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The University of British Columbia Nepal Expedition took place over several months in the fall of 2016 and was comprised of an international team of 37 researchers. This paper describes the objectives, study characteristics, organization and management of this expedition, and presents novel blood gas data during acclimatization in both lowlanders and Sherpa. An overview and framework for the forthcoming publications is provided. The expedition conducted 17 major studies with two principal goals-to identify physiological differences in: 1) acclimatization; and 2) responses to sustained high-altitude exposure between lowland natives and people of Tibetan descent. We performed observational cohort studies of human responses to progressive hypobaric hypoxia (during ascent), and to sustained exposure to 5050 m over 3 weeks comparing lowlander adults (n = 30) with Sherpa adults (n = 24). Sherpa were tested both with (n = 12) and without (n = 12) descent to Kathmandu. Data collected from lowlander children (n = 30) in Canada were compared with those collected from Sherpa children (n = 57; 3400-3900m). Studies were conducted in Canada (344m) and the following locations in Nepal: Kathmandu (1400m), Namche Bazaar (3440m), Kunde Hospital (3480m), Pheriche (4371m) and the Ev-K2-CNR Research Pyramid Laboratory (5050m). The core studies focused on the mechanisms of cerebral blood flow regulation, the role of iron in cardiopulmonary regulation, pulmonary pressures, intra-ocular pressures, cardiac function, neuromuscular fatigue and function, blood volume regulation, autonomic control, and micro and macro vascular function. A total of 335 study sessions were conducted over three weeks at 5050m. In addition to an overview of this expedition and arterial blood gas data from Sherpa, suggestions for scientists aiming to perform field-based altitude research are also presented. Together, these findings will contribute to our understanding of human acclimatization and adaptation to the stress of residence at high-altitude.

Research in traumatic brain injury suggests better patient outcomes when invasive oxygen monitoring is used to detect and correct episodes of brain hypoxia. Invasive brain oxygen monitoring is, however, not routinely used due to the risks, costs and technical challengers. We are developing a non-invasive brain oximeter to address these limitations. The monitor uses the principles of pulse oximetry to record a brain photoplethysmographic waveform and oxygen saturations. We undertook a study in volunteers to assess the new monitor. We compared the temporal changes in the brain and skin oxygen saturations in six volunteers undergoing progressive hypoxia to reach arterial saturations of 70%. This approach provides a method to discriminate potential contamination of the brain signal by skin oxygen levels, as the responses in brain and skin oxygen saturations are distinct due to the auto-regulation of cerebral blood flow to compensate for hypoxia. Conventional pulse oximetry was used to assess skin oxygen levels. Blood was also collected from the internal jugular vein and correlated with the brain oximeter oxygen levels. At baseline, a photoplethysmographic waveform consistent with that expected from the brain was obtained in five subjects. The signal was adequate to assess oxygen saturations in three subjects. During hypoxia, the brain's oximeter oxygen saturation fell to 74%, while skin saturation fell to 50% (P<0.0001). The brain photoplethysmographic waveform developed a high-frequency oscillation of ~7 Hz, which was not present in the skin during hypoxia. A weak correlation between the brain oximeter and proximal internal jugular vein oxygen levels was demonstrated, R =0.24, =0.01. Brain oximeter oxygen saturations were relatively well preserved compared to the skin during hypoxia. These findings are consistent with the expected physiological responses and suggest skin oxygen levels did not markedly contaminate the brain oximeter signal.

Background Optimal fluid therapy in the perioperative and critical care settings depends on understanding the underlying cardiovascular physiology and individualizing assessment of the dynamic patient state. Methods The Perioperative Quality Initiative (POQI-5) consensus conference brought together an international team of multidisciplinary experts to survey and evaluate the literature on the physiology of volume responsiveness and perioperative fluid management. The group used a modified Delphi method to develop consensus statements applicable to the physiologically based management of intravenous fluid therapy in the perioperative setting. Discussion We discussed the clinical and physiological evidence underlying fluid responsiveness and venous capacitance as relevant factors in fluid management and developed consensus statements with clinical implications for a broad group of clinicians involved in intravenous fluid therapy. Two key concepts emerged as follows: (1) The ultimate goal of fluid therapy and hemodynamic management is to support the conditions that enable normal cellular metabolic function in order to produce optimal patient outcomes, and (2) optimal fluid and hemodynamic management is dependent on an understanding of the relationship between pressure, volume, and flow in a dynamic system which is distensible with variable elastance and capacitance properties.

