- Email: [email protected]
Retroperitoneoscopy versus laparoscopy in piglets: Ventilatory and thermic repercussions
Retroperitoneoscopy Versus Laparoscopy in Piglets: Ventilatory and Thermic Repercussions By
I? Diemunsch,
F. Becmeur,
and
P. Meyer
Cedex, France
Background/Purpose: Endoscopic surgery of the retroperitoneal space in children is developing. During preliminary clinical experience, the authors were surprised by the differences observed in comparison with laparoscopic pneumpoeritoneum (PNOP); retropneumpoeritoneum (RPNOP) seemed to have less ventilatory repercussions. Methods:The authors therefore undertook models. Six suckling pigs, newly weaned, kg successively underwent, at 8-day intervals sequence, a right RPNOP with kidney and tion, with insufflation of CO* at 10 mm Hg PNOP with the same pressure of 10 mm Hg. Results: P&O;! increased stable during during RPNOP
a study on animal each weighing 10 and in random vena cava dissecof pressure and a
during PNOP, and it remained (P = .035). The ventilatory peak
R
ETROPERITONEAL endoscopic surgery in children is developing. Many reports have been published dealing mainly with total or partial nephrectomies, pyelic or ureteral surgery, retroperitoneal lymph node biopsies, and procedures on the adrenal glands or the spermatic vessels.‘,* In our early experience (3 nephrectomies for reflux nephropathy and an iliac node biopsy in a testicular cancer patient) we were impressed by the excellent tolerance of these procedures in the children (aged 7 months, 18 months, 22 months, and 7 years, respectively). Despite a partial lateral decubitus and a high insufflation pressure for the age (10 mm Hg),3 we observed neither an increase in the ventilatory pressures nor in the expired CO:! level. To verify these encouraging observations, we used animal models to study the repercussions of the insufflation of either the retroperitoneal space or the peritoneal cavity on ventilatory pressures, expired CO*, and esophageal temperature.
From IRCADIEITS Hdpitaux Universitaires de Strasbourg, Strasbourg, Cedex, France and Laboratoire de Bio Statistiques, Facultd de Mtfdecine Strasbourg, Rue Kirschleger; Strasbourg, France. Address reprint requests to I! Meyer; Laboratoire de Bio Statistiques, Facultk de Midecine Strasbourg, Rue Kirschleger; 67000 Strasbourg, France. Copyright 0 1999 by WB. Saunders Company 0022-3468/99/3410-0015$03.00/O 1514
airway pressures (PawP) increased during PNOP, but were not modified during RPNOP (P = .OOOl). Temperature decreased with time (P = .OOOl) without difference between the two procedures (P = .34). Conclusions: RPNOP was not associated with any adverse effects on the ventilation despite the insufflation pressure of 10 mm Hg, which allowed a satisfactory working area to be created. Operations by RPNOP could be developed in children with fewer respiratory repercussions than those observed during laparoscopy at an equivalent level of pressure.
J Pediatr Surg 34:1514-1517. Saunders Company. INDEX WORDS: ventilatory peak
Laparoscopy, airway pressure,
MATERIALS
Copyright
o 1999 by W.B.
retroperitoneoscopy, temperature.
