Prolonged post-hyperventilation apnea in two young adults with hyperventilation syndrome

Background

The prognosis of hyperventilation syndrome (HVS) is generally good. However, it is important to proceed with care when treating HVS because cases of death following hyperventilation have been reported. This paper was done to demonstrate the clinical risk of post-hyperventilation apnea (PHA) in patients with HVS.

Case presentation

We treated two patients with HVS who suffered from PHA. The first, a 21-year-old woman, had a maximum duration of PHA of about 3.5?minutes and an oxygen saturation (SpO₂) level of 60%. The second patient, a 22-year-old woman, had a maximum duration of PHA of about 3?minutes and an SpO₂ level of 66%. Both patients had loss of consciousness and cyanosis. Because there is no widely accepted regimen for treating patients with prolonged PHA related to HVS, we administered artificial ventilation to both patients using a bag mask and both recovered without any after effects.

Conclusion

These cases show that some patients with HVS develop prolonged PHA or severe hypoxia, which has been shown to lead to death in some cases. Proper treatment must be given to patients with HVS who develop PHA to protect against this possibility. If prolonged PHA or severe hypoxemia arises, respiratory assistance using a bag mask must be done immediately.

     

Plasma adenosine and hypoxemia in patients with sleep apnea

Severe hypoxemia causes ATP depletion and increased adenosine production in many body tissues. Therefore we hypothesized that patients with sleep apnea and severe hypoxemia during sleep have higher adenosine production and higher plasma adenosine levels than patients without hypoxemia. Twelve patients with sleep apnea and six normal volunteers had plasma adenosine levels measured by high-performance liquid chromatography. Each patient with sleep apnea had a polysomnograph sleep study with oxyhemoglobin saturation continuously recorded. Five of 12 patients with sleep apnea had both sleep apnea and severe hypoxemia during sleep. These patients with severe nocturnal hypoxemia had significantly higher plasma adenosine levels (means +/- SD 9.7 +/- 5.5 X 10(-8) M) than either a group of six normal volunteers (3.5 +/- 0.7 X 10(-8) M) or a group of seven patients with sleep apnea without hypoxemia at night (3.1 +/- 1.5 X 10(-8) M) (P less than 0.01). In addition plasma adenosine levels were significantly correlated with two indexes of nocturnal hypoxemia (desaturation index rs = 0.79, and median oxyhemoglobin saturation during sleep rs = -0.75, P less than 0.01). Plasma adenosine markedly fell to a normal level in the only two patients with sleep apnea who had successful treatment of their multiple apneas and accompanying severe hypoxemia during sleep.     

Obstructive sleep apnea. Trends in therapy.

The National Commission on Sleep Disorders Research, in its report to Congress, concluded that the primary care community generally does not understand sleep disorders. Obstructive sleep apnea carries a risk of substantial morbidity and mortality. Excessive daytime sleepiness results from fragmented sleep and microarousals associated with apneic events. It causes poor work performance and increases the incidence of automobile accidents due to driving while drowsy. The commission estimates that the loss of productivity in the United States from excessive daytime sleepiness is more than $20 billion per year. Obstructive sleep apnea is strongly associated with hypertension, myocardial infarction, and stroke. Risk factors for obstructive sleep apnea include male sex, obesity, older age, craniofacial anomalies, and familial risk. Treatment is based on documenting the disorder by polysomnography. Medical management of the syndrome includes weight loss and nasal continuous positive airway pressure. A network of follow-up and support is necessary to maintain compliance. Surgical treatment is reserved for those for whom nasal airway pressure treatment fails. A surgical protocol is presented that demonstrates efficacy equal to nasal airway pressure treatment. Primary care physicians should assume the responsibility of identifying patients at risk for obstructive sleep apnea and refer them appropriately.     

