Halothane administration during liquid ventilation

RESPIRATORY

Original

MEDICINE

(1997)

91, 255-262

Articles

Halothane

administration

during

liquid

ventilation

D. B. KIMLESS-GARBER, M. R. WOLFSON, C. CARLSSON AND T. H. SHAFFER Departments of Physiology, Pediatrics and Anesthesiology, Temple University PA 19140, U.S.A.

School of Medicine,

Philadelphia,

The objective of this study was to test the hypothesis that perfluorochemical (PFC) liquid ventilation (LV) can be used as a vehicle to deliver halothane and induce and maintain analgesia. Seven hamsters were paralysed and stabilized with mechanical gas ventilation, ventilated in alternating cycles with gas and either neat oxygenated PFC liquid or oxygenated PFC liquid mixed with liquid halothane (PFC:hal) 1.50%) (volumekapour); arterial pressure and blood gases were monitored throughout the protocol. After each cycle, the animal was stimulated with a foot clamp for 2 s. Mean arterial pressure (MAP:mmHg) response to this stimulation (percent change from the resting MAP) was used as an index of analgesia. Mean arterial pressure was significantly lower during ventilation with PFC:hal (73 & 7 SE) as compared with MAP during neat PFC (113 f 5 SE) or gas ventilation (107 i SE). Mean arterial pressure response (o/o change in MAP from baseline) to foot-clamp stimulation was significantly lower with PFC:hal ventilation (+ 12 & 5% SE) as compared with neat PFC (+28 f 8% SE) and gas ventilation (+ 29 419% SE). There was no statistically significant difference in resting MAP or MAP response to foot-clamp stimulation between cycles of ventilation with neat PFC alone or gas ventilation; arterial blood gases were not significantly different between modes of ventilation or levels of analgesia. The data indicate that halothane can be administered during LV while supporting gas exchange, and demonstrate the feasibility of inducing analgesia while using PFC LV techniques. RESPIR. MED. (1997) 91, 255-262

Introduction Perfluorochemical (PFC) liquid ventilation (LV) has been successfullyemployed to reduce surface tension, insufflate the lung at lower alveolar pressures than gas ventilation, support gas exchange, and deliver biological agents in premature, newborn and adult animals with respiratory distress (l-8). A recent clinical study demonstrated the feasibility of PFC LV treatment in human premature neonates with respiratory distress (9,lO). Patients ventilated with PFC may require induction and maintenance Received 1 July 1995 and accepted in revised form 1 April 1996. Correspondence should be addressed to: Marla R. Wolfson, Temple University School of Medicine, Department of Physiology, 3420 North Broad Street, Philadelphia, PA 215-707-4573, U.S.A. 0954.6111/97/050255+08

$12.00/O

of analgesia for surgical procedures. It has been demonstrated previously that a fluorinated hydrocarbon (such as halothane) is miscible and soluble in PFC (11). As the PFC liquid can be homogeneously distributed throughout the lung at low inflation pressures,PFC ventilation techniques may also provide an effective means of inducing and maintaining analgesia while supporting gas exchange at lower risk of barotrauma. Therefore, the objective of this study was to test the hypothesis that PFC ventilation can be used as a vehicle to deliver halothane and induce analgesia. Halothane was selected because of its common use in paediatric practice and in animal studies.

clinical

Methods Seven adult female hamsters (Mesocvicetus weighing 125.7f 9 g SD, were studied.

auratus),

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The study was conducted according to standards of the Animal Research Review Committee of Temple University School of Medicine. ANIMAL

PREPARATION

After administration of intraperitoneal sodium pentobarbital (30 mg kg - ‘), a cannula was inserted through a tracheotomy midway along the trachea with its tip positioned proximal to the carina. The trachea was secured to the cannula to avoid leakage in the ventilatory system. The femoral vein was cannulated for venous accessand the carotid artery was cannulated for arterial blood pressure and blood gas assessment. Subcutaneous needle electrodes were placed for electrocardiogram recording of heart rate (HR). A rectal thermometer was placed to monitor temperature. A radiant heart source was adjusted to maintain the animal’s temperature between 37 and 38°C. The animals were paralysed with vercuronium bromide (0.1 mg kg - ’ h - ‘) and mechanically ventilated with a Harvard Apparatus rodent respirator (F,O,= 1) to maintain oxygenation and carbon dioxide elimination. Arterial blood gas tensions and pH were determined on 0.10 ml whole blood samples utilizing a Radiometer ABL 330 analyser, corrected to the animal’s temperature. Withdrawn blood volume was replaced intravenously with warmed normal saline solution. Ventilator settings (tidal volume and rate) were adjusted to normalize arterial blood gas tensions; pH was adjusted by sodium bicarbonate administration if the pH was ~7.25 and the PaCO, I 50 mmHg ([mEq base added= - base excess (mEq 1- ‘) x body weight x 0.31) (12). Arterial blood pressure was measured by connecting the carotid artery catheter to a Statham transducer. Blood pressure and HR were recorded continuously on a recorder (Electronics for Medicine). LIQUID

