Anaesthesia for minimally invasive abdominal and pelvic surgery

Learning objectives.

After reading this article you be able to:

• •Discuss the physiological impact of minimally invasive surgery on patients undergoing procedures in the abdomen and pelvis.
• •Describe the intraoperative effects of CO₂ pneumoperitoneum and positioning on cardiorespiratory function and splanchnic blood flow.
• •Explain the potential problems associated with positioning and access to the patient.
• •Provide safe and effective perioperative analgesia and i.v. fluids.

Key points.

• •Minimally invasive (both laparoscopic and robotic) surgery for major abdominal and pelvic procedures may have significant effects on cardiopulmonary physiology.
• •Many procedures are prolonged, and aspects of management such as fluid balance and analgesia may not be straightforward.
• •Great care is required to ensure the patient's safety and to recognise and manage surgical complications rapidly.
• •Whilst significant reductions in complications and length of hospital stay are possible, other benefits are less certain.

Introduction

Laparoscopic surgery is not new; the technique was described more than 100 yrs ago.¹ However, progress was slow, and it was not until the 1980s that technical advances in both laparoscopes and light sources allowed laparoscopic cholecystectomies and appendicectomies to be undertaken, kindling enormous enthusiasm for the concept. Alongside these developments was the advent of telemanipulation in the 1940s. Originally described for the handling of hazardous materials, this technique allows complex hand and finger movements to be transmitted remotely to a robotic device. Major advances in electronics and computing in the 1980s paved the way for robotically-assisted procedures, the first being performed in the 1990s. Further advances refined the process resulting in high quality three-dimensional images, the elimination of hand tremor, and better ergonomics for the surgeon to allow manipulation of equipment within the abdomen to be accomplished with increased dexterity. Robotic surgery has also been used outside the abdomen and pelvis in many specialties including cardiothoracic and oral surgery.1, 2

One disadvantage of minimally invasive surgery (MIS) is the loss of haptic (sensory) feedback from the tissues to the hands of the surgeon. Haptic feedback is absent in robotic surgery and reduced in laparoscopic surgery because the instruments have a long shaft. Developments are being made in robotic surgery in an attempt to provide some sensory feedback to surgeons from their patients' tissues.³ These technical advances continue to drive the move from open surgery to MIS.

Physiology of pneumoperitoneum

For MIS within the abdomen and pelvis, a pneumoperitoneum is required to create a surgical operating space. CO₂, and not air, as the prefix ‘pneumo’ might suggest, is inert and will not support combustion if diathermy is used. It also has a significantly increased blood solubility than nitrogen or oxygen, minimising the risk of a significant venous embolus should inadvertent intravascular insufflation occur. There are three major areas to consider when managing patients with a pneumoperitoneum:

• i.Increase in intra-abdominal pressure (IAP)
• ii.Patient's position (flat, reverse Trendelenburg, and Trendelenburg)
• iii.Biochemical changes resulting from CO₂ absorption

These factors can give rise to marked changes in a number of physiological systems, particularly cardiac and respiratory, leading to the phrase ‘minimal access surgery, maximum cardiopulmonary stress’.

The increase in IAP is central to understanding many of the physiological changes that occur. The abdomen and pelvis may be considered as a relatively closed box. Initial increases in intra-abdominal volume may be compensated for by the accommodating movement of both the anterior abdominal wall and the diaphragm, so that IAP remains relatively unchanged, although there is little pelvic or posterior flexibility, because of bony encasement. Further increase in intra-abdominal volume exhausts these compensatory mechanisms and thereafter IAP increases rapidly.

As IAP increases several sequelae occur. Compression of the vena cava reduces cardiac preload, whilst compression of the major arteries increases systemic vascular resistance (SVR), reducing cardiac output (CO) and ultimately leading to ventricular failure if pre-existing ventricular function is poor. Vascular compression also reduces visceral perfusion and causes venous pooling, predisposing to deep venous thrombosis. Other transmitted extraperitoneal effects include increases in arterial pressure and blood volume, which is relevant in organs such as the brain because ICP is increased.

