Effect of three different surgical prone positions on lung volumes in healthy volunteers

[Controversies in neuroanaesthesia: positioning in neurosurgery]

Positioning of the neurosurgical patient has several features such as the existence of specific positions (i.e: sitting, prone hyperlordotic, crouching ou kneeling positions) or the range of facilities for the same surgical indications. The last point, a source of controversy, is the subject of this review. Current indications for the sitting position, positioning for lumbar spine surgery and prevention of eye injuries are successively addressed.

Lumbar microdiscectomy with spinal anesthesia: comparison of prone and knee-chest positions in means of hemodynamic and respiratory function

STUDY DESIGN

Prospective clinical study to compare the physiologic changes in lumbar disc surgery regarding to positions.

OBJECTIVE

To compare the perioperative hemodynamic and respiratory functions between prone and knee-chest positions for lumbar disc surgery under spinal anesthesia.

SUMMARY OF BACKGROUND DATA

Spinal anesthesia is a safe but rarely used alternative to general anesthesia for lumbar disc surgery. It reduces blood loss, avoid pressure necrosis, and nerve injuries, and it provides a more comfortable postoperative period. Prone and knee-chest positions are mostly used positions in lumbar discectomy; hemodynamic and respiratory effects of spinal anesthesia and the differences between these 2 positions in spinal anesthesia were evaluated in this study, which only been evaluated in general anesthesia.

METHODS

Forty-five patients were randomized for lumbar microdiscectomy with spinal anesthesia under either prone position (group 1 n = 22) or knee-chest position (group 2 n = 23). All patients were classified as physical status 1 or 2 according to the American Association of Anesthesiology. Spinal anesthesia was performed with hyperbaric bupivacaine. Perioperative continuous hemodynamics and respiratory function test results were recorded after the spinal anesthesia was performed.

RESULTS

Immediately after the spinal anesthesia was performed, both the systolic and diastolic arterial blood pressure values were significantly decreased and heart rates were significantly increased in both groups. Both positions showed significant decrease in forced vital capacity (P = 0.002) and forced expiratory volume in 1 second (P = 0.0015) during the surgery respect to preoperative values. The decrease in peak expiratory flow (P = 0.011) and forced expiratory flow at the 25% of the pulmonary volume (P = 0.011) was significant in knee-chest position respect to prone position.

CONCLUSION

In conclusion, spinal anesthesia is appropriate for lumbar disc surgery with respect to the hemodynamic parameters in both prone and knee-chest positions, however, in terms of pulmonary functions, the knee-chest position can cause a restrictive effect. Therefore this position should be used cautiously in higher-risk patients.

Anaesthesia in the prone position

Prone positioning of patients during anaesthesia is required to provide operative access for a wide variety of surgical procedures. It is associated with predictable changes in physiology but also with a number of complications, and safe use of the prone position requires an understanding of both issues. We have reviewed the development of the prone position and its variants and the physiological changes which occur on prone positioning. The complications associated with this position and the published techniques for various practical procedures in this position will be discussed. The aim of this review is to identify the risks associated with prone positioning and how these risks may be anticipated and minimized.

Effects of prone position on alveolar dead space and gas exchange during general anaesthesia in surgery of long duration

BACKGROUND AND OBJECTIVE

We investigated the effects of prone position on respiratory dead space and gas exchange in 14 anaesthetized healthy patients undergoing elective posterior spinal surgery of more than 3 h of duration.

METHODS

The patients received a total intravenous anaesthetic with propofol/remifentanil/cisatracurium. They were ventilated at a tidal volume of 8-10 mL kg(-1), zero positive end-expiratory pressure and an inspired oxygen fraction of 0.4. Physiological, airway and alveolar dead spaces were calculated by analysis of the volumetric capnography waveform. Measurements were made in supine position (20 min after the beginning of mechanical ventilation) and 30, 120 and 180 min after turning to prone position.

RESULTS

We found that the alveolar dead space/tidal volume ratio did not change. PaO(2)/F(i)O(2) increased, although not statistically significantly. Dynamic compliance was reduced due to a reduction in tidal volume and an increase in plateau pressure.

CONCLUSIONS

Patients undergoing surgery in prone position for a duration of 3 h under general anaesthesia including muscle relaxation and mechanical ventilation without positive end-expiratory pressure have stable haemodynamics and no significant changes in the alveolar dead space to tidal volume ratio. Oxygenation tended to improve.

Prone ventilation--it's time

Prone positioning to improve oxygenation in acute lung injury was first reported over 20 years ago. Although this and several subsequent studies have shown that prone positioning improved oxygenation in the majority of patients, it has failed to become common practice in intensive care units. This paper reviews the mechanism by which prone positioning improves oxygenation and the clinical studies of its use to date.

