Both thoracoscopy and laparoscopy are associated with a significant reduction in the amount of tissue trauma and thereby a reduction in postoperative pain. Studies have shown varying reductions in postoperative pain after MIS in both adults and children. Clinical evidence in adults shows that laparoscopic surgery reduces postoperative stay, respiratory complications, and postoperative pain when compared with open surgery [2, 3]. The decreased postoperative pain of tissue trauma after laparoscopy must be balanced with the possibility of shoulder tip pain, perhaps accounting for the fact that decreased postoperative pain is not always proven. Laparoscopic surgery for moderate to severely invasive operations has proven quicker recovery in many studies. Thoracoscopy in children greatly improves postoperative recovery [4, 5] and the minimisation of postoperative pain.

The improved cosmesis after MIS is one of the hardest advantages to quantify and report. The exchange of large laparotomy and thoracotomy incisions for keyhole incisions is undeniably beneficial. The minimisation of the visible scar associated with the incisions in an important long-term advantage to patients.

Reduction of physical deformity, especially on the chest wall, is also very important. Long-term chest wall deformity is minimised by MIS, and sometimes is eliminated completely. Winging of the scapula, kyphoscoliosis, pectus deformities, and other deformities seen after thoracotomy are reduced by thoracoscopy [6, 7]. Although most often associated with chest wall incisions, such deformities also can be associated with large abdominal wall incisions.

MIS is associated with minimisation of the degree of tissue trauma (as the incisions into the body wall are smaller than in the comparable open operation) and is of benefit in reducing some of the postoperative complications by blunting of the metabolic and stress response. The cytokine response is reduced after operations of a major magnitude performed by MIS [8–10]. One of the major determinants of the metabolic response to surgery is the magnitude of the operative stress [11, 12]. Operations of greater magnitude are associated with a greater metabolic response [13]. Therefore the benefit is more pronounced when bigger operations are performed by MIS.

There is an important association between alteration in thermoregulation and the metabolic response. In the 1960s, it was demonstrated that maintaining a 30 °C environmental temperature blunted the metabolic response to trauma and could therefore play an important role in determining the postoperative metabolic response [14]. Morbidity and mortality were also influenced by thermoregulation. Infants and children are more susceptible to alterations in thermoregulation and environmental temperature than adults. Physiological differences in thermoregulation may be partially responsible for differences between neonates, children, and adults in patterns of metabolic response.

Because MIS is not associated with large open wounds, heat loss and evaporative water loss are prevented, in turn altering thermoregulation. Studies have shown maintenance of core temperature and oxygen consumption in children undergoing thoracoscopy [15, 16] and laparoscopy [17], which was more marked in younger and smaller children. Changes in intraoperative thermoregulation may alter postoperative metabolism and changes in energy expenditure.

Luo et al. performed a trial in adults randomised to open or laparoscopic cholecystectomy [18]. Rest energy expenditure (REE), as measured by indirect calorimetry, was elevated on postoperative day 1 in both groups, but the rise in REE was significantly higher in the open group than in the laparoscopic group. Postoperative energy metabolism is also altered by laparoscopy in children, with a preservation of energy metabolism in comparison with open surgery [19]. There are possible effects on postoperative protein metabolism alongside these alterations. It seems, therefore, that MIS is associated with preservation of homeostasis with regard to energy expenditure.

The visualisation obtained with MIS is often superior to visualisation with open surgery. Access to many deep recesses and folds can be improved with the use of the scope. For instance, access to the oesophageal hiatus, pelvic structures, and apical areas of the lung is greatly facilitated with MIS, compared with open surgery.

A much greater degree of magnification also can be obtained using MIS. Structures that may be difficult to see with the naked eye (e.g., the vagus nerve and its branches during fundoplication and oesophageal atresia repair) are often easily visible on the screen with the optical and digital magnification allowed with MIS.

One of the new dimensions introduced by MIS is the creation of a working space. This technique can involve abdominal wall lifting, but the method most commonly used is insufflation of CO₂ to create a capnoperitoneum (or capnothorax). CO₂ absorbed from the body cavity during MIS causes an increase in CO₂ elimination via the lungs. In adults undergoing laparoscopy, there is typically a brief period of increased CO₂ elimination, but after 10–30 min of insufflation, a plateau is usually reached [20]. In children, the CO₂ profile is different: there is a continuous increase in CO₂ elimination throughout intraperitoneal insufflation of CO₂ in children [21]. The increase in CO₂ elimination was more marked in younger and smaller children, suggesting that age modifies the intraoperative handling of CO₂, and the same difference was true for thoracoscopic surgery [15]. The increased CO₂ load has been calculated to be approximately 16 % accounted for by absorption from the abdomen in one study [22]. In the case of thoracoscopy, nearly 50 % of expired CO₂ is absorbed from the thorax [22].

