intraoperative angioscopy: principles of irrigation and description of a new dedicated irrigation...

Volume 118

Number 2 Fluorescence-guided laser angbsurgery

Ventures for continual discussions of the material presented. Spe- cial thanks are also due to Dr. S. Jacques and M. Keijzer of Well- man Laboratory, Massachusetts General Hospital. Tissue samples were provided by the Pathology departments of the Beth Israel and Brigham and Women’s Hospitals and the Cleveland Clinic Foundation.

REFERENCES

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Alfano RR, Lam W, Zanabi H, Alfano MA, Corder0 J, Tata D, Swenberg C. Human teeth with and without caries studied by laser scattering, fluorescence and absorption spectroscopy. IEEE J Quantum Electron 1984;QE20:1512. Alfano RR, Tata D, Corder0 J, Tomashetsky P, Longo F, Al- fano MA. Laser induced fluorescence spectroscopy from native cancerous and normal tissues. IEEE J Quantum Electron 1984;QE2031507. Kittrell C. Willett RL. de 10s Santos C, Ratliff NB, Feld MS. Diaanosis’of fibrous atherosclerosis using fluorescence. Appl Optics 1985;24:2280. Sartori M, Sauerbrey R, Kubodera S, Tittel F, Roberts R, Henry P. Autofluorescence maps of atherosclerotic human arteries-a new technique in medical imaging. IEEE J Quantum Electron 1987;23:1794. Sartori M, Henry P, Roberts R, Chin R, Berry MJ. Estimation of arterial wall thickness and detection of atherosclerosis by laser induced fluorescence [Abstract]. J Am Co11 Cardiol 1986;7:207A. Sartori MP, Bossaller C, Weilbacher D, Henry PD, Roberts R, Chin RC, Valderrama GL, Berry MJ. Detection of atherosclerotic plaques and characterization of arterial wall structure by laser induced fluorescence [Abstract]. Circulation 1986;74:25. Deckelbaum LI, Lam JK, Cabin HS, Clubb KS, Long MB.

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Discrimination of normal and atherosclerotic aorta by laser induced fluorescence. Lasers Sum Med 1987:7:330. Deckelbaum L, Stetz M, Lam i Clubb KS, Cutruzzola F, Cabin HS, Long MB. Fiberoptic laser induced fluorescence detection of atherosclerosis and plaque ablation; potential for laser angioplasty guidance [Abstract]. Circulation 1986;74:27. Montan S, Svanberg K, Svanberg S. Multicolor imaging and contrast enhancement of cancer tumor localization using laser induced fluorescence in hematoporphyrin-derivative-bearing tissue. Opt Lett 1985;10:56. Chaudhry H, Richards-Kortum R, Kolubayev T, Kittrell C, Ratliff N, Feld MS. Alteration of artery wall fluorescence due to excessive laser irradiation [Abstract]. 37th Annual Scien- tific Session, American College of Cardiology, 1987. Richards-Kortum R. Understanding laser induced fluorescence spectra of human artery wall with applications to diagnosis of atherosclerosis. SM. Thesis. Massachusetts Institute of Technology, June, 1987. Richards-Kortum R, Mehta A, Chaudhry H, Kolubayev T, Ratliff NB, Kittrell C, Feld MS. Physical localization of arterial wall chromophores [Abstract]. Lasers Surg Med 1987;7:81. Richards-Kortum R, Mehta A, Kblubayev T, Hoyt C, Sacks B, Cothren R. Kittrell C. Feld MS. Ratliff NB. Fitzmaurice M. Kramer JR. Spectroscopic diagnosis for control of laser treat: ment of atherosclerosis. In: Svanberg S, Perrson W, eds. Laser spectroscopy IX. Proceedings of the Eighth International Conference of Laser Spectroscopy. Berlin: Springer Verlag, 1987:336. Cothren RM, Kolubayev T, Kjellstrom BT, Richards-Kortum RR, Healy B, Ratliff N, Engelmann G, Loop F, Kramer J, Kittrell C. Feld MS. Areon ion laser induced tissue fluorescence: clinical spectroscopic studies. 1988 Proceedings of the SPIE Symposium on Medical Applications of Lasers, Fiber Optics and Electra-Optics. (In press)

lntraoperative angioscopy: Principles of irrigation and description of a new dedicated irrigation pump

Arnold Miller, MB, ChB, FRCS, FRCS(C), Wayne E. Lipson, MS,a Jonathan L. Isaacsohn, MD,b Frederick J. Schoen, MD, PhD,C and Robert S. Lees, MD.b Boston, Muss., and Luke Success, N.Y.

