Biomedical subjects

Peter E Andersen

Publications and source records attributed to Peter E Andersen.

29 records · Page 2Linked to original sources

PubMed2002

Derivation of a Monte Carlo method for modeling heterodyne detection in optical coherence tomography systems.

A Monte Carlo (MC) method for modeling optical coherence tomography (OCT) measurements of a diffusely reflecting discontinuity embedded in a scattering medium is presented. For the first time to the authors' knowledge it is shown analytically that the applicability of an MC approach to this optical geometry is firmly justified, because, as we show, in the conjugate image plane the field reflected from the sample is delta-correlated from which it follows that the heterodyne signal is calculated from the intensity distribution only. This is not a trivial result because, in general, the light from the sample will have a finite spatial coherence that cannot be accounted for by MC simulation. To estimate this intensity distribution adequately we have developed a novel method for modeling a focused Gaussian beam in MC simulation. This approach is valid for a softly as well as for a strongly focused beam, and it is shown that in free space the full three-dimensional intensity distribution of a Gaussian beam is obtained. The OCT signal and the intensity distribution in a scattering medium have been obtained for several geometries with the suggested MC method; when this model and a recently published analytical model based on the extended Huygens-Fresnel principle are compared, excellent agreement is found.

Computer Simulation↗

PubMed2002

Results of selective neck dissection in management of the node-positive neck.

BACKGROUND: Although increasingly accepted in treatment of the N0 neck, use of selective neck dissection in patients with node-positive squamous cell carcinoma of the head and neck remains controversial. OBJECTIVE: To determine the oncologic efficacy of selective node dissection in patients with node-positive squamous carcinoma of the head and neck. SETTING: Three tertiary care academic/Veterans Affairs medical centers. METHODS: Ten-year retrospective medical chart review of 106 previously untreated clinically and pathologically node-positive patients undergoing 129 selective neck dissections and followed for a minimum of 2 years or until patient death. RESULTS: Regional metastasis was clinically staged as N1 in 58 patients (54.7%), N2a in 5 (4.7%), N2b in 28 (26.4%), N2c in 14 (13.2%), and N3 in 1 (0.9%). Extracapsular extension of tumor was present in 36 patients (34.0%), and postoperative radiation therapy was administered to 76 patients (71.7%). Overall, 9 patients experienced disease recurrence in the neck. Six of these recurrences were in the side of the neck that had undergone selective neck dissection, for a regional control rate of 94.3%. CONCLUSIONS: These results support the use of selective neck dissection in carefully selected patients with clinically node-positive squamous cell carcinoma of the head and neck region. Regional control rates comparable to those achieved with comprehensive operations can be achieved in appropriately selected patients.

Adult↗

PubMed2002

Pulmonary atelectasis after reconstruction with a rectus abdominis free tissue transfer.

BACKGROUND: Atelectasis is one of the most common postoperative complications encountered in head and neck surgery. Risk factors include preexisting pulmonary disease, the procedure performed, and the length of anesthetic. Regional flaps used to reconstruct defects in the head and neck predispose to radiographic atelectasis. The rectus abdominis myocutaneous flap is usually transferred as a free tissue transfer. Harvesting the flap results in abdominal wall pain and postoperative splinting that may contribute to an increased development of atelectasis. To our knowledge, this issue has not been previously examined. DESIGN: Retrospective review. RESULTS: Fifty-three patients underwent rectus abdominis myocutaneous free flap reconstruction following major ablative procedures for head and neck cancer. The flap size ranged from 5 x 7 to 25 x 27 cm. Most flaps were 8 x 15 cm. The cutaneous area transferred ranged from 35 to 600 cm(2) (mean, 120 cm(2)). These patients were compared with a group of 53 patients who were matched for age, sex, length of the procedure, and stage of disease. Postoperative atelectasis was radiographically detected in 37 (70%) of the patients who underwent rectus abdominis myocutaneous free flap reconstruction vs 41 (77%) of the controls. Major atelectasis was not encountered in any patient in either group. Patients with a larger cutaneous paddle (>120 cm(2)) had a higher atelectasis score than patients with smaller cutaneous paddles (< or =120 cm(2)) (P =.02). CONCLUSIONS: The incidence of radiographic postoperative atelectasis in patients undergoing rectus abdominis myocutaneous free tissue transfer is high. The degree of atelectasis is small, and the clinical correlation and relevance are minimal.