BackgroundSpinal anesthesia is commonly administered for lower limb total joint arthroplasty, but the prolonged motor and sympathetic block associated with bupivacaine can delay recovery. In contrast, lidocaine, with its swift onset and intermediate duration, is an attractive alternative that is well-tailored for outpatient lower limb surgery. It has historically been associated with transient neurologic symptoms (TNS), a self-limiting but potentially distressing pain syndrome. The incidence of TNS reported in older studies varies widely, often exceeding 20%, which has led to a decline in the use of lidocaine for spinal anesthesia.ObjectiveThis study aimed to evaluate the contemporary incidence of TNS following lidocaine spinal anesthesia in the context of an established multimodal analgesic protocol for total knee and hip arthroplasty.FindingsA retrospective review of 1026 patients undergoing knee and hip arthroplasty with lidocaine spinal anesthesia was conducted. We queried our postoperative block database, which included questions specifically related to TNS, including the onset of new non-surgical back or thigh pain following resolution of the spinal block and any other associated symptoms related to TNS. Of the 1011 patients included in the final analysis, only two (0.2%, 95% CI 0.02 to 0.71%) were diagnosed with TNS, both of whom had mild, self-limited symptoms that resolved within 48–72 hours. No cases of prolonged motor or sensory block, cauda equina syndrome, or other significant complications were observed. The low incidence of TNS in this cohort contrasts sharply with historical reports and may be attributable to concurrent administration of comprehensive multimodal analgesics, including acetaminophen, non-steroidal anti-inflammatory drug, intravenous ketamine, and dexamethasone.ConclusionsLidocaine spinal anesthesia for total joint arthroplasty is associated with a negligible incidence of TNS in the setting of multimodal analgesia. These findings challenge historical concerns regarding the safety of spinal lidocaine and support its use as a viable alternative for outpatient joint replacement surgery.

The most common approach to the ACB involves a lateral-to-medial needle path.2 This can put the NVM directly in the trajectory of the needle, predisposing it to needle injury. Following this, the nerve can routinely be observed as a hyperechoic structure contrasted against the background of local anesthetic. Adductor canal block versus femoral nerve block for analgesia after total knee arthroplasty: a randomized, double-blind study. The nerves of the adductor canal and the innervation of the knee: an anatomic study. Anatomy and potential clinical significance of the vastoadductor membrane. Surg Radiol Anat 2007; 29: 569–73. doi:10.1007/s00276-007-0230-4 5 Andersen HL, Andersen SL, Tranum-Jensen J. The spread of injectate during saphenous nerve block at the adductor canal: a cadaver study.

The roles of involuntary breathing movements (IBMs) and cerebral oxygen delivery in the tolerance to extreme hypoxemia displayed by elite breath-hold divers are unknown. Cerebral blood flow (CBF), arterial blood gases (ABGs), and cardiorespiratory metrics were measured during maximum dry apneas in elite breath-hold divers (n=17). To isolate the effects of apnea and IBM from the concurrent changes on ABG, end-tidal forcing (‘clamp’) was then used to replicate an identical temporal pattern of decreasing arterial PO2 (PaO2) and increasing arterial PCO2 (PaCO2) while breathing. End-apnea PaO2 ranged from 23  to 37 mm Hg (30±7 mm Hg). Elevation in mean arterial pressure was greater during apnea than during clamp reaching +54±24% versus 34±26%, respectively; however, CBF increased similarly between apnea and clamp (93.6±28% and 83.4±38%, respectively). This latter observation indicates that during the overall apnea period IBM per se do not augment CBF and that the brain remains sufficiently protected against hypertension. Termination of apnea was not determined by reduced cerebral oxygen delivery; despite 40% to 50% reductions in arterial oxygen content, oxygen delivery was maintained by commensurately increased CBF.