VENTILATION

SYSTEM

The liquid ventilation system (LVS) was based on the gravity-assist principle and is schematically shown in Fig. 1. Briefly, tidal volumes of the liquid are exchanged between the reservoirs (inspiratory and expiratory) and the animal’s lungs under a hydrostatic pressurecreatedby the

FIG.

1. Gravity-assistedliquid ventilation system.

relative heights of the reservoirs to the animal’s thorax. The entire circuit was filled with liquid PFC (RIMAR 101: Miteni; Milano, Italy). The PFC was warmed (39”) and oxygenated (>600 mmHg) at the inspiratory reservoir. The inspiratory limb extended from a 50 ml graduated cylinder reservoir, suspended above the animal’s thorax, and was attached to one end of a T-piece which was connected to the tracheostomy tube. The expiratory limb extended from the T-piece into a 50 ml graduated cylinder reservoir. To begin LV, a functional residual capacity of PFC (20 ml kg - ‘) was instilled in the lung from the inspiratory reservoir. Subsequently, the heights of the inspiratory (3060 cm) and expiratory ( - 20- - 30 cm) reservoirs were adjusted so that liquid volumes exchanged between the lungs and reservoirs at tidal volumes at 15ml kg - ‘, rate between 3 and 5 breaths min - ‘, and inspiratory: expiratory-

HALOTHANE

timing of 1:3 using manually operated clamps. This ventilatory schema was based on previous studies of LV which demonstrated effective oxygenation and carbon dioxide elimination (2,13). In addition to neat PFC, animals were ventilated with a solution of PFC and halothane PFC:hal (see Protocol). The PFC was mixed with liquid halothane (Halothane USP) at concentrations equivalent to 1.50volume/vapour calculated by using the molecular weight and density of halothane (14). PROTOCOL

AND DATA

ANALYSIS

Following surgical instrumentation, the animals were paralysed and stabilized with mechanical gas ventilation. Arterial blood gases were assessedand blood pressure and HR were continuously recorded throughout the entire protocol. Blood pressureresponseto a 2 s foot-clamp stimulation was used to evaluate the level of analgesia. Initial baseline studies were performed in two animals: one animal was ventilated for four cycles alternating between neat PFC and gas to evaluate cardiopulmonary and gas exchange stability over time; another animal was ventilated for two cycles alternating between PFC: ha1mixture and gas to examine the independent time course of PFC:hal and return of baseline physiological parameters. Five animals were ventilated in cycles alternating between gas and either neat PFC or PFC:hal mixture. The gas ventilation interval lasted 15-20 min. During LV, the animal received 33.5breaths min - ’ for 5 min (approximately 14-16 breaths). Upon completion of the last breath of each cycle, the animals were stimulated with a foot-clamp and blood samples were drawn for analysis. Metabolic or respiratory abnormalities were treated by ventilatory adjustments or supplemental bicarbonate administration during gas ventilation. Sequential radiographs were obtained at endinspiration in one animal during gas ventilation, neat PFC LV, and sequentially after PFC LV. Relative differencesin opacification were used as a qualitative index in differencesin PFC liquid in the lung. Cardiovascular and arterial blood gas parameters were evaluated at each stage of the

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25 7

100 if 8 75-

! 5o t

25 1 0 Time

(h)

The black markings on the time axis representneat perfluorochemicalventilation; the white markingson the time axis representgasventilation. Mean arterial pressure (MAP: n ), arterial oxygen

FIG. 2.

saturation (SaO,: A), carbon dioxide tension (PaCO,: 0) are stable over four continuous ventilation cycles lasting a total duration of 2.5 h.

protocol. Single factor analysis of variance (ANOVA) was used to determine differences in arterial blood chemistry, mean arterial pressure (MAP) and HR as a function of respiratory medium (i.e. gas, neat PFC, PFC:hal mixture). ANOVA was also used to determine statistical difference in MAP responseto foot-clamp stimulation (expressedas the percent change from the MAP during the respective cycle) as a function of analgesia. Statistical significance was accepted at the PcO.05 level and the Tukey’s post-hoc test was used to determine between which conditions statistical differences existed. Results

