Meanwhile, in consideration to possible jugular impediments and other forms of complications are also associated with the etiologies of circulatory obstruction and venous pooling. Jugular complications arise when head and neck contact come in very close, which usually causes a direct pressure in the neck arterial region. Excess pressure in the head can be caused by the neuropraxia of the posterior auricular nerve (Gill and Hawkins 2005 p. 126). According to Krettek and Aschemann (2005), sitting position may cause over stretching of the cervical medulla with a decrease in spinal perfusion resulting to position-induced tetraplegic injuries (p. 123).
Monitoring the blood pressure and signs of halted venous returns are crucial considerations in assessing a patient who is undergoing surgery under beach-chair position. Although hemodynamic complications during the process of surgical operation occur, Hedge and Avatgere (2000) and Lobato, Gravenstein and Kirby (2007) have considered thee occurrences as non-serious threats to the health of the patient since most cases normally survive the dangers of complications. However, complications that may arise are diverse and complicated in nature.
According to Gill and Hawkins (2005), other complications that arise include the tracheal compression caused by periarticular fluid accumulation, visual loss and opthalmoplegia, pneumomediastinum from subcutaneous emphysema, spontaneous pneumothorax and negative pressure pulmonary edema (p. 126). The series of complications in the thoracic region is contributed mainly by the shifting of intrathoracic pressure to extrathoracic pressure, which changes the prevailing pressure environment within the cardiothoracic region. c. Cardiovascular Implications
Considering the physiological mechanism under the complications resulted by the surgical sitting position, most surgical procedures (e. g. shoulder arthroplasty, laminectomy, etc. ) still utilize such positioning; although, most surgeons prefer not to utilize the said position among cardiovascular cases due to the possibility of further decrease in blood pressure. According to Finlay, Kneedler and Dodge (1994), sitting position mainly compromise the systemic circulation due to the reduction of vascular pressure and cardiac exertion brought by the shifting of gravitational focal point (p. 328).
In studies conducted by Walch and Boileau (1998), hypotension and loss of consciousness have occurred even among non-anaesthetized patients (p. 53). The pooling blood and decrease of venous returns are usually resolved by additional infusion of intravenous fluids. During the events of hypotension, various circulatory responses are expected, specifically (1) the decline in arterial pressure exertion due to the decrease in cardiac output and stroke volume, and (2) the possibility of triggering respiratory distress due to compromised cardiopulmonary circulation and shifting of thoracic pressure from inner to external sections.
According to Lobato, Gravenstein and Kirby (2007), Hypotension is caused by the decline in arterial pressure and vascular resistance, which consequently reduces and prolongs the circulating blood within the systemic circulation (p. 851). Hypotension further aggravates the formulation of VAE, most especially in the upper extremities where circulatory reduction frequently occurs. MAP, as the indicator of circulatory perfusion in organs of the body, is markedly decreased from 7 to 15 mmHg during the occurrence of hypotension (Krettek and Aschemann 2005 p. 123).
In the study conducted by Bithal, Pandia and Dash et al. (2004), four hundred and thirty patients (demographics= 334 adults; age >=18 and 96 children; age <=18) have been scheduled in a planned posterior fossa surgery in sitting position. The implementation has covered the periods of January 1989 to December 1994 wherein end-tidal carbon dioxide monitoring is conducted to test the implications of hypotension or MAP decrease in the formulation of venous air embolism. During the study, marked decline of MAP is further treated with crystalloids and vasopressor with support from fluid replacement.
Results of the study show 28% (n=93 out of 334) incidence of air embolism among adults, while 22% (n=21 out of 96) incidence rate in children have occurred. According to the findings of Bithal, Pandia and Dash et al. (2004) study, embolic episodes were accompanied by marked decline in the MAP among 37% of adults (n=34 out 93) and in 33% of children (n=7 out of 21) (P = 0. 98). In order to resolve the physiological conflict from pre-embolic levels to arterial pressure, 53% of adults (n=18 out of 34) and 43% of children (n=3 out of 7) were administered vasopressors (P = 0. 94).
The conclusion of the study has not shown any significant variations in MAP decrease and VAE occurrences among adults and children. According to Lobato, Gravenstein and Kirby (2007), MAP usually remains unchanged in most positions, such as upright or fowler’s position; however, in the sitting position, an approximate of 15% decrease has been observed in a non-anesthetized patient and can further decrease if the patient is under anesthesia due to the physiological vasodilatation, impaired venous returns and various circulatory alterations (p. 851).