INTRAOCULAR AND INTRACRANIAL PRESSURE DURING RESPIRATORY ALKALOSIS AND ACIDOSIS

Br. J. Anaesth. (1981), 53, 967

INTRAOCULAR AND INTRACRANIAL PRESSURE DURING RESPIRATORY ALKALOSIS AND ACIDOSIS R. B. SMITH, A. A. AASS AND E. M. NEMOTO SUMMARY

Intraocular pressure (IOP) is determined by the rates of formation and outflow of aqueous humour, the volume of intraocular vessels and extraocular compressive forces. During general anaesthesia, surgical and pharmacological factors may alter IOP by direct action on the eye or indirectly through changes in circulation and respiration. A detailed discussion was presented in a recent symposium on Anaesthesia and the Eye (Spence and Norman, 1980). Respiration can effect IOP by altering Pa,^. and by influencing intrathoracic and central venous pressures. Duncalf and Weitzner (1963) recorded anterior chamber pressure of dogs and found that IOP increased by an average of 35.2% when mean Pa^, was increased by 3.33 kPa following inhalation of carbon dioxide. Hyperventilation reduced IOP in three of four experiments as Pace, decreased. The eyes of higher mammals receive their blood mainly from the internal carotid artery, while in the dog the eye is supplied from both the external and the internal carotid arteries (Wolff and Last, 1968). This may invalidate extrapolation of findings in the dog to man, but similar results have been reported in man (Adams and Barnett, 1966; Meyer and Opitz, 1970; Samuel and Beuagie, 1974; Kaufmann,

1975) using indirect and intermittent measurements of IOP. This study investigated the relationship between IOP and PaCOj by direct and continuous IOP measurements in Rhesus monkeys during anaesthesia to obtain results of clinical significance to man. Intracranial pressure (ICP) was measured continuously for comparison with IOP.

METHODS

Nine Rhesus monkeys, weights 2.5—3.5 kg, were anaesthetized with 4% halothane in oxygen. The trachea was intubated (tubes 3-5 mm i.d.) and anaesthesia maintained with 0.5% halothane and 50% nitrous oxide. A peripheral vein was cannulated and 5% dextrose and 0.45% sodium chloride solution infused at a rate of 5 ml kg" 1 h" 1 . Pancuronium 0.2mgkg~' was administered i.v. as required for muscle relaxation and ventilation of the lungs controlled with a Harvard fixed volume ventilator. End-tidal carbon dioxide was monitored continuously with a Godart Capnograph and maintained initially between 4 and 6%. A transurethral catheter was placed in the bladder and a metal probe inserted for continuous recording of R. BRIAN SMITH, M.D., Department of Anesthesiology, The temperature which was maintained between 37 University of Texas Health Science Center at San Antonio, and 39 °C with a warming blanket or lamp. 7703 Floyd Curl Drive, San Antonio, Tx78284, U.S.A. ANNE Catheters for central venous and arterial pressure A. AASS, M.D.; EDWIN M. NEMOTO, PH.D., Department of Anesthesiology, University of Pittsburgh School of Medicine, recordings and blood sampling were inserted to the femoral vessels. ICP was monitored via a Pittsburgh, Pa 15261, U.S.A. Correspondence to R. B. S. multiple-hole silastic catheter inserted subdurally 0007-0912/81/090967-06 801.00

© Macmillan Publishers Ltd 1981

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Intraocular and intracranial pressures (IOP and ICP) were measured at four different arterial carbon dioxide tensions by direct continuous techniques in Rhesus monkeys during anaesthesia with halothane and nitrous oxide. Increases in IOP correlated significantly with /Xx)- ranging from 2.66 to 10.24kPa (P<0.001). Increases in ICP correlated significantly (P-cO.001) with f\:0, between 2.66 and 7.71 kPa, but plateaued thereafter. When Pa^o, was decreased rapidly, Paco,, IOP and ICP decreased exponentially with similar half-times. The fast changes in IOP and ICP can probably be explained by an alteration of intraocular and intracranial blood volumes. IOP usually remained within the normal range, even at maximum

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FIG. 1. Variation in IOP with 4

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f £, 2 Q.

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RESULTS

IOP and ICP at four arterial tensions of carbon dioxide A statistically significant direct correlation was found between the mean values of IOP and P a ^ (P<0.001) (table I, fig. 1). Although mean ICP correlated significantly (P< 0.001) with mean P a ^ between 2.66 and 7.71 kPa, thereafter it did not increase with increasing P a ^ . (table I, fig. 2). Table II shows average increases in IOP per unit increase in Pa^, to be similar at different tensions of carbon dioxide. In contrast, changes in ICP were significantly greater when P a ^ was increased from 2.66 to 5.05 kPa (P < 0.01) and 5.05 to 7.71 kPa (P<0.02) than when Pa^, was increased from 7.71 to 10.24kPa (table II).

