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Specimen collection part 5 - obtaining a sputum sample

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This article, the fifth in a six-part series on specimen collection, explains how to collect a sputum sample

This article has been updated

The evidence in this article is no longer current. Click here to see an updated and expanded article

Author: John Guest, RGN, ENB 100, is senior charge nurse in critical care, University Hospital Birmingham NHS Foundation Trust.

The collection of chest secretions or sputum is important in diagnosing illnesses, infections and conditions such as lung cancer and tuberculosis. The result gives guidance on the course of treatment. This article describes methods of collection (Dougherty and Lister, 2004) from both self-ventilating (non-intubated) patients and from patients with indwelling tracheostomy cannulas. The method for obtaining samples from endotracheal tubes follows the latter closely.

Self-ventilating patients

Patient cooperation is essential. Informed consent and clear instructions of what the patient needs to do are important.
Where possible, the patient should be sat upright. Where a patient has had chest and/or abdominal surgery, the wound needs to be supported to maximise inhalation and minimise pain. Analgesia is important.

Equipment required
The following should be gathered:

  • Apron and gloves;
  • Universal container;
  • Appropriate documentation.

The procedure

  • Wash hands.
  • Obtain informed consent.
  • Don apron and gloves.
  • Sit the patient upright, supporting as necessary with pillows.
  • Instruct the patient to breathe deeply, hold their breath and cough.
  • Collect specimen in pot and seal.
  • Label pot with the patient’s details, date, time and specimen type.
  • Send to relevant laboratory according to local policies and procedures.

Indwelling tracheal cannulas

Performing suction through endotracheal tubes or tracheostomy tubes can be unpleasant and even traumatic for patients. The nurse has a responsibility to minimise this by explaining the procedure and its importance to the patient and gaining informed consent.

The nurse must be aware of the potential of causing trauma to the airways by introducing the catheter too far and rubbing the end of the catheter against the carina as well as through performing suction while not withdrawing the catheter, which can lead to damage to the inner lining of the trachea.

For ventilated patients, closed suction systems can be used. They minimise interruption to ventilation, reduce loss of positive end expiratory pressure (PEEP) and are assumed to cut infection risk. However, much literature seems to suggest there is no difference in infection rates between the methods (Topeli et al, 2004). Closed suction systems are not discussed further here.

Suctioning can cause hypoxia, leading to cardiovascular instability such as bradycardia (Thomson et al, 2000) and the risk of cardiac arrest. To avoid this, pre-oxygenation is suggested before and after suctioning. The fraction of inspired oxygen must be carefully considered, particularly in patients with COPD as they will not be able to tolerate increased oxygen saturations (Thomson et al, 2000).

Tracheal stimulation can cause a vasovagal reflex, leading to arrhythmias and hypotension and the risk of cardiac arrest (Jones and Moffat, 2002). Close monitoring of the patient is essential, potentially including ECG monitoring.
Performing suction via a tracheostomy is a skill that requires appropriate training.

Equipment needed

The following should be gathered:

  • Apron and gloves;
  • Single sterile glove;
  • Suction catheter - of correct size related to lumen of cannula;
  • Sputum trap;
  • Suction pump or wall-mounted suction unit with suction tubing.

The procedure

  • Obtain informed consent.
  • Wash hands.
  • Don apron and gloves.
  • Set suction to correct level.
  • Open sterile glove packet.
  • Hold suction catheter in packet in dominant hand.
  • Open packet, exposing connection end (Fig 5).
  • Attach to suction tubing.
  • Pull out half of catheter, forming a loop.
  • Don sterile glove on dominant hand.
  • Remove rest of catheter with sterile hand.
  • Tell patient that the procedure is about to start.
  • Feed catheter into tracheal tube (Fig 6).
  • At resistance (at the carina) withdraw 1cm without suction.
  • Apply suction while withdrawing catheter.
  • Repeat as necessary.
  • Cap off sputum trap.
  • Label as before and send to laboratory.

Professional responsibilities

This procedure should be undertaken only after approved training, supervised practice and competency assessment, and carried out in accordance with local policies and protocols.


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