AND
P&02,
METHODS
The committee for the protection of laboratory animals in our institute gave its approval for the establishment of the following protocol. Six barely weaned, suckling pigs, weighing 10 kg each, successively underwent a right retroperitoneoscopy with dissection of the kidney and the vena cava and a laparoscopic examination. The CO* insufflation pressure was 10 mm Hg for both the retropneumoperitoneum (RPNOP) and the pneumoperitoneum (PNOP). For each pig to act as its own control, each animal underwent the 2 procedures at 8-day intervals and in random sequence. The experiments were carried out in conditions identical to those in human surgery (preparation, operating field, asepsis) in an incomplete left lateral decubitus position for the retroperitoneoscopies and in a strict dorsal decubitus position for the laparoscopic procedures, respectively. The general anesthesia was standardized for the 12 operations, according to a protocol associating intramuscular premeditation (ketamine, 10 mg/kgg’) followed by intravenous induction (thiopental, 5 mg/ksgt). The orotracheal intubation was facilitated by pancuronium bromide (0.1 mg/kgg ‘). Anesthesia was maintained with isoflurane (FEr isoflurane = 1.5 volume%) in a O&O mixture (Ftos = FIN~O = 0.5) and the relaxation with pancuronium bromide 0.1 mgflrggt/l-t. The controlled ventilation (Drager Cicero) was adjusted to obtain an initial end tidal CO* pressure (P,, CO*) ranging from 30 to 35 mm Hg. The tidal volume (V,) and the ventilatory frequency (f! were then kept constant during the rest of the experiment. The volume of liquid infused (Ringer solution) was 50 ml/h’. After an initial 30minute period of stabilization during which the oxygen saturation of the hemoglobin (Spas) was controlled at lOO%, CO* was insufflated in the space determined by the random selection. The insuftlation was maintained for 60 mmutes and followed by exsuflation. The elements controlled and recorded every 10 minutes included the Spq and the P,rCO~, the maximum ventilatory pressure in the airway (PawP), the total volume of CO2 in&Sated in the peritoneum or the retropetitoneum, and the core temperature (esophagien probe, Odam Physiogard SM785). JournalofPediatricSorgery,
Vol34,
No 10 (October),
1999: pp 1514-1517
RETROPERITONEOSCOPY
VERSUS
1515
LAPAROSCOPY
Statistical study was done with analysis of variance for repeated measures(repeated measuresANOVA). The programs used were SOLO and SPSS.
PAwP mmHg
RESULTS
In proportion to the volume of the space concerned (retroperitoneal space or peritoneal cavity) the quantity of CO2 insufflated was no different. It progressed along with the operations regularly. The Spoz was at 100% throughout all the experiments. The ANOVA applied to the measures of P&O2 considering all the values recorded in the 2 methods of insufflation, showed a significant statistical difference (P < .OOl) between laparoscopy and retroperitoneoscopy. P&O2 increased frankly during laparoscopy, whereas it remained stable or even slightly decreased during retroperitonoscopy (Fig 1). The variations of P&O2 were greater at the start of the insufflation (the first 20 minutes) and after exsufflation. Each animal acted as its own control, at each experiment time, the value of P&O2 recorded during the retroperitoneoscopy was compared with the value of P&O2 recorded during the laparoscopy. The difference observed was statistically significant (P = .035; Fig 1). P&O2 measured before the retroperitoneoscopy was superior for the same animal to the P&O, before the laparoscopy. This difference was probably caused by the positioning of the animal in lateral decubitus for the retroperitoneoscopy (less favorable to proper ventilation). After the start of the insufflation, however, a rapid, then slow increase in the P&O2 during the laparoscopy was observed, whereas the P&O2 stabilized or even decreased during the retroperitoneoscopy. The PawP increased during laparoscopy, whereas it was not modi-
PaC02 mmHg 55 ,
I
50
I
15 J
Fig 2. Ventilatory peak airway pressure P,P during laparoscopy (W), and P,,P during retroperitoneoscopy (A). The first measure recorded when the insufflation started. The 7th measure is at the end of the insufflation. On the vertical axis: P,,P in mm Hg. The measures were recorded every 10 minutes.
fied in retroperitoneoscopy (Fig 2; P = .OOOl between PNOP and RPNOP). The temperature decreased in the 2 situations (laparoscopy and retroperitoneoscopy) with an average cooling down of 0.5”C, after 90 minutes of anesthesia (Fig 3). The ANOVA for repeated measures showed that the decrease in temperature was not significantly different (P = .34) according to the type of insufllation, but that this decrease was significant with time (P = .OOOl). DISCUSSION
RPNOP with a therapeutic and diagnostic aim was recently introduced in surgery. The data available currently concerning the diffusion of CO2 during endoscopic surgery originates from studies in adults and from experimental protocols on models representative of adults. The development of minimally invasive surgery in pediatric surgery prompts an evaluation of the physiopathological repercussions of these new techniques in young children. The clinical observation of a seemingly lesser elimination of CO2 during RPNOP than used to seeing during the PNOP, required experimental verification and an attempt at an explanation. The hemodynamic repercussions of
45 40 35 30 25 ’ Fig 1. P,COt during laparoscopy (m), and P&O2 during retroperitoneoscopy (A). After a 30-minute period of stabilization, the insufflation started. The first measure, which is recorded in this figure, is when the insufflation started. The 7th measure is at the end of the insufflation. On the vertical axis: P&O2 in mm Hg. The measures were recorded every 10 minutes.
