|Year : 2006 | Volume
| Issue : 4 | Page : 304-309
Physiological effects of pediatric urological laparoscopic surgery
Sumit Dave, Walid A Farhat
Division of Urology, The Hospital for Sick Children, 555, University Avenue, Toronto, M5G 1X8, Canada
Walid A Farhat
555 University Ave, Rm M299 - Urology, Toronto
Source of Support: None, Conflict of Interest: None
| Abstract|| |
There is an increasing trend of laparoscopy in pediatric urological practice with more complex and reconstructive procedures being performed in smaller children. The physiological impact of these procedures is not well documented in the pediatric literature and cannot be simply extrapolated from the adult data. This article reviews the current pediatric literature on the physiological effects of both transperitoneal and retroperitoneal laparoscopy. The clinical implication of these changes and the need for proper monitoring is stressed. As surgeons strive to stretch the indications of laparoscopy in pediatric urological practice, the overall beneficial effects of laparoscopy must be balanced with these potential hemodynamic and respiratory changes.
Keywords: Pediatric urology, laparoscopy, physiology
|How to cite this article:|
Dave S, Farhat WA. Physiological effects of pediatric urological laparoscopic surgery. Indian J Urol 2006;22:304-9
There has been a progressive trend towards performing more complex reconstructive urological procedures laparoscopically in younger pediatric patients. On the other hand, the creation of pneumoperitoneum is a complex physiological event which impacts various systems and leads to compensatory homeostatic changes in a pressure and age-dependent manner. These physiologic effects and their impact on the intraoperative and postoperative course of the patient must be counterbalanced with the potential advantages of performing the procedure laparoscopically. As compared to the adult literature, there is paucity of data in pediatric patients of the effects of pneumoperitoneum. Simple translation of the adult data is not possible because of the unique and different physiology of pediatric patients. As pediatric urologists we also have to consider the differences between retroperitoneal versus transperitoneal insufflation. It is also important to keep in perspective whether these changes have any clinical impact on patient outcome or are merely findings which merit monitoring. This article reviews the current literature on the physiological changes secondary to transperitoneal or retroperitoneal laparoscopic urological surgery in pediatric patients.
| Blood gas and acid - base metabolism|| |
An ideal gas for insufflation should have minimal systemic transperitoneal absorption, minimal effects when absorbed, should be rapidly excreted if absorbed, incapable of supporting combustion, should have high blood solubility and limited physiological effects with intravascular systemic embolism. The noncombustible nature and solubility of carbon dioxide makes it the current gas of choice to create pneumoperitoneum. On the other hand, several studies have documented that intraperitoneal CO 2 insufflation leads to a rise in the serum CO 2 (pCO 2) and /or end tidal CO 2 (ETCO 2) levels along with a decrease in the serum pH levels.,,, This is as a direct result of transperitoneal absorption of CO 2 as shown by Ho et al who used a porcine model to measure increased CO 2 production after peritoneal insufflation. Hypercarbia in turn leads to an increase in the heart rate and blood pressure mediated by the sympathetic nervous system. It also sensitizes the myocardium to the arrhythmogenic effects of catecholamines, especially with volatile anesthetic agents.
De Waal et al evaluated the effects of low-pressure pneumoperitoneum (5 mmHg) in children less than three years age. The ETCO 2 increased from 29 ± 4 to 37± 5 and pCO 2 increased from 31 ± 4 to 39 ± 5 ( P <0.001) leading to a decrease in pH from 7.40 ± 0.07 to 7.31 ± 0.07 ( P =0.03). The PAP increased from 16 ± 3 to 18 ± 3 ( P <0.003) which returned to normal values on desufflation. This absorption of CO 2 is age and weight-dependent with younger and smaller children absorbing more CO 2 than older individuals. In a retrospective audit by the French Language Society of Pediatric Anesthetists (ADARPEF), a high ETCO 2 of > 50 mmHg was seen in 37% of children and infants. There were no hypoxic events reported but a low intraabdominal pressure (IAP) of 6 mmHg was used and recommended in all patients under four months of age. McHoney et al also noted a sharp transient increase in CO 2 elimination after desufflation in 35% of the children and attributed it to an increase in venous return from the lower limbs. Hsing et al reported that the plateau of ETCO 2 during CO 2 pneumoperitoneum is reached after 4.2 ± 0.6 min in children 11 months to two years of age and after 6.3 ±1.0 min in children two to five years of age. The study also confirmed the time lag of the ETCO 2 returning to baseline levels after desufflation and this was 6.2 ± 0.5 min in the younger group as compared to 8.3 ± 0.8 min in the older children. These findings warrant close monitoring of younger children during laparoscopy and in the immediate postoperative period.
