Tourniquet apparatus for intravenous regional anesthesia

Tourniquet apparatus for use in intravenous regional anesthesia and limb surgery includes a pressurizing cuff for substantially encircling a limb and applying a varying pressure to an underlying vein in response to variations in a pressure control signal, applied venous pressure sensing means for producing an applied venous pressure signal representative of a pressure applied by the cuff to the underlying vein, venous fluid pressure estimation means for producing a venous fluid pressure signal representative of the pressure of fluid in the vein distal to the cuff, and pressure control means responsive to the venous fluid pressure signal and applied venous pressure signal for generating a pressure control signal to maintain a predetermined relationship between the applied venous pressure signal and the venous fluid pressure signal. The apparatus automatically controls the introduction, retention and release of anesthetic fluid in the limb.

FIELD OF THE INVENTION 
This invention pertains to automated tourniquet apparatus for use in 
intravenous regional anesthesia of a limb for surgery. In particular, the 
invention pertains to apparatus having means for automatically controlling 
the introduction, retention and release of anesthetic fluid in a portion 
of the limb distal to a pressurizing cuff. 
BACKGROUND OF THE INVENTION 
This invention pertains to apparatus for automating the administration and 
management of intravenous regional anesthesia (IVRA) for both upper and 
lower limbs. IVRA is an alternative to general anesthesia for limb 
surgery. IVRA has proven to be a simple and useful technique for 
satisfactorily anesthetizing the upper limb and is potentially well suited 
for greatly expanded utilization in surgery of lower limbs and in 
outpatient settings. In these settings, which are rapidly increasing in 
number worldwide, there is a large and unmet need for a rapid, simple, 
safe, and reliable technique for establishing limb anesthesia. However, 
significant practical problems with the technology of IVRA in the prior 
art, considerable variations in skill involving the manual administration 
of IVRA, and lingering concerns over the potential toxicity of certain 
IVRA agents, particularly for lower limbs, have greatly limited the 
acceptance of this promising technique. 
IVRA is an anesthetic technique which requires the use of surgical 
pneumatic tourniquet. Surgical pneumatic tourniquet systems are frequently 
used on the upper and lower limbs to help maintain a bloodless operative 
field by regulating the maximum pressure applied to the limb by an 
encircling cuff at a pressure sufficient to stop arterial blood flow past 
the cuff for the duration of a surgical procedure. During operations 
performed under IVRA, the pneumatic tourniquet serves an additional role 
of preventing local anesthetic agent introduced into the veins in the limb 
distal to the cuff from flowing proximally past the cuff and out of the 
limb into the circulatory system. An insufficient pressure in the 
tourniquet cuff soon after introduction of the local anesthetic agent into 
the limb may result in the anesthetic agent entering the circulatory 
system in a high concentration, which can cause serious adverse reactions 
such as cardiovascular collapse, respiratory depression, epileptic 
seizures or even death. 
IVRA is typically administered as follows. Blood is first exsanguinated 
from the limb, often by wrapping the limb with an elastic bandage, 
beginning distally and wrapping tightly towards the heart; after 
exsanguination, a tourniquet cuff is applied proximal to the operative 
site and inflated to a predetermined cuff pressure. The elastic bandage is 
removed and an anesthetic agent such as lidocaine mixed with sterile 
saline is introduced into a vein in the limb through an intravenous 
cannula. The anesthetic fluid mixture remains in the veins in the limb as 
long as the tourniquet is inflated to a sufficient pressure. Premature 
release of the agent shortly after introduction, as well as leakage of the 
agent under the cuff during introduction or during surgery, are serious 
and recognized hazards associated with prior art devices used for IVRA. 
Administration of IVRA may involve the use of a single-bladder or a 
dual-bladder tourniquet cuff. If a dual-bladder cuff has been chosen and 
applied to the limb of a patient, typically the proximal bladder of the 
cuff is first inflated, after limb exsanguination, to a pressure intended 
to prevent blood flow past the cuff both proximally and into the 
exsanguinated limb. The anesthetic fluid mixture is then introduced into a 
vein in the limb as described previously. After a period of time 
sufficient for the anesthetic fluid mixture to induce analgesia in the 
limb below the proximal bladder of the cuff, the distal bladder is 
inflated to a pressure intended to prevent the flow of fluid past the cuff 
both proximally and distally. The distal bladder of the cuff is thus 
inflated over anesthetized tissue, thereby resulting in greater comfort 
for the patient for a greater period of time, thus potentially extending 
both the duration of surgical procedures which can be performed under IVRA 
and the number of patients for whom IVRA will be tolerable. 