The effects of increasing IAP are biphasic, with small increases in IAP leading to increases in CO and increased IAPs leading to a reduction in CO as follows:

• i.Low IAP (≤10 mmHg) increases venous return and CO.
• ii.Moderate IAP changes (10–20 mmHg) reduce CO and increase SVR. The effect on MAP mirrors the product of CO and SVR and is often variable.
• iii.High IAP (>20 mmHg) decreases MAP as CO is reduced markedly. These effects have been described in a previous article in this journal.⁴

An increase in IAP, by splinting the diaphragm, reduces lung volumes and causes atelectasis with associated ventilation and perfusion mismatch. This will tend to both increase partial pressure of CO₂ and reduce partial pressure of O_2. The magnitude of these changes can be quantified by an increase in the arterial partial pressure of CO₂ to end-tidal CO₂ (Paco₂₋Pe′co₂) difference and the arterial partial pressure of oxygen to fraction of inspired oxygen (Pao₂/Fio₂) ratio, respectively. The former correlates more strongly with the degree of atelectasis.⁵

In addition to these changes, there are changes in splanchnic blood flow. In any tissue, blood flow ($\dot{Q}$) is represented as:

$$\dot{Q}=\frac{\text{Δp}}{\mathrm{\eta }\mathrm{Z}}$$

where Δp is the arteriovenous pressure difference, η is the viscous resistance, and Z is the geometric resistance.

An increase in IAP causes an increase in arterial pressure (thus reducing Δp) and an increase in Z; both changes reduce $\dot{Q}$. This reduction in blood flow depends on IAP: relatively small increases (e.g. from 10 to 15 mmHg) significantly reduce blood flow to the stomach, small and large intestines, and liver, and increase the potential risk of ischaemia-reperfusion injury.6, 7 Although there is some relative preservation of perfusion to retroperitoneal structures, there is a reduction in renal blood flow and renal function.⁸ These effects add to the neuroendocrine effects on the kidney from major surgery, such as increased antidiuretic hormone and activation of the renin-angiotensin-aldosterone system.

Many of the physiological changes associated with pneumoperitoneum may be exacerbated by positioning of the patient during surgery. Lung volumes are reduced further in the Trendelenburg position, with a greater risk of atelectasis, but with relative preservation of venous return and CO. Conversely, the use of the reverse Trendelenburg position spares many of the respiratory changes as the diaphragm moves caudally, but exacerbates the adverse cardiovascular changes, further reducing venous return and CO, and very often MAP.

CO₂ is absorbed from the large peritoneal surface area, which may continue even after the IAP is reduced. This will result in an increase in measured end-tidal CO₂. In addition, ventilation perfusion ($\dot{V}$/$\dot{Q}$) mismatching caused by both anaesthesia itself and the pneumoperitoneum and may increase alveolar dead space. Overall, the increase in CO₂ load coupled with its reduced elimination will result in CO₂ entering CO₂ body stores and being excreted. Unless the patient's minute ventilation is increased, hypercapnia and a respiratory acidosis will occur.⁹

Preoperative assessment

As surgical and anaesthetic techniques advance, MIS is increasingly being offered to higher-risk patients. The shortened recovery period and reduced complication rate are balanced against the perioperative challenges in patients with reduced physiological reserve, including the effects of extreme positioning and longer procedural duration. In light of the many methods of MIS, a tailored approach to preoperative investigations should be based upon the proposed surgical procedure and patient-specific comorbidities, with an emphasis on those systems that are affected by pneumoperitoneum. The potential need for conversion to an open surgery should be considered.

However, there are a number of pre-existing conditions where MIS is considered to be contraindicated, when the cardiovascular changes caused by increased IAP, positioning of the patient, or both may not be tolerated. These include severe right ventricular or biventricular failure (where the ventricular output may decline as a result of increasing vascular resistance), right-to-left cardiac shunt (which may increase as right ventricular pressures increase), hypovolaemic shock (further reductions in venous reductions may cause dramatic reductions in CO and arterial pressure), and retinal detachment and raised ICP (where further increases in intraocular pressure or ICP may result in a marked reduction in perfusion pressures).