Paradoxically, retroperitoneoscopic procedures lead to a higher CO 2 absorption as compared to transperitoneal procedures. In a prospective study using a standardized anesthesia protocol and a 12 mmHg insufflation pressure, Lorenzo et al showed a significant increase in the ETCO 2 during and after desufflation as compared to preinsufflation values. Increased CO 2 elimination continued for up to 10 min after desuflation of the abdomen. In a previous retrospective study done in our institution, a significantly higher difference in the ETCO 2 values was noted in the left lateral decubitus position as compared to the right lateral decubitus position.
In healthy children without any existing cardiac or pulmonary disease, this hypercarbia is managed efficiently by maximizing plasma and intracellular buffering mechanisms and accelerating CO 2 transport and elimination. In the adult population it has been shown that with preexisting cardiovascular disease, sepsis and chronic obstructive lung disease this homeostatic reserve can get overwhelmed and lead to significant hypercarbia and acidosis with concomitant secondary myocardial depression.
In summary, hypercarbia is a consistent finding with CO 2 insufflation and requires appropriate intraoperative adjustments of the minute ventilation. This CO 2 absorption is more prominent in younger children and in retroperitoneoscopic procedures as compared to transperitoneal laparoscopic procedures and continues for a short period after desufflation.
| Respiratory mechanics|| |
Peritoneal insufflation causes an increase in the intraabdominal volume and pressure which shifts the diaphragm cephalad, limits its excursion and compresses basilar lung segments. This leads to an increase in peak airway pressure (PAP), a decrease in functional residual capacity (FRC) and a reduction in thoracic compliance. These changes, which can be exacerbated by the Trendelenburg position, can lead to an increased ventilation perfusion mismatch and cause hypoxemia. Neonates and smaller children who have a low FRC and high oxygen consumption are therefore more prone to developing hypoxemia during laparoscopy. The increase in IAP can also lead to a smaller increase in the intrathoracic pressure which can exacerbate gastroesophageal reflux and increase the risks of aspiration in unprotected airways. In infants there is an additional risk of right bronchial intubation due to the cephalad displacement of the diaphragm.
Tobias et al prospectively evaluated the respiratory effects of a short <10 min laparoscopic exploration in 53 infants and children. The PAP increased from the baseline value of 20 ± 2.5 to 23 ± 3.2 cmH 2 O ( P <0.01). The ETCO 2 concomitantly increased from 32± 3.1 to a maximum of 35± 4.8 mmHg ( P <0.01). There was no significant change in oxygen saturation as measured by pulse oximetry. In a study carried out on infants where the insufflation pressures were limited to 12 mmHg for <5 kg and 15 mmHg for >5 kg patients, the authors noted significant changes in the pulmonary mechanics. At peak insufflation the PAP increased by an average of 18%, average expiratory tidal volume decreased by 33%, average ETCO 2 increased by 13%, average dynamic compliance decreased by 48% and the oxygen saturation dropped in 41% of patients. Twenty ventilator adjustments were required in the 19 patients in this study to restore expiratory tidal volume and ETCO 2 to within 10% of the baseline values. Manner et al studied the respiratory mechanics in 10 patients (1-15 years) undergoing laparoscopy and evaluated the effects of position on respiratory mechanics. They demonstrated a 17% decrease in lung compliance with Trendelenburg positioning which further decreased by 27% on insufflation to 12 mmHg intraabdominal pressure. The PAP concomitantly increased by 19% with the Trendelenburg position and by 32% with insufflation from the baseline values. However, all parameters returned to baseline levels after removal of CO 2 from the peritoneal cavity. Mattioli et al performed a prospective nonrandomized study comparing the cardiorespiratory effects of laparoscopic fundoplication in children with or without chronic respiratory symptoms. With an IAP of less than 10 cmH 2 O, the authors noted a higher mean value of ETCO 2 and PAP increase in the group with respiratory compromise. However, these changes were easily correctible and did not compromise the intraoperative or postoperative course of these children.