The effect of the prone position on pulmonary mechanics is frame-dependent

By compressing the abdomen and restricting chest wall movement, the prone position compromises pulmonary compliance. For spine surgery, placing the anesthetized patient into the prone position increases the risk of improper ventilation. In this study, we tested the hypothesis that the compromise in pulmonary compliance is related to the patient's body habitus and the surgical frame used to support the patient while in the prone position. Seventy-seven adult patients were divided into three groups according to body mass index: normal (n = 36) < or = 27 kg/m2, heavy (n = 21) 28-31 kg/m2, and obese (n = 20) > or = 32 kg/m2. Patients were placed in the prone position supported by chest rolls, a Wilson frame, or the Jackson spinal surgery table (Jackson table) according to the surgeon's preferences. Peak airway pressure (at the proximal endotracheal tube), pleural pressure (esophageal balloon), and mean arterial pressure were recorded in the supine position and prone position within 15 min of the turn. Dynamic mean (+/- SD) pulmonary compliance (mL/cm H2O) decreased when turning from the supine to the prone position in all three body mass groups when using chest rolls (normal 37+/-5 to 29+/-6; heavy 43+/-2 to 34+/-4; obese 42+/-8 to 32+/-6) or the Wilson frame (normal 39+/-6 to 32+/-7; heavy 43+/-16 to 34+/-10; obese 36+/-11 to 28+/-9). The dynamic pulmonary compliance was not altered in patients positioned on the Jackson table. Regardless of body habitus, using the Jackson table for prone positioning was not associated with a significant alteration in pulmonary or hemodynamic variables. We conclude that moving patients from the supine to the prone position during anesthesia results in a decrease in pulmonary compliance that is frame-dependent but that is not affected by body habitus.

IMPLICATIONS

We hypothesized that compromise in pulmonary compliance in the prone position is related to the patient's body mass index and the surgical frame used. In this study, we demonstrated that prone positioning during anesthesia results in a decrease in pulmonary compliance that is frame-dependent but that is not affected by body mass index.

[Perioperative effects of the prone position: anesthesiologic aspects]

The prone position is commonly used for surgery of the spine and the posterior fossa, and is well tolerated by the majority of patients. As long as the abdomen is not compressed, the physiologic impact of this position on cardiorespiratory function is minor, in some cases even less than with the supine position. However extremes of position, particularly of the head and neck, are poorly tolerated and may lead to a variety of severe neurological complications. In addition, several specific forms of pre-existing pathology may predispose the prone patient to major cardiorespiratory complications. In this paper we have systematically reviewed the English and French literature from 1991 to 1997 using Medline Search of peer reviewed journals for the search terms "prone position" and "prone position and venous air embolism". The 330 collected references were reviewed for quality. In combination with review of current standard textbooks these references form the basis for the current report.

[Cerebral risks in surgical position: position of the body, position of the brain]

The posture of the neurosurgical patient depends first on the approach and working position of the surgeon, and the spatial orientation during surgery. Venous outflow is probably the major factor for optimal brain retraction and for preventing venous haemorrhage. No one of the postures presently in use is fully free from the risk of air embolism. Respiratory and cardiac diseases are often limiting factors for the choice of a posture. Thoracic and abdominal compression must be cautiously avoided.

Experimental therapies to support the failing lung

Many conventional therapies are designed to treat acute lung injury. Although evidence exists that improved outcomes are a result of these therapies, mortality remains high in this population. Perhaps one of the key reasons why mortality remains high in the failing lung population is that current therapies do not "cure" the problem; current therapies are designed to support the lung, rather than fix the pulmonary problem. In this paper, a review of new and experimental therapies to support the failing lung are presented. Therapies such as prone positioning, nitric oxide, and mediator therapies are addressed. It is likely that newer therapies offer the most hope for improving the high mortality associated with acute lung injury.

The effect of four different surgical prone positions on cardiovascular parameters in healthy volunteers

Twenty healthy volunteers were placed in four different surgical prone positions: on pillows, on an evacuatable mattress, on pelvic props and in the knee-chest position. The normal supine position was used as a control for the measurement of cardiovascular parameters. Mean arterial pressure was measured by automated oscillotonometry. Transthoracic electrical bioimpedance was used to measure cardiac output and heart rate. Cardiac index and total vascular resistance index were derived from these data. No significant changes in heart rate or mean arterial pressure occurred when the volunteers were moved from the supine position to any of the four prone positions or when returned to the supine position again. Cardiac index decreased significantly on going from the supine to the knee-chest position (20%) and onto the props (17%) but not onto the evacuatable mattress (11%) or the pillows (3%).