Angioscopy, or cardioscopy as it was first called,ll 2 was performed successfully in the experimental ani-

From the bDepartments of Surgery and Medicine, New England Deaconess Hospital, Boston; CDepartment of Pathology, Brigham and Women’s Hos- pital, Boston; and ‘Olympus Corporation, Lake Success. This work was supported in part by the Olympus Corporation, Lake Suc- cess, N.Y.

Received for publication Feb. 13, 1989; accepted Apr. 1, 1989.

Reprint requests: Dr. Arnold Miller, Dept. of Surgery, New England Dea- coness Hospital, 110 Francis St., Suite 3B, Boston, MA 02215.

mal in 1922 by Allan and Graham1 as the mitral valve was rendered incompetent under direct vision in the beating heart. With the advent of fiber optic technology and its refinement, flexible angioscopes as small as 1 mm or less in external diameter have become available, allowing access to most blood vessels of the body, either intraoperatively or percu- taneously.3-5 The ability to see intraluminal patho- logic changes directly and in vivo has already had a significant impact on the understanding and ap-

391

392 Miller et al. August ,989

American Heart Journal

A

B

Fig. 1. Photograph showing angioscope with outer diameter of 1.4 mm inserted and protruding through the special irrigation catheter (B) of outer diameter 2.5 mm X 1150 mm. Note the two proximal ports of irrigation catheter allowing simultaneous insertion of the angioscope and flushing. The extension tubing for connecting irrigation catheter to pump is shown (A).

preach to the management of atherosclerotic coronary artery disease. 6s7 The value of intraoperative angioscopy in the detection and immediate correction of technical errors and deficiencies during vascular surgery has been documented.8)g With development of the newer intraluminal ablative therapies for occlusive arteriosclerosis,lO-l” angioscopy may become even more important in the management of vascular disease.

The inability to see through blood remains the most significant limitation to the general application of angioscopy, whether the approach be intraoperative or percutaneous. Several methods to remedy this problem have been explored. Total or partial replace- ment of the circulation blood by a transparent oxygen-carrying blood substitute, such as a fluorocarbon solution, remains only theoreticall An inflatable transparent balloon at the end of the angioscope is in current use for the percutaneous in vivo study of the pulmonary circulation in patients with chronic pulmonary hypertension.4 Finally, local irrigation with a balanced salt solution to clear the blood from a restricted field in a particular vessel is the most widely used method at present, particularly in the intraoperative setting. Lack of appreciation of factors governing successful irrigation and the difficulty in achieving adequate flow rates necessary for irrigation during surgery have delayed the incorporation of angioscopy as a routine procedure in the practice of vascular surgery. We have developed an irrigation pump for use during angioscopy. We present here a description of the prototype pump, and the results of its use in vitro and in animal studies in vivo, and de-

fine the factors necessary for the consistent attain- ment of a clear field of view during angioscopy.

METHODOLOGY

Irrigation pump. The angioscopy pump is a peristal- tic pump designed to provide flow rates between 10 ml/min and 400 ml/min when used with 3.1 mm internal diameter tubing (Masterflex No. 6411-16 silicone tubing, Cole-Palmer Instrument Co., Chicago, Ill.) in the Masterflex quick-load pump head (Cole- Palmer Instrument Co.). Three switch-selectable ranges of flow rate are provided. The pump is designed to generate a maximum pressure of 2000 mm Hg at the pump head. A pressure transducer in the pump outlet tubing measures the pump head pressure and automatically shuts the pump off at pressures of 600 mm Hg or greater. Exclusion of the pressure transducer from the outlet tubing removes this automatic shutoff mechanism. The pump flowmeter does not measure the actual flow rate but is programmed to count the number of pump head revoutions and provide an estimate of the flow rate. A foot switch provides remote flow control. Intrave- nous saline solution is connected to the pump inlet tubing via a standard intravenous drip set. A 6-foot length of Tygon tubing with a 3.1 mm internal diameter (Masterflex No. 6409-16, Cole-Palmer Instru- ment Co.) is attached to the outlet tubing of the pump head. This tubing is attached either to the irrigation catheter or to the irrigation channel of the angioscope.

