7.14: High Airway Pressure
- Page ID
- 59717
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)An increase in the pressure needed to ventilate a patient is not uncommon but inspiratory pressures greater than 40 cm H2O must be treated as abnormal.High airway pressure can present in several different ways including problems with ventilating the patient (poor chest expansion, decreased breath sounds, decrease tidal volume), hypoxia,hypercarbia and tachycardia.
Causes of High Airway Pressure
Ventilation may be difficult because of a problem with one of three sites:
-
anaesthetic equipment (ventilator, anaesthetic breathing system)
-
airway device (endotracheal tube, laryngeal mask, face mask)
-
the patient
The anesthetist should immediately look for obvious causes. Airway pressure may be high immediately after intubation, when neuromuscular blockade has decreased and if the airway is kinked.
Management
If there is no obvious cause, the anesthetist should have a systematic approach to the diagnosis of high airway pressure:
Gas supply: Check the oxygen supply, increase the concentration of oxygen.
Breathing circuit: Check the common gas outlet and hose connections. If available,hand-ventilate the patient with a self-inflating resuscitation bag. If the problem is with the breathing circuit or anaesthetic machine then ventilation should be easy with the resuscitation bag. If the problem is with the airway or the patient, then ventilation will continue to be difficult.
Airway: Check the airway. Make sure that it is not kinked or obstructed. Pass a suction catheter down the airway and apply suction to clear any secretions. If the catheter passes easily then the airway is unlikely to be obstructed. If the endotracheal tube is obstructed, deflate the cuff and try to pass the suction catheter again. A herniation of the endotracheal tube cuff can cause obstruction of the tube. If the suction catheter still will not pass freely, remove the endotracheal tube, mask ventilate and reintubate.
Lungs: Look for bilateral chest expansion and listen to both sides of the chest. If breath sounds are only on one side consider endobronchial intubation (withdraw the endotracheal tube 2 cm and reassess) or pneumothorax (check the heart rate and blood pressure, feel to see if the trachea is central and percuss the chest).
If wheezes are present, consider bronchospasm, aspiration or pulmonary oedema.
The surgical procedure or the position of the patient may also make ventilation difficult.
Pneumothorax
A pneumothorax may occur for many reasons including insertion of intercostal nerve blocks or placing a central venous catheter. It can happen spontaneously or because of chest trauma or high ventilation pressure during general anaesthesia.
The awake patient may complain of dyspnoea, chest pain, and be tachypnoeic and hypoxic. In the anesthetised patient, it can be very difficult to diagnose a pneumothorax.
The patient may be hypoxic and have raised inspiratory airway pressures. A large pneumothorax or a tension pneumothorax will cause hypotension, tachycardia and may cause death.
On examination the patient may have reduced or absent breath sounds on one side,increased resonance to percussion, tracheal deviation or subcutaneous emphysema.
The anesthetist must always consider a pneumothorax in their diagnosis, especially if the patient is at increased risk (central venous catheter inserted, chest trauma, asthma,high airway pressure). A pneumothorax may be present with signs and symptoms similar to several other problems, including aspiration of gastric contents,endobronchial intubation, a blocked endotracheal tube and bronchospasm. An erect chest x-ray will help with the diagnosis (a pneumothorax can be very difficult to see on a supine chest x-ray).
Management
Always ensure that the patient is well oxygenated and ventilating.
Turn off the nitrous oxide and give 100% oxygen (70% nitrous oxide will rapidly increase the size of a pneumothorax by 100% in 10 minutes).
Check the blood pressure and pulse rate.
If the blood pressure is low and there is no other cause for a low blood pressure, treat the patient as if they have a tension pneumothorax. A tension pneumothorax can rapidly cause death and must be treated as an emergency.
Inform the surgeon and call for help.
Treat the low blood pressure with intravenous fluids and vasopressor drugs.
Insert a large intravenous catheter into the pleural space to aspirate the pneumothorax. The intravenous catheter should be placed in the second intercostals pace above the rib in line with the middle of the clavicle, to avoid damaging the intercostal nerves and blood vessels. A chest tube must be inserted following insertion of an intravenous catheter.
Bronchospasm
Bronchospasm will cause wheezing (greater on expiration) and increased airway pressures. There are several causes of intra-operative bronchospasm including:
- Mechanical irritation of the airway (secretions, intubation,oropharyngeal airway, suctioning).
- Chemical irritation of the airway (some inhalational anesthetics,smoke).
- Drugs (histamine release from drugs like morphine or atracurium, beta adrenergic blocking agents).
- Aspiration of gastric contents.
Anaesthesia should be delayed for elective surgery if the patient has an upper respiratory tract infection or an acute episode of asthma.
Management
Ensure the patient is oxygenated and ventilating.
Check the blood pressure and pulse rate.
Increase the oxygen concentration if the patient is hypoxic.
Check for other causes of increased airway pressure such as endobronchial intubation, blocked endotracheal tube, pulmonary oedema, aspiration of gastric contents, pneumothorax or anaphylaxis.
Remove any airway irritant.
Increase the depth of anaesthesia. Halothane and other inhalation agents are good bronchodilators.
Give beta-adrenergic agents, anticholinergics and steroids.
Salbutamol
Salbutamol (Ventolin) may be given by inhalation or injection (intramuscular,subcutaneous or intravenously). Side-effects include tachycardia, tremor, nausea,headache and lactic acidosis.
Inhalation: continuous nebulization (5 mg/2.5 ml) or 8 puffs (100 micrograms/puff).
Intravenous bolus (500 micrograms/ml): 200 to 300 micrograms over 10 minutes.Repeat after 15 minutes if needed.
Intravenous infusion add 5 mg (5 ml of 5 mg/ml) to 45 ml of normal saline (equals 100 micrograms/ml). Start at 5 micrograms/min (3 ml/h) and increase by 1 microgram/min up to a maximum of 10 microgram/min.
Ipratropium
Ipratropium 1 ml nebulized every 2 to 4 hours.
Dexamethasone
Dexamethasone 4 mg intravenously every 8 hours.