Retroperitoneal insufflation leads to a similar increase in the PAP; the mean PAP pressure increased from a baseline of 13.6 cmH 2 O to 16.4 cmH 2 O in the first 10 min after insufflation with 12 mmHg pressures ( P <0.05). Halachmi et al showed a significant increase in the respiratory rate, PAP and decrease in oxygen saturation with both retroperitoneal and transperitoneal insufflation.
| Summary|| |
In summary transperitoneal or retroperitoneal insufflation both cause an increase in PAP and decrease FRC and pulmonary compliance. These changes are exacerbated in smaller children and with the Trendelenburg position. Because most pediatric ventilators are pressure cycled, it is important to closely monitor the exhaled tidal volume in pediatric patients undergoing laparoscopy to prevent hypoventilation., Positive end- expiratory pressure can be used to prevent hypoxemia and offset the detrimental effects of a raised IAP. Regardless of the duration of the procedure, minute ventilation may need to be increased by 25-30% to maintain normocarbia. Despite these potentially detrimental effects, consistent benefits with regard to postoperative pulmonary function are seen after laparoscopic surgery, especially in children with compromised cardiorespiratory function and chronic lung disease.
| Cardiovascular effects|| |
Pneumoperitoneum causes cardiovascular changes as a result of increased pCO 2 concentration and an elevation of the IAP. Hypercarbia has direct effects on the myocardium and secondary effects mediated via the autonomic nervous system. In adults, the direct depressive myocardial effects and arteriolar dilatation is compensated by a secondary elevation of the catecholamine levels which may cause an elevation of the heart rate (HR), systolic blood pressure (BP), cardiac output (CO) and left ventricular stroke volume (SV). Cardiovascular function can be further compromised by patient positioning and the use of positive pressure ventilation. Positive pressure ventilation and use of the reverse Trendelenburg position decrease venous return compromising cardiac output. The cardiovascular physiology in children and especially infants is significantly different from that of adults. The BP and systemic vascular resistance are lower in children and the HR, oxygen consumption and CO are relatively higher. In pediatric patients, the level of IAP used determines the cardiovascular response to pneumoperitoneum. Insufflation with an IAP of ³ 10 mmHg augments preload by displacement of blood from the splanchnic circulation while an IAP of > 10-15 mmHg impedes venous return.
De Waal et al recorded noninvasive thoracic electrical bioimpedance cardiac index (CI), stroke volume index, HR and mean arterial pressure (MAP) in 13 children with 5 mmHg insufflation pressures. They noted significant elevations in the CI, HR and MAP with insufflation which returned to baseline values after removal of the CO 2 . Other studies have however noted a decrease in the CO or CI with decreased aortic blood flow during laparoscopy., Significantly, as stated earlier, these studies utilized insufflation pressures more than 10 mmHg which is higher than the usual right atrial pressure and leads to a decrease in venous return, a decrease in left ventricular preload and therefore a decrease in CO and aortic blood flow. In the study by Gueugniaud et al a significant decrease in the aortic blood flow and SV was seen along with an increase in the systemic vascular resistance which maintained the BP. Paradoxically, there was no change in the ETCO 2 . This is explained by the decreased right ventricular cardiac output offsetting the effects of CO 2 absorption. In the ADARPEF report, an IAP of <15 mmHg led to an increase in BP without tachycardia. The authors recommended keeping the IAP below 6 mmHg in infants under four months and under 10 mmHg for the 4-12 months age group to prevent development of high pulmonary vascular resistances that could potentially lead to a right to left shunt. In a study done at our institution in 15 children with a mean age of 8.4 years and weight of 34.1 kg who underwent laparoscopy (12 mmHg) under a standardized anesthetic protocol, we documented ETCO 2 , HR and noninvasive MAP. There was a parallel increase in MAP and end-tidal CO 2 during the first eight minutes of pneumoperitoneum ( P <0.05) while heart rate remained unchanged [Figure - 1]. Despite a continued increase in ETCO 2 after 20 min of pneumoperitoneum ( P <0.05), the MAP reached a plateau and then decreased progressively. Release of pneumoperitoneum was associated with an initial increase in MAP ( P <0.05), followed by a gradual decrease and return to preinsufflation values.