Neonates are particularly prone to acidosis during thoracoscopic surgery owing to the markedly increased CO₂ load, the decreased respiratory elimination from lung collapse, and exaggerated absorption in smaller children [15, 21]. Patients with congenital diaphragmatic hernia, for instance, are also at risk of significant acidosis and secondary effects [23–25]. Thoracoscopic surgery therefore should not be performed without suitable expertise and monitoring, or if the patient is unstable.

Insufflation of CO₂ used during laparoscopy increases intra-abdominal pressure. The optimal intra-abdominal pressure for laparoscopy in children has been established to be between 8 and 12 mm Hg [26], with neonates tolerating lower pressures than older children. The increase in intra-abdominal pressure causes a rise in intrathoracic pressure, which alters respiratory dynamics and leads to impaired respiratory function, including reduced functional residual capacity, increased airway pressure, and decreased lung compliance. Absorption of CO₂ from the abdomen seems to peak about 30 min into surgery, with up to 20 % of expired CO₂ derived from absorption; it decreases back to preoperative levels 30 min postoperatively [27]. During laparoscopy in self-ventilating patients, this change translates into an increase in end-tidal CO₂ and arterial CO₂ tensions [28] that can lead to acidosis.

In children undergoing controlled ventilation during laparoscopy, there is generally a good correlation between end-tidal CO₂ and arterial CO₂ pressures (PaCO₂) [28, 29]. If ventilation parameters are maintained at pre-insufflation values, both end-tidal CO₂ and PaCO₂ increase as intra-abdominal pressure increases. Occasionally, the increase in PaCO₂ is out of step with the increase in end-tidal CO₂ [30]. A 20–30 % increase in minute ventilation is usually sufficient to compensate for the increased CO₂ load [31–33], thus avoiding an increase in end-tidal CO₂ or acidosis.

Intra-thoracic insufflation of CO₂ has different mechanical effects on respiratory dynamics than intra-abdominal insufflation. Greater impaired respiratory capacity imposed by lung collapse has significant implications for oxygenation and CO₂ excretion [34]. Thoracic insufflation of CO₂ may also have a different absorption profile than abdominal insufflation, as it seems not to reach steady state within 30 min [23]. A greater percentage (up to 30 %) of exhaled CO₂ is derived from absorption during thoracoscopy, compared with 20 % during laparoscopy. The greater absorption of CO₂ insufflated into the chest, coupled with the impaired ventilation, can lead to a marked increase in arterial CO₂ concentration, which is especially of concern in neonates and smaller children, who have been shown to have greater CO₂ increases than bigger children [15]. Acidosis can be severe and prolonged in neonates undergoing thoracoscopy [23, 24]. The ability to increase CO₂ excretion in the face of the increased load created by its absorption is crucial to safe thoracoscopy in children. To avoid harm, the anaesthetist must anticipate, monitor, and expertly manage this requirement. Therefore thoracoscopic surgery in these circumstances should be performed only in experienced centres and with good prospective monitoring and management of CO₂ load.

The impact of learning new tasks needed for MIS must be taken account in embarking on such a venture. Many skills are of course transferable between operations, but not always between open and laparoscopic surgery. Intracorporeal suturing is a part of some MIS procedures and must be learned before embarking on operations requiring this technique. There is a role for learning these basic skills first on a form of trainer (of which there are several types available), before or while simultaneously attending a basic course. More advanced courses teaching the combined steps and skills for specific and advanced operations also can be used. Many training models have been developed for specific operations.

Whereas the learning curve can be measured in terms of operative time and hospital stay, better measures are patient safety outcomes such as complications and recurrence rates. Many MIS operations can take significantly longer than the corresponding open operation, especially during the learning curve. This difference must be appreciated by the surgeon, anaesthetist, and theatre staff (as well as patients and family, of course), for good teamwork and success. For most surgeons with advancing skills, however, this difference in time taken lessens and becomes clinically (and occasionally actually) insignificant.

There are various estimates of the number of MIS procedures required to reach the peak of the learning curve. For example, the number of procedures needed for laparoscopic hernia repair is estimated to be between 10 and 30 cases [35, 36]. It must be remembered, however, that the learning curve is both surgeon-specific and procedure-specific.

Being mentored at the outset of the MIS venture is one means of quickly and safely negotiating the learning curve. Inviting experienced operators to mentor surgeons at the beginning of their venture should facilitate quick and safe advancement up the learning curve.