Manual of Airway Management in Critical Care
Livrare gratis la comenzi peste 500 RON. Pentru celelalte comenzi livrarea este 20 RON.
Disponibilitate: La comanda in aproximativ 4 saptamani
Editura: LWW
Limba: Engleza
Nr. pagini: 400
Coperta: Paperback
Dimensiuni: 178 x 254 mm
An aparitie: 28 aug 2024
Your instant access VST eBook offers 22 videos on functional anatomy, applied ultrasound, patient positioning, insertion and removal techniques, airway management of the surgical patient, and special considerations and techniques for the pediatric patient. The eBook also contains zoomable images and additional clinical cases to further the reader's understanding of clinical variability.Patterned after the renowned Walls Manual of Emergency Airway Management, Manual of Airway Management in Critical Care is a concise, focused reference on this challenging topic specifically for ICU providers. Drs. Jarrod M. Mosier, Calvin A. Brown III, Matteo Parotto, and Raquel R. Bartz bring their extensive expertise in critical care airway management to this all-new volume, as well as Dr. Mosier’s experience as director of the nationally recognized The Difficult Airway Course: Critical Care™. An excellent resource for intensivists, advanced practice providers, critical care nurses, and respiratory therapists, this first-of-its-kind text reflects ICU airway management from cover to cover: its unique standards of care, its unique risks, and its unique body of literature that set it apart from other medical disciplines.
Table of Contents:
Video Contents
SECTION I: Principles of Airway Management
1 Why Airway Management Matters
INTRODUCTION
CHAPTER 2 Functional Airway Anatomy
INTRODUCTION
THE NOSE
IMPORTANT ANATOMICAL CONSIDERATIONS
The Mouth
The Pharynx
The Larynx
Trachea
SUMMARY
CHAPTER 3 The Decision to Intubate
INTRODUCTION
INDICATIONS FOR INTUBATION
APPROACH TO THE PATIENT
ACKNOWLEDGMENT
CHAPTER 4 The Difficult Airway
INTRODUCTION
SECTION II: Developing a Strategy
5 Airway Evaluation for Anatomic Difficulty
INTRODUCTION
The Difficult Airway
Difficult Laryngoscopy: LEMON
Difficult BMV: ROMAN
Difficult EGD: RODS
Difficult Cricothyrotomy: SMART
ACKNOWLEDGMENT
CHAPTER 6 The Physiologically Difficult Airway: Hemodynamics
DEFINITION OF THE PHYSIOLOGICALLY DIFFICULT AIRWAY
HEMODYNAMICS
STEPWISE HEMODYNAMIC APPROACH
Who Should Be Intubated Awake?
CHAPTER 7 The Physiologically Difficult Airway: Hypoxemia
INTRODUCTION: SAFE APNEA
PREOXYGENATION
Denitrogenation
Functional Residual Capacity
V/Q Mismatch
REFRACTORY HYPOXEMIA
EVIDENCE
CHAPTER 8 The Physiologically Difficult Airway: Metabolic Acidosis, Induction Drugs, and Positive Pressure Ventilation
INTRODUCTION
EFFECT OF METABOLIC ACIDOSIS
EFFECT OF INDUCTION AGENTS
HEMODYNAMIC EFFECTS OF POSITIVE PRESSURE VENTILATION
Venous Return
Right Ventricular Function
Left Ventricular Function
CHAPTER 9 Developing Your Strategy
INTRODUCTION
THE STRATEGY FRAMEWORK
PICKING A PATH
Case 1: No Predicted Difficulty (Fig. 9.3)