Surgical tourniquet systems of the prior art typically include an 
inflatable cuff for applying to a limb and an automatic pressure regulator 
for regulating the inflation pressure in the cuff near a reference level 
selected by an operator or determined automatically. Some tourniquet 
systems in the prior art have been associated with a number of reported 
hazards and problems which are not specific to IVRA, such as unnecessarily 
high pressures applied by the cuff leading to nerve injury and tissue 
damage beneath the tourniquet cuff, and unexpectedly low pressures applied 
by the cuff leading to sudden blood flow into the surgical site, 
complication of surgery, passive congestion of the limb, and hemorrhagic 
nerve infiltration. Additionally, the cuffs of prior art systems have 
design limitations which make the cuffs difficult to apply consistently to 
limbs of different shapes and sizes. These design limitations of many 
prior art inflatable cuffs and tourniquet systems lead to clinical 
situations in which the maximum pressure actually applied by a prior art 
cuff to a limb is significantly different than the pressure in the 
inflatable bladder of the cuff and thus pressure indicated by the 
tourniquet pressure display. 
There are also specific hazards associated with the use of prior art 
tourniquet systems for IVRA because the pressure of liquid anesthetic 
agents introduced into limb veins has generally not been monitored in the 
prior art, which has led to excessive pressures in the veins distal to the 
tourniquet cuff, thus causing anesthetic agent to flow past the cuff and 
into the general circulation. This can lead to an ineffective regional 
anesthesia in general, and even to cardiac arrest and death in reported 
cases. 
A serious problem associated with the use of prior art tourniquet systems 
in relation to the delivery of anesthetic agents for IVRA is that in the 
prior art the maximum pressure applied by the tourniquet cuff to the limb 
is determined and adjusted independently of, and without knowledge of, the 
delivery pressure of the anesthetic agent. Moreover, the anesthetic agent 
is delivered in the prior art manually at a maximum pressure that is 
highly variable and dependent on the variations in operator technique. 
Most significantly, in the prior art, the pressure of liquid in the veins 
distal to the cuff is not a function of the maximum pressure applied by 
the tourniquet cuff. Consequently, it cannot be assured that the applied 
pressure is sufficiently greater than the venous pressure distal to the 
cuff so that no anesthetic agent will flow unexpectedly past the cuff and 
into the general circulation. 
Another problem associated with prior art tourniquet systems is that no 
provision exists for automatically adjusting the pressure applied by the 
cuff such that bleeding arterial vessels can be observed in the surgical 
wound prior to completion of surgery, while the anesthetic fluid mixture 
is simultaneously retained in the veins of the limb distal to the cuff. 
Bleeding vessels can be observed only if the applied pressure is reduced 
sufficiently to permit arterial inflow; however, at the same time the 
applied pressure must be great enough to stop venous outflow and thereby 
maintain anesthesia. Prior art tourniquet systems do not provide any 
methods for reliably establishing and maintaining this condition. 
For reasons of improved patient safety, there is a clinical need for wider 
tourniquet cuffs which appear to stop blood flow distal to such cuffs at 
lower inflation pressures than narrower cuffs. However, a significant 
problem with prior art cuffs in general, and with wide cuffs in 
particular, is that reliable and consistent sealing of the bladders is 
difficult due to the high forces generated internally because the forces 
on the sealed seams of bladders are generally proportional to the total 
internal area of the cuff multiplied by the inflation pressure. 
A number of problems are associated specifically with prior art pneumatic 
cuffs used for IVRA. First, prior art cuffs have generally employed two 
bladders which can be inflated or deflated independently. Each bladder of 
an IVRA cuff must be narrower than a conventional tourniquet cuff in order 
that the IVRA cuff can fit on the patient's limb and not obstruct the 
desired surgical site. Second, prior art tourniquet cuffs commonly employ 
a flexible thermoplastic stiffener to constrain the inflation of the 
bladder and direct cuff inflation inwardly toward the encircled limb. The 
incorporation of stiffeners into prior art cuffs stabilizes the cuff 
bladders across the bladder width and thus reduces the tendency of cuffs 
to roll longitudinally down a limb when the bladders are pressurized. 