Metabolic effects of the obstructive sleep apnea syndrome and cardiovascular risk

The obstructive sleep apnea syndrome (OSAS) is characterized by collapse of the upper airway during sleep, recurring apneas, intermittent hypoxemia and daytime somnolence. OSAS is often associated with obesity, and its prevalence is expected to rise due to the obesity epidemics worldwide. OSAS is associated with increased cardiovascular risk which appears to be normalized by treatment with nasal continuous positive airway pressure (nCPAP) during sleep, suggesting an independent role of OSAS in accelerating atherosclerosis. Insulin resistance (IR) and the metabolic syndrome (MetS) are often found in OSAS patients, but the relative role played by OSAS and obesity is still unclear. Both OSAS and MetS may exert negative synergistic effects on the cardiovascular system through multiple mechanisms (hypoxemia, sleep disruption, activation of the sympathetic nervous system, inflammatory activation). Besides nCPAP treatment, pharmacologic interventions to treat obesity and the MetS could improve cardiovascular prevention in OSAS.     

右美托咪定复合不同麻醉深度在老年全髋关节置换术患者中的麻醉效果探讨及术后谵妄的危险因素分析

摘要 目的：探讨右美托咪定复合不同麻醉深度在老年全髋关节置换术（THA）患者中的麻醉效果,并分析其发生术后谵妄的危险因素。方法：选取我院2020年7月~2022年1月期间收治的130例老年THA患者。根据术中麻醉意识深度分为A、B、C组,其中A组41例,脑电双频指数（BIS）值为40~49;B组43例,BIS值为50~59;C组46例,BIS值为60~69。观察三组患者的麻醉效果,包括苏醒质量、术后谵妄发生情况、麻醉不良反应。根据术后是否发生谵妄将患者分为无谵妄组和谵妄组,采用单因素和多因素Logistic回归分析老年THA患者发生术后谵妄的危险因素。结果：A组、B组的恢复自主呼吸时间、呼叫开始至睁眼时间短于C组,且B组短于A组（P<0.05）。B组的麻醉不良反应发生率较A组和C组低（P<0.05）。麻醉不良反应发生率A组和C组对比无统计学差异（P>0.05）。B组的谵妄发生率较A组和C组低（P<0.05）。A组、C组的谵妄发生率组间对比无统计学差异（P>0.05）。单因素分析结果显示：术后谵妄的发生与年龄、体质量指数、美国麻醉医师协会分级（ASA）分级、冠心病、术中出血量、血钠浓度、术后低氧血症、术前合并低蛋白血症、术前焦虑、麻醉时间、术后贫血有关（P<0.05）。多因素Logistic回归分析结果显示：年龄偏高、术后贫血、体质量指数偏低、血钠浓度偏低、术中出血量偏多、术后低氧血症、麻醉时间偏长、术前合并低蛋白血症是老年THA患者术后谵妄发生的危险因素（P<0.05）。结论：BIS值为50~59的情况下复合右美托咪定治疗老年THA患者,可获得较好的麻醉效果,可降低术后谵妄、不良反应发生率。此外,年龄、术后贫血、体质量指数、血钠浓度、术中出血量、术后低氧血症、麻醉时间、术前合并低蛋白血症均是老年THA患者术后谵妄发生的影响因素。     

Hypoxemia alone does not explain blood pressure elevations after obstructive apneas