Case 2: Predicted Difficulty With Intubation, But Not Mask Ventilation or Rescue Oxygenation (Fig. 9.4)
Case 3: Predicted Difficulty With Intubation and Mask Ventilation, But Rescue Oxygenation Is not Predicted to Be Difficult (Fig. 9.5)
Case 4: All Predicted to Be Difficult (Fig. 9.6)
Case 5: Forced to RSI (Fig. 9.7)
Case 6: The Cardiac Arrest Airway (Fig. 9.8)
MODIFY THE STRATEGY BASED ON THE PHYSIOLOGICALLY DIFFICULT AIRWAY CHARACTERISTICS
Case 7: Sepsis and ARDS (Fig. 9.9)
Case 8: Refractory Hypoxemia (Fig. 9.10)
CHAPTER 10 Applied Airway Ultrasound
INTRODUCTION
UPPER AIRWAY ANATOMY
Image Acquisition and Structure Identification
IDENTIFICATION OF THE CRICOTHYROID MEMBRANE
EVALUATION FOR LARYNGEAL EDEMA PRIOR TO EXTUBATION
Image Acquisition and Interpretation
CHAPTER 11 Applied Ultrasonography
INTRODUCTION
GASTRIC ULTRASONOGRAPHY
PULMONARY ULTRASONOGRAPHY
ECHOCARDIOGRAPHY
Workflow ( Video 11.2): Parasternal Long Axis
Parasternal Short Axis (PSAX)
Apical 4 and 5 Chamber (A4C, A5C)
Subxiphoid
SUMMARY
SECTION III: Applied Airway Pharmacology
12 Options
INTRODUCTION
RAPID SEQUENCE INTUBATION
SPONTANEOUSLY BREATHING INTUBATION (AWAKE INTUBATION)
DELAYED SEQUENCE INTUBATION
CHAPTER 13 Sedative Agents for Rapid Sequence Intubation
INTRODUCTION
ETOMIDATE
Clinical Pharmacology
Indications and Contraindications
Dosage and Clinical Use
Adverse Effects
KETAMINE
Clinical Pharmacology
Indications and Contraindications
Dosage and Clinical Use
Adverse Effects
PROPOFOL
Clinical Pharmacology
Indications and Contraindications
Dosage and Clinical Use
Additional Adverse Effects
MIDAZOLAM
Clinical Pharmacology
Indications and Contraindications
Dosage and Clinical Use
Adverse Effects
ALTERNATIVE AGENTS
SUMMARY
CHAPTER 14 Neuromuscular Blocking Agents
INTRODUCTION
SUCCINYLCHOLINE
Clinical Pharmacology
Indications and Contraindications
Dosage and Clinical Use
Adverse Effects
COMPETITIVE NEUROMUSCULAR BLOCKING AGENTS
Clinical Pharmacology
Indications
Dosage and Clinical Use
Contraindications and Adverse Effects
Reversal of Nondepolarizing Agents
Decision Making Between Depolarizing and Nondepolarizing Agents
SUMMARY
CHAPTER 15 Vasoactive Agents
INTRODUCTION
VASOPRESSORS
Phenylephrine
Vasopressin
Angiotensin II
INOPRESSORS
Norepinephrine
Epinephrine
Dopamine
INODILATORS
Dobutamine
Milrinone
Isoproterenol
INHALED PULMONARY VASODILATORS
Inhaled Epoprostenol
Inhaled Nitric Oxide
Inhaled Nitroglycerin
Inhaled Milrinone
KEY CLINICAL CONSIDERATIONS
Hypotension and Shock
RV Failure
Pulmonary Hypertension
Neurologically Injured Patient
Tachydysrhythmias
Massive PE
SUMMARY
CHAPTER 16 Topical Anesthetics and Anesthesia for Awake Intubation
INTRODUCTION
TOPICALIZATION OF THE OROPHARYNX, HYPOPHARYNX, AND GLOTTIC STRUCTURES
Variations
TOPICALIZATION OF THE NASOPHARYNX
Topicalization Technique
LIDOCAINE TOXICITY RISK
SEDATION
ACKNOWLEDGMENT
SECTION IV: Preparing the Patient
17 Preoxygenation and Apneic Oxygenation
INTRODUCTION
PRINCIPLES OF PREOXYGENATION
OXYGEN DELIVERY DEVICES
Noninvasive Positive Pressure Ventilation for Preoxygenation
