EFFECT OF PNEUMOPERITONEUM WITH CARBON DIOXIDE (CO₂) ON VARIOUS KINDS OF ANESTHESIA DURING LAPAROSCOPIC OPERATIONS IN DOGS

Wojciech Brzeski, Zbigniew Adamiak, Marek Nowicki, Marek Jałyński, Andrzej Depta, Renata Nieradka, Andrzej Rychlik, Marcin Nowicki

ABSTRACT

Pneumoperitoneum is indispensable in diagnostic laparoscopy and laparoscopic operations. The effect of pneumoperitoneum with carbon dioxide (CO₂) on the course of two kinds of anesthesia before laparoscopy in dogs was studied.. Inhalation anesthesia with a mixture of oxygen and isofluran in a closed system was administered in group I, and infusion anesthesia with Thiopental in group II. Then pneumoperitoneum was produced, with constant intraperitoneal pressure of CO₂ at a level of 12 mm Hg. All dogs were subjected to clinical, hematological and biochemical examinations. Positive results of the experiment indicate that pneumoperitoneum with CO₂ may be used in both kinds of anesthesia.

Key words: pneumoperitoneum, anesthesia, laparoscopy, dog..

INTRODUCTION

Laparotomy is nowadays a common, but not the only, diagnostic and operative method in abdominal surgery in animals. Technological progress observed recently made it possible to introduce a new diagnostic and operative method, requiring modern apparatus and instruments. This method is laparoscopic diagnostics and surgery. Laparoscopy is an endoscopic visual technique enabling direct imaging of the abdominal cavity organs on the screen.

Laparoscopic diagnostics may be applied as a separate method, or as an additional procedure accompanying the diagnostic methods used so far. The range of its application becomes wider and wider, allowing to make a detailed diagnosis of numerous diseases. Laparoscopic surgery reduces the occurrence of injuries during operations, shortens the time of surgical intervention and convalescence. In this way it affects positively the final therapeutic results. Both diagnostic laparoscopy and laparoscopic operations require pneumoperipoteum.

Broad and growing interest in laparoscopy results in the introduction of innovative, advanced technological solutions and therapeutic methods, aimed at increasing the safety of these procedures. In spite of undoubted success in this field, certain problems still need to be investigated. One of them is the correlation between pneumoperitoneum – indispensable to carry out laparoscopic operations – and various kinds of anesthesia in dogs (1,3).

An attempt was made in the studies to determine the effect of pneumoperitroneum with carbon dioxide (CO₂) on the course of two kinds of anesthesia during laparoscopy in dogs.

MATERIAL AND METHODS

The experiment was conducted on 24 mongrel dogs of both sexes, aged between 2 and 10 years, with body weight of 10 - 30 kg. Clinical examinations carried out before anesthesia did not show any deviations from the physiological norms for this animal species. The dogs were divided into two equal groups.

Group I

12 dogs from group I were subjected to general inhalation anesthesia in a closed system. Atropine (Polfa), at a dose of 0.04 mg/kg m.c. in s.c., and Medeothymidine (Domitor), at a dose of 40 µ/kg m.c. in m., were used for premedication. Thiopental (Biochemie Vienna), at a dose of 8 - 10 mg/kg m.c. in v, was administered when symptoms of tranquility became visible.

The first stage of anesthetization made it possible to conduct catheterization of the urinary bladder and pass on to inhalation anesthesia with a mixture of oxygen and isofluran at concentration of 1 - 3%. General inhalation anesthesia in a closed system, with CO₂ absorber, was produced maintaining the breathing rhythm. After achieving the state of general anesthesia referred to as surgical tolerance, pneumoperitoneum was produced.

The abdominal wall was punctured in the periomphalic area, next to linea alba. The skin and subcutaneous tissue were incised there (ca. 5 mm), abdominal integument was lifted up with two Towel clips or Backhaus forceps, and a Verres needle was introduced. This kind of needle – an indispensable instrument in laparoscopy – is a bluntly-ended cannula with a mandrel inside, whose springing mechanism draws it back after abdominal integument puncture, preventing injury to internal organs. The other end of the needle has on its side a small cock, connected with the insufflator’s conductor. The insufflator was switched on to produce pneumoperitoneum by introducing carbon dioxide (CO₂) into the abdominal cavity.

Insufflators are electronic devices enabling automatic control of gas flow. They ensure that the right volume of carbon dioxide is introduced into the abdominal cavity, and that its constant pressure is maintained during the operation. Gas losses are replenished automatically.