In patients with obstructive sleep apnea (OSA), substantial elevations of systemic blood pressure (BP) and depressions of oxyhemoglobin saturation (SaO2) accompany apnea termination. The causes of the BP elevations, which contribute significantly to nocturnal hypertension in OSA, have not been defined precisely. To assess the relative contribution of arterial hypoxemia, we observed mean arterial pressure (MAP) changes following obstructive apneas in 11 OSA patients during non-rapid-eye-movement (NREM) sleep and then under three experimental conditions: 1) apnea with O2 supplementation; 2) hypoxemia (SaO2 80%) without apnea; and 3) arousal from sleep with neither hypoxemia nor apnea. We found that apneas recorded during O2 supplementation (SaO2 nadir 93.6% +/- 2.4; mean +/- SD) in six subjects were associated with equivalent postapneic MAP elevations compared with unsupplemented apneas (SaO2 nadir 79-82%): 18.8 +/- 7.1 vs. 21.3 +/- 9.2 mmHg (mean change MAP +/- SD); in the absence of respiratory and sleep disruption in eight subjects, hypoxemia was not associated with the BP elevations observed following apneas: -5.4 +/- 19 vs. 19.1 +/- 7.8 mmHg (P less than 0.01); and in five subjects, auditory arousal alone was associated with MAP elevation similar to that observed following apneas: 24.0 +/- 8.1 vs. 22.0 +/- 6.9 mmHg. We conclude that in NREM sleep postapneic BP elevations are not primarily attributable to arterial hypoxemia. Other factors associated with apnea termination, including arousal from sleep, reinflation of the lungs, and changes of intrathoracic pressure, may be responsible for these elevations.     

Hemodynamic monitoring and care of the patient of high risk for anesthesia.

Hemodynamic monitoring and care of the patient at high risk for anesthesia require a careful and systematic approach. During preoperative evaluation the patient at increased risk must be identified and correctable problems must be solved. The patient''s current medications must be reviewed because they may influence the choice of anesthetic approach and may alter the physiologic response to the stresses commonly associated with anesthesia. In addition to conventional clinical and electrocardiographic monitoring, perioperative hemodynamic monitoring may be desirable for patients at special risk, who are likely to have significant associated medical problems or to undergo complicated surgical procedures. No ideal induction agent exists, and hypotension secondary to peripheral vasodilation or myocardial depression, or both, is a potential problem. Patients with an inordinately high risk may benefit from mechanical circulatory assistance prior to induction of anesthesia. Attention to oxygenation, blood volume replacement and the prevention of hypertensive episodes are particularly important during anesthesia so that optimal cardiac performance is ensured and ischemia avoided. The stresses during emergence from anesthesia contribute to lability of the cardiovascular status and hypoxemia. The period of risk does not conclude with immediate recovery from anesthesia but extends through the postoperative phase. Careful monitoring and attention to the control of pain, prevention of hypotension and hypertension, adequate oxygenation, early mobilization and resumption of the administration of cardiac medications are important factors in a successful outcome.     

Hypercalcemia in infants presenting with apnea.

To our knowledge apnea in infants has not been associated with hypercalcemia. We describe seven hypercalcemic infants aged 2 days to 3 months who had presented with apnea; six of the seven were otherwise healthy. The apneic attacks were brief, and normal breathing was restored spontaneously or after tactile stimulation. The attacks stopped and the apnea monitoring was discontinued when the children were 1 month to 2 years of age. The only abnormal finding common to all of the patients was hypercalcemia. Idiopathic infantile hypercalcemia was diagnosed in six of the patients and familial benign hypercalcemia in one. Our findings suggest that determination of the plasma calcium level be included in the investigation of apnea in infancy.     

Positive outcome of average volume-assured pressure support mode of a Respironics V60 Ventilator in acute exacerbation of chronic obstructive pulmonary disease: a case report