However, certain problems and hazards are associated with the use of prior 
art stiffeners. First, the incorporation of stiffeners into prior art 
tourniquet cuffs has tended to cause such cuffs to form a substantially 
cylindrical shape when applied to a limb, resulting in a poor shape match 
for limbs that are non-cylindrical in shape in the region underlying the 
encircling cuff. The use of stiffeners in prior art cuffs has also tended 
to cause the cuffs to be more difficult to apply by operating room staff 
in a snug and consistent manner. Also, the incorporation of stiffeners 
into prior art cuffs has added significantly to the costs of manufacture 
of such cuffs. Finally, the incorporation of stiffeners into prior art 
cuffs has created difficulties when the cuffs are cleaned or resterilized 
because certain resterilization processes apply heat to the cuffs, 
distorting the shape of stiffeners which are commonly formed of flexible 
thermoplastic material, thus detrimentally affecting the subsequent 
ability of the distorted cuff to conform smoothly to the encircled limb. 
The present invention overcomes many of the hazards and problems associated 
with technology described in the prior art and significantly reduces 
variations in the quality and safety of IVRA associated with variable 
knowledge, skill and experience of operators. Thus the present invention 
facilitates the increased use of IVRA for anesthesia of both upper and 
lower limbs. 
An object of the present invention is to provide tourniquet apparatus for 
intravenous regional anesthesia which automatically relates the maximum 
pressure applied to a limb by the tourniquet cuff to the maximum pressure 
of fluid in the veins in a portion of the limb distal to the cuff, so that 
the flow of fluid past the cuff proximally and into the circulatory system 
can be automatically regulated and stopped in a safe and reliable manner, 
as desired by an anesthetist or surgeon. 
Another object of the present invention is to provide tourniquet apparatus 
having automatic means for estimation of the lowest pressure which can be 
applied by the cuff of the tourniquet apparatus to a limb in order to stop 
blood flow distal to the cuff, where the cuff has design and physical 
characteristics which are substantially different than those of a 
conventional blood pressure cuff, where the cuff is applied with an 
undetermined degree of snugness at any location along the limb between its 
proximal and distal end, and where there may be a substantial mismatch 
between the shape of the encircled limb and the shape of the encircling 
cuff. 
A related object is to provide tourniquet apparatus having wider and safer 
cuffs for reducing the probability that blood will unexpectedly flow past 
the cuff distally, for reducing the probability that anesthetic fluid 
mixture will unexpectedly flow past the cuff proximally, for reducing the 
probability that clinical staff will make errors in applying the cuff to 
the correct location anatomically, and for increasing the tolerance of the 
patient to the cuff when pressurized so that more patients can take 
advantage of intravenous regional anesthesia. 
Another object of the present invention is to provide means for more 
consistent and safer exsanguination of a portion of the limb distal to the 
tourniquet cuff prior to introduction of anesthetic agent into a vein in 
that limb portion, by automatically regulating the pressure in a pneumatic 
exsanguinating cuff distal to the tourniquet cuff for a period of time, 
and by automatically and sequentially inflating the tourniquet cuff 
proximal to the exsanguinating cuff when sufficient blood has been 
exsanguinated from the surrounded portion. 
The applicant is aware of the following United States Patents which are 
more or less relevant to the subject matter of the applicant's invention. 
______________________________________ 
4,469,099 9/1984 McEwen 128/327 
4,479,494 10/1984 McEwen 128/327 
4,605,010 9/1986 McEwen 128/686 
4,770,175 9/1988 McEwen 128/327 
4,869,265 9/1989 McEwen 128/774 
4,321,929 3/1982 Lemelson 128/630 
4,635,635 1/1987 Robinette-Lehman 
128/327 
4,781,189 11/1988 Vijil-Rosales 128/327 
4,168,063 9/1979 Rowland 273/54B 
3,164,152 1/1965 Vere Nicoll 128/87 
4,667,672 5/1987 Romanowski 128/327 
______________________________________ 
The applicant is also aware of the following United States patent 
application which is more or less relevant to the subject matter of the 
applicant's invention. 
