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Position-Related Complications
Position-related complications are very common mishaps that are usually preventable. Neurosurgery encompasses different surgeries in a varied number of positions for easy surgical accessibility that pose a wide range of problems to both the anesthetic and surgical teams. Positioning surgical patients involves added risk to the patient as the anesthetized patient is not aware of this compromised position in the intraoperative period. Positioning of anesthetized patients for surgery forms an important job of the entire team to ensure optimal physiology and to prevent adverse sequelae and trauma due to the required position. The complications related to these positions are described in detail in this chapter.
Positioning of the head is an integral part of positioning the neurosurgical patients, both for craniotomies and spine procedures. Adequate knowledge of the surgical site and understanding the physiology of that position to target the surgical site will guide the proper positioning. The following types of approach are commonly followed in modern neurosurgery. These include anterior parasagittal, frontosphenotemporal (pterional), subtemporal, posterior parasagittal, midline suboccipital, and lateral suboccipital. Most of the spine procedures are undertaken either in the prone or lateral position. Craniotomies are undertaken either in supine, semilateral, prone, half-prone, three-quarter prone, or sitting position. Other variants include modifications of these positions to suit the surgery and avoiding complications to some extent.
General anesthesia, muscle relaxation, and positive pressure ventilation interfere with venous return, arterial tone, and autoregulatory mechanisms rendering patients under anesthesia especially vulnerable and relatively uncompensated to circulatory effects of changes in position. For these reasons, arterial blood pressure is often particularly labile immediately after initiation of anesthesia and during patient positioning. Hence, interruption in monitoring to facilitate positioning or turning of operating table must be minimized during this dynamic period.
Fixation of the head: In most cases, the head is either fixed using pins or different frames, e.g., Mayfield frame. This maneuver is quite painful and sometimes augments cardiovascular response. This is dangerous especially in patients with unruptured cerebral aneurysms. This can be attenuated with deepening of anesthesia, scalp block, or local infiltration. On the other hand, any movement of the patient with the head fixed may result in complications like scalp injuries, intracranial hematomas, or eye injuries. The pins should be removed before attempting or administration of reversal agents and extubation.
The physiological changes seen with different positions in neurosurgical practice are depicted in Table 1 . Different positions and manipulations with their complications are discussed.
Table 1
Physiological Changes Seen with Different Positions
| Physiological changes in various positions | ||||
|---|---|---|---|---|
| Supine | Lateral | Prone | Sitting | |
| CVS | ||||
| Venous return | ↑ | ↓ | ↓ | ↓ |
| Cardiac output | ↑ | ↓ | ↔ | ↓ |
| Heart rate | ↓ | ↑↔ | ↑↔ | ↑ |
| Systemic BP | ↔ | ↓ | ↓↔ | ↓ |
| Systemic vascular resistance | ↓ | ↑ | ↑ | ↑ |
| Mean arterial pressure | ↓↔ | ↓ | ↓↔ | ↓ |
| RS | ||||
| FRC | ↓ | ↓ | ↑↔ | ↑ |
| TLC | ↓ | ↓ | ↑↔ | ↑ |
| Qs/Qt | ↑ | ↑↑ | ↓ | ↓ |
| V/Q mismatch | ↑ | ↑↑ | ↓ | ↓ |
| CNS | ||||
| Jugular venous flow | ↑↔ | ↑↔ | ↑↔ | ↓ |
| Cerebral perfusion pressure | ↓↔ | ↔ | ↑ | ↔ |
| Intracranial pressure | ↔↑ | ↑ | ↑ | ↓↓ |
| Benefits | Easiest position | Optimal approach to temporal lobe | Optimal posterior approach to spine | Optimal posterior approach to posterior fossa and access to airway |
| Modification | Lawn chair position reverse Trendelenburg | Park bench | Concorde | Semirecumbent |
Abbreviations: CVS, cardiovascular system; BP, blood pressure; RS, respiratory system; FRC, functional residual capacity; TLC, total lung capacity; Qs/Qt, pulmonary shunt; V/Q, ventilation/perfusion; CNS, central nervous system.
Supine Position (Dorsal Decubitus)
Hemodynamic reserve is best maintained in this position because the entire body is close to the level of heart.
Indications: Encountered for cranial and anterior cervical spine surgeries and for carotid explorations.
Physiological changes: Because the venous compartment is a low pressure compartment, venous return to the heart depends on the body position. Venous return may be compromised with increase in ventilation perfusion mismatch. This position is also associated with compression injuries like ulnar and peroneal neuropathies. This position encounters the least complications otherwise.
Complications: Pressure alopecia in occipital region especially in prolonged surgeries, backache, ulnar neuropathy, and stretch on brachial plexus unless head is in neutral position are minimal except for proper placement of arms, head, and neck. Even after short procedures headache and congestion of the conjunctiva and nasal mucosa are observed.
Variants: Its variants include lawn chair position and reverse Trendelenburg position, the advantages being improvement in ventilation perfusion ratio and increase in venous return with better drainage of cerebrospinal fluid. In the lawn chair position the hips and knees are slightly flexed to avoid stress to the back, hips, and knees. In the reverse Trendelenburg position caution is advised to prevent patient from slipping on the table. Use of shoulder braces increases the incidence of brachial plexus neuropathies especially in the steep head down position. Also, the effect of the hydrostatic gradient on the cerebral arterial and venous pressure should be considered in terms of cerebral perfusion pressure.
Special attention: Placement of arterial transducer at the level of the tragus helps in assessment of cerebral perfusion.
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