Ihab R. Kamel

The use of somatosensory evoked potentials to determine the relationship between patient positioning and impending upper extremity nerve injury during spine surgery: a retrospective analysis.

Somatosensory evoked potential (SSEP) monitoring is used to prevent nerve damage in spine surgery and to detect changes in upper extremity nerve function. Upper extremity SSEP conduction changes may indicate impending nerve injury. We investigated the effect of operative positioning on upper extremity nerve function retrospectively in 1000 consecutive spine surgeries that used SSEP monitoring. The vast majority (92%) of upper extremity SSEP changes were reversed by modifying the arm position and were therefore classified as position-related. The incidence of position-related upper extremity SSEP changes was calculated and compared for five different surgical positions: supine arms out, supine arms tucked, lateral decubitus position, prone arms tucked, and the prone “superman” position. The overall incidence of position-related upper extremity SSEP changes was 6.1%. The lateral decubitus position (7.5%) and prone superman position (7.0%) had a significantly more frequent incidence of position-related upper extremity SSEP changes (P < 0.0001, Z-test for Poisson counts) compared with other positions (1.8%–3.2%). No patient with a reversible SSEP change developed a new postoperative deficit in the affected extremity. SSEP monitoring is of value in identifying and reversing impending upper extremity peripheral nerve injury.

The effects of intraoperative hypothermia on surgical site infection: An analysis of 524 trauma laparotomies

Objectives:Our primary study objective was to determine whether intraoperative hypothermia predisposes patients to postoperative surgical site infections (SSI) after trauma laparotomy. Background:Although intraoperative normothermia is an important quality performance measure for patients undergoing colorectal surgery, the effects of intraoperative hypothermia on SSI remain unstudied in trauma. Methods:A review of all patients (July 2003–June 2008) who survived 4 days or more after urgent trauma laparotomy at a level I trauma center revealed 524 patients. Patient characteristics, along with preoperative and intraoperative care focusing on SSI risk factors, including the depth and duration of intraoperative hypothermia, were evaluated. The primary outcome measure was the diagnosis of SSI within 30 days of surgery. Cut-point analysis of the entire range of lowest intraoperative temperature measurements established the temperature nadir that best predicted SSI development. Single and multiple variable logistic regression determined SSI predictors. Results:The mean intraoperative temperature nadir of the study population (n = 524) was 35.2°C ± 1.1°C and 30.5% had at least 1 temperature measurement less than 35°C. Patients who developed SSI (36.1%) had a lower mean intraoperative temperature nadir (P = 0.009) and had a greater number of intraoperative temperature measurements <35°C (P < 0.001) than those who did not. Cut-point analysis revealed an intraoperative temperature of 35°C as the nadir temperature most predictive of SSI development. Multivariate analysis determined that a single intraoperative temperature measurement less than 35°C independently increased the site infection risk 221% per degree below 35°C (OR: 2.21; 95% CI: 1.24–3.92, P = 0.007). Conclusions:Just as intraoperative hypothermia is an SSI risk factor in patients undergoing elective colorectal procedures, intraoperative hypothermia less than 35°C adversely affects SSI rates after trauma laparotomy. Our results suggest that intraoperative normothermia should be strictly maintained in patients undergoing operative trauma procedures.

Positioning patients for spine surgery: Avoiding uncommon position-related complications

Positioning patients for spine surgery is pivotal for optimal operating conditions and operative-site exposure. During spine surgery, patients are placed in positions that are not physiologic and may lead to complications. Perioperative peripheral nerve injury (PPNI) and postoperative visual loss (POVL) are rare complications related to patient positioning during spine surgery that result in significant patient disability and functional loss. PPNI is usually due to stretch or compression of the peripheral nerve. PPNI may present as a brachial plexus injury or as an isolated injury of single nerve, most commonly the ulnar nerve. Understanding the etiology, mechanism and pattern of injury with each type of nerve injury is important for the prevention of PPNI. Intraoperative neuromonitoring has been used to detect peripheral nerve conduction abnormalities indicating peripheral nerve stress under general anesthesia and to guide modification of the upper extremity position to prevent PPNI. POVL usually results in permanent visual loss. Most cases are associated with prolonged spine procedures in the prone position under general anesthesia. The most common causes of POVL after spine surgery are ischemic optic neuropathy and central retinal artery occlusion. Posterior ischemic optic neuropathy is the most common cause of POVL after spine surgery. It is important for spine surgeons to be aware of POVL and to participate in safe, collaborative perioperative care of spine patients. Proper education of perioperative staff, combined with clear communication and collaboration while positioning patients in the operating room is the best and safest approach. The prevention of uncommon complications of spine surgery depends primarily on identifying high-risk patients, proper positioning and optimal intraoperative management of physiological parameters. Modification of risk factors extrinsic to the patient may help reduce the incidence of PPNI and POVL.