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FIG. 2. Variation in ICP with

Changes in c.v.p., HR and Pao, were insignificant. However, m.a.p. decreased significantly (P<0.05) from a mean of 94 (SD 13) mmHg to 82 (SD 15) mmHg as P a ^ was increased from normal to 10.24 kPa. IOP and ICP during rapid change of F\o, There were seven experiments in which Pa^Q was allowed to decrease rapidly (figs 3, 4). After a

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over the parietal cortex and secured with Eastman 910 cement. The anterior chamber of one eye was punctured with afluidfilled 25-gauge needle, care being taken to prevent loss of aqueous humour. IOP, ICP, mean arterial pressure (m.a.p.), heart rate (HR) and central venous pressure (c.v.p.) were measured with strain gauges and recorded continuously. IOP, ICP, m.a.p., c.v.p., HR and arterial pH and gas tensions were determined at four arterial tensions of carbon dioxide. The ventilation rate and tidal volume were first adjusted to set P a ^ , at about 2.66kPa. Normocarbia, moderate hypercarbia, and marked hypercarbia were then produced by adding carbon dioxide to the inhaled gases. Ten minutes or more was allowed for equilibration at each step before recordings were made. Carbon dioxide inhalation was chosen in preference to hypoventilation as the different conditions required for study occurred more rapidly (Nunn, 1975) and changes in intrathoracic pressure were avoided. The experiment was repeated in a few of the animals. IOP and ICP were then studied under conditions of varying Pa^, to establish the time relationship between them. Hypercarbia was produced first and the inhaled carbon dioxide was turned off. IOP, ICP and P a ^ , were then measured at 0, 1, 2, 3, 4, 5, 6, 8 and lOmin. F-test was used for determination of significance of linear correlations and Student's t test for comparison of mean values.

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TABLE I. Intraocular and intracramal pressures at four different arterial tensions of carbon dioxide. n.s. = not significant

Experiment

Pressure (kPa)

1 IOP' ICP 2

IOP ; ICP

3

IOP J ICP IOP J ICP

5

IOP 1 ICP

6

IOP ; ICP

7

IOP' ICP 8

IOP ; ICP

9

IOP ; ICP

10

IOP ; ICP

11

IOP ; ICP

12

IOP ICP

II

III

IV

2.26 2.13 0.80 2.66 1.86 0.86 2.13 1.79 0.80 2.39 1.66 0.27 2.93 2.39 1.60 2.39 2.13 1.53 3.59 2.39 8.64 2.79 1.86 0.93 3.86 2.26 1.60 2.93 2.33 1.53 3.19 1.93 2.13 1.86 1.60 1.06

4.79 2.26 1.33 4.26 1.99 1.20 4.92 2.39 1.46 4.92 1.99 0.66 5.19 2.66 1.86 5.32 2.46 1.86 5.19 2.66 1.60 3.99 2.13 1.46 6.65 2.39 2.66 6.78 2.66 2.86 4.78 1.99 2.66 4.39 1.99 1.60

7.58 2.79 2.33 6.78 2.53 2.79 7.18 2.79 2.59 6.78 2.33 1.20 7.30 2.79 1.46 8.78 2.79 3.72 9.31 2.86 2.66 6.65 2.53 2.59 7.58 2.53 2.39 9.31 2.86 2.86 8.38 2.46 3.99 7.46 2.19 2.13

9.97 3.59 2.46 8.50 3.19 3.06 10.37 3.06 2.59 10.24 2.53 1.46 9.84 2.79 1.46 10.51 3.19 2.66 10.90 3.06 2.79 10.64 2.86 2.66 8.91 2.79 2.53 11.84 2.79 2.79 10.77 2.79 3.59 11.04 2.46 2.26

Correlation with Paco, P<0.05 P<0.05 P<0.05 P<0.05 P<0.05 n.s. P<0.05 P<0.05 n.s. n.s. P<0.05 n.s. P<0.05 P<0.05 P<0.05 n.s. n.s. n.s. P<0.05 n.s. P<0.01 n.s. P<0.05 P<0.05

TABLE II. Relative increase of IOP and ICP tmth

Paco. (kPa) 2.66-5.05

5.05-7.71

7.71-10.24

Mean SD

0.016 0.008

0.017 0.008

0.02 0.016

Mean SD

0.036 0.016

0.035 0.039

0.003 0.027

slight delay, IOP (fig. 3) and ICP (fig. 4) decreased in a similar manner attaining a new steady state in about lOmin. Both pressures showed a significant linear correlation with P a ^ (P< 0.001). The percent decrease of each pressure during the first 5min was plotted semilogarithmically to calculate half-times for the equilibration of P a ^ > IOP anc* ICP (fig. 5). The following half-times were estimated from this: P a ^ 82s; IOP 70s; ICP 75s.