Abstract Objective. To define clinical phenotypes of postamputation pain and identify markers of risk for the development of chronic pain. Design. Cross-sectional study of military service members enrolled 3-18 months after traumatic amputation injury. Setting. Military Medical Center Subjects. 124 recent active duty military service members Methods. Study subjects completed multiple pain and psychometric questionnaires to assess the qualities of phantom and residual limb pain. Medical records were reviewed to determine the presence/absence of a regional catheter near the time of injury. Subtypes of residual limb pain (somatic, neuroma, and complex regional pain syndrome) were additionally analyzed and associated with clinical risk factors. Results. A majority of enrolled patients (64.5%) reported clinically significant pain (pain score ≥3 averaged over previous week). 61% experienced residual limb pain and 58% experienced phantom pain. When analysis of pain subtypes was performed in those with residual limb pain, we found evidence of a sensitized neuroma in 48.7%, somatic pain in 40.8%, and complex regional pain syndrome in 19.7% of individuals. The presence of clinically significant neuropathic residual limb pain was associated with symptoms of PTSD and depression. Neuropathic pain of any severity was associated with symptoms of all four assessed clinical risk factors: depression, PTSD, catastrophizing, and the absence of regional analgesia catheter. Conclusions. Most military service members in this cohort suffered both phantom and residual limb pain following amputation. Neuroma was a common cause of neuropathic pain in this group. Associated risk factors for significant neuropathic pain included PTSD and depression. PTSD, depression, catastrophizing, and the absence of a regional analgesia catheter were associated with neuropathic pain of any severity.

The role of cerebral blood flow (CBF) on a maximal breath-hold (BH) in ultra-elite divers was examined. Divers (n = 7) performed one control BH, and one BH following oral administration of the non-selective cyclooxygenase inhibitor indomethacin (1.2 mg/kg). Arterial blood gases and CBF were measured prior to (baseline), and at BH termination. Compared to control, indomethacin reduced baseline CBF and cerebral delivery of oxygen (CDO ) by about 26% (p < 0.01). Indomethacin reduced maximal BH time from 339 ± 51 to 319 ± 57 seconds (p = 0.04). In both conditions, the CDO remained unchanged from baseline to the termination of apnea. At BH termination, arterial oxygen tension was higher following oral administration of indomethacin compared to control (4.05 ± 0.45 vs. 3.44 ± 0.32 kPa). The absolute increase in CBF from baseline to the termination of apnea was lower with indomethacin (p = 0.01). These findings indicate that the impact of CBF on maximal BH time is likely attributable to its influence on cerebral H washout, and therefore central chemoreceptive drive to breathe, rather than to CDO

The effects of partial acclimatization to high altitude (HA; 5,050 m) on cerebral metabolism and cerebrovascular function have not been characterized. We hypothesized (1) increased cerebrovascular reactivity (CVR) at HA; and (2) that CO2 would affect cerebral metabolism more than hypoxia. PaO2 and PaCO2 were manipulated at sea level (SL) to simulate HA exposure, and at HA, SL blood gases were simulated; CVR was assessed at both altitudes. Arterial–jugular venous differences were measured to calculate cerebral metabolic rates and cerebral blood flow (CBF). We observed that (1) partial acclimatization yields a steeper CO2-H+ relation in both arterial and jugular venous blood; yet (2) CVR did not change, despite (3) mean arterial pressure (MAP)-CO2 reactivity being doubled at HA, thus indicating effective cerebral autoregulation. (4) At SL hypoxia increased CBF, and restoration of oxygen at HA reduced CBF, but neither had any effect on cerebral metabolism. Acclimatization resets the cerebrovasculature to chronic hypocapnia.

We report three patients undergoing cervical spine surgery who required awake fiberoptic intubation, and in whom sedation was provided using a dexmedetomidine infusion. Dexmedetomidine was used to provide a moderate level of sedation without causing respiratory distress or hemodynamic instability during fiberoptic intubation. Conditions for intubation were acceptable in all three patients after co-administration of topical anesthesia. Dexmedetomidine may serve as a useful adjunct for this procedure. The anesthetic management and anesthetic implications of using dexmedetomidine infusions for awake fiberoptic intubation are discussed.