High-Flow Nasal Oxygen
Nonrebreather Mask
Bag-Valve Mask
DEVICES NOT RECOMMENDED FOR PREOXYGENATION
Standard Nasal Cannulas
Simple Face Mask
Venturi Mask
OTHER PREOXYGENATION CONCEPTS
Monitoring the Effectiveness of Preoxygenation Using End-Tidal Oxygen
Concept of Delayed Sequence Intubation to Facilitate Preoxygenation
Apneic Oxygenation
Bagging During the Apneic Period
Rescue Oxygenation
SUMMARY
CHAPTER 18 Physiologic Optimization
INTRODUCTION
MONITORING
PRACTICAL APPROACH TO PHYSIOLOGIC OPTIMIZATION
Optimization by Organ System
Cardiovascular
Postintubation Optimization
MECHANICAL VENTILATION
Postintubation Sedation
SUMMARY
CHAPTER 19 Positioning
INTRODUCTION
POSITIONING FOR PREOXYGENATION
POSITIONING FOR INTUBATION
Fully Upright Position
OPERATOR POSITIONING
POSITIONING FOR CRICOTHYROTOMY
SPECIAL PATIENT POPULATIONS
Obesity
Pregnancy
SUMMARY
SECTION V: Navigating the Airway
20 Maximizing First-Attempt Success
INTRODUCTION
KEYS TO OPTIMIZING FIRST-ATTEMPT INTUBATION SUCCESS AND SAFETY
Use a Standardized Approach to Intubation
The Importance of Neuromuscular Blockade for Tracheal Intubation
Importance of a Preintubation Checklist
Optimal Preoxygenation Is Critical
Make the First Attempt the Best Attempt
A Simple Algorithm Is Invaluable When Intubation Attempts Fail
Backups Need to Be Available, Well-Proven, and Well-Practiced
Calling for Help
Taking Ownership, Continuous Quality Improvement, and the Airway Lead
SUMMARY
CHAPTER 21 Bag-Mask Ventilation
INTRODUCTION
BAG-VALVE-MASK DEVICES
OPTIMAL FACE MASK VENTILATION TECHNIQUE ( Video 21.1)
Optimizing Face Mask Seal
Face Mask Grip for Maximal Mandibular Advancement (Jaw Thrust)
Neuromuscular Blockade to Facilitate BMV
Head and Neck Maneuvers to Open the Upper Airway
Oral and Nasal Pharyngeal Airways
Ventilation Parameters for Bag-Mask Ventilation
Stomach Inflation, Sellick Maneuver, and Aspiration Risk With BMV
DIFFICULT AND IMPOSSIBLE MASK VENTILATION
Predicting Difficult or Impossible BMV
INTERPOSED BAGGING DURING RSI
EXPERIENCE, TRAINING, AND THE LEARNING CURVE FOR BMV
REAL-TIME MONITORING OF MASK VENTILATION
Pitfall of Oxygen Saturation Plethysmography
Importance of Waveform Capnography
Capnography Interpretation ( Video 21.2)
SUMMARY
CHAPTER 22 Extraglottic Devices
INTRODUCTION AND TERMINOLOGY
INDICATIONS FOR AN EGD
Primary Airway
Secondary Airway
CONTRAINDICATIONS FOR USE
INSERTING A SUPRAGLOTTIC DEVICE
General Technique for SGD Use ( Video 22.1)
Complications and Limitations
INSERTING A RETROGLOTTIC DEVICE
Insertion Technique—Assuming No Visualization ( Video 22.2)
Complications and Limitations
MANAGING THE IN SITU EXTRAGLOTTIC DEVICE
Assessing and Troubleshooting an EGD
Assessment
Troubleshooting Ventilation
Troubleshooting Oxygenation
OPTIMIZING EGD FUNCTION
WHEN TO CONSIDER SEMIELECTIVE EXCHANGE
GENERAL APPROACHES TO EGD EXCHANGE
Removal With Routine Intubation via Direct/Video Laryngoscopy
Intubate Through It
Surgical Airway
HOW TO PERFORM A SEMIELECTIVE SGD EXCHANGE FOR AN ETT
Blind Exchange