Though there is paucity of data on retroperitoneal procedures in pediatric patients, the cardiovascular effects are similar and pressure-dependent. Our prospective study with retroperitoneal insufflation showed a significant increase in the MAP without any significant change in the heart rate using a 12 mmHg pressure.
In summarizing, cardiovascular changes in pediatric patients depend on the insufflation pressure; less than 10 mmHg pressure increases the HR, MAP and CO whereas more than 15 mmHg pressure leads to a fall in CO but the MAP is maintained by increasing the systemic vascular resistance. These hemodynamic effects are also altered by the underlying cardiovascular status, intravascular volume, patient positioning and the anesthetic protocol used. In patients with normal cardiovascular function, these changes are well tolerated, however, appropriate preoperative evaluation and alteration of intraoperative anesthetic and surgical technique is required in children with decreased cardiac contractility.
| Renal effects|| |
The predominant renal effect of pneumoperitoneum is oliguria and sometimes even anuria. This finding is not related to a decrease in cardiac output, ureteral compression or systemic hormonal effects as was postulated earlier. Kirsch et al suggested that direct renal vein compression leading to renal vascular insufficiency was responsible for oliguria. In a rat model they demonstrated a diminished urine output at 10 mmHg pressure associated with a 92% decrease in the caval blood flow and a 46% decrease in the aortic blood flow. Similarly, McDougall et al showed a decreased renal vein flow with a decrease in the urine output at 15 mmHg pressure in a porcine model. More importantly, in their study, this decreased flow and diminished creatinine clearance was noted up to two hours following desufflation though no long-term effects were documented. Razvi et al postulated a direct renal parenchymal compression mechanism for the decrease in GFR and oliguria during laparoscopy. Using a pressure cuff around canine kidneys and subjecting them to 15 mmHg pressure led to a 63% decrease in the urine output.
In a recent prospective study in 30 children with normal renal function 88% of the children under one year of age developed anuria as compared to 14% of children above one year of age. Oliguria was noted in all children within 45 min of pneumoperitoneum. There was a significant increase in the urine output from the fourth hour postoperatively. There were no significant changes of the measured resistive indices pre, intra and postoperatively or of the serum creatinine and electrolytes until 24h postoperatively. The mean urine output and arterial pressure did not correlate with the volume of crystalloids infused. In a series reviewing the results of 22 retroperitoneoscopic heminephrectomies, Wallis et al noted two infants who had loss of the ipsilateral lower pole in follow-up. The authors recommended open heminephrectomy in children younger than 12 months and speculated whether the small retroperitoneal space insufflated during the procedure could have an adverse impact on the lower pole perfusion and renal vein flow during surgery.
These studies indicate that the oliguria and anuria in children undergoing laparoscopy is an age-dependent and reversible phenomenon but caution must be maintained in children with impaired renal function. Also, as we expand the indications for laparoscopic surgery to younger patients, we need to further our knowledge about the renal effects of transperitoneal and retroperitoneal insufflation.
| Neurological effects|| |
There are several potential factors which could contribute to the increase in cerebral blood flow and intracranial pressure (ICP) noted with laparoscopy. Hypercarbia increases cerebral blood flow and can increase the ICP. Elevated IAP independent of the pCO 2 levels and a Trendelenburg position can also increase the ICP. Indirectly, the elevated IAP causes a higher intracaval pressure, which transmits to the lumbar veins and decreases CSF absorption, which can also contribute to the elevated ICP. Experimental models have shown that the elevated ICP associated with increased IAP was unresponsive to hyperventilation and hypocarbia. Bloomfield et al evaluated the effects of CO 2 pneumoperitoneum on ICP and cerebral perfusion pressure in an animal model. At a high IAP of 25 mmHg, they noted an increase in ICP from a mean of 7.5 to 21.4 mmHg and a decrease in the cerebral perfusion pressure from a mean of 82 to 62 mmHg. Laparoscopic procedures should therefore be carried out with precaution in children with ventriculoperitoneal shunts and those with altered cerebral compliance.