Anaesthetic management

Airway

Robotic cases require tracheal intubation with a cuffed oral tracheal tube. As increased airway pressures result from pneumoperitoneum and positioning, a tracheal tube enables close control of ventilation and provides protection of the lungs from pulmonary aspiration of gastric contents. However, there is evidence describing the safe use of second-generation supraglottic airways devices for selected laparoscopic surgeries. Some studies show no difference in gastric distension between these and tracheal intubation, with the ProSeal laryngeal mask airway advocated as an effective alternative to tracheal intubation with no associated increase in complications.¹⁰ Care must also be taken not to insufflate the stomach during bag-mask ventilation, as this can obscure surgical views, and may require gastric decompression, which can be awkward to execute during surgery.

Ventilation

Both pneumoperitoneum and positioning of the patient can impair ventilation, with increased inspiratory pressures, hypercapnia, and the risk of barotrauma. It may be possible to correct hypercapnia by increasing alveolar minute ventilation, but this may put the patient at risk of further barotrauma resulting from increased airway pressures, and a small degree of permissive hypercapnia may have to be tolerated as a compromise. Others advocate pressure-controlled ventilation with lower peak inspiratory pressures, and the use of PEEP to mitigate against the increased risk of atelectasis (although PEEP may reduce CO). The use of nitrous oxide is associated with not only greater postoperative nausea and vomiting (PONV) but it may cause greater bowel distension for longer procedures.¹¹

Intravenous fluids

Management of i.v. fluids remains a key area of anaesthesia for major surgery, preventing fluid overload whilst also maintaining vital organ perfusion. Modern surgical practice, especially within enhanced recovery after surgery (ERAS) programmes, usually results in patients arriving in theatres relatively euvolaemic because of carbohydrate loading, reduced bowel preparation, and the avoidance of a prolonged fluid fast.

A key area within fluid management is the concept of oxygen delivery ($\dot{D}$o₂), the product of CO and the oxygen content of arterial blood, expressed in ml min⁻¹. However, to allow comparison between patients, $\dot{D}$o₂ is often expressed as indexed oxygen delivery ($\dot{D}$o₂I), calculated by dividing $\dot{D}$o₂ by body surface area and expressed as ml min⁻¹ m⁻². There is a wealth of literature relating to open surgery to suggest that maintaining a high $\dot{D}$o₂I will reduce morbidity and mortality in open surgery, but there are significant constraints in patients undergoing MIS. The physiological changes outlined above will render some of the basic indicators of fluid assessment (e.g. central arterial pressure measurement) unreliable.¹² In addition, significant reductions in CO associated with positioning and pneumoperitoneum make interpretation difficult, although one study has shown $\dot{D}$o₂I of <400 ml min⁻¹ m⁻² measured during laparoscopy to be a predictor of anastomotic leakage.¹³ A practical approach for these surgeries is to:

• i.Correct any pre-existing fluid deficits if present.
• ii.Aim for near-zero fluid balance where possible, using balanced crystalloid infusions at a rate of 1–4 ml kg⁻¹ h⁻¹ to maintain homeostasis, and replacing measured losses.
• iii.At the end of surgery, when the patient is positioned horizontal and with no pneumoperitoneum, give fluids to optimise stroke volume.
• iv.Reduced volumes of fluids are advocated in patients undergoing cystectomy to reduce volume overload and the incidence of renal injury if there is a significant delay between ureteric clamping and reimplantation.
• v.Intraoperative hypotension, unless related to hypovolaemia, should be treated with vasopressors. The use of lower IAP where feasible may also assist with improving MAP, CO, and $\dot{D}$o₂I.

vi. Urinary catheterisation is required for major/prolonged MIS cases, although perioperative urinary drainage is likely to be poor, particularly in the Trendelenburg position. Permissive oliguria (e.g. 0.3 ml kg⁻¹ h⁻¹) is increasingly considered to be acceptable without leading to an increase in acute kidney injury, and is also viewed as a physiological response to major surgery from increased antidiuretic hormone production.¹⁴

Other markers of adequate perfusion, such as trends in serum lactate, acid-base balance, and central venous oxygen saturation may provide guidance for fluid therapy.

Patients undergoing prolonged surgery in the Trendelenburg position, such as cystectomy, are worthy of highlighting. This position may put these patients at risk of cerebral oedema, which can be exacerbated by excessive i.v. fluids. Monitoring for hyperkalaemia is important, particularly when the ureters have been clamped surgically before urinary diversion (either through an ileal conduit or formation of a neobladder).