After switching the insufflator on, carbon dioxide was introduced through the Verres needle to the peritoneal cavity to produce pneumoperitoneum at a level of 12 mm Hg. This state was maintained for 45 minutes. Then the insufflator was switched off, the valve of the small cock was opened and the abdominal cavity was emptied of carbon dioxide. The oxygen and anesthetic inflow was shut off, the inhalation anesthetic machine was disconnected and the intubation tube was removed from the trachea. During inhalation anesthesia and pneumoperitoneum, all dogs were subjected to clinical, hematological and biochemical analyses, according to the following scheme:

• examination 1 (test 0) – before anesthesia,

• examination 2 (test 01) – after anesthesia, before insufflation,

• examination 3 – 15 min. from the beginning of insufflation,

• examination 4 – 30 min. from the beginning of insufflation,

• examination 5 – 45 min. from the beginning of insufflation

• examination 6 – 2 hours after the completion of anesthesia and insufflation,

• examination 7 – 4 hours after the completion of anesthesia and insufflation,

• examination 8 – 24 hours after the completion of anesthesia and insufflation,

• examination 9 – 48 hours after the completion of anesthesia and insufflation.

Clinical examinations included the determination of the respiratory rate, pulse rate and core temperature.

Blood samples for hematological and biochemical analyses were taken from vena intracapitalis antebrachii, introducing to its lumen venflons whose diameters varied from 0.9 to 1.2 mm, depending on the dog size. Venflons present in the venous lumen during the experiment enabled blood collection for examinations.

Hematological analyses were made using Veterinary Hematological Analyzer VET ABC-18 p. They included the determination of the red blood cell count (Erys), white blood cell count (Lkcs), hematocrit value (Ht), hemoglobin content (Hb), red blood cell indices: mean red blood cell volume (MCV), mean hemoglobin concentration in a red blood cell (MCHC), mean hemoglobin mass in a red blood cell (MCH), mean blood plate volume (MPV) the count of lymphocytes, monocytes, granulocytes (Limf, Mon, Gran) and blood plates (PLT). Biochemical analyses comprised the determination of the acid-base equilibrium (ABE) and the activity of alanine aminotransferase (ALT). The ABE parameters (pH, partial CO₂ pressure, partial O₂ pressure, HCO₃ concentration, BE – base excess or deficiency) – were determined by means of analyzer Ciba Corning C248. The ALT activity was determined by the kinetic method, using spectrocolorimeter Marcel s330.

Group II

General infusion anesthesia was produced in 12 dogs from group II. The anesthetics and their doses were the same as in group I. Thiopental (Biochemie Vienna) in v. was administered to induce general anesthesia. Pneumoperitoneum was produced as in group I. Anesthesia and pneumoperitoneum lasted for 45 minutes. 14 mg/kg m.c. of Thiopental was used on average over this time. Clinical, hematological and biochemical examinations were conducted in all dogs from group II before anesthesia, after anesthesia and insufflation, after 15’, 30’, 45’, and after 2, 4, 24, 48 h.

RESULTS AND DISCUSSION

Diagnostic and operative laparoscopy requiring pneumoperitoneum become more and more popular in the case of small animals. These procedures must be preceded by proper general anesthesia. In the present experiment inhalation anesthesia with a mixture of oxygen and isofluran was produced in group I, and infusion anesthesia with Thiopental in group II. Then pneumoperitoneum was produced in both groups, with constant intraperitoneal pressure of CO₂ at a level of 12 mm Hg. The effect of this kind of treatment on the course of anesthesia was determined on the basis of the results obtained.

It should be emphasized that neither controlled nor supported respiration was used during anesthesia and insufflation – all dogs were breathing spontaneously. Over the experimental period minute ventilation was determined for each dog; its mean values for particular experiment stages are also presented.

An analysis of the results shows that after achieving full anesthesia the respiratory rate decreased in both groups: group I - from 28/min. before anesthesia to 14/min. 2 h after its administration; a gradual increase was noted from the 4^th h to the 24^th h (27/min.); group II – a decrease from 29/min. to 22/min. 4 h after anesthesia. In this group a lower respiratory rate was accompanied by shallow breath and longer respiration phases. Breath normalization took up to 24 h after anesthesia.

An analysis of the peripheral pulse indicates its gradual fall, observed from achieving surgical tolerance till the completion of anesthesia and pneumoperitoneum, followed by a rise two hours after the ending of insufflation, a further rise after four hours, and a return to the initial value after 24 hours.

In group I the average pulse rate decrease from 97/min. before anesthesia to 76/min.was observed till the completion of anesthesia and pneumoperitoneum. In group II an increase in the pulse rate from 89/min. to 100.min. lasted up to four hours after anesthesia. In both groups its normalization took up to 24 hours after anesthesia. The clinical effects concerning the circulatory and respiratory system are presented in Table 3 and Figure 2.

During the experiment the mean values of hematological indices (Erys, Hb, Ht, MCV, MCHC, MCH, PLT, MPV, Limf, Mon) in both groups showed no significant differences and remained within the physiological norms for dogs (11). An increase in the leukocyte count Lkcs (14.2x10⁹/L and 19.3x10⁹/L respectively) and granulocyte count Gran (11.04x10⁹/L and 16.4x10⁹/L respectively.) observed 48 hours after pneumoperitoneum may be connected with local inflammation in the wound caused by the trocar introduction. Mean values of haematological indicators are presented in Table 1.