Fig 3. Esophageal and retroperitoneoscopy conditions.
temperatures decrease during (0). There is no difference
laparoscopy (I), between the two
1516
DIEMUNSCH,
endoscopic surgery have been explored largely in the adult. This aspect is not included in this study and is the subject of another protocol. The adequacy of the circulatory function was nevertheless checked by the continuous monitoring of the Spo2, which remained constant at 100% during the whole study for all the animals and during the 2 types of insufflation. The technical realization of the RPNOP was not difficult in the small pig. It also is easy to perform in the human being. Pneumoperitoneum The PNOP physiological alterations are caused by (1) a rise in intraperitoneal pressure and (2) the diffusion of the insufflated CO2 in the tissues and the blood.9 The mechanical effect of the intraperitoneal pressure is not dependent on the gas insufflated.‘O It is responsible for the increase in intrathoracic pressure explaining the increase in PawP observed during the artificial ventilation (from 30.6 + 1.4 mm Hg to 36.1 2 4.5 mm Hg in our series). This increase in the inspiratory pressure is likely to modify the ventilation to perfusion ratio with an increase in the physiological dead space if the intraperitoneal pressure is higher than 10 mm Hg in the pig.” This increase in dead space (ventilation-perfusion mismatch) is responsible for an increase in the capnia, which comes in addition to that linked to the diffusion of cop At the exsufflation of the PNOP, the ventilatory pressures resumed their basic values. The CO;? diffuses easily from the peritoneal cavity toward the circulation and is transported to the lungs where it is eliminated during hematosis. This exogenous contribution of CO2 determines the increase of P&O, when the minute ventilation is kept constant. This hypercapnia is responsible for a sympathetic stimulation, which may contribute to the increase in systemic vascular resistance observed during laparoscopy and mainly attributed to humoral factors such as vasopressin. Retropneumoperitoneum The RPNOP did not modify the ventilatory pressures in our experimental conditions (32.6 ? 0.5 and 29.1 t 2.05 mm Hg, respectively before and during the RPNOP). The pressure of the RPNOP (10 mm Hg) remains confined in the lodge created and does not transfer to the thorax, contrary to what is observed during the PNOP. The lack of an increase in P&O2 during the RPNOP, contrary to what exists during the PNOP, can be analyzed by considering the terms of the equation of Fick applied to the diffusion of C02: @CO2 = D. A/d. (P-&O,
- PbloodC02)
BECMEUR,
AND
MEYER
(@COZ = Diffusion of C02; D = Diffusability constant of CO*; A = exchange area; d = exchange surface thickness; P RPNOPCOZ = CO2 pressure in the RPNOP; PbloodCOZ= CO2 pressure in the blood). The diffusability, D, of the CO2 can be greater through the thin and richly vascularized peritoneum, than through the tissues of the retroperitoneal space. During the PNOP, the surface of diffusion, A. seems to be larger, and the distance, d, separating the CO* from the blood is shorter than during the RPNOP. The important resorption of the CO2 and the ventilatory perturbations associated with PNPO of more than 10 mm Hg are factors of hypercapnia. This hypercapnia could reduce the CO* pressure gradient between the PNOP and the blood (PpNopCOZ- PbloodC02), as compared with the one existing between the RPNOP and the blood (PRNopCOZ - PbloodC02). The contribution of the ventilatory perturbations to this element seems to be minor in our experimental conditions. It has been shown that the PNOP engenders more hemodynamic and kidney function perturbations than the RPNOP12 The characteristics of the RPNOP in children seem different from those of the pelviscopy in the adult, which causes a larger resorption of CO2 than laparoscopy. l3 Similarly, it seems that the prepneumoperitoneum created for hernia repair in adults may be associated with a larger resorption of CO2 than the PNOP, possibly in relation with a greater diffusion area. Is there a difference in the absorption of CO2 according to age? It has been shown that the young children have very little fat in the retroperitoneal space contrary to adults. The impact of this difference is unknown. Despite insufflation on the right side, ie, on the side of the inferior vena cava, we did not observe a “clamp release” effect during the exsufflation of the retroperitoneal space, which could express itself by an increase in the partial pressure of the expired CO*. Is there a risk of diffusion of CO* outside of the retroperitoneal space with risk of subcutaneous emphysema, pneumomediastinum, or even septic complications? Nothing of this kind was observed in this experiment. The esophageal temperature decreased comparably and by the same proportion during the 2 techniques studied. The amount of this decrease is comparable with what is generally reported for laparoscopic surgery.15-l7 Insufflation of the retroperitoneum does not cause any deleterious effects on the ventilatory function despite an insufflation pressure of 10 mm Hg, which allows a satisfactory working area to be created. Retroperitoneoscopic surgery can be proposed for young children with fewer respiratory repercussions than those observed with similar insufflation pressure during laparoscopy.