Angioscopes, light source, and video system. Three angioscopes (Olympus Corporation, Lake Success,

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Number 2 Intraoperatiue angioscopy 393

N.Y.) were used in this study. Two of the angioscopes, 2.8 mm outer diameter (OD) X 1200 mm and 3 mm OD x 800 mm, have built-in irrigation channels of 1 mm inner diameter (ID) and 0.5 mm ID, respectively. The third angioscope has an outer diameter of 1.4 mm and is 1200 mm long, but has no irrigating channel. This angioscope was used together with the spe- cially designed irrigating catheters described below and is shown in Fig. 1. The angioscope is connected to a 300 W Xenon light source (Olympus CLV-10). The eyepiece is connected to a video-camera (MIC- 6, M.P. Video Inc., Hopkinton, Mass.) that allows continuous monitoring on a color television monitor (AM-1401R, Mitsubishi Electrical Sales America Inc, Cypress, Calif.), and recording on 3/ inch videotape (KCA-60 BRS, Sony Corp. of America, San Diego, Calif.) with a videocassette recorder (VD 5600, Sony Corp.).

Irrigating catheters. Three types of irrigating catheters were used in this study, a standard commer- cially available Intracath, 16 gauge and 8 inches long (Deseret Medical Inc., Parke-Davis & Co., Salt Lake City, Utah), a Fogarty 4F by 800 mm irrigation catheter (Baxter Healthcare Corp., Edwards Division, Santa Ana, Calif.) and single-channel polyurethane angioscopy irrigation catheters of different dimen- sions with two ports at their proximal end, supplied by Olympus Corporation. One port is connected to the irrigation pump with the irrigation tubing (Mas- terflex No. 6409-16 Tygon tubing, Cole-Palmer In- strument Co.), and the angioscope (1.4 mm OD) is inserted through the second port (Fig. 1). The latter port has a special O-ring mechanism, preventing the escape of blood or the irrigation fluid when inserted into the artery and during flushing. When the irrigating catheter is placed within the artery, the angioscope, inserted through the angioscope port, is advanced until it protrudes 5 to 10 cm from the distal end of the irrigating catheter.

In vitro measurement of flow (angioscopy pump ver- sus pressure cuff device). Actual flow rates were determined by allowing the flow from the irrigation system being tested to be collected into a 250 ml graduated glass measuring cylinder over a timed in- terval (15 seconds for the pump and 1 minute for the pressure cuff device). The angioscopy pump was set to deliver flow rates of 100,200,300, and 400 ml/min. At each flow rate, three or more separate measurements were made with each of the irrigation systems. Simultaneous measurements of flow were made with the measuring cylinder and pump flowmeter so that the results could be compared. The pressure cuff device, placed around a liter plastic container of saline, was inflated to a pressure of between 400 and 450 mm

Table I. Consecutive measured flow rates over 1 minute with pressure cuff device inflated and maintained at pressures between 400 and 450 mm Hg around a liter of saline in a plastic container

Flow rate

Pressure = 400-450 mm Hg (mllmin)

IV set only (n = 1) 142

IV set + irrigation catheter (n = 3) (2.5 mm OD X 300 mm)

128 106 90

IV set + 2.8 mm angioscope with 24 irrigation channel (n = 3) 23 (1 mm ID x 1200 mm) 22

n, Number of measurements; IV, intravenous; ID, inner diameter, OD, outer diameter.