Head and Neck Neoplasms↗

PubMed2002

The predictive value of perioperative calcium levels after thyroid/parathyroid surgery.

BACKGROUND: This work was done to determine whether the slope of change between preoperative and early postoperative (2 hr and 8 hr) ionized calcium levels (ciCa) could predict significant postoperative hypocalcemia. METHODS: We did a retrospective chart review of 79 patients undergoing thyroid (n = 56) or parathyroid surgery (n = 23) where overall parathyroid function was felt to be at risk. Results/Conclusions A positive slope between the preoperative ciCa and any postoperative ciCa or the first two postoperative ciCa's predicted normocalcemia in 100% of patients. For the thyroid group, the difference in the slope of the change from preoperative ciCa to first (<2 hours) postoperative ciCa (-15.940%/hours vs -9.375%/hours, p =.082) did not differentiate patients who developed hypocalcemia (n = 11) and those who remained normocalcemic (n = 45). By contrast the slope of change from preoperative ciCa to the second postoperative (8 hr) ciCa (-1.671%/ hour vs -0.849%/hours, p =.006) and first to second postoperative ciCa (-1.022%/hour vs -0.473%/hour, p =.001) did. For the parathyroid group, none of the differences in similar comparisons between the normocalcemic (n = 20) and hypocalcemic patients (n = 3) approached statistical significance. The relatively small number of patients who became hypocalcemic in this study precluded definition of an absolute slope of calcium level change above which normocalcemia can be assured.

Adult↗

PubMed2002

First bite syndrome: a complication of surgery involving the parapharyngeal space.

INTRODUCTION: First bite syndrome (FBS) is the development of pain in the parotid region after the first bite of each meal and can be seen after surgery of the parapharyngeal space. The cause is not clear but has been proposed to involve a loss of sympathetic nerve function to the parotid, causing a denervation supersensitivity of salivary gland myoepithelial cells. The purpose of this study was to review the records of 12 patients with FBS to determine any common features of the operations performed that would support this theory of parotid "sympathectomy" as an etiologic factor of FBS. METHODS: Retrospective review of 12 patients with FBS managed at two tertiary care centers. RESULTS: Twelve patients were diagnosed with FBS after surgery involving the parapharyngeal space. All patients had most of their parotid gland preserved. Six patients exhibited a postoperative Horner's syndrome, suggesting sympathetic chain interruption. The six patients without Horner's syndrome were found to have undergone external carotid artery ligation inferior to the parotid gland, suggesting an interruption of sympathetic innervation to the parotid gland itself. CONCLUSIONS: Preservation of parotid gland tissue and a loss of its sympathetic nerve supply, whether by disruption of the cervical sympathetic chain as evidenced by a Horner's syndrome or more selective denervation by ligation of the external carotid artery with its accompanying sympathetic nerve plexus, were common features of all patients. This series supports the concept of parotid "sympathectomy" as an etiologic factor in FBS.

Carotid Arteries↗

PubMed2002

Management of carotid 'blowout' with endovascular stent grafts.

OBJECTIVES/HYPOTHESIS: Since 1992, endovascular techniques for vascular occlusion and stenting have evolved significantly. Endovascular occlusion of the carotid artery has been used in the management of carotid "blowout." Although it seems logical to expand this application to the use of arterial stents to repair rather than occlude the artery when cerebral cross-circulation is inadequate, concerns remain regarding the placement of a foreign body in a contaminated field. The purpose of the present report is to describe our experience with endovascular stents for control of carotid hemorrhage. STUDY DESIGN: Retrospective case review. METHODS: Retrospective review of three cases of acute or threatened carotid hemorrhage managed with endovascular stent placement. RESULTS: Two patients presented with acute carotid blowout, and one patient with a probable sentinel bleed. All patients previously had been heavily treated with surgery and irradiation: Two had developed pharyngocutaneous fistulas, and one had an open wound filled with tumor that surrounded the carotid artery. All were thought to be at significant risk for stroke if the carotid artery was occluded. In all three patients, stent placement resolved the acute hemorrhage. Mean duration of follow-up was 8.3 months. In two patients, the stent became exposed, ultimately thrombosed or extruded, or both. The third patient had no residual sequelae of stenting but died 3 months later. CONCLUSION: When an unacceptable risk of cardiovascular accident makes occlusion unwise, acute carotid hemorrhage can be successfully managed with directed placement of endovascular stents, but the long-term sequelae of placing these foreign bodies in a field with ongoing contamination make this a temporizing rather than permanent measure for use while more definitive long-term solutions are pursued.

