Principles of anesthesia and physiology


The increased use of robotic surgery across multiple surgical disciplines has required anesthesiologists to refine their approach to continue to provide safe and effective anesthesia.

The anesthesiologist must consider whether the health status of the patient is adequate to withstand the position, duration and physiological demands required of the chosen robotic surgery approach. The conduct of anesthesia needs to be adapted at certain surgical time points to prevent patient harm and promote an uncomplicated recovery.

Preoperative considerations

While there are no absolute contraindications to robotic surgery, adequate assessment of the patient requires consideration of their ability to withstand the planned duration of surgery. Some operating table positions encountered in robotic surgery have a significant impact on body systems. Some patients are unable to withstand these effects and an alternative surgical approach may be necessary. Adequate preoperative assessment, optimization of existing medical conditions and an explanation of the plan for anesthesia need to take place.

Relative contraindications to robotic surgery include morbid obesity, severe cardiovascular and respiratory disease, and conditions that increase intracranial and intraocular pressure, particularly for those procedures that require the Trendelenburg position. Assessment of patients well in advance of surgery in a multidisciplinary fashion is ideal.

Ensuring the operating theater is set up in the most efficient manner is an important consideration. Robotic equipment takes up a great deal of space and thus communication with the theater team including the theater technician allows ideal placement of equipment.

It is critical that theater staff possess the technical expertise required to prepare and use the robot in a safe and sterile manner. As access to the patient is limited ( Fig. 6.1 ), a thorough understanding as to how to undock the robotic apparatus as quickly as possible to facilitate resuscitation in an emergency will prevent undue delays in management. Simulation has been shown to improve efficiency in this situation.

Fig. 6.1

Access to the patient is severely limited while the robotic apparatus is docked.

Furthermore, the theater team need to be prepared for conversion from a robotic approach to an open procedure. In the event of rapid blood loss, the surgeon needs to keep the anesthesiologist and team informed about the feasibility of controlling bleeding using the robotic instruments. If this proves difficult, a decision to convert to an open procedure will be required.

Patient preparation

Vascular access

Prior to procedure commencement, consideration needs to be made regarding bleeding risk. Adequate caliber and the site of intravascular access need to be established. Despite the lower rate of blood transfusion in robotic gynecological and urological surgery, , the placement of an arterial line is preferred because access to the patient during robotic surgery is compromised. Arterial catheterization enables constant evaluation of hemodynamics and intermittent testing of respiratory parameters, bleeding status, and biochemistry.

Robotic cardiac surgery necessitates the placement of cannulas in particular locations. Preparation for cardiopulmonary bypass may require the anesthesiologist to place a 15 to 17 Fr cannula in the right internal jugular vein to facilitate the drainage of the superior vena cava. Further placement of cannulas including a coronary sinus cannula may also be necessary, and the pulmonary artery cannula may need to be placed in an alternative position. Cannulas are placed using transesophageal echocardiography guidance and thus anesthesiologists need to be familiar with this approach. External defibrillation pads need to put in place, as internal defibrillation is not possible.

Patient protection

Extreme operating table positions encountered in robotic surgery require prevention of patient movement. This is achieved through use of antislip mats and patient restraints. Deep muscle relaxation prior to port placement and throughout surgery is required as patient movement may lead to injury. Neuromuscular monitoring sited prior to procedure commencement facilitates adequate relaxation.

Intravascular catheters must be protected from kinking and compression, as after the patient cart has been docked, the arms are not easily accessible. The position of the arterial line transducer should be placed at the same height as the head such that the measured blood pressure reflects cerebral perfusion. This is particularly important in robotic surgeries such as gastric surgery where the reverse Trendelenburg position may compromise cerebral blood flow if not adequately identified and treated.

Long duration and poor visualization of the patient throughout surgery means it is essential that adequate time be taken to ensure the patient is protected from pressure injury. While rare, the effects of peripheral nerve injury may be prolonged. Excessive stretching and direct pressure of nerves must be avoided.

