Mount Sinai Expert Guides. Группа авторов
on minimal pressure support, intact airway reflexes, and baseline mental status.
One should also consider the specific situation such as difficulty of intubation, barriers to reintubation (e.g. jaw wired shut after maxillofacial surgery, significant airway edema), fluid balance, and acid–base balance.
If there is any question of airway patency, one may consider performing a leak test (deflating the ETT cuff and listening for air movement around the ETT and observing a decrease in tidal volume) or extubating over an ETT exchanger with a backup ETT available in case reintubation becomes necessary.
Patients with baseline pulmonary dysfunction may benefit from being extubated to BIPAP or HFNC.
Complications of intubation
Airway trauma
Instrumentation of the airway can cause trauma to soft tissues as well as to teeth and lips.
Although less common with modern ETTs, overinflation of cuffs (typically greater than 30 mmHg) can cause tissue ischemia, leading to inflammation and possibly tracheal stenosis as well as vocal cord paralysis from compression of the recurrent laryngeal nerve. Vocal cord paralysis can produce hoarseness and susceptibility to aspiration.
Physiologic effects of airway instrumentation
Hypotension is a common response to induction and should be anticipated, especially in critically ill patients.
Hypertension and tachycardia can be seen if inadequate anesthetic is provided.
Laryngospasm, an involuntary closure of the laryngeal muscles, is a response to airway stimulation in the setting of light anesthesia. Severe hypoxia, from the inability to mask ventilate through the closed larynx, can result. Treatment includes gentle positive pressure with a mask. If this fails, deepening the plain of anesthesia as well as giving succinylcholine will typically relax the musculature.
Aspiration
Critically ill patients often require airway management in the undesirable setting of a full stomach, or mechanical or physiologic motility disorders, making aspiration of gastric contents a feared complication.
If suspected, the patient should be placed in the Trendelenburg position, the pharynx and trachea (if possible) suctioned, and the airway secured with an ETT as soon as possible.
Therapy is typically supportive and antibiotics and bronchoscopic lavage are usually not necessary unless particulate aspiration is suspected or if signs of infection occur.
Reading list
1 Butterworth JF, Mackey DC, Wasnick JD. Morgan and Mikhail’s Clinical Anesthesiology, 5th edition. New York: McGraw‐Hill Education, 2013.
2 Cook TM. A new practical classification of laryngeal view. Anesthesia 2000; 55:274.
3 El‐Orbany M, Woehlick H, Ramez Salem M. Head and neck position for direct laryngoscopy. Anesth Analg 2011; 113:103.
4 Langeron O, et al. Prediction of difficult mask ventilation. Anesthesiology 2000; 92:1217.
5 Miller RD. Miller’s Anesthesia, 7th edition. Philadelphia: Churchill Livingstone/Elsevier, 2009.
6 Robitaille A, Williams SR, Trembaly MH, Guilbert F, Thériault M, Drolet P. Cervical spine motion during tracheal intubation with manual in‐line stabilization direct laryngoscopy: direct laryngoscopy versus GlideScope videolaryngoscopy. Anesth Analg 2008; 106:935–41.
7 Tanoubi I, Drolet P, Donati F. Optimizing preoxygenation in adults. Can J Anesth 2009; 56:449.
8 Watson CB. Prediction of a difficult intubation: methods for successful intubation. Respir Care 1999; 44:777.
Images
Figure 1.1 Mallampati classification.
Additional material for this chapter can be found online at:
www.wiley.com/go/mayer/mountsinai/criticalcare
This includes multiple choice questions and Video 1.1 .
CHAPTER 2 Sedation and Analgesia
Colin J. Sheehan and Michael Kitz
Icahn School of Medicine at Mount Sinai, New York, NY, USA
OVERALL BOTTOM LINE
Analgesia and sedation are primarily indicated to prevent self‐harm and ensure the comfort of a patient. Examples include intubated patients who are dyssynchronous with a ventilator, those with open wounds postoperatively, and patients who are unable to have their pain controlled by less intensive measures.
Post‐traumatic stress disorder (PTSD) has been found in 20% of patients after discharge from an ICU. Appropriately targeted sedation therapy has been associated with decreased rates of PTSD.
‘Sedation vacations’ are associated with shorter length of ICU stay, fewer days on a ventilator, improved return to independent function at discharge, and trend toward lower ICU mortality.
Pain is experienced at greater rates among the critically ill than among the wider population. Up to 70% of patients will experience moderate to severe pain during their ICU stay. Rates have been measured up to 30% while at rest and the majority will experience pain during routine cleaning and nursing interventions.
Experiencing pain in the ICU has been associated with greater levels of chronic pain in the post ICU setting and of PTSD.
Analgosedation, or the practice of first treating with analgesics before actively sedating the patient with hypnotics, has been linked to shorter ICU length of stay and decreased duration of mechanical ventilation.
Clinical pharmacology
Context‐sensitive half‐time (CSHT) is defined as the duration of time required for plasma concentrations of a drug to decrease by 50% after discontinuing administration of the drug. ‘Context’ is meant to refer to the duration of time that an infusion has been running.
The CSHT is often different from the elimination half‐time and explains differences in duration of effect that exist based on how long an infusion is running versus the effect we see with a single bolus dose of a medication. As an example, if we were to believe that elimination half‐time determined the duration of effect of propofol, then a single bolus should leave our patient obtunded for several hours. Instead we know that a single bolus will wear off in a few minutes due to redistribution of the medication out of the central compartment into the periphery.
Likewise, the CSHT also explains why medications take longer for their effects to wear off after longer infusions. A simplified, if not perfectly scientific, explanation is that anesthetic drug effects wear off as medications redistribute from the central to the peripheral compartments. However, over time, the peripheral compartments can approach saturation, causing the central compartment to refill or maintain a steady state