Acute Disease↗

PubMed2002

Intraoperative parathyroid hormone levels in thyroid and parathyroid surgery.

OBJECTIVE: To determine the utility of intraoperative parathyroid hormone measurement in predicting postoperative hypocalcemia after thyroid and parathyroid surgeries that places total parathyroid function at risk. STUDY DESIGN: Retrospective case review. METHODS: The case records of 23 patients undergoing total or completion thyroidectomy and 30 patients undergoing parathyroid exploration were reviewed. All patients had intraoperative parathyroid hormone levels measured. Samples were taken before dissection and 10 minutes after the resection was completed. Serial ionized calcium levels were measured in the postoperative period. Percentages of reduction in PTH levels from preoperative to postresection levels were calculated. Percentages of reduction in PTH level and the absolute value of the intraoperative PTH values were compared with postoperative ionized calcium levels. RESULTS: In the 23 patients who underwent thyroid surgery, the average preoperative and postoperative PTH values were 50 pg/mL (range, 17-87 pg/mL) and 34 pg/mL (range, 4-93 pg/mL), respectively. The average decrease in PTH was 39% (range, 39%-90%). The incidence of hypocalcemia was significantly higher in patients with intraoperative PTH levels less than 15 pg/mL relative to patients with PTH levels greater than 15 pg/mL in this setting ( P=.006). In the 30 patients who underwent parathyroid exploration, average preoperative and postoperative PTH levels were 291 pg/mL (range, 65-1675 pg/mL) and 113.8 pg/mL (range, 6.5-1263 pg/mL) respectively. The intraoperative PTH level did not correlate with postoperative calcium levels in the parathyroid group. Percentages of decrease in PTH levels greater than 60% was statistically associated with surgical cure in this population. CONCLUSIONS: The study demonstrates that intraoperative PTH levels greater than 15 pg/mL after total or completion thyroidectomy indicate a low risk of postoperative hypocalcemia and that these patients may be candidates for outpatient surgery. In the parathyroid group, intraoperative PTH levels do not correlate well with postoperative calcium levels.

Calcium↗

PubMed2002

'Defatting' tracheotomy in morbidly obese patients.

OBJECTIVES/HYPOTHESIS: Standard-sized tracheostomy tubes often fit morbidly obese patients poorly because of increased submental and anterior cervical girth. The surgeon has two options to overcome this problem: Modify the tracheostomy tube to fit the patient or recontour the neck to accommodate a standard tube. The purpose of the study was to assess the safety and morbidity of the latter technique, the "defatting" tracheotomy. STUDY DESIGN: Retrospective cohort study of 23 patients treated between 1994 and 2001 with cervical lipectomy and tracheotomy. METHODS: Medical charts were reviewed for indications, demographics, body mass index, tracheotomy-related complications, and decannulation results. RESULTS: The average age of patients was 50 years (age range, 34-77 y). The mean preoperative body mass index was 55.9 (range, 39.2-73.5). Indications for the procedure were respiratory failure requiring chronic ventilation in 16 patients (70%) and obstructive sleep apnea in 7 (30%). Four patients died postoperatively from causes unrelated to tracheotomy. The mean follow-up time of survivors was 23 months. The overall tracheotomy-related complication rate was 43%. Four patients developed wound infections in the perioperative period, one patient developed a neck abscess, and one patient required neck exploration for control of hemorrhage. Four patients (22%) developed late complications including tracheitis (1), neck abscess (1), and stenosis of the tracheocutaneous tract (2). Eight patients (44%) ultimately had decannulation. CONCLUSIONS: Defatting tracheotomy is a safe technique that allows for the placement of a standard tracheostomy tube in morbidly obese patients. It is associated with a high rate of minor infectious complications. Even so, we think that cervical lipectomy with tracheostomy tube placement is the preferred surgical option for this patient population.