U.S. application Ser. No. 388,669; Title: Tourniquet for Regulating Applied 
Pressures; Art Unit: 335; Inventor: McEwen. 
SUMMARY OF THE INVENTION 
The invention is directed toward tourniquet apparatus for controlling the 
release of anesthetic fluid contained in a limb vein distal to a 
pressurized cuff, comprising: a pressurizing cuff for substantially 
encircling a limb and applying a varying pressure to an underlying vein in 
response to variations in a pressure control signal; applied venous 
pressure sensing means for producing an applied venous pressure signal 
representative of a pressure applied by the cuff to the underlying vein; 
venous fluid pressure estimation means for producing a venous fluid 
pressure signal representative of the pressure of fluid in the vein distal 
to the cuff; and pressure control means responsive to the venous fluid 
pressure signal and applied venous pressure signal for generating a 
pressure control signal to maintain a predetermined relationship between 
the applied venous pressure signal and the venous fluid pressure signal. 
The venous fluid pressure estimation means may be a signal representative 
of a predetermined constant reference pressure. Interval selection means 
may be included for determining a first time interval and a second time 
interval wherein the pressure control means generates a pressure control 
signal so that during the first time interval the pressure applied by the 
cuff to the underlying vein is greater than the minimum pressure which 
stops the flow of fluid in the vein past the cuff proximally, and during 
the second time interval the pressure applied by the cuff to the vein is 
less than the minimum pressure which stops the flow of fluid in the vein 
past the cuff proximally. 
The invention is also directed to improved cuff apparatus for use in 
intravenous regional anesthesia comprising an occlusive band for applying 
pressure to a limb, and locating means on the band for locating the band 
on the limb at a predetermined distance from an anatomical reference site. 
The invention is further directed to apparatus for estimating the minimum 
pressure which must be applied by a cuff to a limb in order to stop blood 
flow past the cuff, comprising: a pressurizing cuff responsive to cuff 
pressure control means for substantially encircling and applying pressure 
to a limb; distal flow sensing means for sensing the flow of blood past 
the pressurizing cuff; cuff pressure control means for controlling the 
pressure applied by the pressurizing cuff to the limb near a reference 
pressure; and flow detection means responsive to the distal flow sensing 
means for varying the reference pressure to estimate the lowest reference 
pressure at which no blood flow can be sensed past the pressurizing cuff. 
The pressurizing cuff may be a tourniquet cuff having design and 
construction characteristics substantially different than those of a cuff 
required for accurate estimation of blood pressure at the selected 
location by a noninvasive technique. Advantageously, occlusion pressure 
estimation means responsive to the lowest reference pressure at which no 
blood flow can be sensed past the pressurizing cuff may be included for 
producing an estimate of the lowest constant reference pressure at which 
no blood will flow past the pressurizing cuff over a time period that is 
suitably long for the performance of a surgical procedure. 
The invention is also directed to automatic exsanguinating tourniquet 
apparatus to facilitate intravenous regional anesthesia comprising: 
occlusive cuff means for encircling a limb and applying a pressure to the 
encircled limb portion; exsanguinating cuff means for surrounding and 
applying a pressure to a portion of the limb distal to the occlusive cuff 
means; first reference pressure means for producing a first pressure 
signal representative of a pressure to be applied by the exsanguinating 
cuff means to displace blood from the portion of the limb surrounded by 
the exsanguinating cuff means; second reference pressure means for 
producing a second pressure signal representative of a pressure to be 
applied by the occlusive cuff means to occlude blood flow distal to the 
occlusive cuff means; and automatic pressure regulating means for 
regulating pressure applied by the exsanguinating means near a pressure 
indicated by the first pressure signal for a first period of time, and for 
regulating a pressure applied by the occlusive means near a pressure 
indicated by the second pressure signal for a second period of time 
suitably long for the performance of a surgical procedure.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The embodiment illustrated is not intended to be exhaustive or to limit the 
invention to the precise form disclosed. It is chosen and described in 
order to explain the principles of the invention and its application and 
practical use, and thereby enable others skilled in the art to utilize the 
invention. 
