calif.
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