ABSTRACT: INTRODUCTION: We were able to treat a patient with acute exacerbation of chronic obstructive pulmonary disease who also suffered from sleep-disordered breathing by using the average volume-assured pressure support mode of a Respironics V60 Ventilator (Philips Respironics: United States). This allows a target tidal volume to be set based on automatic changes in inspiratory positive airway pressure. This removed the need to change the noninvasive positive pressure ventilation settings during the day and during sleep. The Respironics V60 Ventilator, in the average volume-assured pressure support mode, was attached to our patient and improved and stabilized his sleep-related hypoventilation by automatically adjusting force to within an acceptable range. CASE PRESENTATION: Our patient was a 74-year-old Japanese man who was hospitalized for treatment due to worsening of dyspnea and hypoxemia. He was diagnosed with acute exacerbation of chronic obstructive pulmonary disease and full-time biphasic positive airway pressure support ventilation was initiated. Our patient was temporarily provided with portable noninvasive positive pressure ventilation at night-time following an improvement in his condition, but his chronic obstructive pulmonary disease again worsened due to the recurrence of a respiratory infection. During the initial exacerbation, his tidal volume was significantly lower during sleep (378.9 +/- 72.9mL) than while awake (446.5 +/- 63.3mL). A ventilator that allows ventilation to be maintained by automatically adjusting the inspiratory force to within an acceptable range was attached in average volume-assured pressure support mode, improving his sleep-related hypoventilation, which is often associated with the use of the Respironics V60 Ventilator. Polysomnography performed while our patient was on noninvasive positive pressure ventilation revealed obstructive sleep apnea syndrome (apnea-hypopnea index = 14), suggesting that his chronic obstructive pulmonary disease was complicated by obstructive sleep apnea syndrome. CONCLUSION: In cases such as this, in which patients with severe acute respiratory failure requiring full-time noninvasive positive pressure ventilation therapy also show sleep-disordered breathing, different ventilator settings must be used for waking and sleeping. On such occasions, the Respironics V60 Ventilator, which is equipped with an average volume-assured pressure support mode, may be useful in improving gas exchange and may achieve good patient compliance, because that mode allows ventilation to be maintained by automatically adjusting the inspiratory force to within an acceptable range whenever ventilation falls below target levels.     

小剂量快速注射丙泊酚在胃镜检查中的安全有效性分析

目的：观察小剂量快速注射丙泊酚在无痛胃镜检查中的安全性及有效性,观察该方法对患者识记能力的影响。方法：选择60例行无痛胃镜检查的患者,随机分成A组和B组。所有患者均给予1μg／kg芬太尼。给予芬太尼后1分钟后,A组患者按照5mg／sec的速度给予2mg／kg丙泊酚;B组患者按照20mg／sec的速度给予1mg／kg丙泊酚。患者睫毛反射消失后进行胃镜检查。记录患者基础时及麻醉过程中不同时点的收缩压、舒张压、心率以及脉搏血氧饱和度,记录患者失去意识时间、胃镜检查时间、患者苏醒时间,记录检查过程中有无呛咳、体动,记录患者有无术中知晓,记录患者检查后一周内的有无识记能力的减退。结果：两组患者基本情况无统计学差异;60例患者无一例出现术中知晓;两组患者在麻醉过程中不同时点的循环情况及脉搏血氧饱和度之间没有统计学差异;检查过程中呛咳、体动的发生率组间比较无统计学差异;失去意识时间和苏醒时间组间比较P≤0．05,具有统计学差异;检查后一周内,识记能力减退发生率组间比较具有统计学差异。结论：快速注射小剂量丙泊酚可以保证患者安全、满足无痛胃镜检查的需要,同时可以降低丙泊酚的用量,减少药物蓄积,减少丙泊酚所致的识记功能减退。     

中老年男性缺血性脑血管病与阻塞性睡眠呼吸暂停综合症的临床相关性分析

目的:对中老年男性缺血性脑血管病合并阻塞性睡眠呼吸暂停综合症(obstructive sleep apnea,OSA)的相关性及其危险因素进行临床分析。方法:选择中老年男性急性脑梗死患者(acute cerebral infarction,ACI)40例,短暂性脑缺血发作患者(transient ischemic attack,TIA)36例及健康对照组患者36例用多导睡眠呼吸监测仪进行监测,对患有OSA的患者根据睡眠呼吸暂停低通气指数(apnea hypopnea index,AHI)分成轻中重三组,并对其临床指标及危险因素进行分析。结果:ACI组(15.3±12.3)和TIA组(14.7±10.4)患者AHI显著高于对照组(8.2±6.6,P0.01)。OSA在各组中的发病率分别为60.0%,52.8%和22.2%,与对照组有显著差异。缺血性脑血管病患者的体重指数(BMI),血糖,纤维蛋白原(FIB),胆固醇水平(CHOL),高密度脂蛋白(HDL)以及烟酒等不良嗜好与OSA呈正相关。中重度OSA患者缺血性脑血管病的发病率显著高于轻症患者(P0.01)。结论:OSA是影响老年男性缺血性脑血管病发病的重要因素,其严重程度可能与缺血性脑血管病成正相关。     