Figure 2 displays the typical stability over time observed during alternate ventilation with gas and with neat PFC. Mean arterial pressure, PaCO, and oxygen saturations (SaO,) are not significantly different between cycles. The cardiopulmonary profiles during ventilation with gas, neat PFC and PFC:hal mixture (mean f SE) are summarized in Table 1. There were no significant difference in PaO,, PaCO,, PH, HCO, - or HR as a function of ventilatory medium. Mean arterial pressure was lower (PcO.02) during ventilation with PFC:hal mixture as compared with neat PFC ventilation ( - 35%) or gas ventilation ( - 3 1%). Figure 3 is a typical recording of baseline blood pressure (before foot-clamp) and the

258

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1. Summarized baseline cardiopulmonary

PaO, (mmHg) PaCO, (mmHg) PH (mmHg) HCO, - (mEq 1- ‘) MAP (mmHg) HR (beats min - ‘)

profile (mean f SE)

Gas ventilation (n=7)

PFC ventilation (n=6)

PFC:halothane ventilation

393.6 rt 79.3 28.9 f 10.9 7.29 zt 0.01 13.4 f 1.8 107 f 10.9 227 rt 27.5

282.9 f 52.6 41.7 & 6.4 7.16 f 0.02 14.3 f 4 113.4k4.9 251 f 28.6

353.6 f 58.9 39.7 & 2.3 7.13 f 0.02 13 f 3.6 72.7 &6.5* 227 f 14.0

(n=6)

*P
FIG. 3. Representative recording of blood pressure before and after foot-clamp stimulation (arrow) during (a) gas ventilation and (b) ventilation with the perfluorochemical:halothane (PFC:hal) mixture. While mean arterial pressure (MAP) increased in all animals after foot-clamp stimulation independent of ventilatory medium, the MAP response to stimulation was attenuated subsequent to PFC:hal ventilation.

increase in blood pressure in response to footclamp stimulation during gas and PFC:hal ventilation. Mean arterial pressure increased in all animals after foot-clamp stimulation, independent of ventilatory medium. There was no difference between this response elicited during gas and neat PFC ventilation, In the presence of halothane, the baseline blood pressure before stimulation was significantly lower than that observed for the other ventilation modalities. The responseto foot-clamp stimulation was also reduced with the PFC:hal mixture as compared with neat PFC and gas ventilation. Figure 4 displays the individual values for MAP response (percent change from baseline MAP) to foot-clamp stimulation during gas ventilation and ventilation with PFC:hal. The responseto foot-clamp stimulation was reduced

FIG. 4. Mean arterial blood pressure response to foot-clamp stimulation with gas (0) ventilation and with perfluorochemicahhalothane (PFC:hal) (0) ventilation (calculated as percent change from resting values for individual animals. The blood pressure response to stimulation was significant lower with PFC:hal ventilation as compared with gas ventilation for all animals.

HALOTHANE

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PLATE. 1. Radiographs of one animal during (a) gas ventilation, (b) perfluorochemical (PFC) liquid ventilation (LV), and (c) 4.75 h post LV on gas ventilation. Over time, the opacification, depicting residual liquid in the lung, is less.

with the PFC:hal mixture as compared with neat PFC and gas ventilation. Statistical analysis of the change in MAP as a function of ventilatory medium demonstrated that the increase in MAP (mean f SE) during PFC:hal was attenuated

(+ 1l-9 f 2.3% SE) in comparison with the percent increase in MAP for gas ventilation (+28*6 f 3.7% SE); no significant difference was determined between the increase in MAP response to foot-clamp stimulation during

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gas ventilation as compared with neat PFC ventilation (+ 27.2 f 54% SE). Plate 1 displays radiographs of one animal at end-inspiration with gas ventilation, LV with neap PFC, and subsequent gas ventilation at 2 and 4.75 h after LV. The PFC-filled lung radiograph displays diffuse, homogeneous, opacified liquid-filled lung fields, as compared with the well-aerated normal gas-filled lung. The radiograph 2 h post-LV shows residual homogeneousopacification throughout the lung fields. The radiograph 4.75 h post liquid ventilation displays even less opacification indicating less residual liquid in the lung.