Hg. Using a standard intravenous set (Venoset No. 4967, Abbott Laboratories, North Chicago, Ill.) only and two different irrigation systems, consecutive measurements of maximum flow rates were made.

Animals arid surgery. Yorkshire pigs, weighing between 70 and 90 pounds (Earle Parsons and Sons, Hadley, Mass.) were anesthetized with intramuscu- lar ketamine and intravenous pentathol, intubated, and maintained on halothane and oxygen with a Harvard ventilation pump (Harvard Apparatus Co. Inc., S. Natick, Mass.). The left brachial artery in the forelimb, and the right femoral artery in the hind limb just above the knee joint, were surgically ex- posed and isolated. Teflon catheters (Quik-Cath 14G, Travenol Laboratories Inc., Deerfield, Ill.), filled with saline, were inserted into these arteries and were connected to strain gauges (Statham Model P23 pressure transducers, Spectramed Inc., Cardiovascu- lar Products Division, Oxnard, Calif.). Electrocar- diographic (ECG) leads were placed subcutaneously in each limb and, along with the pressure transducers, were connected to a CRT monitor (Gould V 1000, Gould Inc., Chicago, Ill.) and an eight-channel chart recorder (Gould ES 1000, Gould Inc.). Pressure val- ues in both monitored limbs and the ECG were con- tinuously displayed on the monitor. Hard copy recordings of appropriate pressure measurements were made for later evaluation. Baseline measurements of forelimb and hindlimb arterial pressures were recorded. The abdomen was then opened through a midline incision and the lower aorta and iliac vessels were isolated. The right common iliac artery was ligated flush with the aortic bifurcation with a 0 silk tie. The drop in pressure and the baseline collateral pressure in the distal femoral artery were recorded. A 2 cm arteriotomy in the anterior surface of the

394 Miller et al. August 1989


Table II. Comparison of irrigation pump flowmeter readings and actual measured flow rates with pump settings using different irrigation systems

System Setting Flowmeter Measured ffnu ---~-

Pump only 100 102.7 (4~~ 108 200 205.3 (3) 308

300 312 272 400 389.2 (21.1, 5)t 340.4 (16.6, *5)

Intracath 100 92 (20.8) 97.3 (2.3) (16 gauge X 8 inches) 200 205.3 (2.3) 184

300 300 (20.8) 264 400 409.3 (6.1) 340 (2.3)

Catheter 100 104 100

(2.5 mm OD X 1150 mm) 200 204 188 300 287.7 (36.1) 265.3 400 410 (2.3) 324 (4)

Catheter 100 104 94.7 (6.1) (2.5 mm OD X 1150 mm) 200 205.3 (2.3) 185.3 (2.3)

+ 300 306.7 (10.1) 260

1.4 mm angioscope 400 393.3 (32.6) 321.3 (2.3)

Catheter 100 104 102.7 (4.6) (2.5 mm OD X 300 mm) 200 205.7 (2.9) 185.3 (2.3)

+ 300 309.3 (4.6) 258.7 (2.3) 1.4 mm angioscope 400 421.3 (16.2) 320

Catheter 100 104 100 (3.0 mm ID X 1150 mm) 200 204 188

+ 300 297.3 (18.5) 260

1.4 mm angioscope 400 402.7 (19.73 320

Angioscope 100 104 100 (2.8 mm OD X 1200 mm) 200 202.7 (2.3) 152

t 1 mm ID irrigation 300 288 (20.8) 168

channel 400 385.3 (19.7) 170

All figures in columns “Flow meter” and “Measured flow”are a mean of three or more recordings. except where specified. *(standard deviation). t(standard deviation, number of measurements)

common iliac artery was made for the insertion of the irrigating catheters and angioscopes. Control of back bleeding from the cannulated common iliac artery was prevented by the use of a silicone rubber “vessel loop” (Oxboro Medical International Inc., Minneap- olis, Minn.) looped around the artery just distal to the arteriotomy.