Referring to FIG. 1, an inflatable tourniquet cuff 2, which has locating 
strip 4 for positioning cuff 2 relative to an anatomical landmark, is 
applied to limb 6. Cuff 2 is connected by tubing 8 to pressure transducer 
10 (Spectramed 072911-000-583, Spectramed Inc., Oxnard Calif.), and then 
by tubing 12 to valves 14 (EV0-3-12V, Clippard Instrument Laboratory, 
Cincinnati Ohio). Valves 14 allow tubing 12 to be connected to tubing 16 
and pressure source 18 which provides a source of gas at a regulated 
pressure between zero and 500 mmHg. This arrangement provides a means of 
inflating cuff 2 to apply a distribution of pressures varying from zero to 
some maximum level to the tissues and blood vessels of limb 6 beneath cuff 
2, with the specific pressure distribution dependent upon cuff design and 
application technique. Valves 14 are controlled by an applied pressure 
control signal generated by microcomputer 20. The valves 14 specified 
above, in addition to allowing tubing 12 to be connected to pressure 
source tubing 16, are responsive to a control signal for venting tubing 12 
to atmosphere, thereby to deflate cuff 2. Pressure transducer 10 generates 
an inflation pressure signal which indicates the pressure of gas in cuff 2 
and which is processed by signal conditioner 22, digitized by analog to 
digital converter (ADC) 24, and communicated to microcomputer 20. Limb 
pressure sensor 26, such as the biomedical pressure transducer described 
by McEwen in U.S. Pat. No. 4,869,265, is placed underneath cuff 2 at a 
location such that the maximum pressure applied by cuff 2 to limb 6 is 
transduced. Limb pressure sensor 26 generates an applied pressure signal 
which is indicative of that maximum pressure. The applied pressure signal 
is processed by signal conditioner 28, digitized by ADC 24, and 
communicated to microcomputer 20. Photoplethysmographic flow sensor 30 is 
placed on a portion of limb 6 distal to cuff 2 in order to sense blood 
flow in limb 6. Sensor 30 generates a blood flow signal which is processed 
by signal conditioner 32, digitized by ADC 24, and communicated to 
microcomputer 20. Cannula 34 is inserted in a vein in limb 6 distal to 
cuff 2 and is connected by tubing 36 to pressure transducer 38 to allow 
estimation of the venous fluid pressure; pressure transducer 38 generates 
a venous fluid pressure signal which is processed by signal conditioner 
40, digitized by ADC 24, and communicated to microcomputer 20. Cannula 42 
is inserted in a vein in limb 6 distal to cuff 2 and is connected by 
tubing 44 to pressure transducer 46; pressure transducer 46 is connected 
by tubing 48 to anesthetic container 50 which holds a fluid anesthetic 
such as lidocaine mixed with a sterile saline solution; anesthetic 
container 50 is typically a sterile saline bag in which the fluid 
anesthetic has been previously introduced with a syringe. The mixture of 
fluid anesthetic and sterile saline is delivered by delivery module 52; 
delivery module 52 applies a pressure to anesthetic container 50 and 
thereby forces the mixture from anesthetic container 50 into the vein 
through cannula 42. Delivery module 52 is connected by tubing 54 and 
valves 56 to pressure source 18. Valves 56, which control the delivery 
pressure of the anesthetic fluid mixture, are responsive to the delivery 
pressure control signal. Pressure transducer 46 generates a delivery 
pressure signal representative of the anesthetic fluid mixture pressure 
which is processed by signal conditioner 84, digitized by ADC 24, and 
communicated to microcomputer 20. 
FIG. 2 shows exsanguinating cuff 62 applied to limb 6. Referring to FIG. 1, 
exsanguinating cuff 62, such as the Jobst-Jet Air Splint (Jobst Institute 
Inc., Toledo Ohio) of a size appropriate for the portion of limb 6 to be 
exsanguinated, is connected through tubing 64 to pressure transducer 66; 
pressure transducer 66 is connected through tubing 68 and valves 70 to 
pressure source 18. This arrangement provides exsanguinating cuff 62 with 
a means of inflation. Valves 70 are operated by an exsanguinating control 
signal from microcomputer 20 in order to vary the pressure in 
exsanguinating cuff 62. This produces a variation in the distribution of 
pressures applied by exsanguinating cuff 62 to limb 6. Pressure transducer 
66 generates an exsanguinating pressure signal which is processed by 
signal conditioner 72, digitized by ADC 24, and communicated to 
microcomputer 20. Doppler blood flow sensor 74 positioned under 
exsanguinating cuff 62 over an artery in limb 6 generates a residual blood 
signal which is processed by signal conditioner 76, digitized by ADC 24, 
and communicated to microcomputer 20. 