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OP

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ICP

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Time (min) FIG.

, and IOP during rapid washout of carbon dioxide in seven experiments.

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Time mrialed COj turned off

OICP

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FIG. 5. Per cent total response during rapid washout of carbon dioxide (means of seven experiments). Q.

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FIG. 4. Pa^, and ICP during rapid washout of carbon dioxide in seven experiments. DISCUSSION

Our data confirm previous findings that IOP increases with PacoXDuncalf and Weitzner, 1963; Adams and Barnett, 1966; Meyer and Opitz, 1970; Samuel and Beuagie, 1974; Kaufmann, 1975) and

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suggest a linear relationship between the two pressures. IOP changes were not caused by cardiovascular factors when P&co. w a s allowed to stabilize, since HR and c.v.p. remained stable and m.a.p. decreased slightly at high arterial carbon dioxide tensions. During carbon dioxide washout, a transient decrease in m.a.p. might have influenced IOP and ICP and so reduced their halftimes compared with that of •f>aCO;. The two most likely mechanisms by which carbon dioxide aflFects IOP are alteration of intraocular blood volume and altered formation of aqueous humour. The response of the choroidal and cerebral circulations to changes in PBCO. m t n e baboon has been reported by Wilson, Strang and McKenzie, 1977. They found blood flow in both circulations varied directly with Pa,:o.> the magnitude of the responses being very similar. Spalter, Ten Eick and Nahas (1964) observed that hypercarbia caused intraocular vasodilatation

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maximum de la REFERENCES

Adams, A. K., and Barnett, K. C. (1966). Anesthesia and intraocular pressure. Anaesthesia, 21, 202. Aim, A., and Bill, A. (1972). The oxygen supply to retina. II: Effects of high intraocular pressure and of increased arterial carbon dioxide tension on uveal and retinal blood flow in cats. Ada Physiol. Scand., 84, 306. Duncalf, D., and Weitzner, S. W. (1963). The influence of ventilation and hypercapnea on intraocular pressure during anesthesia. Anesth. Analg. (Clevc), 42, 232. Haggendal, E., Nilsson, N. J., and Norback, B. (1969). Aspects of the autoregulation of the cerebral blood flow. Circulation and anesthesia. Int. Anesthesiol. Clin., 7, 353. Kaufmann, H. (1975). Das glcichsinnige Verhalten von okularcr Durchblutungsgrosse und Augeninnendruck bei Veranderungen der arteriellen Gasspannungen. Dtsch. Ophthalmol. Gcs., 73, 322. Meyer, H. J., Opitz, A. (1970). Intraocular Druck und endexpiratorische CO2Konzcntration. Klin. Monaxsbl. Augenheilkd., 156, 730. Nunn, J. F. (1975). Applied Respiratory Physiology With Special Reference to Anesthesia, Fourth reprint. London: Butterwarth & Co., Ltd. Samuel,/ R., and Beuagie, A. (1974). Effect of carbon dioxide on the intraocular pressure in man during general anesthesia. Br. J. Ophthalmol., 58, 62.

INTRAOKULARER UND INTRAKRANIELLER DRUCK WAHREND ATMUNGSALKALOSE UND AZIDOSE ZUSAMMENFASSUNG

Die intraokularen und intrakraniellen Drucke bei Rhesusaffen wurden wahrend der Anasthesic mit Halothan und Stickoxydul bei vier verschiedenen Arterienkohlendioxyddrucken im direkten kontinuierlichen Verfahren gemessen. Es zeigte sich einc bedeutende Wechselbeziehung zwischen Steigerungen des intraokularen Druckes und P a ^ i m Bereich von 2,66 bis 10,24kPa (P<0,001). Es zeigte sich auch einc bedeutende Wechselbeziehung zwischen Steigerungen des intrakraniellen Drucks und Paco, im Bereich von 2,66 bis 7,71 kPa (P < 0,001), aber danach stellte sich cine Abflachung ein. Als die P&co.> schell reduziert wurde, nahmen P%c£>,< intraokularer und intrakranieller Druck exponentiell ab, und zwar mit ahnlichen Halbwerten. Die schnellen Anderungen des intraokularen und intrakraniellen Druckes lasst sich wahrscheinlich durch eine Anderung des intraokularen und intrakraniellen Blutvolumens crklaren. Der intraokulare Druck blieb auch bei maximaler innerhalb des normalen Bereiches.