Nerves at particular risk include the common peroneal nerve when the modified lithotomy position is used. The brachial plexus is at risk of injury if excessive pressure is placed over the acromioclavicular joint and with excessive abduction of the arm. Utilization of somatosensory evoked potentials to monitor brachial plexus neuropathy is advantageous in robotic transaxillary thyroid and parathyroid surgery.

When a lateral decubitus position is used in thoracic surgery patients, an axillary roll placed inferior to the axilla will protect the brachial plexus. In this position, adequate padding needs to be placed between the knees and ankles and in the dependent arm; hyperextension of the elbow needs to be avoided.

In all surgeries, a neutral position of the head and neck is sought after.

Pressure sores and gluteal injury are possible, particularly when the patient is placed in a lithotomy position.

There are a variety of ways to protect the eyes. Whichever approach is undertaken, it is mandatory to ensure eye lubrication, closure, and protection from pressure. Further eye protection from regurgitation of gastric contents is afforded by nasogastric tube insertion.

The prone position employed in robotic esophagectomy poses increased risk of pressure injury and regular checks need to occur.

In transoral robotic surgery (TORS), utilization of goggles and a mouthguard protect the eyes and teeth, respectively.

Protection of the patient’s head from the robotic arms can be achieved by clamping an anesthetic screen such that it rests immediately above the patient’s face.

Movement of the table once the patient cart is docked can only be achieved if the table-robot interface has been fitted with a specific upgrade that allows dynamic movement of the table while the robot is docked. If this upgrade is not present, movements of the table must be strictly avoided as rigid instruments may cause significant visceral injury.

The prolonged duration of many robotic procedures and the risk of venous stasis due to pneumoperitoneum dictate a plan for deep venous thrombosis (DVT) prophylaxis to be implemented. Use of stockings and pneumatic calf compressors decrease the risk of DVT.

Intraoperative management

Airway management

Endotracheal intubation is essential in intra-abdominal robotic surgery to protect from aspiration of gastric contents. Endotracheal intubation also facilitates muscle relaxation, which improves intra-abdominal exposure.

Cardiothoracic robotic surgery requires lung isolation which can be achieved via insertion of a double lumen tube or use of a bronchial blocker. Both approaches have advantages and disadvantages ( Table 6.1 ). If a double lumen tube is utilized, tube exchange may need to be performed in those who are not candidates for immediate extubation.


Advantages and Disadvantages of Double-Lumen Tubes and Bronchial Blockers

From Lu Y, Dai W, Zong Z, et al. Bronchial blocker versus left double-lumen endotracheal tube for one-lung ventilation in right video-assisted thoracoscopic surgery. J Cardiothorac Vasc Anesth . 2018;32(1):297–301.

Advantages Disadvantages
Double-Lumen Tube a
Easily positioned—fiber-optic bronchoscopy not essential May be difficult to intubate
More stable in bronchus More traumatic
Allows ventilation of both sides of the lung
Capacity to suction both lungs Exchange required if patient remains intubated
Easy application of CPAP Increased sore throat/hoarseness
Easy insert scope in tubes size >35 French
Bronchial Blockers b
Easier to intubate with single lumen tube Requires fiber-optic bronchoscope
Use down existing single lumen tube Longer duration to lung collapse
Lobar/subsegmental block More difficult on right lung
Useful in small airways—e.g., pediatrics Difficult to suction and apply CPAP
Easy application of CPAP Less stable in bronchus

CPAP, Continuous positive airway pressure.

a Gold standard for lung isolation. Large external diameter tubes. Left and right in sizes 26, 28, 35, 37, 39, and 41 French.

b Examples include Univent, Arndt, Cohen, and EZ Blocker.

A double lumen tube has long been considered to be superior in time to operative lung deflation, but recent evidence suggests that deflation with a bronchial blocker occurs more rapidly if an FiO 2 of 1.0 is used and there is a period of apnea prior to lung isolation.

