On-line version ISSN 1678-2674
Acta Cir. Bras. vol.18 suppl.5 São Paulo 2003
Is CO2 gas unsufflator necessary for laparoscopic training in animals?1
O insuflador de gás CO2 é necessário para treino de laparoscopia em animais?
Ricardo Brianezi TiraboshiI; André Luis Alonso DomingosI; José Anastácio Dias NetoI; Ricardo Mesquita PaschoalI; José TravassosII; Antonio Carlos Pereira MartinsIII; Haylton José SuaidIII; Adauto José ColognaIII; Silvio Tucci JrIII.
IMédicos Residentes do HCFMRP-USP
IIDocente Colaborador HFFMRP-USP
IIIDocentes da FMRP-USP
OBJECTIVE: To verify the efficacy and safety of compressed air to produce pneumoperitoneum for laparoscopic surgery in pigs for a training program of residence.
METHODS: Dalland pigs weighing 15-17kg underwent general anethesia and mechanical ventilation. They were divided in 3 groups: A (38) the pneumoperitnoneum was established with an automatic CO2 insufflator, B (7) as in A except the CO2 gas was changed by compressed air, and C (11) abdomen insufflation was obtained with compressed air directly from hospital pipe network system. Intra-abdominal pressure in all groups was kept between 12 and 15 mmHg. The laparoscopic procedures performed were distributed proportionally among groups: 20 bilateral nephrectomy, 20 dismembered pyeloplasty and 16 partial nephrectomy. Arterial blood sampling for gasometry was obtained before and 2h after establishment of pneumoperitoneum in 5 pigs of group C.
RESULTS: The cost of 25 4,5kg CO2 container used in group A was R$ 3,150.00 (U$ 1,050.00). The mean length time of surgeries in groups A, B and C were respectively: 181±30min, 196±39min e 210±47min (p>0.05). Respiratory alkalosis occurred in 3 out of 5 pigs of group C. No animal exhibited signs of gas embolism or died during surgery.
CONCLUSION: The use of compressed air for laparoscopy in pigs was safe, reduced costs and did not require the use of an automatic gas insufflator.
Key Words: Laparoscopy. Nephrectomy. Pyeloplasty. Partial nephrectomy. Pneumoperitoneum. CO2 gas. Compressed air.
OBJETIVO: Testar a eficácia e segurança do pneumoperitônio com ar comprimido para cirurgias videolaparoscópicas em porcos em treinamento de residência médica.
MÉTODOS: Porcos da raça Dalland de peso variável de 15 a 17kg foram submetidos a anestesia geral e respiração controlada. Eles foram divididos em 3 grupos: A 38 animais com pneumoperitônio feito com insuflador automático de CO2 usando este gás; B 7 animais sujeitos ao mesmo procedimento exceto que o CO2 foi substituído por ar comprimido; e, C 11 animais em que o pneumoperitônio foi feito com ar comprimido diretamente da rede hospitalar. Nos 3 grupos a pressão intra-abdominal foi mantida entre 12 e 14mmHg. Os procedimentos realizados foram distribuídos proporcionalmente nos 3 grupos: nefrectomia bilateral 20, pieloplastia desmembrada 20 e nefrectomia parcial 16. Antes e 2h após o pneumoperitônio foi colhido sangue arterial para gasometria em 5 porcos do grupo C.
RESULTADOS: Foram consumidos 25 torpedos de 4,5kg de CO2 a um custo total de R$ 3.150,00 no grupo A. A duração média da cirurgia nos grupos A, B e C foram respectivamente: 181±30min, 196±39min e 210±47min (p>0.05). Alcalose respiratória foi observada em 3/5 porcos testados do grupo C. Nenhum animal apresentou sinais de embolia gasosa ou faleceu durante o procedimento.
CONCLUSÃO: O uso de ar comprimido para laparoscopias em porcos mostrou-se método seguro com redução de custos e tornou desnecessário o uso de insuflador automático.
Descritores: Laparoscopia. Nefrectomia. Pieloplastia. Nefrectomia. Parcial. Pneumoperitônio. CO2. Ar comprimido.
Kelling reported the observation of the abdominal cavity of dogs and humans through an air-filled abdomen for the first time in 1,9021. This procedure named "coelioscopy" became a routine in humans in 1,9142. To reduce the risk of a blind puncture of the abdomen, Goetze developed an automatic needle in 1,918 and reported as ideal the practice of initially establishing a pneumoperitoneum using oxygen3. Since the development of the first automatic CO2 gas insufflator, in 1,9664,5, the practice of creating and maintaining the pneumperitoneum was universally adopted using such a device. The method of animals' abdomen insufflation with CO2 gas under physiological control in hands on laparoscopic training courses, or residency programs are now a standard procedure.
Considering the costs of maintenance of the automatic insufflator, the CO2 gas and the machine electric energy consume as well as the historic reference of air use for abdomen insufflation, it is worthwhile to try a cheaper method of abdominal insufflation by using compressed air in training programs. The aim of this study is to test the safety of air-compressed to establish pneumoperitoneum in our training program of laparoscopy.
From February to September of 2,003, 52 Dalland pigs weighting 15-17kg (40-45 days of age) were used in the Urology laparoscopic residence-training program in the Laboratory of Experimental Surgery of the Hospital das Clínicas FMRP-USP.