The acid-base balance parameters also remained within reference values. At the first stage of the experiment a slow decrease in blood pH was noted in both groups - from 7.31 before the experiment to 7.25 two hours after insufflation in group I, and from 7.29 to 7.22 four hours after insufflation in group II. This decrease was accompanied by an increase in carbon dioxide partial pressure pCO₂ - from 6.64 kPa to 7.83 kPa in the second hour of the experiment, and from 7.10 kPa to 8,74 kPa in the fourth hour after insufflation. This may indicate the beginning of transitory compensated metabolic acidosis, connected with CO₂ absorption from the peritoneal cavity to the blood (10). Then slight fluctuations in oxygen partial pressure p0₂, the level of bicarbonates HC0₃^- (26.8 mmol/L and 27.3 mmol/L respectively) and base excess (-0.59 mmol/L and –0.71 mmol/L respectively) were observed in both groups. They were accompanied by a drop in car bon dioxide partial pressure pCO₂ (6.28 kPa and 7.94 kPa respectively), which suggests transitory compensated respiratory alkalosis and regression of disturbances in the acid-base equilibrium (5).

No significant changes in the activity of alanine aminotransferase (ALT) were observed in either of the experimental groups . This may indicate that pneumoperitoneum and short-lasting general anesthesia had no negative effect on the liver (7). Mean Values of biochemical and acid-base balance indicators are presented in Table 2 and Figure 1.

The results of hematological and biochemical analyses show that general anesthesia and pneumoperitoneum with carbon dioxide, produced in dogs from both experimental groups, have no negative influence on the health state of these animals. Fluctuations in the acid-base equilibrium noted during the experiment tended towards compensated respiratory alkalosis. These are adaptation and compensatory changes. However, it should be stressed that in dogs from group II the above normalization and clinical processes took place later – from the 4^th hour of the experiment. In dogs from group I the first adaptation phase lasted up to 2 hours after insufflation.

Pneumoperitoneum is an indispensable element of each laparoscopic operation. It enables the necessary displacement of the abdominal cavity organs, i.e. exposure of the operative area, and facilitates manipulations with endoinstruments (8,12). Carbon dioxide – most commonly applied gas – was used to produce pneumoperitoneum in the experiment. The application of oxygen or filtrated air is limited, as they prevent the use of electrocatheterization and laser (9). They may also cause the occurrence of life-threatening aeroembolisms in circulating blood. Nitrous oxide is applied less commonly, because this is anesthetic gas which makes full control of anesthesia depth difficult. Moreover, it can also cause embolisms, although to a lower degree than oxygen. Helium is neutral gas, characterized by minimal absorption (2). It has already been used in medicine, but its suitability for veterinary purposes requires further investigations. The application of nitrogen (N₂) is limited b y its high lipid-solubility.

In our studies intraperitoneal pressure of CO₂ at a level of 12 mm Hg was used, as this is the optimum, most commonly applied pressure. In medicine pressure of 10 - 16 mm Hg is usually applied. According to the literature on the topic, pressure has no significant effect on hemodynamics. This effect seems to be connected first of all with carbon dioxide accumulation in the circulatory system. CO₂ absorption from the peritoneal cavity during pneumoperitoneum could contribute to the occurrence of compensated respiratory acidosis in both groups of dogs. Generally, carbon dioxide can be easily eliminated during proper minute ventilation, because of its high solubility and diffusivity. However, if the process of vesicular respiration is disturbed by changed breathing mechanics, additional amounts of CO₂ coming from pneumoperitoneum cannot be eliminated or metabolized completely, which may lead to dangerous hypercapnia and respiratory acidosis (6).

In the experiment increased CO₂ absorption from the peritoneal cavity was compensated by decreased, but sufficient, minute ventilation, breathing rhythm and maintenance of blood parameters close to the physiological ones.

Insufflation completion, accompanied by carbon dioxide elimination from the peritoneal cavity, resulted in the return of hemodynamic and respiration parameters and indices causing hypercapnia to the level observed before gas introduction. The time needed to restore the initial state was shorter in group I. In group II the changes regressed after four hours, with full normalization in the successive ones.

CONCLUSIONS

1. Pneumoperitoneum with carbon dioxide and two kinds of anesthesia produced in the experiment, i.e. inhalation in a closed system and infusion, do not constitute a metabolic threat and may be applied in dogs.

2. Respiratory acidosis observed in both groups was compensated by optimum minute ventilation.

3. The values of hematological, biochemical and hemodynamic indices, important from the anestesthesiological perspective, were close to the physiological norms in both groups.

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