Discussion This study has shown that gas exchange and cardiovascular function can be supported in hamsters during mechanical ventilation with PFC. The significant decreasein resting MAP and MAP response to foot-clamp stimulation also indicates that it was possible to induce and maintain analgesia by PFC:halothane LV of hamsters. Since the original demonstration that mice could successfully breathe while submerged in an oxygenated PFC (16,22), there have been numerous bio-medical applications of the PFC liquid. Perfluorochemicals have been used as emulsions for blood substitutes (11,17,18), applications of liquid breathing have included the study of developmental physiology (1,2,19), temperature regulation (5,20), and in extreme environmental conditions such as aerospace and diving medicine (21,23). More (21) recently, studies have demonstrated the potential of perfluorochemical urochemical LV as an investigational therapy in human neonates (9) and the advantages of LV as compared with gas ventilation in very preterm lambs (24). The use of PFC liquid has proven useful as an alternative respiratory medium because of its high solubility for oxygen and carbon dioxide, low surface tension, and homogeneous distribution in the lung. In addition, the solubility of halothane and other halogenated hydrocarbons in the PFC liquid support the potential for induction and maintenance of analgesia during PFC ventilation (11).

The uptake and distribution of anaesthetic gasesare dependent upon the partial pressureof the anaestheticdelivered, solubility of the anaesthetic agent, cardiac output, pulmonary and systematic blood flow, alveolar-venous partial pressure gradients, and the blood: tissue concentration gradient to allow for the deposition of the anaesthetic (25). In general, the concentration equilibrium betweenblood and the vessel rich group (i.e. brain) occurs in approximately 10-l 5 min for standard gas-ventilation induction. In the present study, all of the hamsters demonstrated an index of analgesia, reduced blood pressure responses to foot-clamp stimulation, during a single 5 min cycle of ventilation with the PFC:halothane mixture. There are some important differences associated with PFC ventilation as compared with gas ventilation which could explain the rapid induction and the ability to maintain analgesia. In a liquid-filled lung, there is homogeneousinflation of the lung which improves the surface area for gas exchange(26). Ventilation and perfusion with PFC breathing is more evenly matched as compared with gas ventilation (27); this factor would support optimal uptake of the anaesthetic agent. The sequential radiographs indicate that the PFC liquid in the lung post-liquid ventilation is reduced over time. The rate of removal of PFC liquid is related to the low vapour pressure and volatilization from the lung during subsequent gas ventilation (28,29). While it was beyond the scope of the present study, it is possible that waking times after PFC ventilation may be proportional to the rate of volatilization. Another method of removing the anaesthetic may incorporate the solubility characteristic of halothane in the PFC liquid. In this respect, previous studies have demonstrated that the solubility of halothane in the PFC liquid is approximately 25 times greater than that in blood (11); therefore, ventilating with neat PFC (not unlike ventilating with pure oxygen during gas ventilation) may prove useful in removing the anaesthetic from the animal. Theoretically, the neat PFC liquid could act as a sink for the anaestheticagent and assist in removal. In summary, this study was designedto examine whether anaesthesiacould be achieved using liquid PFC as a vehicle for halothane. This experimental design did prove that as a measure

HALOTHANE

of anaesthesia,a statistically significant decrease in baseline MAP and an attenuation in blood pressure response to stimulation was achieved during ventilation with the PFC:halothane mixture. An anaestheticeffect of neat PFC alone can be excluded because neither baseline nor foot-clamp MAP responsewas different as compared with gas ventilation. Further evaluation regarding blood levels of anaesthetic, waking times and defining minimal alveolar concentration need to be pursued before using this technique in human studies. Acknowledgements The authors gratefully acknowledge the technical assistance of Mr Thomas Vinciguerra and support of Dr Peter R. Lynch during this project. The PFC used in this research was provided courtesy of Mr Alan Fankhanel of Mercantile Development, Bridgeport, CT, U.S.A. and supplied by Miteni, Milano, Italy. References 1. Wolfson MR, Shaffer TH. Liquid ventilation during early development: Theory, physiological processes and application. J Develop Physiol 1990; 13: 1-12. 2. Wolfson MR, Tran N, Bhutani VK, Shaffer TH. A new experimental approach for the study of cardiopulmonary physiology during early development. J Appl Physiol 1988; 65 (3): 1436-1443. 3. Shaffer TH, Rubenstein SD, Moskowitz GD, Delivoria-Papadopoulos M. Gaseous exchange and acid base balance in premature lambs during liquid ventilation since birth. Pediatr Res 1976; 10: 227-23 1. 4. Richman PS, Wolfson

MR, Shaffer TH, Kelsen SG. Lung lavage with oxygenated fluorocarbon improves gas exchange and lung compliancein cats with acute lung injury. Am Rev Respir Dis 1990; 141: A773. 5. Forman DL, Bhutani VK, Tran N, Shaffer TH. A new approach to induced hypothermia. J Surg Res 1986; 40: 3642. 6. Wolfson MR, Shaffer TH. Pulmonary administration of drugs (PAD). A new approach for drug delivery using liquid ventilation. Faseb J 1990; 4 (4): A1105. 7. Zelinka MA, Wolfson MR, Calligaro I, Rubenstein SD, Greenspan JS, Shaffer TH. Direct pulmonary administration of gentamicin