RETROPERlTONEOSCOPY
VERSUS
1517
LAPAROSCOPY
REFERENCES 1. Gaur DD, Agarwal DR, Purohit KC: Retroperitoneal laparoscopic nephrectomy: Initial case report. J Urol 149:103-105, 1993 2. Valla JS, Guilloneau B, Montupet P, et al: Retroperitoneal laparoscopic nephrectomy in children. Preliminary report of 18 cases. Em Urol30:490-493, 1996 3. Martin L, Duchalais A, Gouchet A, et al: Contre-indications anesthesiques en coeliochirurgie ptdiatrique: oh en sommes nous? Resultats d’une enqu&te nationale. geme Reunion du Groupe d’Etude en Coelio-chirurgie Infantile (GECI), Tours, June 1998 4. Pretre R, Robert J, Mirescu D, et al: Pathophysiology, recognition and management of pneumoretroperitoneum. Br J Surg 80: 1138- 1140, 1993 5. Maldjian PD. Nusbaum AO: Pneumoretroperitoneum secondary to an open reduction and internal fixation of a femoral fracture: Case report. Am Surg 63504-505. 1997 6. Crausman RS, Klinge EM, Irvin C: Pneumomediastinum and pneumoretroperitoneum. Am J Emerg Med 13:310-311,1995 7. Kirchner J, Lorentz M, Heyd R, et al: Pneumoperitoneum und Pneumoretroperitoneum ohne Perforation. Zentralbl Chir 121:861-865, 1996 8. Chiu AW, Chen KK, Wang JH, et al: Direct needle insufflation for pneumoretroperitoneum: Anatomic confirmation and clinical expenence. Urology 46:432-437, 1995 9. Bures E, Fusciardi J, Lanquetot H, et al: Ventilatory effects of laparoscopic cholecystectomy. Acta Anaesthesiol Stand 40:566-573, 1996
10. Mann C, Boccara G, Grevy V, et al: Argon pneumoperitoneum is more dangerous than CO2 pneumoperitoneum during venous gas embolism. Anesth Analg 85:1367-1371,1997 11. Lister DR, Rudston-Brown B, Warriner CB, et al: Carbon dioxide absorption is not linearly related to intraperitoneal carbon dioxide insufflation pressure m pigs. Anesthesiology 80: 126-136, 1994 12. Chiu AW, Chang LS, Birkett DH, et al: The impact of pneumoperitoneum, pneumoretroperitoneum, and gasless laparoscopy on the systemic and renal hemodynamics. J Am Co11 Surg 181:397-406, 1995 13. Mullett CE, Viale JP, Sagnard PE, et al: Pulmonary CO2 elimination during surgical procedures using intra- or extraperitoneal CO2 insufflation. Anesth Analg 76:622-626, 1993 14. Liem MS, Kallewaard JW, De Smet AM, et al: Does hypercarbia develop faster during laparoscopic hemionhaphy than during laparoscopic cholecystectomy? Assessment with continuous blood gas monitoring. Anesth Analg 81:1243-1249, 1995 15. Bessel1 JR, Karatassas A, Patterson JR: Hypothermia induced by laparoscopic msufflation. A randomized study in a pig model. Surg Endosc 9:791-796, 1995 16. Ott DE: Laparoscopic hypothermia. J Laparoendosc Surg 1:127131,199l 17. Ott DE: Correction of laparoscopic insufflation hypothermia. J Laparoendosc Surg 1:183-186,199l
I? Diemunsch,
F. Becmeur,
and
P. Meyer
Cedex, France