After surgery, the reduction in physiological upset and bowel handling associated with MIS often means that many of these patients are able to drink in the early postoperative period and prolonged postoperative i.v. fluids are usually unnecessary; an exception is cystectomy, where postoperative ileus is common. In addition, a degree of permissive oliguria is accepted and not treated with i.v. fluids in the absence of other signs of hypovolaemia.¹⁵

Monitoring

The degree of monitoring is usually dictated by patient comorbidities, expected blood loss, and the length and complexity of surgery. Many use intra-arterial access to allow for reliable BP monitoring and regular blood gas analysis. For any laparoscopic surgery (and in particular robotic surgery) access to the patient is extremely limited. Care must be taken with any lines and monitoring devices that they are not going to be kinked or displaced when the operating table or robot is positioned. Some patients (e.g. the elderly and those undergoing cystectomy or prostatectomy) are at risk of significant postoperative cognitive dysfunction and it may be of benefit to utilise EEG monitoring, such as the bispectral index, to avoid excessively deep anaesthesia.

Positioning

Many of the problems associated with positioning and MIS are related to the extreme Trendelenburg and reverse Trendelenburg positions that may be required (Table 1). Also note that repositioning can be difficult when the operation is underway, particularly during robotic surgery, as the instruments are fixed in position when the robot is docked. Extremes of Trendelenburg positioning may cause other effects such as an increase in ICP and intraocular pressure, ultimately leading to cerebral oedema, which may be relevant in patients with pre-existing pathologies. This process can be exacerbated by excessive administration of i.v. fluids.

Table 1.

Problems associated with MIS

Position	Risk	Consequences	Solution
All	Patient sliding	Direct trauma Visceral injury from indwelling instruments	Non-slip padding/eggshell Straps Foot/shoulder supports Beanbags
	Pressure injuries	Neuropraxia/neuropathy Pressure sores	Avoiding excess stretch (e.g. use of level arm boards) Gel padding/eggshell Padding to plastic i.v. connectors and monitoring devices (e.g. arterial catheter connectors)
	Access to i.v. catheters and monitoring devices	Difficult to access once underway (especially robotic surgery)	Insert all lines/monitoring before docking of the robot
Trendelenburg	Tracheal tube movement	Bronchial intubation	Secure tracheal tube effectively Check tube length after positioning, including auscultation
	Oedema	Cerebral oedema Airway oedema Conjunctival oedema/chemosis	Limit volumes of i.v. fluids Avoid tracheal tube ties Periodic levelling of patient Consider ‘leak test’ before extubation
	Pulmonary	Atelectasis	Use of PEEP
	Gastric content spillage	Pulmonary aspiration Oral ulceration Conjunctival chemical burns	Use a tracheal tube with sufficient balloon pressure Insert and drain nasogastric tube (NGT) Use extra padding around the eyes Periodic monitoring of face
	Compartment syndrome (especially lithotomy syndrome)	(Bilateral) calf compartment syndrome Gluteal compartment syndrome	Adequate padding Avoid use of compression stockings Use heel/ankle supports Periodic ‘levelling out’/moving patients legs perioperatively Monitor foot pulses
	Upper extremity neuropathy	C5–7 distribution	Caution with use of beanbag Head and neck/joint positioning (e.g. avoiding abduction >90° and head contralateral extension) Use padded shoulder bolsters (especially over acromioclavicular joint)
	Lower extremity neuropathy (especially in lithotomy position)	Lateral femoral cutaneous nerve Common peroneal nerve Obturator nerve Sciatic nerve	Use sufficient padding of supports
	Reduced venous return	Hypotension on levelling the patient	Preload with i.v. fluids and consider use of vasopressors before levelling
Reverse Trendelenburg	Reduced venous return	Hypotension	Preload/vasopressor use

Analgesia

The major aim in providing perioperative analgesia for patients undergoing MIS abdominal and pelvic surgery is to use multimodal opioid-sparing drugs. Large doses of opioids are undesirable and are associated with nausea, vomiting, a slower return of gastrointestinal function, respiratory depression and suppression of cough, and the potential for misuse after surgery. Epidural analgesia for major open abdomen and pelvic surgery was seen as the gold standard for many years, but a major advantage of MIS is the reduced incision size and associated tissue injury, resulting in relatively modest requirements for postoperative analgesia. Whilst epidural analgesia has been used for MIS, it was found to be unnecessary and to lead to significant problems after surgery. When compared with patients who had received either spinal anaesthesia or PCA with i.v. morphine, epidural analgesia was associated with reduced mobilisation, increased requirements for i.v. fluid requirements, time to return of bowel function, and length of stay (LOS) in hospital.¹⁶