The user communicates with the system by means of user panel 78. Switches 
80 on user panel 78 are used to input information and commands from the 
user to microcomputer 20, and microcomputer 20 reports pressures, system 
status, and alarms to the user by audio/visual display 82. 
In operation, the user instructs microcomputer 20 by means of user panel 78 
to automatically estimate the lowest reference pressure at which no blood 
flow can be sensed past cuff 2 by photoplethysmographic blood flow sensor 
30. This is accomplished by varying the reference pressure which causes 
the maximum pressure applied by cuff 2 to vary accordingly, and by 
monitoring the resulting variations in blood flow distal to cuff 2 as 
follows. Microcomputer 20 produces an applied pressure control signal 
which activates valves 14 to inflate cuff 2, thereby causing the maximum 
pressure applied to limb 6 by cuff 2 to increase as indicated by the 
applied pressure signal produced by sensor 26. While the reference 
pressure is being increased, microcomputer 20 detects the lowest applied 
pressure at which the flow signal falls below a predetermined threshold 
near zero. This value of the applied pressure is an estimate of lowest 
reference pressure which stops blood flow past cuff 2. Microcomputer 20 
then acts to increase the applied pressure to 20 mmHg above this lowest 
reference pressure, after which an applied pressure control signal is 
generated to deflate cuff 2, thereby decreasing the applied pressure. 
While cuff 2 is being deflated, microcomputer 20 monitors the blood flow 
signal from sensor 30 and detects the applied pressure at which the flow 
signal exceeds the predetermined threshold. This value of the applied 
pressure is an estimate of the highest reference pressure at which blood 
flow past cuff 2 can be sensed. Microcomputer 20 then calculates the mean 
of the highest reference pressure and lowest reference pressure thus 
obtained and adds 75 mmHg to this mean value, thereby producing an 
estimate of the lowest constant reference pressure at which no blood will 
flow past cuff 2 over a time period which is suitably long for the 
performance of a surgical procedure. Once the lowest constant reference 
pressure has been estimated, blood flow sensor 30 is removed if clinically 
desired. For unusual clinical situations in which a blood flow signal 
cannot be detected by microcomputer 20, provision is made for an estimate 
of the lowest constant reference pressure to be entered manually by the 
user through user panel 78. 
Following the estimation of the lowest constant reference pressure, the 
user instructs microcomputer 20 with switches 80 on user panel 78 to 
exsanguinate the portion of limb 6 surrounded by exsanguinating cuff 62. 
This is accomplished as follows. Microcomputer 20 generates an 
exsanguinating control signal which activates valves 70 and thus causes 
exsanguinating cuff 62 to inflate to a predetermined inflation pressure of 
approximately 100 mmHg. The pressure applied to limb 6 by exsanguinating 
cuff 62 is regulated at a constant level by microcomputer 20 using 
pressure transducer 66 and valves 70. Microcomputer 20 monitors the 
residual blood signal from Doppler blood flow sensor 74 to determine the 
period of time that the constant pressure is applied in order to displace 
a significant volume of blood from the portion of limb 6 surrounded by 
exsanguinating cuff 62. As exsanguinating cuff 62 inflates, the amplitude 
of the pulsatile signal detected by Doppler blood flow sensor 74 
decreases, thereby providing an indication that arterial inflow is being 
reduced. After the amplitude of the residual blood signal has fallen below 
a threshold near zero, the pressure is maintained at the constant level 
for two minutes, after which the portion of limb 6 surrounded by 
exsanguinating cuff 62 is considered to be adequately exsanguinated. For 
unusual situations in which a residual blood signal cannot be obtained by 
microcomputer 20 from sensor 74, provision is made for the use to define 
the period of time exsanguinating cuff 62 is to remain inflated. 