The ilio-femoral system was flushed with 0.9% saline with the angioscopy pump at flow rate pump settings of 100,200 and 400 ml/min by the use of the Intracath catheter, the special irrigation catheters with or without the 1.4 mm OD angioscope, and the two angioscopes (2.8 mm OD and 3.0 mm OD) with built-in irrigation channels. The pressure rise in the distal, isolated, ilio-femoral arterial system was re-

corded for each combination. Assessment of the ability to clear the intraluminal blood and maintain this clearing was made from the intraluminal angioscopic video image displayed on the monitor and the time (in seconds) required for the clearing was noted, Each study was repeated three times.

At the time the animals were killed, the iliofemo- ral arterial system used for repeated intubation and irrigation was excised and was placed in 10% form- aldehyde solution. Multiple representative segments were embedded in paraffin, sectioned at 5 pm, stained with hematoxylin and eosin, Masson’s trichrome stain, and Koerhoff van Giesen’s elastic stain, and were examined by light microscopy for evidence of significant acute arterial wall injury. Animals re-

Volume 118 Number 2 lntraoperatiue angioscopy 395

B INFUSION r--- -- -- -. _- .-. 1

BRACHIAL

FEMORAL

BRACHIAL

FEMORAL

100 200 403

FLOW RATE (ml/min)

Fig. 2. Actual blood pressure measurements recorded in Pig No. 2. A, Baseline and post-iliac artery ligation pressure recordings in the brachial and femoral arteries. B,Rise in baseline femoral artery pressure after ligation at pump flow rate settings of 100, 200, and 400 ml/min, with no change in the brachial artery pressure.

ceived humane care in compliance with the Princi- ples of Laboratory Animal Care and the Guide for the Care and Use of Laboratory Animals.14

OBSERVATIONS

Table I shows the results of consecutive measurements of flow through three different routes into a 250 ml measuring cylinder over a l-minute period with the use of a pressure cuff device (C-Fusor 500, Medex Inc. Teaneck, N.J.) around a single liter of saline in a plastic container (Abbott Laboratories Inc., North Chicago, Ill.). When a standard intravenous set (Venoset No. 4967, Abbott Laboratories) was the only resistance, maximum flow obtained was 142 ml/min. When an irrigation catheter (2.5 mm OD X 300 mm) was added in series, the maximum flow rate decreased to 128 ml/min. As the saline container emptied, in spite of a constant pressure in the cuff device of between 400 and 450 mm Hg, the flow rate decreased with consecutive measurements. With the 2.8 mm OD angioscope, with a 1 mm ID by 1200 mm irrigation channel, the maximal flow rate was only 24 ml/min. Again, the flow rate progressively di- minished with consecutive measurements.

The pump flowmeter, programmed to count the

number of pump head revolutions, did not measure the actual flow rate. The flow rate was always over- estimated by the flowmeter, minimally at lower flow rates and with large diameter irrigation catheters, but significantly at the higher flow rates and with the high resistance irrigation catheters (Table II). The results of the in vitro testing with the pump are sum- marized in Table II. Measured flow rates slightly exceeded the pump settings of 100 and 200 ml/min when no irrigation systems were attached to the pump, but at flow settings of 300 and 400 ml/min, even with no resistance attached, measured flow was 9.7% and 15% less, respectively, than the pump setting.

The addition of the catheter irrigation systems was not associated with a change in the measured flow rate at pump settings of 100 ml/min but flow was 6.7 % less than the pump setting at 200 ml/min, 13 % less at 300 ml/min, and 20% less at 400 ml/min. These differences were much greater when the 2.8 mm OD angioscope with a 1 mm ID x 1200 mm long irrigation channel was attached to the system. Al- though the pump was able to achieve a flow rate of 100 ml/min at the pump flow rate setting of 100 ml/ min, increasing the flow setting of the pump to 400



Fig. 3. Photomicrographs of sections from artery intubated repeatedly with different angioscopes and irrigation catheters, and irrigated with saline solution at different flow rates. There are focal adherent inflammatory cells along the intimal surface with the internal elastic lamina intact throughout. A, Section stained with hematoxylin and eosin. B, Section stained with Verhoeff tissue stain (elastic black). (Original magnification of both X 150.)

ml/min achieved a maximum flow rate of only 170 ml/min.