Adipose Tissue↗

PubMed2002

The ulnar fasciocutaneous free flap in head and neck reconstruction.

OBJECTIVES/HYPOTHESIS: The radial forearm fasciocutaneous free flap has become the reconstructive tissue of choice for the majority of soft tissue defects in the head and neck. The forearm skin has many of the ideal soft tissue characteristics that optimize reconstruction and rehabilitation in these patients. The tissue is malleable, supple, and moldable in three dimensions; has a reliable pedicle; and can be harvested with a two-team approach. In some patients, the radial forearm cannot be used. An alternative is to use the adjacent tissue, which shares identical tissue characteristics. This tissue gets its vascular supply from the ulnar artery. The purpose of the report was to describe the authors' experience with the ulnar fasciocutaneous free flap in head and neck reconstruction. STUDY DESIGN: Prospective consecutive case series. METHODS: Retrospective review of all patients undergoing ulnar fasciocutaneous free tissue transfer by a group of microvascular surgeons was performed. Thirty patients underwent free tissue transfer using the ulnar fasciocutaneous free flap. The male-to-female ratio was 3:1. RESULTS: Defects were located in the oral cavity (14), oropharynx (12), neck skin (1), and soft tissue of the lateral skull (3). The average size of the skin paddle that was transferred was 7 x 10 cm (range, 3 x 5 to 9 x 12 cm). The mean area of tissue that was transferred was 70 cm2 (range, 15-108 cm2). Vessel sizes were somewhat smaller than the comparable radial forearm. One patient had complete loss of the skin graft on the donor site. There were no median nerve or other wound-healing problems. Two flaps were lost in the postoperative period. Indications for use of the ulnar fasciocutaneous free flap were failed Allen's test (23), use of a less hairy part of the forearm (3), and surgical preference (4). CONCLUSIONS: The ulnar fasciocutaneous free flap has all of the tissue characteristics of the radial forearm flap. When a radial forearm flap cannot be used and forearm skin is desired, consideration of an ulnar fasciocutaneous free flap should be undertaken.

Female↗

PubMed2002

Metallic tracheal stents: complications associated with long-term use in the upper airway.

The use of metallic airway stents for the treatment of benign airway stenosis is increasingly advocated; however, the long-term safety and efficacy of these devices has not been established. Three case studies involving late but significant proximal tracheal stent complications are reported: 1 related to proximal mechanical stent failure and 2 related to obstructing granulation tissue and stenosis at the proximal stent orifice. Placement of these stents in close proximity to the cricotracheal junction is thought to be primarily responsible for these complications as a result of the excess shearing forces created at the stent-mucosal interface by the differential motion of the stent relative to the rigid subglottic airway and the more distensible trachea. Although the use of metallic stents remains appropriate in cases in which there is a defined and relatively short-term end point for treatment, caution is urged in using them in the proximal trachea for long-term management of benign airway disease.

Endoscopy↗

PubMed2002

Use of allogenic dermis for radial forearm free flap donor site coverage.

OBJECTIVE: The radial forearm free flap has become the method of choice for reconstruction of head and neck defects following oncologic ablation. Harvesting of a radial forearm free flap leaves a donor site defect. This is most commonly closed with a split-thickness skin graft. Morbidity, most commonly owing to a lack of graft take over the tendons, can be quite high. Recently, an acellular matrix (Alloderm) has been advocated to decrease complications at the radial forearm donor site, as well as obviate taking a split-thickness skin graft from the thigh. MATERIAL AND METHODS: Tertiary referral academic centre. Retrospective chart review of 15 patients. Five patients received allogenic dermis, 10 patients received split-thickness skin grafting to the radial forearm donor site. RESULTS: Patients with allogenic dermis took between 12 and 16 weeks to heal completely. Patients undergoing split-thickness skin graft were completely healed within 4 to 6 weeks. Cosmesis was judged to be marginally better in the allogenic dermis group. Allogenic dermis placement had a greater impact on hand function owing to prolonged healing, whereas patients with split-thickness skin graft required wound care at the thigh for a 2- to 3-week period owing to the harvesting of the skin graft. CONCLUSIONS: Allogenic dermis may be a viable alternative to split-thickness skin grafting and radial forearm free flap donor sites. Prolonged healing with subsequent increased health care services use needs to be addressed.

Aged↗