EXCHANGING A RETROGLOTTIC DEVICE
SUMMARY
CHAPTER 23 Direct Laryngoscopy
INTRODUCTION
DIRECT LARYNGOSCOPY AND VIDEO LARYNGOSCOPY SHOULD BE LEARNED TOGETHER
BASICS OF DIRECT LARYNGOSCOPY
ANATOMY FOR DIRECT LARYNGOSCOPY
PREPARATION AND ASSISTANCE
PREINTUBATION ASSESSMENT AND EQUIPMENT CHOICE
HANDLING THE LARYNGOSCOPE AND POSTURE OF THE OPERATOR
PATIENT POSITIONING
STANDARD DIRECT LARYNGOSCOPY TECHNIQUE ( Video 23.1)
PARAGLOSSAL (RETROMOLAR, RIGHT OR LEFT MOLAR) STRAIGHT-BLADE TECHNIQUE
BLIND INSERTION TECHNIQUE FOR THE STRAIGHT BLADE
INTUBATING THE TRACHEA (TUBE PASSAGE)
TROUBLESHOOTING DIFFICULT DIRECT LARYNGOSCOPY
Paralysis
External Laryngeal Manipulation
Positioning
Anterior Mandibular Advancement
Bougie (Endotracheal Tube Introducer)
FAILED LARYNGOSCOPY AND INTUBATION
CONFIRMING INTUBATION OF THE TRACHEA
CHAPTER 24 Video Laryngoscopy
INTRODUCTION
ADVANTAGES OF VIDEO LARYNGOSCOPES
CLASSIFICATION OF VIDEO LARYNGOSCOPES
WHEN TO USE VIDEO LARYNGOSCOPY COMPARED TO DIRECT LARYNGOSCOPY
DIFFERENCES IN TECHNIQUES FOR VIDEO LARYNGOSCOPY COMPARED TO DIRECT LARYNGOSCOPY
STANDARD GEOMETRY VIDEO LARYNGOSCOPES (MACINTOSH-STYLE)
Intubation With a Standard Geometry Video Laryngoscope ( Video 24.1)
Summary
HYPERANGULATED VIDEO LARYNGOSCOPES
Intubation With a Hyperangulated Video Laryngoscope ( Video 24.2)
Summary
VIDEO LARYNGOSCOPY AND THE SOILED AIRWAY
Proper Video Laryngoscope Technique in the Soiled Airway
VIDEO LARYNGOSCOPY AND DUAL-SCREEN INTUBATION
Technique for Dual-Screen Intubation With a Video Laryngoscope and Flexible Endoscope (see Chapter 28, Combination techniques)
COMPLICATIONS OF VIDEO LARYNGOSCOPES
CONCLUSION
CHAPTER 25 Flexible Endoscopic Intubation
INTRODUCTION
FEASIBILITY OF INTUBATING WITH A FLEXIBLE ENDOSCOPE
LEARNING CURVE FOR FLEXIBLE ENDOSCOPIC INTUBATION
INDICATIONS AND CONTRAINDICATIONS
PREPARATION CHECKLIST
APPROACH, PREPARATION AND TECHNIQUE
Patient Preparation
Equipment
Procedure of Flexible Endoscopic Intubation ( Video 25.1)
EDUCATION AND MAINTENANCE OF FLEXIBLE ENDOSCOPIC INTUBATION SKILLS
COMPLICATIONS
CHAPTER 26 Tracheal Intubation Using Optical Stylets
INTRODUCTION
DESIGN CHARACTERISTICS OF OPTICAL STYLETS
TYPES OF OPTICAL STYLETS
INTUBATION TECHNIQUE USING OPTICAL STYLETS ( Video 26.1)
ADVANTAGES OF THE OPTICAL STYLETS (SEE TABLE 26.1)
DISADVANTAGES OF THE OPTICAL STYLETS (SEE TABLE 26.1)
COMPLICATIONS ASSOCIATED WITH THE USE OF THE OPTICAL STYLETS
CLINICAL EVIDENCE OF THE OPTICAL STYLETS FOR TRACHEAL INTUBATION
SUMMARY
CHAPTER 27 Surgical Airways
INTRODUCTION
Description and General Approach
Indications and Contraindications
TECHNIQUE
Anatomy and Landmarks
Equipment
Technique
Complications
Alternatives to Open Surgical Techniques
CHAPTER 28 Combination Techniques
INTRODUCTION
INDICATIONS
COMBINATION OF SUPRAGLOTTIC DEVICE AND FLEXIBLE ENDOSCOPE
Technique ( Video 28.1)
DIRECT/VIDEO LARYNGOSCOPE AND FLEXIBLE ENDOSCOPE
Technique ( Video 28.3)
What Is the Literature Support for a Video Laryngoscope and Flexible Endoscope Combined Technique?