As shown in Fig. 2, ligation of the common iliac artery in the pig resulted in a decrease in the systolic blood pressure of the distal ilio-femoral arterial system. In all five animals, this drop was significant, with

Table III. Systolic blood pressure drop in the pig ilio-femoral arterial system following ligation (L.I.A.) at the aortic bifurcation

BP, Blood pressure: Std dev, standard deviation.

a mean decrease of 82.6 % (standard deviation 12 % ). The actual systolic pressure in the ligated iliac artery in the five experimental animals ranged from 3 to 40 mm Hg, whereas the systemic systolic pressure ranged from 55 to 135 mm Hg (Table III). Table IV shows the minimum (1.7 mm Hg) and maximum (37.7 mm Hg) mean systolic pressure changes in the distal ilio-femoral arterial systems in all five animals. The systolic pressure in the isolated ilio-femoral arterial system was never higher than the systemic diastolic pressure in any of the five animals.

In pigs No. 1 and 2, with the irrigation pump set to shut off automatically at pump head pressures of 600 mm Hg, flow rates greater than 100 ml/min could be generated only when the larger irrigation catheters (3 mm OD X 300 mm and 3 mm OD X 1150 mm) without the 1.4 mm angioscope in place were used. In these two pigs, only the pressure increases within the distal ilio-femoral arterial system and not the time required for clearing the angioscopic visual field of blood were measured. When the automatic high- pressure pump shutoff mechanism was removed from the system, allowing pump head pressures of up to 2000 mm Hg to be generated, flow rates of more than 100 ml/min were achieved with all catheter irrigation systems including the 2.8 mm OD angioscope with the 1 mm ID X 1200 mm irrigation channel. In spite of these high pump pressures, only flow rates of less than 100 ml/min could be attained through the Fog- arty 4F 800 mm long irrigation catheter or the 3 mm OD angioscope with 0.5 mm ID X 800 mm channel. The latter two results were not included in Tables II and V.

In pigs nos. 3, 4, and 5, the time (in seconds) required for clearing at the different pump flow rate settings, 100,200, and 400 ml/min and with different irrigation systems was measured. As shown in Table V, flow rate settings of 400 ml/min not only consis-

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Number 2 Intraoperative angioscopy 397

Table IV. Maximum increase in systolic blood pressure in the ligated ilio-femoral arterial system (L.I.A.) at different flow rates (Q) during irrigation

Pig no. BP (mm Hg)

1 55/25 2 go/50

3 135/100

4 110/80 5 60135

L.I.A. Systolic BP

(mm Hd

I 3

25

40 10

Maximum pressure increase in L.I.A. Systolic BP (mm Hg)

Q = 100 mllmin Q = 200 mllmin Q = 400 mllmin

5.5 (2.4, 13)* 6.5 (1.6, 11) 10.9 (2.5, 9) 1.7 (0.7, 3) 5.7 (1.2, 3) 12.0 (4.2, 2)

17.1 (10.5, 14) 21.8 (10.5, 14) 23.7 (10.9, 15)

16.7 (4.4, 12) 25.8 (6.3, 12) 37.7 (9.8, 11) 18.3 (5.2, 6) 21.7 (2.6, 6) 27.5 (2.7, 6)

*(Standard deviation, number of measurements).