Microcomputer 20 then generates an applied pressure control signal to 
inflate cuff 2 to the lowest constant reference pressure previously 
estimated as described above. This stops blood flow past cuff 2 in the 
exsanguinated portion of limb 6 distal to cuff 2. Thereafter, 
microcomputer 20 continues to automatically regulate the maximum pressure 
applied to limb 6 by cuff 2 near the lowest constant reference pressure to 
stop blood flow past cuff 2 for a period of time suitably long for the 
performance of a surgical procedure. 
After exsanguination, cannula 34 is inserted into a vein in limb 6 distal 
to cuff 2, and cannula 42 is inserted into a vein in limb 6 appropriate 
for introduction of the anesthetic fluid mixture. Microcomputer 20 is then 
instructed by the user through user panel 78 to deliver the anesthetic 
fluid mixture at a maximum pressure such that the anesthetic fluid mixture 
does not flow proximally past cuff 2. Microcomputer 20 analyses the 
applied pressure signal from limb pressure sensor 26 and the delivery 
pressure signal from transducer 46 in order to generate a delivery control 
signal such that the ratio of the delivery pressure signal to the applied 
pressure signal is less than 0.75. Microcomputer 20 does not allow the 
delivery pressure to exceed a maximum level of 100 mmHg for safety 
reasons. In an unusual clinical situation when the delivery pressure 
cannot be controlled, such as when the user may have to pressurize 
anesthetic container 50 manually, provision is included for stopping the 
flow of the anesthetic fluid mixture past cuff 2 proximally by increasing 
the pressure applied to the limb. This is done by having microcomputer 20 
monitor the delivery pressure signal by means of transducer 46 and 
generate an applied pressure control signal such that the ratio of the 
delivery pressure signal to the applied pressure signal is less than 0.75. 
Once the anesthetic fluid mixture has been delivered to a vein in limb 6, 
it must be retained in the portion of limb 6 distal to cuff 2 during most 
of the surgical procedure and released near the end of the surgical 
procedure. The flow of anesthetic fluid mixture past cuff 2 is controlled 
according to the following algorithm. Microcomputer 20 monitors the 
applied pressure signal from sensor 26 and the venous fluid pressure 
signal from transducer 38. Microcomputer 20 then generates an applied 
pressure control signal such that the maximum pressure applied by cuff 2 
is regulated at a pressure at least 50 mmHg above the venous fluid 
pressure. Because the maximum applied pressure is at least 50 mmHg greater 
than the venous fluid pressure, the anesthetic fluid mixture is retained 
within limb 6. 
When release of the anesthetic fluid mixture from limb 6 is desired, 
microcomputer 20 generates an applied pressure control signal such that 
the maximum pressure applied by cuff 2 is regulated at a level below the 
venous fluid pressure to allow outflow of the anesthetic fluid mixture. In 
clinical cases where it is important to identify bleeding arterial vessels 
in the surgical site prior to completion of surgery without releasing the 
anesthetic fluid mixture from limb 6, the user can cause microcomputer 20 
to generate an applied pressure control signal such that the maximum 
pressure applied by cuff 2 is regulated at a pressure less than the lowest 
constant reference pressure previously determined, but above the venous 
fluid pressure. In this way, arterial blood flows past cuff 2 distally, 
but venous fluid does not flow past cuff 2 proximally. This provision 
significantly extends the range of surgical procedures in which 
intravenous regional anesthesia can be used. 
In a condition where it is not possible to use cannula 34 and transducer 38 
to estimate venous fluid pressure, provision is included for microcomputer 
20 to substitute 20 mmHg for the venous fluid pressure. 
Near the end of the surgery, the user instructs microcomputer 20 to release 
the anesthetic fluid mixture from limb 6 in a controlled manner over a 
period of time with user panel 78. This is accomplished as follows. First, 
microcomputer 20 generates an applied pressure control signal so that the 
maximum pressure applied by cuff 2 is regulated at a pressure which allows 
venous outflow from limb 6 for a period of 10 s to allow a portion of the 
anesthetic fluid mixture to be released from the vein of limb 6. 
Microcomputer 20 then generates an applied pressure control signal so that 
the maximum pressure applied by cuff 2 is regulated at a higher pressure 
so that any flow of the anesthetic fluid mixture past cuff 2 is stopped. 