All animals received Ketamine (20mg/kg) as premedication and were submitted to general anesthesia induced with intravenous Thionembutal (40mg/kg) followed by endotracheal intubation, and mechanical controlled ventilation (TakaokaTM device) with 100% O2. Maintenance of anesthesia was accomplished through additional doses of Thionembutal as required. During the laparoscopic surgery hydration was carried out with intravenous physiologic saline at a speed of 4ml/kg/h.
The pigs were divided in 3 groups at random. In the group A with 38 animals pneumoperitoneum was established and maintained by an automatic CO2 gas insufflator (AstusTM). In group B of 7 pigs, abdomen insufflation was performed as in group A but the CO2 gas was changed by air from the hospital network pipe of the central compressed air system. The pneumoperitoneum, in group C of 11 pigs, was produced directly with compressed air as in group B however without the use of the automatic insufflator. In all groups intra-abdominal pressure during laparoscopy was kept between 12 and 14mmHg. In groups A and B the pressure control was achieved by adjusting gas pressure and flow through the automatic insufflator. In group C air pressure was monitored through a manometer connected to the compressed air tubing system, and the pressure control was achieved by adjusting manually the valve opening of such system. All laparoscopic surgeries were performed with a StorzTM equipment.
The following procedures were performed: 20 bilateral total nephrectomy (A 14; B 3; C 3); 20 bilateral dismembered pyeloplasty (A 15; B 3; C 2); and 16 bilateral partial nephrectomy (A 8; B 4; C 4).
The surgical time was registered for each animal. The number of CO2 gas containers consumed to operate on 38 pigs of group A was registered.
In 5 pigs of group C arterial blood sampling for gasometry was obtained before and 2h after establishing the pneumoperitoneum.
At the end of the surgery all pigs were sacrificed by a lethal intravenous injection of 10ml of sulfur ether.
The comparison of operating time among groups was performed by using the unpaired t test (Graphpad Prism, version 3.0). The level of significance was established as <5%.
No death or adverse effect was observed during the surgery in any animal.
The operating time in each group was A 181±30min, B 196±39min and C - 210±47min (p>0.05).
The number of 4,5kg CO2 gas containers consumed in 38 pigs of group A was 25 with a cost of U$ 1,050.00. The air flow required to keep pneumoperitoneum in group C was 5-7L/minute.
The results of gasometry are shown in Table 1.
Although at least 5 different gases or mixture of gases have been used to perform pneumoperitoneum, carbon dioxide is used almost exclusively. Such a gas is rapidly absorbed and excreted and does not support combustion. It is the most soluble in blood of all agents used for abdomen insufflation and is safer than oxygen, air and nitrous oxide (N2O) in preventing gas embolism6,7. However, there is no general agreement on the subject8,9. The absorpsion of CO2 into the blood
contributes to hypercarbia, acidosis, and its tension is raised about 8mmHg in patients undergoing laparoscopy procedures with CO2 pneumoperitoneum when compared with patients with N2O insuflation10. Hypercarbia contributes to hypertension, tachycardia, cardiac arrhythmias, vasodilatation and myocardial depression. Patients breathing spontaneously with halothane-N2O-oxygen anesthesia react by increasing their respiratory rate despite a reduction in tidal volume, but hypoxia, respiratory and metabolic acidosis may result11,12. It is well known that pneumoperitoneum reduces respiratory compliance and diaphragmatic movement11, so it is generally recommended that respiratory and acid-base homeostasis be maintained with mild hyperventilation under general anesthesia and use of endotracheal intubation12,13. In contrast with CO2 pneumoperitoneum, laparoscopy using abdomen wall retractor is not associated with hemodynamics or gas exchange14.
In dry atmospheric air at a barometric pressure of 760mmHg the partial pressures of the main constituent gases would be pO2= 158mmHg, pCO2= 0,3mmHg and pN2= 600mmHg15. Thus, abdomen insufflation with atmospheric air is supposed to offer a lower risk of producing hypercarbia or acidosis due to CO2 absorption inasmuch as venous blood pCO2 in physiologic conditions is 40mmHg15. As a matter of fact our results show that 3 out of 5 pigs with air-filled abdomen developed mild respiratory alkalosis instead of acidosis, possibly due to mechanical controlled hyperventilation.
Central venous blood pressure is nearly 1.4mmHg. As gas pressure required to obtain a good abdomen distension to facilitate laparoscopic procedures is 12-14mmHg the risk of embolism is overwhelming. Besides the gas diffusion through tissues, the main risk seems to be its direct entrance into opened veins since the gas pressure in the abdomen is higher than blood venous pressure. During laparoscopic surgery sometimes the surgeon sees small gas bubbles entering the venous system through the overture of opened veins. Prophylaxis of gas embolism requires a rapid, safe and secure hemostasis as well as to lower as much as possible the intra-abdominal pressure during surgery. The third step in preventing gas embolism would be to choose the most soluble gas in blood which is CO2. Our data, however, show that compressed air is safe enough to perform videolaparoscopy in training programs in pigs. No animal exhibited signs of gas embolism.
The use of compressed air for laparoscopy in pigs was safe, reduced costs and did not require the use of an automatic gas insufflator.
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1 Trabalho realizado pela Divisão de Urologia, FMRP-USP