Oral and craniofacial pain: diagnosis, pathophysiology, and treatment.

The craniofacial region constitutes one of the most common sites of pain in the human body. 1 The multiplicity and frequent interconnections of pain-sensitive structures in the face make it difficult to ascertain the source of pain. Pain is a complex phenomenon that comprises sensory-discriminative, cognitive, affective, and emotional aspects. 1 This fact renders the management of facial pain syndromes a clinical challenge. Thorough knowledge of the various clinical presentations of each disorder is essential for proper management as well as neuroanatomic and patho-physiological aspects of craniofacial pain. Oral medicine and dental treatment plays a pivotal role in delineating underlying pathology and thereby is essential for proper management. Headache can contribute to craniofacial pain in various clinical presentations, since a vast majority of headache disorders can be identified as the cause of craniofacial pain. Headache can be primary headache disorders, where the headache is the illness itself; this category includes migraine, tension-type headache, chronic paroxysmal hemicrania, idiopathic intracranial hemicrania, and cluster headache. Secondary headache may be due to identifiable disorders or structural lesions, such as cervicogenic headache. Due to its breadth and complexity, primary headache is not discussed in this chapter. This chapter comprises the diagnosis, pathophysiology, investigations, and treatment of some of the common and significant etiologies of non-headache, craniofacial pain (Table 1).

N-methyl-D-aspartate (NMDA) antagonists--S(+)-ketamine, dextrorphan, and dextromethorphan--act as calcium antagonists on bovine cerebral arteries.

Ketamine, an intravenous anesthetic and a major drug of abuse, is a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist. Ketamines enantiomer, S(+)-ketamine, acts stereoselectively on neuronal NMDA receptors. The purpose of this in vitro study was to compare the direct effects of S(+)-ketamine, 2 other noncompetitive NMDA receptor antagonists (dextrorphan and dextromethorphan), and the calcium entry blocker nimodipine on the cerebral vasculature, using bovine middle cerebral arteries as an experimental model. Arterial rings were mounted in isolated tissue chambers equipped with isometric tension transducers to obtain pharmacologic dose-response curves. In the absence of exogenous vasoconstrictors, the NMDA antagonists or nimodipine had negligible effects on cerebral arterial tone. When rings were preconstricted with either potassium or the stable thromboxane A2 mimetic U46619, the NMDA antagonists and nimodipine each produced dose-dependent relaxation. Prior endothelial stripping had no effect on subsequent drug-induced relaxation of K+-constricted rings. In Ca2+-deficient media containing either potassium or U46619, the NMDA antagonists and nimodipine each produced competitive inhibition of subsequent Ca2+induced constriction. In additional experiments, arterial strips were mounted in isolated tissue chambers to directly measure calcium uptake, using 45calcium (45Ca) as a radioactive tracer. The NMDA antagonists and nimodipine each blocked potassium-stimulated or U46619-stimulated 45Ca uptake into arterial strips. These results indicate that S(+)-ketamine, dextrorphan, and dextromethorphan, like nimodipine, directly dilate cerebral arteries by acting as calcium antagonists; they all inhibit 45Ca uptake through both potential-operated (potassium) and receptor-operated (U46619) channels in cerebrovascular smooth muscle.

The Use of Somatosensory Evoked Potentials to Determine the Relationship Between Intraoperative Arterial Blood Pressure and Intraoperative Upper Extremity Position-Related Neurapraxia in the Prone Surrender Position During Spine Surgery: A Retrospective Analysis.

