Ventilation Strategies in Obese Patients

Obesity is an increasingly prevalent disease and is a root and complication of conditions necessitating mechanical ventilation. Obese patients require a careful approach due to the particular manner of how ventilatory mechanics is affected, if obstructive sleep apnea (OSA) is present. The two main diagnoses we may encounter while ventilating these patients are obesity hypoventilation syndrome (OHS) and chronic obstructive pulmonary disease (COPD) in an obese patient, which has been recently proposed as a novel phenotype of COPD. The excessive amount of fat in the abdomen, chest wall, and around upper airways warrants the use of special ventilation modes and settings. This chapter provides insight into which issues should be considered when ventilating an obese patient, either in acute or chronic conditions. We stress the importance of acknowledging the high risk of OSA and how OSA affects the ventilation algorithms.

Respiratory mechanics behavior after heart surgery: an experimental study

Changes in ventilatory mechanics and their consequent pulmonary complications are common after surgical procedures, particularly in cardiac surgery (CS), and may be associated with both preoperative history and surgical circumstances. This study aims to compare ventilatory mechanics in the moments before and after cardiac surgery (CS), describing how pulmonary complications occurred. An experimental, uncontrolled study was conducted, of the before-and-after type, and with a descriptive and analytical character. It was carried out in a private hospital in the city of Salvador, Bahia, Brazil, and involved 30 adult patients subjected to CS. In addition to clinical and epidemiological variables, minute volume (VE), respiratory rate (RR), tidal volume (VT), forced vital capacity (FVC), maximum inspiratory pressure (MIP), and peak expiratory flow (PEF) were also recorded. Data were collected in the following moments: preoperative (PRE-OP) period, immediate postoperative (IPO) period, and 1st postoperative day (1st POD). The sample was aged 48.1 ± 11.8 years old and had a body mass index of 25.5 ± 4.9 kg m-2; 60% of the patients remained on mechanical ventilation for less than 24 hours (17.5 [8.7-22.9] hours). There was a significant reduction in VT, FVC, MIP and PEF when PRE-OP versus IPO, and PRE-OP versus 1st POD were compared (p < 0.05). There were no significant changes between IPO and the 1st POD. The highest incidence of pulmonary complications involved pleural effusion (50% of the patients). This study showed that patients subjected to CS present significant damage to ventilatory parameters after the surgery, especially in the IPO period and on the 1st POD. It is possible that the extension of this ventilatory impairment has led to the onset of postoperative pulmonary complications.

Variations in the cerebrospinal fluid dynamics of the American alligator (Alligator mississippiensis)

Background Studies of mammalian CSF dynamics have been focused on three things: paravascular flow, pressure and pulsatility, and “bulk” flow; and three (respective) potential motive forces have been identified: vasomotor, cardiac, and ventilatory. There are unresolved questions in each area, and few links between the different areas. The American alligator (Alligator mississippiensis) has pronounced plasticity in its ventilatory and cardiovascular systems. This study was designed to test the hypothesis that the greater cardiovascular and ventilatory plasticity of A. mississippiensis would result in more variation within the CSF dynamics of this species. Methods Pressure transducers were surgically implanted into the cranial subarachnoid space of 12 sub-adult alligators; CSF pressure and pulsatility were monitored along with EKG and the exhalatory gases. In four of the alligators a second pressure transducer was implanted into the spinal subarachnoid space. In five of the alligators the CSF was labeled with artificial microspheres and Doppler ultrasonography used to quantify aspects of the spinal CSF flow. Results Both temporal and frequency analyses of the CSF pulsations showed highly variable contributions of both the cardiac and ventilatory cycles. Unlike the mammalian condition, the CSF pressure pulsations in the alligator are often of long (~ 3 s) duration, and similar duration CSF unidirectional flow pulses were recorded along the spinal cord. Reduction of the duration of the CSF pulsations, as during tachycardia, can lead to a “summation” of the pulsations. There appears to be a minimum duration (~ 1 s) of isolated CSF pulsations. Simultaneous recordings of cranial and spinal CSF pressures reveal a 200 ms delay in the propagation of the pressure pulse from the cranium to the vertebral canal. Conclusions Most of the CSF flow dynamics recorded from the alligators, are similar to what has been reported from studies of the human CSF. It is hypothesized that the link between ventilatory mechanics and CSF pulsations in the alligator is mediated by displacement of the spinal dura. The results of the study suggest that understanding the CSF dynamics of Alligator may provide unique insights into the evolutionary origins and functional regulation of the human CSF dynamics.

Clinical characteristics of critically ill patients with COVID-19

ABSTRACTObjectiveDescribe the clinical and respiratory characteristics of critical patients with coronavirus disease 2019 (COVID-19).DesignObservational and retrospective study over 6 months.SettingIntensive care unit (ICU) of a high complexity hospital in Buenos Aires, Argentina.PatientsPatients older than 18 years with laboratory-confirmed COVID-19 by reverse transcriptase-polymerase chain reaction (RT-PCR) for SARS-CoV-2 were included in the study.Variables of interestDemographic characteristics such as sex and age, comorbidities, laboratory results, imaging results, ventilatory mechanics data, complications, and mortality were recorded.ResultsA total of 168 critically ill patients with COVID-19 were included. 66% were men with a median age of 65 years (58-75. 79.7% had at least one comorbidity. The most frequent comorbidity was arterial hypertension, affecting 52.4% of the patients. 67.9 % required invasive mechanical ventilation (MV), and no patient was treated with non-invasive ventilation. Most of the patients in MV (73.7%) required neuromuscular blockade due to severe hypoxemia. 36% of patients were ventilated in the prone position. The length of stay in the ICU was 13 days (6-24) and the mortality in the ICU was 25%.ConclusionsIn this study of critical patients infected by SARS-CoV-2 in a high-complexity hospital, the majority were comorbid elderly men, a large percentage required invasive mechanical ventilation, and ICU mortality was 25%.

Ventilatory Mechanics in the Patient with Obesity

A brief review of how central adiposity affects intrathoracic pressures and its effects on spontaneous breathing and artificial ventilation.

A primer on respiratory physiology

According to the principle ‘before you can do what you want to do, you always have to do something else’, this chapter first delves into the basics of respiratory physiology. It begins with summarizing the physical gas laws and their physiological applications to the core process of respiration: diffusion. The chapter finally arrives at introducing the different gas exchange models that can be observed in the various lineages of animals and the basics of ventilatory mechanics. Equipped with this knowledge, it is hoped that the reader will better understand the functional and evolutionary discussions of the respiratory faculties in the following chapters.

Physiologic and Anatomic Changes during Pregnancy

Pregnancy results in physiologic and anatomic changes that allow the mother to adapt to the greater metabolic requirements of pregnancy. These changes include the enlarging uterus, which results in compression of surrounding structures, and increased hormonal production, which exerts its effects on maternal physiology. Cardiac output increases to maintain higher uterine blood flow, and minute ventilation increases, which results in a chronic respiratory alkalosis. Plasma volume increases, which results in physiologic anemia of pregnancy and may contribute to gestational thrombocytopenia. An understanding of these and other changes that occur in pregnancy is important for the anesthesiologist because they have important implications for management of the parturient undergoing an anesthetic procedure. The goal of this chapter is to highlight some of the most salient features of physiologic changes that occur during pregnancy and to begin to offer some basic anesthetic management strategies. This review contains 6 tables, and 36 references. Key Words: airway changes during labor, cardiovascular changes during pregnancy, gastroesophageal reflux disease, gestational thrombocytopenia, hydronephrosis during pregnancy, left uterine displacement, physiologic anemia, ventilatory mechanics