Physiologic Considerations for Minimally Invasive Surgery in Infants and Children



Fig. 1.1.
Two major stimuli produce the observed physiologic changes during abdominal insufflation for laparoscopy: (1) increased intra-abdominal pressure (blue arrows), which impedes full lung expansion and can decrease flow through the aorta and vascular system, and (2) enhanced CO2 absorption (red arrows) by the visceral and parietal peritoneum, which increases the necessary minute ventilation to maintain acid-base balance. Figure courtesy of Sarah Hua.



This chapter describes the effects of abdominal and thoracic insufflation on the cardiovascular, pulmonary, metabolic, and immune/inflammatory systems, with a special emphasis on neonates and infants, as these patients differ significantly from adults and older children both anatomically and physiologically. General principles for preoperative preparation and postoperative care are addressed. Physiologic sequelae of abdominal insufflation are discussed in context of the organ systems affected.



Preoperative Evaluation


As with any pediatric or neonatal operation, general fitness for a planned minimally invasive operation is of paramount importance. Appropriate history related to nutritional status and growth should be obtained for every patient, and any symptoms or signs that could suggest cardiac or pulmonary impairment must be elicited. Anesthetic management plans need to be carefully formulated, especially in neonatal cases with extended procedures, reverse Trendelenburg positioning, and higher insufflation pressures [5]. General endotracheal anesthesia remains the standard for pediatric laparoscopic and thoracoscopic operations to allow the anesthesiologist to contend with the physiologic effects of hypercarbia and increased intra-abdominal or intrathoracic pressures [2].

Several specific comorbidities warrant special consideration in preoperative planning. Minimally invasive procedures are increasingly being performed in infants with congenital heart disease. These patients may be more susceptible to changes in preload due to impaired venous return or changes in systemic resistance associated with increased intra-abdominal pressure [6]. Laparoscopic and thoracoscopic operations can be done safely in these patients in experienced centers with dedicated pediatric cardiac anesthesia teams [68].

Underlying pulmonary disease is another important comorbidity to consider before undertaking a minimally invasive procedure in a child. Excretion of excess CO2 that is absorbed through the visceral and parietal peritoneum is a primary concern of the anesthesiologist managing the infant undergoing laparoscopic or thoracoscopic surgery. Increasing minute ventilation is the primary tool used to remove excess CO2. Any pulmonary condition that may limit the ability to increase minute ventilation or impair gas exchange could rapidly lead to a respiratory acidosis. If laparoscopy is to be undertaken in a patient with baseline pulmonary dysfunction, intensive postoperative monitoring should be utilized to limit risks of hypoventilation from retained hypercarbia. A related problem is portal hypertension, which has been shown to accelerate absorption of CO2 to a level twice that of the already increased absorption displayed in children [9]. Similar to the patient with pulmonary disease, patients with portal hypertension should be managed with increased vigilance to limit the negative effects of hypercarbia in the postoperative period.


Physiologic Effects of Pneumoperitoneum by System



Cardiovascular System


Several studies have examined the cardiovascular effects of pneumoperitoneum in children. Direct measurement of flow in the thoracic aorta by transesophageal echocardiography (TEE) in healthy 6- to 30-month-old infants and children undergoing laparoscopic assisted orchiopexy for undescended testicles with a maximum insufflation pressure of 10 mmHg showed significantly decreased flow, decreased stroke volume, and increased systemic resistance. However, these changes resolved completely after desufflation of the abdominal cavity. Significant changes in mean arterial pressure (MAP) or end-tidal CO2 were not observed during these relatively short procedures, nor were any clinically important sequelae [10]. In another study of healthy 2- to 6-year-old children undergoing laparoscopic inguinal herniorrhaphy, an initial insufflation to an abdominal pressure of 12 mmHg decreased cardiac index (CI ) as measured by TEE [11]. Interestingly, CI returned to baseline with a decrease in insufflation pressure to 6 mmHg and did not decrease with a subsequent increase in abdominal pressure to 12 mmHg, suggesting an adaptation to the change in afterload induced by abdominal insufflation. A recent study exposed neonatal and adolescent piglets to 180 min of abdominal insufflation, which caused a decrease in CI and MAP that persisted well into the recovery period after insufflation ended. This effect was more pronounced in the neonates [12]. The extended response to the pressure stimulus suggests a need for vigilant monitoring in the postoperative period to ensure that hypotension does not ensue. Prolonged exposure to higher insufflation pressures (>8–10 mmHg) may also induce capillary microcirculatory changes and impair venous return [1]. In contrast, a study using low-pressure insufflation no greater than 5 mmHg combined with reverse Trendelenburg positioning in children ages 6 to 36 months undergoing laparoscopic fundoplication actually increased CI, heart rate, and MAP [13].