In the prospective study done at our institution in 15 children with a mean age of 8.4 years and weight of 34.1 kg who underwent laparoscopy (12 mmHg) under a standardized anesthetic protocol, we measured middle cerebral artery blood flow velocity (Vmca) using transcranial Doppler sonography. There was a parallel increase in Vmca, MAP and ETCO 2 during the first eight minutes of pneumoperitoneum ( P <0.05) while the HR remained unchanged [Figure - 1]. Despite a continued increase in ETCO 2 after 20 min of pneumoperitoneum ( P <0.05), both Vmca and MAP reached a plateau and then decreased progressively. Changes in cerebral blood flow velocity in children undergoing transperitoneal laparoscopy are related to the vascular absorption of CO 2 while in the normocarbic range. With further increases in ETCO 2 cerebral vasodilatation reaches a maximum, at which point Vmca appears to be influenced more by systemic blood pressure. In contrast to transperitoneal laparoscopy the results are different in retroperitoneoscopic procedures. A second study looked at 15 children undergoing partial/ total retroperitoneoscopic nephrectomy. Mechanical ventilation with volume control was maintained with a rate set to achieve an initial ETCO 2 of 35 mmHg. All patients were in a flexed lateral decubitus position for the duration of the study. Both cerebral blood flow velocity and ETCO 2 tended to increase progressively throughout the study period until cessation of pneumoperitoneum [Figure - 2]. Cerebral blood flow velocity did not decrease significantly until five minutes after the release of pneumoperitoneum ( P <0.05). During this time there was an insignificant decrease in ETCO 2 . Cerebral blood flow velocity and ETCO 2 seem to increase progressively and gradually during retroperitoneal laparoscopy, as opposed to the more rapid increase and plateau effect seen during transperitoneal CO 2 insufflation. Presumably the smaller absorptive surface area in the retroperitoneal space accounts for this difference.
| Potpourri|| |
Although laparoscopy is known to be associated with reduced insensible losses and reduced heat losses, prolonged CO 2 insufflation in neonates and small children can lead to hypothermia. It is mandatory to use preheated CO 2 especially for smaller children and for high-flow insufflation.
Improper cannula placement or dislodgement can lead to subcutaneous emphysema, pneumothorax or pneumomediastinum which can cause significant cardiorespiratory effects and must be suspected with any sudden deterioration during surgery. The other cause for a sudden cardiovascular deterioration is gas embolism. The risk of gas embolism is however low with CO 2 unless a large quantity is injected intravascularly. When the rate of gas entrainment exceeds the pulmonary excretion, pulmonary artery pressure rises resulting in right heart failure. Transoesophageal echocardiography is the most sensitive monitoring device available for detecting gas embolism but due to its low likelihood with CO 2 insufflation routine monitoring is sufficient.
| Conclusions|| |
The above review shows varying and often statistically significant respiratory and hemodynamic changes with laparoscopy [Table - 1]. Despite these changes, it must be borne in mind that laparoscopic techniques will have some positive effects on these same parameters in the postoperative period. With today's advanced intra and perioperative care and monitoring most patients can be guided through these potentially deleterious intraoperative changes to reap the benefits associated with laparoscopic techniques. We believe that these hemodynamic and cardiorespiratory changes do not strengthen the debate against the rapidly expanding use of laparoscopy in pediatric urology but serve as a reminder of the care and planning needed in performing these procedures, especially in sick and smaller children. As we become more aggressive in using laparoscopy we must realize the multidisciplinary effort needed in ensuring a safe and event-free course for the small pediatric patient.
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[Figure - 1], [Figure - 2]
[Table - 1]
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