Apnea induction for invasive lung function testing in infant olive baboons: Comparison of intravenous propofol versus hyperventilation

Background

In various types of pulmonary research, pulmonary function testing (PFT) is performed to quantify the severity of lung disease. Induction of apnea and positive pressure ventilation are required for accurate PFT measurements in non‐cooperative subjects. We compared two methods of apnea induction in infant olive baboons (Papio anubis).

Methods

Pulmonary function testing results were compared during apnea induced by hyperventilation (CO₂ washout) vs. intravenous propofol (1 dose 10 mg/kg). PFT was evaluated using a hot‐wire pneumotachometer incorporated within an Avea ventilator in nine 1‐month‐old baboons.

Results

Propofol induced apnea faster and more reliably. In both groups, PFT values passed the statistical equivalence test and were not significantly different (Student's t‐test). There was a trend toward less data variability after propofol administration.

Conclusions

Intravenous propofol was non‐inferior to CO₂ washout for apnea induction in infant olive baboons. Propofol induced apnea faster and more reliably and yielded less variable PFT results.     

Brain Connectivity Dissociates Responsiveness from Drug Exposure during Propofol-Induced Transitions of Consciousness

Accurately measuring the neural correlates of consciousness is a grand challenge for neuroscience. Despite theoretical advances, developing reliable brain measures to track the loss of reportable consciousness during sedation is hampered by significant individual variability in susceptibility to anaesthetics. We addressed this challenge using high-density electroencephalography to characterise changes in brain networks during propofol sedation. Assessments of spectral connectivity networks before, during and after sedation were combined with measurements of behavioural responsiveness and drug concentrations in blood. Strikingly, we found that participants who had weaker alpha band networks at baseline were more likely to become unresponsive during sedation, despite registering similar levels of drug in blood. In contrast, phase-amplitude coupling between slow and alpha oscillations correlated with drug concentrations in blood. Our findings highlight novel markers that prognosticate individual differences in susceptibility to propofol and track drug exposure. These advances could inform accurate drug titration and brain state monitoring during anaesthesia.     

呼末二氧化碳监测在ERCP麻醉中预防麻醉期间低氧血症应用效果

摘要 目的：探讨呼末二氧化碳监测在内镜下经胰胆管造影（ERCP）麻醉中预防麻醉期间低氧血症应用效果。方法：选择2022年1月-2023年6月本院-行ERCP治疗的300例患者,用随机数表法分为试验组（n=150）和对照组（n=150）。对照组给予行常规心电图、血压和血氧饱和度监测,试验组在对照组基础上行呼末二氧化碳监测。比较两组一般资料、低氧血症、呼吸暂停、面罩加压给氧及改变头部姿势发生情况。结果：两组一般资料进行比较,无统计学差异（P>0.05）;试验组低氧血症、呼吸暂停、面罩加压给氧均显著低于对照组,改变头部姿势发生率显著高于对照组,两组比较有统计学意义（P<0.05）。结论：ERCP麻醉患者中使用呼末二氧化碳监测可实时指导对患者进行辅助呼吸处理,降低ERCP 麻醉期间低氧血症的发生率和面罩加压给氧率。     

Electrophysiological and neuropsychological outcomes of severe obstructive sleep apnea: effects of hypoxemia on cognitive performance