tently resulted in a clear, blood-free, angioscopic view catheters or irrigation channels of the angioscope, of the interior of the artery but also maintained this requires the generation of a high-pressure head to blood-free environment indefinitely. Results were provide adequate flow rates to clear the visual field of somewhat less consistent at settings of 200 ml/min all blood. Although high pressures may be generated and even more inconsistent at settings of 100 ml/min, at the pump head, either with higher flow rates or where on two occasions although clearing was small diameter and long irrigation systems, this achieved, it required a significantly longer period of pressure is not transmitted across the irrigation sys- flushing. Whenever clearing was rapidly achieved, tem. The pressure at the distal tip of the irrigation the clear visual field could consistently be main- catheter or irrigating channel of the angioscope tained at a significantly lower flow rate than the flow reflects only a small fraction of the pump head pres- rate necessary to establish the initial clearance of the sure (calculation from Poiseuille’s equation). In fact, field. The exact flow rate necessary for a given vessel the limitation to the pump head pressure is not the was variable and depended on the collateral flow, as danger of rupturing the intubated, perfused blood well as on the size and the outflow capacity of the ar- vessel, but the “burst” strength of the tubing and tery being examined. Examination of representative connections used in the irrigation system. As shown segments of removed arteries revealed occasional in- in Table II, a flow rate of only 170 ml/min was flammatory cells adherent to the intimal surface and achieved through the 1 mm ID irrigation channel of focal endothelial cell loss, but there was no evidence the 2.8 mm OD angioscope in spite of flow rate set- of gross vascular damage, and the internal elastic tings of 400 ml/min and maximal pump head pres- lamina was intact throughout (Fig. 3). sures of 2000 mm Hg.

COMMENTS

We have shown the ability of a new catheter irrigation pump system to establish and maintain visibility of the field during intraoperative angioscopy, in contrast to the marked limitations of a standard intravenous pressure system. These results also dem- onstrate the safety of irrigating with high volume flows in peripheral arteries and allow definition of the basic principles of irrigation for angioscopy (Table VI). Poiseuille’s law (Table VII), which describes flow in a cylindrical pipe, is pertinent to the design of an irrigation system for angioscopy. This law states that the pressure head necessary to generate flow is directly proportional to the tube length, rate of flow, and viscosity of the fluid, and inversely proportional to the fourth power of the internal radius of the con- duit. The use of long lengths of tubing to maintain sterile fields for intraoperative angioscopy, and even more significant, the small diameter of the irrigation

A serious concern when infusing fluid intra-arteri- ally into a relatively restricted outflow tract at high flow rates is that excessively high intra-arterial pressures may be generated that could damage either the intimal lining or the inner layer of the arterial wall, even to the extent of complete rupture. To test whether this concern was warranted, our experimental model was designed to provide such a restricted outflow tract. Ligation of the inflow vessel resulted in a mean 82.6% reduction in systolic blood pressure (Table III). Flow rates estimated with the various pump settings (Table II) were accurate at flow settings of 100 ml/min, but were 6.7 % and 20 % less, respectively, than the flow settings at 200 and 400 ml/min. Nevertheless, maximum flow rates of more than 300 ml/min were generated by the pump and were delivered intraarterially. With these flows (Table IV), the systolic pressure in the distal outflow tract never exceeded systemic diastolic pressure in any of the experimental models. Thus fear that these



Table V. Irrigation system, flow rate, and clearing time. -._

Pig 3 Pig -I -___ --..---

Pig 5

Catheter (3 mm OD x 1150 mm)

+ 1.4 mm OD angioscope

Catheter (2.5 mm OD X 1150 mm)


Catheter (2.5 mm OD X 300 mm)


Angioscope (2.8 mm OD x 1200 mm)

t I mm ID channel

100 200 400 100 200 400 100 ‘00 400 (mllmin) (mllmin) (ml/mini

Clearing time in seconds

i 35 11 10 7 3 3 7 3

k 5 2 10 4 4 7 .i 2

+ 2 1 15 7 3 I@ 6 5 _t 5 3 i 3 1

15 3 1 It 3 1

10 5 3 - k 2 2 - -

+ 3 2

-t 2 2 - - + t 2 t 3 2

- + _t 2 * 2 4

- f 2 1 i 3 4

k, no or only partial visual clearing. -, not done.

Table VI. Principles of irrigation for intraoperative angioscopy

Aim l To establish and maintain a COLUMN OF CLEAR

FLUID within the vessel Requirements l No antegrade flow in the main vessel or collateral vessels l Initial fluid bolus of large volume and high flow rate to

establish column of clear fluid l Subsequent small volume and low flow rate, with pressure

in excess of “backflow” pressure, to maintain clear Auid column

flows might result in damage to the arterial tree would seem to be unfounded. Furthermore, light microscopy of the arteries studied, after multiple irri- gations and multiple intubations with different angioscopes and catheter systems, showed no significant mural damage over the entire experimental period of up to 6 hours (Fig. 3).