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while Aim and Bill (1972) found ocular blood flow Spalter, H. F., Ten Eick, R. E., and Nahas, G. G. (1964). Effect of hypercapnia on retinal vessel size at constant intracranial to increase by 200-300% with increase in P^CQ,. pressure. Am. J. Ophthalmol., 57, 741. The increase in IOP with hypercarbia is likely to Spence, A. A., and Norman, J. (cds) (1980). Symposium on result from an increase in intraocular blood Anaesthesia and the Eye. Br. J. Anaesth., 52, 643. volume. Compared with IOP, the response of ICP Wilson, T. M., Strang, R., and McKenzie, F. T. (1977). The response of the choroidal and cerebral circulations to to changes in Pa,^, showed much greater variarterial Pco, and acetazolamide in the baboon. ability, especially at the maximum P&co, studied. changing Invest. Ophthalmol. Vis. Sci., 16, 576. Since the autoregulation of the cerebral circulation Wolff, E., and Last, R. J. (1968). Anatomy of the Eye and Orbit, seems to shift to a higher level with increase of 6th edn. Philadelphia: W. B. Saunders Co. PaCOn (Haggendal, Nilsson and Norback, 1969), the small decrease in m.a.p. might have decreased perfusion. It also seems that increasing Ps^o, may produce a variable response in the cerebral PRESSIONS INTRAOCULAIRE ET circulation (Haggendal, Nilsson and Norback AU COURS D'UNE ALCALOSE 1969). Compensatory mechanisms might also have INTRACRANIENNE ET D'UNE ACIDOSE RESPIRATOIRES interfered. RESUME During sudden hyperventilation, -Paco. decreases exponentially (Nunn, 1975). The half- Nous avons mesure les pressions intraoculaire ct intratime we found in monkeys was shorter than the cranienne (IOP et ICP) a quatre differentes tensions du gaz carbonique arteriel ct par des techniques continues directes sur 3-4 min described for man (Nunn, 1975). des singes Rhesus au cours d'une anesthcsie effectuce a l'aide IOP remained within a normal range in most of d'halothane et de protoxyde d'azote. L'accroissement de 1'IOP our experiments even at the maximum Pa^, a donne une correlation significative avec la Pa CO: sur une plage a achieved. Moderate changes of P&co, appear to de 2,66 a 10,24kPa (P<0,001). L'accroissement de l'ICP sur donne une correlation significative (P < 0,001) avec la Pt^Oi have little clinical significance, but hyperventi- une plage de 2,66 a 7,71 kPa, mais est restee stationnaire apres. lation should be considered and hypoventilation Lorsque la P&co, a decru rapidement, la Pai> ''IOP e t l'ICP avoided when a low IOP is required. The rapid ont decru d'une maniere exponentielle, avec, des demi-temps changes in IOP follow closely the changes in ICP similaires. Les changements rapides dans 1'IOP et l'ICP and can be explained by alteration in intraocular peuvent probablement s'expliqucr par une modification des volumes sanguins intraoculairs et intracraniens. Dans l'enblood volume. semble, 1'IOP est restee dans une plage normale meme au

BRITISH JOURNAL OF ANAESTHESIA

972 PRESION INTRAOCULAR E INTRACRANEAL DURANTE LA ALCALOSIS Y ACIDOSIS SUMARIO

Durante la anestesia con halotano y con oxido nitroso de monos Rhesus, se midieron las presiones intraocular e intracraneal (PIO y PIC), a cuatro diferentes tensiones arteriales de dioxido de carbono siguiendo tecnicas continuas y directas. Los incrementos en la PIO se correlacionaron significativamente (P<0,001) con la P a ^ , , oscilando entrc 2,66 y 10,24kPa. Los incrementos en la PfC correlacionaron significativamente

(P < 0,001) con la Paco,entre 2,66 y 7,71 kPa, siguicndo un valor horizontal posteriormente. Cuando la Pa^-, se disminuyo rapidamente, la P*co,> ' a PIO y ^ PIC disminuyeron exponencialmente con tiempos medios similares. Los rapidos cambios en la PIO y en la PIC pueden explicarse, probablemente, por la variation de los voliimenes sanguineos intracraneal e intraocular. La PIO permanecio, por regla general, dentro de la gama normal, incluso para el valor maximo de la

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