Background/Purpose: Endoscopic surgery of the retroperitoneal space in children is developing. During preliminary clinical experience, the authors were surprised by the differences observed in comparison with laparoscopic pneumpoeritoneum (PNOP); retropneumpoeritoneum (RPNOP) seemed to have less ventilatory repercussions. Methods:The authors therefore undertook models. Six suckling pigs, newly weaned, kg successively underwent, at 8-day intervals sequence, a right RPNOP with kidney and tion, with insufflation of CO* at 10 mm Hg PNOP with the same pressure of 10 mm Hg. Results: P&O;! increased stable during during RPNOP
a study on animal each weighing 10 and in random vena cava dissecof pressure and a
during PNOP, and it remained (P = .035). The ventilatory peak
R
ETROPERITONEAL endoscopic surgery in children is developing. Many reports have been published dealing mainly with total or partial nephrectomies, pyelic or ureteral surgery, retroperitoneal lymph node biopsies, and procedures on the adrenal glands or the spermatic vessels.‘,* In our early experience (3 nephrectomies for reflux nephropathy and an iliac node biopsy in a testicular cancer patient) we were impressed by the excellent tolerance of these procedures in the children (aged 7 months, 18 months, 22 months, and 7 years, respectively). Despite a partial lateral decubitus and a high insufflation pressure for the age (10 mm Hg),3 we observed neither an increase in the ventilatory pressures nor in the expired CO:! level. To verify these encouraging observations, we used animal models to study the repercussions of the insufflation of either the retroperitoneal space or the peritoneal cavity on ventilatory pressures, expired CO*, and esophageal temperature.
From IRCADIEITS Hdpitaux Universitaires de Strasbourg, Strasbourg, Cedex, France and Laboratoire de Bio Statistiques, Facultd de Mtfdecine Strasbourg, Rue Kirschleger; Strasbourg, France. Address reprint requests to I! Meyer; Laboratoire de Bio Statistiques, Facultk de Midecine Strasbourg, Rue Kirschleger; 67000 Strasbourg, France. Copyright 0 1999 by WB. Saunders Company 0022-3468/99/3410-0015$03.00/O 1514
airway pressures (PawP) increased during PNOP, but were not modified during RPNOP (P = .OOOl). Temperature decreased with time (P = .OOOl) without difference between the two procedures (P = .34). Conclusions: RPNOP was not associated with any adverse effects on the ventilation despite the insufflation pressure of 10 mm Hg, which allowed a satisfactory working area to be created. Operations by RPNOP could be developed in children with fewer respiratory repercussions than those observed during laparoscopy at an equivalent level of pressure.
J Pediatr Surg 34:1514-1517. Saunders Company. INDEX WORDS: ventilatory peak
Laparoscopy, airway pressure,
MATERIALS
Copyright
o 1999 by W.B.
retroperitoneoscopy, temperature.