SUMMARY
CHAPTER 29 The Failed Airway
INTRODUCTION
THE FAILED AIRWAY
Failed (Missed) Attempt
Failed (Missed) Intubation
Failed Airway—Can’t Intubate, Can’t Oxygenate
Forced to Act/Forced to RSI
SECTION VI: Post-Intubation Management
30 Mechanical Ventilation and Post-Intubation Sedation, Hemodynamics, and Bundle
INTRODUCTION
MECHANICAL VENTILATION
Ventilation Modes
THE ALARMING VENTILATOR
VENTILATOR STRATEGIES BY CLINICAL PHENOTYPE
Normal Lungs
Acute Hypoxemic Respiratory Failure
Venovenous Extracorporeal Membrane Oxygenation
Exacerbation of Obstructive Lung Disease
ASSESSMENT OF SAFETY AND ADEQUACY OF MECHANICAL VENTILATION
VENTILATOR LIBERATION
SEDATION AND ANALGESIA
HEMODYNAMICS
BUNDLE OF POSTINVASIVE VENTILATION CARE
PEDIATRIC ISSUES
SUMMARY
ACKNOWLEDGMENTS
CHAPTER 31 Extubation and Tube Exchange
INTRODUCTION
EXTUBATION FAILURE
PLANNING FOR EXTUBATION
Extubation Criteria
Risk Stratification
Additional Testing
PROCESS OF EXTUBATION
General Extubation
Unplanned Extubation
Complications
ADJUNCTS TO EXTUBATION
Airway Exchange Catheters
Noninvasive Ventilation and High-Flow Nasal Cannula
Sedation During Extubation
ENDOTRACHEAL TUBE EXCHANGE
EVIDENCE
CHAPTER 32 Percutaneous Tracheostomy
INTRODUCTION
PROCEDURE: INDICATIONS AND TECHNIQUE
PEDIATRIC ISSUES
SUMMARY
SECTION VII: Special (Case-Based) Considerations
33 The Trauma Patient
GENERAL APPROACH TO THE TRAUMA AIRWAY
ASSESSMENT AND PREPARATION
ANATOMIC CONSIDERATIONS
PHYSIOLOGIC CONSIDERATIONS
AIRWAY MANAGEMENT STRATEGIES
Oxygenation/Preoxygenation
Endotracheal Intubation
Protecting the Cervical Spine
Adjuncts
Rapid Sequence Intubation
POSTINTUBATION MANAGEMENT
CHAPTER 34 The Neurologic Patient
INTRODUCTION
THE CLINICAL CHALLENGE—PREVENTION OF SECONDARY BRAIN INJURY
Hypoxemia
Hypotension
Hypercapnia
Elevated Intracranial Pressure
Neuromuscular Blockade Choice
Induction Agent Choice
SEIZURES AND STATUS EPILEPTICUS
NEUROMUSCULAR DISEASE
SUMMARY
CHAPTER 35 The Medical Patient
INTRODUCTION
SEPSIS
The Clinical Challenge
ACUTE HYPOXEMIC RESPIRATORY FAILURE
The Clinical Challenge
UPPER GASTROINTESTINAL BLEEDING
The Clinical Challenge
TOXIC OVERDOSE PATIENT
The Clinical Challenge
RIGHT VENTRICULAR FAILURE
The Clinical Challenge
CARDIOGENIC SHOCK FROM LEFT HEART DISEASE
The Clinical Challenge
UPPER AIRWAY OBSTRUCTION
The Clinical Challenge
SUBGLOTTIC AND TRACHEAL STENOSIS
The Clinical Challenge
OBSTRUCTIVE RESPIRATORY FAILURE
The Clinical Challenge
PREGNANCY
The Clinical Challenge
OBESITY
The Clinical Challenge
CONSIDERATION FOR INFECTION PREVENTION
The Clinical Challenge
SUMMARY
CHAPTER 36 The Pediatric Patient
INTRODUCTION
PREDICTABLE CHALLENGES IN PEDIATRIC AIRWAY MANAGEMENT
Anatomic Differences
Physiologic Differences
Cognitive Load in Pediatric Care
EQUIPMENT AND MEDICATION SELECTION
Equipment Selection
Drug Dosage and Selection
PREDICTING ANATOMIC AIRWAY DIFFICULTY IN PEDIATRICS
PROCEDURAL APPROACHES FOR BASIC AND ADVANCED AIRWAY MANAGEMENT IN CHILDREN