In TORS, team-oriented airway assessment with inclusion of preoperative fiber-optic nasal endoscopy assists in planning for oral or nasal intubation. If nasal intubation is performed, care must be taken to avoid nasal alar necrosis. Limited patient access dictates that all connections be fastened tightly. Orally sited endotracheal tubes can be sutured to the patient by the surgeon to avoid dislodgment.

Ventilation and hemodynamic management

All general anesthetics require ventilation of the patient to allow sufficient uptake of oxygen and removal of carbon dioxide, and this must be provided in a manner that is protective to the lung parenchyma.

While both oxygenation and removal of carbon dioxide are important in all anesthetics, intra-abdominal and cardiothoracic robotic surgery greatly influence the capacity to remove carbon dioxide.

Anesthesiologists must first have a deep understanding of normal carbon dioxide homeostasis. They can then plan for robotic surgery’s associated impacts. Four of these impacts are interrelated and require further explanation:

  • 1.

    Insufflation of the surgical cavity

  • 2.

    Effects secondary to hypercapnia

  • 3.

    Effects of carbon dioxide outside the intended site of administration

  • 4.

    Effects related to the Trendelenburg position.

Normal carbon dioxide homeostasis

The arterial partial pressure of carbon dioxide (PaCO 2 ) is dependent on carbon dioxide production (V˙CO 2 ) and inversely proportional to the alveolar minute ventilation (V˙A) ( Fig. 6.2 ).

Fig. 6.2

Arterial partial pressure of carbon dioxide is related to CO 2 production and alveolar minute ventilation.

In the spontaneously ventilating patient, the respiratory center in the brain detects an elevated blood partial pressure of carbon dioxide and this triggers an increase in minute ventilation.

Under anesthesia, anesthetic drugs decrease the sensitivity of the respiratory center to increase minute ventilation and muscle relaxants decrease the capacity for spontaneous ventilation. Therefore, it is the responsibility of the anesthesiologist to set the minute ventilation on the anesthetic machine.

In defining this minute ventilation, the anesthesiologist must appreciate the difference between the set minute ventilation on the anesthetic machine and the effective alveolar ventilation ( Fig. 6.3 ). A proportion of the set minute ventilation will only reach the conductive airways absent of alveoli. These airways are not able to contribute to removal of carbon dioxide; this volume is termed “dead space.”

Fig. 6.3

Minute ventilation is equal to alveolar ventilation plus dead space ventilation.

Alveolar dead space increases in patients with severe lung diseases such as acute respiratory distress syndrome (ARDS) and chronic obstructive pulmonary disease (COPD), and the proportion also increases with small tidal volumes.

Minute ventilation can be maintained by increasing respiratory rate and decreasing tidal volume. This will decrease the maximum alveolar pressure, but progressive decreases in tidal volume will result in insufficient alveolar ventilation.

If removal of carbon dioxide via the lungs is insufficient or the production of carbon dioxide increases for the same minute ventilation, hypercapnia will result.

Robotic surgery’s associated impacts

Insufflation of the surgical cavity

Multiple robotic surgical disciplines including gynecological, urological, colorectal, and general surgery require pneumoperitoneum. The consequences of pneumoperitoneum on ventilation, carbon dioxide production, and other multisystemic effects need to be realized.

Carbon dioxide is administered into the intraperitoneal space to aid surgical vision and allow adequate space for manipulation of instruments. Carbon dioxide is advantageous as it is inexpensive, does not support combustion, and is colorless. It is more readily soluble than air and thus is taken up into the circulation over time. Typical insufflation pressures are 10 to 15 mm Hg but these pressure levels are occasionally increased for short periods to facilitate reductions in venous bleeding and to enhance surgical visualization.

Effects relate to the properties of gas itself and the effects resulting from the pressure of insufflation. While some effects are expected, some occur uncommonly and an understanding of the pathophysiology related to these unexpected effects is required.

The pathophysiological effects of pneumoperitoneum are wide reaching ( Fig. 6.4 ).

Sep 9, 2023 | Posted by in GENERAL SURGERY | Comments Off on Principles of anesthesia and physiology

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