AND
P&02,
METHODS
The committee for the protection of laboratory animals in our institute gave its approval for the establishment of the following protocol. Six barely weaned, suckling pigs, weighing 10 kg each, successively underwent a right retroperitoneoscopy with dissection of the kidney and the vena cava and a laparoscopic examination. The CO* insufflation pressure was 10 mm Hg for both the retropneumoperitoneum (RPNOP) and the pneumoperitoneum (PNOP). For each pig to act as its own control, each animal underwent the 2 procedures at 8-day intervals and in random sequence. The experiments were carried out in conditions identical to those in human surgery (preparation, operating field, asepsis) in an incomplete left lateral decubitus position for the retroperitoneoscopies and in a strict dorsal decubitus position for the laparoscopic procedures, respectively. The general anesthesia was standardized for the 12 operations, according to a protocol associating intramuscular premeditation (ketamine, 10 mg/kgg’) followed by intravenous induction (thiopental, 5 mg/ksgt). The orotracheal intubation was facilitated by pancuronium bromide (0.1 mg/kgg ‘). Anesthesia was maintained with isoflurane (FEr isoflurane = 1.5 volume%) in a O&O mixture (Ftos = FIN~O = 0.5) and the relaxation with pancuronium bromide 0.1 mgflrggt/l-t. The controlled ventilation (Drager Cicero) was adjusted to obtain an initial end tidal CO* pressure (P,, CO*) ranging from 30 to 35 mm Hg. The tidal volume (V,) and the ventilatory frequency (f! were then kept constant during the rest of the experiment. The volume of liquid infused (Ringer solution) was 50 ml/h’. After an initial 30minute period of stabilization during which the oxygen saturation of the hemoglobin (Spas) was controlled at lOO%, CO* was insufflated in the space determined by the random selection. The insuftlation was maintained for 60 mmutes and followed by exsuflation. The elements controlled and recorded every 10 minutes included the Spq and the P,rCO~, the maximum ventilatory pressure in the airway (PawP), the total volume of CO2 in&Sated in the peritoneum or the retropetitoneum, and the core temperature (esophagien probe, Odam Physiogard SM785). JournalofPediatricSorgery,
Vol34,
No 10 (October),
1999: pp 1514-1517
RETROPERITONEOSCOPY
VERSUS
1515
LAPAROSCOPY
Statistical study was done with analysis of variance for repeated measures(repeated measuresANOVA). The programs used were SOLO and SPSS.
PAwP mmHg
RESULTS
In proportion to the volume of the space concerned (retroperitoneal space or peritoneal cavity) the quantity of CO2 insufflated was no different. It progressed along with the operations regularly. The Spoz was at 100% throughout all the experiments. The ANOVA applied to the measures of P&O2 considering all the values recorded in the 2 methods of insufflation, showed a significant statistical difference (P < .OOl) between laparoscopy and retroperitoneoscopy. P&O2 increased frankly during laparoscopy, whereas it remained stable or even slightly decreased during retroperitonoscopy (Fig 1). The variations of P&O2 were greater at the start of the insufflation (the first 20 minutes) and after exsufflation. Each animal acted as its own control, at each experiment time, the value of P&O2 recorded during the retroperitoneoscopy was compared with the value of P&O2 recorded during the laparoscopy. The difference observed was statistically significant (P = .035; Fig 1). P&O2 measured before the retroperitoneoscopy was superior for the same animal to the P&O, before the laparoscopy. This difference was probably caused by the positioning of the animal in lateral decubitus for the retroperitoneoscopy (less favorable to proper ventilation). After the start of the insufflation, however, a rapid, then slow increase in the P&O2 during the laparoscopy was observed, whereas the P&O2 stabilized or even decreased during the retroperitoneoscopy. The PawP increased during laparoscopy, whereas it was not modi-
PaC02 mmHg 55 ,
I
50
I
15 J
Fig 2. Ventilatory peak airway pressure P,P during laparoscopy (W), and P,,P during retroperitoneoscopy (A). The first measure recorded when the insufflation started. The 7th measure is at the end of the insufflation. On the vertical axis: P,,P in mm Hg. The measures were recorded every 10 minutes.
fied in retroperitoneoscopy (Fig 2; P = .OOOl between PNOP and RPNOP). The temperature decreased in the 2 situations (laparoscopy and retroperitoneoscopy) with an average cooling down of 0.5”C, after 90 minutes of anesthesia (Fig 3). The ANOVA for repeated measures showed that the decrease in temperature was not significantly different (P = .34) according to the type of insufllation, but that this decrease was significant with time (P = .OOOl). DISCUSSION
RPNOP with a therapeutic and diagnostic aim was recently introduced in surgery. The data available currently concerning the diffusion of CO2 during endoscopic surgery originates from studies in adults and from experimental protocols on models representative of adults. The development of minimally invasive surgery in pediatric surgery prompts an evaluation of the physiopathological repercussions of these new techniques in young children. The clinical observation of a seemingly lesser elimination of CO2 during RPNOP than used to seeing during the PNOP, required experimental verification and an attempt at an explanation. The hemodynamic repercussions of
45 40 35 30 25 ’ Fig 1. P,COt during laparoscopy (m), and P&O2 during retroperitoneoscopy (A). After a 30-minute period of stabilization, the insufflation started. The first measure, which is recorded in this figure, is when the insufflation started. The 7th measure is at the end of the insufflation. On the vertical axis: P&O2 in mm Hg. The measures were recorded every 10 minutes.