Tips for Successful Bag-Mask Ventilation in Children
Rapid Sequence Intubation in Children
Tips for Successful Endotracheal Intubation in Children
SELECT CAUSES OF PEDIATRIC DIFFICULT AIRWAYS
Infectious Causes
Noninfectious Causes
Congenital Anomalies
ADDRESSING THE FAILED AIRWAY
Extraglottic Devices
Cricothyrotomy
CHAPTER 37 The Surgical Patient
INTRODUCTION
APPROACH TO THE POSTOPERATIVE PATIENT’S AIRWAY
GENERAL POSTOPERATIVE CONCERNS
Airway Edema
Airway Injury
Recurrent Laryngeal Nerve Palsy
CAROTID ENDARTERECTOMY
Cervical Hematoma
Cranial Nerve Injury
Cervical Plexus Blocks
ESOPHAGECTOMY
Aspiration Risk
Pain Control and Pulmonary Mechanics
Pulmonary Edema and Fluid Overload
Anastomotic Injury
TRACHEAL RESECTION
Tracheal Tension
Laryngeal or Mucosal Edema
Postoperative Bleeding
Tracheal Obstruction
TRACHEOESOPHAGEAL AND BRONCHOPLEURAL FISTULA
LARYNGECTOMY
Preparation and Bedside Safety
Emergency Algorithm
TRACHEOSTOMY DISLODGMENT
Mature Versus Immature Stoma
Emergency Algorithm
OTHER POSTOPERATIVE CONCERNS FOR EMERGENCY AIRWAY MANAGEMENT
Neuromuscular Blockade
CHAPTER 38 Remote and Austere Environments
INTRODUCTION
CRITICAL CARE TRANSPORT
CONSIDERATIONS WITH ALTITUDE
MECHANICAL VENTILATION
MONITORING DEVICES
AIRWAY MANAGEMENT IN REMOTE HOSPITAL LOCATIONS
AIRWAY ASSESSMENT
PREOXYGENATION AND INTUBATION
ORGANIZATION
UNIQUE REMOTE LOCATIONS: RADIOLOGY
INTRAHOSPITAL TRANSPORT
TRULY AUSTERE ENVIRONMENT
SUMMARY
SECTION VIII: Organizational/Human Factors
39 Human Factors
INTRODUCTION
HUMAN EMOTION, STRESS, AND IMPLICATIONS FOR AIRWAY MANAGEMENT
THE PROBABILITY OF SUCCESS . . . OR FAILURE UNDER STRESS
CARDINAL RULE NUMBER 1: DO NOT WANDER, OR RUSH, INTO FAILURE
Thinking and Acting
Break the Cycle
CARDINAL RULE NUMBER 2: INTUBATE WITH A TEAM, NOT AN AUDIENCE
Talk to the Team
Crisis Resource Management
CHAPTER 40 Organizational Factors
INTRODUCTION
CLINICAL PRACTICES GUIDELINES
DRUG ORGANIZATION
AIRWAY CARTS
PREPARING FOR THE DIFFICULT AIRWAY, AND COMMUNICATING THIS TO OTHERS
DIFFICULT AIRWAY RESPONSE TEAMS
AIRWAY LEADS
QUALITY IMPROVEMENT
CHECKLISTS
SIMULATION
PHYSICAL LAYOUT
RESOURCE UTILIZATION
SUMMARY
CHAPTER 41 Airway Management Research
INTRODUCTION
Video Versus Direct Laryngoscopy
Bougie Versus Stylet
Etomidate Versus Ketamine
CHALLENGES WITH AIRWAY MANAGEMENT RESEARCH
Challenge 1: What Is the Patient Population?
Challenge 2: What Is the Intervention?
Challenge 3: What Is the Outcome of Interest?
Challenge 4: What Is the Design?
Challenge 5: Problems With Confounding Variables
TAKEAWAYS, FUTURE DIRECTIONS, AND LINGERING QUESTIONS
Index
An aparitie | 28 aug 2024 |
Autor | Jarrod Mosier MD, PLLC, Calvin A Brown, III MD, Matteo Parotto M.D., Ph.D, Raquel Rae Bartz |
Dimensiuni | 178 x 254 mm |
Editura | LWW |
Format | Paperback |
ISBN | 9781975214203 |
Limba | Engleza |
Nr pag | 400 |
Clientii ebookshop.ro nu au adaugat inca opinii pentru acest produs. Fii primul care adauga o parere, folosind formularul de mai jos.