With the decline of epidural analgesia, a logical alternative was spinal anaesthesia to treat immediate postoperative pain, but also allow rapid mobilisation and restoration of function (without adverse effects such as PONV, ileus, impairment of mobility, or hypotension), and then convert to regular oral multimodal analgesia as soon as possible. This has been widely and successfully used for both laparoscopic and robotic surgeries, such as the first 23-h hospital stay laparoscopic colectomy.¹⁷ A popular method is the use of intrathecal diamorphine to reduce the need for systemic opioids, with doses ranging from 250 μg to as high as 1 mg, depending on the type and duration of surgery, the associated comorbidities, and the location of postoperative care.

There are very few good quality studies to provide definitive guidance on analgesic technique. Local anaesthetic techniques, such as transversus abdominis plane block, may decrease opioid consumption, especially when the block is sited before surgery.¹⁸ Some practitioners have used remifentanil infusions to obtund some of the physiological responses to surgery, but there have been concerns regarding acute tolerance and opioid-induced hyperalgesia.¹⁹

Regular postoperative systemic analgesia with paracetamol and NSAIDs should be used unless contraindicated, with opioids reserved for breakthrough pain. Drugs used less commonly include anticonvulsants, such as pregabalin, and i.v. steroids at high doses. Second-line analgesics have also been advocated, including i.v. lidocaine and ketamine. There has been much recent focus on lidocaine, with a meta-analysis demonstrating that it reduces opioid requirements, PONV, and the time until resumption of diet.²⁰ However, there was much heterogeneity in the timing, dose, and duration of lidocaine infusion, with few studies measuring lidocaine concentrations. A recent Cochrane review, that included both open and laparoscopic surgeries, recorded uncertain benefits and safety, because of the poor quality of the studies. Further and better trials (such as the acceleating gastrointestinal recovery after colorectal urgery (ALLEGRO) trial) are currently underway to help resolve these uncertainties.²¹

Neuromuscular block

Neuromuscular block (NMB) is required to prevent patient movement/coughing and the advent of the combination of rocuronium and sugammadex has permitted deeper NMB to be continued until the end of surgery with no delay in reversal. More recently, deep NMB (e.g. post-tetanic twitch count of one to two twitches) and moderate NMB (with a train-of-four count of one to two twitches) have been compared, with deep NMB theoretically providing good operating conditions at lower IAP (e.g. 8 mmHg compared with 15 mmHg) with less postoperative pain and cardiovascular upset. Whilst it is possible for some surgeons to work at these lower IAPs, to date, the advantages of deep NMB over moderate NMB are inconclusive, and a Cochrane review is awaited. For robotic surgery, reducing patient movement to a minimum is paramount to minimise harm, so deep NMB can be considered, although remifentanil is a suitable alternative to prevent reflex movements. Currently, whilst definitive evidence is awaited for the role of deep NMB, a practical approach is to ensure at least moderate NMB during MIS and then confirm adequate reversal of NMB before leaving the operating theatre.

Antiemetics

Laparoscopy has been implicated as a risk factor for PONV, although the evidence for this is inconclusive. Therefore, multi-modal antiemetic use should be based upon individual risk factors, as is commonly practiced.

Emergencies, complications, and undocking

These can be broadly divided into three areas: complications during surgical access to the abdomen, physiological complications of the pneumoperitoneum/patient positioning; and operative/surgical complications.