Fig 3. Esophageal and retroperitoneoscopy conditions.
temperatures decrease during (0). There is no difference
laparoscopy (I), between the two
1516
DIEMUNSCH,
endoscopic surgery have been explored largely in the adult. This aspect is not included in this study and is the subject of another protocol. The adequacy of the circulatory function was nevertheless checked by the continuous monitoring of the Spo2, which remained constant at 100% during the whole study for all the animals and during the 2 types of insufflation. The technical realization of the RPNOP was not difficult in the small pig. It also is easy to perform in the human being. Pneumoperitoneum The PNOP physiological alterations are caused by (1) a rise in intraperitoneal pressure and (2) the diffusion of the insufflated CO2 in the tissues and the blood.9 The mechanical effect of the intraperitoneal pressure is not dependent on the gas insufflated.‘O It is responsible for the increase in intrathoracic pressure explaining the increase in PawP observed during the artificial ventilation (from 30.6 + 1.4 mm Hg to 36.1 2 4.5 mm Hg in our series). This increase in the inspiratory pressure is likely to modify the ventilation to perfusion ratio with an increase in the physiological dead space if the intraperitoneal pressure is higher than 10 mm Hg in the pig.” This increase in dead space (ventilation-perfusion mismatch) is responsible for an increase in the capnia, which comes in addition to that linked to the diffusion of cop At the exsufflation of the PNOP, the ventilatory pressures resumed their basic values. The CO;? diffuses easily from the peritoneal cavity toward the circulation and is transported to the lungs where it is eliminated during hematosis. This exogenous contribution of CO2 determines the increase of P&O, when the minute ventilation is kept constant. This hypercapnia is responsible for a sympathetic stimulation, which may contribute to the increase in systemic vascular resistance observed during laparoscopy and mainly attributed to humoral factors such as vasopressin. Retropneumoperitoneum The RPNOP did not modify the ventilatory pressures in our experimental conditions (32.6 ? 0.5 and 29.1 t 2.05 mm Hg, respectively before and during the RPNOP). The pressure of the RPNOP (10 mm Hg) remains confined in the lodge created and does not transfer to the thorax, contrary to what is observed during the PNOP. The lack of an increase in P&O2 during the RPNOP, contrary to what exists during the PNOP, can be analyzed by considering the terms of the equation of Fick applied to the diffusion of C02: @CO2 = D. A/d. (P-&O,
- PbloodC02)
BECMEUR,
AND
MEYER
(@COZ = Diffusion of C02; D = Diffusability constant of CO*; A = exchange area; d = exchange surface thickness; P RPNOPCOZ = CO2 pressure in the RPNOP; PbloodCOZ= CO2 pressure in the blood). The diffusability, D, of the CO2 can be greater through the thin and richly vascularized peritoneum, than through the tissues of the retroperitoneal space. During the PNOP, the surface of diffusion, A. seems to be larger, and the distance, d, separating the CO* from the blood is shorter than during the RPNOP. The important resorption of the CO2 and the ventilatory perturbations associated with PNPO of more than 10 mm Hg are factors of hypercapnia. This hypercapnia could reduce the CO* pressure gradient between the PNOP and the blood (PpNopCOZ- PbloodC02), as compared with the one existing between the RPNOP and the blood (PRNopCOZ - PbloodC02). The contribution of the ventilatory perturbations to this element seems to be minor in our experimental conditions. It has been shown that the PNOP engenders more hemodynamic and kidney function perturbations than the RPNOP12 The characteristics of the RPNOP in children seem different from those of the pelviscopy in the adult, which causes a larger resorption of CO2 than laparoscopy. l3 Similarly, it seems that the prepneumoperitoneum created for hernia repair in adults may be associated with a larger resorption of CO2 than the PNOP, possibly in relation with a greater diffusion area. Is there a difference in the absorption of CO2 according to age? It has been shown that the young children have very little fat in the retroperitoneal space contrary to adults. The impact of this difference is unknown. Despite insufflation on the right side, ie, on the side of the inferior vena cava, we did not observe a “clamp release” effect during the exsufflation of the retroperitoneal space, which could express itself by an increase in the partial pressure of the expired CO*. Is there a risk of diffusion of CO* outside of the retroperitoneal space with risk of subcutaneous emphysema, pneumomediastinum, or even septic complications? Nothing of this kind was observed in this experiment. The esophageal temperature decreased comparably and by the same proportion during the 2 techniques studied. The amount of this decrease is comparable with what is generally reported for laparoscopic surgery.15-l7 Insufflation of the retroperitoneum does not cause any deleterious effects on the ventilatory function despite an insufflation pressure of 10 mm Hg, which allows a satisfactory working area to be created. Retroperitoneoscopic surgery can be proposed for young children with fewer respiratory repercussions than those observed with similar insufflation pressure during laparoscopy.