This higher pressure is regulated for a period of 60 s in order to allow 
assimilation of the anesthetic fluid mixture and venous blood into the 
general circulation. The foregoing sequence of increasing and decreasing 
the maximum pressure applied to limb 6 by cuff 2 is repeated three times, 
after which cuff 2 is completely depressurized. This procedure allows for 
complete release of the anesthetic fluid mixture from limb 6 in a safe 
manner. Provision has been made so that the time interval over which the 
applied pressure remains at the lower pressure, the time interval over 
which the applied pressure remains at the higher pressure, and the number 
of times that the applied pressure is cyclically decreased and then 
increased can be overridden or changed. 
FIG. 3 shows details of inflatable tourniquet cuff 2. Cuff 2 is fabricated 
as described by Robinette-Lehman in U.S. Pat. No. 4,635,635. In contrast 
to Robinette-Lehman, as can be seen in FIGS. 3 and 4, cuff 2 has no 
stiffener, is not arcuate in shape, includes locating strip 4 for 
positioning cuff 2 on limb 6 at a predetermined distance from an 
anatomical landmark, is substantially different in width, and is otherwise 
different as described below. 
As can be seen in FIG. 3, tourniquet cuff 2 has an inflatable chamber 86 
which includes a plurality of elongated tubular portions 88 which are 
connected in a generally parallel array, and which are in fluid 
communication by passageways 90. Tubular portions 88 are formed by joining 
together at seams 96 two plastic layers 92,94 which form the walls of 
inflatable chamber 86. Cuffs having chamber widths of 15, 20 and 25 cm, 
instead of the conventional maximum width of less than 9 cm, were 
fabricated. Fabrication of these wider cuffs was possible because the 
plurality of tubular portions 88 in inflatable chamber 86 act to 
significantly reduce the forces on seams 96, because the forces on seams 
96 are generally proportional to the total internal area bounded by seams 
96 multiplied by the inflation pressure. 
The tubular portions 88, their adjacent seams 96, and passageways 90 are 
hereinafter referred to as flutes 98. The plurality of elongated tubular 
portions 88 in inflatable chamber 86 stiffens cuff 2 and allows for a 
desired distribution of pressure to be applied to limb 6 by choosing 
appropriate distances between seams 96, since varying these distances 
results in a change in the pressure distribution underlying cuff 2. Cuff 2 
is wrapped about limb 6 and is held in place by female Velcro strips 58 
and male Velcro strips 60. Cuff 2 is further held in place by tying 
together the ends of strap 100 after cuff 2 has been applied to limb 6. 
Cuff 2 is inflated with gas via ports 102. 
FIG. 4 is a sectional view of inflatable tourniquet cuff which shows 
inflatable chamber 86 and two outer layers 104,106. 
For certain surgical procedures of long duration, dual-bladder cuff 108 
depicted in FIGS. 5, 6, and 7 is used for increased comfort. In cuff 108, 
two bladders 110, 112 overlap and are permanently bonded together such 
that 30 percent of the width of each bladder lies within the overlapping 
region 114. Bladders 110, 112 are independently and selectably inflatable 
by appropriate valves and switching. The overlapping of bladders 110,112 
around limb 6 in a predefined relationship distributes the pressure 
applied by each bladder over a greater length along limb 6 than would be 
possible if narrower bladders which did not overlap occupied the same 
total width. Distribution of pressures over a greater length along the 
limb in this manner lowers the maximum pressure which must be applied to 
prevent fluid flow past cuff 108 thereby resulting in a reduced risk of 
underlying nerve injury and greater comfort for the patient. Locating 
strip 4, which is 1.5 inches wide, cannot be inflated. Locating strip 4 
permits an unskilled user to accurately and consistently apply cuff 108 at 
a fixed distance from an anatomical reference site. In lower limb surgery, 
for example, the top of locating strip 4 is positioned on the head of the 
fibula so that the top of cuff 108 encircles limb 6 approximately 1.5 
inches distal to the head of the fibula. This reduces the likelihood of a 
compression injury to the peroneal nerve below the head of the fibula 
following pressurization of cuff 108. 
It is to be understood that the invention is not to be limited to the 
details herein given but may be modified within the scope of the appended 
claims.