In summary, in the otherwise healthy infant or child, abdominal insufflation pressures of 12 mmHg or less for short- to medium-length procedures may cause changes in CI, MAP, or systemic resistance when specifically measured but rarely (3.2 % of cases) produce clinically significant effects requiring intervention [4]. The location of monitoring may not affect the accuracy of blood pressure measurements. In a piglet model, no difference was found between measured carotid and femoral arterial blood pressures with up to 24 mmHg abdominal insufflation, a level nearly twice that of the highest commonly used clinically [14].


Pulmonary System


The pulmonary effects of pneumoperitoneum in pediatric patients are the result of anatomic and physiologic differences between adults and children. The alveolar surface area to body surface area ratio in infants and children is smaller than that of adults. Therefore, children have a significantly higher minute ventilation and oxygen consumption (up to twice that of an adult) even at baseline to maintain PaCO2 in the normal range [1]. In patients younger than 1 year of age, the space-occupying effects of abdominal insufflation lead to increased peak inspiratory pressure, reduced tidal volume, and decreased compliance [15]. These changes in turn produce decreased functional residual capacity (FRC) , increased pulmonary vascular resistance, and increased shunt fraction, which in combination with the increased CO2 absorption can lead to hypercarbia if the minute ventilation is not increased concomitantly [15].

Hypercapnia is a significant concern in minimally invasive surgery, especially in children with underlying pulmonary disease. In one series of laparoscopic and thoracoscopic procedures performed in neonates (i.e., <1 month of age), hypercapnia >45 mmHg was reported in 2.3 % of cases [4]. The degree of hypercapnia depends on insufflation pressure and duration of pneumoperitoneum. In piglet models, PaCO2 has been shown to increase 25 % with stepwise increases in insufflation pressure with associated increases in mortality from CO2 embolism [16]. In a study of low-pressure (i.e., maximum 5 mmHg) insufflation for fundoplication, CO2 rose 28 % on average when patients up to 3 years of age were exposed for more than an hour [17]. Careful monitoring for hypercapnia is warranted for all pediatric minimally invasive procedures, and laparoscopic insufflation pressures should be limited, with a maximum recommended pressure of 12 mmHg for neonates [15].

An important consideration for respiratory monitoring is that a gradient will develop between the PaCO2 and the end-tidal CO2 after abdominal insufflation because of an increased CO2 and diminished functional residual volume. This gradient has been documented to increase significantly in adults during the first 60 min of insufflation for laparoscopic colorectal surgery but to stabilize or decrease thereafter [18]. In young children with cyanotic congenital heart disease undergoing laparoscopic fundoplication, the gradient increased by a factor of nearly 2.5 soon after initial insufflation of the abdomen [19]. This gradient was shown to be as high as 8 mmHg in one study of laparoscopic fundoplication in children without underlying cardiac or respiratory disease; as in other studies, the gradient decreased with longer insufflation stimulus [20]. Measuring CO2 elimination has also been used to monitor this process. End-tidal CO2 increases disproportionately for younger patients compared to older children with the same insufflation pressures and duration, and it remains elevated even after the conclusion of the procedure [15]. For these reasons, postoperative monitoring of respiratory rate is critical to safely performing laparoscopy in infants and neonates.

Another potential problem in infants undergoing laparoscopy is hypoxemia. In neonates and infants, there is a close relationship between functional residual capacity (FRC) and airway closing pressure. When FRC decreases in response to the increased intra-abdominal pressure, airway closure will exacerbate right-to-left intrapulmonary shunt and can lead to hypoxemia [5].


Inflammatory/Immune System


In children, data from a study of procedures for acute abdominal pain suggested that laparoscopic compared to open operations did not result in differences in major inflammatory mediators such as cortisol and IL-6 [21]. However, several subsequent studies have demonstrated a lesser degree of increase in inflammatory mediators including IL-6, CRP, TNF-α, and cortisol with laparoscopy compared to open approach for a variety of operations [2225]. Cellular responses are also affected by laparoscopy, in a manner similar to the cytokine responses. Both macrophages and neutrophils are recruited to the peritoneal cavity with insufflation, though the numbers are lower with CO2 insufflation compared to air [26].


Other


Compared with adults, children have a greater body surface area to volume ratio [27] and thus are at increased risk for hypothermia . During minimally invasive surgical procedures in infants and children, hypothermia is reported to occur in 1.8 % of cases [4]. Temperature monitoring is especially important in newborns. Dry CO2 insufflation on continuous flow of 5–8 L/min will lead to massive evaporative losses relative to body size, and the accompanying heat loss can approach 40 % of a neonate’s metabolic power capacity, despite their higher-per-kilogram power capacity compared to adults [3]. Additionally, gas leaks around port sites in a neonate can result in a much greater loss of insufflation gas, thereby requiring higher flow rates and potentially exacerbating hypothermia if non-humidified CO2 is used.

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Oct 25, 2017 | Posted by in PEDIATRICS | Comments Off on Physiologic Considerations for Minimally Invasive Surgery in Infants and Children
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