There are a number of different methods of accessing the peritoneal cavity. These can be either closed (e.g. Veress needle) or an open approach under direct vision, with up to 50% of complications occurring at this time. The small bowel is the structure most frequently damaged (25%), followed by the iliac artery (19%), colon (12%), and iliac veins (9%).²² Massive blood loss arising from injury to the major vessels may not be recognised immediately, as bleeding into the mesentery or retroperitoneum may occur. Rapid control is required, which can be especially problematic in patients undergoing robotic procedures, because access to the patient may be limited by the robotic instruments. This highlights the need to have emergency undocking protocols in place, which should be practised regularly.²³ There are also unique additional risks associated with robotic systems. In addition to the potential for human errors, mechanical failures can also occur. Some of the most frequent complications included uncontrolled movements and spontaneous powering on and off (10.1% of all cases reported to the Food and Drug Administration [FDA]) and arcing from the diathermy causing burns to surrounding tissue (e.g. bowel) sometimes outside the surgeons field of view and thereby going unnoticed (10.5% of all cases reported to the FDA).²⁴

The physiological aspects have been described above, but complications directly from establishing the pneumoperitoneum can include subcutaneous emphysema, mediastinal emphysema, pneumothorax, CO₂ retention, postoperative pain related to retained intra-abdominal gas, and air embolism from venous injury.

The positional effects caused by prolonged lithotomy together with steep Trendelenburg positioning, the use of pneumatic compression stockings, i.v. fluids restriction, hypotension, and administration of vasoactive medication, can reduce perfusion and can therefore increase the risk of compartment syndrome occurring in the lower extremity. In addition, prolonged surgery in the Trendelenburg position may predispose to oedema around the face, eyes, and upper airway, which will be exacerbated with excessive i.v. fluids. Postextubation respiratory distress has been described, requiring emergency reintubation.²⁵

Outcomes

Outcomes for patients having undergone MIS for abdomino-pelvic disease is a complex area. The large increase in numbers of patients undergoing MIS surgery has occurred alongside many other changes in perioperative care embodied in initiatives such as the Perioperative Quality Improvement Programme (PQIP) and ERAS. Thus, whilst an overall reduction in hospital LOS, complications, readmissions, and cost has been described, the precise impact of MIS alone is less certain.²⁶

Good quality studies that compare high volume MIS with open surgery may be difficult to undertake, not least because of problems of randomisation. However, there are a few studies that compare open, laparoscopic, and robotic surgeries. Where this has been assessed, postoperative complications (both medical and surgical), blood loss and transfusion rates, and hospital LOS associated with robotically assisted radical prostatectomy are superior to laparoscopic radical prostatectomy.²⁷ Both of these techniques are superior to open radical prostatectomy. Further studies in urology have assessed both death rates and hospital costs, and found a reduction in deaths in MIS, but also an increase in costs for robotic surgery over both laparoscopic surgery and open surgery.

For patients undergoing rectal surgery, a recent comparison has shown that robotic surgery may reduce LOS but increase costs when compared with laparoscopic surgery.²⁸ Both were superior to open surgery in terms of wound infection and LOS, with comparable costs between laparoscopic surgery and open surgery. A major consideration yet to be resolved is whether or not there are differences in long-term oncological outcomes.

Declaration of interest

The authors declare that they have no conflicts of interest.

MCQs

The associated MCQs (to support CME/CPD activity) will be accessible at www.bjaed.org/cme/home by subscribers to BJA Education.

Biographies

Chris Jones FRCA MD (Res) is a consultant in anaesthesia at Royal Surrey County Hospital NHS Trust and St Luke's Cancer Centre, and an honorary senior lecturer at University College, London. He has interests in research, anaesthesia, and perioperative medicine for patients undergoing major oncology surgery including hepato-pancreatico-biliary, oesophagogastric, and major urology procedures. His MD thesis was on enhanced recovery after open liver resection surgery.

Benjamin Carey MA (Oxon) FRCA, is a clinical fellow at St Vincent's Public Hospital, Melbourne. He is a member of the Surrey Crisis Resource Management (SCReaM) team, a project focused on human factors and patients' safety at the Royal Surrey Hospital.

William Fawcett FRCA FFPMRCA is a consultant in anaesthesia and pain medicine at Royal Surrey County Hospital NHS Trust and St Luke's Cancer Centre, and an honorary senior lecturer at University College, London. His major clinical interests are anaesthesia for hepato-pancreatico-biliary, laparoscopic colorectal, and robotic urology procedures. He is chair of the Education Committee and the Featherstone Professor of anaesthesia of the Association of Anaesthetists.

Matrix codes: 1A01, 2A07, 3A03