Obstructive sleep apnea syndrome (OSAS) is a sleep disorder characterized with upper airway obstructions. Some studies showed cognitive and electrophysiological changes in patients with OSAS; however, contradictory results were also reported. The purpose of the present study was twofold: (1) to investigate cognitive changes in severe OSAS patients by using neuropsychological tests and electrophysiological methods together, (2) to investigate influence of hypoxemia levels on cognition. Fifty-four severe OSAS patients and 34 age-, gender- and education matched healthy subjects were participated. OSAS patients were further divided into two subgroups according to minimum oxygen saturation levels. All participants underwent a detailed neuropsychological test battery. A classical visual oddball task was used to elicit ERP P300 and mean P300 amplitudes were measured from F_z, C_z and P_z electrode sites. OSAS patients showed reduced mean P300 amplitudes up to 43–51% on all electrode sites compared to healthy controls. Subgroup analysis revealed significant differences in neuropsychological test scores between healthy controls and high hypoxemia OSAS group, as well as between low and high hypoxemia groups. Moreover, both low and high hypoxemia OSAS groups had lower P300 amplitudes compared with healthy controls. P300 amplitudes showed a gradual decline in parallel with increasing hypoxemia severity; however, the difference between high and low hypoxemia OSAS groups did not reach significance. Moderate correlations were found between sleep parameters, neuropsychological test scores and P300 amplitudes. These results suggest that electrophysiological measures could be better indicators of cognitive changes than neuropsychological tests in OSAS, particularly in mildly affected patients.     

Plasma and cerebrospinal fluid concentration of neuropeptide Y, serotonin, and catecholamines in patients under propofol or isoflurane anesthesia

Propofol is a widely used anesthetic for both induction and maintenance of anesthesia during surgery. A strong feeling of hunger has been reported during the early recovery period after propofol anesthesia. We have investigated the effect of propofol on appetite in 10 patients undergoing a craniotomy and in parallel measured neuropeptide Y (NPY), catecholamines, and serotonin levels in the cerebrospinal fluid and plasma during anesthesia. Ten patients anesthetized with a volatile agent (isoflurane) served as a control group. Plasma NPY and catecholamines levels were not affected by surgery at any time. We observed a strong increase in NPY concentrations in the cerebrospinal fluid independently of the anesthetic technique agent used, whereas catecholamines were unchanged. We found that serotonin concentrations decreased significantly in the plasma (but not in the cerebrospinal fluid) of patients treated by propofol when compared with the control group; this decrease was associated with an increase of hunger early postoperatively. We concluded that the proappetite effect of propofol is mediated through a decrease of serotonin at the peripheral level.     

Kidney Transplantation Is Associated with Catastrophic Out of Pocket Expenditure in India

Kidney transplantation (KT) is only viable renal replacement option for most patients in India. Most patients do not have health insurance and meet treatment expenditure from their own resources. We prospectively evaluated the expenses associated with KT and its impact on the socioeconomic status of families in a public hospital. All direct and indirect expenses incurred by the patients from the time of diagnosis of chronic kidney disease to KT were recorded. Direct expenses included physician fees, cost of drugs and disposables, dialysis, and expenses on investigations and hospitalization. Indirect expenses included travel, food, stay, and loss of income suffered by the family. Educational dropout and financial loss were also recorded. There were 43 males and 7 females between the ages of 12 and 57 years. Direct expenses ranged from US$ 2,151–23,792 and accounted for two-thirds of the total expenses. Pre-referral hospitalization, dialysis and medication accounted for majority of direct expense. Indirect expenses ranged from US$ 226–15,283. Travel expenses and loss of income accounted for most of indirect expense. About 54%, 8%, and 10% of families suffered from severe, moderate, and some financial crisis respectively. A total of 38 families had job losses, and 1 patient and 12 caregivers dropped out of studies. To conclude, KT is associated with catastrophic out-of-pocket expenditure and pushes a majority of the patients who come for treatment to public hospitals into severe financial crisis. Educational dropout and loss of jobs are other major concerns. Systematic efforts are required to address these issues.     