RETROPERlTONEOSCOPY
VERSUS
1517
LAPAROSCOPY
REFERENCES 1. Gaur DD, Agarwal DR, Purohit KC: Retroperitoneal laparoscopic nephrectomy: Initial case report. J Urol 149:103-105, 1993 2. Valla JS, Guilloneau B, Montupet P, et al: Retroperitoneal laparoscopic nephrectomy in children. Preliminary report of 18 cases. Em Urol30:490-493, 1996 3. Martin L, Duchalais A, Gouchet A, et al: Contre-indications anesthesiques en coeliochirurgie ptdiatrique: oh en sommes nous? Resultats d’une enqu&te nationale. geme Reunion du Groupe d’Etude en Coelio-chirurgie Infantile (GECI), Tours, June 1998 4. Pretre R, Robert J, Mirescu D, et al: Pathophysiology, recognition and management of pneumoretroperitoneum. Br J Surg 80: 1138- 1140, 1993 5. Maldjian PD. Nusbaum AO: Pneumoretroperitoneum secondary to an open reduction and internal fixation of a femoral fracture: Case report. Am Surg 63504-505. 1997 6. Crausman RS, Klinge EM, Irvin C: Pneumomediastinum and pneumoretroperitoneum. Am J Emerg Med 13:310-311,1995 7. Kirchner J, Lorentz M, Heyd R, et al: Pneumoperitoneum und Pneumoretroperitoneum ohne Perforation. Zentralbl Chir 121:861-865, 1996 8. Chiu AW, Chen KK, Wang JH, et al: Direct needle insufflation for pneumoretroperitoneum: Anatomic confirmation and clinical expenence. Urology 46:432-437, 1995 9. Bures E, Fusciardi J, Lanquetot H, et al: Ventilatory effects of laparoscopic cholecystectomy. Acta Anaesthesiol Stand 40:566-573, 1996
10. Mann C, Boccara G, Grevy V, et al: Argon pneumoperitoneum is more dangerous than CO2 pneumoperitoneum during venous gas embolism. Anesth Analg 85:1367-1371,1997 11. Lister DR, Rudston-Brown B, Warriner CB, et al: Carbon dioxide absorption is not linearly related to intraperitoneal carbon dioxide insufflation pressure m pigs. Anesthesiology 80: 126-136, 1994 12. Chiu AW, Chang LS, Birkett DH, et al: The impact of pneumoperitoneum, pneumoretroperitoneum, and gasless laparoscopy on the systemic and renal hemodynamics. J Am Co11 Surg 181:397-406, 1995 13. Mullett CE, Viale JP, Sagnard PE, et al: Pulmonary CO2 elimination during surgical procedures using intra- or extraperitoneal CO2 insufflation. Anesth Analg 76:622-626, 1993 14. Liem MS, Kallewaard JW, De Smet AM, et al: Does hypercarbia develop faster during laparoscopic hemionhaphy than during laparoscopic cholecystectomy? Assessment with continuous blood gas monitoring. Anesth Analg 81:1243-1249, 1995 15. Bessel1 JR, Karatassas A, Patterson JR: Hypothermia induced by laparoscopic msufflation. A randomized study in a pig model. Surg Endosc 9:791-796, 1995 16. Ott DE: Laparoscopic hypothermia. J Laparoendosc Surg 1:127131,199l 17. Ott DE: Correction of laparoscopic insufflation hypothermia. J Laparoendosc Surg 1:183-186,199l