Unlike angiography, where it is unnecessary to displace all blood with contrast media but important to establish adequate mixing of blood and contrast media to obtain high quality angiograms, irrigation for angioscopy must displace all blood and provide a clear fluid column within the vessel to be angioscoped. To attain this, it is essential to stop almost all

Table VII. Poiseuille’s law

Q= KLspr4

L

Q, Volume flow; K, fluid viscosity constant; AP, PI-P~ (pressure drop along tube); r, inside tube radius; L, tube length.

antegrade blood flow, from the main vessel as well as from any side branches or collaterals proximal to the tip of the irrigating catheter. Any antegrade blood flow mixing with the irrigation fluid becomes incor- porated in the column of irrigation fluid and inter- feres with intraluminal visualization. A small amount of mixing renders the visual field unclear, hazy, and apparently “out of focus.” Any additional blood results in further deterioration of visibility and even- tually prevents any meaningful intraluminal visualization. To establish such a column of clear fluid within the artery to be angioscoped, a high volume and high flow rate, or bolus of fluid, is needed. The higher the flow rate, the more consistent becomes the clearing of the artery and the shorter the time required for clearing. Flows of irrigation fluid less than 100 ml/min were generally insufficient for clearing (Table V).

The observation that an artery, once cleared, could be kept clear at a much reduced irrigation flow rate

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was confirmed in our clinical experience with the intraoperative use of angioscopy in patients.15 This phenomenon means that the total volume of irrigation fluid used during angioscopy is much less than that which would be extrapolated from the initial irrigation rate. In situations when rapid bolus clearing cannot be achieved but adequate clearing is eventu- ally achieved, a far greater volume of irrigation fluid is always needed (Table V). Table VI summarizes these principles of irrigation for intraoperative angioscopy.

In conclusion, the main obstacle to the incorporation of intraoperative angioscopy as an integral part of vascular surgery has been the problem of adequate clearing of the visual field. The use of intravenous saline under gravity flow or pneumatic cuff pressure has limited angioscopy to situations where only minimal intra-arterial blood volumes and low pressures exist, such as in bypass grafting where inflow, both antegrade and retrograde, can be fully controlled, or in ischemic limbs with minimal collateral flow. The calibrated, operator-controlled, irrigation pump used in this study allows the angioscopist to establish and maintain a field clear of blood with minimal difficulty and no risk to the patient. The pump tested in this study provides a wide range of flow rates and permits precise measurement of the fluid delivered to the patient. The instrument’s display, and its control with a single foot pedal, make its use relatively simple and easy. This obviates the need for additional support personnel and increases the efficacy and safety of the angioscopic examination. Finally, the visibility gained increases the number of situations where angioscopy may be really usefu1,15 such as in the examination of anastomoses, grafts, and native arteries at proposed grafting sites, as well as in combination with intraluminal therapeutic manipulations such as balloon thrombectomy and mechanical atherectomy.

SUMMARY

The value of intraoperative angioscopy in the detection and immediate correction of technical errors and deficiencies during vascular surgery has been previously documented. The inability to see through blood remains the most significant limitation to the general application of angioscopy. Local irrigation with a balanced salt solution is the most commonly used method to clear the blood from a restricted field

Intraoperatiue angioscopy 399

in a particular vessel. We have developed a new catheter irrigation pump system (maximum flow rate 340 ml/min) to establish and maintain visibility of the field during intraoperative angioscopy. Further- more, we have demonstrated the safety of irrigating with high volume flows in the peripheral arteries and defined the basic principles of irrigation for angioscopy. The prototype pump tested in this study provides a wide range of flow rates and permits precise measurements of the fluid delivered. The instrument’s display and its control with a single foot pedal makes its use relatively simple, obviating the need for additional support personnel while increasing the efficacy and safety of the angioscopic examination and increasing the number of situations where angioscopy may be very useful.

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intraoperative angioscopy: principles of irrigation and description of a new dedicated irrigation...

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