BACKGROUND:Peripheral nerve injury is a significant perioperative problem. Intraoperative position-related neurapraxia may indicate impending peripheral nerve injury and can be detected by changes in somatosensory evoked potentials (SSEP). The purpose of this retrospective analysis of spine surgeries performed under general anesthesia with SSEP monitoring was to determine the relationship between intraoperative mean arterial blood pressure (MAP) and intraoperative upper extremity position–related neurapraxia in the prone surrender (superman) position. METHODS:We reviewed a computerized database of spine surgeries performed on adult patients in the prone surrender position. The authors reviewed intraoperative SSEP monitoring reports to identify the patients who developed intraoperative upper extremity position–related neurapraxia (case group) and patients who did not (control group). Propensity matching was performed to derive 2 demographically matched groups. Preoperative and intraoperative variables were included in the univariate Cox regression analysis of risk factors associated with neurapraxia. Multivariate Cox regression models were used to identify the independent risk factors. RESULTS:One hundred fifty-two patients were included in the analysis. The case group included 32 patients, whereas the control group included 120 matched patients. Intraoperative MAP <55 mm Hg for a total duration of ≥5 minutes was an independent risk factor associated with a greater incidence of upper extremity position–related neurapraxia compared with a duration of <5 minutes with MAP <55 mm Hg (hazard ratio, 3.43; confidence interval, 1.445–8.148; P = 0.0052). Intraoperative MAP >80 mm Hg for a total duration of >55 minutes was an independent predictor associated with a lower incidence of neurapraxia compared with a total duration ⩽55 minutes (hazard ratio, 0.341; confidence interval, 0.163–0.717; P = 0.0045). CONCLUSIONS:In this study, we identified the changes in intraoperative MAP as independent predictors associated with upper extremity position–related neurapraxia in the prone surrender position under general anesthesia.

Use of Neuromuscular Blocking Agents in the Intensive Care Unit

In the mid-1980s, the two intermediate-duration neuromuscular blocking (NMB) agents atracurium and vecuronium were introduced into practice; within a few years, these accounted for the majority of NMB agent use in critically ill patients. In association with the introduction of these new agents, there was an expansion of the indications for muscle paralysis in this country, which was at least partially related to new ventilatory modes and technologic advances that necessitated cooperative, sedate, or immobile patients. These new indications for an immobile patient, coupled with an expanded knowledge of available NMB agents, led to a dramatic increase in the use of muscle paralysis in the intensive care unit (ICU). In association with that increased use came a growing awareness of the potential for severe complications and side effects.

Severe intraoperative hypertension and opioid-resistant postoperative pain in a methadone-treated patient.

Patients who are treated with methadone present challenges for the anesthesiologist. We report the untoward effects of rapid preoperative methadone tapering on the operative and perioperative course of a patient who required emergency surgery. The patients exaggerated stress response to surgery and severe intractable postoperative pain might have resulted from unrecognized methadone withdrawal. Continuation of methadone treatment in patients who have surgery may prevent exaggerated intraoperative hemodynamic responses to surgical stimuli and unnecessary postoperative suffering.

Intralipid Therapy for Inadvertent Peripheral Nervous System Blockade Resulting from Local Anesthetic Overdose

Although local anesthetics have an acceptable safety profile, significant morbidity and mortality have been associated with their use. Inadvertent intravascular injection of local anesthetics and/or the use of excessive doses have been the most frequent causes of local anesthetic systemic toxicity (LAST). Furthermore, excessive doses of local anesthetics injected locally into the tissues may lead to inadvertent peripheral nerve infiltration and blockade. Successful treatment of LAST with intralipid has been reported. We describe a case of local anesthetic overdose that resulted in LAST and in unintentional blockade of peripheral nerves of the lower extremity; both effects completely resolved with administration of intralipid.

The use of the Molt mouth gag to assist in oral fiberoptic tracheal intubation of a developmentally challenged patient presenting with severe trismus.

Airway management in developmentally challenged, and often uncooperative, patients presents difficulty for the anesthesiologist and may be further complicated by severe trismus. We describe a case wherein the use of the Molt mouth gag significantly facilitated airway control using fiberoptic tracheal intubation.