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Chapter: Essential Anesthesia From Science to Practice : Clinical management : General anesthesia

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Desaturation - Anesthesia

Hypoventilation Always first assist ventilation to establish normal SpO2 and PaCO2! Then consider causes and their treatment.

Complications

Desaturation

Differential diagnosis

·           Hypoventilation Always first assist ventilation to establish normal SpO2 and PaCO2Then consider causes and their treatment.

Residual neuromuscular blockadeSuspected when the patient shows anabnormal respiratory pattern, particularly the tracheal tug, i.e., downward motion of the larynx with inspiration. Test with the twitch monitor. Treat with reversal agents.

– Residual sedationConsider reversal of benzodiazepines with flumazenil.

– NarcosisTypically a slow, deep respiratory pattern; consider cautious reversalof opioids with naloxone.

– Bronchospasm (wheezing)Intubation is a strong stimulant for bronchospasm;treat with bronchodilators.

– Laryngospasm (stridor)If related to the operation, e.g., neck operation withpossible hematoma formation, it becomes a surgical emergency. Try continu-ous positive airway pressure, letting the patient exhale against resistance (5 to 10 cmH2O) and maintaining that pressure throughout the respiratory cycle.

– PainParticularly with a subcostal incision where deep breathing is painful.

·           Ventilation/Perfusion mismatch

– AtelectasisProbably the most common cause of post-operative hypoxemia.

– Aspiration of gastric contentsParticularly in high-risk patients, or if intubationrequired multiple attempts.

– PneumothoraxEspecially after central venous access. Obtain a chest radio-graph, but be prepared to relieve the pneumothorax by puncture (2nd inter-costal space, mid-clavicular line) should a tension pneumothorax develop in the meantime.

– Pulmonary embolismThromboembolism is the most common. May needV/Q or CT scanning. Most surgical patients require some form of prophylaxis against deep vein thrombosis (DVT).

– Pneumonia 

– Mainstem intubation

·           Diffusion block

– Pulmonary edema

·            Inadequate FiO2


Management

(i)Airway

 

Chin lift, neck extension; continuous positive airway pressure (CPAP) often helps. For this, use a bag and mask system (Mapleson – see The anesthesia machine) with a high flow (15 L/min) of oxygen. Apply the face mask tightly, letting the patient exhale against resistance (5 to 10 cmH2O) and maintain that pressure throughout the respiratory cycle.

 

(ii)     Breathing

 

·           Supplemental oxygen

– Via nasal cannula, but with oxygen flows of 2 L/min the inspired O2only increases by about 6%.

         – Via standard tent face mask for an inspired O2of up to 50%

– Via partial rebreathing face mask for an inspired O2of up to 80%

– Via non-rebreathing face mask for an inspired O2of up to 95%

 

·           Encouragement – “take a breath!” often effective with narcotic depression

·           Bag–Mask – use with self-inflating bag or Mapleson

·           Check ventilator settings, O2 supply and end-tidal CO2 if the patient is intubated.

(iii)         Studies to consider

 

·           Chest radiograph if abnormal breath sounds (pneumonia, atelectasis, pneumothorax, +/ aspiration). Keep in mind, however, that a portable film may not provide the highest quality and consolidation takes some time to manifest radiographically.

·           Arterial blood gas

·           Twitch monitor if patient appears to be partially paralyzed.


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