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during liquid ventilation of the lamb: Comparison of lung and serum levels to IV administration. Pediatr Res 1991; 29 (4): 290A. 8. Wolfson MR, Greenspan JS, Shaffer TH. Pulmonary administration of vasoactive drugs (PAD) by perfluorocarbon liquid ventilation. Pediatr Res 1991; 29 (4): 336A. 9. Greenspan JS, Wolfson MR, Rubenstein SD, Shaffer TH. Liquid ventilation of human preterm neonates. J Peds 1990; 117: 106-l 11. 10. Wolfson MR, Clark LC, Hoffmann RE, Davis SL, Greenspan JS, Rubenstein SD, Shaffer TH. Liquid ventilation of neonates: uptake, distribution, and elimination of liquid. Pediatr Res 1990; 27: 37A.

11. Tremper KK, Zaccari J, Cullen BF, Hufstedler SM. Liquid-gas partition coefficients of halothane and isoflurane in perfluorodecalin, FluosolDA, and blood/Fluosol-DA mixtures. Anesth Anal 1984; 63: 690-692. 12. Rowe PC. The Harriet Lane Handbook. Chicago: Year Book Medical Publishers, 1987. 13. Koen PA, Wolfson MR, Shaffer TH. Fluorocarbon ventilation: maximal expiratory flows and CO, elimination. Pediatr Res 1988; 24: 291-297. 14. Hill DW (ed.) Some mathematical concepts. In: Physics Applied to Anaesthesia fourth edition. Boston: Butterworths, Inc. 1980, pp. l-31. 15. Daniel WW. Biostatistics: A Foundation for Analysis in the Health Sciences. New York, John Wiley and Sons, 1980, pp. 2033223. 16. Clark LC, Gollan F. Survival of mammals breathing organic liquids equilibrated with oxygen at atmospheric pressure. Science 1966; 152: 1755-1756. 17. Clark LC, Becattini F, Kaplan S. The physiological effects of artificial blood made from inert organic oxygen solvents. Ala J Med Sci 1972; 9: 16-29. 18. Chilcoat RT, Gerson JI, Allen FB, Mapleson WW. The effect of Fluosol-DA on induction of inhalation anesthesia, Anesth Analg 1985; 64: 405410. 19. Shaffer TH, Tran N, Bhutani VK, Sivieri EM. Cardiopulmonary function in very pre-term lambs during liquid ventilation. Pediatr Res 1983; 17: 680-684. 20. Shaffer TH, Forman D, Wolfson MR. The physi-

ological effects of breathing fluorocarbon liquids at various temperatures. Undersea Biomed Res 1984; 11: 2877298. 21. Sass DJ, Ritman EL, Caskey PE, Banters N, Wood EH. Liquid breathing prevention of pulmonary arterio-venous shunting during acceleration. J Appl Physiol 1972; 32: 451455.

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D. B. KIMLESS-GARBER

ET AL.

22. Gollan F, Clark LC. Prevention of the bends by breathing an organic liquid. Tram Assoc Am Physicians 1967; 29: 102-109. 23. Lynch PR, Wilson JS, Shaffer TH, Cohen N. Decompression incidence in air and liquid breathing hamsters. Undersea Biomed Res 1983; 10: l-10. 24. Wolfson MR, Greenspan JS, Deoras KS, Rubenstein SD, Shaffer TH. Comparison of gas and liquid ventilation: clinical, physiological, and histological correlates. J Appl Physiol 1992; 72 (3): 102431. 25. Eger EI. Uptake and distribution of inhaled anesthetics. In: Miller RD, ed. Anesthesia. New York: Churchill Livingstone, 1986: 625-647.

26. West JB, Dollery CT, Matthews CM, Zardini P. Distribution of blood flow and ventilation in saline-filled lung. J Apply PhysioZl965; 20: 11071117. 27. Shaffer TH, Lowe CA, Bhutani VK, Douglas PR. Liquid ventilation: effects on pulmonary function in distressed meconium-stained lambs. Pediatr Res 1984; 18: 47-52. 28. Sargent JW, Seffl RJ. Properties of perfluorinated liquids. Fed Proc 1970; 29: 1699-1703. 29. Tham MK, Walker RD, Model1 JH. Physical properties and gas solubilities in selected fluorinated ethers. J Chem Eng Data 1973; 18: 385386.