丙泊酚和依托咪酯混合液持续泵注在无痛胃肠镜麻醉中的应用

目的:探讨丙泊酚和依托咪酯混合液持续泵注在无痛胃肠镜麻醉中的应用效果。方法:2013年9月到2015年2月选择在我院进行无痛胃肠镜检查患者120例,根据随机数字表法分为治疗组60例与对照组60例,对照组给予丙泊酚辅助持续泵注麻醉,治疗组给予丙泊酚和依托咪酯混合液辅助持续泵注麻醉。结果:所有患者都完成检查,两组MAP与HR值在给药后2 min与给药前比较差异都有统计学意义(P0.05),在组间相比较无显著性差异(P0.05),其余时间点的上述值在组内与组间比较均无显著性差异(P0.05)。治疗组的诱导时间与离院时间都明显少于对照组(P0.05),对比两组的检查时间及苏醒时间,无显著性差异(P0.05)。治疗组检查后1天内出现的恶心、呕吐、头晕等并发症发生情况明显少于对照组(P0.05)。结论:丙泊酚和依托咪酯混合液持续泵注在无痛胃肠镜麻醉中的应用对于患者的血流动力学影响小,能促进麻醉效果的提高,减少不良反应的发生,值得推广应用。     

Respiratory responses to cold water immersion: neural pathways, interactions, and clinical consequences awake and asleep.

The ventilatory responses to immersion and changes in temperature are reviewed. A fall in skin temperature elicits a powerful cardiorespiratory response, termed "cold shock," comprising an initial gasp, hypertension, and hyperventilation despite a profound hypocapnia. The physiology and neural pathways of this are examined with data from original studies. The respiratory responses to skin cooling override both conscious and other autonomic respiratory controls and may act as a precursor to drowning. There is emerging evidence that the combination of the reestablishment of respiratory rhythm following apnea, hypoxemia, and coincident sympathetic nervous and cyclic vagal stimulation appears to be an arrhythmogenic trigger. The potential clinical implications of this during wakefulness and sleep are discussed in relation to sudden death during immersion, underwater birth, and sleep apnea. A drop in deep body temperature leads to a slowing of respiration, which is more profound than the reduced metabolic demand seen with hypothermia, leading to hypercapnia and hypoxia. The control of respiration is abnormal during hypothermia, and correction of the hypoxia by inhalation of oxygen may lead to a further depression of ventilation and even respiratory arrest. The immediate care of patients with hypothermia needs to take these factors into account to maximize the chances of a favorable outcome for the rescued casualty.     

Hypoxemia, atelectasis, and the elevation of arterial pressure and heart rate in paralyzed artificially ventilated rat.

Rats prepared while anesthetized with halothane, ether or pentobarbital, subsequently paralyzed with curare, and maintained with or without anesthetic, by artificial ventilation with room air are hypoxemic in association with elevated arterial pressures and heart rates. The hypoxemia can occur with normal Pa_CO2, is associated with a marked increase in the alveolar-arterial P_O2 difference, and is not reversed by hyperventilation or hyperinflation. The lungs, visualized directly through a thoracotomy during ing artificial ventilation, are segmentally collapsed and at postmortem demonstrate focal and diffuse signs of atelectasis. Hypoxemia and an elevation of the alveolar-arterial P_O2 difference occur within 20 minutes after the onset of anesthesia, prior to paralysis. We conclude that anesthetized rats develop atelectasis soon after the onset of anesthesia. The atelectasis, and resultant hypoxemia persist during subsequent paralysis despite an adequate minute volume and absence of anesthesia. Despite atelectasis, blood gases, arterial pressures and heart rates may be maintained near normal values by ventilation of paralyzed rats with 50% O₂ and 50% N₂.